The adiabatic approximation as a diagnostic tool for torsion-vibration dynamics

The adiabatic separation of large-amplitude torsional motion from small-amplitude vibrations is applied as an aid in interpreting the results of fully coupled quantum calculations on a model methanol Hamiltonian. Comparison is made with prior work on nitromethane [D. Cavagnat, L. Lespade, J. Chem. Phys. 106 (1997) 7946]. Even though the torsional potentials are very different, both molecules show a transition from adiabatic to diabatic behavior when the CH stretch is excited to ν_CH = 4 or higher. In the adiabatic approximation, the effective torsional potentials for the various CH stretch vibrational states do not cross, but the CH vibrational amplitude moves from one bond to the next as a function of torsional angle. In the diabatic approximation, the effective torsional potentials do cross, but the distribution of the CH vibrational amplitude remains approximately constant in the vicinity of the crossing. The transition to diabatic behavior is promoted by the normal mode to local mode transition, and the relevant adiabatic and diabatic effective torsional potentials are determined by the torsion-vibration coupling. The torsion-vibration couplings in the four overtone manifolds considered (methanol OH, CH, nitromethane CH, and hydrogen peroxide OH) are large, reaching 265-500 cm⁻¹ by ν_XH = 6, and are of generally similar magnitude. The largest torsion-vibration couplings involve the first Fourier term in the torsional angle (cosγ for the CH stretch in methanol and the OH stretch in HOOH), whereas higher Fourier terms (cos2γ in nitromethane and cos3γ for the OH stretch of methanol) result in somewhat weaker coupling. Nonadiabatic matrix elements in methanol couple the torsional and vibrational energies and they exhibit a slow fall-off with coupling order.     

Geochemical study of black crusts as a diagnostic tool in cultural heritage

This contribution focuses on spectrometric analyses carried out on crust samples covering the stone surface of the boundary walls of the Tower of London. The main goal of this research is to investigate the degradation processes related to the environmental impact on cultural heritage. Specifically, the chemical contamination of stone substrate in the Tower of London due to the crust formation was examined through laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). This technique allowed us to achieve a complete characterization of the damage layers in terms of trace elements. In addition, optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS) and infrared spectroscopic techniques (FT-IR) were also used for an exhaustive characterization of the examined samples. Results obtained demonstrated that such a geochemical approach represents a powerful diagnostic tool in the study of black crusts, since it represents a reliable indicator of the environmental pollution. The higher concentrations of most heavy metals in black crusts with respect to the underlying stone suggest that crusts were greatly influenced by atmospheric inputs in their formation, mainly represented by mobile combustion sources. In addition, the possibility of analyzing in some samples the portion of altered substrate allowed us to hypothesize that some specific heavy metals tend to migrate from the crust to the unaltered substrate over time, becoming catalysts for the formation of new crust. Therefore, this research focuses on the role of diagnostics in order to plan suitable cleaning and consolidation intervention aimed at a better protection of the monument.     

Multi-step geoacoustic inversion with a towed line array

Geoacoustic inversion is important for acoustic field predictions and matched field localizations in shallow water.Combing the Matched-field inversion(MFI) and the Reflectionloss inversion,a multi-step Bayesian inversion for geoacoustic parameters was presented.This method applied the posterior probability density(PPD) or inversion results from one inversion as prior information for subsequent inversion.First,the sensitive parameters were determined by the MFI.Second,the insensitive parameters were determined by the Reflection-loss inversion based on the PPD and inversion results from the MFI.The PPD results indicated that the multi-step inversion method was performed better than direct matched-field inversion,and the inversion results of some parameters were improved significantly.To demonstrate the advantages of the multi-step inversion method on the sound field prediction,the statistical properties of transmission loss based on the posterior probability were introduced.The transmission loss distribution showed that the predicted acoustic fields based on the multi-step inversion method had smaller errors.     

Chemiluminescence as diagnostic tool in the development of gas turbines

To optimise the operation of gas turbine combustors with respect to emission, cycle efficiency and components lifetime, increased attention has to be attributed to diagnostic techniques and more flexible control schemes. Chemiluminescence is an obvious choice and a relatively easy and low cost option for such a diagnostic tool. Application examples include spectral analysis and light intensity scaling, temporal analysis studying flame dynamic effects and imaging techniques resolving spatial distribution of heat release zones, as well as combinations of the methods like phase matched imaging and tracking of ignition kernels using high speed imaging. Further fundamental work should be triggered on the nature for the excited species and their formation pathways as well as their connection to heat release and the NO _x formation processes.     

Light reflection spectra as a diagnostic tool for the structural and biophysical parameters of skin

The calculation scheme and the diagnostic algorithm for diagnosing the structural and biophysical parameters of skin from the spectrum of reflected radiation are constructed. The sought parameters are determined from the solution of the spectroscopic problem under conditions of multiple scattering. The method presented is based on the previously proposed model of the spectral properties of a tissue and on the engineering approaches to the solution of the transfer equation. The sought parameters are the volume concentrations of melanin and capillaries, the thickness of epidermis, the average diameter of capillaries, and the degree of blood oxygenation. In order to optimize the algorithm with respect to wavelength and to elaborate the experimental diagnostic scheme, the sensitivity of the reflection spectrum to the sought parameters is studied. The procedure of their successive restoration is proposed.     

Spectral line shapes. II

A spectral line shape function theory is extended for gaseous systems where reactive collisions can occur. The theory of subdynamics and the Fock-Tani representation are used in order to attempt this goal. The dependence of the spectral shape on the pressure and the reactive transition probability is clarified. Finally^a discussion concerning the above aspects and their possible applications has been included as well.     

采用拖曳线列阵的海洋声学参数联合反演方法研究

匹配场反演方法是快速获取海底声学参数的一种有效途径,但是其反映的是水体和海底空间变化环境的平均效果,对海底密度和衰减系数的敏感性较小,且在复杂海底环境下,不确定性明显增加。匹配场反演方法通常采用垂直阵来实现,其机动性较差,只能获得局部海区的环境参数。利用拖曳线列阵可以实现环境参数的走航式获取。提出了基于匹配场与反射损失联合反演的方法,利用其中之一的反演结果作为下一步反演的先验信息,敏感参数与不敏感参数多步反演,并逐步缩小了参数的优化空间。同时引入贝叶斯理论与蒙特卡罗方法对反演参数的后验概率密度进行分析,并利用反演结果的后验分布计算了传播损失随距离的概率分布。研究结果表明,联合反演方法对地声参数进行了更准确的反演,尤其是对海底声速反演效果提高明显。通过传播损失的概率分布发现,估计得到的海底参数用于声场预报时,误差较小。     

Mössbauer and infrared spectroscopy as a diagnostic tool for the characterization of ferric tannates

The line shape of the (3p???1s) X-ray transition in muonic hydrogen was measured for the first time with a high-resolution crystal spectrometer. The assumption of a statistical population of the hyperfine levels was directly confirmed by experiment, and a measured value for the hyperfine splitting is reported. An X-ray line broadening due to Doppler effect could be clearly identified and attributed to different Coulomb de-excitation transitions which precede the measured radiative transition. The results allow a decisive test of advanced cascade model calculations and establish an alternative and “model free” method to extract the strong-interaction parameters from pionic hydrogen data.     

LIBS used as a diagnostic tool during the laser cleaning of ancient marble from Mediterranean areas

The use of laser ablation for cleaning stone is a tried-and-tested method for preserving outdoor artwork surfaces exposed to environmental stresses. However, it is of interest to spectroscopically characterize the sample surface before and during the laser ablation in order to implement automatic control of the cleaning process. To this aim, we have undertaken systematic LIBS analysis on various clean and dirty surfaces of marble fragments collected from ancient quarries in Mediterranean areas, without the characteristic patina that comes from the protective layers usually deposited on the final artwork. The effectiveness of the cleaning process was then monitored by following the disappearance from the LIBS spectra of the encrustation elements during successive laser shots. The LIBS analysis of the clean surfaces of the samples examined confirmed that main bulk composition is based on calcium and magnesium carbonates, with the addition of strontium and, to a minor extent, of manganese and copper substituents. On the other hand, the encrustations were rich in sodium, aluminum, iron, silicon, titanium, lithium, manganese, and chromium, probably coming from sand/soil deposition and, only to a minor extent, from atmospheric pollution. Although SEM imaging and SEM-EDX analyses performed on the same samples at different resolutions showed remarkable surface inhomogeneities from the crustal region deep into the bulk material, the work demonstrates the possibility of a quantitative, minimally invasive, LIBS stratigraphy. The results from the technique are suitable for monitoring cleaning processes by determining appropriate elemental markers present on the surface at trace level (of the order of 100 ppm). PACS 52.25.Kn; 7.60.Rd; 32.30.Jc; 42.62.Fi     

Spectral line shape variations in time-resolved photoemission from a solid

Laser assisted photoemission by a subfemtosecond ultraviolet pulse is studied by solving the time-dependent Schr?dinger equation for a one-dimensional model crystal. Without the laser field, the shape and the energy location of the spectrum are determined by the energy dependence of the photoemission cross section. In the presence of the laser field, the time growth of the population of the final state is predicted to cause extremely sharp variations of spectral width as a function of release time. This can help enhance time resolution of the measurements. A simple phenomenological model to describe the line shape is proposed.     

Subbottom profiling using a ship towed line array and geoacoustic inversion

Bottom profiling traditionally uses broadband signals received on a line array at long ranges to estimate the bottom layer structure and thickness. In this paper, a subbottom profiling method is developed and applied to a ship-towed line array using the same ship towed source to estimate the subbottom layer structure and thickness. A ship towed line-array system can be used to estimate bottom properties using geoacoustic inversion and can cover a wide area in a short time. It needs some prior information about the subbottom structure and layer thickness, without which the solution can be ambiguous and even erratic when resolving parameters over a wide area. It is shown that the required subbottom information can be obtained from the time-angle relation by beamforming the same acoustic signal data used for geoacoustic inversion. The time-angle analysis is used to expose the prevalent physics intrinsic to geoacoustic inversion. One finds that the tau-p relation of the bottom and the bottom reflection coefficients, sampled at discrete angles associated with bottom and multiple surface-bottom returns, are often adequate, for many practical applications, to uniquely determine the geoacoustic bottom at low (< or =1 kHz) frequencies.     

汤姆孙散射：等离子体参数诊断的强大工具

汤姆孙散射是低能光子与自由电子之间的弹性散射.因为汤姆孙散射光谱携带着等离子体涨落的信息,通过测量汤姆孙散射光谱可以高精度地测量等离子体的多种参数,如电子温度、电子密度、等离子体流速等等.经过多年的发展,汤姆孙散射已经成为等离子体物理研究中最重要的一种诊断工具.     

汤姆孙散射：等离子体参数诊断的强大工具

汤姆孙散射是低能光子与自由电子之间的弹性散射.因为汤姆孙散射光谱携带着等离子体涨落的信息,通过测量汤姆孙散射光谱可以高精度地测量等离子体的多种参数,如电子温度、电子密度、等离子体流速等等.经过多年的发展,汤姆孙散射已经成为等离子体物理研究中最重要的一种诊断工具.     

Sound speed profile inversion using a horizontal line array in shallow water

It is better to use a simple configuration to enhance the applicability of ocean environment inversion in shallow water.A matched-field inversion method based on a horizontal line array(HLA)is used to retrieve the variation of sound speed profile.The performance of the inversion method is verified in the South China Sea in June,2010.An HLA laid at bottom was used to receive signals from a bottom-mounted transducer.Inverted mean sound speed profiles from 9-hour long acoustic signals are in good agreement with measurements from two temperature chains at the sites of the source and receiver.The results show that an HLA can be used to monitor the variability of shallow-water sound speed profile.     

Spectral line formation in dense large-gradient plasma

The positions and profiles of x-ray spectral lines emitted from well characterized laserproduced plasmas have been investigated. The red shifts observed for higher members of the aluminum Lyman series are consistent with theoretical predictions of the line shifts in hot dense plasmas. The experimentally observed profiles of Al XIII Ly_a line are interpreted by modeling the radiative transport through plasma with large transverse gradients. The presented results originated from collaborative effort of the research groups from the Institute of Physics, Prague, University of Jena and University of Oxford. This work was supported by the Grant Agency of the Czech Republic under Grant No. 202/97/1186.