Models Definition and 369 Threads

This might seem like a naive question from someone who doesn't know a whole lot about economics/government: Do governments have 'unified' computer models of the countries they govern, including for example energy generation, agriculture, transport etc.. A bit like simcity or civilisation games...

I have a question as to the actual nature of cyclic models of the universe (e.g. Roger Penrose's Conformal Cyclic Cosmology or the Ekpyrotic universe) - essentially where the universe has no beginning or end it simply goes through cycles eternally in both time directions. So in these situations...

Must all models of ZFC (in a standard formulation) be at least countable? Why I think this: there are countably many instances of Replacement, and so, if a model is to satisfy Replacement, it must have at least countably many satisfactions of it. Does my question only apply to first-order...

I have some questions about this paper: http://arxiv.org/abs/1102.1994v2 The author computes the entropy of the classical simulator using the Shannon entropy, then computes the entropy of the quantum simulator using von Neumann entropy and gets a smaller number, thus concluding that quantum...

Hi, First of all i apologies if this topic already exists I was wonder how the particle model of light and wave model of light compare in regards to energy distribution, amplitude, and frequency? I am having a hard time wrapping my head around this. I have a decient understanding of the...

Weih's data: what "ad hoc" explanations do local and non-local models give? From the thread on Nick Herbert's proof: harrylin: The more I become aware about the tricky details and the impressive experimental attempts to disprove "local realism", the more I am impressed by - to borrow some...

From http://www.lsbu.ac.uk/water/models.html, I see that are many models of water that can "explain" one or some properties of water but no model is accurate enough to explain all the properties of water. From what I understand, all models assume classical mechanics interactions...

3 generation is required for anomaly cancellation, then the 4th generation seems redundant. But there are still papers about the 4th generation, what is the reason? Thanks

Does anyone know of a COMPLETE derivation of the Hubbard Model and then the Heisenberg model from it. What I mean by complete is pedagogical including all (or at least most) steps. Books like Assa Auerbach's and Altland and Simons are worthless for these kind of things (in fact IMHO those...

Hello everyone. I'm trying to do a homework in digital integrated electronics class and feel like I can finish it only if I had a good set of notes. I have problems like comparing the input capacitance of a Mosfet to a wire of certain length, getting RC time loss in a wire, power...

Inflaton Field and Bounce Models In traditional inflation, there is a field known as the inflaton which a boson of the same name. Hybrid models of inflation , if I've understood correrctly(?) have a field to start inflation and a field to stop it. However recent work on bounce mdoels such as in...

This seemed like the least inappropriate place for this. Feel free to move it if I am wrong. Generally speaking, two computational models are equivalent if they recognize the same class of languages. In the case of models that can run indefinitely, we also have the problem of decidability...

Hi guys, I am currently writing my dissertation on Graphene and I am investigateing how graphene remains stable, contradicting existing well established theory which states 2D materials cannot exist independently. With the main area of investigation looking at possible lattice distortions...

I'm halfway through the Selfish Gene, and was intrigued by his talk of strategies. Are there any good books that talk about this development in human behavior?

At another thread under Special and General Relativity the following question was asked: "Why isn't stellar aberration considered to be a one way measurement of c? If the angle of aberration (θ-θ0) is -20.5 arc seconds and the Earth's orbital speed is 29.79 Kilometers/second normal to the...

As far as I have seen, all physical models begin with space, and then put matter that live in space and modify it somehow. Basically the models works fine and describe reality farily well. But at some point they arrive to problems, as infinite curvatures, that prevents them to be unified. It...

I know the default library of LTspice don't have vacuum tube model. Does anyone know where I can get one. If not, any other free spice program have vacuum tube models? The only one I find so far is: http://www.duncanamps.com/technical/ltspice.html I tried to follow the instruction and...

There's a new paper dealing with constraint algebra and Gupta-Bleuler quantization in LQG and SF models. http://arxiv.org/abs/1012.1738 Complex Ashtekar variables and reality conditions for Holst's action Authors: Wolfgang Wieland (Submitted on 8 Dec 2010) Abstract: From the Holst action...

I'm guessing if Quantum Mechanics get modified to allow for physical collapse, the Schrodinger equation is modified. But whatever has already verified Quantum Mechanics thus far, the new theory needs to account for those results but, I would assume, make different predictions in other areas that...

Homework Statement I only need help with problem 16 but included problem 15 because it is referenced in problem 16. 16. Suppose that the growth-rate parameter k = 0.3 and the carrrying capacity N = 2500 in the logistic population model of Excercise 15. Suppose p(0) = 2500. (a) If 100...

Hello all, I'm an amateur interested in nuclear structure. I'm interested in the (by now) age old questions of "Why is alpha radiation so much more prevalent than simple neutron or proton emission?" and "Why aren't nuclear isomers like Tantalum a lot more common or identified?" and especially...

Hi, I was wondering what you guys thought of these models. Is the model on plank's length correct? Have you seen these types of models before (especially model C + D)? If so, do you have a link to something like it online? Also I am wondering how I can include 'ENERGY' and 'C' (velocity?)...

Hi, I have currently been thinking about laser-plasma interaction and I have a simple model in mind. I am going to look for a cylindrically symmetric solution of a cylindrically symmetric laser beam (of radius R) hits a initially charge neutral plasma creating an electron beam in the plasma...

To my intuition, I find more easy to believe that the universe is infinitely old and the big bag was just one of an infinite number of similar events in a larger universe, rather then the universe had a beginning. However, after watching many documentaries, and reading a lot of popular...

I will be entering university in an aerospace engineering program next year but I want to get a head start on it right now. What I mean by that is start building basic rockets and planes, or even more basic than that, I don't know. Why I am here is to ask for guidance on where to start. I...

Hello. I have three questions that I would like to ask.1. Could someone provide me with a resource containing examples of arbitrary parameters in theoretical physics. E.g. a modern example, yet to be varified, is dark energy. A historical example, one which has since been discredited, is the...

Are physics laws (even the laws) mathematical models of reality? Or they describe reality as it is? Are those laws just models, like for example a population's growth mathematical model (just an example that I remembered)? A maths teacher told me that in physics everything are...

Question 1: What is the status of string random matrix models (~ triangulated random surfaces) with c>1? In my limited search, I have just come across a few papers by Frank Ferrari (in 2000-2002) on this. But, they applied, if I understand correctly, to a few cases with some specific kind of...

Does anybody know about a comprehensive list of cosmological models and their properties? E.g. FRW, dS, AdS, ... Goedelspacetime, ... with metrics g, Christoffel symbols, Riemann tensors, Ricci, Ricci scalar, Kretschmann scalar, ... Tom

Hi, I am interested in grand unification with extra dimensions. Especially the case when extra dimensions are broken by orbifolding. Now I am trying to understand how the Goldstonebosons appear in the spectrum of a theory with global (for example SU(N)) symmetry. From the...

Hi there! I'm new here and am currently looking into the Hartle-Hawking and Hawking-Turok Quantum creation models. What I've read about the Hartle-Hawking model is that it predicted a Closed Universe. But isn't that the opposite of what we have learned? The WMAP sattelite has confirmed the...

Let us consider the cosmological metric: {ds}^{2}{=}{dt}^{2}{-}{[}{a}{(}{t}{)}{]}^{2}{[}\frac{{dr}^{2}}{{1}{-}{k}{r}^{2}}{+}{r}^{2}{(}{d}{\theta}^{2}{+}{sin}^{2}{(}{\theta}{)}{d}{\phi}^{2}{]} -------------- (1) For closed models k is positive We shall consider here a closed one: We write...

Linear models is the topic And i believe my professor wrote this n*Sum(XiYi) - Sum(XiYi) = Sum(Xi - Xbar)(Yi - Ybar) i was hoping if some one could tell me if this is true of if it is my bad in typing down. If it is true then can some one please tell me how? I've attached an image...

I would like find references to collisional astrophysics models. I am a computer scientist interested in developing discrete event n body algorithms and would like any help that I can get. I have developed a direct n body algorithm for systems without collisions which seems to work well and...

How accurate are "simple" models of the solar system? Exactly how much effect does the perturbation of other planets have on planetary orbits? That is, if we were to take a naive model of the solar system, just applying Kepler's laws to each planet individually, with no planet-planet...

1,2,3. Homework Statement , and work done. After Lee gives his little sister Kara a big push on a swing, her horizontal position as a function of time is given by the equation x(t) = 3cost(t)*e^{-0.05t} , where x(t) is her horizontal displacement, in metres, from the lowest point of her swing...

I have read that some cosmological models predict a heat death of the universe. Eventually all matter (beggining with superclusters, clusters, then galaxies, then stars) will lose all energy and separate (due to expansion which will eventually occur even on a galactically local level) so that...

Anyone can briefly tell me about this concept? Did it is a undeformable model?

For years I have mastered the art of simulation and testing, but I almost never seem to be able to find SPICE models for real devices. For example, the TI OPA548. It's a high-current power op-amp. I would love to run some simulations...but I can't find a model of it anywhere to use in...

I am doing a project in school and am looking up different cosmological models to research. I have found Steinhardt Turok Model, Kaluza Klein. I know these are not the best models, so I was wondering if there are any more specific models that I can look into.

Homework Statement (2xy-5)dx+(x^2+y^2)dy=0, y(3)=1 (2x+y^2)dx+4xy dy=0, y(1)=1 x^3y'+xy=x, y(1)=2 y'(t)=-4y+6y^3 We're doing these in 2nd yr engineering Math and I have heard the Lecturer say they are useful across all disciplines. I've heard him suggest RLC circuits, springs with...

So physics is about measurements and following models that can explain stuff even if they don't correlate with reality? For example. General Relativity is believed even if space doesn't really curve. Only spacetime curves but not space. Since space is empty and doesn't have structure. It is not...

Are the mathematical models which describe the laws of physics considered simple or complex?

A mathematical model may show that there are two possible states for something in the real world, let's say a coin, that may be either heads or tails; make a computer program to simulate coin flipping and you soon discover that the odds of heads or tails is 50/50. In the real world however...

Models like the Hodgkin-Huxley and Morris-Lecar include a current term: applied current. http://cropsci.illinois.edu/faculty/gca/bioengin/Top/Lit/GENESIS_book/iBoGpdf/chapt4.pdf From what I understand, experimentally, this is the injected current, applied by the experimenter. But what is it...

I know there are three models of the universe: closed, flat and open. But which one of these models is the most accepted by scientists and why? I read that the WMAP satellite discovered that the universe is flat. But other observations have shown that, from 7.5 billion years after the Big...

Three facts: (1)The constructible universe L is the minimal model for ZFC; (2) L is a model of "there exists an inaccessible cardinal \kappa"; and (3) if V=L, an inaccessible cardinal \kappa with the membership relation \epsilon is a model of ZFC. So, what is confusing me is: if...

Hi! I am amateur in mathemathicals growth models but I am doing my graduated work in adjust five differents models in some growth parameters in onion, [PLAIN]http://img820.imageshack.us/img820/2929/models.png So my doubt is basically in a derivate for gauss model, i can't derivate this model...

I do not understand how On, the class of ordinals, can be included in the universe of an inner model of ZFC such as < V\kappa, epsilon>, where \kappa is the first inaccessible ordinal. My confused attempts to do so have led me to believe that I am getting off on the wrong foot in my analysis...

Hello all! :smile: You know, I thought I knew something about ideal gas mixtures, but now I am not so sure. I am reading through a section of a text that discusses the Dalton and the Agamat models of ideal gas mixtures. I will briefly describe each: Dalton Model: The underlying assumption...