Showing papers on "Energy (signal processing) published in 2014"

Theory and Application of Statistical Energy Analysis

Abstract: The development of statistical energy analysis energy description of vibrating systems energy sharing by coupled systems the estimation of response statistics in statistical energy analysis applications of SEA modelling the system evaluating the mode count evaluating the damping loss factor evaluating the coupling loss factor evaluating the input power solving for the energy distribution evaluating the dynamical response variables transient SEA an example.

Extracting the jet transport coefficient from jet quenching in high-energy heavy-ion collisions

Abstract: Within five different approaches to parton propagation and energy loss in dense matter, a phenomenological study of experimental data on suppression of large-${p}_{T}$ single inclusive hadrons in heavy-ion collisions at both the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC) was carried out. The evolution of bulk medium used in the study for parton propagation was given by 2 + 1 dimensional or 3 + 1 dimensional hydrodynamic models which are also constrained by experimental data on bulk hadron spectra. Values for the jet transport parameter $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$ at the center of the most central heavy-ion collisions are extracted or calculated within each model, with parameters for the medium properties that are constrained by experimental data on the hadron suppression factor ${R}_{AA}$. For a quark with initial energy of 10 GeV we find that $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}\ensuremath{\approx}1.2\ifmmode\pm\else\textpm\fi{}0.3$ GeV${}^{2}$/fm at an initial time ${\ensuremath{\tau}}_{0}=0.6$ fm/$c$ in Au + Au collisions at $\sqrt{s}=200$ GeV/n and $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}\ensuremath{\approx}1.9\ifmmode\pm\else\textpm\fi{}0.7$ GeV${}^{2}$/fm in Pb + Pb collisions at $\sqrt{s}=2.76$ TeV/n. Compared to earlier studies, these represent significant convergence on values of the extracted jet transport parameter due to new constraints provided by recent experiment data from the LHC.

Simultaneous Information and Energy Transfer in Large-Scale Networks with/without Relaying

Abstract: Energy harvesting (EH) from ambient radio-frequency (RF) electromagnetic waves is an efficient solution for fully autonomous and sustainable communication networks. Most of the related works presented in the literature are based on specific (and small-scale) network structures, which although give useful insights on the potential benefits of the RF-EH technology, cannot characterize the performance of general networks. In this paper, we adopt a large-scale approach of the RF-EH technology and we characterize the performance of a network with random number of transmitter-receiver pairs by using stochastic-geometry tools. Specifically, we analyze the outage probability performance and the average harvested energy, when receivers employ power splitting (PS) technique for "simultaneous" information and energy transfer. A non-cooperative scheme, where information/energy are conveyed only via direct links, is firstly considered and the outage performance of the system as well as the average harvested energy are derived in closed form in function of the power splitting. For this protocol, an interesting optimization problem which minimizes the transmitted power under outage probability and harvesting constraints, is formulated and solved in closed form. In addition, we study a cooperative protocol where sources' transmissions are supported by a random number of potential relays that are randomly distributed into the network. In this case, information/energy can be received at each destination via two independent and orthogonal paths (in case of relaying). We characterize both performance metrics, when a selection combining scheme is applied at the receivers and a single relay is randomly selected for cooperative diversity.

Matching Demodulation Transform and SynchroSqueezing in Time-Frequency Analysis

Abstract: The authors introduce an iterative algorithm, called matching demodulation transform (MDT), to generate a time-frequency (TF) representation with satisfactory energy concentration. As opposed to conventional TF analysis methods, this algorithm does not have to devise ad-hoc parametric TF dictionary. Assuming the FM law of a signal can be well characterized by a determined mathematical model with reasonable accuracy, the MDT algorithm can adopt a partial demodulation and stepwise refinement strategy for investigating TF properties of the signal. The practical implementation of the MDT involves an iterative procedure that gradually matches the true instantaneous frequency (IF) of the signal. Theoretical analysis of the MDT's performance is provided, including quantitative analysis of the IF estimation error and the convergence condition. Moreover, the MDT-based synchrosqueezing algorithm is described to further enhance the concentration and reduce the diffusion of the curved IF profile in the TF representation of original synchrosqueezing transform. The validity and practical utility of the proposed method are demonstrated by simulated as well as real signal.

Optimal Energy Management for a Residential Microgrid Including a Vehicle-to-Grid System

Abstract: An optimization model is proposed to manage a residential microgrid including a charging spot with a vehicle-to-grid system and renewable energy sources. In order to achieve a realistic and convenient management, we take into account: (1) the household load split into three different profiles depending on the characteristics of the elements considered; (2) a realistic approach to owner behavior by introducing the novel concept of range anxiety; (3) the vehicle battery management considering the mobility profile of the owner and (4) different domestic renewable energy sources. We consider the microgrid operated in grid-connected mode. The model is executed one-day-ahead and generates a schedule for all components of the microgrid. The results obtained show daily costs in the range of 2.82 ${\rm C}\!\!\!\!{\scriptstyle ^{=}}$ to 3.33 ${\rm C}\!\!\!\!{\scriptstyle ^{=}}$ ; the proximity of these values to the actual energy costs for Spanish households validate the modeling. The experimental results of applying the designed managing strategies show daily costs savings of nearly 10%.

Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor

Abstract: We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (${T}_{c}\ensuremath{\sim}8\text{ }\text{ }\mathrm{K}$), which exhibits a tetragonal-to-orthorhombic structural transition at ${T}_{s}\ensuremath{\sim}90\text{ }\text{ }\mathrm{K}$. At low temperature, we found splitting of the energy bands as large as 50 meV at the $M$ point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to $T\ensuremath{\sim}110\text{ }\text{ }\mathrm{K}$, slightly above ${T}_{s}$, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.

Linear Parameter-Varying Controller Design for Four-Wheel Independently Actuated Electric Ground Vehicles With Active Steering Systems

Abstract: This paper presents a linear parameter-varying (LPV) control strategy to preserve stability and improve handling of a four-wheel independently actuated electric ground vehicle in spite of in-wheel motors and/or steering system faults. Different types of actuator faults including loss-of-effectiveness fault, additive fault, and the fault makes an actuator's control effect stuck-at-fixed-level, are considered simultaneously. To attenuate the effects of disturbance and address the challenging problem, a novel fault-tolerant (FT) robust linear quadratic regulator (LQR)-based $H_{\infty}$ controller using the LPV method is proposed. With the LQR-based $H_{\infty}$ control, the tradeoff between the tracking performance and the control input energy is achieved, and the effect from the external disturbance to the controlled outputs is minimized. The eigenvalue positions of the system matrix of the closed-loop system are also incorporated to tradeoff between the control inputs and the transient responses. The vehicle states, including vehicle yaw rate, lateral and longitudinal velocities, are simultaneously controlled to track their respective references. Simulations for different fault types and various driving scenarios are carried out with a high-fidelity, CarSim®, full-vehicle model. Simulation results show the effectiveness of the proposed FT control approach.

Precise Measurement of the Neutrino Mixing Parameter \theta_{23} from Muon Neutrino Disappearance in an Off-axis Beam

Abstract: New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} protons on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) x 10^{-3} eV^2/c^4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.

Lifting of xz / yz orbital degeneracy at the structural transition in detwinned FeSe

Abstract: We study superconducting FeSe $({T}_{\mathrm{c}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}9\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ exhibiting the tetragonal-orthorhombic structural transition $({T}_{\mathrm{s}}\phantom{\rule{0.16em}{0ex}}\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}90\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ without any antiferromagnetic ordering, by utilizing angle-resolved photoemission spectroscopy. In the detwinned orthorhombic state, the energy position of the ${d}_{yz}$ orbital band at the Brillouin zone corner is $50\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ higher than that of ${d}_{xz}$, indicating the orbital order similar to the NaFeAs and ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ families. Evidence of orbital order also appears in the hole bands at the Brillouin zone center. Precisely measured temperature dependence using strain-free samples shows that the onset of the orbital ordering (${T}_{\mathrm{o}}$) occurs very close to ${T}_{\mathrm{s}}$, thus suggesting that the electronic nematicity above ${T}_{\mathrm{s}}$ is considerably weaker in FeSe compared to ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ family.

Precise measurement of the neutrino mixing parameter θ23 from muon neutrino disappearance in an off-axis beam

Abstract: New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} protons on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) x 10^{-3} eV^2/c^4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.

Quantum Radiation Reaction in Laser–Electron-Beam Collisions

Abstract: It is possible using current high-intensity laser facilities to reach the quantum radiation reaction regime for energetic electrons. An experiment using a wakefield accelerator to drive GeV electrons into a counterpropagating laser pulse would demonstrate the increase in the yield of high-energy photons caused by the stochastic nature of quantum synchrotron emission: we show that a beam of ${10}^{9}$ 1 GeV electrons colliding with a 30 fs laser pulse of intensity ${10}^{22}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$ will emit 6300 photons with energy greater than 700 MeV, $60\ifmmode\times\else\texttimes\fi{}$ the number predicted by classical theory.

Energy Cooperation in Cellular Networks with Renewable Powered Base Stations

Abstract: In this paper, we propose a model for energy cooperation between cellular base stations (BSs) with individual hybrid power supplies (including both the conventional grid and renewable energy sources), limited energy storages, and connected by resistive power lines for energy sharing. When the renewable energy profile and energy demand profile at all BSs are deterministic or known ahead of time, we show that the optimal energy cooperation policy for the BSs can be found by solving a linear program. We show the benefits of energy cooperation in this regime. When the renewable energy and demand profiles are stochastic and only causally known at the BSs, we propose an online energy cooperation algorithm and show the optimality properties of this algorithm under certain conditions. Furthermore, the energy-saving performances of the developed offline and online algorithms are compared by simulations, and the effect of the availability of energy state information (ESI) on the performance gains of the BSs' energy cooperation is investigated. Finally, we propose a hybrid algorithm that can incorporate offline information about the energy profiles, but operates in an online manner.

Coordinated Multicell Multiuser Precoding for Maximizing Weighted Sum Energy Efficiency

Abstract: Energy efficiency optimization of wireless systems has become urgently important due to its impact on the global carbon footprint In this paper we investigate energy efficient multicell multiuser precoding design and consider a new criterion of weighted sum energy efficiency, which is defined as the weighted sum of the energy efficiencies of multiple cells This objective is more general than the existing methods and can satisfy heterogeneous requirements from different kinds of cells, but it is hard to tackle due to its sum-of-ratio form In order to address this non-convex problem, the user rate is first formulated as a polynomial optimization problem with the test conditional probabilities to be optimized Based on that, the sum-of-ratio form of the energy efficient precoding problem is transformed into a parameterized polynomial form optimization problem, by which a solution in closed form is achieved through a two-layer optimization We also show that the proposed iterative algorithm is guaranteed to converge Numerical results are finally provided to confirm the effectiveness of our energy efficient beamforming algorithm It is observed that in the low signal-to-noise ratio (SNR) region, the optimal energy efficiency and the optimal sum rate are simultaneously achieved by our algorithm; while in the middle-high SNR region, a certain performance loss in terms of the sum rate is suffered to guarantee the weighed sum energy efficiency

Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

Abstract: We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of $1{0}^{\ensuremath{-}14}\text{ }\text{ }\mathrm{eV}$. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant $\ensuremath{\beta}g5.8\ifmmode\times\else\texttimes\fi{}1{0}^{8}$ at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength ${g}_{s}{g}_{p}g3.7\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}16}$ ($5.3\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}16}$) at a Yukawa length of $\ensuremath{\lambda}=20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ (95% C.L.).

Band gap renormalization and Burstein-Moss effect in silicon- and germanium-doped wurtzite GaN up to 10 20 cm − 3

Abstract: The interplay between band gap renormalization and band filling (Burstein-Moss effect) in n-type wurtzite GaN is investigated. For a wide range of electron concentrations up to $1.6\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ spectroscopic ellipsometry and photoluminescence were used to determine the dependence of the band gap energy and the Fermi edge on electron density. The band gap renormalization is the dominating effect up to an electron density of about $9\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$; at higher values the Burstein-Moss effect is stronger. Exciton screening, the Mott transition, and formation of Mahan excitons are discussed. A quantitative understanding of the near gap transition energies on electron density is obtained. Higher energy features in the dielectric functions up to $10\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ are not influenced by band gap renormalization.

Achievable Throughput of Energy Harvesting Cognitive Radio Networks

Abstract: We consider energy harvesting cognitive radio networks to improve both energy efficiency and spectral efficiency. The goal of this paper is to analyze the theoretically achievable throughput of the secondary transmitter, which harvests energy from ambient sources or wireless power transfer systems while opportunistically accessing the spectrum licensed to the primary network. By modeling the temporal correlation of the primary traffic according to a time-homogeneous discrete Markov process, we derive the upper bound on the achievable throughput as a function of the energy arrival rate, the temporal correlation of the primary traffic, and the detection threshold for a spectrum sensor. The optimal detection threshold is then derived to maximize the upper bound on the achievable throughput under an energy causality constraint and a collision constraint. The energy causality constraint mandates that the total consumed energy should not exceed the total harvested energy, while the collision constraint is required to protect the primary network from secondary transmission. Analytical results show the temporal correlation of the primary traffic to enable efficient usage of the harvested energy by preventing the secondary transmitter from accessing the spectrum that may be occupied by the primary network.

Remnant mass, spin, and recoil from spin aligned black-hole binaries

Abstract: We perform a set of 36 nonprecessing black-hole binary simulations with spins either aligned or counteraligned with the orbital angular momentum in order to model the final mass, spin, and recoil of the merged black hole as a function of the individual black-hole spin magnitudes and the mass ratio of the progenitors. We find that the maximum recoil for these configurations is ${V}_{\mathrm{max}}=526\ifmmode\pm\else\textpm\fi{}23\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, which occurs when the progenitor spins are maximal, the mass ratio is ${q}_{\mathrm{max}}={m}_{1}/{m}_{2}=0.623\ifmmode\pm\else\textpm\fi{}0.038$, the smaller black-hole spin is aligned with the orbital angular momentum, and the larger black-hole spin is counteraligned (${\ensuremath{\alpha}}_{1}=\ensuremath{-}{\ensuremath{\alpha}}_{2}=1$). This maximum recoil is about $80\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ larger than previous estimates, but most importantly, because the maximum occurs for smaller mass ratios, the probability for a merging binary to recoil faster than $400\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ can be as large as 17%, while the probability for recoils faster than $250\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ can be as large as 45% when the spins are aligned or counteraligned by accretion. We provide explicit phenomenological formulas for the final mass, spin, and recoil as a function of the individual black-hole spins and the mass difference between the two black holes. Here we include terms up through fourth order in the initial spins and mass difference and find excellent agreement (within a few percent) with independent results available in the literature. The maximum radiated energy is ${E}_{\text{rad}}/m\ensuremath{\approx}11.3%$ and final spin ${\ensuremath{\alpha}}_{\text{rem}}^{\mathrm{max}}\ensuremath{\approx}0.952$ for equal-mass, aligned, maximally spinning binaries.

Multiphase equation of state for carbon addressing high pressures and temperatures

Abstract: We present a 5-phase equation of state for elemental carbon which addresses a wide range of density and temperature conditions: $3\mathrm{g}/\mathrm{cc}l\ensuremath{\rho}l20\mathrm{g}/\mathrm{cc},0\phantom{\rule{0.28em}{0ex}}\mathrm{K}lTl\ensuremath{\infty}$. The phases considered are diamond, BC8, simple cubic, simple hexagonal, and the liquid/plasma state. The solid phase free energies are constrained by density functional theory (DFT) calculations. Vibrational contributions to the free energy of each solid phase are treated within the quasiharmonic framework. The liquid free energy model is constrained by fitting to a combination of DFT molecular dynamics performed over the range $10 000\text{K}lTl100 000\text{K}$, and path integral quantum Monte Carlo calculations for $Tg100 000\text{K}$ (both for $\ensuremath{\rho}$ between 3 and 12 g/cc, with select higher-$\ensuremath{\rho}$ DFT calculations as well). The liquid free energy model includes an atom-in-jellium approach to account for the effects of ionization due to temperature and pressure in the plasma state, and an ion-thermal model which includes the approach to the ideal gas limit. The precise manner in which the ideal gas limit is reached is greatly constrained by both the highest-temperature DFT data and the path integral data, forcing us to discard an ion-thermal model we had used previously in favor of a new one. Predictions are made for the principal Hugoniot and the room-temperature isotherm, and comparisons are made to recent experimental results.

Thermalization after/during reheating

Abstract: If reheating of the Universe takes place via Planck-suppressed decay, it seems that the thermalization of produced particles might be delayed, since they have large energy/small number densities and number violating large angle scatterings which decrease the momentum of particles by large amount are inefficient correspondingly. In this paper, we study the thermalization of such “under occupied” decay products in detail, following recent developments in understanding the thermalization of non-abelian plasma. Contrary to the above naive expectation, it is shown that in most cases thermalization after/during reheating occurs instantaneously by properly taking account of scatterings with small angles and of particles with small momenta. In particular, the condition for instantaneous thermalization before the completion of reheating is found to be $ {\alpha^{{{8 \left/ {5} \right.}}}}\gg \left( {{{{{m_{\phi }}}} \left/ {{{M_{\mathrm{pl}}}}} \right.}} \right){{\left( {{{{M_{\mathrm{pl}}^2{\varGamma_{\phi }}}} \left/ {{m_{\phi}^3}} \right.}} \right)}^{{{1 \left/ {5} \right.}}}} $ , which is much milder than that obtained in previous works with small angle scatterings taken into account.

Specific emitter identification based on Hilbert-Huang transform-based time-frequency-energy distribution features

Abstract: A novel specific emitter identification method based on transient communication signal's time-frequency-energy distribution obtained by Hilbert-Huang transform (HHT) is proposed. The transient starting point is detected using the phase-based method and the transient endpoint is detected using a self-adaptive threshold based on the HHT-based energy trajectory. Thirteen features that represent both overall and subtle transient characteristics are proposed to form a radio frequency (RF) fingerprint. The principal component analysis method is used to reduce the dimension of the feature vector and a support vector machine is used for classification. A signal acquisition system is designed to capture the signals from eight mobile phones to test the performance of the proposed method. Experimental results demonstrate that the method is effective and the proposed RF fingerprint can represent more subtle characteristics than the RF fingerprints based on instantaneous amplitude, phase, frequency and energy envelope. This method can be equally applicable for any wireless emitter to enhance the security of the wireless networks.

Interpolated-DFT-Based Fast and Accurate Frequency Estimation for the Control of Power

Abstract: The energy produced by renewable energy systems must fulfill quality requirements as defined in the respective standards and directives. Improvement of the quality could be achieved through a more accurate estimation of the frequency of the grid's signal that is used to control an inverter. This paper presents an overview of a method for spectrum interpolation and frequency estimation, and a generalized method for very accurate frequency grid estimation using the fast Fourier transform procedure coupled with maximum decay sidelobe windows. An important feature of this algorithm is the elimination of the impact associated with the conjugate's component on the estimation's outcome (i.e, the possibility of designating the frequency even if the signal's measurement time is on the order of 2.5 periods), and the implementation of the algorithm is straightforward. The results of the simulation show that the algorithm could be successfully used for a fast and accurate estimation of the grid signal frequency. The systematic frequency estimation error is approximately 5·10 -11 Hz for a 5-ms measurement window. The algorithm could be used not only for a single sinusoidal signal, but also for a multifrequency signal. This is assuming that the appropriate spectrum leakage reduction (by a time window) will be performed.

Exploiting Intrinsic Triangular Geometry in Relativistic He 3 + Au Collisions to Disentangle Medium Properties

Abstract: Recent results in $d+\mathrm{Au}$ and $p+\mathrm{Pb}$ collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from $p+\mathrm{Pb}$, $d+\mathrm{Au}$, and $^{3}\mathrm{He}+\mathrm{Au}$ or $t+\mathrm{Au}$ collisions at the same $\sqrt{{s}_{NN}}$ . Using a Monte Carlo Glauber simulation we find that a $^{3}\mathrm{He}$ or triton projectile, with a realistic wave function description, induces a significant intrinsic triangular shape to the initial medium. If the system lives long enough, this survives into a significant third-order flow moment ${v}_{3}$ even with viscous damping. By comparing systems with one, two, and three initial hot spots, one could disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools for answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

Collaborative Wireless Energy and Information Transfer in Interference Channel

Abstract: This paper studies the simultaneous wireless information and power transfer (SWIPT) in a multiuser wireless system, in which distributed transmitters send independent messages to their respective receivers, and at the same time cooperatively transmit wireless power to the receivers via energy beamforming. Accordingly, from the wireless information transmission (WIT) perspective, the system of interest can be modeled as the classic interference channel, while it also can be regarded as a distributed multiple-input multiple-output (MIMO) system for collaborative wireless energy transmission (WET). To enable both information decoding (ID) and energy harvesting (EH) in SWIPT, we adopt the low-complexity time switching operation at each receiver to switch between the ID and EH modes over scheduled time. Based on this hybrid model, we aim to characterize the achievable rate-energy (R-E) trade-offs in the multiuser SWIPT system under various transmitter-side collaboration schemes. Specifically, to facilitate the collaborative energy beamforming, we propose a new signal splitting scheme at the transmitters, where each transmit signal is generally composed of an information signal component and an energy signal component for WIT and WET, respectively. With this new scheme, first, we study the two-user SWIPT system and derive the optimal mode switching rule at the receivers and the corresponding transmit signal optimization to achieve various R-E trade-offs over the fading channel. We also compare the R-E performance of our proposed scheme with transmit energy beamforming and signal splitting against two existing schemes with partial or no cooperation of the transmitters, and show remarkable gains over these baseline schemes. Finally, the general case of SWIPT systems with more than two users is studied, for which we propose and compare two practical transmit collaboration schemes.

Energy Harvesting Broadband Communication Systems With Processing Energy Cost

Abstract: Communication over a broadband fading channel powered by an energy harvesting transmitter is studied. Assuming non-causal knowledge of energy/data arrivals and channel gains, optimal transmission schemes are identified by taking into account the energy cost of the processing circuitry as well as the transmission energy. A constant processing cost for each active sub-channel is assumed. Three different system objectives are considered: 1) throughput maximization, in which the total amount of transmitted data by a deadline is maximized for a backlogged transmitter with a finite capacity battery; 2) energy maximization, in which the remaining energy in an infinite capacity battery by a deadline is maximized such that all the arriving data packets are delivered; and 3) transmission completion time minimization, in which the delivery time of all the arriving data packets is minimized assuming infinite size battery. For each objective, a convex optimization problem is formulated, the properties of the optimal transmission policies are identified, and an algorithm which computes an optimal transmission policy is proposed. Finally, based on the insights gained from the offline optimizations, low-complexity online algorithms performing close to the optimal dynamic programming solution for the throughput and energy maximization problems are developed under the assumption that the energy/data arrivals and channel states are known causally at the transmitter.

Electron transport modeling and energy filtering for efficient thermoelectric Mg2Si1-xSnx solid solutions

Abstract: We present a comprehensive electron transport model to analyze thermoelectric properties of both $n$- and $p$-type bulk ${\text{Mg}}_{2}$${\text{Si}}_{1\text{\ensuremath{-}}x}$${\text{Sn}}_{x}$ ($0\ensuremath{\le}x\ensuremath{\le}1$) solid solutions. A temperature-dependent multiparabolic bands model is used to describe the band structures of the alloys, and the transport properties are calculated using the linearized Boltzmann transport equations under the relaxation time approximation. A variety of experimental data from literature are fitted very well by this model and analyzed for further material optimization. Our analysis shows that the compositions of $x$ = 0.6 to 0.7 exhibit the highest thermoelectric figure of merit zT among $n$-type ${\text{Mg}}_{2}$${\text{Si}}_{1\text{\ensuremath{-}}x}$${\text{Sn}}_{x}$ in the midtemperature range 600 to 900 K due to both the high power factors achieved by the convergence of the two conduction bands and low electronic thermal conductivities. For the $p$-type materials, we find that the bipolar electronic thermal conductivity is a major factor limiting the figure of merit. Low Sn content ($x$ 0.4) alloys show a larger figure of merit among the $p$-type materials due mainly to their lower bipolar thermal conductivities with larger band gaps. Finally, we propose that hot carrier energy filtering can be very useful for these alloys as it can simultaneously reduce the electronic thermal conductivity and enhance the power factor. A zT greater than 3 is possible for $n$-type ${\text{Mg}}_{2}$${\text{Si}}_{0.4}$${\text{Sn}}_{0.6}$ ($x$ = 0.6) at 700 K, if electrons with energies lower than 0.4 eV are effectively prevented from participating in transport.

Indirect-to-direct gap transition in strained and unstrained Sn x Ge 1 − x alloys

Abstract: The transition from an indirect to a direct gap semiconductor in unstrained as well as compressively and tensile strained ${\mathrm{Sn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ alloys is investigated as a function of the Sn content 0 \ensuremath{\le} $x$ \ensuremath{\le} 1 by means of both a very accurate supercell approach and the more approximate virtual crystal approximation (VCA). In the local density approximation we calculate the bowing parameter of the lattice constant of unstrained ${\mathrm{Sn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ alloys. Provided that pseudopotentials suitable for the VCA are used, the random supercell and VCA approaches yield consistent bowing parameters for the lattice constant of \ensuremath{-}0.21 and \ensuremath{-}0.28 \AA{}, respectively, in the entire Sn concentration range. The band structures and energy gaps are calculated using the modified Becke-Johnson potential, which, for Ge, yields a one-electron band gap in very good agreement with experimental data. The crossover from an indirect to a direct gap semiconducting alloy is determined at about 4.5% Sn in unstrained ${\mathrm{Sn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$. When ${\mathrm{Sn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ is grown commensurately and thus strained on Ge(100), a transition to a direct gap is also observed but at Sn concentrations of about 10%. We finally predict the direct and indirect band gaps as a function of the in-plane lattice constant and Sn concentration for ${\mathrm{Sn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ alloys grown on (100) substrates.

Joint Energy Allocation for Sensing and Transmission in Rechargeable Wireless Sensor Networks

Abstract: Different from a traditional wireless sensor network (WSN) powered by nonrechargeable batteries, the energy management policy of a rechargeable WSN needs to take into account the process of energy harvesting. In this paper, the authors study the energy allocation for sensing and transmission in an energy harvesting sensor node with a rechargeable battery and a finite data buffer. The sensor aims to maximize the expected total amount of data transmitted until the sensor stops functioning subject to time-varying energy harvesting rate, energy availability in the battery, data availability in the data buffer, and channel fading. Since the lifetime of the sensor is a random variable, the authors formulate the energy allocation problem as an infinite-horizon Markov decision process (MDP), and propose an optimal energy allocation (OEA) algorithm using the value iteration. They then consider a special case with infinite data backlog and prove that the optimal transmission energy allocation (OTEA) policy is monotonic with respect to the amount of battery energy available. Finally, they conduct extensive simulations to compare the performance of their OEA algorithm, OTEA algorithm, the finite-horizon transmission energy allocation (FHTEA) algorithm extended from [2], and the finite-horizon OEA (FHOEA) algorithm from [1]. Simulation results show that the OEA algorithm transmits the largest amount of data, and the OTEA algorithm can achieve a near-optimal performance with low computational complexity.