On the source of auroral kilometric radiation

The radiation pattern has been determined on the basis of the comparative analysis of auroral kilometric radiation (AKR) received in the space-diversity mode by two satellites, Interball-2 and Polar. The radiation propagates in a cone with an opening angle ∼±25° and the axis aligned with the local magnetic field. The results con-firm the theoretical estimates that the source boundaries play a significant role in the generation of the auroral kilometric radiation and in the formation of the radiation pattern. Original Russian Text ? M.M. Mogilevsky, T.V. Romantsova, J. Hanasz, T.M. Burinskaya, R. Schreiber, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 11, pp. 819–821.     

Direct measurements of auroral kilometric radiation in a limited source

The enhancement of auroral kilometric radiation near its lowest frequency has been detected in the polar edge of the auroral zone in the POLRAD experiment with the INTERBALL-2 satellite. The difference between the local electron cyclotron frequency and the lowest frequency of enhanced radiation is 8–20 kHz, indicating the closeness to the source of auroral kilometric radiation. According to the detailed analysis of low-frequency auroral kilometric radiation, its amplitude is larger than the “background” values by a factor of 20–70 and has amplitude modulation with characteristic periods of 40-60 s. The increase in the intensity at low frequencies is attributed to the intersection of the source region by the satellite and the detection of waveguide modes in it.     

Regimes of Resonant Interactions of Electrons with Auroral Kilometric Radiation

Radiophysics and Quantum Electronics - We analyze the resonant interaction of energetic electrons with auroral kilometric radiation (AKR). Possible regimes of such an interaction are studied on the...     

利用LBH辐射图像数据反演大气O/N2方法

利用极光Lyman-Birge-Hopfield (LBH) 辐射图像数据可用来研究太阳风磁场与地球磁场耦合、亚暴与磁暴等过程,综合LBH辐射图像数据和O原子135.6nm辐射数据可反演电离层氧原子与氮气分子O/N2比值分布,进而研究高层大气组分信息及电离层分布变化,对科学研究和空间天气预报具有重要意义. 本文给出了LBH辐射传输机理和我国自主研制的搭载在风云三号D星（FY-3D）上的广角极光成像仪（Wide-field Auroral Imager, WAI）在轨获得的LBH 140-180nm波段极光辐射图像数据. 结合大气紫外辐射积分代码（Atmospheric Ultraviolet Radiance Integrated Code, AURIC）计算O135.6nm辐射数据、LBH辐射光谱以及MSISE00大气模型计算的O、N2数据,给出了利用WAI观测的LBH辐射图像数据反演大气O/N2比值理论计算方法,该方法将为利用我国自主观测LBH辐射数据和O135.6nm辐射数据开展空间信息反演研究打下基础.     

Auroral Kilometric Radiation as a Diagnostic Tool for the Properties of the Magnetosphere

JETP Letters - Auroral kilometric radiation is used as a tool for the remote diagnostics of processes in the Earth’s magnetosphere. Using satellite data and the spectrum of fluctuations of...     

Approximate and exact technique for multidimensional radiation transport in a plane parallel atmosphere; Application to the 4.3 μm auroral arc

We develop an integral equation formulation for the solution of multidimensional radiation transport problems in a plane-parallel atmosphere. The formulation is applied to a nominal case of a 4.3 μm auroral arc. The accuracy of a computation-saving, approximate method is investigated.     

Steerable reflective high-gain antenna array based on loaded dipole scatterers

We present the results of studying experimentally a constructively simple and inexpensive centimeter-wave antenna having a radiation pattern, whose shape can be controlled. Specifically, the main lobe of the pattern can be scanned in a wide angular range, its width can be changed, and minima of the pattern can be formed in specified directions. The feed being the only active element of the antenna is located in front of the mirror made up by a system of steerable passive scatterers, which are dipole antennas loaded by semiconducting diodes. The capacity of the diode loads is changed under the action of controlling signals, which set specific bias voltages at each diode. The studies aimed at testing experimentally the operability of the antenna and assessing the practically achievable parameters of the proposed antenna design. The developed laboratory model of the antenna operates at frequencies near 2.4 GHz with a gain of more than 21 dBi and the possibility of scanning the main lobe of the radiation pattern in the horizontal and vertical planes to ±60° and ±15°, respectively, for the antenna with overall dimensions 100 × 60 × 30 cm.     

Untersuchung der Cerenkovstrahlung mit 50 keV-Elektronen in dünnen Siliziumschichten

For wavelengths near 5000 Å the index of light refraction in silicon is so large, that a considerable amount of Cerenkov radiation is generated by 50 keV electrons. We discuss experimental radiation pattern of transition radiation including Cerenkov radiation emitted from 50 keV electrons traversing thin silicon foils of 2000 Å thickness at different angles of electron incidence. There is good agreement of the experimental results with theory.     

The effect of selective chemical etching on the directivity pattern for radiation of a semiconductor laser

The effect of the selective wet chemical etching of the emitting surface on the directivity pattern of radiation in the plane normal to the p-n junction is studied for InGaP/GaAs lasers with InGaAs quantum wells. It is found by atomic-force microscopy that the cylindrical lens (converging or diverging, depending on the type of etchant) is self-formed on the emitting surface due to the different etching rate of wide-gap layers (InGaP) and active layers (GaAs, InGaAs) of the lasers. By adjusting the corresponding etching time, the aperture angle of the laser radiation pattern in the plane normal to the p-n junction can be changed in the range of 57°–82° at the initial aperture angle at the half maximum level of 6°.     

Evolution of the auroral oval during a weak substorm

The present paper deals with a detailed study of the dynamics of the polar cap boundaries. The study involves the data from two satellites of the APEX project, and the data from three DMSP satellites. The APEX (Active Plasma Experiment) satellites moving along the polar orbit provide charged particle measurements in a small spatial scale (due to variable distance between both spacecrafts), up to 2 000 km. The large scale changes are studied by the comparison of the APEX and the DMSP (Defense Meteorological Satellite Program) data. Different regions are identified using the characteristics of the precipitating particles in the energy range 0.1–20 keV which have been registered onboard all satellites. This satellite configuration allows us to determine the evolution of the small structures as well as the motion of the whole precipitating region. The main attention is concentrated on the rising phase of the substorms when the width of the auroral oval decreases with the increasing geomagnetic activity and the velocity of the auroral oval motion can reach 0.2° per minute. The observed phenomena are compared with the changes of the interplanetary magnetic field and the solar wind parameters as provided by the IMP-8 spacecraft.     

Excitation of multilayered plasma columns with the ring of magnetic currents

The excitation of gaseous plasma column having semiconductor plasma columns on either side is studied with the excitation source being the ring of magnetic currents. The whole structure being cylindricalin shape, contains the conductor along its axis. The effect of radii of all the columns including that of the ring on radiation pattern, is studied which shows a peak of maximum radiation in a certain direction along with some other less ntense peaks. In most cases the peak occurs roughly at 61° at which fine structure is given. Also three intense peaks of radiation occur when radius of the plasma (outer semiconductor) column is 0.058 m.     

Photo-stimulated field emission of barium-coated tungsten

Photo-stimulated field emission of electrons is shown using a barium covered tungsten tip illuminated by a focused laser beam. The laser is a low power (1 mW) HeNe type emitting a 6328 Å (1.96 eV) radiation. The pattern given by photoelectrons shows that high work function planes such as (011), (121), (211) which are dark in field emission pattern become bright in photo-stimulated field emission pattern.     

X波段微带余割平方扩展波束天线阵赋形优化遗传算法研究

提出了一种改进型自适应遗传算法, 该算法用logistic函数拟合交叉概率和变异概率, 以赌轮盘选择和精英保留相结合的方式, 在全局寻找最优解. 与经典遗传算法相比, 改进型自适应遗传算法可以大大提高算法的求解质量. 本文基于改进的自适应遗传算法研究设计了-3 dB范围为0°-12°, -10 dB波束宽度为65°, 波束覆盖为65°, 天线频带范围为8.5-9.8 GHz, 中心频率为9.05 GHz的X波段微带余割平方扩展波束天线阵. 研究结果表明改进型自适应遗传算法对方向图的拟合程度具有较大提高, 适应度值可以从0.07以下提升到0.09以上.     

Reformed Solitary Kinetic Alfven Waves due to Dissipations and Auroral Electron Acceleration

The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades. Some recent observations from the auroral orbit satellites, FREJA and FAST, showed that large amplitude solitary kinetic Alfvén waves (SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere. In a low-β (i.e., β/2<<m_e/m_i<<1) plasma, the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions. This leads to instabilities and causes dissipations of SKAWs. In the present work, based on the analogy of classical particle motion in a potential well, it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included. The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of m_ev_A²/e over a characteristic width of several λ_e. As a consequence, the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local Alfvén velocity. In particular, we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron acceleration problem. The result shows that not only the location of acceleration regions predicted by this model is well consistent with the observed auroral electron acceleration region of 1—2 R_E above the auroral ionosphere, but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several μA/m² which are comparable to the observations of auroral electrons.     

Measurement of properties of a smooth-walled spline-profile feed horn around 840 GHz

For astrophysical applications at submillimeter wavelengths, efficient coupling of the feed horn pattern in the focal plane to the radiation pattern of the telescope is paramount. To date, at 840 GHz with high band width, corrugated feed horns have been used with very good results. The goal of developing instruments for KOSMA above 1 THz where state-of-the-art heterodyne systems are still governed by receiver noise rather than by radiative background, requires fabrication of corrugated structures of the order of λ/3 or less. This is non-trivial, and here we present the performance of a smooth-walled spline-profile feed horn, which is considerably easier to manufacture compared to a corrugated feed horn. The performance is assessed via radiation patterns in H, E and 45° D-Plane in co- and cross-polarization.     

A compact square loop patch antenna on high dielectric ceramic–PTFE composite material

Design and prototyping of a low profile, compact square loop microstrip line fed miniature patch antenna on 1.9 mm thick ceramic-polytetrafluoroethylene (PTFE) high dielectric composite material substrate is presented in this paper. The measured ?10 dB return loss bandwidths of the antenna are 300 MHz (0.75–1.05 GHz) and 800 MHz (2.4–3.2 GHz) with 3.4 dBi, 8.86 dBi and 7.42 dBi at 900 MHz, 2.5 GHz and 3.0 GHz, respectively. The measured symmetric and almost stable radiation pattern makes the proposed antenna suitable for RFID, GSM, ZIGBEE, WBAN, LR-WPAN etc. integrated mobile devices.     

Response of auroral regions to directional changes of the interplanetary magnetic field: Case study

Summary On October 6, 1979, the low-altitude polar-orbiting satellites DMSP-F2 and-F4 crossed the auroral electron precipitation region in the opposite hemispheres at nearly the same universal time (UT) and in the same magnetic local-time (MLT) sector near midnight. Three pairs of such nearly simultaneous conjugate crossings took place during a period of enhanced magnetic activity and strongly turning northward or southward of the interplanetary magnetic field (IMF). These conjugate observations allowed the study, with time resolution better than six minutes, of the variation, in response to directional changes of the interplanetary magnetic field, of the latitudinal position and width of the auroral regions; these are believed to map the central plasma sheet (CPS) and boundary plasma sheet (BPS). During the equatorward expansion of the whole auroral electron precipitation region, its latitudinal width is observed to decrease markedly when the IMF turns from a northern to a southern direction. In particular, a different response of the equatorward boundary of the auroral oval with respect to the poleward boundary results from the observations, showing that the speed of the equatorward expansion of the equatorward boundary, measured at a temporal resolution of less than 6 minutes, is lower than the speed of the poleward boundary. The BPS/CPS boundary moves coherently with the southward turning of the IMF, with intermediate speed. It follows that the latitudinal width of the poleward part of the auroral region, assumed to map the boundary plasma sheet, decreases more dramatically than the width of the equatorward part of the region mapping the central plasma sheet. These findings could be explained in terms of changes of the total open magnetic flux. Actually, the equatorward shift of the poleward boundary of the auroral oval and the subsequent dramatic thining of the BPS region seem to be the consequence of a larger number of geomagnetic flux line interconnected with the IMF during a southward IMF condition.     

X-ray masks based on epoxygraphite

A simple fabrication technology of hard X-ray masks with thin (50–150μm thick) X-ray transparent bearing membranes made of a new material, i.e., polymerized epoxy resin with graphite filler (hereafter, epoxygraphite), is described. The first results of using such masks in pattern scanning synchrotron X-ray lithography in the exposing radiation wavelength range λ ≈ 0.5–3 Å are presented. The prospects of applications of such masks in the softer spectral range λ ≈ 3–7 Å are considered.     

Features of propagation of HF signals on mid-latitude paths under conditions of geomagnetic disturbances

We present the results of experimental studies of the features of HF-signal propagation on oblique-sounding paths in the Eurasian longitude sector between England and Magadan during geomagnetic disturbances. The joint analysis of the satellite data and the data of vertical and oblique sounding of the ionosphere shows that the appearance of additional signals during magnetic disturbances can be stipulated by refraction of radio waves in the region of the auroral oval and the main ionospheric trough as well as by scattering from small-scale magnetic-field-aligned irregularities near the equatorial boundary of the auroral oval. Based on calculations and comparison with experimental data of oblique sounding of the mid-latitude ionosphere, we identify the lateral spreading signals registered on the Magadan — Irkutsk and Inskip (England) — Rostov-on-Don paths as signals scattered by small-scale field-aligned irregularities whose location coincides with the southern boundary of the auroral oval. We show that the Russian and global chirp-ionosonde networks are promising for studying the dynamics of the main ionospheric trough and the auroral oval during geomagnetic disturbances as a manifestation of space weather in the near-Earth environment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 12, pp. 1041–1056, December, 2004.