Gopalendu Pal

Time-resolved optical tomography using short-pulse laser for tumor detection.

Our objective is to perform a comprehensive experimental and numerical analysis of the short-pulse laser interaction with a tissue medium with the goal of tumor-cancer diagnostics. For a short-pulse laser source, the shape of the output signal is a function of the optical properties of the medium, and hence the scattered temporal optical signal helps in understanding the medium characteristics. Initially experiments are performed on tissue phantoms embedded with inhomogeneities to optimize the time-resolved optical detection scheme. Both the temporal and the spatial profiles of the scattered reflected and transmitted optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation using the discrete ordinates technique. Next experiments are performed on in vitro rat tissue samples to characterize the interaction of light with skin layers and to validate the time-varying optical signatures with the numerical model. The numerical modeling results and the experimental measurements are in excellent agreement for the different parameters studied. The final step is to perform in vivo imaging of anesthetized rats with tumor-promoting agents injected inside skin tissues and of an anesthetized mouse with mammary tumors to demonstrate the feasibility of the technique for detecting tumors in an animal model.

A Narrow Band-Based Multiscale Multigroup Full-Spectrum k-Distribution Method for Radiative Transfer in Nonhomogeneous Gas-Soot Mixtures

The full-spectrum k-distribution (FSK) approach has become a promising method for radiative heat transfer calculations in strongly nongray participating media, due to its ability to achieve high accuracy at a tiny fraction of the line-by-line (LBL) computational cost. However, inhomogeneities in temperature, total pressure, and component mole fractions severely challenge the accuracy of the FSK approach. The objective of this paper is to develop a narrow band-based hybrid FSK model that is accurate for radiation calculations in combustion systems containing both molecular gases and nongray particles such as soot with strong temperature and mole fraction inhomogeneities. This method combines the advantages of the multigroup FSK method for temperature inhomogeneities in a single species, and the modified multiscale FSK method for concentration inhomogeneities in gas-soot mixtures. In this new method, each species is considered as one scale; the absorption coefficients within each narrow band of every gas scale are divided into M exclusive spectral groups, depending on their temperature dependence. Accurate and compact narrow band multigroup databases are constructed for combustion gases such as CO 2 and H 2 O. Sample calculations are performed for a 1D medium and also for a 2D axisymmetric combustion flame. The narrow band-based hybrid method is observed to accurately predict heat transfer from extremely inhomogeneous gas-soot mixtures with/ without wall emission, yielding close-to-LBL accuracy.

Hybrid Full-Spectrum Correlated k-Distribution Method for Radiative Transfer in Nonhomogeneous Gas Mixtures

The full-spectrum k-distribution (FSK) approach is a promising model for radiative transfer calculations in participating media. FSK achieves line-by-line (LBL) accuracy for homogeneous media at a tiny fraction of LBL’s high computational cost. However, inhomogeneities in gas temperature, total pressure, and component-gas mole fractions change the spectral distribution of the absorption coefficient and can cause inaccuracies in the FSK approach. In this paper, a new hybrid FSK method is proposed that combines the advantages of the multigroup FSK (MGFSK) method for temperature inhomogeneities in a single gas species and the multiscale FSK (MSFSCK) method for concentration inhomogeneities in gas mixtures. In this new hybrid method, the absorption coefficients of each gas species in the mixture are divided into M spectral groups depending on their temperature dependence. Accurate MGFSK databases are constructed for combustion gases, such as CO2 and H2O. This paper includes a detailed mathematical development of the new method, method of database construction, and sample heat transfer calculations for 1D inhomogeneous gas mixtures with step changes in temperature and species mole fractions. Performance and accuracy are compared to LBL and plain FSK calculations. The new method achieves high accuracy in radiative heat transfer calculations in participating media containing extreme inhomogeneities in both temperature and mole fractions using as few as M 2 spectral groups for each gas species, accompanied by several orders of magnitude lower computational expense as compared to LBL solutions. DOI: 10.1115/1.2909612

k-Distribution Methods for Radiation Calculations in High-Pressure Combustion

The objective of this paper is to investigate the applicability and performance of the k-distribution methods for radiation calculations in high-pressure combustion systems. Since stronger line overlap is expected among various gas species at pressures higher than atmospheric pressure, which may lead to inaccuracy in the underlying mixing model of k-distribution methods, the mixing model was tested for various pressures (above atmospheric pressure), temperatures and gas compositions. Heat transfer calculations for 1-D homogeneous and nonhomogeneous media and 2-D combustion flames at high pressures were also tested using various k-distribution methods. It was observed that the narrow band-based mixing model yields excellent accuracy for almost the entire spectrum except near 3400 cm −1 where it incurs some inaccuracy due to strong overlap between CO2 and H2O. This localized inaccuracy in mixing has no effect on overall heat transfer calculations using k-distribution methods. Indeed accuracies of k-distribution methods at high pressures were found to be better than their corresponding atmospheric counterparts in 1-D and 2-D media.

Vacuum System of the Large Cyclotrons at VECC

Variable Energy Cyclotron Centre (VECC) has two large cyclotrons, K-130 cyclotron and K-500 cyclotron. The first beam in the room temperature K-130 cyclotron (RTC) was accelerated in June 1977. The cyclotron accelerated and delivered alpha and proton beams consistently to the cyclotron users for several years. Heavy ion beams were available in this cyclotron from 1997 to 2007. Presently, the cyclotron is working as a primary source for RIB production. The cyclotron has an acceleration chamber volume of about 28 m3. The total length of beam line is about 65 m. Vacuum of the order of 1 x 10−6 mbar is presently maintained in the cyclotron and beam line using diffusion pumps. It is one of the largest vacuum systems operating in India. It is consistently being operated 24 x 7 round the year giving beam to the cyclotron users. A K-500 superconducting cyclotron (SCC) with K=520 has been constructed at Kolkata. SCC will be used to accelerate beams to 80 MeV/A for light heavy ions and about 10 MeV/A for medium mass heavy ions. Three turbo molecular pumps are connected to the acceleration chamber. Three cryopanels placed inside the lower dees in the valley gap of the superconducting magnet are available in the accelerating chamber for achieving high vacuum. The acceleration chamber having a volume of about 1.0 m3 was operated using turbomolecular pumps, liquid nitrogen cooled panels and liquid helium cooled cryopanels at different stages during beam commissioning. Differential pumping is provided across the RF liner to avoid distortion. The first beam line of about 21 m has been installed in the cyclotron. The outer vacuum chamber of the cyclotron magnet cryostat has active pumping. The vacuum system of the superconducting cyclotron is also operating reliably round the clock throughout the year. The paper describes the details of the vacuum systems of the large cyclotrons at VEC Centre Kolkata India, its commissioning and operating experience.

A New Hybrid Full-Spectrum Correlated k-Distribution Method for Radiative Transfer Calculations in Nonhomogeneous Gas Mixtures

The full-spectrum k-distribution (FSK) approach is a promising model for radiative transfer calculations in participating media. FSK achieves line-by-line (LBL) accuracy for homogeneous media at a tiny fraction of LBL’s high computational cost. However, inhomogeneities in gas temperature, total pressure and component-gas mole fractions change the spectral distribution of the absorption coefficient and can cause inaccuracies in the FSK method. In this paper, a new hybrid FSK method is proposed that combines the advantages of the multi-group FSK (MGFSK) method for temperature inhomogeneities in a single gas specie and the multi-scale FSK (MSFSK) method for concentration inhomogeneities in gas mixtures. In this new hybrid method the absorption coefficients of each gas specie in the mixture are divided into M spectral groups depending on their temperature dependence. New and accurate MGFSK databases are constructed for combustion gases, such as CO2 and H2 O. This paper includes a brief mathematical development of the new method, method of database construction and sample heat transfer calculations for 1-D inhomogeneous gas mixtures with step changes in temperature and species mole-fractions. Performance and accuracy are compared to LBL and traditional FSK calculations. The new method achieves high accuracy in radiative heat transfer calculations in participating media containing extreme inhomogeneities in both temperature and mole fractions using as few as M = 2 spectral groups for each gas specie, accompanied by several orders of magnitude lower computational expense as compared to LBL solutions.Copyright

Transient radiation modeling of short-pulse laser detection of tumors in animal model

The objective of this paper is to perform a comprehensive experimental and numerical analysis of the short pulse laser interaction with tissue medium with the goal of tumor / cancer diagnostics. For a short pulse laser source, the shape of the output signal is a function of the optical properties of the medium and hence the scattered temporal optical signal helps in understanding of the medium characteristics. In this paper the scattered reflected optical signals from the tissue medium are modeled using the transient radiative transport equation (RTE) solved by the discrete ordinates technique. In vivo imaging was performed on anaesthetized rats with tumorogenic agents injected inside skin tissues and on anaesthetized mouse with mammary tumors. The numerical results are compared with the experimental data to validate the model and demonstrate the feasibility of the time-resolved technique in detecting tumors in animal model.

Analysis of Short Pulse Laser Interaction With Tissues for Tumor Detection

The objective of the work is to perform both experimental and numerical analysis of short pulse laser interaction with tissue medium with the goal of tumor / cancer diagnostics. Short pulse laser probing techniques for diagnostics have distinct advantages over very large pulse width or continuous wave lasers primarily due to the additional information conveyed by the temporal distribution of the optical signals. For short pulse laser source, the shape of output signal is a function of the optical properties of the medium and hence the scattered optical signal provides information about the medium characteristics. Two laser systems are used: a mode-locked short pulse laser (wavelength = 514 nm and pulsewidth = 200 ps) and a frequency doubled diode short pulse laser (wavelength = 776 nm and pulsewidth = 1.3 ps). The scattered optical signals are measured with a Hamamatsu streak camera. First in vitro experiments are performed on mouse skin tissue samples injected with India ink in order to simulate presence of inhomogeneities. Finally, in vivo imaging is performed on anaesthetized rats with tumorogenic agents injected inside skin tissues and on anaesthetized mouse with mammary tumors. Both the temporal and the spatial profiles of the scattered reflected optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation using the discrete ordinates technique. The goal is to demonstrate the feasibility of the time-resolved technique in detecting tumors in animal model.© 2009 ASME

A k-DISTRIBUTION-BASED SPECTRAL MODULE FOR RADIATION CALCULATIONS IN MULTI-PHASE MIXTURES

k-distribution-based approaches are promising models for radiation calculations in strongly nongray participating media. Advanced k-distribution methods were found to achieve close-to benchmark line-by-line (LBL) accuracy for strongly inhomogeneous multi-phase media accompanied by several orders of magnitude smaller computational cost. In this paper, a k-distribution-based portable spectral module is developed, incorporating several state-of-the-art k-distribution methods along with compact and high-accuracy databases of k-distributions. The module construction is flexible — the user can choose among various k-distribution methods with their relevant k-distribution databases, to carry out accurate radiation calculations. The spectral module is portable, such that it can be coupled to any flow solver code with its own grid structure, discretization scheme, and solver libraries. This open source code module is made available for free for all noncommercial purposes. This article outlines in detail the design and the use of the spectral module. The k-distribution methods included in the module are briefly described with a discussion of their advantages, disadvantages and their domain of applicability. Examples are provided for various sample radiation calculations in multi-phase mixtures using the new spectral module and the results are compared with LBL calculations.Copyright

K-distribution Methods for Radiation Calculations in High Pressure Combustion

a = nongray stretching factor for fill-spectrum k-distribution method I = radiative intensity,W∕m sr Ib = blackbody intensity/Planck function, W∕m sr k = reordered absorption coefficients in k distribution, cm−1 L = length of one-dimensional medium, cm M = total number of groups of nth gas component N = total number of species/scales P = total pressure, bar PL = pressure path length, P × L, bar‐cm q = heat flux, W∕m ŝ = unit direction vector T = temperature, K x = gas species mole fraction η = wave number, cm−1 κ = absorption coefficient, cm−1 λ = overlap parameter, cm−1 σs = scattering coefficient, cm −1 τ = narrow-band transmissivity Φ = scattering phase function φ = composition variable vector Ω = solid angle, sr