Multiple electromagnetic scattering by a linear array of electrified raindrops

The Discrete Sources Method is used to construct a computational algorithm for the problem of multiple electromagnetic scattering by a linear array of axisymmetric particles. Numerical implementation is made for radiophysical and radio location characteristics using models for raindrops of different shapes, depending on the orientation of the particles and the polarization of the incident field.     

流散美国的晋式青铜器:乐器篇

笔者于1999年应邀在美国华盛顿弗利尔美术馆作访问学者,并有机会到美国部分大学和博物馆参观访问,期间着重看了一些流散于美国的东周晋式青铜器。作为晋人后裔,我认为有必要把它们再记录一番,以期为晋文化研究补充点资料或信息。但藏于美国的晋式铜器资料分散,有些尚未著录,又因参观访问行色匆匆,故只能择要录之。在进入正题前,我们不妨先从李峪铜器谈起,国近代以来、晋式铜器的首次集中亮相,即始于李峪铜器群的偶然出＿上。从“李峪类型铜器”到“晋式钢器’1923年2月,山西浑源县李峪村村民掘土时,偶然掘出数十件青铜器。它们…     

A quasi-DC model of electric fields in the ionosphere-ground region due to electrified clouds

The penetration of the quasi-DC electric fields, E due to electrified clouds, into the middle- and high-latitude ionosphere is theoretically studied during the initial stage of cloud charge separation. The electrification process is characterized by a source function S(t), whose variations are on the time scale of the relaxation process in the cloud. A first-order approximation solution for the time variation of E is obtained as an explicit function of the electric field in the steady-state case. Some features of the time variations of E at different altitudes (in the ionosphere and also in the atmosphere) are investigated, depending on the source function and the relaxation time constants. This result can also be applied for slowly electrifying clouds which do not produce lightning.     

VLF scattering from a column of ionization in the Earth-ionosphere waveguide

Choosing a highly idealized model, we analyze the scattering of VLF radio waves from a thin vertical column of ionization within the Earth-ionosphere waveguide. It is shown that mode conversion is produced if the column is limited in height and/or if the ionization is a function of height. However, the relative higher-mode content would be small in some situations such as in the case of the ionization produced by a cloud-to-ionosphere lightning discharge.     

Incoherent scattering from the collision dominated D-region. Comparison of theories with experimental data

There has been a long standing controversy as to the introduction of the collisional term in the incoherent scattering theory. This has profound implications in interpreting the incoherent scatter spectra from the collision dominated D- and E-regions. Among the different theoretical formulations, those by Dougherty and Farley and Waldteufel have been used for the interpretation of incoherent scatter data. Waldteufel's formulation apparently improves on the theoretical model of Dougherty and Farley by allowing for momentum conservation and temperature changes during collisions.Using incoherent scatter data from D-region heights over Arecibo we show for the first time that Dougherty and Farley's formulation is the correct one. This is due to the fact that during a collision ions lose both momentum and energy to neutrals and so far as the ion gas is concerned, neither should be conserved.Once the correct formulation has been established, it can be seen that the incoherent scatter technique offers a unique advantage in inferring mesospheric parameters with very high precision. For example, the ratio of the number density to neutral temperature in the D-region over Arecibo could be measured to accuracies of a few per cent. The results of such measurements are in excellent agreement with the CIRA 1972 model and show a day-to-day variability limited to within 10–15%.     

Small angle neutron scattering study of ancient pottery from Syracuse (Sicily,Southern Italy)

This paper is focused on a spectroscopic study of some pottery shards from an archaeological site in Syracuse (Sicily, Southern Italy), dating back to the Hellenistic–Roman period. Structural characterization was performed at different scales of observation, i.e. from macroscopic to mesoscopic. The main goal was to point out the potentiality of the small angle neutron scattering (SANS) technique as a non-invasive analytical tool in archaeometry, also in conjunction with other, more usual, methodologies. Correlation of experimental data, i.e. macroscopic typology and texture, obtained from petrographic analysis, and radius of gyration and fractal dimension of the interfaces of the mesoscopic aggregates obtained using SANS, together with mineralogical X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, allowed hypotheses to be made on the production technology of the investigated samples.     

Improved methodology for extraction and amplification of DNA from single grains of charred wheat

Comparisons were made between two commonly used methods for the extraction of ancient DNA from charred plant remains. Using artificially charred wheat seeds, we show that silica-binding is the most efficient method for extraction of DNA. We describe a improved silica-binding procedure, including pre-incubation with N-phenacylthiazolium bromide and increased washing of bound DNA, which yields amplifiable DNA from seeds heated at 200 °C for up to 8 h, conditions which promote the formation of Maillard products which often copurify with aDNA and inhibit subsequent PCRs. We believe that this method will be effective in ancient DNA extraction with most types of charred archaeobotanical material. Both cold- and hot-start PCR procedures gave good amplicon yields with extracts prepared in this way, but cold-start PCRs also resulted in synthesis of short artefact products. Addition of bovine serum albumin to PCRs, an inert carrier substance thought to enhance amplification efficiency by binding contaminants, had no advantageous effect and in fact reduced amplicon synthesis.     

Theory for stimulated scattering of electromagnetic waves

In order to describe the nonlinear coupling of a large amplitude electromagnetic pump wave with the low-frequency modes in the ionosphere, we introduce new systems of equations that are related to the conventional Zakharov equations. In particular, we consider the excitation of ion-acoustic, electron gyro, and collisional gradient drift modes.     

电磁法在三星堆遗址祭祀区中的探索与应用

自2019年12月,三星堆遗址启动全面的勘探工作,相继在祭祀区新发现6座祭祀坑,为制定科学的考古发掘及文物保护预案,需在考古发掘之前对地下文物有一定的了解。根据一号、二号坑出土物情况,以金属埋藏物为探测对象,使用地球物理勘探方法中的电磁法先期通过实验获取经验值,然后再对祭祀区进行详细探测,并与实际发掘结果比对,说明电磁法对青铜器探测具有一定的可行性,可为前期考古发掘提供重要的参考信息。     

Ultrastructure and DNA sequence analysis of single Concentricystis cells from Alta Val Tiberina Holocene sediment

We successfully combined ultrastructure and chloroplast DNA analysis for single specimens of Concentricystis isolated from Holocene sediment by a palynology method based on filtration, progressive sieving and percoll-gradient sedimentation to concentrate fossil cells. We compared our method with the traditional harsh chemical treatment commonly used to isolate fossil pollen and spores. With our method, the cytoplasm of Concentricystis was sufficiently preserved to distinguish several cell structures by light and electron microscopy. DNA analysis of Concentricystis involved PCR amplification using specific primers for a spacer region of the chloroplast genome. Significant homologies were found with the Angiosperm chloroplast genome by BLAST DNA search for PCR product sequences.     

Application of a scattering theory of VHF transequatorial propagation

Numerical application is made of the theory of scattering by long, curved, field-aligned irregularities of ionization density in the F-region developed by Ferguson and Booker. Using an intermediate-scale regime of irregularities with an outer scale equal to the scale height of the F-region and an inner scale equal to the ion gyroradius, combined with a small-scale regime with an outer scale equal to the ionic gyroradius and an inner scale equal to the electron gyroradius, calculations are made corresponding to (i) equatorial spread-F in the VHF and UHF bands, (ii) long-range transequatorial propagation of the type observed by Nielson and (iii) short-range transequatorial propagation of the type observed by Cohen and Bowles. The same ionospheric model yields field-strengths of the right order of magnitude in all three cases. The theory also predicts a focusing phenomenon that should be looked for experimentally.     

In-situ observations of magnetospheric electron scattering by a VLF transmitter

High resolution pitch angle measurements of outer zone electrons in the energy range 12 keV−1.6 MeV were obtained at high altitude in the region of the high power VLF transmitter UMS [300 kW radiated at 17.1 kHz (Watt A. D., 1967, VLF Radio Engineering, Pergamon Press, Oxford)] while a resonant wave-particle interaction was in progress. Additional complementary electron measurements in the range of 36–316 keV were obtained in the drift loss cone by another satellite at low altitude along the drift path 75° east of the interaction region. The data from the low-altitude satellite confirm that UMS was precipitating particles in the inner zone, in the slot, and in the outer zone at the time that the high-altitude satellite was obtaining its data. The high-altitude pitch angle distributions indicate that, for this event, two types of scattering interactions were in progress. Particles with small pitch angles, up to 17.2° at the Equator, were being removed, resulting in an enhanced loss cone. Particles which were mirroring between 6500 km and the altitude of the spacecraft (7200) km were also being strongly scattered, resulting in a relative minimum in the pitch angle distribution around 90°. The data are interpreted as indicating that a cyclotron mode interaction with UMS waves was precipitating electrons with equatorial pitch angles up to 17.2° and that another process, perhaps electrostatic (ES) waves arising from the UMS radiations through a mode-conversion process, was present in the region above 6500 km and was efficiently scattering those particles which mirrored in that region     

Iterative methods for treating the multiple scattering of radio waves

An iterative method is developed for treating multiple scattering in an extended random medium. The basis of the method is to use the single-scatter theory to derive a recurrence relation for the complex field. Since no restriction is placed on the incremental layer thickness, the single scatter theory can always be applied in this manner, subject only to the narrow-angle-scatter restriction. Indeed, in the differential limit of zero layer thickness, the recurrence relation, which is a difference equation, converges to the parabolic wave equation.The recurrence relation for the complex field is then used in conjunction with the Markov assumption to derive recurrence relations for the complex field moments of all orders. The recurrence relations for the general complex field moments converge to well known differential equations in the limit of zero layer thickness. The result is derived without constraints on the stastics of the index of refraction fluctuations. Moreover, the method of development suggests that the conditions for narrow-angle scattering alone are sufficient to guarantee the validity of the Markov approximation.Finally, a local phase-screen approximation is used to develop alternative recurrence relations for the complex field and the general complex field moments that are conceptually simpler and more efficient for numerical computation. Throughout the development, a formulation is used that retains an explicit dependence on the propagation angles relative to an arbituary but fixed co-ordinate system.     

Electromagnetic wave propagation in a field-aligned-striated cold magnetoplasma with application to the ionosphere

The problem of wave propagation in a cold magneto-ionic medium with plane or circular cylinder small scale random density fluctuations is considered. By including second or terms in the perturbation it is possible to derive a refractive index for a “mean” wave in the medium. It is shown that the striations cause new cutoffs and resonances to occur. The validity of the theory for a warm plasma will depend on the plasma temperature and on the spatial spectrum of fluctuations. Possible applications are considered.     

Three-channel autoregressive bispectral analysis for the laser scattering measurement of turbulence

The bispectral analysis for detecting the nonlinear quadratic mode-mode couplings in fluid and plasma turbulences is developed in a numerical technique with respect to the three-wave vector electro-magnetic wave scattering observation using the coherent signal detection technique. The autoregressive method of Raghuveer-Nikias is extended to a three-channel complex diagonal form by taking into account the sum rule of wave vectors for nonzero bispectrum of stationary homogeneous fluctuations. Some results of simulation and experiment are presented.     

Variations of the lower ionosphere parameters measured by the resonance scattering method

This paper presents the results of diagnostics of the lower ionospheric parameters by using the resonance scattering method (RSM) of radio waves on periodic artificial irregularities (PAI). The following ionospheric parameters have been measured by the heating facilities ‘Zimenki’ and ‘Sura’: electron density including the E-F interlayer valley and the lowest height of the ionosphere; the velocity of the vertical wind; the relaxation times of the PAI characterizing coefficients of ambipolar diffusion, and coefficients of attachment and detachment of electrons from negative ions. Variations of these parameters have been considered as a function of height, local time, season, solar activity as well as being induced by passing acoustic-gravity waves and by ionospheric disturbances.     

Multiple-frequency studies of the high-latitude summer mesosphere : implications for scattering processes

The characteristics of polar mesosphere summer echoes (PMSE) are studied at 53.5 and 224 MHz. Observations at 2.78 MHz, simultaneous with the ones at the other two frequencies, were carefully compared for indications of PMSE, but no obvious relation was found. Relationships between relative scattering cross-section, spectral width and vertical velocity are studied for the 224 MHz radar, and observations at 53.5 MHz are compared with those at 224 MHz. Results of aspect sensitivity measurements at 53.5 MHz are presented. The implications of these characteristics for several possible scattering mechanisms are discussed. We rule out incoherent scatter and chemically induced fluctuations from the evidence that we have. In view of the extremely low temperatures near the high-latitude mesopause in summer, we discuss several scenarios involving heavy cluster ions and charged aerosol particles.