Practical model for the calculation of multiply scattered lidar returns

An equation to predict the intensity of the multiply scattered lidar return is presented. Both the scattering cross section and the scattering phase function can be specified as a function of range. This equation applies when the cloud particles are larger than the lidar wavelength. This approximation considers photon trajectories with multiple small-angle forward-scattering events and one large-angle scattering that directs the photon back toward the receiver. Comparisons with Monte Carlo simulations, exact double-scatter calculations, and lidar data demonstrate that this model provides accurate results.     

Bridging the quasi-static and the physical optics approximations: an elliptic disk case

A reformulated integral equation is solved inside an elliptic disk particle for an electromagnetic field formulation bridging the quasi-static and the physical optics approximations. The scattering amplitude tensor elements associated with such a field formulation are derived and then used to formulate the extinction cross sections. It is shown that the extinction cross sections have a frequency dependence and an incidence angle dependence similar to those associated with the physical optics approximation, and they have a particle shape dependence similar to that associated with the quasi-static approximation. Furthermore, at the high-frequency limits, it is shown that those cross sections could reach the value known in the literature by the extinction paradox, namely, twice the particle geometric shadow area.     

Scattering from infinitely sloped surfaces by use of the Kirchhoff approximation

A simple reformulation of the double-scatter Kirchhoff approximation is presented to extend the use of this calculation method to infinitely sloped surfaces. Examples are presented for square grooves and lines on perfectly conducting surfaces. The results presented show the accuracy of the method and the errors produced by not including higher-order scattering in the calculations.     

Crack path prediction of thermal cracks arising in self-stressed two-phase brittle compounds

Conclusions The crack path prediction of thermal cracks in self-stressed two-phase compounds subjected to uniform and nonuniform temperature distributions, respectively, has been studied by using the finite element method as well as by applying an appropriate crack growth criterion. A series of different self-stressed two-phase solids subjected to uniform as well as nonuniform temperature distributions, respectively, have been investigated. A comparison of the numerically obtained results in case of the existence of a uniform temperature distribution in the cross sections of two-phase composite structures for both the thermal crack paths and the corresponding fracture mechanical data at the crack tips with the experimental results gained from associated cooling experiments showed a good agreement.In addition, the influence of additional local temperature changes onto the prospective thermal crack paths has been investigated by means of the crack growth criterion already mentioned. Thereby some remarkable effects of interference between the centers of local temperature changes located in the vicinity of the tips of thermal cracks and their further crack paths could be stated. This interference is also observable concerning the corresponding fracture mechanical parameters at the tips of the arising curvilinear thermal cracks.Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 28, No. 1, pp. 85–91, January–February, 1992.     

Scaling the dynamic electron scattering in imaging the graphene sheets by the high-angle annular dark-field microscopy

Employing the graphene sheets (GSs), the electron scattering constants are measured in the high-angle annular dark-field (HAADF) imaging by the scanning transmission electron microscopy. Single scattering is found to be dominant until the layer number of 200, complying with a simple relation of I = Io(1 - e(-tau/lambda)). The discrete layer counting of the GSs enables precise determination of incident depths. This work results values of lambda = 48.2, 61.4, 97.9 and 115.6 nm for 80, 120, 160 and 200 keV electrons, respectively. The uncertainties with the mean free paths and the cross sections are confined to 10 percent. The dependences on the electron beam energy and the collection angle are discussed based on a multislice simulation.     

Charge transfer and ionisation by intermediate-energy heavy ions

The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u(-1) or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7(+), 32 MeV sulphur ions have an equilibrium charge of approximately 11(+), and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C(+) ions with energies of 100 and 200 keV u(-1) are described.     

Multiple Scattering from Rough Dielectric and Metal Surfaces Using the Kirchhoff Approximation

Abstract

The Kirchhoff double-scatter method for calculating the intensity distribution scattered from a rough surface is extended to dielectric and metal surface materials. The material properties are contained in the Fresnel reflection coefficients only. It is shown that the results agree well with calculations using the exact method for a surface of Gaussian statistics with standard deviation of height σ = 1·93λ and 1/e correlation length τ = 5·02λ.     

Excitation of 6S0, 6P0, and 6D0Levels of Niobium Atom by Electron Impact

The excitation of odd sextet levels of the niobium atom in collisions with slow electrons is investigated experimentally. The measured values of the excitation cross sections of the spectral lines of NbI are used to determine the excitation cross sections of energy levels. The available reference data on the branching factors are used for more complete inclusion of branching. The obtained values of excitation cross sections of the levels of the niobium atom are compared with the theoretical values.     

Computation of cross sections and dose conversion factors for criticality accident dosimetry

In the application of criticality accident dosemeters the cross sections and fluence-to-dose conversion factors have to be computed. The cross section and fluence-to-dose conversion factor for the thermal and epi-thermal contributions to neutron dose are well documented; for higher energy regions (>100 keV) these depend on the spectrum assumed. Fluence is determined using threshold detectors. The cross sections require the folding of an expected spectrum with the reaction cross sections. The fluence-to-dose conversion factors also require a similar computation. The true and effective thresholds are used to include the information on the expected spectrum. The spectra can either be taken from compendia or measured at the facility at which the exposures are to be expected. The cross sections can be taken from data computations or analytic representations and the fluence-to-dose conversion factors are determined by various standards making bodies. The problem remaining is the method of computation. The purpose of this paper is to compare two methods for computing these factors: analytic and Monte Carlo.     

Spectroscopic investigation of Nd ion in LiNbO3, MgO:LiNbO3 and LiTaO3 single crystals relevant for laser applications

The polarized absorption and luminescence properties of Nd³⁺ doped isostructural LiNbO₃, MgO:LiNbO₃ and LiTaO₃ nonlinear bulk single crystals are reported. Pump-probe experiments associated with the Judd-Ofelt approach are used to estimate two types of room temperature cross sections: polarized emission cross sections of the dominant ⁴F_3/2 → ⁴I_1//2 transition near 1085 and 1093 nm and polarized excited-state absorption cross sections in the same spectral domain and in the green spectral range corresponding to self frequency doubling. Self frequency-doubling results are also given in Nd:LiNbO₃ and Nd:MgO:LiNbO₃ versus sample temperature.     

Lidar aerosol backscatter cross sections in the 2-νm near-infrared wavelength region

Lidar backscatter cross-sectional measurements at 1.064, 0.532, and 1.54 μm were acquired during November 1989 and May-June 1990 around the Pacific region by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The primary motivation for the Global Backscatter Experiment was the study of lidar backscatter cross sections for the development of a spaceborne wind-sensing lidar. Direct backscatter measurements obtained by the NASA Goddard Space Flight Center visible and infrared lidar are compared with backscatter cross sections calculated from aerosol size distributions obtained by particle counters. Results for one flight with pronounced aerosol layers in the upper troposphere southeast of Japan are presented. Because 2-μm region wavelengths are possible candidates for a spaceborne wind-sensing lidar, the visible and infrared lidar backscatter cross sections at 1.064, 0.532, and 1.54 μm are extrapolated to the 2-μm region. The extrapolated 2-μm cross sections are compared with lidar measurements at 9 μm. A significant range in the ratio of 2-9-μm backscatter cross sections is found, but a large number of points concentrate near ratios of three to ten. A large number of 1.064- and 1.54-μm cross sections were binned to provide an estimate of backscatter for various percentiles for the flight. The ratio of the 50-percentile backscatter values at 1.064 and 1.54 μm suggest a λ(-1.9) to λ(-3.0) wavelength dependence of aerosol backscatter cross section in the near infrared for the observational case.     

Real and virtual radiation

Electrodisintegration cross sections are related to the corresponding photonuclear processes through virtual-photon spectra. A brief review of virtual-photon theory is presented. Calculations of DWBA virtual-photon spectra for finite nuclei are compared with experimental results. The multipole decomposition of electrodisintegration cross sections using these spectra is discussed and several experimental results are presented. A brief review for the bremsstrahlung cross section is also presented.     

Genetic algorithm for discrete‐sizing optimal design of trusses using the force method

In the process of discrete‐sizing optimal design of truss structures by Genetic Algorithm (GA), analysis should be performed several times. In this article, the force method is employed for the analysis. The advantage of using this method lies in the fact that the matrices corresponding to particular and complementary solutions are formed independently of the mechanical properties of members. These matrices are used several times in the process of the sequential analyses, increasing the speed of optimization. The second feature of the present method is the automatic nature of the prediction of the useful range of sections for a member from a list of profiles with a large number of cross‐sections. The third feature consists of a contraction process developed to increase the efficiency of the GA by which an optimal design for the first sub‐string associated with member cross‐sections is obtained. Improved designs are achieved in subsequent cycles by reducing the length of sub‐strings. Copyright © 2002 John Wiley & Sons, Ltd.     

Spectrally resolved absolute fluorescence cross sections for bacillus spores

Absolute fluorescence cross sections for Bacillus subtilis and B. cereus bacterial spores as both aqueous suspensions and aerosols were measured at a number of excitation wavelengths between 228 and 303 nm. The fluorescence was spectrally resolved at each excitation wavelength. We found that the optimum excitation wavelength for spore fluorescence is between 270 and 280 nm. The fluorescence cross section for aqueous suspensions is four times larger than for dry aerosols when measured under similar conditions. Measurements on wet aerosols showed an increase in fluorescence cross section over dry aerosols, indicating an enhancement of the fluorescence when the bacterial spores are wet. Mie scattering cross sections at 90 degrees to the direction of the incident radiation and extinction cross sections as a function of wavelength for B. subtilis suspensions and fluorescence cross sections for tryptophan are also reported.     

加载路径对变径管内高压成形影响的模拟研究

基于Dynaform有限元模拟软件,在获得合适总轴向进给量以及最大内压力的基础上,重点探讨了轴向进给路径以及内压力加载路径对变径管内高压成形的影响。结果表明：按照前段进给速度大于后段进给速度的双线性轴向进给方式进给能得到一条最优的轴向进给路径;梯形内压加载方式的成形结果要明显优于线性内压加载方式,且当内压区间为40～60MPa时,梯形内压加载方式的成形结果达到最优化。     

Scattering Properties of Spin-Polarized Liquid 3He

In this paper, the scattering properties of spin-polarized liquid ³He (³He^??) are studied using the Galitskii-Migdal-Feynman (GMF) formalism. The effective cross sections??including the total, diffusion and viscosity cross sections??are calculated. It is found that these cross sections tend to decrease with increasing spin polarization f. The S-wave scattering cross section is the most significant partial wave contributing to the total cross section at low energy. This contribution decreases with increasing f; whereas the contribution of the higher angular-momentum waves, especially the P-wave, increases with increasing f. The most prominent features of our calculations are a resonance and a Ramsauer-Townsend minimum in the cross sections at low temperatures. For comparison purposes, the effective cross sections in the Brueckner-Bethe-Goldstone (BBG) formalism are calculated. These remain zero up to the Fermi momentum, beyond which they are equal to those given by the GMF formalism. We deduce that hole-hole scattering plays an essential role in the scattering properties.     

Backscatter signatures of biological aerosols in the infrared

To develop a deeper understanding of the optical signatures of both biological aerosols and potential interferents, we made field measurements of optical cross sections and compared them to model-based predictions. We measured aerosol cross sections by conducting a hard-target calibration of a light detection and ranging system (LIDAR) based on the Frequency Agile Laser (FAL). The elastic backscatter cross sections are estimated at 19 long-wave infrared (LWIR) wavelengths spanning the range from 9.23 to 10.696 μm. The theoretical modeling of the elastic backscatter cross sections is based on the measured refractive index and size distribution of the aerosols, which are used as inputs into Mie calculations. Both model calculations and experimental measurements show good agreement and also indicate the presence of spectral features based on single particle absorption in the backscatter cross sections that can be used as a basis for discrimination for both standoff and point sensors.     

Carbon K-shell vacancy production and K-K electron capture cross sections for 0.4–1.5 MeV 1H ions incident on CH4 targets

The ratios of the carbon K-K electron capture cross sections to the total K-vacancy production cross sections are measured in a coincidence between carbon KLL Auger electrons and charge-changed ions detected by time-of-flight. The vacancy production cross sections are determined from the carbon total KLL Auger electron production in a separate experiment, and electron capture cross sections are obtained by multiplying the measured ratios by the vacancy production cross sections. The data are compared to first Born and perturbed stationary state theories. Both the carbon K-K electron capture and the vacancy production measurements are found to be in excellent agreement with the ECPSSR theory. K-shell fluorescence yields for carbon in CH₄ are extracted by comparison of the present work and other Auger-electron work to X-ray production measurements. They are found to be independent of ₁¹H⁺ energy from 0.05 to 1.0 MeV where both X-ray and Auger electron data exist.     

Compact Fitting Formulas for Electron-Impact Cross Sections

Compact fitting formulas, which contain four fitting constants, are presented for electron-impact excitation and ionization cross sections of atoms and ions. These formulas can fit experimental and theoretical cross sections remarkably well, when resonant structures are smoothed out, from threshold to high incident electron energies (< 10 keV), beyond which relativistic formulas are more appropriate. Examples of fitted cross sections for some atoms and ions are presented. The basic form of the formula is valid for both atoms and molecules.     

Collision cross sections of proteins and their complexes: a calibration framework and database for gas-phase structural biology

Collision cross sections in both helium and nitrogen gases were measured directly using a drift cell with RF ion confinement inserted within a quadrupole/ion mobility/time-of-flight hybrid mass spectrometer (Waters Synapt HDMS, Manchester, U.K.). Collision cross sections for a large set of denatured peptide, denatured protein, native-like protein, and native-like protein complex ions are reported here, forming a database of collision cross sections that spans over 2 orders of magnitude. The average effective density of the native-like ions is 0.6 g cm(-3), which is significantly lower than that for the solvent-excluded regions of proteins and suggests that these ions can retain significant memory of their solution-phase structures rather than collapse to globular structures. Because the measurements are acquired using an instrument that mimics the geometry of the commercial Synapt HDMS instrument, this database enables the determination of highly accurate collision cross sections from traveling-wave ion mobility data through the use of calibration standards with similar masses and mobilities. Errors in traveling-wave collision cross sections determined for native-like protein complexes calibrated using other native-like protein complexes are significantly less than those calibrated using denatured proteins. This database indicates that collision cross sections in both helium and nitrogen gases can be well-correlated for larger biomolecular ions, but non-correlated differences for smaller ions can be more significant. These results enable the generation of more accurate three-dimensional models of protein and other biomolecular complexes using gas-phase structural biology techniques.