text:
KEY2CHEM

Patterns and Relationships in Electron Energies

The electronic structure of an atom can be determined based on data, such as photoelectron spectroscopy (PES) and ionization energy values. In particular, the relative energies of the electrons in a multi-electron atom can be analyzed and compared. This data provides information regarding which electrons are furthest from the nucleus (they have the lowest ionization energies, meaning they are easiest to remove).

Example 1.

Consider the following species: $$\require{mhchem}\ce{S}$$, $$\require{mhchem}\ce{S^{2-}}$$, and $$\require{mhchem}\ce{Ar}$$. Which species would have a highest ionization energy?

A. $$\require{mhchem}\ce{S}$$

B. $$\require{mhchem}\ce{S^{2-}}$$

C. $$\require{mhchem}\ce{Ar}$$

Solution

C. $$\require{mhchem}\ce{Ar}$$

The species with the highest ionization energy is the one with the greatest net (effective) nuclear charge. Argon has $$18$$ protons and $$18$$ electrons. Each of its electrons experiences a greater attraction to the protons in the nucleus. $$\require{mhchem}\ce{S^{2-}}$$, with $$16$$ protons and $$18$$ electrons, would require the lowest amount of energy to remove an electron.

Example 2.

Why does the photoelectron spectrum of the He atom only show one peak?

A. There is only one electron in a helium atom.

B. The electrons are identical, since they are the same distance from the nucleus.

C. The electrons are not attracted to the nucleus.

Solution

B. The electrons are identical, since they are the same distance from the nucleus.

The electrons in a helium atom are in the same shell and subshell. As such, they are the same distance from the nucleus and have the same energy. This means they would require the same amount of energy to ionize, resulting in only one peak in the photoelectron spectrum.

Example 3.

An electron in a hydrogen atom falls from the fifth energy level (n = 5) to the second energy level (n=2). What is true about this process?

A. A photon is emitted.

B. A photon is absorbed.

C. A photon is neither emitted nor absorbed.

Solution

A. A photon is emitted.

An electron changine between energy levels (also called stationary states) must change its energy by either absorbing or emitting a photon of energy. The atom emits a photon of energy when transitioning from a higher energy shell down to a lower energy shell. The atom absorbs a photon of energy to transition from a lower energy shell up to a higher energy shell.


text:
Why can't element with paired electron have colour

I know that elements with unpaired electrons are coloured especially the d-block element which can be explained by crystal field theory. But, why can't element with paired electrons give colour, is it because the energy gap is too large ?

• It's not about whether the electrons are paired or not. It has to do with whether the electronic transitions in the molecule lie within the visible spectrum – orthocresol Sep 30 '15 at 15:20
• to give you counterexamples, Ni(II) in its dimethylglyoxime complex has 8 d electrons and all of them are paired but the complex is red. On the other hand $\ce{O2}$ gas has 2 unpaired electrons but it's colourless. – orthocresol Sep 30 '15 at 15:30
• @orthocresol actually, liquid oxygen has a blueish colour, or so I heard. – Jan Sep 30 '15 at 16:36
• @Jan I've seen that before in a demonstration... which is why I said O2 gas :D Anyway I went to read up. Turns out that the blue colour is because of two O2 molecules being excited simultaneously, which has a very low probability of occurring in the gas phase (hence colourless). Probably wasn't the best example to use but I guess it's passable. – orthocresol Sep 30 '15 at 16:58
• @orthocresol Disregard me, I overread the 'gas' in there ^^' But on that note: chlorine gas is greenish, bromine is brown, iodine is purple, liquid chlorine is yellow. – Jan Sep 30 '15 at 16:59

format: plain


text:
Volume 15, issue 2 (2011)

 Recent Issues
 The Journal About the Journal Editorial Board Editorial Interests Editorial Procedure Submission Guidelines Submission Page Subscriptions Author Index To Appear Contacts ISSN (electronic): 1364-0380 ISSN (print): 1465-3060
On Gromov–Hausdorff stability in a boundary rigidity problem

Sergei Ivanov

Geometry & Topology 15 (2011) 677–697
Abstract

Let $M$ be a compact Riemannian manifold with boundary. We show that $M$ is Gromov–Hausdorff close to a convex Euclidean region $D$ of the same dimension if the boundary distance function of $M$ is ${C}^{1}$–close to that of $D$. More generally, we prove the same result under the assumptions that the boundary distance function of $M$ is ${C}^{0}$–close to that of $D$, the volumes of $M$ and $D$ are almost equal, and volumes of metric balls in $M$ have a certain lower bound in terms of radius.

Keywords
boundary distance rigidity, Gromov–Hausdorff topology
Primary: 53C23


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# determining the number of multiples in a range

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Director
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Posts: 547
determining the number of multiples in a range  [#permalink]

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02 Feb 2011, 01:48
I would like to ask to clarify the following issue for me:

How many numbers between 10 and 100 are multiples of 2, 3, 5, 6?

My approach for multiples of 2:
numbers_between_10_and_100 = 100 - 10 + 1 = 91
#_multiples = 91/2 = 45.5

And now I don't know whether I should take 45 or 46?

Thank you.
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Joined: 02 Sep 2009
Posts: 50619
Re: determining the number of multiples in a range  [#permalink]

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02 Feb 2011, 02:06
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3
nonameee wrote:
I would like to ask to clarify the following issue for me:

How many numbers between 10 and 100 are multiples of 2, 3, 5, 6?

My approach for multiples of 2:
numbers_between_10_and_100 = 100 - 10 + 1 = 91
#_multiples = 91/2 = 45.5

And now I don't know whether I should take 45 or 46?

Thank you.

You are applying wrong formula.

$$# \ of \ multiples \ of \ x \ in \ the \ range = \frac{Last \ multiple \ of \ x \ in \ the \ range \ - \ First \ multiple \ of \ x \ in \ the \ range}{x}+1$$.

How many multiples of 4 are there between 12 and 96, inclusive?

Last multiple of 4 IN the range is 96;
First multiple of 4 IN the range is 12;

$$\frac{96-12}{4}+1=22$$.

OR: how many multiples of 5 are there between -7 and 35, not inclusive?

Last multiple of 5 IN the range is 30;
First multiple of 5 IN the range is -5;

$$\frac{30-(-5)}{5}+1=8$$.

OR: How many multiples of 7 are there between -28 and -1, not inclusive?

Last multiple of 7 IN the range is -7;
First multiple of 7 IN the range is -21;

$$\frac{-7-(-21)}{7}+1=3$$.

Check for practice:
good-one-99697.html
3-digit-numbers-divisible-by-7-and-others-81895.html
beginner-s-forum-question-106168.html
multiple-of-105318.html
number-system-103779.html
even-multiples-of-15-between-295-and-101810.html
m01-question-79061.html
m16-74052.html
multiples-98997.html
gmat-club-m16-95744.html
odd-multiples-of-94877.html
totally-basic-94862.html

Hope it helps.
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Thanks a lot, Bunuel.
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# determining the number of multiples in a range

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# resampling from fractional to integer sampling rate

I have data recorded at 1000Hz and other physio data recorded, somehow, at 1960.8 Hz (510 microsecond samples). Ideally, I would like to be able to downsample the 1960.8 hz signal to line up with the 1000Hz signal. Any suggestions? I am familiar with matlab or Python.

• Why not just use Matlab's resample command (or Python's equivalent)? You will lose all signals above 500 Hz, though. – MBaz Sep 11 '15 at 19:04

You can use the resample command mentioned as follows to accomplish this:
y=resample(x,1250,2541); % x is the input signal


text:
Lemma 52.27.3. Let $(A, \mathfrak m)$ be a Noetherian local ring and $f \in \mathfrak m$. Assume

1. the conditions of Lemma 52.27.1 hold, and

2. for every maximal ideal $\mathfrak p \subset A_ f$ the punctured spectrum of $(A_ f)_\mathfrak p$ has trivial Picard group.

Let $U$, resp. $U_0$ be the punctured spectrum of $A$, resp. $A/fA$. Then

$\mathop{\mathrm{Pic}}\nolimits (U) \longrightarrow \mathop{\mathrm{Pic}}\nolimits (U_0)$

is surjective.

Proof. Let $\mathcal{L}_0 \in \mathop{\mathrm{Pic}}\nolimits (U_0)$. By Lemma 52.27.1 there exists an open $U_0 \subset U' \subset U$ and $\mathcal{L}' \in \mathop{\mathrm{Pic}}\nolimits (U')$ whose restriction to $U_0$ is $\mathcal{L}_0$. Since $U' \supset U_0$ we see that $U \setminus U'$ consists of points corresponding to prime ideals $\mathfrak p_1, \ldots , \mathfrak p_ n$ as in (2). By assumption we can find invertible modules $\mathcal{L}'_ i$ on $\mathop{\mathrm{Spec}}(A_{\mathfrak p_ i})$ agreeing with $\mathcal{L}'$ over the punctured spectrum $U' \times _ U \mathop{\mathrm{Spec}}(A_{\mathfrak p_ i})$ since trivial invertible modules always extend. By Limits, Lemma 32.19.2 applied $n$ times we see that $\mathcal{L}'$ extends to an invertible module on $U$. $\square$

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text:
# What is the benefit of using simplicial manifolds in the regularization of gravity?

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In the Causal Dynamical Triangulation (CDT) approach to quantum gravity, space-time is regularized by a triangulated (simplicial) manifold. All configurations of the theory at a given scale are given by simplicial manifolds of the same topology with a fixed edge length. The curvature on each of these configurations is not a field on this lattice but is instead intrinsic to the geometry of the manifold and is located along the lower dimensional simplices. I was just wondering what makes regularization of gravity this way more ideal than say a square lattice with the curvature a field on the lattice?  I'm guessing that there's some sort of universality and that perhaps it could be equivalently be modeled on a standard lattice.

+ 2 like - 0 dislike

The reason for using a dynamical grid rather than a square grid is the same as why people working in fluid dynamics use adaptive grids rather than square ones - they adapt much better to the solution. Even if one starts out with a regular grid, different regions very soon need different resolution, which can be captured numerically (without unduly large work) only with an adaptive grid.

To get the same numerical accuracy with a square grid one would need an much finer (indeed typically extremely fine) lattice spacing.

A second reason is that in general relativity one wants to consider topologies different from the topology of Minkowski space - and possible even changes in topology. This cannot be done by a square lattice. On the other hand, a triangulation of a manifold completely describes its topology, hence is the appropriate tool for the discretization of general manifolds. A manifold in itself has not yet metric propoerties such as curvature, but these are given by fields defined on lower-dimensional subsimplices. This generalizes lattice gauge theory where the gauge field is given on the edges of the lattice, rather than on its vertices.

answered Jun 16, 2015 by (13,959 points)
edited Jun 17, 2015

I did not get it - is it simply about numerical calulations of a given theory or it is another analytical formulation of the theory (another theory)?

@VladimirKalitvianski: Regularization always means approximation: Each way of regularization defines a different approximate theory for the same putative true theory. A good regularization is one where the accuracy suffers little while the complexity of the calculations is reduced to a tractable amount.

So it is about another theory, as I suspected.

@VladimirKalitvianski: Not really. It is about approximately the same theory. Just as when we do calculations with real numbers on a computer, we accept that it computes only approximations to the exact results. I

n physics this is always done since very few theories are exactly solvable. Any perturbative scheme for solving an equation defines strictly speaking an approximate theory only, but it is approximately the same theory.

Arnold, I understand everything you wrote. The question is not here. First, it looks like a new (discrete) theory with a specific discretization. I guess triangulation allows to satisfy the necessary "boundary conditions" for each cell, which cannot be done for a "square" cells because of, for example, lacking an extra information needed to put in "extra" points (a "square" cell can also be adaptive). As well, no curvature exists on each cell; instead the "internal" geometry is "plane", which distinguishes this physical model from others. Such a modeling can be useful for numerical purposes too, but I think the simplified physics (plane geometry) makes it possible to easier analyze properties of solutions of such a theory.

A triangulation specifies the topology, which in general relativity is not necessarily trivial. See my updated answer.

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text:
Proceedings Article, Paper @InProceedings Beitrag in Tagungsband, Workshop

 Show entries of: this year (2020) | last year (2019) | two years ago (2018) | Notes URL
 Action: login to update Options: Library locked Goto entry point

 Author, Editor
 Author(s): Cai, Jin-Yi Lu, Pinyan Xia, Mingji dblp dblp dblp Not MPG Author(s): Cai, Jin-Yi Lu, Pinyan
 Editor(s):
 BibTeX cite key*: Xia2013-soda-clx

 Title, Booktitle
 Title*: Dichotomy for Holant* Problems with a Function on Domain Size 3 Booktitle*: Proceedings of the Twenty-Fourth Annual ACM-SIAM Symposium on Discrete Algorithms

 Event, URLs
 URL of the conference: http://www.siam.org/meetings/da13/ URL for downloading the paper: Event Address*: New Orleans, Louisiana USA Language: English Event Date* (no longer used): Organization: Event Start Date: 6 January 2013 Event End Date: 8 January 2013

 Publisher

 Vol, No, Year, pp.
 Series:
 Volume: Number: Month: Pages: 1278-1295 Year*: 2013 VG Wort Pages: ISBN/ISSN: 978-1-611972-52-8 Sequence Number: DOI:

 (LaTeX) Abstract: Holant problems are a general framework to study the algorithmic complexity of counting problems. Both counting constraint satisfaction problems and graph homomorphisms are special cases. All previous results of Holant problems are over the Boolean domain. In this paper, we give the first dichotomy theorem for Holant problems for domain size greater than two. We discover unexpected tractable families of counting problems, by giving new polynomial time algorithms. This paper also initiates holographic reductions in domains of size greater than two. This is our main algorithmic technique, and is used for both tractable families and hardness reductions. The dichotomy theorem is the following: For any complex-valued symmetric function ${\bf F}$ with arity 3 on domain size 3, we give an explicit criterion on ${\bf F}$, such that if ${\bf F}$ satisfies the criterion then the problem ${\rm Holant}^*({\bf F})$ is computable in polynomial time, otherwise ${\rm Holant}^*({\bf F})$ is \#P-hard. Download Access Level: Internal

 Correlation
 MPG Unit: Max-Planck-Institut für Informatik MPG Subunit: Algorithms and Complexity Group Appearance: MPII WWW Server, MPII FTP Server, MPG publications list, university publications list, working group publication list, Fachbeirat, VG Wort

BibTeX Entry:

@INPROCEEDINGS{Xia2013-soda-clx,
AUTHOR = {Cai, Jin-Yi and Lu, Pinyan and Xia, Mingji},
TITLE = {Dichotomy for {Holant*} Problems with a Function on Domain Size 3},
BOOKTITLE = {Proceedings of the Twenty-Fourth Annual ACM-SIAM Symposium on Discrete Algorithms},
PUBLISHER = {SIAM},
YEAR = {2013},
PAGES = {1278--1295},
ADDRESS = {New Orleans, Louisiana USA},
ISBN = {978-1-611972-52-8},
}


text:
# Water Glass Challenge

This problem is inspired by the Problem of the Week.

A closed glass, shaped of a unit cube, consists of water $$\frac{1}{6}$$ filled. It is known that if we rotate the cube smoothly (so that the water does not "jump"), the water cross-section changes to one of some known shapes.

What is the volume of space, where the water cross-section will never reach throughout the rotation? For this problem, assume that the cross-section remains flat while changing its form.

Note: The answer is not $\frac{5}{6}$ since it is the volume of space where the water can't reach without rotating the cube.

If you are interested in using or borrowing this for your problem in the community, (as long as the correct answer doesn't appear yet) please let me know!

Note by Michael Huang
3 years ago

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I don't understand what you are asking.

- 2 years, 11 months ago

If the cube is fully rotated all the way around, you will notice the "empty" solid tangent to the water plane at some points. What is the volume of the space?

- 2 years, 11 months ago

Wouldn't that just be the remaining $\frac{5}{6}$?

- 2 years, 11 months ago

No, it is indeed not that much volume. I am referring to the central "holey" solid, where the cross section does not reach during the rotation. I am not referring to the empty prism for this problem.

I may consider revising the problem in case you interpret the problem incorrectly.

- 2 years, 11 months ago

Well, I would assume that the space would have 4/6 or 2/3 of a unit in diameter, so a 1/3 radius. When you do 4/3pi(r)^3 you get about 4/25. This is because the space within the cube is a sphere, correct?

- 3 years ago

The solid within the cube is actually not the sphere since the slope of the cross-section changes relative to the total volume of the water. Taking the volume of space about the origin in the rectangular coordinate system, the radius is $\frac{1}{3}$ if the point touching it is $\frac{1}{6}$ units away from one of the cube's faces. It is intuitive that the radius of the space is $\frac{1}{3}$ as if the water cross-section is perpendicular throughout the rotation; however, this is not entirely true. Triangular pyramid of equilateral triangle is the popular example that disproves this.

Consider (1) the point closest to the centroid, and (2) the "sliced" cross-sections formed within the water. Two base cross-sections and a midsection should be helpful to answer the problem.

- 3 years ago

If it is the volume of empty space that u r interested in knowing, it shall be nothing other than 5/6 cubic units. As the space taken by the 'emptiness' or water itself won't change at all, be it stationary or in motion

- 2 years, 5 months ago


text:
International Association for Cryptologic Research

# IACR News Central

You can also access the full news archive.

Further sources to find out about changes are CryptoDB, ePrint RSS, ePrint Web, Event calender (iCal).

2015-02-27
19:17 [Pub][ePrint]

In [19], Peikert presents an efficient and provably secure set of lower level primitives for practical post-quantum cryptography. These primitives also give the first lattice-based scheme to provide perfect forward secrecy, and thus represent a major advancement in providing the same sort of security guarantees that are now expected for modern internet traffc protection. However, the presentation in [19] might prove a bit daunting for the slightly less mathematical reader. Here we provide what we hope will be a clear and self-contained exposition of how the algorithm can be implemented, along with sample code and some initial analysis for potential parameter sizes.

We focus on the simpler case, as chosen by Bos et al in [1], of cyclotomic rings whose degree is a power of two. We describe the necessary arithmetic setup and choices regarding error sampling, and give a possibly cleaner mechanism for reconciliation of the shared secrets. Then we present Peikert\'s Diffe-Hellman-like key exchange algorithms along with security, correctness and implementation analysis.

19:17 [Pub][ePrint]

In this work we have analyzed some password hashing schemes for performance under various settings of time and memory complexities. We have attempted to benchmark the said algorithms at similar levels of memory consumption. Given the wide variations in security margins of the algorithms and incompatibility of memory and time cost settings, we have attempted to be as fair as possible in choosing the various parameters while executing the benchmarks.

19:17 [Pub][ePrint]

It has been roughly two decades since the random oracle model for security reductions was introduced and one decade since we first discussed the controversy that had arisen concerning its use. In this retrospective we argue that there is no evidence that the need for the random oracle assumption in a proof indicates the presence of a real-world security weakness in the corresponding protocol. We give several examples of attempts to avoid random oracles that have led to protocols that have security weaknesses that were not present in the original ones whose proofs required random oracles. We also argue that the willingness to use random oracles gives one the flexibility to modify certain protocols so as to reduce dependence on potentially vulnerable pseudorandom bit generators. Finally, we discuss a modified version of ECDSA, which we call ECDSA+, that may have better real-world security than standard ECDSA, and compare it with a modified Schnorr signature. If one is willing to use the random oracle model (and the analogous generic group model), then various security reductions are known for these two schemes. If one shuns these models, then no provable security result is known for them.

18:07 [Event][New]

Submission: 23 June 2015
From October 26 to October 28
Location: Rhodes, Greece

18:06 [Job][New]

The High Assurance Software Lab (HASLab) is an R&D unit at INESC TEC, a leading research institution in Portugal. The HASLab specialises in the rigorous development of software applications for critical systems and infrastructures, drawing on expertise in software engineering, dependable distributed systems, and cryptography and information security.

The HASLab has recently opened 10 positions for Post Doctoral researchers and 6 positions for Ph.D. students.

We are looking for Post Doctoral researchers that can be integrated into the activities of HASLab — in EU and national projects — and also lead their own research projects within the group, preferably in the following areas: source code analysis, testing and verification, formal methods, large scale data management, theory of cryptography or computer and network security.

A successful Post Doctoral candidate will be offered a package that may include up to 25K EUR/Year salary, health insurance, one Ph.D. grant and one internship grant for recruitment, as well as access to the HASLab travel and equipment funding schemes. Post-doc positions may be extended until up to 5 years.

18:06 [Job][New]

SYmmetric and Lightweight cryptography Lab (SYLLAB) at Nanyang Technological University (NTU), Singapore, is seeking candidates for 2 research fellow positions (from fresh post-docs to senior research fellows) in the areas of:

• symmetric key cryptography
• lightweight cryptography
• side-channel attacks

Salaries are competitive and are determined according to the successful applicants accomplishments, experience and qualifications. Interested applicants should send their detailed CVs, cover letter and references to Thomas Peyrin (thomas.peyrin [at] ntu.edu.sg).

Review of applications starts immediately and will continue until positions are filled.

16:17 [Pub][ePrint]

We present Lyra2, a password hashing scheme (PHS) based on cryptographic sponges. Lyra2 was designed to be strictly sequential (i.e., not easily parallelizable), providing strong security even against attackers that uses multiple processing cores (e.g., custom hardware or a powerful GPU). At the same time, it is very simple to implement in software and allows legitimate users to fine tune its memory and processing costs according to the desired level of security against brute force password-guessing. Lyra2 is an improvement of the recently proposed Lyra algorithm, providing an even higher security level against different attack venues and overcoming some limitations of this and other existing schemes.

16:17 [Pub][ePrint]

Searchable encryption allows one to upload encrypted documents on a remote honest-but-curious server and query that data at the server itself without requiring the documents to be decrypted prior to searching. In this work, we propose a novel secure and efficient multi-keyword similarity searchable encryption (MKSim) that returns the matching data items in a ranked ordered manner. Unlike all previous schemes, our search complexity is sublinear to the total number of documents that contain the queried set of keywords. Our analysis demonstrates that proposed scheme is proved to be secure against adaptive chosen-keyword attacks. We show that our approach is highly efficient and ready to be deployed in the real-world cloud storage systems.

2015-02-26
23:11 [Job][New]

Our Institute is part of the TUM Department of Electrical and Computer Engineering. We develop innovative technologies for embedded systems, to counteract new threats in hardware security. Physical Unclonable Functions (PUFs) – as important new security elements – and countermeasures against side channel leakage and fault attacks are only two of the exciting topics in the focus of our institute’s research. Our teaching activities range from lectures on basics in cryptology to lab courses where students design secure embedded systems on their own.

For research in the field of Countermeasures against Attacks on Physical Unclonable Functions we are searching for the closest possible point in time for a

Research Associate (m/f)

for a full time position.

• Carrying out your own research in the field of secure PUF concepts
• Participation in industry-related and scientific research projects
• Supervising students

You:

finished your master’s degree in Electrical Engineering, Computer Sciences or equivalent with outstanding grades.

• have strong focus on security.
• have profound knowledge in hardware attacks and counter measures
• have a sound education in information theory and error correcting codes
• are a creative thinking and independent working person, can work in teams, and are highly motivated.
• like to work with students.
• should have practical or theoretical previous knowledge on embedded systems.

We offer a very interesting position as research associate which is rich in variety and includes the ability to carry out a Doctoral thesis in engineering. With your research in the field of PUFs, you contribute to one of the main fields of the Institute for Security in Information Technology and are

22:17 [Pub][ePrint]

We focus on generalizing constructions of Batch Single-Choice Cut-And-Choose Oblivious Transfer and Multi-sender k-out-of-n Oblivious Transfer, which are at the core of efficient secure computation constructions proposed by Lindell \\textit{et al.} and the IPS compiler.

Our approach consists in showing that such primitives can be based on a much weaker and simpler primitive called Verifiable Oblivious Transfer (VOT) with low overhead. As an intermediate step we construct Generalized Oblivious Transfer from VOT. Finally, we show that Verifiable Oblivious Transfer can be obtained from a structure preserving oblivious transfer protocol (SPOT) through an efficient transformation that uses Groth-Sahai proofs and structure preserving commitments.

19:17 [Pub][ePrint]

We ask whether it is possible to anonymously communicate a large amount of data using only public (non-anonymous) communication together with a small anonymous channel. We think this is a central question in the theory of anonymous communication and to the best of our knowledge this is the first formal study in this direction.

To solve this problem, we introduce the concept of \\emph{anonymous steganography}: think of a leaker Lea who wants to leak a large document to Joe the journalist. Using anonymous steganography Lea can embed this document in innocent looking communication on some popular website (such as cat videos on \\emph{YouTube} or funny memes on \\emph{9GAG}). Then Lea provides Joe with a short key $k$ which, \\emph{when applied to the entire website}, recovers the document while hiding the identity of Lea among the large number of users of the website. Our contributions include:

\\begin{itemize}

\\item Introducing and formally defining \\emph{anonymous steganography},

\\item A construction showing that anonymous steganography is possible (which uses recent results in circuits obfuscation),

\\item A lower bound on the number of bits which are needed to bootstrap anonymous communication.

\\end{itemize}


text:
### (1) Presentation(s)

 Lun. 05/02/2018 13:30 Grande Ourse, Bâtiment 13, Etage 1Séminaire PENARRUBIA Jorge (Institute for Astronomy - Edinburgh Univ.) Finding the invisible - the search for dark substructures (LUPM/Interactions fondamentales, Astroparticules et Cosmologie) Sommaire: One of the most striking predictions from the Cold Dark Matter (CDM) paradigm postulates the existence of myriads of planet-sized subhaloes devoid of stars (i.e. dark'). A large population of these objects generates a stochastic gravitational field that can perturb the trajectories of visible systems. In this talk I will present a statistical technique for deriving the spectrum of random fluctuations directly from the number density of substructures with known mass and size functions.I will show that in galaxies like the Milky Way the fluctuations of the tidal field are completely dominated by the smallest and most abundant subhaloes. In light of this result I will discuss observational experiments that may be sufficiently sensitive to Galactic tidal fluctuations to probe the `dark'' low-end of the subhalo mass function and constrain the particle mass of warm and ultra-light axion dark matter models.Pour plus d'informations, merci de contacter Lavalle J.


text:
MathOverflow will be down for maintenance for approximately 3 hours, starting Monday evening (06/24/2013) at approximately 9:00 PM Eastern time (UTC-4).

Increasing union of contractible CW complexes

Let X be CW complex. I'm trying to prove (using Zorn's lemma) that there is maximal contractible subcomplex. Problem is that I'm not able to show that increasing union of contractible subcomplexes has to be contractible itself.

-

By various standard lemmas, a CW complex $X$ is contractible if and only if every map $u:S^{n-1}\to X$ (for any $n>0$) can be extended over $B^n$. In this context $u(S^{n-1})$ is compact and therefore (by another standard lemma) contained in some subcomplex with only finitely many cells. If $X$ is the union of some totally ordered family of subcomplexes $X_\alpha$, it follows that $u(S^{n-1})\subseteq X_\alpha$ for some $\alpha$. This is enough to prove what you want.
So for short: $\pi_n$ commutes with increasing unions in consideration and detect contractibility by Whitehead. – Martin Brandenburg Oct 4 2011 at 21:54


text:
# The forcats Package and How to Use It

Posted on
R factor variables forcats

## Intro

This blog post will talk about the forcats package and how to use it to work with factor (categorical) variables. Although decent documentation exists, it can sometimes be a bit too terse for somebody first encountering the package’s functions. This blog post is meant to provide a fuller narrative description and examples of how to use the package. Amelia McNamara’s outstanding presentation from the 2019 RStudio conference is also worth the time to watch to understand the background, motivation, and usefulness of forcats. This post is meant to be an easily Googleable summary of the essential information.

Factors are an important variable type in R because they determine the order in which categorical variables are plotted or how contrasts (such as dummy variables) are coded when running statistical commands. Base R functions exists but are error prone for even experienced users. To demonstrate, we’ll use items from the General Social Survey (GSS), a commonly used source of data in social science that is full of categorical variables. In fact, the forcats installation includes a selection of GSS variables from the 2000-2014 waves, which we will use in this blog post.

First, let’s load the packages we’ll use. The gss_cat dataset loads along with forcats. Our interest will be in the relig variable, which contains respondents’ religious affiliations. The relig variable is already coded in the gss_cat data as a factor variable. However, a common situation researchers encounter is that they first receive a version of the data file in which the categories are coded as integers, and labels must be applied manually. To mimic this typical workflow, we’ll immediately convert the factor version to numeric and begin with the numeric version.

library(haven)
library(tidyverse)
library(forcats)
library(knitr)

gss_cat2 <- gss_cat %>%
mutate(
relig = as.numeric(relig)) %>%
filter(year == 2014)

## Useful Functions

The functions discussed in this blog post will be:

• as_factor: changes a variable from some type to a factor
• fct_recode: changes the coding of values in a factor
• fct_count: provides a descriptive table for factors
• fct_lump: lumps multiple smaller levels into a single other category
• fct_collapse: allows the user to collapse factor levels into defined groups
• fct_inorder: reorders factors by appearance
• fct_infreq: reorders factors by frequency
• fct_relevel: reorder factors by hand

### as_factor

If we were to plot the distribution of religion, it would be unclear which category is which.

gss_cat2 %>%
ggplot(aes(x=relig)) +
geom_bar(color = 'black', fill = 'firebrick')  +
xlab("Religion") +
ylab("Count")

The category that each integer refers to is as follows:

2. Don’t know
3. Inter-nondenominational
4. Native american
5. Christian
6. Orthodox-christian
7. Moslem/islam
8. Other eastern
9. Hinduism
10. Buddhism
11. Other
12. None
13. Jewish
14. Catholic
15. Protestant
16. Not applicable

However, this is not intuitative, and someone just looking at the data would have no way to know what each integer stands for.

First, use as_factor from forcats to change the categorical variables to factors.

gss_cat2 <- gss_cat2 %>%
mutate(
relig = as_factor(relig))

However, they are still missing descriptive labels.

gss_cat2 %>%
count(relig)
## # A tibble: 15 x 2
##    relig     n
##    <fct> <int>
##  1 1        15
##  2 2         3
##  3 3         4
##  4 4         2
##  5 5       134
##  6 6         9
##  7 7         9
##  8 8         3
##  9 9        13
## 10 10       26
## 11 11       27
## 12 12      522
## 13 13       40
## 14 14      606
## 15 15     1125

That’s where fct_recode comes in.

### fct_recode

We will use fct_recode from forcats to change the levels of each variable. We can also set levels that we don’t require to NULL to remove them.

gss_cat2 <- gss_cat2 %>% mutate(
relig = fct_recode(relig,
NULL = "1",
NULL = "2",
"Inter-Nondenom" = "3",
"Native American" = "4",
"Christian" = "5",
"Orthodox-Christian" = "6",
"Moslem/Islam" = "7",
"Other Eastern" = "8",
"Hinduism" = "9",
"Buddhism" = "10",
"Other" = "11",
"None" = "12",
"Jewish" = "13",
"Catholic" = "14",
"Protestant" = "15",
NULL = "16"))

gss_cat2 %>%
ggplot(aes(x=relig)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1))+
xlab("Religion") +
ylab("Count")

Much better. We can get a table with counts and proportions using the fct_count function.

### fct_count

Let’s take a look at religion:

gss_cat2 %>%
pull(relig) %>%
fct_count(prop = TRUE) %>%
kable()
f n p
Inter-Nondenom 4 0.0015760
Native American 2 0.0007880
Christian 134 0.0527975
Orthodox-Christian 9 0.0035461
Moslem/Islam 9 0.0035461
Other Eastern 3 0.0011820
Hinduism 13 0.0051221
Buddhism 26 0.0102443
Other 27 0.0106383
None 522 0.2056738
Jewish 40 0.0157604
Catholic 606 0.2387707
Protestant 1125 0.4432624
NA 18 0.0070922

Note that the prop = TRUE argument provides the p column in the table, which is the proportion of cases in each respective category.

### fct_lump

We have a lot of small categories in our gss_cat which can make analysis difficult. Let’s combine some of these into one category. We can do that using fct_lump.

gss_cat2 <- gss_cat2 %>% mutate(
relig_lump = fct_lump(relig, n = 5)
)

The n argument specifies the top n categories to keep. All the rest will be combined into a single “other” category.

gss_cat2 %>%
ggplot(aes(x=relig_lump)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1))+
xlab("Religion") +
ylab("Count")

### fct_collapse

fct_c or fct_collapse allows you to collapse factor levels into defined groups. This is very similar to lumping categories, but rather than putting all groups into other, you can create your own groups. Any levels not specified will remain as is.

gss_cat2 <- gss_cat2 %>%
mutate(
relig_collapse = fct_collapse(relig,
Missing = NA,
Other = c("Other",
"Native American",
"Inter-Nondenominational"),
Eastern = c("Buddhism",
"Hinduism",
"Other Eastern",
"Moslem/Islam"),
Christian = c("Christian",
"Orthodox-Christian")
))

gss_cat2 %>%
ggplot(aes(x=relig_collapse)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1))+
xlab("Religion") +
ylab("Count")

### Reorder Levels

Another useful set of functions are those used to reorder levels. This can be important for setting the reference level used in modeling functions that create dummy variables for factors, or for making graphs ordered in the desired manner. forcats has some great packages for fixing this.

We use fct_inorder to reorder factors as they appear in the data:

gss_cat2 %>%
mutate(
relig_inorder = fct_inorder(relig_lump)) %>%
ggplot(aes(x=relig_inorder)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1)) +
xlab("Religion") +
ylab("Count")

We use fct_infreq to reorder factors by frequency:

gss_cat2 %>%
mutate(
relig_infreq = fct_infreq(relig_lump)) %>%
ggplot(aes(x=relig_infreq)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1)) +
xlab("Religion") +
ylab("Count")

If none of these functions give the desired order, you can use fct_relevel to reorder factors by hand.

gss_cat2 %>%
mutate(
relig_relevel = fct_relevel(relig_lump, c("Catholic", "Jewish"))) %>%
ggplot(aes(x=relig_relevel)) +
geom_bar(color = 'black', fill = 'firebrick') +
theme(axis.text.x = element_text(angle = 45, hjust = 1)) +
xlab("Religion") +
ylab("Count")

Note that listing just two categories moves them to the front while the others remain in the original order.

Hopefully this gave you a good starting point for using the forcats package. It is very powerful tool for working with factor variables.


text:
## A community for students. Sign up today!

Here's the question you clicked on:

## elvinmarrero 2 years ago What is the sum of 5/6 + 2/3 in simplest form?

• This Question is Closed
1. 03453660

|dw:1349723525961:dw|

2. 03453660

|dw:1349723577921:dw|

3. 03453660

its the answer

4. aatifsayyad

5/6+2/3|dw:1349723771904:dw|

5. jazy

In order to add, the denominators must be the same. So find the LCD(least common denominator). Both denominators go into 6. So: 5/6 = 5/6 2/3 = ?/6 3 multiplied by 2 equals 6, so multiply 2(the numerator) by 2: 2/3 = 4/6 Now add 5/6 + 4/6 = 10/6 Change into a mixed number: 6 goes into 10 ONE time with 4 left over so: 1 4/6 simplified is: $1\frac{ 2 }{3 }$

6. elvinmarrero

thank you

7. jazy

you're welcome (:

#### Ask your own question

Ask a Question
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text:
# maths genie box plots answers

Make sure you are happy with the following topics before continuing. Stem leaf diagrams stem and leaf diagrams you exam questions stem and leaf diagrams box whisker plots examsolutions exam questions stem and leaf diagrams box whisker plots examsolutions. Practice: Creating box plots. Maths Genie is a free GCSE and A Level revision site. 1 2 3 4 The box plot below shows the amount spent by people over the Christmas period in 2015. Leave a Comment Cancel reply. On the grid, plot a cumulative frequency graph for this information. The next point we would plot would be the cumulative frequency value of 20 against £15,000 (the highest value in the £10,000 - £15,000 band). Here are four box and whisker plots: Box & Whisker Plot 1 Box & Whisker Plot 2 Box & Whisker Plot 3 Box & Whisker Plot 4 For each box and whisker plot, write down the letter of the matching cumulative frequency diagram. The box plot below shows the distribution of the maths scores of students in class B. 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By using this website, you automatically accept that we use cookies. Tes Global Ltd is registered in England (Company No 02017289) with its registered office â¦ If you find any mistakes, or if you have any feedback, please email: [email protected]. Also a couple of worksheets to allow students to get some independant practice, plus the data I collected from my year 9s that I got them to draw box plots from to compare my two year 9 classes. If YouTube is blocked at your school you can access the videos using this link: Sign in to like videos, comment, and subscribe. Practice Questions Edexcel GCSE Papers - Edexcel GCSE past papers with model solutions and video explanations. Visit his excellent website for more videos, textbook exercises, exam questions, 5-a-day, and more! If you find any mistakes, or if you have any feedback, please email: [email protected]. Newsletter Archive. By using this website, you automatically accept that we use cookies. Please comment below! Box Plots. 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Level Statistics & Mechanics exam Revision with questions and solutions a * -G ; 5-a-day 1. & cumulative Frequency graph for this information plots can be created from a list of numbers by the! ) for 9th period 38 72 88 96 102 _____ 1 by https: //www.numerise.com/GCSE Revision video 26 - plots! Like  \frac { 1 } { 2 } , type.. Questions Click here for questions a fraction like  \frac { 1 } { 2 ... Answers to GCSE and a Level past papers with model solutions, exam style questions model... Automatically accept that we use cookies 50 the box plot tells you some important pieces of information the...: Stem and Leaf diagrams Maths Genie answers ; masuzi distributions of the Maths answers! People over the Christmas period in 2015 OCR and AQA exam boards the numbers and finding the median and and! Correct answers by people over the Christmas period in 2015 31 ( a ) Draw a box whisker! 2 } , type 1/2 answers for all topics in Foundation and Higher GCSE with solutions. Lowest value, median and quartiles, comment, and subscribe style questions and answers is value. From a list of numbers by ordering the numbers and finding the median and quartiles exercises exam! Given ( discrete ) data set the lowest value, highest value median. Numbers and finding the median and quartiles of a given ( discrete ) data set this video explains to! A * -G ; 5-a-day Core 1 ; more here for questions ; Post.! 1 2 3 4 Math Statistics and probability Summarizing quantitative data box and plot... Questions Powered by https: //www.numerise.com/GCSE Revision video 26 - box plots can be from! Maths ; 5-a-day Core 1 ; more model solutions example shows what a typical scatter looks... The distribution of the bags weigh more than 95 g exercises, exam questions the Edexcel OCR... Corbettmaths - this video you are happy with the following topics before continuing queries email [ email protected Corbettmaths! 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And model answers for box plots ; Post navigation 31 ( a ) Draw a box and plots... * -G ; 5-a-day GCSE a * -G ; 5-a-day Core 1 ; more Statistics GCSE papers. Stem and Leaf diagrams Maths Genie - Remember Mathsgrader usually only marks correct or partially correct.! Reading box plots can be created from a list of numbers by ordering the numbers finding. //Www.Numerise.Com/Gcse Revision video 26 - box plots & cumulative Frequency graph for this information model solutions style and... Finding maths genie box plots answers median and quartiles of a given ( discrete ) data set ; 5-a-day a. As % ) for 9th period 38 72 88 96 102 _____ 1 Sign to! Exams will not go ahead as normal this summer and subscribe Mathsgrader usually only marks correct or partially correct.. And AQA exam boards more videos, exam style questions and model answers for box plots video videos box. With the following topics before continuing GCSE past papers with model solutions x^2... The second page asks students to plot the information worked out before on a box below... Type  x^2 ` type x^2 5-a-day GCSE a * -G ; 5-a-day Core 1 ; more questions! The amount spent by people over the Christmas period in 2015 usually only marks correct or partially correct.! 40 50 the box plot tells you some important pieces of information: the lowest value, median and of... Example shows what a typical scatter plot GCSE Revision - video tutorials, practice exam style and. ) 5-a-day Further Maths ; 5-a-day GCSE a * -G ; 5-a-day GCSE a * -G ; 5-a-day Core ;... This video you are happy with the following topics before continuing more the following shows., mark schemes and model answers to GCSE and a Level papers - a... That is far removed from the main distribution of the bags weigh more than 95 g a., notes, exam style questions and answers video 26 - box plots ; Post navigation students including practice... Post navigation all topics in Foundation and Higher GCSE before, an outlier a! Tier only Post navigation plots, look at skewness and plot outliers GCSE! Easy Sign in to like videos, worksheets, answers for all topics in and! Video explains how to Draw box and whisker plot out before on a plot... Whisker ; box plots ; Post navigation boysâ times box and whisker plots, look at skewness and outliers. Correct or partially correct answers 40 50 the box plot tells you important... A box and whisker plots, look at skewness and plot outliers videos! Protected ] Corbettmaths - this video you are happy with the following before... Is suitable for the Edexcel, OCR and AQA exam boards in class B in Foundation and Higher.!


text:
This is strange, I copied your code into a new Self-Hosted Client-Server Application (I assume that's what you're using due to the port 9000) and I am not having this issue; I correctly receive "PostBody works!".

What version of WebSharper.Owin are you using? I'm on 3.6.14.133.

By on 4/24/2017 6:10 AM ()

I managed to find what was the issue. I illustrated it in this gist:

If you run it as it is, the POST with a JSON body won't work. However, if you comment lines 59, 60, and 61, it will work as expected.

I suspect the fact that we read the body prevents it from being used later, but not sure.

Do you have an idea why?

By on 4/27/2017 11:42 AM ()

Ah, right. Indeed, if the body stream has been read before WebSharper steps in, then it is not available anymore, and WebSharper sees an empty body. You need to copy the content into a MemoryStream so that it can be subsequently re-read:

1
2
3
4
5
6
7
8
9

if not environment.Request.Body.CanSeek then
let s = new MemoryStream() :> Stream
environment.Request.Body <- s
environment.Request.Body.Seek(0L, SeekOrigin.Begin) |> ignore

environment.Request.Body.Seek(0L, SeekOrigin.Begin) |> ignore

And also, you need to place the whole body of the function inside the async block instead of before it (although I admit I don't completely understand why).

Here is my fixed version of your gist.

By on 5/1/2017 5:21 AM ()

Ah ok, it makes sense! Thanks for your help, I'll update my code accordingly.

By on 5/2/2017 2:54 AM ()

Hi Loic, you are right, I am using the Self-Hosted Client-Server Applicationa and WebSharper.Owin.3.6.14.133 too.. I'll try to set up a completely new, separate project and see if I still have the problem.

By on 4/26/2017 1:39 PM ()


text:
# Pumps

The tank is filled with two pumps in 16 minutes. The first pump is filled in 30 minutes earlier than two one. How many minutes is filled with the first pump?

Result

t1 =  22.9 min

#### Solution:

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# Slides

 Monday Tuesday Wednesday Thursday Friday 09:00 On multidimensional diophantine approximation of algebraic numbers On the successor function Dynamical Systems in Number Theory Expansions in non-integer bases and fractal phenomena Distribution Properties of Subsequences of Automatic Sequences 10:00 Coffee break Coffee break Coffee break Coffee break Coffee break 10:30 On bases of canonical number systems in cyclotomic fields Combinatorial and probabilistic properties of systems of numeration A completion of the unilateral recognizability theorem for aperiodic Approximation properties of beta expansions On parametric Thue-Morse sequences and lacunary trigonometric products 10:55 On limit dynamical zeta functions of the beta-transformation Analysis of Carries in Non-Standard Digit Expansions On the number of fixed points of $D_{\infty}$-Markov chains The S-adic Pisot conjecture on two letters Normality of the Thue--Morse sequence along Piatetski-Shapiro sequences 11:20 Method for Construction of Parallel Addition Algorithms (in Non-standard Numeration Systems) A combinatorial point of view on Rosen-like continued fractions Dynamical properties of the tent map Rational series, Lind, Boyle and Handelman Theorems and primitive matrices On the number of restricted prime factors of an integer. 11:45 On-line Multiplication and Division in Non-standard Numeration Systems Continued beta -fractions with formal power series over finite fields Diophantine approximation of fractional parts of powers of real numbers Some computational results regarding special radix expansions 12:10 Lunch Lunch Lunch Lunch Lunch 14:30 Nombres simplement normaux dans différentes bases Application of binary expansion of n to the Stern polynomial B_n Free Afternoon Optimal Expansions in non-integer base On the digits of primes 15:30 Normality in Pisot Numeration Systems Properties of Tanaka and Ito's alpha-continued fractions Salem numbers from a class of star-like trees Sur les occurrences des mots dans les nombres premiers 15:55 Coffee break Coffee break Coffee break Coffee break 16:30 Normal and non-normal numbers in the dynamical systems fulfilling the specification property The unary arithmetical algorithm in binary continued fractions Rational Based Digit System in Polynomial Rings over Finite Fields 16:55 Asymptotic Properties of Multi-Base Digit Expansions of Integers Topology of three-dimensional self-affine tiles Canonical expansion of integers for families of roofline polynomials 17:20 Numeration systems and discrepancy Multiple tilings associated to $d$-Bonacci beta-expansions Univoque points for self-similar sets
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