Localized Short-Pulse Scattering from Coated Cylindrical Objects: Experimental Measurements and Numerical Models

1995 ◽  
pp. 421-430
Author(s):  
James G. Maloney ◽  
Morris P. Kesler ◽  
Eric J. Kuster
Keyword(s):  
Short Pulse ◽  
Numerical Models ◽  
Experimental Measurements

scholarly journals Numerical studies on the properties of femtosecond laser plasma Kα sources

2001 ◽  
Vol 19 (1) ◽  
pp. 147-150 ◽  
Author(s):  
CH. REICH ◽  
P. GIBBON ◽  
I. USCHMANN ◽  
E. FÖRSTER
Keyword(s):  
Short Pulse ◽  
Numerical Models ◽  
X Rays ◽  
Hot Electron ◽  
X Ray ◽  
Compact Source ◽  
Electron Generation ◽  
Short Pulse Laser ◽  
Numerical Studies ◽  
Femtosecond Laser Plasma

One of the features of ultra high intensity (UHI) short pulse laser–matter interactions is the prospect of creating a cheap, compact source of hard X rays with femtosecond pulse duration. The properties of such Kα sources are studied using analytical and numerical models of hot electron generation and subsequent transport in a range of materials (Reich et al., 2000). First, we find that there is an optimum laser intensity for Kα generation from bulk targets, which scales as Z4.4. Second, we show that efficient hard X-ray pulses with durations below 100 fs can be generated at intensities of ∼1016 W/cm2.

scholarly journals The role of hollow atoms in the spectra of an ultrashort-pulse-laser-driven Ar cluster target

2008 ◽  
Vol 26 (1) ◽  
pp. 83-94 ◽  
Author(s):  
J. Colgan ◽  
J. Abdallah ◽  
A. Y. Faenov ◽  
T. A. Pikuz ◽  
I. Y. Skobelev ◽  
...  
Keyword(s):  
Pulse Laser ◽  
Ultrashort Pulse ◽  
Short Pulse ◽  
Line Emission ◽  
Rate Equations ◽  
Experimental Measurements ◽  
Ultrashort Pulse Laser ◽  
Ion Distributions ◽  
Dependent Rate

AbstractAn investigation is made of the role of hollow atoms in the spectra of an ultrashort-pulse-laser-driven Ar cluster target. Experimental measurements are presented from an Ar cluster-gas target using short-pulse lasers with various intensities, durations, and contrasts. Calculations in support of these measurements have been performed using a detailed atomic kinetics model with the ion distributions found from solution of the time-dependent rate equations. The calculations are in good agreement with the measurements and the role of hollow atoms in the resulting complicated spectra is analyzed. It is demonstrated that, although the presence of hollow atoms is estimated to add only around 2% to the total line emission, signatures of hollow atom spectra can be identified in the calculations, which are qualitatively supported by the experimental measurements.

Experimental Measurements and Numerical Modeling Validation of Temperature Distribution in Tissue Medium During Short Pulse Laser Irradiation

2007 ◽  
Author(s):  
Ashim Dutta ◽  
Kyunghan Kim ◽  
Kunal Mitra ◽  
Zhixiong Guo
Keyword(s):  
Numerical Modeling ◽  
Heat Conduction ◽  
Temperature Distribution ◽  
Laser Beam ◽  
Pulse Laser ◽  
Short Pulse ◽  
Hyperbolic Heat Conduction ◽  
Experimental Measurements ◽  
Conduction Model ◽  
Short Pulse Laser

The objective of this paper is to analyze the temperature distributions and heat affected zone in skin tissue medium when irradiated with either a collimated or a focused laser beam from a short pulse laser source. Single-layer and three-layer tissue phantoms containing embedded inhomogeneities are used as a model of human skin tissue having subsurface tumor. Q-switched Nd:YAG laser is used in this study. Experimental measurements of axial and radial temperature distribution in the tissue phantom are compared with the numerical modeling results. For numerical modeling, the transient radiative transport equation is first solved using discrete ordinates method for obtaining the intensity distribution and radiative heat flux inside the tissue medium. Then the temperature distribution is obtained by coupling the bio-heat transfer equation with either hyperbolic non-Fourier or parabolic Fourier heat conduction model. The hyperbolic heat conduction equation is solved using MacCormack’s scheme with error terms correction. It is observed that experimentally measured temperature distribution is in good agreement with that predicted by hyperbolic heat conduction model. The experimental measurements also demonstrate that converging laser beam focused directly at the subsurface location can produce desired high temperature at that location as compared to that produced by collimated laser beam for the same laser parameters.

scholarly journals Application of the Sectional Method to Investigate Particle Number and Soot Mass in Ethanol and Gasoline Fueled Premixed Spark Ignition Engines

2020 ◽  
Vol 197 ◽  
pp. 06009
Author(s):  
Valentina Pessina ◽  
Marco Del Pecchia ◽  
Sebastiano Breda ◽  
Luca Dalseno ◽  
Massimo Borghi
Keyword(s):  
Equivalence Ratio ◽  
Particle Number ◽  
Numerical Models ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Gasoline Direct Injection ◽  
Experimental Measurements ◽  
Pure Ethanol ◽  
Soot Mass ◽  
Wide Range

Emission modelling is still a timely topic in the engine research community. Soot emission reduction has gained its spotlight among the pollutants-related issues mainly due to the renewed interest in Gasoline Direct Injection. The conjunction of experimental measurements and numerical investigations provides an effective tool to cope with the constant evolution of the emission regulations. Thus, numerical models must be validated over a wide range of engine operating points and fuels. To this aim, the Sectional Method was applied to investigate Particulate Matter and Particle Number produced during combustion in a premixed spark ignition engine using 3D-CFD. Soot-related quantities were investigated for different values of equivalence ratio (from 1.0 up to 1.5) as well as for different fuels. Three different fuel types were examined: a commercial nonoxygenated American gasoline (TIER-2), a commercial Chinese gasoline (CHINA-6) with ethanol 10 %vol and pure Ethanol (E100). A detailed chemistry-based tabulated approach was exploited to compute a dedicated soot library, for each of the analyzed fuels, by means of 0D chemical kinetic simulations using a constant pressure reactor approach. Numerical results were compared to a database of experimental measurements collected from literature. The sooting tendency threshold dependency on equivalence ratio was also investigated and the results showed that the ethanol is the less sooting among the examined fuels, while the non-oxygenated gasoline exhibited the highest soot mass and Particle Number. This paper provides a CFD-based benchmark for soot mass and Particle Number for three fuel types with largely different chemical nature.

Transient Discrete Ordinate Method and Experiments of Pulsed Radiative Transfer Through Scattering Absorbing Media

Volume 4 ◽  
2004 ◽  
Author(s):  
Ashish Trivedi ◽  
Soumyadipta Basu ◽  
Kunal Mitra
Keyword(s):  
Radiative Transfer ◽  
Pulse Laser ◽  
Transfer Equation ◽  
Radiative Transfer Equation ◽  
Short Pulse ◽  
Laser Source ◽  
Discrete Ordinates ◽  
Experimental Measurements ◽  
Short Pulse Laser ◽  
Absorbing Media

The objective of this paper is to validate the solution of transient radiation transfer equation with experimental measurements using short pulse laser source having a Gaussian distribution. The transient radiative transfer equation for the case of short pulse laser propagation through scattering absorbing media such as tissue is an integrodifferential equation and is therefore complicated to solve. The time-dependent discrete ordinates method in conjunction with high order upwind piecewise parabolic interpolation scheme is used to solve the transient radiative transfer equation for the case of anisotropically scattering absorbing medium having a rectangular geometry in which an inhomogeneity is embedded. A parametric study involving different scattering and absorption coefficients of the medium, inhomogeneity and inhomogeneity size as well as the detector position is performed. The numerical modeling results and experimental measurements are in excellent agreement for various parameters studied in this paper.

scholarly journals THE CALCULATION AND MEASUREMENT OF THE NATURAL FREQUENCIES OF THE BUCKET WHEEL EXCAVATOR SCHRS 1320/4X30

Transport ◽  
2010 ◽  
Vol 25 (3) ◽  
pp. 269-277 ◽  
Author(s):  
Jakub Gottvald
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Dynamic Load ◽  
Natural Frequencies ◽  
Numerical Models ◽  
Dynamic Properties ◽  
Experimental Measurements ◽  
The Real ◽  
Comparison Of Results

Natural frequencies and shapes are the basic dynamic properties of each structure. On the basis of their knowledge, the sensitivity of the structure to a dynamic load could be estimated. While designing, natural frequencies are based on calculations and numerical simulations. However, computational numerical models do not exactly correspond with real structures and there are many details which have to be simplified. It means that the real natural frequencies of structures may differ from the calculated ones. It is advantageous to verify the calculated results by suitable experimental measurements in case of structures where a dynamic load dominates. The paper deals with the experimental measuring of the natural frequencies of the bucket wheel excavator SchRs 1320/4x30 and a comparison of results obtained from experimental measurements and detailed numerical simulation applying ANSYS.

scholarly journals Thermal Cycles and Residual Stresses in FSW of Aluminum Alloys: Experimental Measurements and Numerical Models

2015 ◽  
Vol 9 ◽  
pp. 87-96 ◽  
Author(s):  
Luciano Buglioni ◽  
Leonardo N. Tufaro ◽  
Hernán G. Svoboda
Keyword(s):  
Aluminum Alloys ◽  
Residual Stresses ◽  
Numerical Models ◽  
Experimental Measurements ◽  
Thermal Cycles

Comparison of Experimental and Numerical Temperature Distributions in Tissues During Short Pulse Laser Irradiation Using Focused Beam

2006 ◽  
Author(s):  
Ashim Dutta ◽  
Gopalendu Pal ◽  
Kunal Mitra ◽  
Michael S. Grace
Keyword(s):  
Heat Transfer ◽  
Numerical Modeling ◽  
Short Pulse ◽  
Experimental Measurements ◽  
Pulse Laser Irradiation ◽  
Tissue Samples ◽  
Short Pulse Laser ◽  
Temperature Distributions ◽  
Tissue Phantoms ◽  
Focused Beam

The objective of this work is to perform experimental measurements validated with numerical modeling results for analyzing the temperature distributions and heat affected zone during short pulse laser irradiation of tissues using focused beam. A Q-switched laser is used as a radiation source. A threelayered tissue phantom model of skin consisting of epidermis, dermis, and fatty tissues is first considered for model validation. Tumors are simulated with inhomogeneities embedded inside the tissue phantoms. Experiments are next conducted with freshly excised skin tissue samples from mice and finally on live anaesthetized mice to consider the bulk effect of convective heat transfer due to blood flow. Experimental measurements of axial and radial temperature distributions for all the cases are compared with numerical modeling results obtained using Pennes' bio-heat transfer equation coupled with either traditional Fourier parabolic or non-Fourier hyperbolic heat conduction formulation. Experimentally measured temperature profiles in tissue phantoms, skin tissue samples, and live anaesthetized mice are found to match extremely well with the predictions from the non-Fourier model than the Fourier formulation by considering skin as a multi-layered medium. It is also observed that focused laser beam produces desired temperature rise at the target site with lesser radial spread compared to a collimated laser beam source.

Investigation of Transient Signals in Nonuniform Media Based on Diffusion Approximation

2009 ◽  
Author(s):  
Sheng-gang Wang ◽  
Li-ming Ruan ◽  
Hong Qi ◽  
Xi-ying Wang ◽  
Bing-xi Li
Keyword(s):  
Optical Properties ◽  
Diffusion Approximation ◽  
Near Infrared ◽  
Short Pulse ◽  
Numerical Models ◽  
Optical Tomography ◽  
Laser Pulses ◽  
Biological Tissues ◽  
Infrared Light ◽  
Short Laser Pulses

With the development of the ultra-short laser technology, a new optical detection field based on the transient laser pulse signals will emerge in the future. Ultra-short laser pulses have been used in biological fields to obtain the optical properties of vivo tissues. There are many numerical models to simulate the propagation of short laser pulses in tissue medium. However, since most biological tissues show a high scattering and low absorption characteristics for near-infrared light, the most popular model is diffusion approximation method. Although with many limitations, its greatest advantage is higher computational efficiency. The propagation of short pulse laser in two dimension nonuniform medium is simulated based on the diffusion approximation model in present paper. The numerical method is validated by comparing the numerical results with the theoretical analysis results in semi-infinite uniform slab medium. Then diffusion approximation is used to simulate the transfer process of ultra-short pulses in two dimensional inhomogeneous medium. Finally, The influences of inclusions with different sizes and optical properties on time-resolved reflected signals are presented. This can help to choose suitable detection parameters in diffuse optical tomography.

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