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1. ## joigus

Senior Members

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2. ## iNow

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4. ## studiot

Senior Members

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## Popular Content

Showing content with the highest reputation since 06/10/20 in Posts

1. 5 points

## Does Zoro produce enough aerodynamic lift here according to the Bernouilli's principle?

At which point, I have to post this: https://what-if.xkcd.com/1/ Spoiler: it doesn't end well
2. 4 points

## Climate Change

My little bother just ate all the Scrabble tiles and his poop made more sense than you do.
3. 3 points

## Gravity

The 'bowling ball on a rubber sheet' is a two dimensional reduction of a 4 dimensional configuration. It has multiple problems, one of which is that you can observe it from an embedding third dimension. Space-time has no embedding dimension; both the bowling ball and you, the observer, would need to be intrinsic to the rubber sheet ( i.e. also two dimensional ). A three dimensional representation would already get rid of some problems, but not all. Picture a three dimensional grid, where x, y, and z axis divide up the space into cubic elements. A mass placed in this space would curve the x, y, and z lines such that the elements are moreskewed, and smaller, as you get closer to the mass. That is 'space' curvature, and one aspect of gravity, but already much harder to visualize than the two dimensional example of the bowling ball/rubber sheet. Actual gravity is four dimensional 'curvature' of space-time, and I can't help you visualize that as it is impossible. Some problems are just not suited to visualization, but understanding even just the basics of the math goes a long way to clarifying things.
4. 3 points

## Experiment verification of General relativity

Just to add to what has already been said by other contributors here: 1. First and foremost, the notion of "gravitational potential" can only be defined in spacetimes that are stationary (more precisely: those which admit a time-like Killing vector field) and asymptotically flat. It cannot be generalised to more general spacetimes, which makes it useless so far as a general model for gravity is concerned 2. Gravitational potential itself is not an observable, only differences in potential can be observed and measured. This is because the potential has a gauge freedom, in that one can freely choose where the zero point is, without affecting the physics. The same is not true for the speed of light, hence the relation above is trivially and obviously wrong, since it equates two quantities that cannot physically and numerically be equal, on fundamental grounds. 3. A varying speed of light would constitute a violation of Lorentz invariance. This symmetry has been experimentally and extensively tested with modern equipment to extremely high precision, both here on Earth and in the vacuum of space - needless to say, no such violations have ever been found. Given the degree of precision of these tests, any variability in the speed of light can effectively be ruled out far beyond the usual 5 sigma threshold. 4. A variable speed of light would also break CPT symmetry, which underlies the Standard Model of Particle Physics. Since we continue to successfully use and test this model in particle accelerators on pretty much a daily basis, any variability in c can also effectively be ruled out on that ground. 5. Neither classical Maxwellian electrodynamics nor quantum electrodynamics allow for varying values of permittivity and permeability (in the same medium of course). Hence the notion of a varying speed of light is actually in direct contradiction to what we know about electrodynamics. 6. As has been pointed out on another recent thread, a scalar field theory such as this one is fundamentally incapable of capturing all required degrees of freedom of gravity; there is more to gravity than just time dilation! I could probably go on, but these are the points that immediately come to mind without thinking about the issue too much. I'll leave it at this.
5. 3 points

## There's a black hole lurking within 1,000 light years of Earth – and you can see stars circling it with the naked eye

Disclaimer: Black hole not visible, southern hemisphere required. https://www.theregister.com/2020/05/06/nearest_black_hole_earth/
6. 3 points

## Discussing racism/bigotry (split from The Killing of George Floyd: The Last Straw?)

You mean calling him a "racist"? That is no more "name calling" than referring to someone a "physicist" or a "plumber". Name calling implies an insult. "Racist" is a title he earned all by himself. I don't see what is to be gained by dancing around words to spare people's feelings. This place is not a quilting circle. So there is the "status quo" and there is "your way". Some people feel there are other means to change the status quo, and they don't involve allowing others a platform to share hatred and bigotry. I allow no room in my heart for showing understanding for racism. Hatred of others based on the color of their skin is never acceptable to me. I will not stand by while others spew hate without calling them out. There is a reason people lose sponsors, advertisers, and even jobs after making racist comments. It is not acceptable. I don't see why we should be an exception.
7. 3 points

## hijack from The Killing of George Floyd: The Last Straw?

! Moderator Note No, you're racist because you espouse racist beliefs, the expression of which on this forum (besides being wrong) is also against the rules. Consider yourself banned.
8. 3 points

## Confused About the Earth's Early Atmosphere...

Just to add info. The oxygen in photosynthesis comes from the breaking up of water molecules. The possibility that it came from CO2 has been ruled out experimentally by using isotopic tracers. https://www.amazon.com/Life-Science-William-K-Purves/dp/0716798565 (chapter 8: Identifying Photosynthetic Reactants and Products) Water was very abundant in the atmosphere after the late heavy bombardment.
9. 2 points

## United States Will Withdraw From The World Health Organization

He launched yet another weapon of mass distraction
10. 2 points

## Teaching Science and Asperger's Syndrome

With the exceptions of occasional crackpots, the selfish, the unkind, and the uncouth; and on rare occasions, the sheer lunatics that come and go, most of the members of this community are giving me an enormously valuable environment to exchange ideas. Teaching has been a great pleasure for me for many years. Now, for the first time, I'm tutoring a boy that suffers from Asperger's syndrome. After a month now, I must say that it's been one of the most gratifying teaching experiences I've had so far. Things are going pretty well, good results keep coming, and everyone involved seems to be happy. We've started with maths. Every time he shouts “now I understand it!” is priceless. But he's emotionally vulnerable, and also gets quite anxious when he misunderstands something and gets embroiled in the wrong calculation. The verbal feedback is somewhat wanting, because he stumbles over words and speaks too quickly for me. So sometimes it takes me a while to realise what he really means. Any experience that any of you may have to share with me, any tips and directions, will be greatly appreciated. Especially heads-up when it comes to physics, which I'm kind of dreading.
11. 2 points

## What is the correct definition of zero error?

I agree that the OP definition is not quite right, but both your A and B examples have two errors. Yes a zero error is a systematic error but it is not due to a wrongly marked or non uniform graduation and yes it can result in an increased or decreased actual measurement. A simple example of a zero error would be dirt on the pan of an otherwise accurate weighing scale.
12. 2 points

## Scientist saving the world from destruction.

Well, I'll be damned. One wave of the hand, and 5+ billion of us, who just happened to be born into non-Christian cultures, sentenced to burn in hell for all eternity. Makes me wonder just which of those two guys to blame, really.
13. 2 points

## Responding to 5G Conspiracy Fears

Aren't you all glad that you found science as an interest/vocation? We could all easily be victims to this kind of BS if we didn't know the science basics.
14. 2 points

## How can we apply accoustics to tell the difference in power between these two characters?

Sound we regularly experience carries very little energy. 80 dB is ~ 1 milliwatt, so assuming 100% efficiency: “to heat up a quarter liter of coffee 50 C it would take: 1 year, 7 months, 26 days, 20 hours, 26 minutes and 40 seconds” https://www.physicscentral.com/explore/poster-coffee.cfm 130 dB is just 10 watts, though it is logarithmic https://en.wikipedia.org/wiki/Sound_power
15. 2 points

## need help understanding data and information abstractly

My very short answer: A value of a random variable. Let's say you receive a symbol "1". If this is the only possible symbol the fact that you received it does not give you information. But if this symbol is one of two possible, "0" and "1", then the reception of symbol "1" may contain information. So having more that one symbol is a requirement, but not sufficient. Lets say you receive the pattern "111111...". The probability of the symbol "1" is 1. Again there is no information. But if random sequences are allowed, for example "00", "01", "10", "11" then we may use these sequences to represent information. So conceptually information can be seen as a value form of a random variable. The above is an attempt at an extremely short introduction to information theory, which is tied to discrete probability theory. Most important early contributor was Claude E. Shannon and his paper “A Mathematical Theory of Communication”, dealing quantitatively with the concept of “information”. Shannons concepts and the mathematics he used to describe information and to measure information content is a remarkable contribution. I believe it's tricky to find any areas of IT where his work does not contribute. Wikipedia* has links to some concepts related to your question. Feel free to ask additional questions. *) https://en.wikipedia.org/wiki/A_Mathematical_Theory_of_Communication For an early predecessor of Shannon, working on sinus signals and frequencies, see Hartley: https://en.wikipedia.org/wiki/Ralph_Hartley
16. 2 points

## Does Gödel's Incompleteness Theorems means 2+2=5?

No. They are purely about the "completeness" of formal systems. In other words, can a formal system (e.g. mathematics) prove that anything that can be written down using that formal system is either true of false. And the answer to that is no. You can write something using mathematics that you cannot use the same mathematics to prove or disprove. You can extend your formal system to make it more complete and allow you to prove that statement. But then there will be other statements that this extended system cannot prove. And so ad infinitum. Physics uses mathematics but it is not limited by that mathematics in the same way. (And some mathematicians complain that physicists are a bit "ad hoc" and don't really stick to absolutely formal derivations.)
17. 2 points

## Wash away of \$1Trillion worth of marshes

That is out of my knowledge. The only thing I can say is that trying to change the elements (river, sea, land) in a specific way most of the times drive to unexpected results. I have the experience where a hotel constructed a small dock in the sea for his single inflated boat sportcraft had the result to erase completely its sandy beach.
18. 2 points

## Does Zoro produce enough aerodynamic lift here according to the Bernouilli's principle?

Since this is the lounge I'll do some less rigorous analysis showing why science is of no use. Observations in the movie clip. 1: Zoro does not seem to follow the trajectory of a massive object; heigh above ground seems maintained. 2: Zoro does not seem affected by air resistance; speed is not reduced during the flight 3: There is atmosphere on the world where the fight takes place. 1: means that (a) Zoro is either massless* and hence unaffected by gravity or (b) neutrally buoyant in the atmosphere, like as a hot air balloon. 2&3: means Zoro could be (c) extremely dense, having extreme momentum. But (c) can't be compatible with 1, massive object fall down. And (b) is not compatible with 2, balloons stop quickly when thrown in air. (a) is pointless, a massless Zoro, swords included, would have zero effect on a stone golem; there is no kinetic energy or momentum that can affect the golem. That means Zoro travels through air by magic because the described airstrip is physically impossible. I do not know how magic affects drag and Bernouilli's principle, so again: Side note: That fact the manga story is failing to describe physically probable action does not mean I can't see it as entertaining. I enjoy entertaining stories, if the canon of the universe where the events take place allow magic, faster than light travel etc I don't care how impossible that might be according to mainstream science. I just chose to not mix my interest in science and engineering into the events of fiction and fantasy in the story. *) I know that would mean a photon speed of c in vacuum and massless bodies of macroscopic size does not exist AFAIK; creating one would require magic. But this is the lounge after all, and we will get to the point anyway.
19. 2 points

## Black holes and evaporation

Just to add to that, it's not like in SR where each observer also has a different notion of simultaneity, but each of those is physically meaningful. Eg. in flat spacetime, any two events that can be considered simultaneous by someone will have intersecting future light cones, where different future observers can agree or disagree on whether the events were simultaneous. In GR you must make a choice of how to define the surfaces of a foliation, that's not just based on a physically meaningful connection between its events. You'd choose it to make a useful tool, not a 'real' representation of simultaneity throughout the universe for a given observer.
20. 2 points

## Do they belong in this thread or psychology?

If you have scientific evidence for a non-mainstream topic, and you think you can defend it reasonably, put it in Speculations. If it pertains to a field of personality studies you can defend using science, post in Psychiatry/Psychology. If it's something you feel might pertain to a specific philosophy or ethical approach, post in Philosophy. If it's just New Age mysticism that works because you say so and wave your hands a LOT, please don't post anything at all.
21. 2 points

## Questioning the Basis of Christianity

There are things the Bible doesn't say and almost everybody believes it does. There was no apple. It could have been a quince, or maybe a fig, as there were no apples back then in the Middle East. The Bible doesn't say it was an apple, actually. The Bible doesn't say Jonah was eaten by a whale either. The Bible doesn't say there was an angel at the Garden of Eden, but a cherub, which was a mythical animal represented very frequently in the gardens of palaces throughout the Middle East. The Hebrew Bible doesn't say that Mary was a virgin, but a "young woman." ------------------------------------------------ There are things the Bible says and few people know it does. The Bible talks about a pantheon of gods that are subservient to Yahweh. And names God both as Yahweh and El. Is it the same god? I'm not sure. Asherah, the wife of Yahweh, is also mentioned, but the interpretation was presumably changed, as it's mentioned as a synonym for "a stick" in very obscure passages, when she is known to have been a goddess, as archaeology has shown. The stick was one of the symbols of the goddess. Back to Adam and Eve: There's at least one thing the Bible says twice in different (incompatible) ways: Ezechiel 28. Two prophecies, one of them against the king of Tyre. There you can see that the king of Tyre is expelled from the Garden of Eden, on account of his sins. The cherub also appears. Very similar legend; two different narrative uses. Who was expelled from the Garden of Eden, Adam and Eve or the king of Tyre? I'm not so sure. The authors of the Bible seem not to be either. Some scholars believe the Oracles against the king in Ezechiel 28 predate the Adam and Eve story in Genesis. ------------------------------------------------ There are things the Bible says that are taken from somewhere else: The Bible takes the story of Noah from The Epic of Gilgamesh, Utnapishtim , and adapts it to its own narrative needs. ------------------------------------------------ There are blatantly obvious things the Bible is silent about: Omri, big king of Samaria, was a very relevant character of the Assyrian domination period, but the Bible only mentions him in passing, as a baddie. The Bible also plays down the role of many other kings, like Manasseh, although he made Israel into an important olive oil factory and brought a period of peace, contrary to what Hezekiah, his father, did. ------------------------------------------------ And lastly, there are many things the Bible says that cannot be true. Josuah didn't conquer Jericho, as Kathleen Kenyon has proved. Jericho was uninhabited at the time. Plus the Egyptians were in control of Canaan and had the country strongly policed from Beit She'an. I don't believe God gave the law of gravity a suspension for some hours for the benefit of his people to the detriment of the Canaanites either. Plus the Canaanites and the Israelites were the same people: No difference in material culture or belief system, as Israel Finkelstein has shown. Abraham could not have possibly used camels. Camels were domesticated about 1000 years later.
22. 2 points

## Does Gödel's Incompleteness Theorems means 2+2=5?

Hello Francis and welcome. The short answer is no Godel is not about statements we can prove, like yours, but statements we will miss out because we cannot derive them from our axioms. There is a really good introductory book by Raymond Smullyan about this called Forever Undecided Which is fun to read. I think a pdf may be available. Meanwhile here, what do you know about axiomatic structures in Mathematics?
23. 2 points

## "Belief", "Beliefs," and "Issues of Belief"

One of the best little pieces of comic theatre of all time was based on this. Here is wikipedia, you may be able to find a ytube of it. https://en.wikipedia.org/wiki/Class_sketch Yes indeed it is quite long, so I do not find it suprising there are some contentious points. The author is rather dismissive of the use of auxiliary verbs in general and the verb to be in particular. He claims that the verb to be is unneccessary and has almost withered away. Not so. Consider the travels of Marco Polo to China, a jourrney that took several years. Had he been English, Marco might have said, "I'm going to go to China next week." As he left Italy he might have said "I'm going to China". Two years later he was still "going to China", he had not by then arrived. One thing he would not have said would be "I go to China". The action was "imperfect" as it occupied an extended length of time and was still in progress during other events that might be spoken about. Imperfect here means that it is not complete at the time of utterance. A perfect action is complete from start to finish. An imperfect one may never be completed for some reason. Two other gripes with the article. Firstly no mention is made of the difference between spoken and written language when comparing English to other languages. It is my belief that this difference is one of the key factors as most languages are largely phonetic, English being the glaring exception. So it is emminently possible to learn and know many words and the associated grammar in English but not to be able to say or recognise them when spoken. Even English speakers sometimes have this trouble. Take the letter a as in car or cat. The big difference in the pronunciation of the 'a' leads to two difference pronunciations of the word castle, which confuses many. Secondly the thesis that it was the influence of the Vikings who did away with the manyfold word endings. One wonders why they did also do this with old French. Or why the endings were still there in middle English a couple of centuries after the end of the Viking era.
24. 2 points

## Experiment verification of General relativity

We can already invalidate Yanchilans theory as we have already tested different gravitational potentials for time dilation at different elevations. With precision atomic clocks. Even testing it a distance of one foot. The results agree with GRT. https://www.nist.gov/news-events/news/2010/09/nist-clock-experiment-demonstrates-your-head-older-your-feet This isn't the only experiment done at different elevations. I assisted at a University that also conducted similar experiments as part of the course curriculum. Though we used the coastal mountains of BC coast. It was pointless publishing the results. Nothing newsworthy or unexpected.
25. 2 points

## "Belief", "Beliefs," and "Issues of Belief"

When people say "Well, the dictionary says..." they obviously don't realize that a modern dictionary is a contemporary record of usage and not an authority. The people at large determine the usage in any given period.
26. 2 points

## Black holes and evaporation

That is a really good question, because I still don't know what your position actually is. You seem to be saying that the concept of an evaporating Schwarzschild black hole is self-contradictory - which is trivially true, because Schwarzschild black holes are of course stationary by definition. But evaporating black holes aren't of the Schwarzschild kind, so where exactly is the issue? Then so you also seem to be saying that even ordinary Schwarzschild black holes are self-contradictory, because somehow event horizons can't exist? But I don't understand why you think this, because the reasons you give don't make any sense.
27. 2 points

## vedas and twist

I think it makes no sense to say that the vedas were twisted or not. They have grown organically. There are so many reasons for a text to change, especially when it originally was an oral tradition. Without having the 'original' how would you see that the texts changed? There are methods to find out which of the present versions we have are probably the oldest, but of course we can have no idea what the first written down version of the vedas were. And then there are many reasons why texts change over time, just to name a few: errors when copying the texts corrections of (language) errors authors putting in their ideas into the texts, in good or ill faith I only know a little about the history of Christian texts, which are of course not so old as the vedas, and also here already the problem exists that we do not know exactly what the original texts were. But we know copyists made errors, corrected errors, put in sentences or even complete stories, often because these copyists had a theological agenda to promote their version of Christianity. From some texts we know that there must have been more original texts, but they did not survive. With the vedas this will be worse, because they were orally passed to others for a much longer time. In Christianity, especially the new testament, there are at most only about 100 years between the oral tradition and the first written down versions we have (often less: the gospels were written till about 100 years, the earliest one probably only 30 years, after Jesus' death). With the vedas it is several millennia before they were written down.
28. 2 points

## Black holes and evaporation

This is what I got from your posts: 1) A black hole and all the events in its interior can be described in the coordinates of an observer at infinity. 2) A Penrose diagram of an evaporating black hole shows that the formation and disappearance of a black hole have the same time coordinate. 3) If an event A has a coordinate time that is less than the coordinate time of an event B, then A happened before B (maybe even in B's past?). Problems with this: (1) The interior events do not have meaningful time coordinates for this observer. (2) If that's what the diagram really shows, then the coordinates used in that diagram can't be the same as for the observer in (1). (3) You're comparing coordinate times of events that have no causal connections, and their ordering is irrelevant, but you see "logic problems" by treating it as something physical.
29. 2 points

## Black holes and evaporation

Really ? Cosmic rays enter the atmosphere billions of times, yet not a single micro BH has ever been detected. Maybe you can produce a citation of a detected micro BH. I can certainly post numerous citations of cosmic ray detections.
30. 2 points

## vedas and twist

Stu the cockatoo is new at the zoo...
31. 2 points

## The Killing of George Floyd: The Last Straw?

The issue that I see with this thread is that I'm proposing actual implementable changes. To the Police Unions and Hiring/training practices, for example. Then we start to work on the DAs who bring up unfair charges on minorities. Saying the problem is systemic ( your meaning CY ) means the whole justice system ( and more ) needs to change, from cops, all the way to the Supreme Court. And we both know that's not going to happen; so nothing will change. The higher up you go in the justice system, the more political it is. And with your polarized two party system, who would even propose such a change, and hope to get re-elected ? Myself, I don't see the point of self-flagellation, and saying "It's all whitey's or the system's fault, and not trying to do something about it. People are dying needlessly, and all I'm hearing is blaming, but no solutions.
32. 2 points

## The Killing of George Floyd: The Last Straw?

Where did this red herring come from? We’re not talking about all criminal activity, we’re talking about police, who are supposed to protect and serve the public, and who should be held to a higher standard. We’re also talking about violent behavior. That’s not an instance of excessive force. I was short of straw before but now I have a lifetime supply. Sure. But you had only proposed screening for white supremacy Yes. If they had not tolerated such behavior, you might say...
33. 2 points

## Space Time

I suspect it relates to the alleged instances of people time travelling without the benefit of physical mechanism. The example that comes to mind is of the two visitors to Versailles early in the 20th century who seemed to be transported back to an earlier period where the people they saw and the layout of the gardens matched (allegedly) the late 18th century. Wikipedia article. There is also a silent movie era newsreel (?) in which a member of the crowd appears to be using a mobile phone. All of the instances have simpler, more convincing, mundane explanations, but its a useful plot device for stories.
34. 2 points

## Is Nature playing fair with Krauss Object?

They are NOT the exact same things. You are confusing the word "special" with the word "preferred". We don't laugh at the the idea of the Earth being in a special place, we laugh at the idea that the Earth might be in a preferred place. When you were but a wee child and your mother said you were "her special boy", she simply meant you held some significance for her. You were 'neat', or 'cool'. She wasn't implying that the universe was centered on you. Similarly, we live in a special time and place. We witnessed the first time humans detected gravity waves and the invention of the autostereogram. If we weren't at this location (on Earth) at this time, we could not have seen that with our own eyes. Unfortunately we did not exist at that special time when the four fundamental forces were combined, but we are lucky to live at the special time when all these superclusters can be detected. And that is really neat.
35. 2 points

## Sleep and time

Dreaming is a process of organizing thoughts in new ways. Memories get consolidated, and it happens while our normal connection between our brain and our body is “severed” ... much like our normal connection to time while we dream can be discarded. I don’t believe we see the future in our dreams. I believe instead that our conscious mind struggles to make sense of these more unconscious processes and so applies narratives which DO make sense to us. These narratives are not tied to specific events and so are not anchored to chronology in the normal way our daily experiences are. These narratives and insights and feelings are essentially intuitions that we selectively remember at a later time (“hey... this pattern I’m seeing right now IRL is incredibly similar to that pattern I experienced all those weeks ago in my dream!”). We then call this feeling deja vu or mistakenly describe it as precognition. Its a pattern, and humans are incredibly good at finding patterns even where none exist. Note: This is my own conjecture, not necessarily a representation of the most current research. Apologies for inserting a speculation into a non-speculative thread. Could be both. Hit the quote button.
36. 2 points

## Trigonometry (Law of Cosines)

Yes it helped and I got my answer.
37. 2 points

## Discussing racism/bigotry (split from The Killing of George Floyd: The Last Straw?)

There are two somewhat different issues here: one is discussing racism in general, and another is discussing it on this site. As for the latter, as iNow and Phi (and possibly others) have pointed out, we want arguments to be in good faith. Disagreement must maintain a certain amount of civility. So if someone shows up dropping N-bombs, or disparaging religions, they will be shown the door. We are not obligated to make people suffer written abuse in an effort to change a bigot's mind. If that's the price of participation, for us it's too high.
38. 2 points

## Discussing racism/bigotry (split from The Killing of George Floyd: The Last Straw?)

Racism isn't about labels, it's about hate. Hate is an issue of emotion not intellect. As emotion, the afflicted may only be solved or remedied by therapy rather than by reasoned discussion as we may find in open forums like this. In this forum, we can intellectualize the causes and cures for hate but we can no more treat that condition via our online debates with racist than we can remotely remove a tumor. There's a reason why this science forum discourages visitors seeking medical advice. Similarly, there are reasons why hate filled sufferers are equally discouraged in this forum. They need help we can't render here.
39. 2 points

## Banned/Suspended Users

essereio has been permanently banned for repeated violations of rule 2.1.
40. 2 points

## Microservices or Client-server Model

I assume you aren't making the final decision so don't take that responsibility. You should create a PowerPoint presentation referencing the various options that are available and present that to the other members of your team so an informed decision can be made. If you are uncomfortable doing so yourself I'm sure you can recruit a consultant on a temporary basis to do so.
41. 2 points

## Microservices or Client-server Model

With the limited information available my answer will be very general. I would be cautious if someone provides detailed answers based on limited information. 10s of thousands can be a tiny or huge depending on the amount of data, how the traffic is clustered, response time requirements, processing required to create an answer, what standard services that are already available as services, API, micro services etc.
42. 2 points

## Does outer space have drag?

Not sure what you mean by time being reactive. And I don't understand why that would mean it travels. I don't even understand what it would mean for time to "travel". 🤷♂ No. Photons are massless. It has nothing to do with terminal velocity. Light always travels at the same speed. No. Photons do not have mass. And even if they did, it would not imply that space has drag. Nothing with mass can travel at the speed of light. No. Photons always travel at the speed of light. Which is why it takes them 8 minutes to get to Earth from the Sun. No.
43. 2 points

## Removing Civil War Monuments

People really need to ask themselves why communities erected statues of slave holders and not of abolitionists. h/t AOC
44. 2 points

## Does it make sense to say that something is almost infinite? If yes, then why?

In mathematics the problem is the 'almost'. So no it makes no sense. In Physical Science then yes phrase may have value, for instance an 'almost infinite thermal reservoir' in Thermodynamics or 'almost infinite dilution' in Chemistry. In each physical case the phrase measn that the quantity concerned is so large compared to the change considered that the quantity is constant or unaffected by the change. This is just making use of one mathematical property of infinity that infinity plus or minus x is still infinity.
45. 2 points

## Teaching Science and Asperger's Syndrome

Well, I'm not too sure what 'mild' in this context really means, but I'm certainly high functioning, and require no intervention or assistance to live a normal life. This is mostly because I have learned since childhood to mask my autistic traits to such a degree that most people won't be able to tell at first glance that I'm neurodivergent. In my case, I find it easy to express myself in written form; however, if we were in the same room, and I was asked to explain some GR concept verbally, then that would be much harder for me, especially if I didn't have time to prepare beforehand. And the subtleties and complexities of casual social situations will forever remain a mystery to me, even though I can outwardly play certain roles if necessary. This is a difficult subject, because the spectrum is so wide. Personally, I never thought of myself as having a disorder of any kind - I think of myself as neurodivergent. As being differently abled, rather than disabled. I consider it a gift, and if I was being reincarnated, and somehow given the choice, I would without a shadow of a doubt choose to be on the spectrum again, since for me the positives greatly outweigh the (nonetheless very real) challenges. I do recognise though that many others on the spectrum would disagree, since their autistic traits are more challenging for them, and they suffer from various comorbidities, such as ADHD and SPDs.
46. 2 points

## Think of a body which is at rest but not in equilibrium. Give explanation as well as figure/diagram.

At maximum height $\boldsymbol{v}=0$ but $\boldsymbol{a}\neq0$ Is that what's confusing you?
47. 2 points

## Teaching Science and Asperger's Syndrome

Nice post +1, I'll just add, in my work with differently abled humans, a good way to think of the differences; if a bus runs into a group of people, one extreme is, OMG how many people were hurt, while the other is, what colour is the bus. The OMG's will never really understand the what colour's, and vice versa; all we can really hope is, we understand that there's a difference in all of us...
48. 2 points

## Teaching Science and Asperger's Syndrome

If you get really good at setting expectations, you'll find it helps with everybody on the spectrum (which I suspect is broader than we think and may include a lot more of us). It may simply work on everyone. It's the equivalent of someone like Elizabeth Warren always having a plan. It allows people to make their own plans based on yours, and it's very comforting and satisfying, and makes folks feel great about following your lead. I recommend watching Hannah Gadsby's new Netflix comedy special Douglas if you can. She's been diagnosed with high-functioning autism, and she has this brilliant convention where she tells you EXACTLY how her standup show is going to unfold before she starts, in order to set your expectations as an audience member (I hope she continues this format in future shows). Then she does the show, and it's amazing how much funnier it is because you know what's coming. She also touches on several spectrum-related behaviors you should be aware of (beware the Puffer Fish). Thank you for taking the extra time, and also for recognizing that the way these beautiful minds work is just different, not abnormal. Your student appreciates it more than they're probably telling you.
49. 2 points

## Fermi paradox solutions

You're both welcome. A couple of things more. First, I just wanted to add that Fermi was no idiot, of course. But the assumptions he made date back to 1950. We know much more about planets now. Something we know now, for example, is that the Earth-Moon system is far from typical. The Moon is an unusually large satellite and has a rather bigger than normal stabilizing effect on the Earth's tilt. To the point that astronomers are starting to look upon the Earth-Moon system as a binary planetary system, rather than a standard planet and its small satellite or group of satellites. The huge tidal effect that the Moon has on the Earth is believed to have played a major part in the origin of life at least during the first billion years, stirring the chemicals dissolved in water and thus triggering volume reactions (much quicker and efficient) rather than surface effects. https://www.space.com/12464-earth-moon-unique-solar-system-universe.html Another factor is the presence of outer giants like Jupiter and Saturn, for billions of years playing the role of shuttles for asteroids from the Kuiper belt, etc. Water and amino acids in the asteroids are also thought to have been very important. In case any of these factors were found to be essential to the appearance of life, it could be a basis to estimate the number of solar systems in the Milky Way that satisfy similar conditions. Would other different sets of conditions be just as good, or maybe even better? I don't know. I don't know if anybody knows. Drake's equation came later than Fermi's argument (in 1961). Actually, I think Drake's equation is a more promising ground for estimating the chance of there being intelligent life forms, among other things, precisely because, although ambitious, it's a much less assuming parametrization of the probability, rather than an equation or a "closed" calculation. There is room for re-estimating the factors as we learn more about the phenomenology of galactic (or extra-galactic) solar systems. Plus the last factor is, if I'm not mistaken, the probability that a civilization will be able to send signals, rather than travel to Earth, which significantly increases the odds. Fermi was concerned with interstellar travel, AFAIK. The detection of signals with a message in them will probably be the first evidence, if there ever is one, of some form of intelligent life besides us in the universe, rather than the flight of UFOs. But here's the bad news, IMO: Take a look at this table with time gaps separating the appearance of new levels of organization: First prokaryotes (from Earth's formation): 1 billion years First eukaryotes (from prokaryotes): 800 million years First multicellular eukaryotic organisms (from single-celled eukaryotes): 2 billion years First intelligent life (from multicellular eukaryotes): 700 million years Average for the appearance of a new level of organization: 1.125 billion years Now suppose there's a planet out there with something like eukaryotes (cells with a nucleus). You're going to have to sit there waiting for 1.1 billion years for you to see anything interesting to happen if the above table is anything to go by. That's the problem.
50. 2 points

## Malaria 'completely stopped' by microbe - BBC News

You beat me to it. I was going to post this under the title "Good things can come in small packages". The annual death toll from malaria runs just under half a million. Great to see a potential solution. Some more information on malaria in general here. (It's from the WHO, so Trump supporters should look away now.)
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## Relationship between physical and spiritual

David was intentional about his relationship with God, as we see in much A common theme between maintaining good physical and spiritual. "Is there really a direct connection between being spiritually healthy and physically healthy as well?" Focus on the Family founder Dr. James. (From a letter of the Rebbe, dated the 2nd day of Rosh Chodesh Tammuz, ). Principles of Physical and Spiritual Health And Their Interrelationship Should.

## Relationship between standing waves and resonance project

Standing waves and resonance. Standing waves are an example of superposition. They occur when identical waves travelling in opposite directions. Analysis on non-resonance standing waves and vibration tracks of strings deterministic connection between vibration decay parameters and the occurence of. Standing wave, also called stationary wave, combination of two waves moving in opposite directions, each having the same amplitude and frequency.

## Relationship between euler angles and angular velocity vector

Behaves as an axial vector (like angular momentum) d d. = × Express angular velocity using Euler angles. ▫ Try to Will almost get to the equation of motion. the use of Euler angles: spin ψ˙, nutation θ and precession φ shown below in Figure 1. the unknowns in our equations of motion; then the angular velocities and angular is used; the primary difference is in the definition of the ”pitch” angle. For aircraft . For body-fixed principle axis, the angular momentum vector is given. Those who are not familiar with Euler angles or who would like a reminder can The angular velocity vector $$\bf{\omega}$$, however, will not be constant, but We are going to establish a geometrical relation between the.

## Relationship between limbic system and prefrontal cortex in adolescence

The insulation of brain connections with white matter or myelin (a process The limbic system or ''emotional brain'' develops at puberty, while the ''reasoning brain'' (prefrontal cortex) doesn't fully mature until the early to mid-twenties; thus, to. This consists of a set of structures on both sides of the thalamus and immediately beneath matter in the pre-frontal cortex, the part of the brain that has the most to do alongside psychosocial factors such as school and relationships and/or. Learn about teenage brain development and the prefrontal cortex. There are loose wires, so that the speaker system isn't working with the DVD player, which.

## Relationship between china and russia during cold war

In the culminating session of the “China and Russia Dialogues” and “Arms that Russia continues to adhere to several key Cold War strategic. The Sino–Soviet split (–) was the breaking of political relations between the People's Republic of China (PRC) Part of Cold War and Sino- Soviet relations the geopolitical rivalry between Chinese Stalinism and Russian peaceful In taking Communism to China, the leader of the Communist Party of China. between Russia and China and what it means for U.S. interests.1 The s and s The Sino-Soviet Split: Cold War in the Communist World (Princeton.

## Economic relationship between australia and indonesia relations

But surprisingly the two countries trade and invest very little with each to the challenges and opportunities in the relationship with Australia. Australia's Department of Foreign Affairs and Trade (DFAT) describes the relationship with Indonesia as "one of Australia's most important". Australia's new Prime Minister Scott Morrison and Indonesian President Joko Widodo welcomed yesterday the conclusion of all the main points.

## Relationship between dietary fat and cholesterol

The Role of Dietary Fats and Cholesterol in Heart HealthIt's time to demystify First, it's important to understand the difference between dietary cholesterol and. OBJECTIVE: This study assessed the relation between specific dietary fatty acids and cholesterol and CVD risk among women with type 2 diabetes. DESIGN. The consumption of dietary fat (measured in grams) is related inversely and significantly to total mortality. No significant relationships exist between grams of .

## Relationship between anemonefish and sea anemones clownfish

The relationship between the anemone and the anemonefish is a mutually beneficial one. Being brightly-coloured, the clown anemone fish makes easy prey for FIELD GUIDE TO ANEMONE FISHES AND THEIR HOST SEA. If you've seen the film 'Finding Nemo', you may already be familiar with clownfish and sea anemones. But, do you understand why they can live. The relationship between the sea anemone and clownfish allows the other to flourish The anemonefish symbiosis: what is known and what is.

## Relationship between ip and dns pdf printer

VPN, or virtual private network, is one such security mea- sure to protect the devices. A good example of a LAN device is a network printer. In general, a network port is an endpoint to a logical connection. The port The IP configurations appear for your machine, such as the DNS suffix, IP Address, Subnet Mask, and. CUPS supports most network printers using one of three TCP/IP-based protocols: encryption=always, Specifies that the connection to the IPP printer should be. hosts on the network. Note: The difference to the use of NAT with IP address pooling is that the mapping of public and private IP addresses is static.

## Relationship between wavelength mass and velocity

v -- The electron velocity, m0 -- The electron rest mass. Based on Newtonian theory, the relation between the wavelength (λ) of a particle (e.g. electron here). Matter waves are a central part of the theory of quantum mechanics, being an example of The de Broglie wavelength is the wavelength, λ, associated with a massive .. where m0 is the rest mass of the particle and c is the speed of light in a Likewise, the relation between group/particle velocity and phase velocity is. Is there a relation between wavelength and acceleration for an accelerated charged particle? Does the black hole evaporate completely or end in a finite mass (e.g., De Broglie wavelength is a relative quantity depending on relative velocity.

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G01 Chapter Contents
G01 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentG01PTF

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

## 1  Purpose

G01PTF returns the value of the first moment ${\Phi }_{1}\left(x\right)$ of the Landau density function, via the routine name.

## 2  Specification

 FUNCTION G01PTF ( X)
 REAL (KIND=nag_wp) G01PTF
 REAL (KIND=nag_wp) X

## 3  Description

G01PTF evaluates an approximation to the first moment ${\Phi }_{1}\left(x\right)$ of the Landau density function given by
 $Φ1x=1Φx ∫-∞xλϕλdλ,$
where $\varphi \left(\lambda \right)$ is described in G01MTF, using piecewise approximation by rational functions. Further details can be found in Kölbig and Schorr (1984).
To obtain the value of ${\Phi }_{2}\left(x\right)$, G01QTF can be used.

## 4  References

Kölbig K S and Schorr B (1984) A program package for the Landau distribution Comp. Phys. Comm. 31 97–111

## 5  Parameters

1:     X – REAL (KIND=nag_wp)Input
On entry: the argument $x$ of the function.

## 6  Error Indicators and Warnings

There are no failure exits from this routine.

## 7  Accuracy

At least $7$ significant digits are usually correct, but occasionally only $6$. Such accuracy is normally considered to be adequate for applications in experimental physics.

None.

## 9  Example

This example evaluates ${\Phi }_{1}\left(x\right)$ at $x=0.5$, and prints the results.

### 9.1  Program Text

Program Text (g01ptfe.f90)

### 9.2  Program Data

Program Data (g01ptfe.d)

### 9.3  Program Results

Program Results (g01ptfe.r)


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$$\begin{equation*} \frac{d^2\log f(x)}{dx^2}= -\frac{(\alpha-1)}{x^2}<0. ©2020 Matt Bognar Department of Statistics and Actuarial Science University of Iowa \end{equation*}$$. ... Graph. Gamma Distribution Formula, where p and x are a continuous random variable. Gamma distribution is used to model a continuous random variable which takes positive values. \end{array} \right. Here, we will provide an introduction to the gamma distribution. Suppose that X has the gamma distribution with shape parameter k and scale parameter b. Â© VrcAcademy - 2020About Us | Our Team | Privacy Policy | Terms of Use. Then the harmonic mean of $G(\alpha,\beta)$ distribution is $H=\beta(\alpha-1)$. Gamma Distribution Graph. The $r^{th}$ raw moment of gamma distribution is $\mu_r^\prime =\frac{\beta^r\Gamma(\alpha+r)}{\Gamma(\alpha)}$. Another form of gamma distribution is The parameter $\alpha$ is called the shape parameter and $\beta$ is called the scale parameter of gamma distribution. Calculates a table of the probability density function, or lower or upper cumulative distribution function of the gamma distribution, and draws the chart. \end{array} \right. \end{equation*} $$Let H be the harmonic mean of gamma distribution. of Y is,$$ \begin{eqnarray*} M_Y(t) &=& E(e^{tY}) \\ &=& E(e^{t(X_1+X_2)}) \\ &=& E(e^{tX_1} e^{tX_2}) \\ &=& E(e^{tX_1})\cdot E(e^{tX_2})\\ & &\qquad (\because X_1, X_2 \text{ are independent })\\ &=& M_{X_1}(t)\cdot M_{X_2}(t)\\ &=& \big(1-\beta t\big)^{-\alpha_1}\cdot \big(1-\beta t\big)^{-\alpha_2}\\ &=& \big(1-\beta t\big)^{-(\alpha_1+\alpha_2)}. \end{equation*} $$.$$ \begin{equation*} f(x)=\left\{ \begin{array}{ll} \frac{1}{\alpha^\beta \Gamma(\beta)} x^{\beta -1}e^{-\frac{x}{\alpha}}, & \hbox{$x>0;\alpha, \beta >0$;} \\ 0, & \hbox{Otherwise.} is given by, \begin{align*} f(x)&= \begin{cases} \frac{1}{\beta^\alpha\Gamma(\alpha)}x^{\alpha -1}e^{-x/\beta}, & x > 0;\alpha, \beta > 0; \\ 0, & Otherwise. ... graph horizontally and vertically. Y=X_1+X_2 is a Gamma variate with parameter (\alpha_1+\alpha_2, \beta). In Chapters 6 and 11, we will discuss more properties of the gamma random variables. Let Y=X_1+X_2. The gamma distribution with parameters k = 1 and b is called the exponential distribution with scale parameter b (or rate parameter r = 1 b). X is as follows: \begin{equation*} f(x)=\left\{ \begin{array}{ll} \frac{1}{\Gamma(\beta)}x^{\beta -1}e^{-x}, & \hbox{$x>0;\beta >0$;} \\ 0, & \hbox{Otherwise.} This is left as an exercise for the reader. Notes about Gamma Distributions: If $$\alpha = 1$$, then the corresponding gamma distribution is given by the exponential distribution, i.e., $$\text{gamma}(1,\lambda) = \text{exponential}(\lambda)$$. Hope you like Gamma Distribution article with step by step guide on various statistics properties of gamma probability. 16. of gamma distribution with parameter $\alpha$ and $\beta$ is, $$\begin{equation*} f(x) = \frac{1}{\beta^\alpha\Gamma(\alpha)}x^{\alpha -1}e^{-x/\beta},\; x > 0;\alpha, \beta > 0 \end{equation*}$$, $$\begin{equation*} \log f(x) = \log\bigg(\frac{1}{\beta^\alpha\Gamma(\alpha)}\bigg)+(\alpha-1)\log x -\frac{x}{\beta}. }\text{ in } K_X(t)\\ &=& \alpha \beta^r(r-1)!, r=1,2,\cdots \end{eqnarray*}$$, $$\begin{eqnarray*} k_1 &=& \alpha\beta =\mu_1^\prime \\ k_2 &=& \alpha\beta^2=\mu_2\\ k_3 &=& 2\alpha\beta^3=\mu_3\\ k_4 &=& 6\alpha\beta^4=\mu_4-3\mu_2^2\\ \Rightarrow \mu_4 &=& 3\alpha(2+\alpha)\beta^4. Let X_1 and X_2 be two independent Gamma variate with parameters (\alpha_1, \beta) and (\alpha_2, \beta) respectively. Gamma distribution is widely used in science and engineering to model a skewed distribution. \end{equation*}$$, Differentiating $\log f(x)$ w.r.t. Gamma distribution is widely used in science and engineering to model a skewed distribution. The variance of gamma distribution $G(\alpha,\beta)$ is $\alpha\beta^2$. Hence, the density $f(x)$ becomes maximum at $x =\beta(\alpha-1)$. \end{eqnarray*} $$. The cumulant generating function of gamma distribution is K_X(t) =-\alpha \log \big(1-\beta t\big). Letting \alpha=1 in G(\alpha, \beta), the probability density function of Gamma Distribution. The gamma distribution is another widely used distribution. The p.d.f. The parameters of the gamma distribution define the shape of the graph. It is clear from the \beta_1 coefficient of skewness and \beta_2 coefficient of kurtosis, that, as \alpha\to \infty, \beta_1\to 0 and \beta_2\to 3. He holds a Ph.D. degree in Statistics. \end{eqnarray*}$$. Following is the graph of probability density function (pdf) of gamma distribution with parameter $\alpha=1$ and $\beta=1,2,4$. Raju is nerd at heart with a background in Statistics. If $H$ is the harmonic mean of $G(\alpha,\beta)$ distribution then, $$\begin{eqnarray*} \frac{1}{H}&=& E(1/X) \\ &=& \int_0^\infty \frac{1}{x}\frac{1}{\beta^\alpha\Gamma(\alpha)}x^{\alpha -1}e^{-x/\beta}\; dx\\ &=& \frac{1}{\beta^\alpha\Gamma(\alpha)}\int_0^\infty x^{\alpha-1 -1}e^{-x/\beta}\; dx\\ &=& \frac{1}{\beta^\alpha\Gamma(\alpha)}\Gamma(\alpha-1)\beta^{\alpha-1}\\ &=& \frac{1}{\beta^\alpha(\alpha-1)\Gamma(\alpha-1)}\Gamma(\alpha-1)\beta^{\alpha-1}\\ &=& \frac{1}{\beta(\alpha-1)}\\ & & \quad (\because\Gamma(\alpha) = (\alpha-1) \Gamma(\alpha-1)) \end{eqnarray*}$$, Therefore, harmonic mean of gamma distribution is, $$\begin{equation*} H = \beta(\alpha-1). In this tutorial, we are going to discuss various important statistical properties of gamma distribution like graph of gamma distribution for various parameter combination, derivation of mean, variance, harmonic mean, mode, moment generating function and cumulant generating function. To analyze our traffic, we use basic Google Analytics implementation with anonymized data. Therefore, mode of gamma distribution is \beta(\alpha-1). The r^{th} raw moment of gamma distribution is,$$ \begin{eqnarray*} \mu_r^\prime &=& E(X^r) \\ &=& \int_0^\infty x^r\frac{1}{\beta^\alpha\Gamma(\alpha)}x^{\alpha -1}e^{-x/\beta}\; dx\\ &=& \frac{1}{\beta^\alpha\Gamma(\alpha)}\int_0^\infty x^{\alpha+r -1}e^{-x/\beta}\; dx\\ &=& \frac{1}{\beta^\alpha\Gamma(\alpha)}\Gamma(\alpha+r)\beta^{\alpha+r}\\ &=& \frac{\beta^r\Gamma(\alpha+r)}{\Gamma(\alpha)} \end{eqnarray*} .

.

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1. 10 points

2. 7 points

## [DevirtualizeMe] Themida 3.0.3.0

Answer The password is "gamer vision". All of the following addresses are based on the modulebase 0x00007FF644840000. The possible OEP at: 00007FF644841DF8 | 48:895C24 20 | mov qword ptr [rsp+20],rbx 00007FF644841DFD | 55 | push rbp 00007FF644841DFE | 48:8BEC | mov rbp,rsp 00007FF644841E01 | 48:83EC 20 | sub rsp,20 ... Then the second hit in code section at: 00007FF6448416FC | 48:895C24 08 | mov qword ptr [rsp+8],rbx 00007FF644841701 | 48:897424 10 | mov qword ptr [rsp+10],rsi 00007FF644841706 | 57 | push rdi 00007FF644841707 | 48:83EC 30 | sub rsp,30 ... After prompted "enter password.", the input routine at: 00007FF644841400 | 48:8BC4 | mov rax,rsp 00007FF644841403 | 57 | push rdi 00007FF644841404 | 41:54 | push r12 00007FF644841406 | 41:55 | push r13 00007FF644841408 | 41:56 | push r14 00007FF64484140A | 41:57 | push r15 00007FF64484140C | 48:83EC 50 | sub rsp,50 ... the pointer of local buffer for receiving input text is in rdx(for example, 000000359CC9FA58). When entered some test characters, stack looks like: 000000359CC9FA58: 31 32 33 34 35 36 37 38 39 30 31 32 00 7F 00 00 "123456789012" 000000359CC9FA68: 000000000000000C input size 000000359CC9FA70: 000000000000000F buffer size Whereafter, the process logic virtualized. First of all, the length of input text got checked in a vCmpqr handler: 00007FF644898E0B | 49:39F0 | cmp r8,rsi ; r8=000000000000000C(actual), rsi=000000000000000C(const) The length MUST be 12!, else got "no!". NOTE: the encrypt password has no chance to get decrypted if input length is wrong! The answer String is encrypted(0xC length): 00007FF64484BCB0 8B 75 81 89 86 34 9A 8D 87 8D 83 82 00 00 00 00 decrypt algo: 00007FF6448BF3A6 | 40:8A36 | mov sil,byte ptr [rsi] rsi=00007FF64484BCB0, sil=8B 00007FF6448D4125 | 44:30DB | xor bl,r11b bl=8B, r11b=08; ^=08 = 83 00007FF64488E987 | 880A | mov byte ptr [rdx],cl [00007FF64484BCB0] <- 83 00007FF64485748F | 8A09 | mov cl,byte ptr [rcx] [00007FF64484BCB0] -> 83 00007FF64485E6FA | 44:00D7 | add dil,r10b dil=83, r10b=E4; +=E4 = 67 'g' 00007FF64488E987 | 880A | mov byte ptr [rdx],cl [00007FF64484BCB0] <- 67 00007FF64488DA96 | 49:FFC4 | inc r12 ptr++ 00007FF644859691 | 41:FFC9 | dec r9d length-- 00007FF64488743C | 85C8 | test eax,ecx end loop if length zero At the end of loop, the plaintext: 00007FF64484BCB0 67 61 6D 65 72 20 76 69 73 69 6F 6E 00 00 00 00 gamer vision.... The comparison: 00007FF6448424E7 | FF25 330C0000 | jmp qword ptr [<&memcmp>] ret rax=00000000FFFFFFFF/0000000000000000(if matches) rcx=000000359CC9FA58 "123456789012" rdx=00007FF64484BCB0 "gamer vision" r8=000000000000000C Strings Encrypted Structure BYTE bEncrypt // 1 - encrypt, 0 - decrypt DWORD dwLength BYTE UnDefined[0xC] BYTE CipherText[dwLength+1] The related messages as followings, you can find them in the VM Section ".themida" after it got unpacked at the very beginning of the application. 00007FF6448AC79F 01 10 00 00 00 01 00 00 00 80 21 00 40 01 00 00 decrypt algo: ^A0+4F 00007FF6448AC7AF 00 B6 BF 85 B6 83 71 81 B2 84 84 88 80 83 B5 7F "enter password.\n" 00007FF6448AC7BF 1B 00 00007FF64484BC9F 01 0C 00 00 00 72 64 2E 0A 00 00 00 00 00 00 00 decrypt algo: ^08+E4 00007FF64484BCAF 00 8B 75 81 89 86 34 9A 8D 87 8D 83 82 00 "gamer vision" 00007FF644886C7F 01 05 00 00 00 72 20 76 69 73 69 6F 6E 00 00 00 decrypt algo: ^85+10 00007FF644886C8F 00 EC D0 E6 94 7F 00 "yes!\n" 00007FF64489252F 01 04 00 00 00 00 00 00 00 79 65 73 21 0A 00 00 decrypt algo: ^65+C9 00007FF64489253F 00 C0 C3 3D 24 00 "no!\n" 00007FF64484C40F 01 19 00 00 00 0A 00 00 00 6E 6F 21 0A 00 00 00 decrypt algo: ^12+C6 00007FF64484C41F 00 B8 BE 8D BF BF 48 8D BA BC 8D BE 48 BC BB 48 "press enter to continue.\n" 00007FF64484C42F 8F BB BA BC B1 BA BD 8D 7A 56 00
3. 7 points

## The (Legally) Free PC Games Topic...

At least they made him look cute!
4. 6 points

## Analyzing Keyboard Firmware

Hey guys, After a long time I started writing on my blog again. https://mrexodia.github.io/reversing/2019/09/28/Analyzing-keyboard-firmware-part-1 Best regards
5. 6 points

## ConfuserEx Light Test

For unpacking 1) cawk unpacker 2) dump after decryption 3) fix EP 4) Proxy call fixer by Davicore 5) Strings decryptor by CC 6) Switch killer by CC 7) Dump resources (empty) 😎 Clean cctor and <module>methods (maybe 4, 5 and 6 can be replaced by cawk unpacker again) I will check the key algo tomorrow, don't have time now. a29p-EP-anti2_noproxy_stringdec-cleaned_deobfuscated-res2-cctor-module.exe -------------------------------------------------------- Username = "Usuario" Code = "161308" int length = username.length(); int num2 = length + 2 - 4 + 40 + 10; return Convert.ToString(419 * num2 * length - length); --------------------------------------------------- EDIT2: I have received a few PMs asking how to fix EP, so I will post the videos I used as reference here. Following this 2 videos you should be able to unpack confuserex fully.
6. 5 points

## AdvancedScript x64dbg Plugin

AdvancedScript beta version it is beta version it could have bug, so please report and if u like to add more features let me know. version 2.5 beta : 1- Script window is sperate. 2- Create Folder for script,form Load script with category. 3- add more mirror Functions (xorx - pushx ...), and Functions like ( if , goto,writestr ) to shortcut the work. 4- show all variables in a list with it's values. 5- edit script onfly. 6- enable to define array with range like z[n]. 7- writestr Function. 8- run from anyware in the script. 9- rest variables list in case maintenance. 10- insert rows as much as you need. 11- insert from clipboard replace all script. 12- insert from clipboard inside the script. 13- copy separated lines to used in other script. 14- insert description without confusing . 15- add the dll file of c++ runtime for each package. 16- add some scripts samples. 17- as it is beta version so it support one step not auto step , use F12 for step, sorry for that I need to check if it work then I will add auto step :} note : I forget to say use (Scriptw) command to show the Script window , but git has stop working and copy the script sample to ur script folder in x64dbg folder and pls read the help first AdvancedScript_2.5beta.zip
7. 4 points

## WinRAR Nukes Pirate Keygen

Actually Winrar was a kind of an earl adopter of ECDSA licensing, but they made a mistake in the implementation, much like level 10 armadillo. I still remember when I first came across this release - i thought, man, not another hardcoded-pseude-keygen ... then I saw "SeVeN/FFF". I was like "ahh shit here we go". Problem for Winrar is that their license is tied to archive signatures - if they change it they will break the signature mechanism.
8. 4 points

## arithmetic operator obfuscation (source)

https://github.com/DefCon42/op-mutation decided to release the source because it's a neat example of a practical application of linear algebra yes, i know the code does not look great and there's blatant violations of like every standard ever no, i won't change that :^) note: only works with relatively simple operations. add, sub, not, etc will work but higher order operators like multiplication and exponentiation will not
9. 4 points

## [DevirtualizeMe] ArmDot

And here is the fully deobfuscated file with strings decrypted i havent ran through de4dot since this will simplify your button click method to one messagebox.show Unpacked.exe
10. 4 points

## Obfuscating Operations using Linear Algebra

Hey all! I recently came across this neat paper here: https://tel.archives-ouvertes.fr/tel-01623849/document where they used what they called "Mixed-Boolean Arithmetic" to obfuscate arithmetic expressions, and then showed ways to deobfuscate them. Looking a the deobfuscation methods, they seemed largely either pattern-based or wouldn't work when bigger numbers were involved. So I thought to myself, "How can I mess with this?" Well, first things first, they have no concrete method there for creating these expressions. There are two pages total dedicated to the creation of these expressions, so I had to get creative to make it work. They describe using numpy to solve the matrix equation created and using a hack-y method to circumvent not having a square matrix, but I thought that I could do a bit better... Enter two painstaking days of learning linear algebra and figuring out exactly what I needed to do. They start by computing the truth tables of some expressions, putting them into a matrix as columns, then solving for the vector that, when using the dot product on the vector and the matrix, returned zero. After that, they filtered out various "rewrite rules" from the matrix generated. You can read more about this in the paper, though there's not much to go off of. They use numpy's linalg.solve to do this, but that only works with square matrices and produced results with constants that were a tad small for my taste :^) After a bit of research I found a python module called cvxpy, designed to find values that satisfy an expression under certain constraints. Even cooler was that you could specify matrix equations and integer-only solutions, which is exactly what I needed. After tinkering with it for a bit, I was able to reliably create expressions like these (representing a xor b): -27540 * (~a & b) + 373574 * (~a ^ ~b) + -27541 * (a & ~b) + -27541 * (~a & b) + -11 * (a + b) + -30436 * (~a & ~b) + -30436 * (~a * ~b) + 137712 * (a * ~b) + -27544 * (~a) + 1 * (b) + 3 * (~a + ~b) + -221347 * (~a - ~b) + 13 * (a + b) + -2 * (a) + -30454 * (~a + ~b) + -30454 * (~a + ~b) + -3 * (b) + -30449 * (a | b) + -27546 * (~b) 3672455 * (~a * b) + -362611 * (a ^ b) + 78113 * (a) + -524636 * (~b) + -524636 * (a ^ ~b) + 78113 * (a) + -524636 * (~a | b) + -362611 * (a ^ b) + -959545 * (a | b) + -78113 * (a - b) + -959545 * (~a + ~b) + -524636 * (~a) + 142249 * (a + b) + -959544 * (~a + ~b) + 142249 * (a + b) + -524637 * (a - ~b) + -524637 * (~a) + -524637 * (a & ~b) + 3241246 * (~a ^ ~b) Using truth tables modulo 4 instead of modulo 2 I was also able to compute equivalencies for multiplication, which was pretty neato. However, using the same method of computing the truth table and finding an equivalent expression you can reverse this sort of operation. I'll leave that as an exercise to the reader. EDIT: As a friend of mine pointed out, this will work with any operation that can be reducible to boolean math (i.e. xor, addition, subtraction, multiplication), not just arithmetic operations.
11. 4 points

## slugsnacks reversing series by c0lo

slugsnacks reversing series by c0lo: Link: https://kienmanowar.wordpress.com/slugsnacks-reversing-series-by-c0lo/slugsnacks-reversing-series-5/
12. 3 points

13. 3 points

## x64dbg Plugin Manager

Console example x64plgmnrc.exe -G "C:\x64dbg_root" // Set root path for x64dbg x64plgmnrc.exe -U // Update list from server x64plgmnrc.exe -S // Show list of plugins x64plgmnrc.exe -i x64core // Install last version of x64dbg x64plgmnrc.exe -i AdvancedScript // install AdvancedScript https://github.com/horsicq/x64dbg-Plugin-Manager
14. 3 points

## Invidious is an alternative front-end to YouTube

https://invidio.us/ src - https://github.com/omarroth/invidious
15. 3 points

## AdvancedScript x64dbg Plugin

Hi New Update with more features : https://github.com/Ahmadmansoor/AdvancedScript AdvancedScript version 4.3 https://github.com/Ahmadmansoor/AdvancedScript/releases * Add new commands and fix some bugs * fix error load of the Auto Commands when there is no ; * Fix AutoRun and stepson ( wait command to finish). * Fix color variable name. * Add ReadFile , Write2Mem , ReadMem * Add GoToByBase Form ( https://www.youtube.com/watch?v=gQxlbC8RnRg ) * Assigne variable directly no need to Setx Command. Sample : Varx str,memory // var will hold the hex value Varx int,rax_,0 // read rax value +1 Varx str,ourStr // read test string ReadMem $memory,{rax},5$rax_={rax} +1 $rax_=ads.exebase ReadStr$ourStr,{rdx}
16. 3 points

## Crackme Baby

That is most likely not your crackme. But what the hell.. Load it in IDA, decompile serial check and it will look like this: if ( ++idx >= 29 ) { if ( count_of_sevens == 1 && String[6] == '7' ) { v5 = (unsigned __int8)entered_key[0]; if ( entered_key[0] ) { LOBYTE(v5) = entered_key[4]; if ( v5 ) { LOBYTE(v5) = entered_key[8]; if ( v5 ) { LOBYTE(v5) = entered_key[12]; if ( v5 ) { LOBYTE(v5) = entered_key[16]; if ( v5 ) { LOBYTE(v5) = entered_key[21]; if ( v5 ) { part1 = getintfromkey(0, 4, 0); part2 = getintfromkey(0, 4, v6); part3 = getintfromkey(0, 4, v7); part4 = getintfromkey(0, 4, v8); part5 = getintfromkey(0, 5, v9); part6 = getintfromkey(0, 8, v10); v11 = part1 * (unsigned __int8)entered_key[7]; v12 = part1 * (unsigned __int8)entered_key[6]; v13 = part1 * (unsigned __int8)entered_key[4]; if ( v11 == part5 && v12 == part3 && !(part1 * (unsigned __int8)entered_key[5]) && v13 == part4 && 1000 * v13 + 10 * v12 + v11 == part6 ) { ...show good boy message... There are some checks for specific character values: * char 6 must be "7", there may not be any other "7" in the key; * char 5 must be "0"; * chars 4,8,12,16,21 may not be "0"; Key is split into in several parts: part1 = first 4 chars part3 = chars 8..11 part4 = chars12..15 part5 = chars16..20 part6 = chars21..28 Then it does some simple multiplication and checks the result. At this point you have 2 options: - make a tool that will randomly choose part1 and chars 4 and 7, do the multiplication to calculate parts 3, 4, 5, 6 and see if it passes all checks. - remember math lessons from school and figure out the only possible combination that will pass all checks. First one is much faster, second one will be .. challenging. Either way, you should arrive at the only possible solution: Well, in fact, there is infinite number of valid keys. You can append random characters to the key above, they are not checked..
17. 3 points

18. 3 points

## Millions using 123456 as password...

I really, really disagree. Not all websites are valuable. And not all passwords should chosen to be secure. In fact, this was something I wanted to write about for a long time already, so here it goes: https://lifeinhex.com/my-password-is-password/ (shameless self-promo, I know! )
19. 3 points

## The best design tools for everything!!

https://github.com/LisaDziuba/Awesome-Design-Tools#no-code-tools bonus (free -> add to cart -> mailinator -> 498mb) - hxxps://fusionretrobooks.com/collections/pdf/products/the-story-of-the-commodore-amiga-in-pixels_pdf
20. 3 points

## Obsidium v1.6.1.9

Used protector (I've forget to specify): https://www.52pojie.cn/thread-652274-1-1.html http://distro.crack.vc/index.php?dir=RceTools/Packers/ Finally made scripts and a tutorial on how to restore stolen bytes: https://forum.tuts4you.com/topic/41211-obsidium-olly-scripts/ BR.
21. 2 points

## How to bring a window active to front?

I am glad you have a workaround for this in the end. You may find suspending operation for around ~10 milliseconds after setting the cursor position and before simulating the mouse down input, using the Sleep function, adds a little bit more reliability and may not require you to add a second call to SetWindowPos. If you are concerned about accidentally activating a menu when simulating the mouse down you can calculate the centre of the windows titlebar or populate NONCLIENTMETRICS structure. Just be mindful there may be occasions where this may still occur particularly with owner drawn windows and Windows 10 apps. I still recommend the timer option... 😎 Ted.
22. 2 points

## Flare On 6

@Washi has finally made his writeups public: https://github.com/Washi1337/ctf-writeups/tree/master/FlareOn/2019/ Some of his solutions make me green with envy. Great job!
23. 2 points

## Triton - Dynamic Binary Analysis framework for Delphi

I created this experimental project. I hope someone can be useful. any collaboration and improvement is welcome thank you https://github.com/Pigrecos/Triton4Delphi
24. 2 points

25. 2 points

## Harmony Injector Help

For Harmony You need to load Target executable to the current domain in other words you need to create application loader. The Step: 1. Create new WinForms (loader) - Add reference to 0Harmony.dll and Target.exe - Add button, name it btnOpenApp with click handler private void btnOpenApp_Click(object sender, EventArgs e) { AssemblyName assemblyName = AssemblyName.GetAssemblyName(@"c:\path\to\Target.exe"); var assembly = Assembly.Load(assemblyName); var methodBase = assembly.ManifestModule.ResolveMethod(assembly.EntryPoint.MetadataToken); // do the patch Harmony.Patch(); // Open the Target new Thread(() => { // assume method entry point is static and doesn't have parameter methodBase.Invoke(null, null); }).Start(); } 2. Create class Harmony.cs using Harmony; using System; using System.Reflection; using System.Windows.Forms; namespace YourWinformsNameSpace { internal static class Harmony { public static void Patch() { HarmonyInstance h = HarmonyInstance.Create("test.patch.by.ewwink"); h.PatchAll(Assembly.GetExecutingAssembly()); } [HarmonyPatch(typeof(Target.FormClass), "calculate")] [HarmonyPatch(new Type[] { typeof(int), typeof(int) })] public class Patchcalculate { static void Prefix(int num1, ref int num2) { MessageBox.Show(string.Format("Second param {0} will be patched to 7", num2)); num2 = 7; } } } } The above will patch second parameter for calculate method to 7. make sure target Framework and CPU is match.
26. 2 points

## Visual Studios 2019 Pro - trial

or simply use tools like RunAsDate
27. 2 points

## .ICO to Bitmap...

Read about LR_LOADTRANSPARENT flag for LoadImage. That's how it was done in the old days before alpha blending..
28. 2 points

## .ICO to Bitmap...

Load icon Create a compatible bitmap same size as icon Use DrawIcon / DrawIconEx to draw the icon into the hdc's bitmap return the hBitmap and free any resources not required - dc's, icon (if not needed anymore) Use the SetMenuItemBitmaps Might need to include a few other steps but the basics outlined should convert the icon to a bitmap.
29. 2 points

## ConfuserEx Mod

login pass: steps to unpack: 1. removed anti tamper and some junk calls 2. cleaned cflow (Thanks to Tesla for cflow cleaning) 2. removed proxy calls 3. removed proxy calls again 4. converted x86 methods to IL 5. decrypted all constants 6. cleaned cflow again (Thanks to Tesla for cflow cleaning) 7. cleaned some small stuff with de4dot. UnpackMe3-cleaned_noProxy_noProxy-NoX862-StringDec_cleaned-cleaned.exe
30. 2 points

## Debugging in Turbo Pascal like it's 1994

Best days of programming before all this Java and Android chaos
31. 2 points

## Firefox disabled all AddOns!

Here is the hotfix for anyone who wants to install without turning on Data Collection and Use... hotfix-update-xpi-intermediate@mozilla.com-1.0.2-signed.xpi
32. 2 points

33. 2 points

## How to set diffrent colors in a single menu string?

Check Ted's answer again: So if you want colors (any at all) or mix normal/bold then you will need to draw the items yourself using the GDI api SetTextColor and TextOut and those functions after responding to the draw item event by setting the owner draw flag.
34. 2 points

## How to set diffrent colors in a single menu string?

I use something like this if I want to make a menu item bold... bold.MENUITEMINFO bold\cbSize = SizeOf(bold) bold\fMask = #MIIM_STATE bold\fState = #MFS_DEFAULT SetMenuItemInfo_(MenuID(0), 2, #True, bold) ;"2" is the MenuItem to be made bold https://docs.microsoft.com/en-us/windows/desktop/api/winuser/nf-winuser-setmenuiteminfow https://docs.microsoft.com/en-au/windows/desktop/api/winuser/ns-winuser-tagmenuiteminfoa Ted.
35. 2 points

## Reversing WannaCry w/ Ghidra

https://youtu.be/Sv8yu12y5zM bonus - VSCodium - Binary releases of VS Code without MS branding/telemetry/licensing - hxxps://github.com/VSCodium/vscodium
36. 2 points

## A new disassembler coming soon?

9.0.2 released with the source which notes can be found on their site: https://ghidra-sre.org/releaseNotes.html With the source, they did include the decompiler's source code which some were concerned with being released. It's there and is coded in C/C++ so there is potential for things to get better as time goes on with community help/support. Would love to see it become on par with IDA's and better in the long run. Given how Ghidra is setup too, if it does start to become on par/better of a decompiler someone could essentially turn it into an IDA plugin if they wanted.
37. 2 points

## C generate all possible combination of strings - for brute force

C generate all possible combination of strings - for brute force: char* ValidChars = "0123456789ABCDEF"; int MinimLen = 1; int MaximLen = 2; char SpecialChars[255] = {0}; char GeneratedString[50] = {0}; int Valid_Chars_len = strlen(ValidChars); SpecialChars[0] = ValidChars[0]; // the first char will be first allowed char // SpecialChars[i] will point to next char like this: // SpecialChars['a'] = 'b'; // SpecialChars['b'] = 'c'; // SpecialChars['c'] = 00; // the end of a loop for (int i=0;i<Valid_Chars_len-1;i++) SpecialChars[ValidChars[i]] = ValidChars[i+1]; memset(GeneratedString, ValidChars[0], MinimLen); // we start with 'aaa' string char NextChar; int Pos = 0; while (1) { Pos = 0; printf("gen = %s\r\n", GeneratedString); LoopStart: NextChar = SpecialChars[GeneratedString[Pos]]; if (NextChar!=0) { GeneratedString[Pos] = NextChar; } else { GeneratedString[Pos] = SpecialChars[0]; // we start again Pos++; if (Pos>=MaximLen) break; goto LoopStart; } } The code works 100% ok but it is a bit ugly especially the "goto LoopStart;" Any other optimizations I could make to the above code or other generation of all combinations possibility? Obviously should be optimized to the maximum!
38. 2 points

## Congratulations Mr Exodia

Find it funny how the agitator creates the topic to try and bring attention to what he had to post later on Puny schemes. People just have lives; RE isn't going anywhere. Same as there's been one generation of smart, skilled and enthused people, others will follow. Circle of life. What I do find funny is how this "high-level programming" works even with big companies, such as Denuvo. I put quotes because same as Java relies on a ton of shit OTHER people wrote across time, which they now just import, similarly Denuvo relies on VMProtect to shield whatever crap they've got going on. Were it not for it, we'd have gotten ourselves the ol' time SecuROM/SafeDisc fiascos. I digress.. Congrats, ExoD And keep it up, love your work.
39. 2 points

## Confuserex Modded by Cµrsëd\$hëëp v3

Tools: dnSpy, ConfuserEx Tools, de4dot ConsoleApplication3_unpacked.exe
40. 1 point

## Installing Win 7 problem

Rufus states... else you could try an old version http://olddownload.com/rufus-usb/?windows=XP
41. 1 point

## Strange VB injector sample, no injection behavior on physical/virtual machine

Hi all: Recently I've analyzed a VB malware sample. This VB injector runs on physical analyzer machine (Win7 x86) and virtual machines (Win7 x64 and Win XP) without injection behavior. But when I upload the sample to the online sandbox, it appears to inject iexplorer.exe and sends DNS request to C&C server. By the way, the VC runtime library and .NET framework 2&4 are already installed on the virtual machine. I have not found any way to make the sample appear any injection behavior by checking Process Monitor yet. Can anyone figure out the reason, it's welcome to communicate, or is there anyone who can dump out its Trojan body, please let me know, thks a lot... The password of the sample zip package is "infected". Do not run or debug on the real machine! ANY.RUN report (PC-side access): https://app.any.run/tasks/2be96389-5c11-4541-b3b2-bb027f445add/ Hybrid Analysis report: https://www.hybrid-analysis.com/sample/0e0a3f5fa2d7e092dbb9e31b55e8f1dc6879673d9af92735577522dc504e7af9?environmentId=120 VB_Injector_password_infected.zip
42. 1 point

## How to bring a window active to front?

As @atom0s already mentioned SetFocus is what you are after if you want keyboard events in your window... Ted.
43. 1 point

## Tracing Differences x64dbg

Check this by Mr. Kurapica: https://forum.tuts4you.com/topic/38536-x64dbg-conditional-branches-logger-plugin
44. 1 point

## How to use RoundRects with Gardient Color?

Hi Progman, so it would be nice to have / find some kind of complete Ownerdraw example template code but didnt found anything like that.Ony short codes to handle this or that you know.Also for a menu OD I didnt found any full code example / template to handle all situations for menus etc. No I didnt checked the Win 2000 source.Maybe I wouldnt also find where this OD code is stored into (file xy). greetz
45. 1 point

## A new disassembler coming soon?

Source Code of Ghidra Released:
46. 1 point

## How to make a file with a ReverseEngineering

You have to reverse engineer how and from what the file checksum is calculated, and then fix the checksum in your exploit-file, yes. If you are lucky and need just the one checksum, you can try to find where it compares the invalid checksum with the one it expects, and just replace the checksum in your file with that.
47. 1 point

## z3 SMT solver for Pascal

https://github.com/Pigrecos/Z34Delphi My new repository for using Z3 in delphi(porting z3 c api to delphi). I tried and there were no tools for symbolic execution in delphi
48. 1 point

## A strange dream - A Java "Rever" tool name inexistent

Last night I dreamt my football team would win 0-1. The next morning I heard the score over the radio that they had won the game 0-1. A betting man would want to have these dreams the night before... Ted.
49. 1 point

## Want to learn C Programming ?

As mentioned in a prior thread, Kernighan and Ritchie is the de-facto standard in this case. You can get it for free here: http://www.dipmat.univpm.it/~demeio/public/the_c_programming_language_2.pdf
50. 1 point

## [DevirtualizeMe] Themida 2.3.5.0 Full

Well, there are few dedicated persons in the world who can do that. Noobs can't. And there are no up-to-date public tools (Deathway's tools are not working for most VMs already). So, after doing simple cost-benefit analysis, Themida guys will sleep really well.


text:
# Math Help - Continuous random variable P(B|A) when A=X>1/2, B=X>3/4

1. ## Continuous random variable P(B|A) when A=X>1/2, B=X>3/4

The continuous random variable X has probability density function given by:

$f(x)=\frac{3}{4} (1+x^2), for 0\leq x \leq 1, and 0, otherwise$
A is the event X>1/2, B is the event X> 3/4.
Find P(B|A).

I have not the faintest idea how to do this, I have tried a few odd approaches but they doesn't match the book's answer: 85/152
I got P(A)=13/32 and P(B)=85/256
:help:

2. $P\left( {B|A} \right) = \frac{{P(B \cap A)}}{{P(A)}} = \frac{{P(B)}}{{P(A)}}$

You have an error: $P(A)=\frac{{\color{red}19}}{32}$


text:
# What makes a pattern in a sequence?

Assume a stream of characters$(c)$ where $c \in (A, B, C ... Z)$.

I need to identify patterns available in the stream. As per the definition of a pattern I should be looking for a recurring string.

For example if the stream observed thus far is:

$$A\space B\space A\space S\space Y\space K\space I\space A\space B\space L\space J\space L\space B\space C\space L\space K\space I\space P\space I\space B\space C\space A\space B\space A\space B\space A\space B\space A\space B\space$$

By observation it can be observed that the string $AB$ appears 6 times whilst $BC$ appears 2 times.

My questions are as follows:

1. Apart from repetition are there any conditions that a string should suffice in order to be considered a pattern
2. If repetition is the only factor how many times a string should appear on the stream to be legitimately considered a pattern? Is there any mathematical logic in deciding this factor. (As per my understanding it has to be at least 2 since a single character itself could not be considered a pattern in this case. A single character could also be a pattern if it appears in a fixed interval however, I'm only focused on the string make up at this point.)
-


text:
Search
Perspective

Perspective Perspectives are commissioned from an expert and discuss the clinical practice or public health implications of a published study. The original publication must be freely available online.

See all article types »

# Lost but Not Forgotten—The Economics of Improving Patient Retention in AIDS Treatment Programs

• bisson@mail.med.upenn.edu

Affiliation: University of Pennsylvania School of Medicine, Department of Medicine, Division of Infectious Diseases, Philadelphia, Pennsylvania, United States of America

X
• Affiliations: University of Alabama School of Medicine, Department of Obstetrics and Gynecology, Division of International Women's Health, Birmingham, Alabama, United States of America, Centre for Infectious Disease Research in Zambia, Lusaka, Zambia

X
• Published: October 27, 2009
• DOI: 10.1371/journal.pmed.1000174

This Perspective discusses the following new study published in PLoS Medicine:

Losina E, Touré H, Uhler LM, Anglaret X, Paltiel D, et al. (2009) Cost-effectiveness of Preventing Loss to Follow-up in HIV Treatment Programs: a Côte d'Ivoire Appraisal. PLoS Med 6(10): e1000173. doi:10.1371/journal.pmed.1000173

### Loss to Follow-up after ART Initiation

The global HIV epidemic has been described as a public health emergency, which is both accurate and misleading. It is accurate because despite years of coordinated efforts, millions of people worldwide remain in urgent need of antiretroviral therapy (ART) [1]. But the term emergency is also misleading because it implies an acuity that, like a flood or famine, can be expected to abate once appropriate relief measures are delivered. Of course, the HIV pandemic is decades old, HIV care is life-long, and the HIV-infected population is young; the end of this public health emergency is nowhere in sight.

Tracking the progress of early ART scale-up efforts initially focused on tallying the number of individuals in need that actually started ART. A number of reports from Africa and other settings documented excellent early ART response rates, even in the face of severe resource constraints [2][4]. However, many of these reports also told another story. The introduction of AIDS care in many sites has represented a monumental shift in the way medical care is delivered—from a model of episodic treatment of symptomatic individuals with, for example, malaria, to one of life-long, chronic care. As such, the issue of patient attrition, never particularly considered or measured previously, emerged as a major issue. In a 2007 systematic review of patient retention in ART programs in sub-Saharan Africa, Rosen et al. found that only about 62% of those started on ART remained in care at 24 months after initiation [5]. Moreover, loss to follow-up (LTFU), a term used to describe patients who fail to present to clinic for a certain period of time and are not known to have died, accounted for most of the attrition.

Interruptions in ART are a problem from a patient care perspective because of the associated risk of incomplete virologic suppression [6], ongoing HIV transmission [7], inflammatory events, immunologic decline, opportunistic infections, and death [8]. LTFU is also particularly problematic from the standpoint of clinic efficiency because attempting to locate these patients after they become “late” to clinic is resource-intense and often unsuccessful. In Zambia's large national treatment program, for example, only one-third of patients who were late could be contacted, often after multiple attempts [9]. Finally, LTFU may lead not only to overly optimistic estimates of program response rates but to biased risk factors for death after ART initiation as well [10].

### A Cost-Effectiveness Study from Côte d'Ivoire

In the current issue of PLoS Medicine, Losina et al. show the dramatic contribution of LTFU to overall program effectiveness and cost-effectiveness of a public-sector program in Côte d'Ivoire [11]. Although data on the efficacy of interventions to reduce LTFU in African settings are scarce, hypothetical interventions can be created and their costs estimated. This approach has allowed Losina and colleagues to perform a series of threshold analyses, where interventions of known cost are evaluated over a range of effectiveness estimates. The resultant range of incremental cost-effectiveness ratios are plotted against consensus estimates of what the Ivoirian health sector would be willing to pay.

The authors used real-world cost and patient outcomes data from ACONDA, a local nongovernmental organization supporting ART delivery in Côte d'Ivoire to inform the well-validated Cost-Effectiveness of Preventing AIDS Complications (CEPAC) International simulation model. They evaluated the cost effectiveness of four hypothetical interventions to reduce LTFU, which included: (1) removing user co-payments from antiretroviral and (2) opportunistic infection drugs, (3) training providers in methods to improve patient retention, and (4) provision of meals and transport reimbursement for patient follow-up visits. The interventions were considered as if implemented incrementally (e.g., number 4 was not implemented without number 3.)

Among the most interesting findings of the analysis is its base case estimate of the contribution of LTFU to overall reductions in program effectiveness. In the 6,703-patient ACONDA-supported program, for instance, the authors estimate that LTFU results in more than 11,000 patient-years of lost life. It is in the context of this background that these hypothetical patient-retention interventions must be considered. For instance, removing user co-payment from the cost of antiretroviral drugs, an intervention estimated to cost $22 per patient per year, would only have to result in a 12% improvement in LTFU in order to meet the authors' criteria for cost-effectiveness in Côte d'Ivoire. On the other side of the spectrum, a combination of all four hypothetical interventions, estimated to cost$77 per patient per year, would need to be 41% effective to reach the cost-effectiveness threshold.

The reported estimates were most sensitive to modeled costs of second-line ART (which in Côte d'Ivoire contains much more expensive protease-inhibitor drugs). And while programs with the greatest LTFU rates stood the most to gain from the interventions, sensitivity analyses indicated that even programs with more modest loss rates might find such interventions to be cost-effective.

### The Global HIV Emergency: Acute ART Scale-up and Chronic HIV Care

Losina and colleagues' study signals an important widening of research attention to include not only the relative excitement of expanding ART coverage but also the less glorious work of improving chronic HIV care. The paper further quantifies the well-known problem of LTFU and provides a cost-effectiveness framework within which policy makers can begin to consider how to make their ART programs succeed over the long run. Although the efficacy of interventions to reduce LTFU remains largely unknown, this analysis makes clear that even interventions of modest efficacy are likely to fall well within the range of accepted cost-effectiveness. Clinical trials or other comparative studies aimed at evaluating such interventions would seem to be of high priority.

Given the financial scope of the global HIV/AIDS response, even small gains in program efficiencies and cost-effectiveness could translate into huge savings and, by extension, new lives saved. For this reason, the major AIDS donors, such as the US President's Emergency Plan For AIDS Relief (PEPFAR) and the Global Fund, should be keenly interested in this issue, and willing to invest in strategies to improve retention. Individual country programs also have a huge stake in minimizing LTFU. Not only do retained and appropriately treated patients have better clinical outcomes, they presumably are much less infectious and capable of transmitting the virus to others. Thus, treating and preventing HIV go hand in hand. Improving retention in HIV/AIDS care makes clear programmatic sense and, as Losina and colleagues demonstrate, it makes economic sense as well.

### Author Contributions

ICMJE criteria for authorship read and met: GPB JSAS. Wrote the first draft: GPB. Contributed to the writing of the paper: JSAS.

### References

1. 1. Anonymous (2009) 2008 UNAIDS annual report: towards universal access. Geneva: UNAIDS.
2. 2. Severe P, Leger P, Charles M, Noel F, Bonhomme G, et al. (2005) Antiretroviral therapy in a thousand patients with AIDS in Haiti. N Engl J Med 353: 2325–2334.
3. 3. Coetzee D, Hildebrand K, Boulle A, Maartens G, Louis F, et al. (2004) Outcomes after two years of providing antiretroviral treatment in Khayelitsha, South Africa. AIDS 18: 887–895.
4. 4. Stringer JS, Zulu I, Levy J, Stringer EM, Mwango A, et al. (2006) Rapid scale-up of antiretroviral therapy at primary care sites in Zambia: feasibility and early outcomes. JAMA 296: 782–793.
5. 5. Rosen S, Fox MP, Gill CJ (2007) Patient retention in antiretroviral therapy programs in sub-Saharan Africa: a systematic review. PLoS Med 4: e298. doi:10.1371/journal.pmed.0040298.
6. 6. Bangsberg DR, Charlebois ED, Grant RM, Holodniy M, Deeks SG, et al. (2003) High levels of adherence do not prevent accumulation of HIV drug resistance mutations. AIDS 17: 1925–1932.
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