Anisotropic Structure of Small-Scale Ionospheric Turbulence

We consider various theoretical models for the spectrum of small-scale ionospheric turbulence. The particular role of the generalized model of the ionospheric-turbulence spectrum, which takes into account that the anisotropy (extension) of small-scale irregularities of the upper ionosphere along the Earth's magnetic field direction depends on the transverse scale of those irregularities, is emphasized. The results of the. rst target experiments on radio sensing of the midlatitude ionosphere by signals from on-orbit satellites at frequencies 150 and 400 MHz under conditions of increased solar activity are presented. The experiments were performed at the radiophysical facility in the Nizhny Novgorod region in 2003. We studied statistical characteristics of the amplitude fluctuations of the received signals for different angles ϑ between the line of sight from a satellite to a ground-based reception point and the Earth's magnetic field direction. It was found in the course of the experiments that the spectrum slope of amplitude fluctuations of the received radiation is a function of the angle ϑ. The obtained result agrees with the generalized model of the ionospheric-turbulence spectrum and can be an argument in favor of the pronounced anisotropic structure of small-scale electron-density irregularities of the midlatitude ionosphere under disturbed geophysical conditions. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 5, pp. 382–387, May 2005.     

Multifractal Structure of Intermittency in a Developed Ionospheric Turbulence

We present the results of studying the multifractal structure of intermittency in a developed ionospheric turbulence during special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2005–2006. It is shown, in particular, that the determination of multidimensional structural functions of the energy fluctuations of received signals permits one to obtain the necessary information on multifractal spectra of the studied process of radio-wave scattering in the ionosphere. Experimental data on multifractal spectra of slow fluctuations in the received-signal energy under conditions of a developed small-scale turbulence are compared with the existing concept of the radio-wave scattering within the framework of the statistical theory of radio-wave propagation in the ionosphere. It is inferred that under conditions of a developed ionospheric turbulence, the multifractal structure of the intermittency of slow fluctuations in the received-signal energy is a consequence of the intermittency of small-scale fluctuations in the electron number density of the ionospheric plasma on relatively large spatial scales of about several ten kilometers. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 485–493, June 2008.     

Studying the Features of Transport Processes in the Upper Ionosphere using HF-Induced Artificial Ionospheric Turbulence

We analyze measurements of the velocity at which the artificial plasma turbulence, induced in the regions of resonance interaction between a powerful wave and a plasma, spreads along the geomagnetic field. The experimental data were obtained in 1996–2000 during experiments at the Sura heating facility on HF modification of the ionospheric F region. The stimulated electromagnetic emission (SEE) of the ionosphere was used for diagnosing the artificial plasma turbulence. The spread velocity was usually higher than the ion thermal velocity. In many cases, this velocity was close to and sometimes even much higher than the electron thermal velocity. We consider the dependence of the evolution features of the observed phenomena on the scheme of measurements (frequency and power of pumping and diagnostic waves, their timing, the distance between the levels of pumping- and diagnostic-wave reflection, etc.). A possible effect of the ionospheric D and E regions on the features of the observed phenomena is discussed. Based on the measurements performed, we formulate the requirements for future experiments.     

The Spectrum of Decaying 2D Self-Similar Turbulence

Doklady Physics - A decaying 2D homogeneous and isotropic turbulent flow is considered in the self-similar limit, which is achieved with large values of the Reynolds number formed using the time...     

Shell Models of MHD Turbulence and the Problem of Superequipartition

Within the framework of the shell model of turbulence, we consider the long-time evolution of the magnetic field in a turbulent flow of conducting fluid. A weak initial magnetic field rapidly increases up to magnitudes corresponding to the equipartition with kinetic energy, and then the stage of slow evolution begins. It is shown that in some cases, the magnetic energy can significantly exceed the kinetic energy of the turbulence at this stage. We discuss the possible observational evidences for such a superequipartition of the magnetic field. It is shown that the superequipartition is realized if the initial energy of the magnetic field exceeds the kinetic energy, although even in such cases the equipartition is reached in many realizations.     

Spatial Spectrum of Artificial Ionospheric Irregularities Induced by Powerful HF Radiowaves

We present measurement results and spatial-spectrum shapes of the dependence of the relaxation time on the scale across the geomagnetic field for artificial ionospheric irregularities (AIIs) induced in the upper ionosphere by powerful HF radiation of the SURA heating facility. The irregularity diagnostics was based on observing amplitude scintillations of a 243-MHz beacon signal from a quasi-geostationary, solar-synchronous satellite and on measuring field-aligned scattering at frequencies 15 and 20 MHz. The satellite signal was received at the Kazan State University Observatory. The field-aligned scattering signals were received and analyzed by a bistatic HF radar based on the UTR-2 radio telescope located near Kharkov (Ukraine). It is shown that irregularities of the electron density, whose two-dimensional spectrum in the plane perpendicular to the geomagnetic field is the power law æ ^-p with index p2, are developed in the scale range 30–60 l 200–400 m. In this case, the relative fluctuations (N²)^1/2 of the electron density increase with decreasing scale l=2/æ. The estimate N²)^1/2 1–1.5% is obtained for a heating power of 150 MW and irregularity scales l 30–60 m at which the fluctuations are maximum. The measured dependence of the AII relaxation time, defined as the e-folding time of the amplitude-scintillation intensity, has the form _r l . If l 30–60 m, then the index is close to 2, whereas the effective diffusion coefficient D (2–3)· 10^-1 m²/s corresponds to the ambipolar cross-field diffusion coefficient in a magnetized plasma. The time _r for scales l 60–100 m is independent of l and increases with decreasing velocity of regular drift of the plasma. The Doppler-spectrum broadening (²)^1/2 0.6 Hz observed when receiving field-aligned scattered signals can be related to chaotic motions of plasma-density disturbances whose random drift velocities amount to (v²)^1/2 2–3 m/s for scales l 20 m at which the power-law index changes drastically.     

Study of the Excitation Conditions and Characteristics of Ionospheric Plasma Turbulence at the Development Stage of the Ponderomotive Parametric Instability

We present the results of studying the development features of nonlinear effects at the initial stage of interaction of powerful HF radio waves with the plasma in the ionospheric F region. Experimental measurements were performed at the Sura heating facility for a wide pump frequency range (4.5–9.0 MHz) and a variety of pulse durations (0.3–100 ms) and effective radiated powers (1–30 MW) at various times of a day. The performed measurements allow us to study the excitation thresholds and time–amplitude characteristics of the ponderomotive self-action of a pump wave as well as the relaxation characteristics of the stimulated electromagnetic emission of the ionosphere as functions of the pump parameters and ionospheric conditions. The measured development features of the ponderomotive parametric instability in the ionospheric plasma are compared with the calculation results. The instability threshold fields (E_th 220 mV/m) and the damping rates (_e 450 s^-1) of plasma waves, measured under evening-time conditions, are close to the estimates obtained on the assumption of collisional damping of Langmuir turbulence. A significant increase in the threshold field and the damping rate (by factors of up to 3 and 6, respectively) was observed under daytime conditions. In this case, the minimum values of these quantities (E_th 350 mV/m and _e 600 s^-1) were observed for pump-wave reflection heights of about z 230 km. The measurement and simulation results are indicative of the dominant effect of photoelectrons on the development features of ionospheric plasma turbulence under daytime conditions. We discuss the possibilities of using the developed method for comprehensive monitoring of the parameters of Langmuir turbulence and the background ionospheric plasma.     

基于修正大气谱的湍流相位屏高精度生成方法

为了更准确地反映湍流的实际特征,在光波的大气传输模拟中应采用修正大气折射率谱模型.本文针对该谱模型提出了一种高精度湍流相位屏生成方法.通过改变模型在低频区的采样设置,实现了基于修正大气谱的湍流相位屏高精度生成.通过与原始FFT法、次谐波法以及改进前的优化方法相比发现,本文提出的改进后的优化方法能将相位屏低频区域的最大相对误差从改进前的6.75%减小到1%,作为比较,原始FFT法在低频区的最大相对误差为22.99%,次谐波法为16.81%.利用该方法所生成的相位屏对高斯光束在湍流中的传输进行了模拟并对光束扩展和光束漂移等二阶统计特性进行了估计.结果表明,在弱扰动条件下,模拟结果和理论预测的结果是一致的;在强扰动条件下,随着距离的增加,模拟结果与理论结果偏差越来越大,其中光束扩展与理论预测的偏差最大可达6cm,而光束漂移可达1cm,这是由于理论模型无法预测漂移饱和现象而导致的.在与Von-Karman谱的模拟结果比较时发现,修正大气谱估计的光束扩展大于Von-Karman谱的估计且在光束漂移的预测中比Von-Karman谱更快的达到饱和,这正是修正大气谱高波数处存在"凸起"的结果.本文提出的方法生成的相位屏能够有效的表征实际大气的折射率扰动特性.     

On the Jones Index Values for Conformal Subnets

We consider the smallest values taken by the Jones index for an inclusion of local conformal nets of von Neumann algebras on S ¹ and show that these values are quite more restricted than for an arbitrary inclusion of factors. Below 4, the only non-integer admissible value is 4 cos² π/10, which is known to be attained by a certain coset model. Then no index value is possible in the interval between 4 and ${3 +\sqrt{3}}$ . The proof of this result is based on α-induction arguments. In the case of values below 4 we also give a second proof of the result. In the course of the latter proof we classify all possible unitary braiding symmetries on the ADE tensor categories, namely the ones associated with the even vertices of the A _n , D _2n , E ₆, E ₈ Dynkin diagrams.     

Continuous Spectrum of Automorphism Groups and the Infraparticle Problem

This paper presents a general framework for a refined spectral analysis of a group of isometries acting on a Banach space, which extends the spectral theory of Arveson. The concept of a continuous Arveson spectrum is introduced and the corresponding spectral subspace is defined. The absolutely continuous and singular-continuous parts of this spectrum are specified. Conditions are given, in terms of the transposed action of the group of isometries, which guarantee that the pure-point and continuous subspaces span the entire Banach space. In the case of a unitarily implemented group of automorphisms, acting on a C*-algebra, relations between the continuous spectrum of the automorphisms and the spectrum of the implementing group of unitaries are found. The group of spacetime translation automorphisms in quantum field theory is analyzed in detail. In particular, it is shown that the structure of its continuous spectrum is relevant to the problem of existence of (infra-)particles in a given theory.     

Density Fluctuation Spectrum of Solar Wind Turbulence between Ion and Electron Scales

We present a measurement of the spectral index of density fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1?AU was found to be -2.75±0.06, steeper than predictions for pure whistler or kinetic Alfvén wave turbulence but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.     

Fourier Transform Spectrum and Term Values for the CO-Stretching Mode of CD3OH Methanol

The Fourier transform infrared (FTIR) spectrum of the CO-stretching fundamental band of CD₃OH has been recorded at a resolution of 0.002 cm^-1. Assignments are reported for 35 subbands in the n = 0 ground torsional state, covering K = 0 to 9 for all torsional symmetries plus K = 10 A, and 12 assorted A and E subbands in the n = 1 first excited torsional state ranging from K = 0 up to K = 5. The subband wavenumbers have been fitted to J(J + 1) power-series energy expansions to obtain subband origins and a compact representation of the spectral observations. With the use of known ground-state energies, CO-stretch energy term values have been determined and tabulated. Least-squares fitting of the subband origins to a fourth-order Hamiltonian model for the CO-stretch mode is discussed.     

植被结构特征对MODIS光谱干旱指数的影响

基于MODIS光谱反射信息的干旱指数在农业生产实践中有广泛的应用。利用PROSAIL模型和山东2010年的观测数据,研究了植被叶面积指数和生理生长周期等结构特征对MODIS光谱干旱指数的影响。结果表明,MODIS近红外与短波红外三个波段的反射率随植被叶片含水量变化明显,由他们构建的五种MODIS光谱干旱指数能够监测植被叶片水分含量。然而,各干旱指数均受叶面积指数(LAI)的影响,在LAI较低时影响较为严重,随着LAI的增大,这一影响逐渐减弱;植被生理生长周期也会影响干旱指数的大小。因此,在使用MODIS光谱干旱指数进行区域干旱监测时,必须考虑植被结构特征,谨慎分析监测结果。研究结论将为干旱遥感监测提供理论基础。     

On the Well-Posedness Problem and the Scattering Problem for the Dullin-Gottwald-Holm Equation

In this paper, we study the well-posedness of the Cauchy problem and the scattering problem for a new nonlinear dispersive shallow water wave equation (the so-called DGH equation) which was derived by Dullin, Gottwald and Holm. The issue of passing to the limit as the dispersive parameter tends to zero for the solution of the DGH equation is investigated, and the convergence of solutions to the DGH equation as ²0 is studied, and the scattering data of the scattering problem for the equation can be explicitly expressed; the new exact peaked solitary wave solutions are obtained in the DGH equation. After giving the condition of existing peakon in the DGH equation, it turns out to be nonlinearly stable for the peakon in the DGH equation.     

氢原子光谱实验的误差及其优化问题研究

主要介绍了利用精密光栅单色仪扫描氢原子光谱获得光谱波长,定性和定量地探究实验最佳条件的选择,对氢原子光谱实验进行误差分析,并提出优化改进方案,从而对学生实验进行指导,加深学生对近代物理的了解。     

On the Gribov Problem for Generalized Connections

 The bundle structure of the space of Ashtekar's generalized connections is investigated in the compact case. It is proven that every stratum is a locally trivial fibre bundle. The only stratum being a principal fibre bundle is the generic stratum. Its structure group equals the space of all generalized gauge transforms modulo the constant center-valued gauge transforms. For abelian gauge theories the generic stratum is globally trivial and equals the total space . However, for a certain class of non-abelian gauge theories – e.g., all SU(N) theories – the generic stratum is nontrivial. This means, there are no global gauge fixings – the so-called Gribov problem. Nevertheless, for many physical measures there is a covering of the generic stratum by trivializations each having total measure 1. Finally, possible physical consequences and the relation between fundamental modular domains and Gribov horizons are discussed. Received: 4 March 2002 / Accepted: 20 August 2002 Published online: 30 January 2003 Communicated by H. Nicolai     

Geomagnetic Control of the Spectrum of Traveling Ionospheric Disturbances Based on Data from a Global GPS Network

An attempt is made to verify the hypothesis on the role of geomagnetic disturbances as a factor determining the intensity of traveling ionospheric disturbances (TIDs). To improve the statistical validity of the data, we used the method of global spatial averaging of disturbance spectra of the total electron content (TEC), which is based on the new GLOBDET technology. To characterize the TID intensity quantitatively, we propose using a new global index of the degree of disturbance, which is equal to the mean value of the r.m.s. TEC variations within the chosen range of TID periods (20-60 min in the present case). The analysis was made for a set of 100 to 300 GPS stations, and for 10 days with different levels of geomagnetic activity (the Dst index varied from -13 to -321 nT and the Kp index, from 3 to 9). It was found that as the magnetic disturbance increases, the total intensity of TIDs also increases monotonically; however, the latter correlates not with the absolute value of Dst but with the value of the time derivative of Dst (the maximum correlation coefficient reaches -0.94). The delay about 2 h in the TID response is consistent with the viewpoint that TIDs are generated in auroral regions and propagate toward the equator with a velocity of about 300-400 m/s.