Narrowband and broadband active control in an enclosure using the acoustic energy density

An active control system based on the acoustic energy density is investigated. The system is targeted for use in three-dimensional enclosures, such as aircraft cabins and rooms. The acoustic energy density control method senses both the potential and kinetic energy densities, while the most popular control systems of the past have relied on the potential energy density alone. Energy density fields are more uniform than squared pressure fields, and therefore, energy density measurements are less sensitive to sensor location. Experimental results are compared to computer-generated results for control systems based on energy density and squared pressure for a rectangular enclosure measuring 1.5 x 2.4 x 1.9 m. Broadband and narrowband frequency pressure fields in the room are controlled experimentally. Pressure-field and mode-amplitude data are presented for the narrowband experiments, while spectra and pressure-field data are presented for the broadband experiment. It is found that the energy density control system has superior performance to the squared pressure control system since the energy density measurement is more capable of observing the modes of a pressure field. Up to 14.4 and 3.8 dB of cancellation are achieved for the energy density control method for the narrowband and broadband experiments presented, respectively.     

Generalized acoustic energy density

The properties of acoustic kinetic energy density and total energy density of sound fields in lightly damped enclosures have been explored thoroughly in the literature. Their increased spatial uniformity makes them more favorable measurement quantities for various applications than acoustic potential energy density (or squared pressure), which is most often used. In this paper, a generalized acoustic energy density (GED), will be introduced. It is defined by introducing weighting factors into the formulation of total acoustic energy density. With an additional degree of freedom, the GED can conform to the traditional acoustic energy density quantities, or it can be optimized for different applications. The properties of the GED will be explored in this paper for individual room modes, a diffuse sound field, and a sound field below the Schroeder frequency.     

The Gravitational Energy–Momentum Density of Radially Accelerated Observers in Schwarzschild Spacetime

A hybrid machinery that is useful for calculations in teleparallel theories when the spacetime is spherically symmetric is developed. Using this machinery, the gravitational energy–momentum tensor density of the Schwarzschild spacetime is evaluated in a frame adapted to observers that accelerate in the radial direction. The energy density, the total energy, and the gravitational energy-momentum flux are obtained. The regularization procedure and the limit where gravity is absent is discussed. It turns out that the regularized energy and energy–momentum flux are consistent in the whole spacetime. The continuity equation for the gravitational energy–momentum also holds for any point outside the black hole. Finally, the static and freely falling cases are discussed. It is found that a static observer measures a negative gravitational energy density, while a freely falling one measures a vanishing density.     

Error analysis of a practical energy density sensor

The investigation of an active control system based on acoustic energy density has led to the analysis and development of an inexpensive three-axes energy density sensor. The energy density sensor comprises six electret microphones mounted on the surface of a 0.025-m (1 in.) radius sphere. The bias errors for the potential, kinetic, and total energy density as well as the magnitude of intensity of a spherical sensor are compared to a sensor comprising six microphones suspended in space. Analytical, computer-modeled, and experimental data are presented for both sensor configurations in the case of traveling and standing wave fields, for an arbitrary incidence angle. It is shown that the energy density measurement is the most nearly accurate measurement of the four for the conditions presented. Experimentally, it is found that the spherical energy density sensor is within +/- 1.75 dB compared to reference measurements in the 110-400 Hz frequency range in a reverberant enclosure. The diffraction effects from the hard sphere enable the sensor to be made more compact by a factor of 3 compared to the sensor with suspended microphones.     

Spatial distribution of electron characteristic in argon rf glow discharges

The spatial distributions of the electron density and the mean electron energy of argon radio frequency (rf) glow discharge plasma in a plasma-enhanced chemical vapour deposition (PECVD) system have been investigated using an established movable Langmuir probe. The results indicate that in the axial direction the electron density tends to peak at midway between the two electrodes while the axial variation trend of mean electron energy is different from that of the electron density, the mean electron energy is high near the electrodes. And the mean electron energy near the cathode is much higher than that near the anode. This article focuses on the radial distribution of electron density and mean electron energy. A proposed theoretical model distribution agrees well with the experimental one: the electron density and the mean electron energy both increase from the centre of the glow to the edge of electrodes. This is useful for better understanding the discharge mechanism and searching for a better deposition condition to improve thin film quality.     

Acoustic energy in ducts: Further observations

The transmission of acoustic energy in uniform ducts carrying uniform flow is investigated with the purpose of clarifying two points of interest. The two commonly used definitions of acoustic “nergy” flux are shown to be related by a Legendre transformation of the Lagrangian density exactly as in deriving the Hamiltonian density in mechanics. In the acoustic case the total energy density and the Hamiltonian density are not the same which accounts for two different “energy” fluxes. When the duct has acoustically absorptive walls neither of the two flux expressions gives correct results. A re-evaluation of the basis of derivation of the energy density and energy flux provides forms which yield consistent results for soft walled ducts.     

Energy flow model considering near field energy for predictions of acoustic energy in low damping medium

The Acoustic Energy Flow Boundary Element Method (AEFBEM) is developed to predict the acoustic energy density and intensity of an engineering system. Up to now, the acoustic energy flow model has been used only for analysis of high frequencies or radiation noise because of plane wave and far-field assumptions. In this research, a new energy flow governing equation that can consider the near field acoustic energy term and spherical wave characteristics is derived successfully to predict the acoustic energy density and intensity of a system in the medium-to-high frequency range. A near field term of acoustic energy in spherical coordinate is added to the relationship between energy density and energy flow. But with the far-field assumption, this term vanishes, so the relationship between energy density and energy flow becomes the same as that of the plane wave. By considering the near field energy term without far-field assumption, the energy density at medium frequencies can be estimated. However, the governing equation has to be numerically manipulated for use in the analysis of complex structures; therefore, the Boundary Element Method (BEM) is implemented. AEFBEM is a numerical analysis method formulated by applying the boundary element method to an acoustic energy flow governing equation. It is very powerful in predicting the acoustic energy density and intensity of complex structures in medium-to-high frequency ranges, and can analyze interior noise and radiating sound. To verify its validity, several numerical results are provided. BEM and AEFBEM were compared with respect to energy density, and the results from both methods were similar.     

纳秒激光脉冲在空气中聚焦的临界自由电子密度问题

实验研究了高功率纳秒量级激光脉冲在空气中聚焦时的能量透过率随输入激光脉冲能量变化的规律,发现在纳秒激光脉冲聚焦半径相同的情况下,激光脉冲的能量透过率随入射激光脉冲能量的变化可分为三种情况：当入射激光脉冲能量较低时,激光脉冲能量全部通过;当入射激光脉冲能量增大后,激光脉冲的能量透过率由近100%迅速减小;当入射激光脉冲的能量进一步增加时,激光脉冲的能量透过率继续缓慢变小.用临界自由电子密度以及所对应的临界时间点对上述实验现象进行了理论分析得到了如下结论：当自由电子密度未达到临界自由电子密度时,多光子电离过程起主要作用,而当自由电子密度超过临界自由电子密度后,逆韧致吸收过程起主要作用,临界时间点是入射激光脉冲与空气作用过程中自由电子密度达到临界自由电子密度的时刻.入射激光脉冲能量决定了临界时间点在脉冲作用时间上的位置,临界时间点的位置决定了激光脉冲的能量透过率.可以通过测量激光脉冲的能量透过率来计算出临界自由电子密度,从而确定出激光脉冲在空气中聚焦时的能量透过特性. 关键词： 临界自由电子密度 临界时间点 多光子电离 逆韧致吸收     

Quantum Inequality Bounds for Free Rarita-Schwinger Field in Flat Spacetime

Although quantum field theory allows the local energy density negative, it also places severe restrictions on the negative energy. One of the restrictions is the quantum energy inequality (QEI), in which the energy density is averaged over time, or space, or over space and time. By now temporal QEIs have been established for various quantum fields, but less work has been done for the spacetime quantum energy inequality. In this paper we deal with the free Rarita-Schwinger field and present a quantum inequality bound on the energy density averaged over space and time.Comparison with the QEI for the Rarita-Schwinger field shows that the lower bound is the same with the QEI. At the same time, we find the quantum inequality for the Rarita-Schwinger field is weaker than those for the scalar and Dirac fields. This fact gives further support to the conjecture that the more freedom the field has, the more easily the field displays negative energy density and the weaker the quantum inequality becomes.     

Stability of the curvature perturbation in dark sectors' mutual interacting models

We consider perturbations in a cosmological model with a small coupling between dark energy and dark matter. We prove that the stability of the curvature perturbation depends on the type of coupling between dark sectors. When the dark energy is of quintessence type, if the coupling is proportional to the dark matter energy density, it will drive the instability in the curvature perturbations; however if the coupling is proportional to the energy density of dark energy, there is room for the stability in the curvature perturbations. When the dark energy is of phantom type, the perturbations are always stable, no matter whether the coupling is proportional to the one or the other energy density.     

热核静态性质的一个简单模型

以扩展Skyrme力为基础,计入唯象的表面效应和Coulomb相互作用,推导了核系统的能量密度。对于有限温度情形,通过索末菲展开,得到了能量密度、自由能密度以及熵密度的解析公式。由此计算了热核物质和有限核的状态方程,每核子熵及每核子自由能。对计算结果作了比较和分析,预言了在同一框架下研究热核动力学演化的可能性。 关键词：     

Binding energy for inhomogeneous nuclear matter

For a spatial finite nuclear density distribution a binding energy formula is developed. A modified Thomas-Fermi method which deduces the mixed density by taking into account an anisotropic local momentum space occupation is used. This method presents the binding energy as a functional of the proton and neutron density distributions. It was possible within this framework to derive in a consistent way the energy correction terms due to density inhomogeneities. The structure of these energy correction terms is shown and an estimate is given for the adjustable parameters of this model to fit the experimental nuclear masses.     

Stability analysis of a Morris-Thorne-Bronnikov-Ellis wormhole with pressure

The model of a spherical Morris-Thorne-Bronnikov-Ellis wormhole is analyzed for stability. The matter of this wormhole is composed of a radial monopole magnetic field and a quasi-perfect phantom fluid. In the stationary case, the energy density of this fluid is negative and equal in magnitude to twice the energy density of the magnetic field. There is no pressure of this fluid in the stationary case (phantom dust), while in the case where the fluid energy density deviates from its stationary value, the pressure is proportional to the deviation of the energy density from its stationary value. An example of a wormhole stable against radial perturbations has been obtained.     

强流脉冲离子束能量密度分布的红外诊断

强流脉冲离子束在靶上的能量密度分布是其研究和应用的一个重要参数。为了解决现有束流能量密度诊断方法的不足,利用红外成像仪测量靶背面的温度分布,从而建立了强流脉冲离子束能量密度分布的红外诊断方法。对能量密度1J/cm2量级、脉冲宽度为102 ns量级的束流,该方法测量误差好于5%,空间分辨率可达到1~2mm,具有操作简便、成本低的优点,是强脉冲能量沉积分布的一种高效迅速的诊断方法。     

双动边界一维空腔中的能量密度

利用广义Moore方程的数值解，计算了具有做简谐振动的双边界一维空腔中的能量密度. 能量密度的性质与运动边界的振幅、频率和相差密切相关.取某些特殊的参数值时，能量密度呈现出波包结构. 关键词： 双动边界 广义Moore方程 能量密度     

Inclusion of the Δ resonance in the optical potential between two nuclei and its application to medium energy12C-12C scattering

An energy dependent complex optical potential between two nuclei is calculated from the potential energy density for two colliding nuclear matters generated by solving the Bethe-Goldstone equation in whichNΔ and ΔΔ channels are explicitly coupled to theNN channel. By adding the contributions from the third and fourth order ring diagrams and the relativistic correction to the calculated potential energy density, the saturation property of a nuclear matter is reasonably well reproduced. This is used together with the kinetic energy density to calculate the optical potential for the¹²C+¹²C system in the energy density formalism with the local density approximation. The surface correction term and the symmetry energy term in the energy density functional are determined to reproduce the observed binding energy and the rms radius of¹²C. Using this potential, the differential cross sections for elastic¹²C-¹²C scattering atE _lab=1440 and 2400 MeV are calculated and compared with recent experimental data.     

Spherically symmetric static inhomogeneous cosmological models

Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum) energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third of the combined value of radiation pressure and density.     

Energy of Gravitational Field of Static Spherically Symmetric Neutron Stars

By using the Einstein-Tolman expression of the energy-momentum pseudo-tensor, the energy density of the gravitational field of the static spherically symmetric neutron stars is calculated in the Cartesian coordinate system.It is exciting that the energy density of gravitational field is positive and rational The xmmerical results of the energy density of gravitational field of neutron stars are calculated. For neutron stars with M=2M, the ratio of the energy density of gravitational field to the energy density of pure matters would be up to 0.54 at the surface.     

Determination of electron density and energy influx in a hollow cathode glow discharge used for powder modification

The electron density and energy influx in an argon hollow cathode glow discharge were determined to obtain adequate parameters for subsequent surface modification of low density polyethylene (LDPE) powder to change the wettability. The electron density was studied by Langmuir probe measurement in dependence on process gas pressure and hollow cathode material. Besides the determination of the rate of increasing electron density with input power an optimal experimental pressure was determined. The energy influx was studied by thermal probe measurements in dependence on process gas pressure, bias voltage, axial position and hollow cathode material. Inside the hollow cathode the energy influx is nearly constant along the whole cathode length. With increasing pressure the energy influx decreased. At biased thermal probe the energy influx was observed to decrease up to the floating potential and beyond it increases with increasing voltage. Using different hollow cathode materials the electron density as well as the energy influx reach higher values for aluminum than for copper and stainless steel.     

On the stability of the Hartree-Fock homogeneous density solution for nuclear matter

The nuclear matter energy density used by Overhauser is shown not to be realistic. The consequence of a static density fluctuation thus seems doubtful. The application of the method of Baym, Bethe and Pethik, developed for neutron star matter problems, shows that for a more realistic nuclear energy density containing the Thomas-Fermi part plus gradient terms, both spatially periodic compression and decompression about the saturation density, augment the energy. In addition, positive gradient terms tend to prevent a rippled density.