question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Cold fusion is being mentioned a lot lately because of some new setup that apparently works. This is an unverified claim.</p>
<p>See for example:</p>
<ul>
<li><a href="http://hardware.slashdot.org/story/11/01/24/1550205/Italian-Scientists-Demonstrate-Cold-Fusion">http://hardware.slashdot.org/story/11/01/24/1550205... | 640 |
<p>Watching quantum mechanics lectures and it was mentioned that it is pointless/meaningless to try to talk/question things that can not be tested/measured.</p>
<p>Is this a principle? And if so what is it's name?</p>
<p>Also does this apply to questions other than Quantum mechanics? E.g. does it make sense to ask if... | 3,907 |
<p>The title says it all. Why are snowflakes <a href="http://en.wikipedia.org/wiki/Snowflake#Gallery">symmetrical in shape</a> and not a mush of ice? </p>
<p>Is it a property of water freezing or what? Does anyone care to explain it to me? I'm intrigued by this and couldn't find an explanation.</p> | 521 |
<p>I was reading this interesting recent review on arxiv about particle identification:</p>
<p><a href="http://arxiv.org/pdf/1101.3276">Particle Identification</a></p>
<p>In figure 2, there is an interesting comparison between the CMS and ATLAS calorimeter performances. I hope the paper author won't mind if I reprodu... | 3,908 |
<p>Whereas I can calculate the <strong>Chern number</strong> of a quantum state (or band) from the integration of the Berry curvature in all space.</p>
<p>How can I infer the topology of the quantum state from this result? What is the physical meaning of a quantum state with non-zero Chern number?</p> | 3,909 |
<p>One morning I woke up to a text message and picked up my phone but I was not yet fully awake and my eyes had not really gotten its focus.
When I stared at the phone I saw two phones. Which is obviously just a depth perception and missed focus. There is even and art form called <a href="http://en.wikipedia.org/wiki/S... | 3,910 |
<p>What are the current most important <em>theoretical</em> problems on quantum entanglement?
What is that we don't yet understand about how it works?
(Not considering interpretation etc problems)</p> | 3,911 |
<p>I remember a while ago my father dropped a glass lid and it smashed. <a href="http://images.google.com/imgres?imgurl=http://www.webvert-cookware.co.uk/flatglasslid-300.jpg&imgrefurl=http://www.webvert-cookware.co.uk/flatglasslid.htm&usg=__dPS-9DaG0CrN-iOj0zLN8v15L9k=&h=300&w=300&sz=21&hl=no&a... | 3,912 |
<p>I essentially have three questions concerning <a href="http://en.wikipedia.org/wiki/High-energy_radio-frequency_weapons" rel="nofollow">weapons based on EM waves</a> or more <a href="http://en.wikipedia.org/wiki/Directed-energy_weapon#Lasers" rel="nofollow">generally</a>.</p>
<ol>
<li><p>Focusing on the weapons usi... | 3,913 |
<p>Laser beams are said to have high <a href="http://en.wikipedia.org/wiki/Laser">"spacial coherence"</a>. This means that the beam is highly concentrated even at long distances (low spread).</p>
<p>Can this be achieved with radio waves (much longer waves) or is it due to laser's <a href="http://en.wikipedia.org/wiki/... | 3,914 |
<p>With regard to the recent arXiv article:</p>
<p>J. D. Shelton, <em>Eddy Current Model of Ball Lightening</em><br>
<a href="http://arxiv.org/abs/1102.1224" rel="nofollow">http://arxiv.org/abs/1102.1224</a></p>
<p>I wonder if this is a reasonable explanation of ball lightening, or if there is such an explanation. Th... | 3,915 |
<p>Is it possible that the process of quantum entanglement creates new space time?</p>
<p>If two entangled particles' quantum states cannot be described individually, even if they are separated to us, is it possible that observation causes the space time they occupy to "separate"? Hence the near instantaneous informat... | 3,916 |
<p>I know that in string theory, D-branes are objects on which open strings are attached with Dirichlet boundary conditions. But what exactly is a brane? Are they equally fundamental objects like string? If so then do they also vibrate? If the visible universe itself is not a brane then what is the dynamics of these br... | 3,917 |
<p>Bell-type experiments look at the violation of this inequality: $|S|\leq 2$.</p>
<p>where $S=E(a,b)-E(a,b')+E(a',b)+E(a',b')$ and $E$ is the correlation function.</p>
<p>Mathematically, the maximal violation of the inequality is reached when $|S|=4$ (because the bounds of $\cos \theta_{ab}$ are $\pm 1$).</p>
<p>H... | 3,918 |
<p>I have a 4' hose that is closed at one end and connected to a Airdata Test Set (precise control of pressure) and a high accuracy pressure monitor on the other end with a T and valve. The valve allows the Airdata Test Set connection to be closed off resulting in a hose connected to the pressure monitor and closed at... | 3,919 |
<p>if the universe is a 0 energy universe, could the value of G be worked out through summing up the strong, weak and electromagnetic force strengths for an elementary particle up to an infinite distance, and take the value of the negative energy gravity provides as that value in reverse? </p>
<p>Or at the very least ... | 3,920 |
<p>What used to be functions in the context of classical mechanics like position, linear momentum, angular momentum, etc in quantum mechanics are operators (these operators act on the state to get results). So the question is: Historically, conceptually, and mathematically how functions become operators in quantum mech... | 118 |
<p>Do all planets have an electric charge? </p>
<p>If yes, is positive or negative?
And how much each magnitude? </p>
<p>I have read some articles which really confused me. Some of these articles said that all planets have a negative charge and the sun has a positive charge. Some other articles said the the exact op... | 3,921 |
<p>Most modern texts spend some time deriving the <a href="http://en.wikipedia.org/wiki/LSZ_reduction_formula" rel="nofollow">LSZ reduction formula</a> that connects S matrix elements to time ordered field correlation functions. It seems essential, and really helps clear up what you are calculating. Yet some earlier te... | 3,922 |
<p>Vaporization is an interesting engineering subject, but unfortunately much about it has always been unclear to me.</p>
<p>Recent research of mine has brought my mind to link <i>vapor pressure</i> to <i>boiling</i> and <i>partial pressure</i> to <i>evaporating</i>. So I would just like to confirm the following two u... | 3,923 |
<p>It is more or less known that a given antisymmetric tensor $F$ in two indices can be written in terms of spinorial indices, splitting into self-dual and anti-self-dual parts
$$ F_{\mu\nu} =
F_{\alpha\beta}
(\sigma_\mu)^{\alpha\dot\alpha}(\sigma_\nu)^{\beta\dot\beta}
\varepsilon_{\dot\alpha\dot\beta} +
F_{\dot\alpha\... | 3,924 |
<p>I come from a maths background and am struggling with some of the more physical texts on SUSY. In particular they claim that the fermionic generators $Q_A^i$ <strong>carry</strong> a representation of the Lorentz group. What does this mean? I have never heard the word 'carry' applied to representations in a mathemat... | 3,925 |
<p>We know from conservation of momentum or energy that energy (lets think about one quantity at a time) is conserved before and after collision. But how the energy is distributed between the bodies? I mean $1+3=4$ otherwise we can say $2+2=4$. Which distribution would be preferable?</p> | 3,926 |
<p>I recently got a more complete proof of photons having no mass. (I knew it before, but now I <em>really</em> know it.) But now, I'm curious how gravitational lensing can occur without a mass to act on.</p>
<p>I have heard that space is like a sheet and gravity works because the more massive an object is, the more i... | 3,927 |
<p><em>I've studied the AC circuit for an ideal inductor in many physics books. After deriving the final equation for current the integration constant $C$ is assumed to be $0$ by giving inadequate reasons. In this question I seek for an adequate reasons.</em> </p>
<p>Suppose an ideal AC voltage source is connected ac... | 3,928 |
<p>I am trying to initialize a <strong>traveling</strong> wave for a 1d simulation as one can see from the attached figure.
<img src="http://i.stack.imgur.com/J0iOi.png" alt="enter image description here"></p>
<p>Such that it will be <strong>traveling to the right</strong>.
However, I cannot initialize the right velo... | 3,929 |
<p>By biot-savart:</p>
<p>$$\bar{H} = \frac{I}{4\pi} \oint \frac{d\bar{l} \times \bar{r}}{r^{3}}$$</p>
<p>so</p>
<p>$$\bar{H} = \frac{I}{2a} \hat{n}$$</p>
<p>Please, explain the last implication. I cannot find such integral to match the results. The radius of the loop is $a$. The current is $I$. $d\bar{l}$ is a vec... | 3,930 |
<p>I'm trying to find out if black holes could be created by focusing enough light into a small enough volume.</p>
<p>So far I have found (any or all may be incorrect):</p>
<ul>
<li>Maxwell's equations are linear, dictating no interaction of radiation.</li>
<li>The Kerr effect and self-focusing has been observed in m... | 3,931 |
<p>I am trying to come up with everyday size objects comparisions of atomic scales items, e.g. if a proton probability cloud was of size basketball how far would the next atoms to it be?</p>
<p>reason being is to give an idea of the space in between the atoms and giving student some idea of relative atomic object size... | 3,932 |
<p>I am wondering if, for a particle moving close to the speed of light (so that we must examine things relativistically rather than classically) does the centripetal force equation $F_c=m\frac{v^2}{r}$ still hold? If not, what is the correct equation for centripetal force?</p> | 119 |
<p>If I take two plane EM waves travelling in opposite direction e.g. $E = E_0 \sin(kx-\omega t)$ and $E=E_o \sin (kx + \omega t)$, they sum to give a standing wave with a time-averaged Poynting vector of zero.</p>
<p>If I use the appropriate special relativistic transformations to derive how these fields appear to an... | 3,933 |
<p>Do Dyson's <a href="http://en.wikipedia.org/wiki/Bladeless_fan" rel="nofollow">bladeless fans</a> produce enough air pressure to cool say an air conditioning unit and do they produce a vortex pressure like a bladed fan?</p> | 3,934 |
<p>I have a finite state ensemble with an energy functional (you can think of it as an ferromagnetic Ising model if you like), and I need very careful estimates of the partition function. What methods are available to me to get reasonable estimates (in reasonable temperature regimes) of $Z(\beta)$?</p> | 3,935 |
<p>If you drop a proton and a neutron in a gravitational field, they both fall, but the proton has a charge and accelerating charges radiate energy, so that leaves less kinetic energy for the proton and by this reasoning, it should fall more slowly than a charge-free object.</p>
<p>The issue is discussed but not in th... | 3,936 |
<p>I'll be teaching a seminar for first-year undergraduates next year. The idea of my university's first-year seminar program is to expose students to exciting ideas and important texts in a somewhat interdisciplinary way. My course will focus on three epochs in the history of cosmology in which our ideas about the siz... | 3,937 |
<p>At xmas, I had a cup of tea with some debris at the bottom from the leaves. With less than an inch of tea left, I'd shake the cup to get a little vortex going, then stop shaking and watch it spin. At first, the particles were dispersed fairly evenly throughout the liquid, but as time went on (and the vortex slowed... | 196 |
<p>Flux, as I understand it, is the amount of substance passing through a particular surface over some time. So, from a simple perspective, considering photons that go through some virtual surface $A$ (or $S$, doesn't matter). They have a fixed speed in vacuum, $v=299,792,458$ $\text m/\text s$. To simplify even furthe... | 3,938 |
<p>I tried reading the Wikipedia article to no avail - I simply cannot understand the <a href="http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation" rel="nofollow">Schrödinger Equation</a> (what does each of the variables mean, especially the wave function), and the Schrödinger Model of the Atom. Could someone explai... | 3,939 |
<p>If a servant lifts 10 cubic meter of liquid from a tank, which is at a depth of 40m . If the work done by him is 1600J, then find the density of the liquid (g = 10 m/s^2)</p> | 3,940 |
<p>Firstly apologies if this is not the correct place to post this but wasn't sure which site would be good to ask regarding about measurement uncertainty calculation.</p>
<p>I am trying to calculate the combined measurement uncertainty, however the uncertainties I want to combine are using different scales:</p>
<p>C... | 3,941 |
<p>In an interacting theory I expect there to be caustics, resonances, and other situations in which <em>some</em> observables would give an infinite experimental result. Of course, these are idealized states and observables -- if a real device's measurement results are quite accurately modeled by such an observable, a... | 3,942 |
<p>Has it been observed that charged high capacitance capacitors do generate a strong positive electrostatic charge on their exterior insulating surfaces?</p>
<p>Has it been observed that charged high capacitance capacitors attract exterior negative electrostatic charges to their exterior insulated surfaces?</p> | 3,943 |
<p>Title pretty much states the question. How much hotter do air conditioning units make it outside in a large city like NYC, Chicago, etc?</p> | 3,944 |
<p><strong>What is the conversion factor for qubits (qudits) to bits/bytes in classical information theory/computation theory?</strong></p>
<p>I mean, how can we know how many "bits/bytes" process, e.g., a 60 qubit quantum computer (quamputer), are equivalent to classical bits (dits)?What about memories and velocitie... | 3,945 |
<p>According to <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow">Noether's theorem</a>, <em>Every continuous symmetry of the action leads to a conservation law.</em> For example, conservation of linear momentum corresponds to translational symmetry, conservation of angular momentum corresponds... | 3,946 |
<p>Consider two parallel wires of finite radius. When a current is applied to one of the wire for a short period of time, what is the current induced in the other wire?</p>
<p>Applying Maxwell's equations, it seems that there is a change in magnetic field perpendicular to the second wire, and as a result, the induced ... | 3,947 |
<p>In Morse & Feshbach (P512 - 514) they show how 10 different orthogonal coordinate systems (mentioned on <a href="http://mathworld.wolfram.com/HelmholtzDifferentialEquation.html" rel="nofollow">this page</a>) are derivable from the confocal ellipsoidal coordinate system $(\eta,\mu,\nu)$ by trivial little substitu... | 3,948 |
<p>Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted? </p>
<p>Would the speeds of the galaxies necessary for Doppler redshift to explain all of the observed galaxies redshift be unreasonable or is there something else that prev... | 3,949 |
<p>This is a problem concerning covariant formulation of electromagnetism.</p>
<p>Given
$$\partial^{[\alpha} F^{\beta\gamma]}= 0 $$</p>
<p>how does one prove that $F$ can be obtained from a 4-potential $A$ such that</p>
<p>$$F^{\alpha \beta}=\partial^{\alpha} A^{\beta} - \partial^{\beta} A^{\alpha} $$</p> | 3,950 |
<p>I am sure this is a silly question, but I was reading something that described the pre big-bang universe as having "nearly infinite mass."</p>
<p>How can something be "nearly" infinite? The term seems to make no sense. </p> | 3,951 |
<p><a href="http://www.ted.com/speakers/brian_greene.html" rel="nofollow">Brian Greene</a> in this <a href="http://www.ted.com/talks/brian_greene_why_is_our_universe_fine_tuned_for_life.html" rel="nofollow">TED talk about possible multiverse</a>, claims tomwards the end (At around 18:00 mark) this statement. 'Because t... | 3,952 |
<p>I have recently entered university — studying CS — and I have spoken to many physics students on campus. Most of these — when propmted — will gladly proclaim that QM is counterintuitive, and not something you are supposed to understand.</p>
<p>To my knowledge, no one proclaims similar things... | 3,953 |
<p>How would one show that the nonabelian ${F_{\mu\nu}}$ field strength tensor transforms as ${F_{\mu\nu}\to F_{\mu\nu}^{\prime}=UF_{\mu\nu}U^{-1}}$ under a local gauge transformation? Rather than going through this in a very manual manner (i.e., gauge transform ${A_{\mu}\to A_{nu}^{\prime}}$ and use the explicit expre... | 3,954 |
<p>I am trying to understand the some of the properties of wakefields, namely the energy change. So, as a preface I am interested in primarily the wakefield due to electron beams as they progress through a curved section (the eletcrons radiate strongly when they are in circular motion). There are two main/simple regime... | 3,955 |
<p>If a body travelling at speed falls to the ground through an arc from a certain height (someone walking who trips, for example), how does friction of the ground surface affect the forces impacting upon the body (treating it as a point mass) when it reaches the ground? How can the net forces on the body and the net v... | 3,956 |
<p>For a system of two interacting particles <code>1</code>, <code>2</code> we get from the conservation of momentum
$$ \dot{\bf{p_1}} + \dot{\bf{p_2}} = 0$$
and from conservation of angular momentum
$$ \bf{r_1} \times \dot{\bf{p_1}} + \bf{r_2} \times \dot{\bf{p_2}} = 0$$
so
$$ \bf{F_1} = -\bf{F_2} $$
and
$$ \bf{r_{12}... | 3,957 |
<p><strong>What I'm looking for:</strong></p>
<p>Let $\vec{W}$ be the vector of conserved variables for a 1-dimensional, adiabatic, (special) relativistic, electrically neutral fluid. (Yes, something that simple!) I'm looking for a paper that derives the form of the matrix $A$ that linearizes the evolution equation. T... | 3,958 |
<p>I was asked to think of a situation where a car driver only feels centripetal acceleration, but exerts no tangential acceleration.</p>
<p>The first thing that came to mind was orbit, where the satellite does not need to speed up but be caught by the gravity of Earth, and keeps orbiting around it.</p>
<p>So, my que... | 3,959 |
<p>I'm a tutor. This is a high school level problem. In high school, every one have might have solved a problem of <a href="http://www.crbond.com/papers/ent2-3.pdf">effective resistance of a ladder of resistors having infinite steps.</a> Now the problem is little different. what if it has <code>n</code> steps instead o... | 3,960 |
<p>I have a test in a few hours, and my professor gave us a practice test, and I'm stuck. Could you give me a hint as to how to approach this problem, equations I could use.
It's an algebra based class so I'd avoid using calculus equations. Thank you.</p>
<p><em>Three thin infinite wires carrying currents I in the sam... | 3,961 |
<p>When does the total time derivative of the Hamiltonian equal the partial time derivative of the Hamiltonian? In symbols, when does $\frac{dH}{dt} = \frac{\partial H}{\partial t}$ hold?</p>
<p>In Thornton & Marion, there is an identity in one of the problems, for any function $g$ of the generalized momentum and... | 3,962 |
<p>The eigenfunctions of Laplace-Beltrami operator are often used as the basis of functions defined on some manifolds. It seems that there is some kind of connection between eigen analysis of Laplace-Beltrami operator and the natural vibration analysis of objects. I wonder, is my intuition true? What is the physical me... | 3,963 |
<p><a href="http://en.wikipedia.org/wiki/Liquid_metal" rel="nofollow">http://en.wikipedia.org/wiki/Liquid_metal</a> describes some alloys which are liquid at room temperature containing gallium, and sodium-potassium. We are advised not to handle them, and mercury, with unprotected skin. Are there any which are safe (as... | 3,964 |
<p>When I was using ultrasonic horn in a beaker, I notice that there are convection currents in the beaker and stir up my substance. I don't understand why it produce water current, I thought that it will just vibrate like the ultrasonic bath. So why does ultrasonic horn create water currents? Thank you.</p> | 3,965 |
<p>Can anyone explain in a simple manner why interacting noncommutative quantum field theories with space-time noncommutativity of the Moyal bracket sort are unitary?</p>
<p>Thanks.</p> | 3,966 |
<p>I have been studying differential equations in RLC circuits: <strong><em>(a generator with fixed EMF $=E$,a capacitor $C$, an inductor with inductance $L$ and internal resistance $r$, and a separate resistor $R$)</em></strong>
with the elementary cases accounting for $q$ (the charge on the capacitor), $V_c$ its v... | 3,967 |
<p>I would like to abide by the site policies on not asking open-ended/chatty questions so if someone feels there is a better location or wording for this question, please feel free to modify it as appropriate.</p>
<p>I am normally a big fan of open source/open access work and I believe I have learned a great deal fro... | 3,968 |
<p>In a cavity of dimension L, the wave must give zero amplitude at the wall, means wave equation has zero amplitude. Why?
Answer from hyperphysics "since a non-zero value would dissipate energy and violate our supposition of equilibrium. To form a standing wave, the reflection path around the cavity must produce a clo... | 3,969 |
<p>How is it possible to demagnetize a magnet with a laser?</p>
<p>Source: <a href="http://www.helmholtz-berlin.de/pubbin/news_seite?nid=13657&sprache=en&typoid" rel="nofollow">http://www.helmholtz-berlin.de/pubbin/news_seite?nid=13657&sprache=en&typoid</a></p>
<p>And the paper: <a href="http://prb.ap... | 3,970 |
<p>In the discussion of the amplituhedron paper (<a href="http://arxiv.org/abs/1312.2007" rel="nofollow">arXiv:1312.2007</a>), there is the following discussion in paragraph 14.outlook (page 28):</p>
<blockquote>
<p>Quantum mechanics forces us to divide the world in two pieces - an
infinite measuring apparatus and... | 3,971 |
<p>My goal is to monitor the change in specific gravity of a liquid over a period of time. My question is: What are the appropriate formula for determining expected apparent weight of an object immersed in a liquid where the liquids specific gravity g/ml is expected to change?</p>
<p>EG. If I were to take an object wh... | 3,972 |
<p>I have just discovered that if I rotate my left spectacle lens about the vertical axis by 10 degrees in one direction, the vision in that eye becomes much crisper.</p>
<p>Note that the sphere and cylinder prescriptions in the (unrotated) lens were confirmed yesterday by an optometrist as being the best I could get ... | 120 |
<p>I am trying to understand a line in the quantum mechanics book by Merzbacher, specifically the second line of equation 14.106.</p>
<p>The problem is a forced quantum harmonic oscillator. The Hamiltonian operator in the Schrodinger picture is</p>
<p>$H_S(t) = \hbar \omega_0 (a^{\dagger}a + 1/2) + \hat{x}f_x(t) +\ha... | 3,973 |
<p>does anybody here know an analytical approximation of the bonding hydrogen orbital MOLECULE?</p>
<p>I am looking for a good approximation to this orbital, that might be in some textbooks to get an impression how this whole concept of bonding antibonding works?</p> | 3,974 |
<p>This <em>should</em> be easy, but I think I have a mind-block... </p>
<p>For $\beta^-$-decay, what is the maximum possible momentum for the electron? The two equations I can use are conservation of energy and conservation of momentum, but I have three unknowns: Momentum of electron, nucleus and anti-neutrino, so wh... | 3,975 |
<p>Suppose I can solve time-dependent Schrödinger equation for several 1D particles (currently 3). I'd like to see, what an electronic hole is and how it behaves — in a series of numerical experiments.</p>
<p>I know that a hole is lack of electron in a sea of occupied electron states, but I think I don't quite underst... | 3,976 |
<p>I'm wondering if there are any free particle physics datasets out there, for use in teaching, demonstrations, developing analysis techniques etc.. I'm looking for data events e.g. as ROOT trees or in a similar format, together with a standard set of background events and postprocessing, or maybe even a simple framew... | 3,977 |
<p>I read about <a href="https://en.wikipedia.org/wiki/Vacuum_energy#Implications" rel="nofollow">vacuum energy</a>. It explains the Hawking radiation, the black hole necessary radiation:</p>
<blockquote>
<p>Physical insight into the process may be gained by imagining that
particle-antiparticle radiation is emitte... | 3,978 |
<p>In what part of the spectrum is it radiating? In the infrared, in the microwave? Or is not radiating anymore at all? </p>
<p>In russian:</p>
<p>Чему сейчас равна температура поверхности и ядра нейтронной звезды, которая образовалась 12 миллиардов лет назад?
В каком диапазоне она сейчас излучает? В инфракрасном, ми... | 3,979 |
<p>Why is electric flux through any closed surface $q/\epsilon_0$? In schools we are only taught of its simplest case, i.e. flux through a sphere with charge centered at origin. And then it is generalised to all closed surfaces. Is there really any proof of flux through all closed surfaces.</p> | 3,980 |
<p>I have naive question about Einstein action for field-free case:
$$
S = -\frac{1}{16 \pi G}\int \sqrt{-g} d^{4}x g^{\mu \nu}R_{\mu \nu}.
$$
It contains the second derivatives of metric. When we want to get the Einstein equation (which doesn't contain the third derivatives), we must use variational principle. The var... | 3,981 |
<p>If classical particles fall through a Galton Board they pile up in the limit of large numbers like a normal distribution, see e.g. <a href="http://mathworld.wolfram.com/GaltonBoard.html">http://mathworld.wolfram.com/GaltonBoard.html</a></p>
<p><img src="http://i.stack.imgur.com/ll7PE.gif" alt="Galton Board"></p>
<... | 3,982 |
<p>I have been trying to do all the calculations in the Green, Schwarz and Witten Superstring Theory textbook. </p>
<p>At the end of chapter 3, the author did one-loop calculation for Weyl invariance for the bosonic string, in section 3.4.2 and 3.4.5. In the latter section more fields were included, and not much calcu... | 3,983 |
<p>For example, consider the following measurement: A sensor can measure a specific physical quantity, and has a range of $0$ to $100$. All values above $100$ will be shown as 100. We now take the following measurements: $78$, $100$, $82$, $94$, $100$, and we conclude that the average is $90.8$. However, the true value... | 3,984 |
<p>When the pressure on the liquid surface is less than the vapor pressure of the liquid at a given temperature, the liquid will start to evaporate. This is common sense. </p>
<p>The problem is more difficult when the liquid and its vapor are heated inside a rigid container, with the specific volume of the mixture les... | 3,985 |
<p>I was answering a question on proving the parallel axis thereom for angular momentum and came across this:
$$\int Yy'dm=Y\int y' dm=0$$
Where the position of the center of mass of an object is given by $(X,Y,Z)$, $(x',y',z')$ is a position relative to the centre of mass and m is the mass of the object. </p>
<p>My t... | 3,986 |
<p>Are there any optical filters which filter the signal's frequency and not based on the wavelength of the light? So what I mean is, if I have a modulated/pulsating light signal riding on a large DC offset, is there some way I can filter out the DC offset using optics alone? I've tried searching the internet for this ... | 3,987 |
<p>Consider a cylinder filled partially with a liquid (e.g. water). The cylinder is sealed, and is at held at room temperature (e.g 298K). At equilibrium (or when no external disturbance is imparted to the system), the liquid in the cylinder exists in equilibrium with its vapor at the vapor pressure of the liquid, appl... | 3,988 |
<p>Does <a href="http://en.wikipedia.org/wiki/Redshift" rel="nofollow">redshift</a> depend on the
spatial orientation of <a href="http://www.sdss.org/" rel="nofollow">SDSS galaxies</a> with redshift in the range 0.19 to 0.20 ?</p> | 3,989 |
<p>We know that linear speed of object going around a circle is $\omega * r $
Now let us take an elastic string and rotate a body of negligible mass with $\omega = 500 rad/s$
It is possible to further stretch this string while maintaining $\omega$ constant using a super powerful motor.</p>
<p>If we extend the chord l... | 121 |
<p>Suppose we have a rigid token-ring network. An observer at any node can seemingly determine the angular momentum of the network by measuring the time it takes for a packet to travel around the ring in each of the two directions. Is it possible by any means for an observer to determine whether the network is knotte... | 3,990 |
<p>One of the arguments in favor of TeV scale SUSY breaking is that it leads to the appropriate running of the gauge coupling strengths leading to grand unification, i.e. $k_Y = \frac{5}{3}$ instead of $k_Y = \frac{4}{3}$. With the LHC ruling out TeV scale SUSY breaking, what is the current consensus on grand unificati... | 3,991 |
<p>I don't know if anyone else has noticed this but in most buildings and most rooms, radiators are predominantly placed under a window. </p>
<p>Now, in my eyes, that is the worst place to put them; hot air rises, reaches the window (which no matter how well insulated it's still letting out heat, in loose terms) and t... | 3,992 |
<p>The dominant method of neutron star cooling is neutrino emission. There are two regimes usually presented, the "direct Urca" and "modified Urca" processes, each of which are sequences of neutron decay and inverse reactions. The direct Urca looks like this:
$$n\rightarrow p+l+\overline{\nu_l},\quad p + l \rightarrow ... | 914 |
<p>I was on my workshop lab today and had to <a href="http://en.wikipedia.org/wiki/Filing_%28metalworking%29" rel="nofollow">file</a> (rub on metal surface with rough surface to smooth-en it) an iron bar. It made iron dust fall of the surface. To mark some points on the bar I then had to hammer a pointed another Iron b... | 3,993 |
<p>Is there any way to produce food without sun, synthetically? I mean if we face solar winter. look at: <a href="http://physics.stackexchange.com/questions/30095/is-there-any-way-to-survive-solarwinter-like-in-sunshine-movie">Is there any way to survive solarwinter like in Sunshine - movie?</a></p> | 3,994 |
<p>Reading about the spectacular Opera claim, I`m (again ;-P) wondering if a confirmation of superliminous neutrinos could help settle some still open quantum gravity issues ...?</p>
<p><a href="http://physics.stackexchange.com/questions/14973/what-would-be-the-immediate-effects-if-light-does-not-go-at-the-maximum-spe... | 3,995 |
<p>There’s an interesting <a href="http://www.scientificamerican.com/article.cfm?id=raizen-entropy-cooling-experiment-interactive&posted=1" rel="nofollow">article on Scientific American</a>
that tells how to cool individual atoms to within a very tiny fraction of Absolute Zero.</p>
<p>It uses two laser beams actin... | 3,996 |
<p>Consider a magnetic spring as seen on this <a href="http://www.youtube.com/watch?v=jMeCbFX80W4" rel="nofollow">YouTube</a> video, but ignore gravity. If I wanted to calculate the effective spring rate (Force vs. Deflection) curve for the top magnet, how would I go by doing that?</p>
<p>Consider $N$ permanent magnet... | 3,997 |
<p>If a power source is supplying a current I and a voltage V, that travels to its destination through resistors of restance R is the power delivered at the destination = $VI - RI^2$, where $(Pi=) VI$ is the power input of the power source (i.e. the total power supplied) and $RI^2$ is the power wasted over the restan... | 3,998 |
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