Revealing surface anomalies in structures by in situ measurement of acoustic energy absorption

An improved method is proposed for revealing surface anomalies in structures by in situ relative measurement of acoustic energy absorption. Characterization and mapping of particular structures, such as plasters of antique mural paintings are taken into account as a possible application. In situ measurements of the acoustic energy absorption are carried out, employing a diagnostic technique based on the Cepstrum algorithm. Tests on samples with artificially prepared specimens, simulating surface anomalies, are described and a collection of acoustic images is presented. Properties of the specimens and features of the experimental technique are discussed.     

X-ray Bragg reflectivity and photoabsorption of KAP in the O-K region

The variations of X-ray Bragg reflectivity of KAP present strong anomalies in the vicinity of the K - absorption edge of oxygen contained in this crystal. Such an anomalous behaviour is related to the maxima observed in the KAP photoabsorption spectrum in this region. We conclude that great care must be exercised when using a KAP monochromator for studying the absorption spectrum of oxygen.     

Polarization phenomena in the transparency and adsorption effects induced by the field of counterpropagating waves

The physical processes that form the resonances of saturated absorption and magnetic scanning in the field of counterpropagating waves of an arbitrary intensity when their polarizations change are numerically simulated. The atomic transition with level moment J = 1 is used as an example to show that the anomalies in the experimental saturated absorption spectra are determined by the degree of opening of the atomic transition. In the case of magnetic scanning, the anomalies are caused by the magnetic coherence induced by the wave fields at the levels of the lower state rather than by its transfer from the excited states, as was proposed earlier.     

基于HJ-1A-HSI提取稀土元素地球化学异常信息研究

稀土元素的特征谱带基本不随赋存状态的不同而变化,不能用于矿物种类的探测,却能够证实其自身的存在。通过研究稀土元素及其化合物在遥感可见光-近红外波段的光谱特征,分析了稀土元素含量与特征谱带吸收指数的定量关系。以内蒙古白云鄂博稀土富集地区为例进行试验,通过采集矿区典型岩矿标本的光谱、测试分析样品中Nd含量,表明Nd含量与各特征谱带的吸收深度、吸收指数均存在明显的正相关线性关系,相关性均在0.778以上。其中,726～772 nm谱带的吸收指数与Nd含量相关性最好,达到0.937。在此基础上,结合HJ-1A-HSI高光谱遥感数据的波段设置,构建了定量反演Nd含量的最优模型,并以此反演了区域Nd元素遥感地球化学异常信息。结果表明：与1∶20万水系沉积物地球化学异常对比,二者总体相关性良好。为快速获取区域稀土元素地球化学异常提供了新的手段。     

Low-temperature relaxation in the ZnSe : V<Superscript>2+</Superscript> crystal

Low-temperature anomalies in absorption of the fast transverse and longitudinal ultrasonic waves are revealed in a ZnSe crystal lightly doped (5.6 × 10¹⁸ cm^?3) with V²⁺ ions. These anomalies are interpreted as a manifestation of the Jahn-Teller effect. The temperature dependence of the relaxation time of the impurity 3d electrons is established.     

Threshold phenomena in electron-atom scattering in a laser field

Effective-range theory is developed to describe the processes of multiphoton bremsstrahlung absorption and the emission of laser radiation that accompanies the scattering of electrons from atoms in a laser field. It is found that the cross sections for multiphoton absorption in the plateau region increases resonantly for electron energies corresponding to the thresholds of induced bremsstrahlung (i.e., multiples of the photon energy). It is shown that this effect is caused by the laser-field modified threshold phenomena in the cross sections for multichannel reactions (Baz’ threshold anomalies).     

Luminescence and absorption spectra of polyatomic molecules subjected to conformational transitions

A general approach and results of specific calculations of conjugated vibronic absorption and fluorescence spectra of “soft” molecules subjected to conformational transitions are presented. The vibronic spectra of these molecules exhibit significant anomalies such as a large energy gap between the fluorescence and absorption spectra, a strong deviation from the mirror symmetry, etc., which cannot be explained within the framework of the theory of vibronic spectra based on single-well adiabatic potentials.     

红外吸收峰的强度与反常吸收现象

红外光谱测量有时需要在强的背景信号下得到弱的样品吸收峰,如在大量溶剂中测量溶质的红外光谱.理论上,只要某一组分在背景样品和待测样品的含量(分子个数)完全一致,则该组分的光谱信号就不会出现在最终的红外光谱图上.而实际测量时结果并非总如此.本文在测量聚苯乙烯及硬脂酸的“基线”时发现,在样品吸收较强的峰位(吸光度A＞1.0)...     

Diffraction gratings: An amazing phenomenon

The paper describes and explains the most surprising Woodʼs anomaly: the total absorption of a plane wave by a shallow metallic grating.After a numerical and experimental evidence of the total absorption, we develop a quantitative phenomenological theory. Assuming that the anomalies are caused by the excitation of surface plasmon polaritons on the grating surface, we use theorems on analytic functions of the complex variable for representing the amplitudes of the scattered waves accurately through a phenomenological formula.The original rigorous grating theory used for numerical computations is outlined and some practical applications of strong absorptions are presented.     

Plasma annealing state of semiconductors; plasma condensation to a superconductivity- like state at 1000 K?

The high reflectivity, fluid “plasma annealing” phase of semiconductors, particularly Si, subjected to short, intense pulses of laser or electron or ion beam irradiation is known to exhibit a combination of properties for which no adequate explanation has previously been given. These include an almost crystalline Raman spectrum, a lattice temperature that is an extremely non-linear function of absorbed energy density, an optical band gap with no detectable free carrier absorption, a flat absorption spectrum above the gap. We propose a bose condensation of the carriers excited by the irradiation into a state having properties similar to those of a superconductor to explain these anomalies.     

Mixed valency and first order phase transition in EuPdAs

The intermetallic alloy EuPdAs exhibits a first order phase transition at 180 K. The transition is seen by anomalies in lattice parameters, susceptibility, resistivity, Moessbauer effect and X-ray absorption. It is accompanied by an increase of the Eu valence from 2.15 to 2.40 between 300 K and 4 K. The nature of the non-integral valence and the phase transition are discussed.     

Traces of the theta+ pentaquark in K+ -nucleus dynamics

Long-standing anomalies in K(+)-nucleus integral cross sections could be resolved by extending the impulse-approximation trho optical-potential framework to incorporate K(+) absorption on pairs of nucleons. Substantially improved fits to the data at p(lab) approximately 500-700 MeV/c are obtained. An upper bound on the absorption cross section per nucleon is derived, sigmaabs((K(+))/A approximately 3.5 mb. We conjecture that the underlying microscopic absorption process is K(+) nN--> Theta+ N, where Theta(+) (1540) is the newly discovered exotic Y = 2, I = 0, Z = 1 pentaquark baryon, and estimate that sigma(K(+) d--> Theta(+) p) is a fraction of millibarn. Comments are made on Theta(+) production reactions on nuclei.     

Pressure dependence of the absorption edge in ZnTe

Pressure dependence of the absorption edge in ZnTe has been studied at room temperature. In contrast with the previous result by Drickamer, a monotonous high-energy shift was observed up to about 90 kbar. Small anomalies observed at 30 and 50 kbar may correspond to the resistance decrease of ZnTe.     

On the energy spectrum of protons produced in <Superscript>16</Superscript>O<Emphasis Type="Italic">p</Emphasis> collisions at a momentum of 3.25 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

New experimental data concerning the mechanisms of the production of protons originating as fragments from oxygen-nucleus interactions in a hydrogen bubble chamber at high energies are presented. It is shown that anomalies observed in the energy spectrum of protons at kinetic energies in the range T = 70–90 MeV are associated with the absorption of slow pions by a quasideuteron nucleon pair.     

Low-Temperature Schottky Anomalies and the Magnetic State of the <Emphasis Type="Italic">p</Emphasis> Electrons of Oxygen in Substituted Gd<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>CoO<Subscript>3 – δ</Subscript> Cobaltites

The XANES spectra (X-ray absorption near-edge spectra) at the K edge of Co and the L₃ edge of Gd in polycrystalline Gd_0.4Sr_0.6CoO_{3 – δ} rare-earth oxides with an ordered and disordered distribution of Gd³⁺ and Sr²⁺ cations over the A sites in the crystal lattice are measured. The results of XANES measurements do not reveal a noticeable shift in the absorption edge with increasing Sr concentration as compared to the GdCoO₃ parent composition. The measured temperature dependences of the heat capacity of polycrystalline ordered and disordered samples and a single-crystal ordered Gd_0.4Sr_0.6CoO_2.85 sample exhibit two Schottky anomalies. These anomalies are thought to be related to the high-spin state of the Co³⁺ ions in the pyramidal environment caused by oxygen deficiency and to the magnetic state of oxygen p electrons induced by the doping-assisted generation of a hole in the 2p state. The absence of a noticeable shift in the absorption edge and the presence of two Schottky anomalies support the fact that the charge state of cobalt remains unchanged in the compounds under study.     

Effects of oxygen on the ultrasonic properties of amorphous germanium

The ultrasonic absorption and variation of the sound velocity with temperature has been measured in RF-sputtered films of a-GeO_x from 0.45 to 300 K at a frequency of 300 MHz. Incorporation of oxygen suppresses the strong absorption maximum observed in pure a-Ge at 135 K and results in the formation of two-level tunneling states which give rise to acoustic anomalies as observed in ordinary glasses at low temperature.     

基于反射光谱吸收特征勘探天然气的方法研究

反射光谱学提供了一种高效和低成本的鉴别物质成分和结构的方法;油气微渗漏理论则建立了油气藏与其上部地表的特定异常之间的因果关系。因此,可以通过检测地表异常的反射光谱来勘探油气。野外实地测量和高光谱遥感均能够实现反射光谱的检测。文章通过对青海某地区野外测量的反射光谱的分析,首先提出了典型气田区测点的光谱曲线的宏观吸收特征;然后,完成了反射光谱中的吸收特征的提取,包括吸收波段深度、位置、宽度和对称度,以此分析测区采集的样品光谱,建立了该地区的特征光谱库;提出了检测地表烃类物质的方法;最后基于线性解混模型,实现了半定量地提取测区主要蚀变矿物的丰度信息。     

On the anomalies and role of water clusters in atmospheric absorption of millimeter and submillimeter radio waves

Experimental data are presented which do not confirm the existence of anomalies observed by many investigators in the atmospheric absorption of millimeter and submillimeter radio waves and make questionable the hypothesis on the importance of large water clusters in absorption that is invoked to explain the anomalies.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 4, pp. 483–495, April, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Project No. 94-02-05407-a).     

Polarization Phenomena in Transparency and Absorption Effects Induced by the Field of Unidirectional Waves

Physical processes that form the spectra of saturated absorption and magnetic scanning resonances on an atomic transition with level momentum J = 1 in the field of unidirectional waves of arbitrary intensity under variation in their polarization directions are investigated by numerical simulation and analytically. It is shown that anomalies in nonlinear resonance spectra are determined by the polarization of the waves and the degree of openness of the atomic transition, while anomalies in the experimentally observed magnetic scanning spectra are attributed to the magnetic coherence induced by the fields directly on the levels of the lower state, rather than to its transfer from the excited states, as was assumed earlier.