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We study in detail the electromagnetic fields and the Poynting flux in the case of a uniformly accelerated charge, in order to examine whether such a charge does `emit' radiation, especially in view of the widely accepted fact that there is no radiation reaction on the charge. Our concern, in particular, is with the Poynting flow computed at large distances (approaching infinity!) from the time-retarded positions of uniformly accelerated charge, and taken as an evidence of radiation emitted by the charge, which we shall demonstrate to be not true. As the charge picks up speed due to a constant acceleration, the energy in its self-fields accordingly increases and the Poynting flow, usually inferred as radiation, actually forms part of the requisite energy being fed into fields, at a rate just sufficient to match the increasing energy in its self-fields at various distances from the uniformly accelerated charge, including that in the far-off regions. In fact, for the decelerating charge, the energy in its self-fields decreases, at all distances from the charge, till it comes to momentary rest with no energy in its transverse fields, and this decrease in energy is shown {\em everywhere} by an inward radial flow of the Poynting vector, toward the `present' position of the decelerating charge. Moreover, there is a convective flow of self-fields of the charge, seen as a Poynting flow component always along the `present' direction of motion of the charge. Further, we shall show that effectively the electromagnetic fields, including the acceleration fields, even when they are at large distances from the time-retarded position of the charge, they continue to be all around the `present' position of the charge which itself is moving toward infinity due to the uniform acceleration., Comment: 29 pages, 10 figures, accepted in Foundations of Physics

We examine here the discrepancy between the radiated power, calculated from the Poynting flux at infinity, and the power loss due to radiation reaction for an accelerated charge. It is emphasized that one needs to maintain a clear distinction between the electromagnetic power received by distant observers and the mechanical power loss undergone by the charge. In literature both quantities are treated as almost synonymous, the two in general could, however, be quite different. It is shown that in the case of a periodic motion, the two formulations do yield the power loss in a time averaged sense to be the same, even though, the instantaneous rates are quite different. It is demonstrated that the discordance between the two power formulas merely reflects the difference in the power going in self-fields of the charge between the retarded and present times. In particular, in the case of a uniformly accelerated charge, power going into the self-fields at the present time is equal to the power that was going into the self-fields at the retarded time plus the power going in acceleration fields, usually called radiation. From a comparison of the far fields with the instantaneous location of the uniformly accelerated charge, it is shown that all its fields, including the acceleration fields, remain around the charge and are not {\em radiated away} from it., Comment: 16 pages, 4 figures

Suggestion mining tasks are often semantically complex and lack sophisticated methodologies that can be applied to real-world data. The presence of suggestions across a large diversity of domains and the absence of large labelled and balanced datasets render this task particularly challenging to deal with. In an attempt to overcome these challenges, we propose a two-tier pipeline that leverages Discourse Marker based oversampling and fine-grained suggestion mining techniques to retrieve suggestions from online forums. Through extensive comparison on a real-world open-domain suggestion dataset, we demonstrate how the oversampling technique combined with transformer based fine-grained analysis can beat the state of the art. Additionally, we perform extensive qualitative and qualitative analysis to give construct validity to our proposed pipeline. Finally, we discuss the practical, computational and reproducibility aspects of the deployment of our pipeline across the web.

We derive here, from first principles, the energy-momentum densities of a perfect fluid, in the form of an ideal molecular gas, in an inertial frame where the fluid possesses a bulk motion. We begin from the simple expressions for the energy density and pressure of a perfect fluid in the rest frame of the fluid, where the fluid constituents (gas molecules) may possess a random motion, but no bulk motion. From a Lorentz transformation of the velocity vectors of molecules, moving along different directions in the rest frame of the fluid, we compute their energy-momentum vectors and number densities in an inertial frame moving with respect to the rest frame of the liquid. From that we arrive at the energy-momentum density of the fluid in a frame where it has a bulk motion. This way we explicitly demonstrate how a couple of curious pressure-dependent terms make appearance in the energy-momentum density of a perfect fluid having a bulk motion. In addition to an ideal molecular gas, we compute the energy-momentum density for a photon gas also, which of course matches with the energy-momentum density expression obtained for a molecular gas having ultra-relativistic random motion., Comment: 16 pages, 2 figures, to appear in Eur. J. Phys

The electric field of a uniformly accelerated charge shows a plane of discontinuity, where the field extending only on one side of the plane, terminates abruptly on the plane with a finite value. This indicates a non-zero divergence of the electric field in a source-free region, implying a violation of Gauss law. In order to make the field compliant with Maxwell's equations everywhere, an additional field component, proportional to a $\delta$-function at the plane of discontinuity, is required. Such a "$\delta$-field" might be the electromagnetic field of the charge, moving with a uniform velocity approaching $c$, the speed of light, prior to the imposition of acceleration at infinity. However, some attempts to derive this $\delta$-field for such a case, have not been entirely successful. Some of the claims of the derivation involve elaborate calculations with some not-so-obvious mathematical approximations. Since the result to be derived is already known from the constraint of its compliance with Maxwell's equations, and the derivation involves the familiar text-book expressions for the field of a uniformly moving charge, one would expect an easy, simple approach, to lead to the correct result. Here, starting from the electromagnetic field of a uniformly accelerated charge in the instantaneous rest frame, in terms of the position and motion of the charge at the retarded time, we derive this $\delta$-field, consistent with Maxwell's equations, in a fairly simple manner. This is followed by a calculation of the energy in the $\delta$-field, in an analytical manner without making any approximation, where we show that this energy is exactly the one that would be lost by the charge because of the radiation reaction on the charge, proportional to its rate of change of acceleration, that was imposed on it at a distant past., Comment: 10 pages, 5 figures

A quantum state transformation can be generally approximated by single- and two-qubit gates. This, however, does not hold with noisy intermediate-scale quantum technologies due to the errors appearing in the gate operations, where errors of two-qubit gates such as controlled-NOT and SWAP operations are dominated. In this work, we present a cost efficient single-copy certification for a realization of a two-qubit gate in the presence of depolarization noise, where it is aimed to identify if the realization is noise-free, or not. It is shown that entangled resources such as entangled states and a joint measurement are not necessary for the purpose, i.e., a noise-free two-qubit gate is not needed to certify an implementation of a two-qubit gate. A proof-of-principle demonstration is presented with photonic qubits., Comment: 9 pages. arXiv admin note: text overlap with arXiv:1812.02087

We present the first direct-detection search for eV-to-GeV dark matter using a new ~2-gram high-resistivity Skipper-CCD from a dedicated fabrication batch that was optimized for dark-matter searches. Using 24 days of data acquired in the MINOS cavern at the Fermi National Accelerator Laboratory, we measure the lowest rates in silicon detectors of events containing one, two, three, or four electrons, and achieve world-leading sensitivity for a large range of sub-GeV dark matter masses. Data taken with different thicknesses of the detector shield suggest a correlation between the rate of high-energy tracks and the rate of single-electron events previously classified as "dark current." We detail key characteristics of the new Skipper-CCDs, which augur well for the planned construction of the ~100-gram SENSEI experiment at SNOLAB., Comment: 5 pages, 4 figures, 1 table + Supplemental Materials (5 pages, 8 figures) + References. v3: matches version published in PRL