Edge Definition and 265 Threads

Guys, what do you think is beyond the edge of the universe? There are a lot of theories, and I believe that the universe expands the same speed as light because if it goes any slower, it would meet. I think light interacts with dark matter to form a "boundary" of the universe in form of pure...

Homework Statement Two disks, rotating in the opposite direction of the other, are held together on their rotating ends, acting as toothless gears. The bottom disk is slightly skewed in one direction, and therefore causes a frictional force on the top disk, and thus an equal and opposite force...

I have a hazy idea that comes from a few video lectures (see below for example) where the following is stated: The condition for constructive interference (Bragg condition) in reciprocal space is that the wave vector should touch a Brillouin zone boundary. In this case, the standing wave that...

in the case of the picture below, for the central plate of thickness 1 inch, is it the force on a bolt F/2 divided by 2at that results in F/4at ?thanks

A current hobby of mine. Long term savings in that a DE blade costs 10-30 cents compared to $1-4 disposable razors/cartridges. An initial purchase of a razor and brush together would cost no more than $40 on Amazon and they last a lifetime. I've tried electric razors ; anything under $150...

If the universe is finite then there must be some farthest object or farthest place at the extreme edge of the universe. If that is true and you are standing at that place what would you see? Would you see stars in one direction and black emptiness in the other? tex

The 2016 question: WHAT DO YOU CONSIDER THE MOST INTERESTING RECENT [SCIENTIFIC] NEWS? WHAT MAKES IT IMPORTANT? Includes some interesting physics related essays. A couple of them are on the theme that the big news is what was not found: Paul J. Steinhardt The Big Bang Cannot Be What We Thought...

Homework Statement A particle is fixed to the edge of a disc of negligible mass making an angle θ0 with the ground in a uniform gravitational field, and is free to rotate about the center of the disc. I need to find the equations of motion. Homework Equations The definition of the Lagrangian...

I have two metal half-spheres, each with a hole in the center. If I put these two together, perhaps with electrical tape, and apply a charge, how will the voltage due to the nonuniform charge distribution be different from that of a perfect sphere? I am assuming that the charge distribution...

I can see, about 5 Km Not bothered about Isobars or Kilojules... So, on that basis, if I am stood on the Earth, looking at a star that is shining...not caring if it went out years ago. How far away, can I see a star, shining, in the night sky, using just my eyes ? On a clear, not...

Hi. I have to analyse the energy spectrums of several nuclides and observe their photopeaks and the Compton edges originated by these. I only see one Compton edge on all the spectrums, no matter how many photopeaks they are. At first I thought I should only expect photopeaks under 1022 keV to...

Hi all, I'm currently trying to investigate the edge current on a finite strip of Zigzag Haldane model (spinless, pi/2 phase) and I measure the current (in my code) by taking the expectation value of my current operator which is a function of wavevector k, for each eigenvector of the...

For a circle with radius R centered at R along the X-axis so that the edge of the circle touches the origin, what is the length of a line drawn between the origin and an edge of the circle in terms of the angle between that line and the X-axis? This isn't a homework problem, just something I'm...

I read in texts that when a rays of light are diffracted from a straight edge, the phenomenon can be explained using the half period zones. The things that is confusing me is this: "Odd number of half period zones, if exposed, lead to a bright fringe. Even number of half period zones exposed...

Dear PF Forum, I have a simple and cliche question. What is the edge of the universe? 1. We live on the surface of the earth. It's 2 dimensions against Earth 3 dimensions. If we start from Equador which lies on the equator to the east, we'll reach Columbia then Brazil then Atlantic ocean...

I have been reading about Z2 topological invariant recently. However, after some literature survey, I still cannot understand Z2 invariant in language of time reversal polarization. Basically, my struggle includes the following two questions: As the ref paper says(see the picture below): On...

Homework Statement (Important disclaimer: I came up with this problem out of curiosity in a classical mechanics course, so it might not be in a textbook, in the right place, or even solvable for that matter. However, I feel like it should be solvable, and most likely with elementary methods...

I have been doing a literature survey about topological insulators for some time. What surprises me is the close relation between difference of chern number and number of edge states. However, I found most review or tutorial in topological insulator avoided direct proof of the relation. So can...

Homework Statement The number of stars in the galaxy is N=10^12 and the radius of the galaxy is Rgalaxy = 20 kPc Let m be the average mass of a star in the galaxy. what is the velocity of a star at the edge of the galaxy (relative to the center of the galaxy) Homework Equations The Attempt at...

Homework Statement We have a cubical hollow box, edge length ##a## suspended horizontally from a frictionless hinge along one of its edges. The box is displaced slightly and undergoes SHM. Show that the period of the oscillation is given by ## T = 2\pi \sqrt{\frac{7\sqrt{2}a}{9g}} ## Homework...

So, I've heard that it would be theoretically possible to get around the light speed barrier without violating known physics by warping space-time. Anyway, my question is this: what would happen if you just kept going? Would there just be an infinite amount of planets and suns that closely...

Homework Statement The cylinder with mass 200[kg] and radius 0.8[m] tries to climb a 0.3[m] high edge with a force F exerted at an angle of 300. what's the force and what's the minimum force for the cylinder to climb Homework Equations Moments: F1L1=F2L2 The Attempt at a Solution The weight...

Hi everyone:) Is there anyone who has worked on the phenomena near the band edge of photonic crystals? for example spontaneous emission near the band edge? there are lots of articles specially from Sajeev John " spontaneous emission near the edge of a photonic band gap" Phys.Rev.A vol50 num 2...

Homework Statement A rod of mass M and length L is placed horizontally on a table such that the center of mass is a distance L/6 from the edge of the table (CoM is hanging off the table). The rod is released from rest and slips after reaching an angle θ. Find the coefficient of friction \mu 2...

Hello! (Wave) I want to apply the Depth-first search algorithm at the following graph. We consider that at the iteration of the algorithm, we look at the nodes alphabetically. Also the nodes are registered alphabetically in each list. I want to calculate the "discovery" time and the "finish"...

Today in class we learned about how if a force F is applied to a dumbbell on its center of mass and then separately applied to the edge where it gets its maximum torque, the dumbbell will have the same CM velocity after. It makes sense when you think about it in terms of momentum. F times T...

Homework Statement A solid spherical ball is placed carefully on the edge of a table in the position shown in the figure. The coefficient of static friction between the ball and the edge of the table is 0.5 . It is then given a very slight push. It begins to fall off the table. Find the angle...

I recently read a few articles that contradict Einstein's Singularity theorem. The idea being that black holes are wormholes to other universes; with a white hole on the other side of the black hole (Poplawski's theory). What if instead of being a portal to another universe, the Event Horizon of...

Homework Statement Damped driven oscillator: ruler example. Suppose the ruler used in the classroom demonstration has a length of 12 and 13/16ths inches, a width of 1 ½ inches, is 1/16th inch thick with a density of 1.2 g/cm3. It swings from a pivot point ¼ of an inch from the top end. a) Find...

Let L be the level number of a bipartite graph G, and so L1 be the first level of n1 vertices, L2 be the second level of n2 vertices, ... Lk be the kth level of nk vertices. Then a bipartite graph G12 is created by a combination of L1 and L2, G23 is of L2 and L3,...,Gij is of Li and Lj. The...

Alright, so, I'm sorry but I posted this back when I was getting my CS degree and have been looking back on my previously asked questions. Sooo, here goes a two year old question that I think time may have changed the results of.I've been mauling some questions about the end/edge of our...

I was thinking a bit about the farthest parts of the universe we can see and I came to a few interesting questions that are maybe obvious to more studied physicists but new to me. Is the ~14 billion light year distance we can see in all directions slowly expanding with time? In another billion...

How to find if a graph has a cut-edge/bridge and cut vertices. In other words, i am mixed up between cut edge and cut vertices? What is the difference and how one can find these in a graph?

There is no edge of the Universe. Alright, I kinda realize this, I'm not a layman. However, nobody addresses what would happen if you traveled far enough. There's only a limited amount of matter out there and going off the theory that the volume of our Universe is finite, there's 'an edge'...

Gas from another galaxy is hitting our own, triggering the birth of bright new stars and adding fresh luster to the Milky Way. Link: Scientific American

I've have just registered here in order to post this question. I know it's a good idea to read a forum for weeks and months (years!) before daring to post, in case a question has already been discussed in detail -- but it's a burning question! (And it's not homework.) If it is off-topic, or...

Homework Statement In uranium (Z=92) the K absorption edge is 0.107 Å and the Kα line is 0.126 Å. Determine the wavelength of the L absorption edge. Homework Equations K-edge: EK= (Z-1)2*13.6 L-edge: EL= (Z-σL)2*13.6*1/4 what is σ and how was calculated. Characteristic X-rays: Ex = h*ν=...

I'm here to test an idea and if anyone wants to help make it better, they are welcome to add their own. I have a story planned that will be happening on a pretty savage world. The characters were sent there as prisoners and as their punishment they have to mine the exotic materials that came to...

Homework Statement A 45° triangular plate ABC built in at BC and loaded by a uniform pressure p0 on the upper edge AB. The inclined edge AC is traction free. Find the stresses in the plate. Homework Equations Stress function: \phi =...

Homework Statement Two edge dislocations having an equal, but opposite in sign, burgers vector are gliding on parallel (111) planes in copper (FCC). Calculate the number of point defects required to bring the two dislocations together. The vertical separation between the dislocations is 1...

What happens when light gets to the edge of space or universe, does it get reflected back. Assuming that light gets reflected back at the edge of universe. We are seeing the reflections of the same star galaxy, at different points of time, at different location. Since the reflected photons...

let's say I have 10 data points. And one of my data points is 270. Then let's say two of my bins are 260-270 and 270-280. Which bin would you put the 270 in? Or would such a choice of bin range be inappropriate and new ranges have to be chosen?

Does anyone know of an article that has a good in-depth, side by side comparison of DFB edge emitting lasers and VCSEL lasers? From my research it seems to me that the VCSEL papers are all trying to justify why laser production should shift towards VCSEL, and mostly list the advantages over an...

Homework Statement Twelve resistors of equal resistance are connected so as to form a cube ABCDEFGH shown. Equivalent resistance between points A and G is 5/3 ohm. If a battery of voltage 100 V is connected across the points A and G, find the current (in ampere) flowing through the...

Still going after 36 years. Voyager surfs Solar System's edge By Jonathan Amos Science correspondent, BBC News http://www.bbc.co.uk/news/science-environment-23075332

I was doing some simple physics with a ball resting on a table and I made this curve (0,0) (25, 6.8) (50, 27.51) (75, 63.4) (100, 112.34) (125, 175.7) (150, 253.3) (175, 345.4) I was wondering if anyone could identify what sort of curve it is? I am just curious. This is not a homework...

Homework Statement A homogeneous cube, each edge of which has a length \ell, is initially in a position of unstable equilibrium with one edge in contact with a horizontal plane. The cube is then given a small displacement and allowed to fall. Find the angular velocity of the cube when one face...

I have a tube with a rod inserted into it at a set depth. The rod is held in place by a round pin that passes through a hole in the side of the tube and into the rod. Assuming the pin and hole are the same diameter or very close, I'd like to know how to calculate the stress area on the edge of...

Thin Film Interference Problem: A hair is placed at the edge... Homework Statement Thin Film Interference Problem: A hair is placed at the edge between two 10.0 cm glass plates of n= 1.52. Light of 400 nm wavelength shines on the glass and an interference pattern is formed. If the...

Where is the edge/boundary of the universe may sound like a simple question but I can see 3 possibilities. 1 Observed, this puts us inside a sphere looking out towards an edge which is beyond visible range, some estimates appear to give up to around 50 bly away. 2 Expanding universe...