Models Definition and 400 Threads

  1. Buzz Bloom

    I Qs re Cosmological Models Using Bayesian Probability Methods

    I am familiar with non-Bayesian methods for calculating best fit values of various parametric models, but I have not had any experience with cosmological models calculations. My understanding is that these models have five parameters: H0, Ωr, Ωm, Ωk, ΩΛ, and the last four satisfy the constraint...
  2. Auto-Didact

    Determinism: mathematical models

    Ever since Newton, determinism - i.e. the concept that the prior state of a system determines the next state of the system - has become an integral part of science, in particular of physics. This is particularly because Newton invented a mathematization of the concept of change: the calculus; in...
  3. QuarkDecay

    A Different FRW Cosmological Models

    ρο/a4 ρο/a3 k Λ Βig Bang Big Crunch Polynomial Expansion Exponential Expansion x 0 x 0 >0 x +1 x +1 x 0 <0 x -1 x -1 >0...
  4. A

    I De Broglie-Bohm theory and Bohm-like models - how is vacuum treated?

    Hi all, I've been looking at de Broglie-Bohm theory and more recent attempts at Bohm-like models that are relativistic and attempt to reproduce QFT. What I'm not clear on (non-expert) is how the vacuum is modeled in these cases? If we have a set of infinite quantum harmonic oscillators...
  5. Spinnor

    I A Quadrillion Standard Models from F-theory arxiv.org/pdf/1903.00009

    https://arxiv.org/pdf/1903.00009.pdf "We present an explicit construction of O(1015) globally consistent string compactifications that realize the exact chiral spectrum of the Standard Model of particle physics with gauge coupling unification in the context of F-theory. Utilizing the power of...
  6. R

    Extrapolating data points using models

    Homework Statement I have made a number of measurements of current against optical power for a given laser. As shown below, my measurements only go up to 8 amps. I am trying to use the data to predict the output power at 9 amps. In the ideal case, the behaviour is expected to be linear, but...
  7. A

    Simplified SUSY models with different mixing cases

    Hi Probably a bit technical, but here it is. I am trying to construct some simplfied SUSY models (that is, you only tune the masses of the core process, while all the rest are decoupled), and I would like to play with different mixing scenarios for the neutralino and charginos, so to get a...
  8. J

    Theoretical models of the Earth's Electric Field?

    I am doing some research into atmospheric energy harvesting. To design a proper feasibility experiment, I need to establish some theoretical baselines. I see a lot of values for the field strength for example, tossed about from various papers. However, there does not seem to be a standard...
  9. Rafid Mahbub

    A Exploring parameter space of inflation models

    I have been studying primordial black hole formation through inflation for a while and I was curious to know how the parameters in an inflation model are determined such that they are consistent with CMB constraints. In my literature reviews, there are quite a few models that exhibit an...
  10. L

    Solving State-Variable Models Homework

    Homework Statement Homework Equations ##\dot{x} = Ax + Bu## - Input Function ##y = Cx + Du## - Output Function The Attempt at a Solution I'm having trouble with the output functions specifically .. In a.) the correct solution for the output is: \begin{align} & y_1 = x_1 \\ & y_2 = x_2 \\ &...
  11. tatkhj

    How do the Mobius and Klein models illuminate string theory?

    I'm a speculative fiction writer and playwright, a retired archirect with a master of architecture degree in theory, and a theater producer, director, and acting improvisor. I'm currently working on a TV series of 169 episodes exploring life in a contemporary parallel universe very much like...
  12. FallenApple

    A Using incorrect models to infer correct ones.

    I see this happening a lot and have done this in my analysis as well. But it doesn't seem too intuitive to me as to why it works. So if we fit a linear regression, and the residual vs fitted plots are curved, we tweak the input variables to get a random residual vs fitted plot. But we have used...
  13. Nikhil N

    Model developed from performance curves are dynamic models?

    I am trying to model a real heat exchanger in simulink. I don't have the geometry data. But I have UA curve with me. If I have developed the model with UA curve, will it be dynamic in nature?
  14. Derek P

    A Discrete Models for Arguments and Continuous Variables in Quantum Mechanics

    Arguments can often be presented using a discrete model on the assumption that continuous variables can be accommodated by taking the limit as the resolution is increased. I would have thought that this would be just fine in QM where functions are continuous. But maybe mathematicians here can...
  15. M

    I "Centaurus A Contradicts Dark Matter Models"

    According to the article in Astronomy Magazine June 2018, the satellite galaxies of Centaurus A are rotating in the same direction in a relatively thin plane, vs randomly distributed if there is a dark matter halo/sphere surrounding large galaxies. Any thoughts on this new finding? I've only...
  16. Leonardo Machado

    A Beta equilibrium for free and interacting nucelar models

    Good evening. I'm currently studing dense matter and nuclear matter above 10^8 g/cm^3, and i know well how to insert a beta equilibirum condition in a free Fermi gás at T=0. \sqrt{K^2_{F,n}+m^2_n}=\sqrt{K^2_{F,p}+m^2_p}+\sqrt{K^2_{F,e}+m^2_e} But how do i insert the same condition of...
  17. F

    I Are these models true or even relevant?

    Hi everyone. I'm new to the forum so sorry if the title or the "sub-topic" is wrong, and I tried my best not to break the posting guidelines, if I did, let me know. (First of all, I want to clarify what's my stance on all of this, I'm not a proponent of these ideas; in fact, I'm always sceptical...
  18. M

    Pick a,b,c,d for y=ax^3+bx^2+cx+d that models path of plane.

    Homework Statement A plane starts its descent from height ##y =h## at ##x = -L## to land at ##(0,0)##. Choose ##a, b, c, d## so its landing path ##y =ax^3 + bx^2 + cx + d## is "smooth". With ##\frac{\mathrm {d}x}{\mathrm {d}t} = V =##constant, find ##\frac{\mathrm {d}y}{\mathrm {d}t}## and...
  19. SemM

    A What are some recommended books on non-standard quantum mechanical models?

    By fresh42's invitation, I here attach a paper which is related to the post on non-standard qm-models https://arxiv.org/pdf/cond-mat/9705290
  20. B

    I Continuous Lensing Models: Discrete Data

    Hello, I am not sure if this question is better suited to the mathematics section, but I thought it would be easier to explain the problem here. In Schneider, Kochanek and Wambsganss's "Gravitational Lensing: Strong Weak and Micro" pages 279-280, they derive a relation for determining the...
  21. SemM

    A Can Quantum Mechanics be Studied in Banach Spaces or Other Non-Hilbert Spaces?

    Hi, are there any models known in QM where the wavefunctions do not have to be infinitely differentiable, and thus can exist in other spaces than the Hilbert space? I assume Banach spaces allow elements that are not infinitely differentiable as subsets. Can therefore certain phenomena in QM be...
  22. L

    I Fitting two models in sequence with parameters in common

    I wonder if anyone can please help / point me to some info on how to solve this problem. I posted the same question on another website, and so far there is no conclusive answer. I have some pharmacokinetic data for a molecule that was administered in rat, first IV (intra-venously), then PO...
  23. M

    I Exploring Different Models of the Universe

    Dear All I know that my question is not so related to this, but i will appreciate any answer. Why could we have 2 different models for the universe ( one expanding, collapsing...) although both are receiving the same experimental data... I need to write an essay about this topic. I have ideas...
  24. O

    A Classical field models with infinite conserved quantities

    Couldn't really fit the precise question in the title due to the character limit. I want to know what are some sufficient conditions for a model in classical field theory to possesses infinitely many conserved quantities. The sine-Gordon and KdV equations are examples of such systems. Now...
  25. D

    LaTeX Why Analyze Sensitivity in Omnivory Models?

    \chapter{Sensitivity Analysis} The first step in our method to obtain the sensitivity of each parameter value is to differentiate the right hand side of each model with respect to each model parameter. The partial derivatives for the right hand side of our linear response model...
  26. A

    How realistic are modern neuron models?

    Nowadays we hear a lot about AI deep learning artificial neural networks. People speak about simulations of billions of neurons and even much more synapses. However, as far as I understand it, the artificial neurons used in these simulations are extremely simplified models of real biological...
  27. N

    Using Ideal and Constant Voltage Drop Models

    Homework Statement I am practicing diode circuit analysis for an ideal diode model and constant voltage drop model.I have an initial circuit shown here: Which I then redraw to look like this: I want to make sure my process in redrawing this was correct. When I attempt to get current through...
  28. f95toli

    Why do e.g. smoke detectors need specific battery models?

    I have once again come across a smoke detector which requires not only a specific type of battery (9V alkaline) but also a specific model (in this case Duracell MN1604) to be used. I had a similar problem with a CO detector about a year ago (which came with a list of about 10 models that should...
  29. ohwilleke

    I Looking for literature re imperfect quantum gravity models

    Preface There are lots of times in physics when we use approximations of a more accurate or fundamental physics theory because it is easier to work with. For example, in quantum chromodynamics (QCD) lots of calculations are done using the Schwinger-Dyson equations rather than the actual...
  30. Buzz Bloom

    I Models of accretion disc emissions contradicted by experiment

    Ref: http://www.spaceref.com/news/viewpr.html?pid=51416 I would be very interested to see comments from knowledgeable people about this. My impression is that this is one more example of a need to remain at least somewhat skeptical about theoretical models that have not yet been validated by...
  31. UsableThought

    New book on dynamical, agent-based models for economics

    This may be of special interest to mathematicians, physicists, and anyone who is skeptical of the various "social sciences." The book is The End of Theory: Financial Crises, the Failure of Economics, and the Sweep of Human Interaction, by Richard Bookstaber; 2017, Princeton U. Press. I've only...
  32. FritoTaco

    How Does the Logistic Equation Model the Growth of the Pacific Halibut Biomass?

    Homework Statement The Pacific halibut fishery has been modeled by the differential equation. \displaystyle\dfrac{dy}{dt}=ky\left(1-\dfrac{y}{M} \right) where y(t) is the biomass (the total mass of the members of the population) in kilograms at time t (measured in years), the carrying...
  33. H

    B ? about oscillating models of the Universe and Entropy

    I know that early oscillating models of the universe fail due to the second law of thermodynamics. One thing that I am unclear about is since as far as i know the laws of physics break down in a singularity can the second law of thermodynamics break down also? When I see comments to the...
  34. S

    Which Software is Best for Drawing Simple Engineering Models?

    Hi there, I am wondering if you have any suggestions how to draw these simple engineering models? Thank you in advance.
  35. W

    A Transcription from SQL to FOL (First Order Logic)

    Hi All, When a query is made in SQL , it is transcribed into FOL in the back end , and, if the transcription is a wff , the models, if any, are returned as the answer to the query. I have an idea of how the transcription works for basic statements, but, does anyone know the actual "...
  36. K

    I Interesting controversy about inflation models of the universe

    I'm opening this thread for discussion on the latest debate over inflationary cosmology as outlined over at scientific american the original article on inflation was Scientific American published an article by Ijjas, Steinhardt and Loeb https://www.cfa.harvard.edu/~loeb/sciam3.pdf then a...
  37. W

    I Plateau models of inflation after Planck

    Reading some of the critics and defenders of inflation in various papers, one thing I note they have in common is that both seem to agree the plateau models of inflation are favoured by Planck. According to one of the critics of inflation "The plateau-like potentials selected by Planck2013 are...
  38. BillTre

    Attempts to Unify Climate and Weather Prediction Models

    Open access news article from Science magazine news. I found this interesting, but it is really beyond my ability to provide a short explanation.
  39. Nathan Warford

    I Theoretical Models for Sizes of Fundamental Particles

    I am aware that according to the Standard Model of Particle Physics, fundamental particles such as electrons and quarks are treated as point-like particles. However, if fundamental particles are indeed 0-dimentional points with no spatial extent, it creates problems (i.e. fundamental particles...
  40. T

    A How to start my reading for 2D screening models

    Hi All, I needed some help or guidance starting my MSc reading, as there is tonnes of literature out there and it's difficult to understand what is necessary. I am beginning to look at applying screening models to a 2D system, such as the Thomas-Fermi continuum screening model, to a 2D system...
  41. anubodh

    A Resources for GRW, CSL collapse models

    I have extensively searched the internet but failed to find any exhaustive literature on the different collapse models of quantum mechanics.It would be really helpful if someone who knows can guide me on some exhaustive resources for the same.
  42. FallenApple

    A Should I Ignore Data Driven Models or Use Bayesian Methods for Model Selection?

    So it was mentioned that one should ignore data driven models because this could inflate the type 1 error as a result of overfitting. So the model should be decided even before looking at the data set. But at the same time, other sources say we should look at the scatterplot matrix to determine...
  43. gonadas91

    A Are two models with the same S matrix directly related by their parameters?

    Hello, I was wondering if two models show the same S matrix by a direct relation between their parameters, does that necessarily mean that both models are exactly equivalent? My idea is that this is true, but would like to know about a solid argument about it if possible, thank you!
  44. D

    Comparing Calculated Models to Real-Life Situations

    Hi :) im wondering if there is a video where a calculated model and the same situation in reality gets compared ? :) e.g. water drop, or something crashing with a certain speed :) thanks for any help :)
  45. J

    I Is proton decay considered in neutron star models (and LHC)?

    Although it is definitely not simple, there are many reasons to consider that baryon number can be violated, for example: - while baryogenesis there was created more matter than antimatter, - hypothetical Hawking radiation can finally turn any matter (mainly baryons) into massless radiation...
  46. F

    Parallel transformers - checking my models

    So on the left is a circuit which shows a voltage source and 2 coupled inductors in a parallel magnetic circuit shown on the right (transformer with a parallel core). Can someone tell me if I am modelling it correctly with the following equations? Rc1,Rc2,Rc3 are the reluctance of each branch of...
  47. durant35

    I Finite Universe Models: Exploring Plausible Models

    Hi guys, Based on what I know about the status of modern cosmology the question whether the universe is infinite or finite in extent is still open. Are there any plausible models in which the universe is finite and closed, despite the curvature being close to flat? Thanks in advance.
  48. M

    Lattice Models for Fluids - Regular Solution Model

    1. Problem Statement: For the regular solution model, develop the equations for the compositions of the coexisting phases in a binary system and plot the phase boundary as a function of χ/RT.2. This question stems from Sandler's Introduction to Applied Statistical Thermodynamics. The Attempt...
  49. Martin1234

    ANSYS Material Models: Compression vs Tension

    Hello, I am doing a non-linear analysis in ANSYS. I have curve for the strain,stress curve for the material in tension, however, in the problem I'm working on I'm compressing the material. Does anyone know, if ANSYS just mirrors the material curve about origo as I have not given it data for...
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