Models Definition and 369 Threads

Hi, my question is if there exists a study systematically comparing different cosmological models in how well they fit the same standard cosmological data sets (CMB, luminosity, BOA, SNe, lensing,...). I can find very little besides LCDM. In the rare case of a comparison, it leads to...

How do the different inflationary models different form each other. Is is just the shape of the potential or the number of fields assumed or...?

Homework Statement 5.The small town of Pi-ville wants to construct a road that connects to the Linear Super Highway. The road must provide a route that covers the shortest distance possible from the town to the highway. Write an equation that models the best route for the road. Homework...

I am looking for 3D (or 4D, etc.) images of waves (such as light or sound), but seem to be having difficulty locating such models. Can someone please direct me to this kind of display, or is it not something being currently done?

Hi, I am trying to fully understand the meaning and usage of phase space in the various contexts it's used. For example particle physics, classical mechanics, statistical mechanics, thermodynamics, relativity. Also, there is configuration space, parameter space, and state space. How are all of...

Suppose that I have a set of axioms in first-order logic. And suppose that I have several inequivalent models for this set of axioms. And suppose that I want to choose one specific model. To choose it, I need to make some additional claims which specify my model uniquely. My question is the...

I'm sure the inductor model, i.e. vL(t) = iL'(t)*L follows without directly from Faraday's eq. But even there, with Faraday's equation we think of the changing magnetic field as inducing the voltage in the loop, where in the model it seems the other way around, that is, the voltage increases...

Are there any good models, software or codes that can predict the probabilities of nuclear reactions where an atom of a given type strikes another atom of another type with a given energy? Or is this information only obtainable experimentally? To further clarify, I am interested determining...

The FCC's propagation models for the FM broadcast band seem grotesquely inaccurate in some places, where stations can be received that the models say are absolutely out of range. I'm not even talking about DX conditions like ducting or skip, I'm talking about baseline. When I lived in...

What role do theories, models, and laws play in the scientific process? Is there a clear dividing line between a theory and a law? Are models used in both theories and laws? All theories and laws? Do our best current models perfectly represent reality to the best of our knowledge, or are they a...

Homework Statement The task is to write the following equations of motion as in equation (2) considering the inputs and outputs as in equation (3) \begin{equation} \begin{cases}...

Different things keep popping up in the literature that pose Dark matter and Dark energy are not needed to explain the universe, the latest MOG i have come across is this: http://arxiv.org/pdf/1510.07037.pdf What are the chances that a modified gravity theory will replace the standard model?

Hi again, say we are given the relational table: TEAM(TeamID, TeamName, TeamColor, Game, DatePlayed). Question is: how many games can we play, meaning, while preserving the properties of relational tables? This is what I have.We know We know TeamID, TeamName andTeamColor are fixed in any...

Big bounce cosmic models, as a research topic, shouldn't be confused with cyclic models where there is a recurrent bounce. The earlier thread by mykamakiri got a bit distracted because of that kind of confusion so I thought I would split off a separate topic just to focus on the question in the...

We know that the universe is expanding at an accelerating rate. In big bounce (or oscillatory) models of the universe, why does the expansion of the universe end? And what drives the following, contracting phase? Is it possible that dark energy could inverse its action at some point in the...

Just noticed a new article of C Furey not arxived, but readable in SCOAP Phys.Lett. B742 (2015) http://inspirehep.net/record/1342971?ln=es Charge quantization from a number operator Well, it is not new but I have not found a thread mentioning it. It seems to continue the quest from her...

I have no experience working with mice models, but why, for example, in pronuclear injection (or even other methods of transgenesis), is the injected gene of interest randomly integrated? In other words, why would the integration site of the DNA not be known or in a targeted region? I apologize...

I'm not sure my question belongs here or in the physics section I'm aware that in addition to the poisson-boltzmann equation, there's also the Debye-Huckel approximation, which is used at low ionic strengths and dilute solutions. I also know that the Stern layer includes the finite size of ions...

I reading article "The Cosmological Constant and Dark Energy" P. J. E. Peebles, Bharat Ratra http://arxiv.org/abs/astro-ph/0207347 They use following sources of density: ## \Omega_{M0}+\Omega_{R0}+\Omega_{\Lambda0}+\Omega_{K0}=1## Next I see " The measurements agree with the relativistic...

Nonlinear sigma models are particular field theories in which the fields take values in some nontrivial manifold. In the simplest cases this is equivalent to saying that the fields appearing in the lagrangian are subject to a number of constraints. Since the lagrangian fields are not independent...

I seem to recall a documentary that I watched a few years ago describing the multiverse, with M-theory, as being similar to slices of bread, all next to each other. (Obviously just an analogy for the lay person). And when these two universes next to each other collided, it would create a new...

Hi, Are there any self contained models of the BB that are "front-runners" as explanations for the big bang? I understand that all models have some problems with them, but which models are currently taken most seriously among working cosmologists, and are there explanations of those models for...

We know that different models of the Reals are elementary equivalent but not isomorphic. In the hyperreals, we have that the Archimedean principle does not hold but it does hold in the standard Reals ( i.e., the hyperreals allow for the existence of indefinitely-small and indefinitely -large...

Currently reading Peter Coles, Cosmology a very short introduction. There is a bit I don't understand. In a section discussing Friedmann Models, and how going on the cosmological principle density of the universe is the same in every place, and therefore space must be warped in the same way at...

Homework Statement A rectangular 4 x 8 foot sheet of plywood is fixed to a sled which moves on a track. The face of the plywood is perpendicular to the direction of the track. The sled is pushed a distance of 3 inches. What is the volume of air swept out during this motion. Homework Equations...

Hello! I'm studying various dark energy models, and as a part of the project, I need to be able to numerically solve the Klein-Gordon (KG) equation and the Friedmann Equation (FE) in the context of a canonical scalar field. I wasn't sure whether or not this belonged here or in the computational...

Homework Statement Here is a math problem I would to make sure I have understood correctly. a) Billy goes to be bank. He deposite 500 dollars in his account. The bank offers a interest of 2 percent a year. Sally goes to the bank 4 years later.She deposite 250 dollars at the same bank...

I think this is now a legitimate topic. If not, I apologize. I would like to hear comments on the paper "Why models run hot", discussed in this article. Do people on this forum agree that the IPCC models overestimate the amount of positive feedback in the Earth's climate system.? Or is this...

Hello all, Could someone offer an example of case where an empirical model was developed first due to absence of theoretical models and later (possibly years later), the theoretical models caught up and were able to explain the mechanistic detail that the empirical model could not? Thank you, QP

Hi all, I'm currently working on a 3D game and am in the city development phase (its done procedurally). The issue is is that once I get to 22 000 buildings (80 000-100 000 models roughly) it causes a drop to 5fps(frames per second) (even with collision detection off). I'm using instancing to...

Hi, I have been reading a number of papers by Dragan Hajdukovic's on his work related to models for dark matter. How mainstream / well regarded is his work / models?

From my understanding, average trajectories based on weak "measurements", obey the 'no-crossing rule'. These average trajectories strongly resemble the single-photon trajectories predicted by Bohmian mechanics: For instance compare these average trajectories...

I have just found a review on this topic by Volkas and Joshi http://inspirehep.net/record/21549?ln=esBut it is very old... 1988. I was just in the middle of the undergraduate. I know that the topic got some push from Seiberg dualities, but that is still the XXth century. Does anybody know of...

Hi, I would like to model various projectiles and capsules being fired at hypersonic speeds by a coilgun or equivalent mass driver. Does anyone know of any programs that could simulate a launch or at least parts of the flight? (ie. setting the atmospheric density for a given region, calculating...

You can use transfer matrix method for 2d Ising model. Is there a list of models for which this method could be of use. Such as classical Heisenberg perhaps? Or Potts?

Hi Everyone, So I think this is a bit of a loaded question, but how do professional physicists find/learn the most recent models? I have been trying to find the correct search terms on web of science for the past few days, but so far I have only found papers dealing with experimental or...

Homework Statement Homework Equations — The Attempt at a Solution Confused with (d) a little. Rocket explodes at ##h=3.85262 ## miles ## -16t^2+1400\sin(\alpha)t=3.852624*5280## ## \alpha=\arcsin\left(\dfrac{3.852624*5280+16t^2}{1400t}\right) ## But what do I do...

When we generate solid by rotating a curve around an axis, we use "slabs" of cylinders to approximate the volume of this solid of revolution. When we want the find the surface area, we instead use "slabs" of conical frustums (ie. the slope of the differential length of curve is taken into...

Hi ll, I am currently working on 3d in xna. i have ismple collision detcetion working but I want to do triangle by triangle collision detection.How would I get a models base triangles? I have this adapted from online to fit in with my game: public struct TriangleVertex {...

For zebrafish and Xenopus, are there currently any effective gene knockout strategies? From literature, these two organisms have effective gene knockdown strategies in practice. Thanks for any help.

What are main differencies between Bianchi models and Kantowski-Sachs models. Can anyone give mathematical definition clearly and possibly simple form?

In a spatially homogeneous model, spacetime is filled with a one-parameter set of invariant hypersurfaces H(t). Spatial homogeneity means that the metric on each H(t) is described in terms of constants. Meaning that the metric becomes a function of time only. I guess that this means that...

In a Bianchi IX universe the metric must be invariant under the SO(3) group acting on the 3-sphere. Hence, the metric must be translation invariant in the spatial parts, where t=constant. This implies that the metric must take the form such that: ds^2 = dt^2 - g_ij(t)(x^i)(x^j), where g is a...

Hello experts! I was taking class of optical fiber and communication. My teacher was teaching the class via projector and slides (transparencies). He taught us light models and he just changed his slide after reading the few lines. I was not able to note down the main points of the slides...

Hi people. I just read this somewhere and I can't get my head around it. How is the Uncertainty Relation uncompatible with the idea of a proton-electron nucleus? And can you explain why this model predicted those values for the nuclear spin? Thank you.

Please can someone explain the clear concept between large signal model and small signal models in BJT. Please explain what to assume in large signal and small signals problem solving wise and also the concept. Amongst vBE, VBE, vbe which is large signal?, small signal? and what we assume in...

Hi all I am comparing the performance of two models and have calculated the coefficient of determination R squared for each. I would like however to test the significance of this value. The F test however requires that the number of degrees of freedom for each model. The trouble is one...

Hi everyone, :) This is a question that one of my friends sent me. It is kind of open ended and I don't have any clue about the particular area of research he is undertaking. Therefore I am posting the question here with the hope that anybody knowledgeable in this area would be able to help...

How does a zero separation of parallel D-branes give mass to the particles that correspond to strings stretched between them? Is there a scalar field corresponding to the separation of the D-branes which takes the role of a higgs field, or how does it work?

I originally posted this on the Biology message boards. But I have not received any responses. In models of exponential growth, we have an intrinsic growth rate (r) that is calculated as the difference of birth rates to death rates. With the logistic growth model, we also have an intrinsic...