darklight03/StackMIAsub huggingface dataset:
I hope that this is the correct site to ask this question, but since I was unable to find one specifically for modeling, I decided to ask here (and please feel free to correct me, if any of my statements is bogus): There are tools which allow one to do parametric modeling like Rhino's Grasshopper or Blender's Geometry Nodes. The modeling happens in a bottom-up manner, e.g., twisting and bending some input shape according to some parametric functions. And then there are implicit modeling tools like nTop (formerly "nTopology") which allow modeling with implicit functions, and therefore enable a top-down workflow, e.g., you have some shape and describe with combinations of implicit functions that is shall have rounded corners and be filled with a fancy pattern. But the implicit modeling tools are, I think, relatively new on the market and generally only smaller and light-weight tools. I specifically wonder about the reasons for that. And my question would be: Is there something that can easily be done with parametric modeling which is hard to be done with implicit modeling? And if so, what and why?
I have been interested in hyperbolic (negatively curved) space and I have been reading enough about it to feel that I understand it relatively well intuitively (e.g. the Poincare disc). But the problem is when I flip the curvature sign in my head to positive curvature and elliptic space nothing seems to make sense. For instance: In elliptic space, locally "parallel" lines will converge and intersect given a great enough distance, but if there is really a positive curvature, then it seems like the lines will eventually converge after the intersection to intersect again. This leads to the result that the lines will intersect an infinite number of times. Is this correct? I cannot find the right search terms to find this answer. Is elliptic space really a sphere? Does the positive curvature mean that if you travel far enough, you will end up back at the starting point? If so, then it seems to imply that elliptic space is finite, where Euclidean and hyperbolic space are infinite, which seems wrong. I likely have some misunderstanding of elliptic space, so If you can correct me where I may have gone wrong, please do. Thanks
I'm looking for the best BE substitute for the AmE word "ornery" in the phrase "an ornery bunch". Complicating the task for this second-language speaker of English is that according to the Oxford Dictionary of English, "ornery" means "bad-tempered and combative" in AmE whereas it means "bad-tempered or difficult to deal with" in BE. Does this mean that BE speakers tend to understand the word "ornery" slightly differently than Americans generally do (that BE speakers may perceive ornery characters as not necessarily being bad-tempered?)? Also, are there any synonyms that BE speakers usually prefer as substitutes for "ornery", or do BE speakers rather use several words to cover the AmE meaning of "ornery" (in the latter case, for my task: instead of "an ornery bunch, perhaps "a coarse and combative bunch"?)?
When I compile my document with pdflatex with natbib and either the plainnat or the dinat style on my computer, the author list is translated to German. E.g., I get "und" between authors instead of "and" and instead of "et al" I get "u. a.". I am very puzzled, because I don't know why. In my bibliography file all references are in English and I also write "and" between each author. So the original is in English and there obviously happens an unwanted translation somewhere. When I upload the very same document (i.e. all .tex files and also the .cls file, exactly as they are on my computer) to Overleaf, everything is fine and the compiled document has all references in English. I use TexStudio to write and I also compile from TexStudio. Could it be because of TexStudio? What could I change to make sure that nothing is translated?
Consider two samples of visit lengths to two different Emergency Departments. We want to test whether or not the means of the samples are different. A basic requirement is independence between and within samples. However, while we know that there are no patients that had visits in both samples, there are patients who had multiple visits within a given sample. Therefore, we cannot consider the visit lengths within a given sample to be independent. How do we deal with this? The visit lengths are labeled with patient identifiers. If, for every set of visits associated with a patient (most of which will contain a single visit) we randomly sample one visit, can we use the resulting sub-sample for hypothesis testing, or will this process inject bias? If so, how could we control for the bias? I've done a fair amount of searching on this topic, but there's a lot of obfuscation. Maybe I just need someone on here to tell me what terms I should be searching for.
I started running a tabletop RPG campaign set in the distant future where mankind has degraded to a primitive hunter-gatherer society, and I'm looking for flavorful terms for NPCs to describe directions. As research, I started watching the show "See" which has a similar premise, and they use the term "sun grave" to refer to west, because that's where the sun sets. And I love it! But what about the other directions? (I'm only midway through the first season of "See" and I haven't noticed them refer to another direction.) East could be "away from the sun grave," but what about north and south? "Right of the sun grave?" That feels awkward to me. Is there another more primitive way of describing a perpendicularity like that, or perhaps another point of reference besides the sun?
I saw this post which says: The way you do it is just a simple logic. Imagine a tennis ball and imagine you can't really see it, just like you can't see an electron. So the only way you can see where the tennis ball is is to hit it with another tennis ball or with an enormous amount of light that it will actually displace the tennis ball position, move it that is. At that moment the light brings you the information into your eyes and you see the tennis ball. Does the author mean the reflected light? Because if the light isn't reflected (i.e. a new photon emitted), how would we see the electron or tennis ball? It seems like, unless light is reflected/a new photon is emitted, we won't be able to see the electron. If my reasoning is correct, then we can't detect electrons in the photoelectric effect this way, because no photons are emitted in that case, but we can in the Compton effect. Is my reasoning correct or did I make a mistake?
I am doing some research into social interactions and the data is represented in a series of square matrices for analysis. I am interested if the grouping of matrix elements above/below off-diagonal, as highlighted by blue and green in the following diagram, are known by a specific name? These groupings of matrix elements differs from the upper/lower triangular matrix as they don't include the main diagonal and all the elements can be greater than zero. I have searched for a name but have not found anything yet. Also does the sum of these groupings have a specific name? (Akin to the sum of the main diagonal being called the trace). If there are no conventional names, I am okay to defining a name for each grouping and their respective sums as part of the research.
I am trying to understand the basics of quantum mechanics and I am having some issues in understanding the main mathematical properties of quantum operators. In particular, it's clear to me that: Quantum operators must be Hermitian to guarantee: real eigenvalues, that can be measured an orthogonal basis, so that after each measure the state of the system collapses onto a precise base-state Unitary operators are needed because they preserve norms: if we apply a non unitary operator to a system, its total probability would not be preserved. It's clear to me that the Hamiltonian is both a hermitian and unitary operator. In any book I have read, I have only found statements such as "operators in quantum mechanics must be hermitian" or "time evolution is unitary", but I've never found a statement such as "operators must be both hermitian and unitary": why is that? Shouldn't all operators be both, to guarantee measurability and conservation of norm?
Although neutron stars are mostly made of neutronium, the pressure at the surface is not very high which allows regular atomic matters to exist. Emission spectrum can reveal the chemical composition of distant stars. However, neutron stars are surrounded with extremely strong magnetic field which is enough to distort the atomic structures. Atomic nuclei should be more resistant against the magnetic field because they are much more compact and tightly bound, but I am not sure if atomic nuclei emit characteristic spectrum like the electron clouds. If we can determine the composition of the neutron star crust, will there be any variations? Neutron stars formed due to iron core collapse should have an iron crust. Some neutron stars are formed due to the electron capture of the O-Ne-Mg core. Would these neutron stars have a different chemical composition in the crust? Many neutron stars are accreting hydrogen and helium gas from companion stars. Will the accreted matters show up on the surface?
this is my first post, please excuse my non-technical language. I would like to simulate the return of a stock, that is correlated with other stocks, that meets the mean and variance of a given empirical time series. The usual way to do this is to set up a geometric brownian motion and to use a cholesky factorization on the correlation matrix of the returns of a set of stocks. As far as i know the moments of this GBM are functions of time but the log of the GBM doesn't contain any skewness. My question is: In what way can i extend the GBM to introduce a target level of skewness while keeping the other moments as in the standard GBM? Would you mind providing the explicit form of the SDE? Thank you very much in advance! Thomas
Ok, this is my first question on this site. But it's one I've been thinking about for a while. Say through whatever means, we place a device capable of generating thrust/ kinetic energy on the surface of the Earth. The goal being to remove Earth from its orbit and exit the solar system. By "perfect conditions" I mean that hypothetically when this does happen, no other planets or space debris will be in its path. I'm thinking that first it would be easier to stop the rotation of the Earth, and then use our device, but I don't quite know how the Sun's gravitational field will affect all this. Also, there can be two versions of this: one where the device generates continuous thrust and the other where it's more of an impulse. How much energy would the device need and, if any, what other conditions are needed in order to exit the solar system?
I'm a native English speaker, and I noticed that I sometimes use accusative pronouns (him, her, me) to replace actors in certain clauses. I have a feeling this is prescriptively considered incorrect usage, but I want to be able to describe it. "What does that have to do with me not coming to class?" "I want to hear about them starting a new game." "Him winning that contest has nothing to do with his family." Maybe the prescriptively correct form is the possessive, and this is confusion based on "her" which is the same in both? Or maybe it is because when the clause comes second, the pronoun makes sense as an object of the larger sentence? But that doesn't apply for the third sentence as much unless you flip it around: "His family has nothing to do with him winning that contest." How do you describe what is happening here? Why does it happen? Is it considered "incorrect", and if so, how widely? (I have the intuitive sense not to write it in an essay, but it comes so easily out of my mouth...)
"Such" has many meanings, one of them being to refer to something of a particular kind/type (see "of this or that kind"). However, in many legal documents and laws in Malta, "such" is used instead of "this" or "that", or instead of "the said thing". For example, a legal document might read as follows: The following are the terms and conditions regulating the relationship between A and B. Such terms and conditions are.... Here, "such" is not used to mean "of this or that kind", but is used instead of "these" (the terms and conditions previously mentioned). Is this use of "such" limited to the legal English used in Malta or is this a common feature of the legal English used in the UK, USA and countries where English is an official language?
Not really sure if physics question or engineering question. If we can apply energy to make an object in space move faster, the reverse should be possible - we should be able to extract energy while causing the object to slow down. So in theory, if we use rail gun to launch a projectile in space, we should be able to extract energy out of it if we "catch" it with another rail gun. Considering that, since we can use gravity slingshot to accelerate objects, we should be able to extract MORE energy out of the projectile when we "catch" it. The extra energy would come from the gravity of the celestial body used for the slingshot, which is practically huge. We could use part of this extra energy to redirect the object to the original course, thus creating a stable loop that would allow us to extract vast amount of energy from the gravity of other planets. Why wouldn't this work?
I ordered a book online, unseen, and the invoice told me the book, or at least its pages, were 'foxed'. I had never come across the expression, did not know the word could be a verb and discovered : Foxing is the age related browning, or brown-yellowish spots, that can occur to book paper over time. When this aging process happens to the paper in a book it is referred to as "foxed". The term may come from the rust brown color of the paper aging process or from a chemical used to coat paper called ferric oxide. Foxing may also be caused by fungal growth on the paper, chemical reactions, or high humidity. Biblio.co.uk Is there any more information anywhere to clarify the idea of ferric oxide being involved, which sounds a little far-fetched to me, or to demonstrate the history of the word in that particular context?
In condensed matter and materials physics it is often assumed that the response of a condensed phase to some perturbation is determined by the fluctuations of the system at equilibrium (without perturbations). For example, the electric resistance of a liquid (the response of the current to an applied field) is determined by the mean squared displacement of the charge carriers (the fluctuations) at equilibrium. Pictorially, this makes sense because if the charge carriers move slowly at equilibrium it will be probably not be easy to make them move, so for small fluctuations the current response would probably be small. Another way to say this, the difference between motion at equilibrium (without field) and motion out of equilibrium (with applied field) is that there is a small bias in the direction of the field, but the motion is otherwise essentially the same. Formally, this relation is proven by the fluctuation-dissipation theorem for a statistical mechanical (micro-canonical or canonical) system subject to small perturbation (small term added to Hamiltonian). My concern is that I think that the validity of this FDT relation can be formulated for systems more general than statistical mechanical (micro-canonical and canonical) systems. Pictorially, I think whenever the system can be described as a stochastic variable fluctuating in some potential landscape between some potential minima, then the response should always be related to the barrier heights of those minima, which also determine the magnitude of the fluctuations at equilibrium (without bias). So is it possible to derive FDT also for this setting ?
In order to obtain phonon spectrum, we usually do Born-Oppenheimer approximation and assume that the electrons are always at the ground state when the atoms move, and by calculating the force on each atom (usually using DFT) we are able to assemble the dynamic matrix of the atoms and obtain the phonon modes. After this we can calculate the electron-phonon vertex and then do Feynman diagrammatic calculations to get things like polaron. So the whole formalism is based on the BO approximation. The question then is how we can write down a set of Feynman rules about both electrons and atoms without the BO approximation. Can we still define phonons (hence phonon propagator, etc.) in this case? If we already have a theory under the BO approximation, is it possible to, say, add more interaction vertices and/or adjust the coupling strength to go beyond BO?
In An Argument Against Abolishing Christianity it is written: Another advantage proposed by the abolishing of Christianity is the clear gain of one day in seven, which is now entirely lost, and consequently the kingdom one seventh less considerable in trade, business, and pleasure; besides the loss to the public of so many stately structures now in the hands of the clergy, which might be converted into play-houses, exchanges, market-houses, common dormitories, and other public edifices. I hope I shall be forgiven a hard word if I call this a perfect cavil. I readily own there hath been an old custom, time out of mind, for people to assemble in the churches every Sunday, and that shops are still frequently shut, in order, as it is conceived, to preserve the memory of that ancient practice; but how this can prove a hindrance to business or pleasure is hard to imagine. What if the men of pleasure are forced, one day in the week, to game at home instead of the chocolate-house? Are not the taverns and coffee-houses open? I looked up chocolate in Wiktionary and chocolate house in Wikipedia. Of what chocolate house does Swift write here?
In a power grid, the grid itself has a certain amount of inertia from all the spinning loads and generators. If at a given moment in time the production and consumption of active power does not match, the power mismatch will be provided/absorbed by the spinning energy stored in the grid, and the frequency of the whole grid will raise or lower in lockstep to compensate. Eventually the generators' governors and the load/frequency relationship will arrest the frequency drop, and it will arrive at a new steady-state value, but it's not something that happens immediately. Does it work similarly for reactive power? If a capacitor bank supplying reactive power suddenly trips, does the voltage immediately drop to its new steady-state value? Or is there a period of voltage decline as the missing reactive power is siphoned from somewhere?
Suppose there is a plank on a smooth surface and a man is standing on one end of it. The surface of plank is rough. Now the person starts to move towards the other end with some acceleration and the plank also starts to shift to keep the COM stationary as the only forces acting here are all internal. Now my question is,as the direction of the friction force on the man is in the direction of the displacement of man and same is the case with plank. Then in this case isn't work done by friction on the whole system coming out to be positive which should not be happening as if it is the case of static friction then the net work done should be zero and if it is the case of kinetic friction then the net work done should have been negative? Also please tell me whether the friction present here is kinetic or static.
Note: this question is not a duplicate of the following questions: How to remove vertices from a graph that are not coverable by cliques? How to remove vertices from a graph while preserving clique coverage of specific vertices? This question is with respect to removing vertices that are not reachable from a set of vertices, regardless of clique membership. How can I remove vertices from a graph that are not reachable from a given set of vertices? Here is a toy example and solution: In the graph below, I want to remove the vertices that are not reachable from any vertex with an "x". The orange vertices are the vertices to be removed. toy example graph image The current approach is doing depth-first search from each of the vertices marked with an "x", and keeping track of which vertices are visited. All vertices from the graph that are not in that set of visited vertices are removed from the graph. However, this could take a while if the graph is large, so I was wondering if there is a faster way of doing this.
Let's say we entangle four electrons based on their spin. Now, let's say we measure the spin of electron A along the z-axis (up/down), and we observe a spin of 'up'. My understanding is that this means that the remaining three electrons would need to have some combination of spin which adds up to 'down'. Next, we measure the spin of a second electron, but along the x-axis (left/right), and say we observe 'right'. My question is, what does this mean for the up/down spin of the entangled system? I'm thinking since it can't be that the remaining two electrons add up to a 'down' spin, it must be that the second electron we measured also still has a state for up/down spin that has not been observed yet. But that would also imply that it's still entangled with the other electrons; this is where I'm confused, cause it was my understanding that a measurement would break entanglement. Is that correct, or no? What actually breaks the entanglement in this case? Hope the question makes sense, and thanks in advance!
I need a word that describes someone who advocates for harmful laws or policies; it would describe someone who writes policy without listening to the people it affects or someone who doesn't pay attention to actual effects of that policy, kind of like politically or socially tone-deaf. They might continue to stand behind that policy even after it was proven to be ineffective or harmful. It would be like ignorant or deluded, but specifically regarding knowledge of people's situations or societal problems and solutions. A word to describe the actions of that person would be helpful as well. As an example: It was very __ of the senator to vote for the harmful bill that would require every homeless person to own a car. The word wouldn't refer to someone doing this knowingly and maliciously, but I would like it to have a negative connotation. Thank you!
I want to start learning model theory for my master's thesis, but I can't find the right book for me. For some context, last year as an undergrad I had a class on logic where we learned the following: So I already had contact with formal languages, structures, models, and both the semantic and syntactic aspects of first-order logic and now I want to follow from this and start learning some real Model theory. I started using David Marker's "Model Theory. An Introduction" but I'm personally not a big fan of that book: It's full of typos and I don't like how informal some of his proofs and expositions are, for example, this definition: Do you have some recommendations for a rigorous book/resources to learn Model theory, ideal for someone with a little background on the subject?