Energy Density Fluctuations Research Articles

Optical phonon dynamics and electronic fluctuations in the Dirac semimetal Cd3As2

Raman scattering in the three-dimensional Dirac semimetal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ shows an intricate interplay of electronic and phonon degrees of freedom. We observe resonant phonon scattering due to interband transitions, an anomalous anharmonicity of phonon frequency and intensity, as well as quasielastic $(E\ensuremath{\sim}0)$ electronic scattering. The latter two effects are governed by a characteristic temperature scale ${T}^{*}\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ that is related to mutual fluctuations of lattice and electronic degrees of freedom. A refined analysis shows that this characteristic temperature corresponds to the energy of optical phonons which couple to interband transitions in the Dirac states of $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$. As electron-phonon coupling in a topological semimetal is primarily related to phonons with finite momenta, the back action on the optical phonons is only observed as anharmonicities via multiphonon processes involving a broad range of momenta. The resulting energy density fluctuations of the coupled system have previously only been observed in low dimensional or frustrated spin systems with suppressed long range ordering.

Thermodynamics of Low-Dimensional Trapped Fermi Gases

The effects of low dimensionality on the thermodynamics of a Fermi gas trapped by isotropic power-law potentials are analyzed. Particular attention is given to different characteristic temperatures that emerge, at low dimensionality, in the thermodynamic functions of state and in the thermodynamic susceptibilities (isothermal compressibility and specific heat). An energy-entropy argument that physically favors the relevance of one of these characteristic temperatures, namely, the nonvanishing temperature at which the chemical potential reaches the Fermi energy value, is presented. Such an argument allows interpreting the nonmonotonic dependence of the chemical potential on temperature, as an indicator of the appearance of a thermodynamic regime, where the equilibrium states of a trapped Fermi gas are characterized by larger fluctuations in energy and particle density as is revealed in the corresponding thermodynamics susceptibilities.

Particle-in-cell Simulations of Electron and Ion Dissipation by Whistler Turbulence: Variations with Electron β

Abstract Two ensembles of three-dimensional particle-in-cell (PIC) simulations of the forward cascade of decaying whistler turbulence have been carried out on a model of collisionless, homogeneous, magnetized plasma with parameters similar to those of the solar wind near Earth. Initial, relatively isotropic, narrowband spectra of relatively long wavelength modes cascade to anisotropic, broadband spectra of magnetic fluctuations at shorter wavelengths. Electron and ion dissipation rates are computed as functions of the initial electron beta, β e, over the range 0.1 ≤ β e ≤ 5.0, where this quantity is varied by changes in the background magnetic field magnitude B o. Ensemble One holds the value of the dimensionless initial magnetic fluctuation energy density ϵ o ≡ Σk constant; Ensemble Two follows solar wind observations, imposing the initial condition ϵ o = 0.20 β e. In both ensembles, the maximum dissipation rate of the electrons, Q e, and the maximum dissipation rate of the ions, Q i, satisfy Q e ≫ Q i. In Ensemble One, both dissipation rates scale approximately as , whereas over 0.1 ≤ β e ≤ 1.0 in Ensemble Two, Q e is approximately constant while Q i scales approximately as . These results, when combined with conclusions from earlier PIC simulations, suggest that sufficiently long wavelength and sufficiently large-amplitude magnetosonic-whistler turbulence at sufficiently large β e may heat ions more rapidly than electrons.

Scalar and vector perturbations in a universe with discrete and continuous matter sources

We study a universe filled with dust-like matter in the form of discrete inhomogeneities (e.g., galaxies and their groups and clusters) and two sets of perfect fluids with linear and nonlinear equations of state, respectively. The background spacetime geometry is defined by the FLRW metric. In the weak gravitational field limit, we develop the first-order scalar and vector cosmological perturbation theory. Our approach works at all cosmological scales (i.e. sub-horizon and super-horizon ones) and incorporates linear and nonlinear effects with respect to energy density fluctuations. We demonstrate that the scalar perturbation (i.e. the gravitational potential) as well as the vector perturbation can be split into individual contributions from each matter source. Each of these contributions satisfies its own equation. The velocity-independent parts of the individual gravitational potentials are characterized by a finite time-dependent Yukawa interaction range being the same for each individual contribution. We also obtain the exact form of the gravitational potential and vector perturbation related to the discrete matter sources. The self-consistency of our approach is thoroughly checked. The derived equations can form the theoretical basis for numerical simulations for a wide class of cosmological models.

RECONNECTION PROPERTIES OF LARGE-SCALE CURRENT SHEETS DURING CORONAL MASS EJECTION ERUPTIONS

ABSTRACT We present a detailed analysis of the properties of magnetic reconnection at large-scale current sheets (CSs) in a high cadence version of the Lynch & Edmondson 2.5D MHD simulation of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the resistive tearing and break-up of the three main CSs into chains of X- and O-type null points and follow the dynamics of magnetic island growth, their merging, transit, and ejection with the reconnection exhaust. For each CS, we quantify the evolution of the length-to-width aspect ratio (up to ∼100:1), Lundquist number (∼103), and reconnection rate (inflow-to-outflow ratios reaching ∼0.40). We examine the statistical and spectral properties of the fluctuations in the CSs resulting from the plasmoid instability, including the distribution of magnetic island area, mass, and flux content. We show that the temporal evolution of the spectral index of the reconnection-generated magnetic energy density fluctuations appear to reflect global properties of the CS evolution. Our results are in excellent agreement with recent, high-resolution reconnection-in-a-box simulations even though our CSs’ formation, growth, and dynamics are intrinsically coupled to the global evolution of sequential sympathetic coronal mass ejection eruptions.

About Dark Energy and Dark Matter in a Three-Dimensional Quantum Vacuum Model

A model of a three-dimensional quantum vacuum based on Planck energy density as a universal property of a granular space is suggested. The possibility to provide an unifying explanation of dark matter and dark energy as phenomena linked with the fluctuations of the three-dimensional quantum vacuum is explored. The changes and fluctuations of the quantum vacuum energy density generate a curvature of space–time similar to the curvature produced by a “dark energy” density. The formation of large scale structures in the universe associated to the flattening of the orbital speeds of the spiral galaxies can be explained in terms of primary fluctuations of the quantum vacuum energy density without attracting the idea of dark matter.

About a Three-Dimensional Quantum Vacuum as the Ultimate Origin of Gravity, Electromagnetic Field, Dark Energy ... and Quantum Behavior

A unification model where matter is a structure of energy of a three-dimensional quantum vacuum and diminishes its energy density is proposed. Mass and gravity are carried by variable energy density of the three-dimensional quantum vacuum. Electric field and magnetic field are carried by regions of polarized quantum vacuum generated by appropriate oscillations depending on fluctuations of the quantum vacuum energy density. The quantum behavior of matter derives directly from elementary energy fluctuations of the three-dimensional quantum vacuum. Dark energy is itself energy of the three-dimensional quantum vacuum.

Decorrelation of anisotropic flow along the longitudinal direction

The initial energy density distribution and fluctuation in the transverse direction lead to anisotropic flows of final hadrons through collective expansion in high-energy heavy-ion collisions. Fluctuations along the longitudinal direction, on the other hand, can result in decorrelation of anisotropic flows in different regions of pseudo rapidity ($\eta$). Decorrelation of the $2$nd and $3$rd order anisotropic flows with different $\eta$ gaps for final charged hadrons in high-energy heavy-ion collisions is studied in an event-by-event (3+1)D ideal hydrodynamic model with fully fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. The decorrelation of anisotropic flows of final hadrons with large $\eta$ gaps are found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The decorrelation is found to consist of both a linear twist and random fluctuation of the event-plane angles. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flows in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation, indicating larger longitudinal fluctuations at lower beam energies. Our study also calls into question some of the current experimental methods for measuring anisotropic flows and extraction of transport coefficients through comparisons to hydrodynamic simulations that do not include longitudinal fluctuations.

Non-Gaussian normal diffusion induced by delocalization.

Non-Gaussian normal diffusion, i.e., the probability density function (PDF) is non-Gaussian but the mean squared displacement (MSD) depends on time linearly, has been observed in particle motions. Here we show by numerical simulations that this phenomenon may manifest itself in energy diffusion along a lattice at a nonzero, finite temperature. The studied model is a one-dimensional disordered lattice with on-site potential. We find that the energy density fluctuations are spatially localized if the nonlinear interaction is suppressed, but may spread with a non-Gaussian PDF and a linear time-dependent MSD when the nonlinear interaction is turned on. Our analysis suggests that the mechanism lies in the delocalization properties of the localized modes.

Fluid dynamic propagation of initial baryon number perturbations on a Bjorken flow background

Baryon number density perturbations offer a possible route to experimentally measure baryon number susceptibilities and heat conductivity of the quark gluon plasma. We study the fluid dynamical evolution of local and event-by-event fluctuations of baryon number density, flow velocity and energy density on top of a (generalized) Bjorken expansion. To that end we use a background-fluctuation splitting and a Bessel-Fourier decomposition for the fluctuating part of the fluid dynamical fields with respect to the azimuthal angle, the radius in the transverse plane and rapidity. We examine how the time evolution of linear perturbations depends on the equation of state as well as on shear viscosity, bulk viscosity and heat conductivity for modes with different azimuthal, radial and rapidity wave numbers. Finally we discuss how this information is accessible to experiments in terms of the transverse and rapidity dependence of correlation functions for baryonic particles in high energy nuclear collisions.

Influence of thermodynamic properties of a thermo-acoustic emitter on the efficiency of thermal airborne ultrasound generation

In this work we experimentally verify the theoretical prediction of the recently published Energy Density Fluctuation Model (EDF-model) of thermo-acoustic sound generation. Particularly, we investigate experimentally the influence of thermal inertia of an electrically conductive film on the efficiency of thermal airborne ultrasound generation predicted by the EDF-model. Unlike widely used theories, the EDF-model predicts that the thermal inertia of the electrically conductive film is a frequency-dependent parameter. Its influence grows non-linearly with the increase of excitation frequency and reduces the efficiency of the ultrasound generation. Thus, this parameter is the major limiting factor for the efficient thermal airborne ultrasound generation in the MHz-range. To verify this theoretical prediction experimentally, five thermo-acoustic emitter samples consisting of Indium-Tin-Oxide (ITO) coatings of different thicknesses (from 65nm to 1.44μm) on quartz glass substrates were tested for airborne ultrasound generation in a frequency range from 10kHz to 800kHz. For the measurement of thermally generated sound pressures a laser Doppler vibrometer combined with a 12μm thin polyethylene foil was used as the sound pressure detector. All tested thermo-acoustic emitter samples showed a resonance-free frequency response in the entire tested frequency range. The thermal inertia of the heat producing film acts as a low-pass filter and reduces the generated sound pressure with the increasing excitation frequency and the ITO film thickness. The difference of generated sound pressure levels for samples with 65nm and 1.44μm thickness is in the order of about 6dB at 50kHz and of about 12dB at 500kHz. A comparison of sound pressure levels measured experimentally and those predicted by the EDF-model shows for all tested emitter samples a relative error of less than ±6%. Thus, experimental results confirm the prediction of the EDF-model and show that the model can be applied for design and optimization of thermo-acoustic airborne ultrasound emitters.

Mode couplings and resonance instabilities in finite dust chains.

Employing a numerical simulation, the normal modes are investigated for finite, one-dimensional horizontal dust chains in complex plasma. Mode couplings induced by the ion flow within the sheath are identified in the mode spectra and the coupling rules are determined. Two types of resonance-induced instabilities are observed, one bidirectional and one unidirectional. Bidirectional instability is found to cause melting of the chain with the melting proceeding via a two-step process which obeys the Lindemann criterion. The relationship between the normal mode spectra observed in finite systems and the wave dispersion relations seen in larger systems was also examined using a dust chain model. For this case, the dispersion relation was obtained through multiplication of the mode spectra matrix by a transition matrix. The resulting dispersion relations exhibit both the general features observed in larger crystals as well as several characteristics unique to finite systems, such as discontinuities and strong energy-density fluctuations.

Assessment of Wind Shear and Wind Energy Potential in the Baltic Sea Region of Latvia

Abstract The paper is devoted to the investigation into the wind energy potential based on long-term observations of the wind speed and energy density fluctuations at heights from 10 to 160 m on the Baltic Sea coast of Latvia. During the observations (2004 - 2013), the wind speed and direction values were measured, and the statistical database was accumulated using a LOGGER 9200 Symphonie measuring systems mounted on 60 m masts - one on the western coast and another on the north-east of Latvia. From June 2011 to May 2012, these measurements were complemented with the data for the heights from 40 to 160 m obtained by means of a ZephIR lidar and with the metrological data provided by “Latvian Environment, Geology and Meteorology Centre” for the same period. The graphs of seasonal fluctuations in the wind speed were obtained for the heights up to 160 m by measurements over the period of 2007 - 2013. The results of the research on the wind speed distribution up to 200 m are promising for evaluation of the wind energy potential of Latvia and will be helpful in assessment of prospective sites for construction of WPPs.

Numerical investigation of short-pulse laser radiation propagation in a turbulent atmosphere

An algorithm is presented for the numerical simulation of short-pulse optical radiation propagation in a turbulent atmosphere on the basis of the solution to the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. We present examples of the use of this algorithm for simulating the propagation of a pulsed coherent spatially limited beam and a plane wave. It is shown that in the regime of strong optical turbulence the relative variance of fluctuations of energy density of femtosecond radiation becomes much smaller than the relative variance of the intensity of cw radiation.

Space-Time Curvature Of General Relativity And Energy Density Of A Three-Dimensional Quantum Vacuu

AbstractA three-dimensional quantum vacuum condensate is introduced as a fundamental medium from which gravity emerges in a geometro-hydrodynamic limit. In this approach, the curvature of space-time characteristic of general relativity is obtained as a mathematical value of a more fundamental actual variable energy density of quantum vacuum which has a concrete physical meaning. The fluctuations of the quantum vacuum energy density suggest an interesting solution for the dark energy problem.

Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.

Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere have been studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It has been shown that under conditions of strong optical turbulence, the relative variance of energy density fluctuations of pulsed radiation of femtosecond duration becomes much less than the relative variance of intensity fluctuations of continuous-wave radiation. The spatial structure of fluctuations of the energy density with a decrease of the pulse duration becomes more large-scale and homogeneous. For shorter pulses the maximal value of the probability density distribution of energy density fluctuations tends to the mean value of the energy density.

TURBULENCE TRANSPORT MODELING OF THE TEMPORAL OUTER HELIOSPHERE

The solar wind can be regarded as a turbulent magnetofluid, evolving in an expanding solar wind and subject to turbulent driving by a variety of in situ sources. Furthermore, the solar wind and the drivers of turbulence are highly time-dependent and change with solar cycle. Turbulence transport models describing low-frequency magnetic and velocity fluctuations in the solar wind have so far neglected solar cycle effects. Here we consider the effects of solar cycle variability on a turbulence transport model developed by Zank et al. This model is appropriate for the solar wind beyond about 1 AU, and extensions have described the steady-state dependence of the magnetic energy density fluctuations, correlation length, and solar wind temperature throughout the outer heliosphere. We find that the temporal solar wind introduces a periodic variability, particularly beyond ~10 AU, in the magnetic energy density fluctuations, correlation length, and solar wind temperature. The variability is insufficient to account for the full observed variability in these quantities, but we find that the time-dependent solutions trace the steady-state solutions quite well, suggesting that the steady-state models are reasonable first approximations.

Minimal extension of General Relativity: Alternative gravity model with non-minimal coupling between matter and curvature

We examine an extension of General Relativity with an explicit non-minimal coupling between matter and curvature. The purpose of this work is to present an overview of the implications of the latter to various contexts, ranging from astrophysical matter distributions to a cosmological setting. Various results are discussed, including the impact of this non-minimal coupling on the choice of Lagrangian density, on a mechanism to mimic galactic and cluster dark matter, on the possibility of accounting for the accelerated expansion of the Universe, energy density fluctuations and modifications to post-inflationary reheating. The equivalence between a model exhibiting a non-minimal coupling and multi-scalar-theories is also discussed.

Investigation of Wind Energy Distribution in Height in Latvia

In the National Development Plan of Latvia for the time 2014 – 2020 a significant role is assigned to the renewable energy, whose share in the total energy production should be 40 %. This will facilitate the efficient use of wind energy. The paper is devoted to the investigation into the wind energy potential based on long-term observations of the wind speed and energy density fluctuations at heights from 10 to 160 m in the Latvian territory and on the coast of Baltic Sea.The wind speed and wind direction values were measured and the statistical database has been accumulated during long-term observations in 2004 – 2013 using a LOGGER 9200 Symphonie measuring systems mounted on 60 m masts – one on the western coast and the second on the north-east of Latvia. From June 2011 to May 2012, these measurements were complemented with the data for the heights from 40 to 160 m obtained by means of a ZephIR lidar located on the western coast of Latvia and with the metrological data provided by “Latvian Environment, Geology and Meteorology Centre” for the same period. The results are presented in the form of tables, bar charts and graphs. The graphs of seasonal fluctuations in the wind speed have been obtained for the heights up to 160 m by measurements over the period of 2007 – 2013. The histograms are composed for the relative frequency of repetition of the wind speed. The wind speed distribution on heights up to 200 m are analysed and the coefficients of approximating functions for two areas with different terrain types are calculated. Extrapolation results of the distribution curves of wind velocity and density mean values on heights up to 200 m are presented. The results of the research on the wind speed distribution up to 200 m are promising for evaluation of the wind energy potential in Latvia and should help in assessment of prospective sites for construction of WPPs.

Generalised hydrodynamic description of the time correlation functions of liquid metals: ab initio molecular dynamics study

A new methodology of calculation of dispersion and damping of collective excitations from ab initio molecular dynamics (AIMD) of liquid metals is proposed. It is suggested to use for the analysis of AIMD-derived time correlation functions a thermo-viscoelastic dynamic model within an approach of the generalised collective modes. The proposed scheme, in which the viscoelastic matrix elements of the generalised hydrodynamic matrix are directly calculated from AIMD and the matrix elements requiring knowledge of energy density fluctuations in the system are treated as fitting parameters, allows to recover AIMD time correlation functions in a wide range of wave numbers. The dispersion and damping of collective excitations are obtained as a complex-conjugated pair of the generalised hydrodynamic matrix. An issue of sum rules in the proposed scheme is discussed. The methodology is applied for calculations of dispersion and damping of generalised acoustic modes in molten lithium.