Showing papers on "Energy (signal processing) published in 2011"

Optimal Energy Allocation for Wireless Communications with Energy Harvesting Constraints

Abstract: We consider the use of energy harvesters, in place of conventional batteries with fixed energy storage, for point-to-point wireless communications. In addition to the challenge of transmitting in a channel with time selective fading, energy harvesters provide a perpetual but unreliable energy source. In this paper, we consider the problem of energy allocation over a finite horizon, taking into account channel conditions and energy sources that are time varying, so as to maximize the throughput. Two types of side information (SI) on the channel conditions and harvested energy are assumed to be available: causal SI (of the past and present slots) or full SI (of the past, present and future slots). We obtain structural results for the optimal energy allocation, via the use of dynamic programming and convex optimization techniques. In particular, if unlimited energy can be stored in the battery with harvested energy and the full SI is available, we prove the optimality of a water-filling energy allocation solution where the so-called water levels follow a staircase function.

Multimatrix models and tri-Sasaki Einstein spaces

Abstract: Localization methods reduce the path integrals in $\mathcal{N}\ensuremath{\ge}2$ supersymmetric Chern-Simons gauge theories on ${S}^{3}$ to multimatrix integrals. A recent evaluation of such a two-matrix integral for the $\mathcal{N}=6$ superconformal $U(N)\ifmmode\times\else\texttimes\fi{}U(N)$ Aharony-Bergman-Jafferis-Maldacena theory produced detailed agreement with the AdS/CFT correspondence, explaining, in particular, the ${N}^{3/2}$ scaling of the free energy. We study a class of $p$-matrix integrals describing $\mathcal{N}=3$ superconformal $U(N{)}^{p}$ Chern-Simons gauge theories. We present a simple method that allows us to evaluate the eigenvalue densities and the free energies in the large $N$ limit keeping the Chern-Simons levels ${k}_{i}$ fixed. The dual M-theory backgrounds are ${\mathrm{AdS}}_{4}\ifmmode\times\else\texttimes\fi{}Y$, where $Y$ are seven-dimensional tri-Sasaki Einstein spaces specified by the ${k}_{i}$. The gravitational free energy scales inversely with the square root of the volume of $Y$. We find a general formula for the $p$-matrix free energies that agrees with the available results for volumes of the tri-Sasaki Einstein spaces $Y$, thus providing a thorough test of the corresponding ${\mathrm{AdS}}_{4}/{\mathrm{CFT}}_{3}$ dualities. This formula is consistent with the Seiberg duality conjectured for Chern-Simons gauge theories.

Electromagnetic field evolution in relativistic heavy-ion collisions

Abstract: The hadron string dynamics (HSD) model is generalized to include the creation and evolution of retarded electromagnetic fields as well as the influence of the magnetic and electric fields on the quasiparticle propagation. The time-space structure of the fields is analyzed in detail for noncentral Au $+$ Au collisions at $\sqrt{{s}_{\mathit{NN}}}=200$ GeV. It is shown that the created magnetic field is highly inhomogeneous, but in the central region of the overlapping nuclei it changes relatively weakly in the transverse direction. For the impact parameter $b=10$ fm, the maximal magnetic field--- perpendicularly to the reaction plane---is obtained of order ${\mathit{eB}}_{y}/{m}_{\ensuremath{\pi}}^{2}~$5 for a very short time $~$0.2 fm/$c$, which roughly corresponds to the time of a maximal overlap of the colliding nuclei. We find that at any time, the location of the maximum in the ${\mathit{eB}}_{y}$ distribution correlates with that of the energy density of the created particles. In contrast, the electric field distribution, being also highly inhomogeneous, has a minimum in the center of the overlap region. Furthermore, the field characteristics are presented as a function of the collision energy and the centrality of the collisions. To explore the effect of the back reaction of the fields on hadronic observables, a comparison of HSD results with and without fields is exemplified. Our actual calculations show no noticeable influence of the electromagnetic fields---created in heavy-ion collisions---on the effect of the electric charge separation with respect to the reaction plane.

Multi-target tracking by continuous energy minimization

Abstract: We propose to formulate multi-target tracking as minimization of a continuous energy function. Other than a number of recent approaches we focus on designing an energy function that represents the problem as faithfully as possible, rather than one that is amenable to elegant optimization. We then go on to construct a suitable optimization scheme to find strong local minima of the proposed energy. The scheme extends the conjugate gradient method with periodic trans-dimensional jumps. These moves allow the search to escape weak minima and explore a much larger portion of the variable-dimensional search space, while still always reducing the energy. To demonstrate the validity of this approach we present an extensive quantitative evaluation both on synthetic data and on six different real video sequences. In both cases we achieve a significant performance improvement over an extended Kalman filter baseline as well as an ILP-based state-of-the-art tracker.

Laser field absorption in self-generated electron-positron pair plasma.

Abstract: Recently, much attention has been attracted to the problem of limitations on the attainable intensity of high power lasers [A. M. Fedotov et al., Phys. Rev. Lett. 105, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by a strong laser field via the development of the electromagnetic cascades. The numerical model for a self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for a not extremely high laser intensity $I\ensuremath{\sim}{10}^{24}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ achievable in the near future.

Networking low-power energy harvesting devices: Measurements and algorithms

Abstract: Recent advances in energy harvesting materials and ultra-low-power communications will soon enable the realization of networks composed of energy harvesting devices. These devices will operate using very low ambient energy, such as indoor light energy. We focus on characterizing the energy availability in indoor environments and on developing energy allocation algorithms for energy harvesting devices. First, we present results of our long-term indoor radiant energy measurements, which provide important inputs required for algorithm and system design (e.g., determining the required battery sizes). Then, we focus on algorithm development, which requires nontraditional approaches, since energy harvesting shifts the nature of energy-aware protocols from minimizing energy expenditure to optimizing it. Moreover, in many cases, different energy storage types (rechargeable battery and a capacitor) require different algorithms. We develop algorithms for determining time fair energy allocation in systems with predictable energy inputs, as well as in systems where energy inputs are stochastic.

A universal inequality for CFT and quantum gravity

Abstract: We prove that every unitary two-dimensional conformal field theory (with no extended chiral algebra, and with c, \( \tilde{c} > 1 \)) contains a primary operator with dimension ∆1 that satisfies \( 0 < {\Delta_1} < \frac{{c + \tilde{c}}}{{12}} + 0.473695 \). Translated into gravitational language using the AdS3/CFT2 dictionary, our result proves rigorously that the lightest massive excitation in any theory of 3D matter and gravity with cosmological constant Λ < 0 can be no heavier than \( {{1} \left/ {{\left( {4{G_N}} \right)}} \right.} + o\left( {\sqrt {{ - \Lambda }} } \right) \). In the flat-space approximation, this limiting mass is twice that of the lightest BTZ black hole. The derivation applies at finite central charge for the boundary CFT, and does not rely on an asymptotic expansion at large central charge. Neither does our proof rely on any special property of the CFT such as supersymmetry or holomorphic factorization, nor on any bulk interpretation in terms of string theory or semiclassical gravity. Our only assumptions are unitarity and modular invariance of the dual CFT. Our proof demonstrates for the first time that there exists a universal center-of-mass energy beyond which a theory of ”pure” quantum gravity can never consistently be extended.

Demonstration of a narrow energy spread, ∼0.5 GeV electron beam from a two-stage laser wakefield accelerator.

Abstract: Laser wakefield acceleration of electrons holds great promise for producing ultracompact stages of GeV scale, high-quality electron beams for applications such as x-ray free electron lasers and high-energy colliders. Ultrahigh intensity laser pulses can be self-guided by relativistic plasma waves (the wake) over tens of vacuum diffraction lengths, to give $g1\text{ }\text{ }\mathrm{GeV}$ energy in centimeter-scale low density plasmas using ionization-induced injection to inject charge into the wake even at low densities. By restricting electron injection to a distinct short region, the injector stage, energetic electron beams (of the order of 100 MeV) with a relatively large energy spread are generated. Some of these electrons are then further accelerated by a second, longer accelerator stage, which increases their energy to $\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{GeV}$ while reducing the relative energy spread to $l5%$ FWHM.

Summing up all genus free energy of ABJM matrix model

Abstract: The localization technique allows us to compute the free energy of the U(N) k × U(N)−k Chern-Simons-matter theory dual to type IIA strings on AdS 4 × CP 3 from weak to strong ’t Hooft coupling λ = N/k at finite N, as demonstrated by Drukker, Marino, and Putrov. In this note we study further the free energy at large ’t Hooft coupling with the aim of testing AdS/CFT at the quantum gravity level and, in particular, sum up allthe1/N corrections, apart from the worldsheet instanton contributions. The all genus partition function takes a remarkably simple form — the Airy function, $ {\text{Ai}}\left( {{{\left( {{{{\pi {k^2}}} \left/ {{\sqrt {2} }} \right.}} \right)}^{{{2} \left/ {3} \right.}}}{\lambda_{\text{ren}}}} \right) $ , with the renormalized ’t Hooft coupling λren.

Pair creation constrains superluminal neutrino propagation.

Abstract: The OPERA collaboration claims that muon neutrinos with a mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about $7.5\text{ }\text{ }\mathrm{km}/\mathrm{s}$ or 25 ppm. However, we show that superluminal neutrinos may lose energy rapidly via the bremsstrahlung of electron-positron pairs ($\ensuremath{ u}\ensuremath{\rightarrow}\ensuremath{ u}+{e}^{\ensuremath{-}}+{e}^{+}$). For the claimed superluminal velocity and at the stated mean energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. This presents a significant challenge to the superluminal interpretation of the OPERA data. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.

Monoenergetic Proton Beams Accelerated by a Radiation Pressure Driven Shock

Abstract: We report on the acceleration of impurity-free quasimononenergetic proton beams from an initially gaseous hydrogen target driven by an intense infrared ($\ensuremath{\lambda}=10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) laser. The front surface of the target was observed by optical probing to be driven forward by the radiation pressure of the laser. A proton beam of $\ensuremath{\sim}\mathrm{MeV}$ energy was simultaneously recorded with narrow energy spread ($\ensuremath{\sigma}\ensuremath{\sim}4%$), low normalized emittance ($\ensuremath{\sim}8\text{ }\text{ }\mathrm{nm}$), and negligible background. The scaling of proton energy with the ratio of intensity over density ($I/n$) confirms that the acceleration is due to the radiation pressure driven shock.

Controlling light by light with an optical event horizon.

Abstract: A novel concept for an all-optical transistor is proposed and verified numerically. This concept relies on cross-phase modulation between a signal and a control pulse. Other than previous approaches, the interaction length is extended by temporally locking control and the signal pulse in an optical event horizon, enabling continuous modification of the central wavelength, energy, and duration of a signal pulse by an up to sevenfold weaker control pulse. Moreover, if the signal pulse is a soliton it may maintain its solitonic properties during the switching process. The proposed all-optical switching concept fulfills all criteria for a useful optical transistor in [Nat. Photon. 4, 3 (2010)], in particular, fan-out and cascadability, which have previously proven as the most difficult to meet.

First measurement of the total proton-proton cross section at the LHC energy of {\surd} s =7 TeV

Abstract: TOTEM has measured the differential cross-section for elastic proton-proton scattering at the LHC energy of {\srud}s = 7TeV analysing data from a short run with dedicated large {\beta} * optics. A single exponential fit with a slope B = (20:1{\pm}0:2stat {\pm}0:3syst)GeV-2 describes the range of the four-momentum transfer squared |t| from 0.02 to 0.33 GeV2. After the extrapolation to |t| = 0, a total elastic scattering cross-section of (24:8{\pm}0:2stat {\pm}1:2syst) mb was obtained. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98:3{\pm}0:2stat {\pm}2:8syst) mb was deduced which is in good agreement with the expectation from the overall fit of previously measured data over a large range of center-of-mass energies. From the total and elastic pp cross-section measurements, an inelastic pp cross-section of (73:5{\pm}0:6stat +1:8 -1:3 syst) mb was inferred. PACS 13.60.Hb: Total and inclusive cross sections

Modeling of Node Energy Consumption for Wireless Sensor Networks

Abstract: Energy consumption is the core issue in wireless sensor networks (WSN). To generate a node energy model that can accurately reveal the energy consumption of sensor nodes is an extremely important part of protocol development, system design and performance evaluation in WSNs. In this paper, by studying component energy consumption in different node states and within state transitions, the authors present the energy models of the node core components, including processors, RF modules and sensors. Furthermore, this paper reveals the energy correlations between node components, and then establishes the node energy model based on the event-trigger mechanism. Finally, the authors simulate the energy models of node components and then evaluate the energy consumption of network protocols based on this node energy model. The proposed model can be used to analyze the WSNs energy consumption, to evaluate communication protocols, to deploy nodes and then to construct WSN applications.

System and method for three-dimensional geolocation of emitters based on energy measurements

Abstract: According to an embodiment of the present invention, a three-dimensional (3-D) energy-based emitter geolocation technique determines the geolocation of a radio frequency (RF) emitter based on energy or received signal strength (RSS) of transmitted signals The technique may be employed with small unmanned air vehicles (UAV), and obtains reliable geolocation estimates of radio frequency (RF) emitters of interest

Calculation of high energy neutrino-nucleon cross sections and uncertainties using the Martin-Stirling-Thorne-Watt parton distribution functions and implications for future experiments

Abstract: We present a new calculation of the cross sections for charged current and neutral current $\ensuremath{ u}N$ and $\overline{\ensuremath{ u}}N$ interactions in the neutrino energy range ${10}^{4}l{E}_{\ensuremath{ u}}l{10}^{12}\text{ }\text{ }\mathrm{GeV}$ using the most recent Martin-Stirling-Thorne-Watt (MSTW) parton distribution functions (PDFs), MSTW 2008. We also present the associated uncertainties propagated from the PDFs, as well as parametrizations of the cross section central values, their uncertainty bounds, and the inelasticity distributions for ease of use in Monte Carlo simulations. For the latter we only provide parametrizations for energies above ${10}^{7}\text{ }\text{ }\mathrm{GeV}$. Finally, we assess the feasibility of future neutrino experiments to constrain the $\ensuremath{ u}N$ cross section in the ultrahigh energy regime using a technique that is independent of the flux spectrum of incident neutrinos. A significant deviation from the predicted standard model cross sections could be an indication of new physics, such as extra space-time dimensions, and we present expected constraints on such models as a function of the number of events observed in a future subterranean neutrino detector.

Optimal and Sub-Optimal Spectrum Sensing of OFDM Signals in Known and Unknown Noise Variance

Abstract: We consider spectrum sensing of OFDM signals in an AWGN channel. For the case of completely known noise and signal powers, we set up a vector-matrix model for an OFDM signal with a cyclic prefix and derive the optimal Neyman-Pearson detector from first principles. The optimal detector exploits the inherent correlation of the OFDM signal incurred by the repetition of data in the cyclic prefix, using knowledge of the length of the cyclic prefix and the length of the OFDM symbol. We compare the optimal detector to the energy detector numerically. We show that the energy detector is near-optimal (within 1 dB SNR) when the noise variance is known. Thus, when the noise power is known, no substantial gain can be achieved by using any other detector than the energy detector. For the case of completely unknown noise and signal powers, we derive a generalized likelihood ratio test (GLRT) based on empirical second-order statistics of the received data. The proposed GLRT detector exploits the non-stationary correlation structure of the OFDM signal and does not require any knowledge of the noise power or the signal power. The GLRT detector is compared to state-of-the-art OFDM signal detectors, and shown to improve the detection performance with 5 dB SNR in relevant cases.

Magnetic helicity spectrum of solar wind fluctuations as a function of the angle with respect to the local mean magnetic field

Abstract: Magnetic field data acquired by the Ulysses spacecraft in high-speed streams over the poles of the Sun are used to investigate the normalized magnetic helicity spectrum {sigma}{sub m} as a function of the angle {theta} between the local mean magnetic field and the flow direction of the solar wind. This spectrum provides important information about the constituent modes at the transition to kinetic scales that occurs near the spectral break separating the inertial range from the dissipation range. The energetically dominant signal at scales near the thermal proton gyroradius k{sub perpendicular{rho}i} {approx} 1 often covers a wide band of propagation angles centered about the perpendicular direction, {theta} {approx_equal} 90{sup 0} {+-} 30{sup 0}. This signal is consistent with a spectrum of obliquely propagating kinetic Alfven waves with k{sub perpendicular} >> k{sub ||} in which there is more energy in waves propagating away from the Sun and along the direction of the local mean magnetic field than toward the Sun. Moreover, this signal is principally responsible for the reduced magnetic helicity spectrum measured using Fourier transform techniques. The observations also reveal a subdominant population of nearly parallel propagating electromagnetic waves near the proton inertial scale k{sub ||} c/{omega}{sub pi} {approx} 1more » that often exhibit high magnetic helicity |{sigma}{sub m}| {approx_equal} 1. These waves are believed to be caused by proton pressure anisotropy instabilities that regulate distribution functions in the collisionless solar wind. Because of the existence of a drift of alpha particles with respect to the protons, the proton temperature anisotropy instability that operates when T{sub pperpendicular}/T{sub p||} > 1 preferentially generates outward propagating ion-cyclotron waves and the fire-hose instability that operates when T{sub pperpendicular}/T{sub p||} < 1 preferentially generates inward propagating whistler waves. These kinetic processes provide a natural explanation for the magnetic field observations.« less

Vortex-induced dissipation in narrow current-biased thin-film superconducting strips

Abstract: A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness $d$ on the order of the coherence length $\ensuremath{\xi}$ and of width $w$ much narrower than the Pearl length $\ensuremath{\Lambda}\ensuremath{\gg}w\ensuremath{\gg}\ensuremath{\xi}$. At high bias currents ${I}^{*}lIl{I}_{c}$ the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here ${I}_{c}$ is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate ${I}^{*}$ to be roughly ${I}_{c}/3$. Furthermore, we argue that such ``hot'' vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between ${I}^{*}$ and ${I}_{c}$. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below ${I}^{*}$, that is, in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing.

First Limits on Left-Right Symmetry Scale from LHC Data

Abstract: We use the early Large Hadron Collider data to set the lower limit on the scale of left-right symmetry, by searching for the right-handed charged gauge boson ${W}_{R}$ via the final state with two leptons and two jets, for $33\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ integrated luminosity and 7 TeV center-of-mass energy This signal is kinematically observable for right-handed neutrino lighter than ${W}_{R}$ In the absence of a signal beyond the standard model background, we set the bound ${M}_{{W}_{R}}\ensuremath{\gtrsim}14\text{ }\text{ }\mathrm{TeV}$ at 95% CL This result is obtained for a range of right-handed neutrino masses of the order of few 100 GeV, assuming no accidental cancellation in right-handed lepton mixings

Collision of an innermost stable circular orbit particle around a Kerr black hole

Abstract: We derive a general formula for the center-of-mass (CM) energy for the near-horizon collision of two particles of the same rest mass on the equatorial plane around a Kerr black hole. We then apply this formula to a particle which plunges from the innermost stable circular orbit (ISCO) and collides with another particle near the horizon. It is found that the maximum value of the CM energy ${E}_{\mathrm{cm}}$ is given by ${E}_{\mathrm{cm}}/(2{m}_{0})\ensuremath{\simeq}1.40/\sqrt[4]{1\ensuremath{-}{a}_{*}^{2}}$ for a nearly maximally rotating black hole, where ${m}_{0}$ is the rest mass of each particle and ${a}_{*}$ is the nondimensional Kerr parameter. This coincides with the known upper bound for a particle which begins at rest at infinity within a factor of 2. Moreover, we also consider the collision of a particle orbiting the ISCO with another particle on the ISCO and find that the maximum CM energy is then given by ${E}_{\mathrm{cm}}/(2{m}_{0})\ensuremath{\simeq}1.77/\sqrt[6]{1\ensuremath{-}{a}_{*}^{2}}$. In view of the astrophysical significance of the ISCO, this result implies that particles can collide around a rotating black hole with an arbitrarily high CM energy without any artificial fine-tuning in an astrophysical context if we can take the maximal limit of the black hole spin or ${a}_{*}\ensuremath{\rightarrow}1$. On the other hand, even if we take Thorne's bound on the spin parameter into account, highly or moderately relativistic collisions are expected to occur quite naturally, for ${E}_{\mathrm{cm}}/(2{m}_{0})$ takes 6.95 (maximum) and 3.86 (generic) near the horizon and 4.11 (maximum) and 2.43 (generic) on the ISCO for ${a}_{*}=0.998$. This implies that high-velocity collisions of compact objects are naturally expected around a rapidly rotating supermassive black hole. Implications to accretion flows onto a rapidly rotating black hole are also discussed.

Maximizing DC power in energy harvesting circuits using multi-sine excitation

Abstract: Summary form only given, as follows. This paper presents an approach to signal excitation specially designed to improve the DC power obtained in a RF to DC converter and consequently its RF-DC efficiency conversion. In this sense, a multi-sine signal is used as the excitation, and it is proved either theoretically, by simulations and by measurements, that a multi-sine signal with 0° phase relationship between the tones present better DC values in energy harvesters, when compared with a single tone excitation with the same input power

Theoretical Unimolecular Kinetics for CH4 + M ⇄ CH3 + H + M in Eight Baths, M = He, Ne, Ar, Kr, H2, N2, CO, and CH4

Abstract: Ensembles of classical trajectories are used to study collisional energy transfer in highly vibrationally excited CH4 for eight bath gases. Several simplifying assumptions for the CH4 + M interaction potential energy surface are tested against full dimensional direct dynamics trajectory calculations for M = He, Ne, and H2. The calculated energy transfer averages are confirmed to be sensitive to the shape of the repulsive wall of the intermolecular potential, with an exponential repulsive wall required for quantitative predictions. For the diatomic baths, the usual “separable pairwise” approximation for the interaction potential is unable to describe the orientation dependence of the interaction potential accurately, and the ambiguity in the resulting parametrizations contributes an additional uncertainty to the predicted energy transfer averages of 20–40%. On the other hand, the energy transfer averages are shown to be insensitive to the level of theory used to describe the intramolecular CH4 potential, w...

Probability distribution of Majorana end-state energies in disordered wires.

Abstract: One-dimensional topological superconductors harbor Majorana bound states at their ends. For superconducting wires of finite length $L$, these Majorana states combine into fermionic excitations with an energy ${\ensuremath{\epsilon}}_{0}$ that is exponentially small in $L$. Weak disorder leaves the energy splitting exponentially small, but affects its typical value and causes large sample-to-sample fluctuations. We show that the probability distribution of ${\ensuremath{\epsilon}}_{0}$ is log normal in the limit of large $L$, whereas the distribution of the lowest-lying bulk energy level ${\ensuremath{\epsilon}}_{1}$ has an algebraic tail at small ${\ensuremath{\epsilon}}_{1}$. Our findings have implications for the speed at which a topological quantum computer can be operated.

Existence and asymptotic stability of a viscoelastic wave equation with a delay

Abstract: In this paper, we consider the viscoelastic wave equation with a delay term in internal feedbacks; namely, we investigate the following problem $$u_{tt}(x,t)-\Delta u(x,t)+\int\limits_{0}^{t}g(t-s){\Delta}u(x,s){d}s+\mu_{1}u_{t}(x,t)+\mu_{2} u_{t}(x,t-\tau)=0$$ together with initial conditions and boundary conditions of Dirichlet type. Here $${(x,t)\in\Omega\times (0,\infty), g}$$ is a positive real valued decreasing function and μ 1, μ 2 are positive constants. Under an hypothesis between the weight of the delay term in the feedback and the weight of the term without delay, using the Faedo–Galerkin approximations together with some energy estimates, we prove the global existence of the solutions. Under the same assumptions, general decay results of the energy are established via suitable Lyapunov functionals.

Core-crust transition in neutron stars: predictivity of density developments

Abstract: The possibility to draw links between the isospin properties of nuclei and the structure of compact stars is a stimulating perspective. In order to pursue this objective on a sound basis, the correlations from which such links can be deduced have to be carefully checked against model dependence. Using a variety of nuclear effective models and a microscopic approach, we study the relation between the predictions of a given model and those of a Taylor density development of the corresponding equation of state: this establishes to what extent a limited set of phenomenological constraints can determine the core-crust transition properties. From a correlation analysis, we show that (a) the transition density ${\ensuremath{\rho}}_{t}$ is mainly correlated with the symmetry energy slope $L$, (b) the proton fraction ${Y}_{p,t}$ with the symmetry energy and symmetry energy slope $(J,L)$ defined at saturation density, or, even better, with the same quantities defined at $\ensuremath{\rho}=0.1$ fm${}^{\ensuremath{-}3}$, and (c) the transition pressure ${P}_{t}$ with the symmetry energy slope and curvature $(L,{K}_{\mathrm{sym}})$ defined at $\ensuremath{\rho}=0.1$ fm${}^{\ensuremath{-}3}$.

Spatially resolved femtosecond pump-probe study of topological insulator Bi 2 Se 3

Abstract: Carrier and phonon dynamics in Bi${}_{2}$Se${}_{3}$ crystals are studied by a spatially resolved ultrafast pump-probe technique. Pronounced oscillations in differential reflection are observed with two distinct frequencies and are attributed to coherent optical and acoustic phonons, respectively. The rising time of the signal indicates that the thermalization and energy relaxation of hot carriers are both sub-ps in this material. We found that the thermalization and relaxation time decreases with the carrier density. The expansion of the differential reflection profile allows us to estimate an ambipolar carrier diffusion coefficient on the order of 500 cm${}^{2}$/s. A long-term slow expansion of the profile shows a thermal diffusion coefficient of 1.2 cm${}^{2}$/s.

Quarkonium states in a complex-valued potential

Abstract: We calculate quarkonium binding energies using a realistic complex-valued potential for both an isotropic and anisotropic quark-gluon plasma. We determine the disassociation temperatures of the ground and first excited states considering both the real and imaginary parts of the binding energy. We show that the effect of momentum-space anisotropy is smaller on the imaginary part of the binding energy than on the real part of the binding energy. In the case that one assumes an isotropic plasma, we find disassociation temperatures for the $J/\ensuremath{\psi}$, $\ensuremath{\Upsilon}$, and ${\ensuremath{\chi}}_{b}$ of $2.3{T}_{c}$, $2.9{T}_{c}$, and $1.8{T}_{c}$, respectively. We find that a finite oblate momentum-space anisotropy increases the disassociation temperature for all states considered and results in a splitting of the $p$-wave states associated with the ${\ensuremath{\chi}}_{b}$ first excited state of bottomonium.

Carrier density and compensation in semiconductors with multiple dopants and multiple transition energy levels: Case of Cu impurities in CdTe

Abstract: Doping is one of the most important issues in semiconductor physics. In many cases, when people describe carrier concentration as a function of dopant density and Fermi energy, they usually assume only one type of dopant with single transition energy level in the system. However, in reality, the situation is often more complicated, that is, in a semiconductor device, it usually contains multidopants and each can have multitransition energy levels. In this paper, using detailed balance theory and first-principles calculated defect formation energies and transition energy levels, we derive formulas to calculate carrier density for semiconductor with multidopants and multitransition energy levels. As an example, we studied CdTe doped with Cu, in which ${\mathrm{V}}_{\mathrm{Cd}}$, ${\mathrm{Cu}}_{\mathrm{Cd}}$, and ${\mathrm{Cu}}_{\mathrm{i}}$ are the dominant defects/impurities. We show that in this system, when Cu concentration increases, the doping properties of the system can change from a poor p-type, to a poorer p-type, to a better p-type, and then to poor p-type again, in good agreement with experimental observations.