Energy Loss Rate Research Articles

Numerical study of energy absorption in aluminum foam sandwich panel structures using drop hammer test

The sandwich structures with aluminum foam core and metal surfaces have widespread use in the absorption of energy, because they are light weighted with high performance in dissipating energy. The cell structure of the foam core is subjected to plastic deformation in the constant compression level that absorbs a lot of kinetic energy before destruction of the structure. In this research, experimental tests of low-velocity impact on the sandwich structure by a drop machine are simulated by LS-DYNA software. Numerical results are obtained for different velocities and weights of projectile on samples of aluminum foam core sandwich panels with relative density (the ratio of the density of aluminum foam to the density of solid aluminum) of 18, 23, and 27. The results are compared with experimental results which reveal a good conformity. As well, from the numerical simulations, the effect of weight, velocity and energy of the projectile and the density of the foam core on the global deformation and energy loss rate of projectile have been studied.

Neutrino Pair Cerenkov Radiation for Tachyonic Neutrinos

The emission of a charged light lepton pair by a superluminal neutrino has been identified as a major factor in the energy loss of highly energetic neutrinos. The observation of PeV neutrinos by IceCube implies their stability against lepton pair Cerenkov radiation. Under the assumption of a Lorentz-violating dispersion relation for highly energetic superluminal neutrinos, one may thus constrain the Lorentz-violating parameters. A kinematically different situation arises when one assumes a Lorentz-covariant, space-like dispersion relation for hypothetical tachyonic neutrinos, as an alternative to Lorentz-violating theories. We here discuss a hitherto neglected decay process, where a highly energetic tachyonic neutrino may emit other (space-like, tachyonic) neutrino pairs. We find that the space-like dispersion relation implies the absence of a q2 threshold for the production of a tachyonic neutrino-antineutrino pair, thus leading to the dominant additional energy loss mechanism for an oncoming tachyonic neutrino in the medium-energy domain. Surprisingly, the small absolute values of the decay rate and energy loss rate in the tachyonic model imply that these models, in contrast to the Lorentz-violating theories, are not pressured by the cosmic PeV neutrinos registered by the IceCube collaboration.

Stellar energy loss rates in the pair-annihilation process beyond the standard model

We calculate the stellar energy loss due to neutrino-pair production in $e^+e^-$ annihilation in the context of a 331 model, a left-right symmetric model and a simplest little Higgs model in a way that can be used in supernova calculations. We also present some simple estimates which show that such process can act as an efficient energy loss mechanism in the shocked supernova core. We find that the stellar energy loss is almost independent on the parameters of the models in the allowed range for these parameters. This work complements other studies on the stellar energy loss rate in $e^+e^-$ annihilation.

Energy density of light quark jet using AdS/CFT

We study the energy loss rate of light quarks via the AdS/CFT correspondence in both a static and an expanding plasma. Unlike heavy quarks, light quark energy loss in AdS/CFT is surprisingly dependent on both the string initial conditions and the very definition of the jet itself in the gravity theory. We aim to more closely match the string initial conditions to those expected from perturbative quantum chromodyanics (pQCD)-the theory known to describe the physics of high-momentum particles at early times in heavy ion collisions-by computing the energy-momentum tensor associated with the propagation of the classical string solution. The jet energy-momentum tensor in a strongly-coupled calculation can be found by a superposition of contributions from a collection of point particles whose paths approximate the evolution of the string world-sheet. My results show that some times after creation the pair of quark-anti quark, the energy density is not time dependent. This means that the corresponding jet does not lose energy and the associated nuclear modification factor would be one as expected. Also, the results reveal the virtuality dependency of energy density distribution over space. As expected, the energy of a more virtual jet is spread over wider angles.

Difference in hot carrier cooling rate between Langmuir-Blodgett and drop cast PbS QD films due to strong electron-phonon coupling.

The carrier dynamics of lead sulphide quantum dot (PbS QD) drop cast films and closely packed ordered Langmuir-Blodgett films are studied with ultra-fast femtosecond transient absorption spectroscopy. The photo-induced carrier temperature is extracted from transient absorption spectra and monitored as a function of time delay. The cooling dynamics of carriers in PbS QDs suggest a reduction of the carrier energy loss rate at longer time delays through the retardation of the longitudinal optical (LO) phonon decay due to partial heating of acoustic phonon modes. A slowed hot carrier cooling time up to 116 ps is observed in the drop cast film. A faster cooling rate was also observed in the highly compact Langmuir-Blodgett film due to the enhanced carrier-LO phonon coupling strength arising from the Coulombic interaction in neighboring QDs, which is verified by temperature dependent steady state PL measurements.

Composition and orientation dependent annealing of ion tracks in apatite - Implications for fission track thermochronology

The annealing behaviour of swift heavy-ion tracks in apatite from different origins is studied as a function of their crystallographic orientation and the mineral composition. The tracks were generated by irradiating the apatite samples with 2.3GeV Bi ions, which have a comparable rate of energy loss to fission tracks in this mineral. The track radius was investigated using synchrotron-based small-angle x-ray scattering (SAXS) combined with ex situ annealing. Results indicate that tracks parallel to the c-axis are initially larger and anneal slower than those perpendicular to the c-axis. Natural variation in the mineral composition shows stronger annealing resistance of ion tracks with higher chlorine content. The SAXS results are consistent with previous studies on etched tracks and provide evidence that the orientation and composition effects are directly linked to the property of the un-etched track and not to preferential etchability. The study helps to connect the empirical studies on etched fission tracks to more fundamental solid-state processes.

Drag phenomena from holographic massive gravity

We consider the motion of point particles in a strongly coupled field theory with broken translation invariance. We obtain the energy and momentum loss rates and drag coefficients for a class of such particles by solving for the motion of classical strings in holographic massive gravity. At low temperatures compared to the graviton mass the behaviour of the string is controlled by the appearance of an exotic ground state with non-zero entropy at zero temperature. Additionally, we find an upper bound on the diffusion constant for a collection of these particles which is saturated when the mass of the graviton goes to zero.

Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

We investigate the 1/f noise properties of epitaxial graphene devices at low temperatures as a function of temperature, current and magnetic flux density. At low currents, an exponential decay of the 1/f noise power spectral density with increasing temperature is observed that indicates mesoscopic conductance fluctuations as the origin of 1/f noise at temperatures below 50 K. At higher currents, deviations from the typical quadratic current dependence and the exponential temperature dependence occur as a result of nonequilibrium conditions due to current heating. By applying the theory of Kubakaddi [S. S. Kubakaddi, Phys. Rev. B 79, 075417 (2009)], a model describing the 1/f noise power spectral density of nonequilibrium mesoscopic conductance fluctuations in epitaxial graphene is developed and used to determine the energy loss rate per carrier. In the regime of Shubnikov-de Haas oscillations a strong increase of 1/f noise is observed, which we attribute to an additional conductance fluctuation mechanism due to localized states in quantizing magnetic fields. When the device enters the regime of quantized Hall resistance, the 1/f noise vanishes. It reappears if the current is increased and the quantum Hall breakdown sets in.

The effects of degeneracy of the carrier ensemble on the energy loss rate and the high field mobility characteristics under the conditions of low lattice temperatures

The rate of loss of energy of the non-equilibrium electrons to the acoustic mode lattice vibration in a degenerate semiconductor is obtained under the condition, when the lattice temperature is low enough, so that the traditional approximations like the elastic nature of the electron-phonon collisions and the truncation of the phonon distribution to the equipartition law are not valid any more. Using the results of the energy loss rate, the non-ohmic mobility is then calculated. Evaluating the loss rate and the non-ohmic mobility in degenerate samples of Si and Ge we find that significant changes in both the characteristics have been effected compared to that in the non-degenerate samples, in the regime of lower energy and for relatively lower fields. The effected changes are more significant the lower the lattice temperature is.

Nodal Impact Assessment and Alleviation of Moving Electric Vehicle Loads: From Traffic Flow to Power Flow

Large-scale adoption of moving electric vehicle (EV) loads significantly accelerates the integration of power and traffic systems. This paper proposes an approach to assess and alleviate the impacts of stochastic EV charging and movement in an integrated power and traffic system. Level of Congestion (LoC), Nodal Voltage Deviation (NVD) and Energy Loss Rate (ELR) are proposed as nodal indices to spatially and temporally assess the impacts due to the inter-node movement of EVs on power system operation. Nodal Time-of-Use (NTOU) price and Road Traffic Congestion (RTC) price are developed to shift the charging and movement of EV loads. EV driver's charging and driving decisions are modeled by fuzzy logic inference system in response to NTOU and RTC prices. Two transportation systems have been developed and integrated with the Roy Billinton test power system (RBTS) to illustrate the proposed technique and model.

Ab initio study of electronic excitations and the dielectric function in molybdenum disulfide monolayer

The propagator of the induced dynamically screened Coulomb interaction ${W}^{\mathrm{ind}}(\mathbf{Q},\ensuremath{\omega},z,{z}^{\ensuremath{'}})$ is calculated for the ${\mathrm{MoS}}_{2}$ monolayer. The energy-loss rate of a point charge placed near the ${\mathrm{MoS}}_{2}$ monolayer is calculated (using the spatial resolution of the ${W}^{\mathrm{ind}}$ in the direction perpendicular to the ${\mathrm{MoS}}_{2}$ plane) and successfully compared with very recent electron-energy-loss spectroscopy measurements of Hong et al. [J. Hong et al., Phys. Rev. B 93, 075440 (2016)]. The induced propagator ${W}^{\mathrm{ind}}$, compared with its classical analogous propagator, is used to determine the effective dielectric function ${\ensuremath{\epsilon}}_{\mathrm{eff}}(\ensuremath{\omega})$ of atomically thick crystals. It is shown that ${\ensuremath{\epsilon}}_{\mathrm{eff}}(\ensuremath{\omega})$ extracted from ${W}^{\mathrm{ind}}$ is in good agreement with the dielectric function of the ${\mathrm{MoS}}_{2}$ extracted from the ellipsometry measurements. A recently proposed method for calculation of the dielectric tensor in quasi-two-dimensional crystals is used to calculate the parallel ${\ensuremath{\epsilon}}_{\ensuremath{\parallel}}(\ensuremath{\omega})$ and perpendicular ${\ensuremath{\epsilon}}_{\ensuremath{\perp}}(\ensuremath{\omega})$ dielectric functions in ${\mathrm{MoS}}_{2}$, which are compared with some previous measurements and calculations.

Spectral indices for radio emission of 228 pulsars

We determine spectral indices of 228 pulsars by using Parkes pulsar data observed at 1.4 GHz, among which 200 spectra are newly determined. The indices are distributed in the range from −4.84 to −0.46. Together with known pulsar spectra from literature, we tried to find clues to the pulsar emission process. The weak correlations between the spectral index, the spin-down energy loss rate E and the potential drop in the polar gap ΔΨ hint that emission properties are related to the particle acceleration process in a pulsar's magnetosphere.

On the difference between γ-ray-detected and non-γ-ray-detected pulsars

We compare radio profile widths of young, energetic gamma-ray-detected and non-gamma-ray-detected pulsars. We find that the latter typically have wider radio profiles, with the boundary between the two samples exhibiting a dependence on the rate of rotational energy loss. We also find that within the sample of gamma-ray-detected pulsars, radio profile width is correlated with both the separation of the main gamma-ray peaks and the presence of narrow gamma-ray components. These findings lead us to propose that these pulsars form a single population where the main factors determining gamma ray detectability are the rate of rotational energy loss and the proximity of the line of sight to the rotation axis. The expected magnetic inclination angle distribution will be different for radio pulsars with and without detectable gamma rays, naturally leading to the observed differences. Our results also suggest that the geometry of existing radio and outer-magnetosphere gamma-ray emission models are at least qualitatively realistic, implying that information about the viewing geometry can be extracted from profile properties of pulsars.

On the possible wind nebula of magnetar Swift J1834.9–0846: a magnetism-powered synchrotron nebula

Recently, the magnetar Swift J1834.9–0846 has been reported to have a possible wind nebula. It is shown that both the magnetar and its wind nebula are understandable in the wind braking scenario. The magnetar's rotational energy loss rate is not enough to power the particle luminosity. The required particle luminosity should be about 1036 erg s−1 to 1038 erg s−1. It is obtained in three different approaches: considering wind braking of Swift J1834.9–0846; the spectral and spatial observations of the wind nebula; and an empirical upper bound on wind nebula X-ray luminosity. The nebula magnetic field is about 10−4 G. The possible wind nebula of Swift J1834.9–0846 should be a magnetar wind nebula. It is powered by the magnetic energy released from the magnetar.

Energy loss of a nonaccelerating quark moving through a strongly coupledN=4super Yang-Mills vacuum or plasma in strong magnetic field

Using AdS/CFT correspondence, we find that a massless quark moving at the speed of light $v=1$, in arbitrary direction, through a strongly coupled $\mathcal{N}=4$ super Yang-Mills (SYM) vacuum at $T=0$, in the presence of strong magnetic field $\mathcal{B}$, loses its energy at a rate linearly dependent on $\mathcal{B}$, i.e., $\frac{dE}{dt}=-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}$. We also show that a heavy quark of mass $M\neq 0$ moving at near the speed of light $v^2=v_{*}^2=1-\frac{4\pi^2 T^2}{\mathcal{B}}\simeq1$, in arbitrary direction, through a strongly coupled $\mathcal{N}=4$ SYM plasma at finite temperature $T\neq 0$, in the presence of strong magnetic field $\mathcal{B}\gg T^2$, loses its energy at a rate linearly dependent on $\mathcal{B}$, i.e., $\frac{dE}{dt}=-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}v_{*}^2\simeq-\frac{\sqrt{\lambda}}{6\pi}\mathcal{B}$. Moreover, we argue that, in the strong magnetic field $\mathcal{B}\gg T^2$ (IR) regime, $\mathcal{N}=4$ SYM and adjoint QCD theories (when the adjoint QCD theory has four flavors of Weyl fermions and is at its conformal IR fixed point $\lambda=\lambda^*$) have the same microscopic degrees of freedom (i.e., gluons and lowest Landau levels of Weyl fermions) even though they have quite different microscopic degrees of freedom in the UV when we consider higher Landau levels. Therefore, in the strong magnetic field $\mathcal{B}\gg T^2$ (IR) regime, the thermodynamic and hydrodynamic properties of $\mathcal{N}=4$ SYM and adjoint QCD plasmas, as well as the rates of energy loss of a quark moving through the plasmas, should be the same.

Spectra and rates of bremsstrahlung neutrino emission in stars

We calculate the energy-differential rate for neutrino emission from electron-nucleus bremsstrahlung in stellar interiors taking into account the effects of electron screening and ionic correlations. We compare the energy-differential and the net rates, as well as the average $\bar{\nu}_e$ and $\bar{\nu}_x$ $(x = {\mu}, {\tau})$ energies, for this process with those for $e^{\pm}$ pair annihilation, plasmon decay, and photo-neutrino emission over a wide range of temperature and density. We also compare our updated energy loss rates for the above thermal neutrino emission processes with the fitting formulas widely used in stellar evolution models and determine the temperature and density domain in which each process dominates. We discuss the implications of our results for detection of $\bar{\nu}_e$ from massive stars during their pre-supernova evolution and find that pair annihilation makes the predominant contribution to the signal from the thermal emission processes.

Bounds on the Bondi energy by a flux of curvature

We consider smooth null cones in a vacuum spacetime that extend to future null infinity. For such cones that are perturbations of shear-free outgoing null cones in Schwarzschild spacetimes, we prove bounds for the Bondi energy, momentum, and rate of energy loss. The bounds depend on the closeness between the given cone and a corresponding cone in a Schwarzschild spacetime, measured purely in terms of the differences between certain weighted L^2 -norms of the spacetime curvature on the cones, and of the geometries of the spheres from which they emanate. This paper relies on the results in [1], which uniformly control the geometry of the given null cone up to infinity, as well as those of [18], which establish machinery for dealing with low regularities. A key step in this paper is the construction of a family of asymptotically round cuts of our cone, relative to which the Bondi energy is measured.

Accelerated quarks and energy loss in confinement theory

We study the energy loss rate (ELR) of the accelerated quark in terms of the holographic models for the two different motions, linear acceleration and uniform rotation. They are examined by two different nonconformal models with confinement. We found in both models that the value of ELR is bounded from below by the string tension of the linear confinement potential between quark and antiquark. The lower bounds of ELR are independent of the types of the motion of the quark. They are determined by the string tension at the worldsheet horizon of the model. These results are obtained when the model has the diagonal background metric. Then we find the common perspective for the lower bounds of ELRs of the two different motions.

SUPPRESSION OF PARALLEL TRANSPORT IN TURBULENT MAGNETIZED PLASMAS AND ITS IMPACT ON THE NON-THERMAL AND THERMAL ASPECTS OF SOLAR FLARES

ABSTRACT The transport of the energy contained in electrons, both thermal and suprathermal, in solar flares plays a key role in our understanding of many aspects of the flare phenomenon, from the spatial distribution of hard X-ray emission to global energetics. Motivated by recent RHESSI observations that point to the existence of a mechanism that confines electrons to the coronal parts of flare loops more effectively than Coulomb collisions, we here consider the impact of pitch-angle scattering off turbulent magnetic fluctuations on the parallel transport of electrons in flaring coronal loops. It is shown that the presence of such a scattering mechanism in addition to Coulomb collisional scattering can significantly reduce the parallel thermal and electrical conductivities relative to their collisional values. We provide illustrative expressions for the resulting thermoelectric coefficients that relate the thermal flux and electrical current density to the temperature gradient and the applied electric field. We then evaluate the effect of these modified transport coefficients on the flare coronal temperature that can be attained, on the post-impulsive-phase cooling of heated coronal plasma, and on the importance of the beam-neutralizing return current on both ambient heating and the energy loss rate of accelerated electrons. We also discuss the possible ways in which anomalous transport processes have an impact on the required overall energy associated with accelerated electrons in solar flares.

Medium Recoil and Jet Modification in Heavy Ion Collisions

A complete set of elastic processes and induced gluon radiation within the higher-twist approach have been implemented in the Linear Boltzmann Transport model for jet propagation and interaction with quark-gluon plasma in high-energy heavy-ion collisions. We impose global energy momentum conservation in the 2→n processes of induced radiation which will influence the final gluon spectra. We will compare the elastic and the radiative energy loss of partons and their effects on reconstructed jets. The energy loss of a leading parton is found to have a quadratic distance dependence only for a short distance, but will have much weak distance dependence because of the accumulated energy loss and the strong energy dependence of the local energy loss rate. Since reconstructed jets recover some of the energy lost by the leading parton, the quadratic path length dependence persists for a longer distance. The spatial distribution and time evolution of the jet-induced medium excitation are also discussed.