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1

It would actually be neither. Percentage is always positive, so we invoke absolute value to get $$E=\frac{|A-B|}{B}\times 100$$ Actually, we can also use $$E=\frac{|B-A|}{B}\times 100$$ Percent error is always taken with respect to the known quantity because it is important to know how far off the measurement is from the known value, and not vice versa - ...


1

Typically it is the ferrite cores in inductors/transformers that resonate mechanically, or through magnetostrictive effects that produce a high pitched whine. Switching PSUs are the main culprit. It can also occur when the EM fields interact with steel components in the PSU.


0

To convert one voltage to a higher voltage one often uses a transformer or a ladder network (or a combination of these). The above from Wikipedia shows a Cockroft-Walton multiplier - commonly used to step up an alternating waveform. It acts like a bucket brigade - the charge on each capacitor is being passed on to the next capacitor, at a higher voltage, ...


0

The problem is that your analysis is all done from the perspective of the frame that measures the box to be moving at 0.1c -- in this frame, it's true that the time for the light to get from the source to the wall is different from the time for the light to get from the wall back to the source. But if these same events are measured by someone inside the box ...


2

Since John is not addressing positrons one should know that positrons are easily created once a photon has more energy than twice the mass of the electron, in electron positron pairs. This can be seen clearly in this bubble chamber picture: where the positron is shown in purple on the right. One knows they are electrons (positrons) because of the ...


1

(This is only a partial answer to one-third of your question.) I'm sure you already know this but ... Inhomogeneous broadening is what you're talking about where different Nd atoms are in different microscopic environments and therefore emit at different wavelengths. Homogeneous broadening is where even a single Nd atom can emit at some range of different ...


12

Creating anti-protons is straightforward in principle because any high energy collision produces a shower of protons, antiprotons and various types of pions. The pions decay in a few nanoseconds, so you just have to wait for the pions to decay then separate the antiprotons from the protons. At Fermilab a 120GeV proton beam was collided with a nickel target ...


0

This page has a good simple summary of the experiment, they present the following simple schematic of a delayed choice quantum eraser (the same as Figure 1 in the original paper by Kim et al.): In this case, if the entangled "idler photon" is detected by Alice at D3 or D4 then she will know whether the "signal photon" went through slit A or slit B, but if ...


3

It is hard to prove something experimentally that is actually an equivalence of two theories on a mathematical level. The AdS/CFT correspondence is supposed to be an exact correspondence between a quantum field theory and a string theory. However, it is in principle possible to find support for the correspondence in the following way: construct the ...


0

The procedure for using such a container is described here The basis of the procedure is simple - "Make sure your eye is on a level with the mark. A Paralax Error will result, otherwise. Always read the meniscus from the bottom."


0

No. Friction is a force that does not act normal to the surface, but rather perpendicular to the surface. Trains do not derail when travelling on high speeds across turns simply because the train tracks are slightly inclined.


2

The following has ben found via Wikipedia page “Gravitational interaction of antimatter”. Another experimental test has been provided by the supernova SN1987a (anti)neutrinos, and this has been published in two brief reports in Phys. Rev. D in 1988 [1] and 1989 [2]. After the explosion of this supernova, 19 antineutrinos have been detected at IMB and ...


4

As well as the antihydrogen experiments, ALPHA, AEGIS and GBAR that were mentioned in other answers, there are a couple of other experiments, though they haven't had any results. In the 60's, they tried the obvious thing of dropping positrons down a metal tube (paper), but it didn't work, for the subtle reason that the electrons in the metal sag under ...


1

There are, by my count, 33 other official weather observation stations within Sydney. Here's a map: With regard to the Sydney - Observation Hills (Station ID 066062) station -- That freeway didn't exist when the station was built. How could it? That station dates back to 1858. The station was moved 150 meters to its current location in 1917. That tiny ...


2

There are different layers of reconstruction, at each step the amount of data is reduced with the goal of inferring the momenta, type and direction of the particles produced first in the collision: pulse shape reconstruction: the electronic signals caused by particles interacting with the detector cells are digitized at a rate of 40 MHz at LHC. Some ...


0

It no doubt does. Solar radiation will heat surfaces, and the rate at which a black surface absorbs that heat is greater than for other colors. That heat is then partly lost by radiation, partly by conduction, and partly by convection. If you assume the last two terms will be the same regardless of the color, then you can see why a black surface will become ...


19

The only experiment I know of was done by the ALPHA team at CERN. The results are published in this paper. The error bounds are huge - all the team were able to say is that the upper limit for the gravitational mass of antihydrogen is no greater than 75 times its inertial mass! However I believe an updated version of the experiment, ALPHA2, is in progress ...


2

The paper you point to describes the experimental test by Rowe et al., in Wineland’s group in 2001. This experiment was performed in an ion trap, where Alice and Bob are separated by 3 µm, and therefore it is impossible in practice to close the locality loophole. As they say in the methods section, even though all known interactions would cause ...


0

I am curious about the following line in your derivation: Our quadcopter measures 47cm motor-to-motor, so r = 0.235m. Let’s calculate the torque. Presumably to pitch the copter without changing the over all lift, you need one pair of rotors to slow down and the other pair to speed up. It was not clear to me that the factor of two that this results in ...


0

You just have to make sure you hit the center of mass to give it a velocity you need, irrespective of the position of the pivot, whether it is at the end of the rod or 0.1m away from it. If you hit the center of mass of the rod and make it move with a velocity that is just enough for it to reach the vertical position above the pivot, that velocity will be ...


1

The statement is not true, because there are counter examples. A U(1) spin liquid is gapless, but it is insulating. An $s$-wave superconductor is fully gapped, but it is (super)conducting.


1

the cooling process depends on many factors: - convection, radiation and conduction inside the body. Exponential decay is good only if the lumped capacitance model is appropiate and if the relation with radiation is linear. I would say that in your case you also had convection inside the fluid. And ontop of that the relation with radiation is not linear it ...


1

It is not generally true that a gapped system is insulating. Or more precisely, this statement is not detailed enough to be said true or false generically. One case where this is true is for non-interacting particles (say, free electron in a lattice). For interacting particles, it is much more subtle. In particular, just stating "gapped system" is not ...


1

Your understanding is basically correct. Some materials, intrinsic semiconductors, have small band gaps so that at room temperature (for example) there is enough thermal energy around to promote some electrons to the conduction band, and some holes to the valence band. These materials have the kind of gap that you describe, but are not insulators. Another ...


0

http://qudev.ethz.ch/content/courses/QSIT08/pdfs/Rowe01.pdf The experiment is repeated Ntot 20 000 times at each of the four sets of phases So it's about 80 000 to achieve $2,25 \pm 0,03$


5

You do exactly the same thing: you "rotate" the state and then measure along whatever axis your measurement apparatus happens to measure. The only difference here is that the "rotation" does not necessarily correspond to a rotation in space like it does for a true spin. What follows is a detailed description of how we do rotations of a generic 2 level ...


0

You could try PEBBLES which is freeware AFAIK


0

The human eye, in dark-adapted conditions, has been shown to be capable of detecting a single photon (which is to say, the retina reacts, the signal gets to the brain, and [magic happens] to generate a response in the conscious parts of the brain. Since what you're asking about is the release of one photon, it doesn't matter what the source is. So long ...


2

You can consider this to be true for any parcel of air, even in the open. In the real world however, there are usually added dynamics due to convection mechanisms (i.e. winds and the sort) that screw this up. But a good for instance would be a bubble out of a divers snorkel, in depth. the boundary for the bubble is in no way rigid, and the bubble expands ...


1

Usually experimental Bell tests are performed using photon polarization. However, experiments have also been devised to test Bell inequalities using so-called "time-bin" entanglement. Essentially, the quantum information is encoded in the time-of-arrival of the photons. Also, there are Bell-type tests using continuous variables. These continuous variables ...


1

The answer is due to the area-Mach number relation for hydrodynamic shocks. G.B. Whitham has a great book (check out Chapter 8) on all sorts of various waves and has a good discussion of this topic. The idea is that one can define the Mach number as a function of the cross-sectional area of a ray tube. The simple form is: $$ \frac{ 1 }{ A } \frac{ d A }{ ...


2

Assuming your screen is "far away", then the pattern you see on the screen is the Fourier transform of the aperture function. So if you take the (inverse) Fourier transform of the image on the screen, you get back to the aperture function. Small complication: the intensity image no longer contains the phase information which you need to fully reconstruct ...


3

Firstly, I suspect that oxidation will throw a spanner into any such plan. For metals like aluminum, which have a very high affinity for oxygen, a "virgin" surface will begin to tarnish almost immediately. The second problem is that metals have microstructure. Neighboring crystals in a polycrystalline aggregate such as a metal piece have to satisfy certain ...


1

As John Rennie points out in his comment, energy is NOT conserved in an expanding universe. This finding is much more modern than your beginning predicate that "matter cannot be created nor destroyed", which really began to be abandoned wholesale about the time of Einstein's famous 1905 special relativity paper "Zur Elektrodynamik bewegter Körper" (on the ...


1

Due to evaporation a layer of air forms between the water droplet and the hot surface which causes the system to vibrate by letting air escape in bursts and produce sound. I suggest reading about the description of the sound that was recorded in the Leidenfrost experiment. Article: http://www.nature.com/srep/2012/121010/srep00720/full/srep00720.html Video: ...


0

With the two options, the temperature difference and bag insulation R-factor are the same. The five-bag option has five times the surface area (if truly "separate" and not stacked). So the one big bag should be the better choice. A less snicker-inducing version of the "two people - two sleeping bags - how to keep warmer" problem...


2

My guess is it's best to put each pizza into its own insulator, but then stack them for transport so that the stack has the same size and surface area a larger insulating container would have. Stacking the boxes in transport minimizes heat loss since it's proportional to exposed outside area. Opening a container would let significant heat out, so that ...


0

If they were ideal insulators, the 5 separate bags would be better because you wouldn't have repeated heat loss from opening the same bag 5 times. Primarily this heat loss would be in the escape of hot air, exchanged for colder outside air. If the hot bags were extremely poor insulators - effectively as if you weren't using any - then you'd want the pizzas ...


0

I don't think there will be any difference. Provided the bags are ideal insulators and the pizzas are at the same temperature, there will be no exchange of heat. Even with all of them in the same bag, there will be no exchange of heat as no temperature gradient exists!


2

Let charge A be at the origin, moving to the right (along the positive x axis). Let charge B be at coordinates (1,0), moving in the positive y direction. A's magnetic force on B vanishes, since by symmetry the magnetic field due to A is zero at B's position. B's magnetic force on A doesn't vanish. Does the law already fails in magnetostatics? I guess ...


2

It is an old conundrum how and why Newton's 3rd law fails for the differential form of Biot-Savart. To quote Bleaney & Bleaney:"Page and Adams {1945) have shown that there is no real violation, since the electromagnetic field of the current elements possesses momentum which is changing at a rate just equal to the difference of the two forces." Leigh Page ...


0

To see if this is possible we can use a formal material selection approach of the kind presented in "Material Selection in Mechanical Design", Elsevier, M.F.Ashby. Our objective is to maximize buoyancy while keeping within the no-buckling constraint. To make things easier I suggest some simplifications. First, Poisson's Ratio does not vary much for most ...



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