Lunar tides in the electric field of the atmospheric boundary layer

Investigations are aimed at a search for and an estimation of a correlation between the electric field in the atmospheric boundary layer (ABL) and the lunar tides. The lunar tides and their correlation with the electric field in the ABL can be studied either by accumulation of a large experimental data arrays or by the method of signal reception at spatially separated points. The problem of investigating lunar tide manifestations in the electric field in the ABL is solved using a network of stations for monitoring the vertical electric field strength component, specially constructed models and their consequences, and procedures developed for experimental data processing.     

Solar and lunar tides in the geomagnetic field

Amplitudes of spectral geomagnetic field components and signal/noise ratios are estimated at frequencies of lunar and solar tides based on the data registered at the experimental site of Vladimir State University (VlSU) and Japanese geomagnetic stations Kakioka (1913–2006) and Memambetsu (1950–1999). The influence of thermal solar tides S1, S2, S3, and S4 and lunar gravitational tides O1, M2, and N2 on the geomagnetic field of the surface layer of the atmosphere is reliably distinguished.     

Ultralow-Frequency Electric Field in the Ground Atmospheric Layer

The problem of propagation of electric field disturbances from the ionosphere to the lower atmosphere is considered with allowance for a finite electrical conductivity of the Earth crust. The results of synchronous registration of the ultralow-frequency electric field on a network of stations separated in space that included the Experimental Site of Vladimir State University (VSU), the Station of the Radio Physical Faculty of VSU, and the Portable Station of the Scientific-Research Center of Remote Sensing of the Atmosphere of the Main Geophysical Observatory (Saint Petersburg) have been registered using an optimal receiver and reliable estimates of amplitudes of spectral components of the electric field in the ground atmospheric layer are given. The signal-to-noise ratios and error probabilities are calculated at frequencies of thermogravitational solar tides. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 33–39, August, 2005.     

Photoreflectance investigations of AlGaN/GaN heterostructures with a two dimensional electron gas

Undoped AlGaN/GaN heterostructures with different content and thickness of AlGaN layer are investigated by photoreflectance (PR) spectroscopy. We have observed PR resonances related to an absorption in both GaN and AlGaN layers. The character of these resonances has been analyzed, and PR lines associated with excitonic and band-to-band absorption in the GaN layer and band-to-band absorption in the AlGaN layer have been identified. The transition related to band-to-band absorption possesses characteristic Franz–Keldysh oscillations (FKOs) associated with a built-in electric field. The electric field in the AlGaN layer obtained on the basis of the analysis of FKOs has been found to be in the range of 244–341 kV/cm. The value of the field has been found to decrease with the increase in AlGaN thickness and to increase with the increase in Al concentration. The surface potential for AlGaN layers has been found to increase with the increase in Al mole fraction and has been estimated to be in the range of 1.0–1.7 eV.     

Lunar and Solar Tides in the Electric Field of the Earth's Atmosphere

The paper is aimed at solving one of the problems of modern geophysics, namely, investigating a correlation between the Earth's extremely low frequency (<30 Hz) electromagnetic field in the ground atmospheric layer and the global geophysical processes like lunar and solar tides.     

Ionic liquids in external electric and electromagnetic fields: a molecular dynamics study

The non-thermal effects of external electric and electromagnetic fields in the microwave to far-infrared frequency range and at (r.m.s.) electric field intensities of 10^?3 to 0.25?V/Å_r.m.s. on neat salts of 1,3-dimethyl-imidazolium hexafluorophosphate ([dmim][PF₆]) and 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF₆]) have been investigated by means of non-equilibrium molecular dynamics simulation. Significant alterations in molecular mobility were found vis-à-vis zero-field conditions. Using Green–Kubo and transient time correlation function analysis, the electrical conductivity of these ionic liquids has been estimated. The results indicate that ionic liquids respond most significantly to frequencies much lower than those of smaller polar solvents such as water, although the mechanism of the field response is almost exclusively translational.     

Thin ferroelectric films: Preparation and prospects of integration

The properties of (Ba,Sr)TiO₃ and BiFeO₃ thin films and related nanostructures have been considered. The films have been prepared by rf sputtering in an oxygen atmosphere at an elevated pressure, and the nanostructures have been produced using focused ion-beam etching. The electric field has been applied across a planar interdigital structure of electrodes. The structure, dielectric, electro-optical, and nonlinear optical properties of the prepared samples have been investigated over wide ranges of thicknesses and electric field frequencies. The high efficiency of the planar switching and its influence on the optical properties of the produced structures have been demonstrated. The nanostructuring makes it possible to change the dielectric and optical properties of the materials under investigation, thus increasing the range of switching of functional parameters.     

Piezoelectric measurements on BiFeO3 single crystal by Raman scattering

The piezoelectric response of BiFeO₃ at low temperature has been investigated by Raman scattering measurements. The application of an external electric field at T=10 K induces frequency shifts of the lowest frequency mode related to the Bi-O bonds and corresponding to the soft mode of the ferroelectric transition. The piezoelectric effect is responsible for the softening of this mode via the tensile stress leading to the expansion of the crystal. The phonon deformation potential associated with the soft mode has been estimated around −200 cm⁻¹/strain units using the linear piezoelectric coefficient d₃₃=16 pm/V. It found in the range of the ones obtained for typical piezoelectrics.     

Pedersen mode ducting in a randomly stratified ionosphere

Abstract

A new HF propagation mechanism giving rise to a Pedersen mode has been discovered. The boundary frequency f _b dividing the Pedersen mode frequency range into parts with different HF propagation mechanisms is determined. A known sliding propagation mechanism characterized by an exponential decrease in the field with the distance travelled by waves along the layer prevails at frequencies f > f _b. At the low end of the Pedersen mode frequency range (f < f _b) the stable wave formation associated with a field localization effect under HF propagation in a randomly stratified ionosphere appears. The observed phenomenon is described in terms of the wave theory of diffraction. Numerical calculation of the wave field amplitude is performed using the parabolic equation method. The Pedersen mode ducting effect due to multiple re-reflection of a sliding beam at anisotropic irregularities elongated along the F2 layer with characteristic scales from hundreds of metres to several kilometres vertically and tens of kilometres horizontally is demonstrated. The irregularities with anisotropy coefficients ～1–3 also localize waves but the size of the effect is between one and two orders smaller than in a model of strong stratified irregularities with η ～10–30.     

Influence of a magnetic field on the mutual rectification of alternating currents induced by electromagnetic waves in graphene

The direct component of the electric current induced in graphene placed in a constant magnetic field has been found in the case where two electromagnetic waves with two mutually perpendicular planes of polarization are normally incident on the surface of the sample. It has been demonstrated that the direct component of the current along the direction of the electric field vector of the wave with the frequency ω₁ arises only when the ratio between the frequencies of the incident waves is ω₁/ω₂ = 2 or 1/2. In the latter case, the direct current component appears only in the presence of a magnetic field.     

Parametrische Anregung von elektrostatischen Oberflächenwellen in einer inhomogenen Plasmaschicht durch ein amplituden-moduliertes UHF-Pumpfeld

Parametric resonance phenomena are investigated in a plasma layer with thickness d and thin inhomogeneous boundary regions. The modulated UHF electric field is parallel to the plasma layer. We consider both strong and low modulation of the field amplitude and suppose, that the carrier frequency ω₀ of the pump wave is much larger than the Langmuir frequency ω_Le. We find the region for the modulation frequency ω, in which the parametric growing of the asymmetric and symmetric surface waves occurs. The maximum growth rates of these waves, the direction of their propagation and the threshold value of the modulation depth α of the UHF pump field are calculation.     

Supercooling molecular hydrogen down through the superfluid transition

Recent calculations by Vorobev and Malyshenko [JETP Lett. 71, 39 (2000)] show that molecular hydrogen may stay liquid and superfluid in strong electric fields of the order of 4x10(7) V/cm. I demonstrate that strong local electric fields of similar magnitude exist beneath a two-dimensional layer of electrons localized in the image potential above the surface of solid hydrogen. Even stronger local fields exist around charged particles (ions or electrons) if the surface or bulk of a solid hydrogen crystal is statically charged. Measurements of the frequency shift of the 1 --> 2 photoresonance transition in the spectrum of a two-dimensional layer of electrons above a positively or negatively charged solid hydrogen surface performed in the temperature range 7-13.8 K support the prediction of electric field induced surface melting. The range of surface charge density necessary to stabilize the liquid phase of molecular hydrogen at the temperature of superfluid transition is estimated.     

Dielectric behaviour of polycrystalline lead germanate

The dielectric behaviour of ferroelectric Lead Germanate (Pb₅Ge₃O₁₁) is reported in the frequency region 60 Hz-100 KHz for various particle size ranges from 40 to 300 μ m. The dielectric constant and conductivity decrease with decreasing particle size. The dielectric anomaly in small particle size unsintered samples disappears at lower frequencies, while at 100 KHz a broad diffuse phase transition is observed for all the samples, irrespective of particle size. A strong dielectric dispersion has been observed in the frequency range 60 Hz–100 KHz. The dielectric constant of sintered samples for the same panicle size range, and the dielectric anomaly which was absent at lower frequencies for unsintered samples re-appears in sintered samples. These results have been explained by assuming a high resistivity surface layer having a lower dielectric constant than the bulk at the boundary of particles.     

Microwave surface resistance measurements on the heavy fermion superconductor UPt3

The relative change of the microwave surface resistance has been measured as a function of temperature in the superconducting and normal states of UPt₃ using a cavity perturbation technique. With our frequency range of ∼9–38 GHz, the microwave photon energy (ℏω) is ∼20–95% of the estimated zero-temperature (BCS) energy gap (2Δ₀) of UPt₃. The surface resistance shows a change in slope as the signature of T_c and has a significantly weaker temperature dependence in the superconducting state than would be predicted by the Mattis–Bardeen theory. At higher frequencies, the slope tends to change by a smaller amount. No indication of collective modes at any of the frequencies was observed down to the lowest temperatures measured (∼0.1 K).     

氢负离子在均匀电场和金属面附近的光剥离研究

利用闭合轨道理论,计算了氢负离子在均匀电场和金属面附近的光剥离截面.结果表明,在均匀电场的基础上加上金属面之后,在电离阈附近氢负离子的光剥离截面发生了很大的变化,和仅有均匀电场存在时的光剥离截面相比,截面的振荡幅度增大,振荡频率减小.并且在电场强度相同时,随着金属面与氢负离子距离的不断增大,光剥离截面振荡的幅度不断减小,振荡的频率不断增大,当金属面和氢负离子的距离增大到一定值时,金属面的影响消失,氢负离子的光剥离截面趋近于只有电场存在时的情况.这一结果对于研究负离子体系在界面附近的光剥离问题具有一定的参考价值.     

Temperature dependence of the effective anchoring energy for a nematic-ferroelectric interface

Specific features of the anisotropic interaction between a nematic mixture and a polar surface of a ferroelectric triglycine sulfate crystal have been studied over a wide temperature range including the substrate's Curie point T_c. The mixture was composed of two nematic liquid crystals, 60% of p-methoxybenzylidene-p-n-butylaniline (MBBA) and 40% of p-ethoxybenzylidene-p-n-butylaniline (EBBA), and doped with a small amount of a dichroic dye. The temperature dependence of the polarized components of optical density D_j of the dye absorption band for the nematic and isotropic phases of the MBBA+EBBA mixture has been obtained using polarization optic techniques. The temperature-induced structural changes in the nematic layer near T_c were found to be related to the changes in the orientational part of the tensor order parameter Q_ik. The experimental data have been interpreted using the model, in which the dispersive van der Waals forces of the substrate stabilize the planar orientation of the nematic in the bulk competing with the short-range anchoring forces in the vicinity of T_c. At the same time, the anisotropic part of the surface energy has two terms with the orthogonal easy axes. The nature of the surface electric field and its effect on the director alignment at the interface have been clarified. Taking into account the known relation between anchoring strength and the nematic order parameter, the effective anchoring energy w_eff for the studied system has been determined as a function of temperature.     

Quasistationary electric field of atmospheric space charge produced by powerful sound pulse

The electric field created by atmospheric ions in vertical acoustic sounding from the earth's surface is examined. It is shown that ions of different types are completely entrained by an acoustic pulse and create a quasistationary electric field in the surrounding space, particularly on the earth's surface. The shape of the electric-field pulse is calculated is calculated and its amplitude is estimated numerically.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 8, pp. 641–651, August, 1992.     

Behavior of rigid-porous layers at high levels of continuous acoustic excitation: theory and experiment

A model for the propagation of high amplitude continuous sound through hard-backed rigid-porous layers has been developed which allows for Forchheimer's correction to Darcy's law. The nonlinearity associated with this is shown to be particularly important in the range of frequencies around layer resonance. The model is based on the introduction of particle velocity dependent flow resistivity into the equivalent fluid model expression for complex tortuosity. Thermal effects are accounted for by means of a linear complex compressibility function. The model has been used to derive analytical expressions for surface impedance and reflection coefficient as a function of incident pressure amplitude. Depending on the material parameters, sample thickness, and frequency range the model predicts either growth or decrease of reflection coefficient with sound amplitude. Good agreement between model predictions and data for three rigid-porous materials is demonstrated.     

雷暴电场对宇宙射线次级粒子μ 子的影响研究

西藏羊八井宇宙射线观测站的中子监测器主要探测宇宙射线次级粒子中能量在500 MeV—20 GeV的核子成分和少量的负μ子成分. 本文分析了2008—2010年观测站附近发生的62次雷暴期间中子监测器和大气平均电场仪的同步观测资料, 发现27次雷暴期间中子监测器计数率发生明显变化, 显著性S>5σ, 其中13次变化显著, 显著性S>10σ . 显著性S>10σ的13次个例信号变化百分比与地面电场场强幅值之间存在大体一致的变化趋势, 而显著性在5σ <S<10σ之间的14次个例信号变化百分比与地面电场场强幅值之间不存在相似的变化趋势. 较强雷暴当顶时中子监测器计数率变化一般不明显, 而中子监测器计数率变化明显的个例则多发生于雷暴云不当顶, 但探测器仍处于雷暴云下部正电荷层的控制范围之内时, 或者当顶雷暴处于形成或消散阶段. Dorman等把雷暴期间中子监测器计数率的变化归因于雷暴云内电场对宇宙射线次级粒子μ子的作用, 并建立了雷暴期间中子监测器计数率变化与雷暴地面电场相关联的理论. 本文分析发现雷暴期间羊八井中子监测器计数率变化与地面电场场强之间相关性较小或者没有相关性, 不支持Dorman的理论.     

介质阻挡均匀大气压辉光放电数值模拟研究

通过数值求解一维电子、离子连续性方程和动量方程，以及电流连续性方程，计算了氦气介 质阻挡大气压辉光放电电子、离子密度和电场在放电空间的时空分布，以及放电电流密度和 绝缘介质板充电电荷密度随时间的变化. 分析讨论所加电压频率、幅值及介质板性质等对均 匀大气压辉光放电性质的影响. 当外加电压频率足够高时，大量离子被俘获在放电空间，空 间电荷场又引起足够多的电子滞留在放电空间. 这些种子电子使得在大气压下发生汤森放电 ，放电空间结构类似于低气压辉光放电，即存在明显的阴极位降区、负辉区、法拉第暗区和 等离子体正柱 关键词： 大气压辉光放电 介质阻挡 数值模拟 等离子体