Measurements of emission spectra from hot,dense germanium plasma in short pulse laser experiments

Heating of thin foil targets by an high power laser at intensities of 10¹⁷–10¹⁹ W/cm² has been studied as a method for producing high temperature, high density samples to investigate X-ray opacity and equation of state. The targets were plastic (parylene-N) foils with a microdot made of a mixture of germanium and titanium buried at depth of 1.5 μm. The L-shell spectra from the germanium and the K-shell spectra from the titanium were taken using crystal spectrometers recording onto film and an ultra fast X-ray streak camera coupled to a conical focussing crystal with a time resolution of 1 ps. The conditions in the microdot were inferred by comparing the measured spectra to synthetic spectra produced by the time-dependent collisional–radiative (CR) models FLY and FLYCHK. The data were also compared to simulated spectra from a number of opacity codes assuming local thermodynamic equilibrium (LTE). Temperature and density gradients were taken into account in the comparisons. The sample conditions were inferred from the CR modelling using FLYCHK to be 800 ± 100 eV and 1.5 ± 0.5 g/cc. The best fit to the LTE models was at a temperature 20% lower than with the CR model. Though the sample departs from LTE significantly useful spectral comparisons can still be made. The results and comparisons are discussed along with improvements to the experimental technique to achieve conditions closer to LTE.     

Simulation of X-ray scattering diagnostics in multi-dimensional plasma

X-ray scattering is a powerful diagnostic technique that has been used in a variety of experimental settings to determine the temperature, density, and ionization state of warm dense matter. In order to maximize the intensity of the scattered signal, the x-ray source is often placed in close proximity to the target plasma. Therefore, the interpretation of the experimental data can become complicated by the fact that the detector records photons scattered at different angles from points within the plasma volume. In addition, the target plasma that is scattering the x-rays can have significant temperature and density gradients. To address these issues, we have developed the capability to simulate x-ray scattering for realistic experimental configurations where the effects of plasma non-uniformities and a range of x-ray scattering angles are included. We will discuss the implementation details and show results relevant to previous and ongoing experimental investigations.     

沟槽面与光滑面湍流边界层特性比较

应用ＬＤＶ技术对沟槽面及光滑面湍流边界层流速和湍流度分布进行了精细的测量，实验结果表明：与光滑面相比，沟槽面湍流边界层时均流速分布对数公式中具有较大的积分常数Ｃ值，且沟槽面湍流度最大值较小，但其出现的位置距壁面较远。另外，偏斜因子及平坦因子的分布特性区别不大，但是在近壁区内沟槽面结果波动较大。     

Comparison of fatigue effects in simulated and actual earthquakes

One of the unresolved aspects of simulated earthquake testing concerns the amount of low-cycle fatigue produced by a series of single-frequency-vibration tests compared to random-motion excitation. The recommended sinebeat vibration input using 5 cyc/beat at each measured equipment natural frequency is considered conservative because it can produce more fatigue damage than the most severe earthquake being postulated. A computer-aided analysis has been made of simple mass-spring-damper systems representing the uncoupled structure and equipment response to well-known acceleration-time histories available for both the El Centro-1940 and San Fernando-1971 earthquakes. In the proposed testmachine simulation, the comparable sine-beat-vibration input was adjusted to duplicate the building-floor response at the base of the equipment, which was represented as a series of oscillators geometrically spaced in the 1 to 25-Hz range of damaging earthquake effects. Both large- and small-strain ranges have been compared, but these values are assumed for convenience and cannot be used as actual seismic effects in specific pieces of equipment.     

Interfacial separation between elastic solids with randomly rough surfaces: Comparison between theory and numerical techniques

We study the distribution of interfacial separations at the contact region between two elastic solids with randomly rough surfaces. An analytical expression is derived for the distribution of interfacial separations using Persson's theory of contact mechanics, and is compared to numerical solutions obtained using (a) a half-space method based on the Boussinesq equation, (b) Green's function molecular dynamics technique and (c) smart-block classical molecular dynamics. Overall, we find good agreement between all the different approaches.     

Comparison between the relaxation spectra obtained from homogenization models and finite elements simulation for the same composite

The objective of this work is to determine the relaxation spectrum of spherical particles reinforced viscoelastic and isotropic composites from 3D Finite Elements (FE) simulations of the microstructure. The matrix and the reinforcements are assumed to be incompressible and Maxwellian. The spectra obtained from the FE simulations are compared with those obtained from analytical homogenization models. This paper presents the procedure used for generating the FE models as well as the procedure used for obtaining relaxation spectra meeting the thermodynamics requirements imposed on linear viscoelastic materials. It seems that the relaxation spectrum for the microstructure studied in this paper is composed of a negligible continuous part and a discrete part of higher intensity. In any case, the resulting material does not have a Maxwellian behavior.     

A fundamental relationship between the relaxation spectra and the tangent distribution function in the theory of linear viscoelasticity

The tangent distribution function (TDF) is analyzed within the theory of linear viscoelasticity on mechanical properties. A proof is given that both the relaxation and retardation spectra can be derived from the TDF, through a Fredholm integral equation. Furthermore, the relaxation strength can be calculated as a consequence of this relationship. Finally, as an example, the relationship is applied to discrete spectra.     

Global wave-induced loads in abnormal waves: Comparison between experimental results and classification society rules

It is important to assess the consequences of ship encounters with abnormal waves due to the perceived dangers of such encounters. A starting point for this is the assessment of global loads, with a focus on examining how the design rules fare with respect to loads induced by abnormal wave encounters. This paper presents the results of an experimental investigation into the global wave induced loads experienced in a range of abnormal sea states. Results are obtained for a segmented, flexible backbone model of a typical naval frigate. Abnormal wave encounters result in a significant increase in the global wave-induced loads compared to the equivalent random sea, with slamming becoming considerably more severe. Through comparisons with the experimental measurements it is concluded that the design rules which allow for an extreme wave encounter provide a reasonable safety margin for the global loads in abnormal waves, although discrepancies occur towards the aft of the vessel. Further investigation of the amount and conditions in which the design rules may be exceeded by an abnormal wave encounter is required.     

Experimental study and modeling of particle drying in a continuously-operated horizontal fluidized bed

Multistage fluidized beds are frequently used for product drying in industry. One advantage of these fluidized beds is that they can achieve a high throughput, when operated continuously. In this study, γ-Al₂O₃ particles were dried in a pilot-scale horizontal fluidized bed, without considering any comminution effects. For each experiment, the particle moisture content distribution and residence time distribution were determined. To take into account particle back mixing in our experiments, a one-dimensional population balance model that considers particle residence time was introduced into a fluidized bed-drying model. Experimental particle residence time distributions were reproduced using a tank-in-series model. Subsequently, the moisture content distribution was implemented, as a second dimension to the population balance in this model. These two-dimensional simulations were able to describe the experimental data, especially the spread in the residual particle moisture distribution, much more accurately than one-dimensional simulations. Using this novel two-dimensional model, the effects of different operating parameters (process gas temperature, solid feed rate, superficial air velocity) on the particle moisture content distribution were systematically studied.     

Quantitative measurement of hard X-ray spectra from laser-driven fast ignition plasma

Absolute Kα line spectroscopy is proposed for studying laser–plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100 keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems were calibrated using pre-characterized laser-produced X-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta Kα lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time.     

Theoretical and experimental analysis of iron-exchanged X-zeolite catalyst for SI engine emission control

The fuel economy potential of lean-burn gasoline engines can be utilized without any adverse effect on the environment, only if a suitable catalytic system for converting NO_x in an oxidizing atmosphere is available. Selective catalytic reduction of NO_x over metal-exchanged zeolite can be one of the solutions for reducing NO_x in automobile exhaust containing excess oxygen. Iron-exchanged X-zeolite catalyst (Fe–X) has been developed and tested in the exhaust of an actual SI engine over a wide range of air–fuel ratio, space velocity (SV) and catalyst temperature. Maximum conversion efficiencies of 55.8% and 57.4% were recorded for NO_x and CO, respectively. The catalyst also maintains its high performance through a wide range of temperatures. A mathematical model has been developed as well for predicting the performance of the catalytic converter containing Fe–X catalyst and the numerical solutions are presented. The predicted results agree well with the experimental results and are within the experimental uncertainty limits. The absolute average deviations are found to be within 6% and 5% of the predicted conversion efficiencies for NO_x and CO, respectively.     

Experimental and numerical investigation of a capacitively coupled low-radio frequency nitrogen plasma

A capacitively coupled nitrogen discharge driven at a frequency of 40 kHz was analyzed using a particle-in-cell (PIC) code, electrical probe measurements and optical emission spectra (OES). The configuration studied is used to generate plasmas for surface modification of polymer webs and consists of a pair of coplanar electrodes spaced several centimeters from the web plane and housed in a grounded shield. Both the probe measurements and the simulations indicate the presence of a group of high-energy electrons in concentrations of order 0.1% of the bulk electron concentration. Furthermore, bulk electron temperatures from the simulations are less than 1 eV. The energetic electrons and the low temperature of the bulk electrons are both characteristics of discharges operating in the gamma regime, where secondary electron emission from ion bombardment of the cathode sustains the ionization in the discharge. Because ions can respond to the instantaneous potential at the low-driving frequency used, half of the current at the electrode location is ion current. (In contrast, displacement current from the electron motion dominates at significantly higher driving frequencies.) The energetic electrons can provide a valuable source of N⁺ ions through dissociative ionization. The formation of the N⁺ ion was not included in the simulation, but was detected by the OES measurements. The atomic nitrogen ions and neutrals, together with the high-energy electrons, may be responsible for the formation of nitrogen-containing species in the surface region of polymer films treated with nitrogen plasmas using the configuration studied in this work.     

Comparison of electrical and laser spark emission spectroscopy for fuel concentration measurements

Emission spectra from electrical and laser sparks in flowing methane–air mixtures of various compositions have been collected and analysed. The differences and similarities between the electrical and laser sparks in the context of their emission are discussed. The emission spectra from the laser spark were characterized by a weak continuum, onto which several strong atomic lines and some molecular bands were superimposed, in contrast to the spectra of electrical spark where a strong continuum, few atomic lines and several strong molecular bands were evident, making thus the laser spark spectroscopy a more accurate technique to measure hydrocarbon concentration. For both types of spark, the total intensity of the CN chemiluminescence around 388 nm was found to correlate almost linearly with fuel concentration in methane–air mixtures.     

Generating line spectra from experimental responses. Part II: Storage and loss functions

A computer algorithm is described which allows the determination of a discrete distribution of relaxation times from simulated or smoothed storage or loss modulus data, or of retardation times from simulated or smoothed storage or loss compliance data. The distributions faithfully reproduce the input data and are suitable for data storage as well as for generating any other response curves.     

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames.     

Generating line spectra from experimental responses. Part I: Relaxation modulus and creep compliance

We describe a recursive computer algorithm which generates line spectra from relaxation modulus or creep compliance data without producing negative spectrum lines. We apply the algorithm here to data read from mathematical models for the relaxation modulus. Since these data were thus free of the usual experimental error, we could use a relatively simple form of the basic algorithm that is applicable also to smoothed data. The spectra faithfully reproduced the input functions and may serve for data storage as well as for predicting other experimental responses.     

Effect of an electric field on the nitrogen oxide emission and structure of a laminar propane diffusion flame

The effect of an electric field E on the structure and nitrogen oxide NO_x emission of an individual laminar propane diffusion flame is experimentally investigated. The current-voltage characteristics of the flame, its deformation, the fuel-air ratio and the NO_x emission are determined for positive and negative burner polarities. A reduction in NO_x emission (up to 30% with respect to the emission index) is demonstrated in the case of negative burner polarity. A cause-and-effect relationship between the processes in the flame is proposed: the presence in the flame of positively charged ions and soot particles; the motion of the ions in the E field and the onset of an induced electrohydrodynamic flow directed towards the negatively charged burner; the retention and increase in the concentration of soot particles in the lower region of the flame, which leads to an increase in soot particle radiation and hence to a decrease in the temperature of the flame front and a corresponding reduction in NO_x emission. The electrohydrodynamic aspects of the problem are subjected to a qualitative analysis.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 13–23, March–April, 1995.     

COMPARISON OF STABILITY BETWEEN NAVIER-STOKES AND EULER EQUATIONS

The stability about Navier-Stokes equation and Euler equation was brought into comparison. And by taking their typical initial value problem for example, the reason of leading to the difference in stability between Navier-Stokes equation and Euler equation was also analyzed.