Global Definition and 430 Threads

Before posting anything, please review the Physics Forums Global Guidelines. CC/GW threads in this forum are intended for discussion of the scientific content of well-researched models of weather, climatology, and global warming that have been published in peer-reviewed journals and...

Suppose we have a vector field ##V## defined everywhere on a manifold ##M##. Consider now point ##p \in M##. As a consequence of the existence and uniqueness theorem of differential equations. this implies that ##V## gives rise to a unique local flow $$\theta:(-\epsilon,\epsilon) \times U \to...

I am wondering how big the local coordinate charts in a coordinate atlas of General Relativity can be. Is it just a few nanometres or all the way to the furthest stars? Also I wonder how the speed of light is defined in GR. Is the velocity defined as the differential with respect to coordinate...

I was forced into learning Java. I feel reasonably fluent in C++, so the main problem is with the differences between the way languages are designed. There are no global variables in Java. However, I need one - or at least some equivalent. I have something like a database object that I want...

"Global simultaneity surfaces" For a long time I had basically taken for granted the usual interpretation of one-parameter families of orthogonal space-like hypersurfaces relativized to a time-like congruence as "global simultaneity surfaces" (c.f. MTW section 27.3), and left it at that. See...

Hi all, I'm a 1st year physics student in the UK and I'd like to ask if anyone could point me to where I can learn about the in-depth science of global warming/climate change. I don't like having to appeal to authority (even when the authority is legitimate) during debates on global warming and...

Global brands ban angora wool after PETA investigation http://www.cbsnews.com/news/global-brands-ban-angora-wool-after-peta-investigation/ I'm not a huge fan of PETA, but this seems to be good work from them. I'm glad pressure has been put on these companies because imo fur is completely...

Hi, I am a computer science engineer and I am trying to simulate the gravity on my computer; several objects with different masses randomly distributed in a Three-dimensional space. I would like to compute a global measure that describes the dynamic of that system at each instant T. My question...

Homework Statement using a climate sensitivity of 0.5K per watt per square meter, estimate how much of the .9 c global temperature increase since 1900 could be due to solar forcing who value is the range of .06 to .24 w/m2 Homework Equations The Attempt at a Solution .5 x .06 =...

Hi MHB. Can someone help me with this one please? I've worked out that the critical points are (0,0) and (2,1). But looking at the boundary x = 0, there seems to be no limit to the minimum value. Also, on the boundary y = 1, the value of f(x,1) = -1. So, would I be correct in saying that the...

On this year's Virginia Tech test there was a problem to prove: \frac{x}{1+x^2}+\frac{y}{1+y^2}+\frac{z}{1+z^2}\leq \frac{3\sqrt{3}}{2} when x+y+z=xyz So my approach was to consider the function, f, where f(x, y, z)=\frac{x}{1+x^2}+\frac{y}{1+y^2}+\frac{z}{1+z^2} then restrict f to the...

Homework Statement This problem relates to nothing we talked about in class... Determine the global extreme values of f(x,y) = x^2 + 2y^2 on the unit square D={(x,y):0<x,y<1} So first of all I don't see how D={(x,y):0<x,y<1} defines a square. df/dx = 2x df/dy = 4y anyone want to...

Hi, I would like to ask about how the exchange rates are determined. I understood the concept of supply and demand, but my question is more technical than conceptual, i mean where is the information of the rates are coming from? Is there any center that keeps the track of, for example every...

As outlined in this article - http://nz.finance.yahoo.com/news/anniversary-great-recession-whats-changed-145605229.html - today marks the fifth year in which the financial crisis 'started'. I quote 'started' as the initial lead up occurred when those with very terrible credit ratings were...

So my question which part of the Em spectrum(sun) is responsible for heating of the atmosphere ? Is it visible or infrared or both ?

Does the sun contribute to global warming?

Dear All, I'm very familiar with the composition of finite element local stiffness, mass matrices as per any arbitrary element rod, beam, plate, shell and integration of it into a global stiffness matrix. But I find it but of an obscure on how to integrate the constraint matrix into the...

I'm testing an algorithm to find the global mimina of a function. Can someone give me a few examples of optimization test functions in 2 or 3 dimensions, like the Rastrigin function. I'm hoping to find functions with several local minima.

Just wondering if the Java experts here could help me. As part of a project I'm making a function rand9() that returns a pseudo-random number 0 through 9. The problem is that each time it's called I need a certain number to increment so that it can generate a new (not necessarily different)...

Hi I have some function f = f(x1,x2,...xn) over some domain [0,1]^n, and I'd like to find the global minimum. The function is *highly* non-linear and takes about 1 second to evaluate. I know it's positive because it's the sum of squares of about 1,000,000 arguments, each of which pretty much...

I don't know how (1.10) pops up and why the ##T^a##s satisfy the Lie algebra. Is there any physical intuition? Any comment would be very appreciated!

Hi there all, I have a personal project I'm working on and since I haven't done any linear algebra in many years I'm not sure what I think is right, is right. I'm also not entirely sure this is the right place to ask but I'm asking more for confirmation/clarification of methodology than...

I'm posting this here even though it is related to photography, just to make sure it gets enough eyes. Don't miss casting your votes for your favorite Global Particle Physics PhotoWalk contest. http://www.interactions.org/cms/?pid=6000 You get to select and vote for 3 of them. And...

Hi everyone, I have an inhomogeneous Bernoulli type ODE given by u'(t) = \kappa u(t) + \ell(t) u^{\gamma}(t) + v(t),\ \ \ u(T)=b>0,...(1) where t\in[0,T],\ \ \gamma\in (0,1) . My concern is that how to prove the existence and uniqueness of the solution u(t) for all t\in [0,T]...

We've occasionally discussed this, but I hadn't seen this talk before: https://www.youtube.com/watch?v=ramBFRt1Uzk Basic point: we live in the most peaceful time in human history...But our media and even school system tries to convince us otherwise. Lots of good stats. And discussion...

hi pf, this is my 1st math question. i am a undergraduate grade 12 student and my question is what is the basic difference between local maxima minima & global maxima minima?

Tomita time is an intrinsic observer-independent time variable available to us for fully general relativistic analysis. As far as I know it is the only such time available for things like general covariant statistical mechanics GC statistical quantum mechanics GC quantum field theory Here I...

(Okay, I'm suddenly back in a rut right now, but this question is worth asking anyway.) I graduated recently and got a job. Now I've got a bit of disposable income, and coincidentally some stability in life. So I dicided that the best place to apply free money and effort would be major global...

Hi everyone! :smile: I'm newbie in this forum, please help me for my question. In differential equation we know that the differential equation has a solution and uniqueness. which is usually called the existence and uniqueness theorem. my question, what is the difference of local existence...

given a compact, orientable, n-dim. Riemann manifold, what is a sufficient condition for globally vanishing curvature i.e. global flatness? I can get necessary conditions from the generalized Gauss-Bonnet theorem, but not sufficient ones thanks in advance

Find the global max/min for z=xy^2 - 5 on the region bounded by y=x and y=1-x^2 in the xy-plane.

Hi all, I would like to know if its possible and consistent to compose the global system matrix with different FEM elements such as frame, plane, shell solid etc... Theoritically all of them will have the same DOF per node just only comprising the local matrix will differ. And as long as we...

Homework Statement f(x)={0 for x<0, \sqrt{x} else} a) Is f(x) globally Lipschitz? Explain b) Find the area for which f(x) is locally Lipschitz. Homework Equations The Attempt at a Solution a) f(x) is not globally Lipschitz in x on [a,b]xRn since there is a discontinuity at x=0. b) I would...

Homework Statement Combine five element matrices into single matrix forming a global stiffness matrix for simple truss analysis (five elements, four nodes). Homework Equations -See attached image- The Attempt at a Solution Where the four sub-matrices overlap in the global matrix...

I understand that CH4 absorbs more long-wave radiation, on a molecule-per-molecule basis, than CO2. I also understand that "four indirect radiative effects of CH4 emissions have been identified (see Prather et al., 2001; Ramaswamy et al., 2001). Methane enhances its own lifetime through changes...

I am struggling with this question which appears in every adv. calculus exam paper I practise and would love some help or advice on how to even approach it! I have no trouble getting the extreme points and determining whether they are local minimum, local maximum or saddle points, but proving...

Homework Statement If the set \Z of integers is equipped with the relative topology inherited from ℝ, and κ:\Z→\Z_n (where κ is a canonical map and \Z_n is the residue class modulo n) what topology/topologies on \Z_n will render κ globally continuous? Homework Equations The Attempt...

Hi All, I’m implementing a code to solve the equation of motion using the 4-step Adams-Bashforth method. Here’s my section of code that does this: a=F/m; upnew= up + delta *( (55/24)*a - (59/24)*am1 +(37/24)*am2 - (3/8)*am3 )...

Hi I was just wondering if the Global Temperature anomaly fluctuates up and down rapidly be cause of photosynthesis. http://www.skepticalscience.com/images/co2_temp_broad.gif see image above. as you can see the red line fluctuates rapidly...is this photosynthesis, or is it because the...

My QFT class has been discussing anomalies in the Standard Model. I'm starting to wonder... are there any global symmetries that DON'T have anomalies?

Hello friends Iam naveen and new to this forum.I have a question regarding the transformation matrix from world frame to the base frame of a Spatial serial manipulator. The frames are attached like this. The Z-axes are along the link lengths. The Xi axis is oriented such that Xi = Zi X Zi+1...

What is the relationship between continental drift/sea-floor spreading and global sea-level rise? Kind regards. Lucas Olsson University of Gothenburg Earth Sciences lucas@student.gu.se

MIT researchers forecast "global economic collapse" by 2030 http://news.yahoo.com/blogs/sideshow/next-great-depression-mit-researchers-predict-global-economic-190352944.htmlAnything we don't already know? Can anyone find the actual study?

Homework Statement I really, really don't understand. My work shows one thing, and a simple look at the function shows another. f(x,y) = .25x^2 + 5y^7 + 6y^2 - 3x Find global max and min if they exist. Homework Equations The Attempt at a Solution Took partial derivatives...

I was going through my notes on different finite difference methods and came across something I don't quite understand. I have code that will calculate an approximate solution we can call this U_nm that I define on a grid using h and dt for the change in x and time respectively. Now I have...

Does anybody know what interpretation the invariant corresponding to the global U(1) invariance of the Dirac Lagrangian is? I have always had it in my head that it's charge, but then I realized that uncharged free particles such as neutrinos satisfy this equation too! Any thoughts much...

Hi all, I don't know if this is the right section, but I really need to solve this problem. I've been searching for the correct formula for two days. OK, here's the picture: The global rotation of all objects (rot_x, rot_y, rot_z): red object (0.00, 45.00, 0.00), blue object (45.00, 0.00...

This emerged from random thoughts on a story about a victim of domestic violence: http://www.bbc.co.uk/news/world-asia-16201961 Human rights groups in Bangladesh have demanded a severe punishment for the husband of a young wife who allegedly cut off most of her right hand. I believe we never...

I am creating a 3D mesh for beam188 elements (L sections). Method - create keypoints, create lines between KP, define section, apply all relevant properties to the line and mesh the line. When I view the mesh (/ESHAPE,1) it appears as you would expect with an extruded L-shaped 3D...

I hear the statement that global symmetries in the boundary field theory corresponds to gauge symmetries in the bulk. 1) Is this a generic statement that is expected to hold for all holography pairs? (Maldacena states this towards the end of his first lecture at PiTP2010, which was supposed to...