Ratio Of Energy Density Research Articles

A realization of sound focused personal audio system using acoustic contrast control

A personal audio system that does not use earphone or any wire would have great interest and potential impact on the audio industries. In this study, a line array speaker system is used to localize sound in the listening zone. The contrast control [Choi, J.-W. and Kim, Y.-H. (2002). J. Acoust. Soc. Am. 111, 1695-1700] is applied, which is a method to make acoustically bright zone around the user and acoustically dark zone in other regions by maximizing the ratio of acoustic potential energy density between the bright and the dark zone. This ratio is regarded as acoustic contrast, analogous with what is used for optical devices. For the evaluation of the performance of acoustic contrast control, experiments are performed and the results are compared with those of uncontrolled case and time reversal array.

Self-consistent current structures in a relativistic collisionless plasma

Based on the method of invariants of particle motion in a relativistic collisionless plasma, we obtain a series of exact nonlinear solutions describing stationary neutral current-carrying structures with self-consistent magnetic field in planar, cylindrical, and 2D geometries. The solutions correspond to space-inhomogeneous anisotropic particle distributions and have a functional degree of freedom, i.e., they do not require a known fixed form of energy distribution. Physical properties of the current sheets and filaments, including current localization and value, degree of anisotropy of the particle distribution, and constraints on the particle and magnetic-field energy-density ratio, are discussed.

Forbush decreases and turbulence levels at coronal mass ejection fronts

Aims. We seek to estimate the average level of MHD turbulence near coronal mass ejection (CME) fronts as they propagate from the Sun to the Earth. Methods. We examined the cosmic ray data from the GRAPES-3 tracking muon telescope at Ooty, together with the data from other sources for three closely observed Forbush decrease events. Each of these event is associated with frontside halo coronal mass ejections (CMEs) and near-Earth magnetic clouds. The associated Forbush decreases are therefore expected to have significant contributions from the cosmic-ray depressions inside the CMEs/ejecta. In each case, we estimate the magnitude of the Forbush decrease using a simple model for the diffusion of high-energy protons through the largely closed field lines enclosing the CME as it expands and propagates from the Sun to the Earth. The diffusion of high-energy protons is inhibited by the smooth, large-scale magnetic field enclosing the CME and aided by the turbulent fluctuations near the CME front. We use estimates of the cross-field diffusion coefficient D ⊥ derived from the published results of extensive Monte Carlo simulations of cosmic rays propagating through turbulent magnetic fields. We then compare our estimates with the magnitudes of the observed Forbush decreases. Results. Our method helps constrain the ratio of energy density in the turbulent magnetic fields to that in the mean magnetic fields near the CME fronts. This ratio is found to be ∼2% for the 2001 April 11 Forbush decrease event, ∼6% for the 2003 November 20 Forbush decrease event and ∼249% for the much more energetic event of 2003 October 29.

Static Dielectric Constant of Room Temperature Ionic Liquids: Internal Pressure and Cohesive Energy Density Approach

Measurements of the static dielectric constant (epsilon) of ionic liquids (ILs) are very difficult because of the decay of field by the ionic conductivity of ILs. Herein, we describe an easy method for the prediction of epsilon of various imidazolium-based ILs [C_n mim] from n, i.e. the ratio of internal pressure (P_i) and cohesive energy density (ced). A calibration curve of n vs epsilon for conventional organic solvents (mainly the linear alcohols) has been used to estimate the epsilon of the ILs. Estimated epsilon values for ILs having the anions [Cl]-, [BF 4]-, [PF 6]-, [TfO]-, and [Tf 2N]- showed a very good comparison with the literature results, whereas ILs having the anions [C_n OSO3]- tend to deviate from such correlation. Also, for a series of ILs having a common anion, the epsilon is shown to follow a very good correlation with the molecular volumes. Predicted values show that both the nature of the anion and alkyl chain length of the cation contribute significantly to the epsilon of the ILs. The method developed makes use of properties which can be either experimentally determined or estimated with good accuracy and can be extended to the other categories of ILs with ease and reasonable accuracy.

Phase transition in Schwarzschild-de Sitter spacetime

Using a static massive spherically symmetric scalar field coupled to gravity in the Schwarzschild-de Sitter (SdS) background, first we consider some asymptotic solutions near horizon and their local equations of state (E.O.S.) on them. We show that near cosmological and event horizons our scalar field behaves as a dust. At the next step near two pure de Sitter or Schwarzschild horizons we obtain a coupling dependent pressure to energy density ratio. In the case of a minimally coupling this ratio is −1 which springs to the mind thermodynamical behavior of dark energy. If having a negative pressure behavior near these horizons we concluded that the coupling constant must be ξ<¼. Therefore we derive a new constraint on the value of our coupling ξ. These two different behaviors of unique matter in the distinct regions of spacetime at present era can be interpreted as a phase transition from dark matter to dark energy in the cosmic scales and construct a unified scenario.

The nickel–carbon asymmetric supercapacitor—Performance, energy density and electrode mass ratios

The performance of nickel hydroxide/carbon asymmetric supercapacitors has been studied with a range of positive and negative active material ratios. The utilisation of the nickel hydroxide electrode in asymmetric supercapacitors was found to be a function of the mass ratio of the positive and negative electrode materials and not independent as previously assumed. Previous models describing the behaviour of asymmetric supercapacitors assumed that the voltage swing was entirely due to the polarisable electrode. These models were found to be inadequate for describing the rate dependant charge/discharge behaviour of asymmetric supercapacitors. The mass ratio of the active materials was determined to be an important factor in predicting the observed behaviour and has been incorporated into an improved model.

Intensive radiosonde observations of gravity waves in the lower atmosphere over Yichang (111°18´ E, 30°42´ N), China

Abstract. The characteristics of dynamical and thermal structures and inertial gravity waves (GWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) were statistically studied by using the data from intensive radiosonde observations in August 2006 (summer month) and January 2007 (winter month) on an eight-times-daily basis. The background atmosphere structures observed in different months exhibit evident seasonal differences, and the zonal wind in winter has a prominent tropospheric jet with a maximum wind speed of about 60 ms−1 occurring at the height of 11.5 km. The statistical results of the inertial GWs in our two-month observations are generally consistent with previous observations in the mid-latitudes. In the summer month, the mean intrinsic frequency and vertical wavelength of the inertial GWs in the troposphere are still larger than those in the lower stratosphere with the absence of intensive tropospheric jets, suggesting that the Doppler shifting due to the tropospheric jets cannot completely account for the differences between the GWs in the troposphere and lower stratosphere. Compared with the observations in the summer month, some interesting seasonal characteristics of the GWs are revealed by the observations in the winter month: 1) more and stronger tropospheric GWs are observed in the winter month; 2) less and weaker GWs are observed in the lower stratosphere in winter; 3) the ratio of the mean GW kinetic energy density to potential energy density is smaller than 1 in winter, which contrasts to that in summer. Most of the seasonal differences can be explained by the intensive tropospheric jets in winter. In both the summer and winter months, the fitted spectral slopes of the vertical wave number spectra for GWs are generally smaller than the canonical spectral slope of −3. Correlation analyses suggest that the tropospheric jet induced wind shear is the dominant source for GWs in both the troposphere and lower stratosphere. Moreover, the tropospheric (lower stratospheric) GWs are found to be modulated by the quasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs are relatively weak.

Disproportionate available to dissipated energy density model related to emission of CO 2 and evaluation of structural energy efficiency

Continuing deterioration of the climate has been attributed to the notoriously low efficiency (30–40%) of power generation plants and energy conversion processes in general. This is not because of the shortcoming of technical know how but rather the lack of effective policy making. The need for a model that can rank the energy based efficiency of housing and building is apparent. Consistency can then be achieved to make check and balance of energy thresholds. The available and dissipated energy density ratio is chosen as the pertinent parameter for reaching the tolerable threshold of CO 2 at the time t ∗. This concept was applied to three models, namely the IPPC (ISP92a), K-e-a and S&P, each of which would yield different years for the CO 2 level to reach 700 ppm as the assumed tolerable level. The estimated years are t a = 2090 for IPPC (ISP92a), t k = 2066 for K-e-a and t ∗ = 2077 for S&P model. Note that the models of IPPC (ISP92a) and K-e-a are, respectively, the upper and lower limits. The time t ∗ = 2077 to point 6 ∗ in a time plot of the available to dissipated energy density ratio. This happens to correspond with the result for the S&P model that is close to being the average of t a and t k . The means for quantifying the efficiency of stationary structures and high speed vehicles are also defined and computed. The operating efficiency of ordinary buildings can be improved from about 30% to 50% by adapting energy saving technologies. The efficiencies of the Boeing 787-3, -8 and -9 that use 50% composite material air transports were found to be 38.7%, 49.9% and 53.0%, respectively. The metal structure Boeing 757-200 had a considerable lower efficiency of 28%. While the Boeing 787-9 has the highest passenger capacity and hence the largest energy dissipation but it has the highest efficiency. This is because the 787-9 has the lowest dissipation to available energy density ratio. The consideration of energy efficiency is vital to controlling the emission of green house gas such as carbon dioxide and nitrous oxide.

Analytical Solutions for Expanding Fireballs

Many models of gamma-ray bursts (GRBs) as well as of soft gamma repeaters (SGRs) involve a fireball — an optically thick concentration of radiation energy with a high ratio of energy density to rest mass. We study the asymptotic behavior of an ultrarelativistic fireball consisting of electron-positron pairs and photons. We show that in the ultrarelativistic limit, after photons decouple from the pairs, the photon distribution function remains a blackbody spectrum in some appropriate Lorentz frame, allowing us to define an effective Lorentz factor and temperature for the photon gas. We also study the freezing out of electron-positron pairs and their asymptotic Lorentz factor γ∞. The dependence of these quantities on initial conditions can be described by simple scaling laws. We apply our results to SGR 1806-20 and find that the energy carried by electron-positron pairs is higher than calculated by former estimates, but is still an order of magnitude short of the minimum energy required to produce the observed afterglow. A viable solution of the energy budget is that the fireball is loaded by baryons or electromagnetic flux.

Wave propagation in strongly scattered random elastic media: Energy equilibration and crossover from ballistic to diffusive behavior

We studied the energy equilibration process of elastic wave propagation through a strong-scattering random medium via multiple-scattering theory and the radiative transfer equation. The equilibration of the shear and compressional energy densities due to the mode conversions is clearly observed in both calculations, although the ratio of the shear energy density to the compressional energy density obtained from the multiple-scattering theory is higher than that obtained from the radiative transfer equation, which has the value predicted by the principle of the equipartition of wave modes. The discrepancy is due to the presence of a negative interference energy inside the sample. This is in contrast to the common belief that the interference energy density of a weak-scattering random medium always averages to zero inside the medium except near its boundaries. We also showed that the negative interference energy is concentrated near the boundary of each scatterer and, therefore, cannot be averaged to zero. In addition, we studied various distribution functions of the transmitted waves in thin samples before the establishment of the energy equilibration. We found that these distribution functions are described well by a random-phasor-sum model and they exhibit crossover behavior from ballistic to diffusive transport.

Hybridization of backward acoustic waves in piezoelectric plates

The phenomenon of hybridization of the backward acoustic waves propagating in a piezoelectric crystal plate has been studied. In an electrically free plate (in particular, of potassium niobate) with a crystal orientation for which a sagittal plane is the symmetry plane, the dispersion curves of backward acoustic waves exhibit points of intersection and hybridization is absent. However, for a small change in the direction of wave propagation, the dispersion curves exhibit “repulsion” and the waves become coupled. The degree of hybridization is quantitatively evaluated in terms of the hybridization coefficient, which is defined as the ratio of the total mutual energy density and the total energy density of the interacting waves. It is demonstrated that the extent of repulsion of the dispersion curves for the interacting waves is determined by the dependence of the hybridization coefficient on the product of the plate thickness and the wave frequency.

Transition from Moderate to Strong Hydrogen Bonds: Its Identification and Physical Bases in the Case of O−H···O Intramolecular Hydrogen Bonds

A systematic investigation aimed at identifying the transition from moderate (M) to strong (S) hydrogen bonds (HBs) and the physical bases of the main geometry-based HB strength classifications reported in the literature has been undertaken using the quantum theory of atoms in molecules (QTAIM). Correlations between the Laplacian of the electron density (rho) at the O...H hydrogen bond critical points (HBCPs), nabla2rhohb, specifically between the more intuitive parameter Lhb = -nabla2rhohb and other QTAIM parameters, have also been explored. The transition from MHBs to SHBs has been identified as the minimum (maximum) in the geometric dependence of Lhb (nabla2rhohb). For O-H...O intramolecular (IM) HBs (including resonance-assisted HBs), the transition is obtained, in a truly remarkable agreement with the existing geometry-based HB strength classifications, when the O...O (O...H) distance is approximately 2.51 ( approximately 1.55) A and when the ratio of the potential energy density (|Vhb|) to the kinetic energy density (Ghb) approximately 1.3. Accordingly, the ranges of the |Vhb|/Ghb ratios are >2-1.3 and 1.3-1 for, respectively, SHBs and MHBs. When the O...O distance is not a genuine indicator of HB strength, the |Vhb|/Ghb ratio and other parameters should be considered to characterize the strength of the HBs. Rationalizations have been provided by way of decoding the physical bases of the transition in terms of the properties of rho and the mechanical characteristics of the interactions that created the HBCPs. Lhb was found to correlate, with a very high degree of fidelity, with at least three parameters (in addition to O...O and O...H distances and the IMHB energy), Vhb/Ghb, Hhb/rhohb (the ratio of the total energy density, Hhb, to the electron density, rhohb (the so-called bond degree parameter)), and deltahb(O,H) (the delocalization index), demonstrating the importance and utility of Lhb (nabla2rhohb) for the study of HB interactions. A new refined energetics-based classification of O-H...O IMHB strengths has been advanced. The approach taken in this investigation can be extended to other HB systems.

Interacting holographic dark energy

We demonstrate that a transition from decelerated to accelerated cosmic expansion arises as a pure interaction phenomenon if pressureless dark matter is coupled to holographic dark energy whose infrared cutoff scale is set by the Hubble length. In a spatially flat universe the ratio of the energy densities of both components remains constant through this transition, while it is subject to slow variations for non-zero spatial curvature. The coincidence problem is dynamized and reformulated in terms of the interaction rate. An early matter era is recovered since for negligible interaction at high redshifts the dark energy itself behaves as matter. A simple model for this dynamics is shown to fit the SN Ia data. The constant background energy density ratio simplifies the perturbation analysis which is characterized by non-adiabatic features.

Quantum rearrangement and self-consistent BCS-BEC crossover thermodynamics

Based on previous works, analytical calculational procedures for dealing with the strongly interacting fermion ground state are further developed through a medium-dependent potential in terms of the Bethe-Peierls contact interaction model. The methods are exact in the unitary limit regime and they lead to self-consistent equations analogous to the Hartree ones. The single particle energy spectrum rearrangement effects on the thermodynamics due to the Hugenholtz--van Hove theorem constraint are addressed. These effects lead to an additional instantaneous correlation potential contribution to the system physical chemical potential and pressure, i.e., equation of state, in order to enforce the classical thermodynamic consistency. The Dyson-Schwinger equations represent implicitly the various Bethe-Goldstone expansion ones. In a thermodynamically self-consistent way, the universal dimensionless factor is analytically calculated to be $\ensuremath{\xi}=\frac{4}{9}$, which defines the ratio of the unitary fermions energy density to that of the ideal noninteracting ones at $T=0$.

Constraints on a new post-general relativity cosmological parameter

A new cosmological variable is introduced to characterize the degree of departure from Einstein's general relativity with a cosmological constant. The new parameter, $\ensuremath{\varpi}$, is the cosmological analog of $\ensuremath{\gamma}$, the parametrized post-Newtonian variable which measures the amount of spacetime curvature per unit mass. In the cosmological context, $\ensuremath{\varpi}$ measures the difference between the Newtonian and longitudinal potentials in response to the same matter sources, as occurs in certain scalar-tensor theories of gravity. Equivalently, $\ensuremath{\varpi}$ measures the scalar shear fluctuation in a dark-energy component. In the context of a vanilla, cosmological constant-dominated universe, a nonzero $\ensuremath{\varpi}$ signals a departure from general relativity or a fluctuating cosmological constant. Using a phenomenological model for the time evolution $\ensuremath{\varpi}={\ensuremath{\varpi}}_{0}{\ensuremath{\rho}}_{\mathrm{DE}}/{\ensuremath{\rho}}_{\mathrm{M}}$ which depends on the ratio of energy density in the cosmological constant to the matter density at each epoch, it is shown that the observed cosmic microwave background temperature anisotropies limit the overall normalization constant to be $\ensuremath{-}0.4l{\ensuremath{\varpi}}_{0}l0.1$ at the 95% confidence level. Existing measurements of the cross-correlations of the cosmic microwave background with large-scale structure further limit ${\ensuremath{\varpi}}_{0}g\ensuremath{-}0.2$ at the 95% CL. In the future, integrated Sachs-Wolfe and weak lensing measurements can more tightly constrain ${\ensuremath{\varpi}}_{0}$, providing a valuable clue to the nature of dark energy and the validity of general relativity.

Polarimetry toward theIRASVela Shell. II. Extinction and Magnetic Fields

We explore correlations between visual extinction and polarization along the western side of the IRAS Vela Shell using a published polarimetric catalog of several hundreds of objects. Our extinction maps along this ionization front (I-front) find evidence of clumpy structure with typical masses between 1.5 and 6 solar masses and a mean length scale L ~ 0.47pc. The polarimetric data allowed us to investigate the distribution of the local magnetic field in small (~pc) scales across the I-front. Using the dispersion of polarization position angles, we find variations in the kinetic-to-magnetic energy density ratio of, at least, one order of magnitude along the I-front, with the magnetic pressure generally dominating over the turbulent motions. These findings suggest that the magnetic component has a significant contribution to the dynamical balance of this region. Along the I-front, the mean magnetic field projected on the sky is [0.018 +/- 0.013]mG. The polarization efficiency seems to change along the I-front. We attribute high polarization efficiencies in regions of relatively low extinction to an optimum degree of grain alignment. Analysis of the mass-to-magnetic flux ratio shows that this quantity is consistent with the subcritical regime (lambda < 1), showing that magnetic support is indeed important in the region. Our data extend the overall lambda-N(H2) relation toward lower density values and show that such trend continues smoothly toward low N(H2) values. This provides general support for the evolution of initially subcritical clouds to an eventual supercritical stage.

Internal shocks in relativistic outflows: collisions of magnetized shells

(Abridged): We study the collision of magnetized irregularities (shells) in relativistic outflows in order to explain the origin of the generic phenomenology observed in the non-thermal emission of both blazars and gamma-ray bursts. We focus on the influence of the magnetic field on the collision dynamics, and we further investigate how the properties of the observed radiation depend on the strength of the initial magnetic field and on the initial internal energy density of the flow. The collisions of magnetized shells and the radiation resulting from these collisions are calculated using the 1D relativistic magnetohydrodynamics code MRGENESIS. The interaction of the shells with the external medium prior to their collision is also determined using an exact solver for the corresponding 1D relativistic magnetohydrodynamic Riemann problem. Our simulations show that two magnetization parameters - the ratio of magnetic energy density and thermal energy density, \alpha_B, and the ratio of magnetic energy density and mass-energy density, \sigma - play an important role in the pre-collision phase, while the dynamics of the collision and the properties of the light curves depend mostly on the magnetization parameter \sigma. The interaction of the shells with the external medium changes the flow properties at their edges prior to the collision. For sufficiently dense shells moving at large Lorentz factors (\simgt 25) these properties depend only on the magnetization parameter \sigma. Internal shocks in GRBs may reach maximum efficiencies of conversion of kinetic into thermal energy between 6% and 10%, while in case of blazars, the maximum efficiencies are \sim 2%.

Rheologic fracture of PMMA material at different strain rates

Polymethyl methacrylate(PMMA) is a kind of typical viscoelastic polymer materials, whose deformation and rheologic fracture are related not only with time and temperature, but also with strain rate on loading. By the quasi-static uniaxial tension test at defferent loading rates, the strain-rate-dependent stress-time equation of PMMA material was gotten with H-K mode. In the range of given strain rates, tes, E 2(\(\dot \varepsilon \)) is almost not varied with strain rate, but E 1(\(\dot \varepsilon \)) and η1(\(\dot \varepsilon \)) augment with strain rate reducing, which shows that viscosity of PMMA material responds more strongly; whereas, they reduce with strain rate increasing, which shows that the viscosity of PMMA material responds more feebly; when the strain rate is added up to infinite, E 1(\(\dot \varepsilon \)) goes to constant and η1(\(\dot \varepsilon \)) to naught, which shows that PMMA material responds elasticity by constitutive mode. Based on the theory of continuum mechanics, median stress is defined as the ratio of fracture strain energy density to fracture strain, according to the energy conservation law and Cauchy median law. The median stress of PMMA is not related with strain rate in the range of the given strain rates, so it is represented as a parameter to scale the fracture of PMMA.

An examination of income-related disparities in the nutritional quality of food selections among Canadian households from 1986–2001

Socio-economic disparities in nutrition have been documented in numerous countries, and have been linked to health inequalities. Social and economic policy changes occurring over the last several years have resulted in growing levels of income inequality in many countries. However, the extent to which these temporal changes have affected nutrition disparities is largely unknown. Our research examined income-related disparities in the nutritional quality of food selections among Canadian households from 1986 to 2001. Data from the 1986, 1992, 1996 and 2001 Family Food Expenditure surveys were pooled together ( n=35 048). The relationships between household income and the nutritional quality of food purchases (considering nutrients both as absolute amounts and adjusted for energy, and total energy density) were estimated using general linear models, including tests of significance for differences across the survey years. Results revealed significant positive relationships between income and most nutrients, which persisted over time, and for some nutrients grew stronger. One exception was folate, where the positive relationship between income and folate (independent of energy) was no longer apparent in 2001; this could be attributed to the mandatory fortification of some cereal grain products with folic acid, which came into effect in 1998, resulting in greater availability of folate from grain products. There was also a significant negative relationship between income and total energy density (ratio of food energy to food weight), which persisted across the survey years. At a time of growing income inequality and worsening problems of poverty, food policy makers need to pay attention to the potential for policy interventions to exacerbate or improve nutrition disparities.

The spectral energy distribution of PKS 2004-447: a compact steep-spectrum source and possible radio-loud narrow-line Seyfert 1 galaxy

An investigation of the spectral energy distribution (SED) of the compact steep-spectrum (CSS) source and possible radio-loud narrow-line Seyfert 1 galaxy (NLS1), PKS 2004–447, is presented. Five out of six well-studied radio-loud NLS1 share this dual classification [optically defined as an NLS1 with radio definition of a CSS or gigahertz-peaked spectrum (GPS) source], suggesting that the connection could have a physical origin. The SED is created from simultaneous observations (within 24 h) at radio (from Australia Telescope Compact Array), optical/near-infrared (NIR) (from Siding Spring) and UV/X-ray (from XMM–Newton) wavelengths. The X-ray data show evidence of short-term variability (primarily a ∼30 per cent increase in the final 4 ks of the observation), a possible soft excess and negligible absorption. Together with the rest of the SED, the X-ray emission is excessive in comparison to synchrotron plus synchrotron self-Compton (SSC) models. The SED can be described with a two-component model consisting of extended synchrotron/SSC emission with Comptonization in the X-rays, though SSC models with a very high electron-to-magnetic energy density ratio cannot be excluded either. The peak emission in the SED appears to be in the NIR, which can be attributed to thermal emission (T≈ 1000 K) from a dusty torus. Analysis of a non-contemporaneous, low-resolution optical spectrum suggests that the narrow-line region (NLR) is much more reddened than the X-ray emitting region suggesting that the gas-to-dust ratio in PKS 2004–447 may be very different than in our own Galaxy. This could be achieved if the radio jets in PKS 2004–447 deposits material from the nucleus into the NLR. Long-term radio monitoring of PKS 2004–447 shows a rather constant light curve over nearly a six-month period with the exception of one outburst when the 6.65-GHz flux increased by ∼35 per cent over 19 d. It is not possible to differentiate between intrinsic or extrinsic (i.e. interstellar scintillation) origins for this outburst, but the detection of the rare event demonstrates the importance of intensive monitoring campaigns. In comparison to general samples of GPS sources, which appear to be X-ray weak, NLS1-CSS/GPS sources possess stronger X-ray emission relative to radio (comparable to normal radio-loud AGN). In addition, NLS1-CSS/GPS sources also exhibit lower intrinsic absorption than GPS sources of similar X-ray luminosity. This is consistent with the additional X-ray component required for PKS 2004–447, but larger samples of NLS1-CSS/GPS are needed before any conclusive remarks can be made.