Band Model Parameters Research Articles

Effective action approach to the Leggett's mode in two-gap superconductors

When electrons of two electronic bands participate in superconducting phenomena, it is said to be two gap superconductor. There are two set of cooper pairs in different energy gap with different energy. The observation of Leggett’s mode in two band superconductor provides an additional information about superconductor. By using the effective action, the thermodynamic potential in the case of neutral and charged two gap superconductor are calculated. Using phase dependent action, we investigate a collective excitation (Leggett’s mode) corresponding to small fluctuations of the relative phase of two condensates in two band superconductor. We consider the possibility of observing Leggett’s mode in MgB2 superconductor and conclude that for the known values of two band model parameters for MgB2, Leggett’s mode rises above the two particle threshold.
 BIBECHANA 17 (2020) 74-79

Comparison of CK model and line by line method using old and updated parameters/databases

Thermal radiation transfer in a 2D enclosure filled with non-gray gases, namely H2O, CO2, or their mixture, is calculated using the line-by-line approach and the correlated-k (CK) model. This study shows the effect of spectral databases on the accuracy of LBL and CK model calculations. Line-by-line calculations were carried out using two databases for high temperature, i.e. the HITEMP1995 and the HITEMP2010 high-resolution databases. Calculations of the CK model were conducted using two sets of parameters, i.e. the old (earlier) parameters {A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H2O, CO2and CO and correlated-k (CK) model for H2O and CO2, Int. J. Heat Mass Transfer 40 (1997) (987–991)} and the new (updated) parameters {(Rivière, P. and A. Soufiani, Updated band model parameters for H2O, CO2, CH4and CO radiation at high temperature, International Journal of Heat and Mass Transfer, 2012. 55(13), 3349–3358)}. The angular and spatial discretization of the radiative transfer equation is performed using the discrete ordinates method and finite volume method, respectively. Seven test cases with different medium temperature (both isothermal and non-isothermal) and homogeneous or non-homogeneous concentrations of participating gases are considered. This study intends to provide a comprehensive evaluation of the CK model with two sets of parameters and LBL method using the HITEMP95 database in a wide range of medium temperatures (from 1000 to 2500 K) and concentration of participating gases (from 10% to 100% mole fraction). The line-by-line results based on the HITEMP2010 high-resolution spectral database are used as benchmarks to evaluate the accuracy of other approximate models. Very good agreement for both the wall heat flux and the radiative source term was observed between the LBL results using the HITEMP2010 database and the results of the CK model in all the test cases. It is concluded that for all considered test cases, the CK method with the new parameters provides better accuracy than with the old ones.

气体高温辐射特性窄谱带模型参数库构建

气体高温辐射特性窄谱带模型参数库构建

A regional remote sensing algorithm for total suspended matter in the East China Sea

The East China Sea (ECS) is well known for its high concentration of total suspended matter (TSM). Some regions of the ECS have concentrations higher than 5000gm−3, exceeding the valid ranges of many TSM remote sensing algorithms. To overcome the limitation of the existing algorithms, a new TSM model, the “complex proxy TSM model” (CPTSM), is developed in this study. The model is established on the basis of a complex proxy of remote sensing reflectance. The proxy is designed to convert the non-linear relationship between reflectance and TSM to a quasi-linear function over the entire range of TSM concentrations. This proxy is deduced from four indices defined by combinations of the reflectance at different bands. The four indices take advantage of the different relationships between the band combinations of the reflectance and total TSM concentrations. The band selections and model parameters are based on correlation coefficients and regression analysis between the indices and TSM. The results show that the correlation coefficient of 0.912 between the proxy and TSM is higher than that between any individual index and TSM. To validate the CPTSM model, TSM, turbidity, and reflectance data were collected in the ECS during 4 cruises in 2006 and 2007. The actual TSM concentration was measured by weighing the samples collected on filter papers. Turbidity was measured by a Seapoint Turbidity Meter. The turbidity data with values higher than 750FTU were re-calibrated using an empirical equation. All turbidity values were converted to TSM concentrations using a linear equation. The in situ reflectance was measured using the above-water method at 459 stations and the in-water method at 146 stations. A total of 87 pairs of reflectance measured by both methods were used for inter-comparison with a relative difference of 4.5%. The reflectance values were used to retrieve TSM concentrations using the CPTSM model. A comparison with in situ measurements gave a mean relative error of 23%. Applying the CPTSM model to the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data and analyzing the errors from a match-up dataset of SeaWiFS and in situ data, we found that the average relative error was 24.5%. We propose to use the CPTSM model to map TSM concentrations from satellite data in the ECS.

Updated band model parameters for H2O, CO2, CH4 and CO radiation at high temperature

Statistical narrow-band (SNB) model parameters for H2O, CO2, CH4 and CO, and correlated-k (CK) parameters for H2O and CO2 are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H2O, CO2 and CO and correlated-k (ck) model for H2O and CO2, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H2O and CO2, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data.

The k-moment method for the narrow band modeling of radiative properties of nonuniform gaseous media

Moments of the absorption coefficient distribution function are used for the derivation of statistical narrow band (SNB) model parameters of nonuniform optical paths in gases. The approach yields approximations for the path-averaged first- and second-order k-moments from which equivalent SNB parameters are determined in the frame of the Malkmus model. The approach is assessed through comparisons with LBL data. The nonuniform approximation is shown to enable the computation of transmissivities and radiation intensities with accuracy similar to or higher than those achieved by the Curtis–Godson one.

Approximate radiative properties of methane at high temperature

Band model parameters for high-temperature methane have been generated up to 2000 K from an extended spectroscopic database. Part of the spectroscopic data are issued from calculations made in the framework of the effective Hamiltonian approach. These data have been completed by a statistical extrapolation. The calculations of global radiative properties such as band absorbtances and total emissivities are in good agreement with the available experimental data showing that the contribution of the hot bands is correctly taken into account. Finally, the degree of correlation between CH 4, CO 2 and H 2O spectra in typical conditions of combustion applications is discussed. Band model parameters are available upon request.

PREDICTION OF SELF-ABSORPTION IN OPPOSED FLOW DIFFUSION AND PARTIALLY PREMIXED FLAMES USING A WEIGHTED SUM OF GRAY GASES MODEL (WSGGM)-BASED SPECTRAL MODEL

A weighted sum of gray gases model (WSGGM)-based low-resolution spectral model for calculating radiation transfer in combustion gases is applied to estimate self-absorption of radiation energy in one-dimensional opposed-flow flames. Development of such a model is necessary in order to enable detailed chemistry-radiation interaction calculations including self-absorption. A database of band model parameters which can be applied to various one-dimensional opposed-flow diffusion and partially premixed flames is created. This in-situ flame property-based database is necessary for the application of the WSGGM to real flames, since previously developed databases were only for homogeneous and isothermal radiation paths. For the validation of the model and database, low-resolution spectral intensities leaving the flat flame in a direction normal to the fuel exit plane are calculated and compared with the results of a narrow-band model based on the Curtis-Godson approximation. Good agreement has been found between them. The resulting radiation model is coupled to the OPPDIF code to calculate the self-absorption of radiant energy and compared with the results of an optically thin calculation and the results of a discrete ordinates calculation in conjunction with the statistical narrow-band model. Significant self-absorption of radiation is found for the flames considered here, particularly on the fuel side of the reaction zone. However, the self-absorption does not have significant effects on the flame structure in this case. Even in the cases of low-velocity diffusion flame and a partially premixed flame having a low equivalence ratio, the effects of self-absorption of radiation on the flame temperature and the production of minor species are not significant.

The Absorptance of Infrared Radiation by Methane at Elevated Temperatures

In large-scale fires and flames, radiative transport can be an important factor determining the rate of fuel volatilization and flame spread in condensed fuels, and in general can affect the amount of soot that is produced by the flame. The radiant flux can be significantly attenuated by core hydrocarbon gases that have absorption features in the infrared. The spectral absorptance of the υ3 (centered at approximately 3020 cm−l) and υ4 (centered at approximately 1306 cm−l) fundamental bands of methane were measured at elevated temperatures. The measurements were made using a FTIR spectrometer coupled to a gas cell that was maintained at a constant temperature in a furnace. The partial pressure of the methane was varied between 5 and 95 percent, yielding pressure path lengths between 1.14 and 21.72 atm-cm. The total pressure was maintained at 1 atm. Measurements were made at temperatures between 296 and 900 K. The effect of spectral resolution on the measurements and derived parameters was examined. Spectral resolutions between 4 and 32 cm−1 were used. The spectral mean parameters of line strength and line shape were determined for the Elsasser narrow band radiation model using the data taken at a resolution of 4 cm−1. The band model parameters were incorporated into RADCAL, a narrow band model used to predict spectral intensity and transmittance. The results are compared with lower resolution predictions and experimental spectral transmittance data. Tabulated narrow band parameters are available on the Internet (WWW) at URL http://www.me.utexas.edu/~combust/students/paul/research.

An isotropic two band model for hot electron transport in silicon: Including electron emission probability into SiO2

An isotropic two band model is proposed for electrons in silicon, that has the same density of states and magnitude of group velocity as those of the full band structure based on empirical pseudopotential method calculations. The band model and transport parameters are calibrated through extensive comparisons with Monte Carlo simulation results and various experiments related to electron transport in silicon. Specifically, the drift velocity, impact ionization coefficient, quantum yield, 2p core level line intensity and broadening from x-ray photoemission spectroscopy have all been used in calibration. Through the study of electron emission at the Si/SiO2 interface in metal-oxide-semiconductor structures using the Monte Carlo method, it is demonstrated that the model has good accuracy in modeling high field transport phenomena in silicon.

Development of a monte carlo method for numerical analysis on radiative energy transfer through non‐grey‐gas layer

AbstractAn analytical method is developed to study the radiative energy transfer in a non‐grey‐gas layer by using a Monte Carlo method. The gas is composed of water vapour, carbon dioxide and nitrogen. The profiles of the monochromatic absorption coefficient of each component gas are calculated by using the Elsasser model and wide band model parameters derived by Edwards. The validity of this method is confirmed by comparing the results of the gas emissivity with the ones obtained from Hottel's chart. By using this method, radiative energy transfer is analysed through a one dimensional gas layer between two parallel solid walls with different temperatures. From the analyses, it is shown that the temperature profile in the gas layer is not properly estimated by using Hottel's gas‐emissivity charts, though the net heat flux between the bounding walls is estimated properly.

Band-model parameters for 4.3μm CO 2 band in the 300–1000 K temperature region

Moderate resolution (0.06 cm -1) Fourier-transform transmission spectra of the 4.3-μm band of CO 2 were acquired at selected pressures and concentrations over a temperature range from 300 to 1000 K. These spectra were degraded to a 5 cm -1 bandpass and fit to a combined Lorentz-Doppler-broadening band model to determine band-model parameters utilizing a nonlinear least-square algorithm. Comparisons of selected band-model parameters obtained by us are made with preexisting data. Spectrally-degraded, line-by-line spectral calculations are compared with spectra calculated using our band-model parameters determined in this work.

Incorporation of the thermal radiative effect of CH4, N2O, CF2Cl2, and CFCl3 into the National Center for Atmospheric Research community climate model

This paper documents the incorporation of the radiative effect of trace gases CH4, N2O, CF2Cl2, and CFCl3 into the National Center for Atmospheric Research community climate model (CCMl) longwave scheme, which presently includes the radiative effect of H2O, CO2, and O3. This development is intended for using the CCMl to study the combined greenhouse effect of increasing atmospheric CO2, CH4, CF2Cl2, CFCl3, and N2O. The radiative effect of the trace gases in a homogeneous layer is parameterized based on Wang and Shi's (1988) analytical expression for the total band absorptance. For an inhomogeneous path, a scaling approximation is used to calculate the effective total band model parameters. The same treatment of the overlapping gaseous absorption bands used in the present CCMl scheme is adopted for the new trace gases.

Band discontinuities: a simple electrochemical approach

A simple but general analytic description of the band discontinuities at a semiconductor heterojunction is derived from the fundamental electrochemical principle. The effects of nonuniform band structure and carrier degeneracy (Fermi-Dirac statistics), dielectric image forces, quantum-mechanical exchange-correlation forces, and dipole forces across the interface are included. These nonideal effects (band model parameters) are expressed in terms of the activity coefficients (thermodynamic parameters) of the carriers. A simple but general correlation between the energy band discontinuities and the activity coefficients of the carriers is found. Such a mathematical link between the two quantities shows that the thermodynamic parameters are important to the physics that determines the band discontinuities. >

Band-model parameters of the 2.7-μm band of H 2O

A Fourier-transform spectrometer operating with a resolution of 0.06 cm -1 was utilized in obtaining transmission spectra of heated water vapor at 300–1000 K in the spectral range of 3000–4500 cm -1 over a range of optical depths from 0.4 to 20.3 atm-cm. These high-resolution spectra were degraded to 25 cm -1 bandpass transmittances and reduced to band-model parameters assuming a combined Lorentz-Doppler model. Comparisons are made with other sources of band-model data, as well as line-by-line spectral calculations.

A consistent model for carrier transport in heavily doped semiconductor devices

A self-consistent model for describing carrier transport in heavily doped semiconductor devices has been developed. The proposed model allows convenient treatment of non-uniform semiconductors in a manner that is both thermodynamically consistent and consistent with the transport equations, the steady-state continuity equations and the electrostatic potential with explicit boundary conditions at the contacts. The complex problems are reduced to determining two types of quantities: the reference electrostatic potential and the activity coefficient of the carriers. In order to find the simple working equations for the model, two choices of reference for the electrostatic potential are discussed. The presented transport equations are written in a simple Shockley-like form, in which the effects associated with the non-uniform band structure and the influence of Fermi-Dirac statistics are described by a thermodynamic property, the activity coefficient of the carriers, which is expressed in terms of two band model parameters, the effective band-gap shrinkage, Delta Eg, and the effective asymmetry factor, A. In this form they are convenient for use in computer-aided analysis and the design of heavily doped semiconductor devices.

Effect of antimony on the electrical properties of Pb 0.8Sn 0.2Te thin films

Antimony doped films of Pb 0.8Sn 0.2Te, the composition of interest for IR detectors, were grown by flash evaporation. Hall coefficient and d.c. conductivity studies were made on these films in the temperature range 77–500 K. Results have been analysed in the light of double valence band model and various band parameters, e.g. valence band separation, effective mass ratio, population ratio, light to heavy hole mobility ratio etc have been calculated as a function of doping density of antimony.

Determination of the temperature profile of axisymmetric combustion-gas flow from infrared spectral measurements

A numerical iteration technique for determining both the temperature and CO 2 concentration profiles of axisymmetric combustion-gas flow from low resolution infrared spectral measurements has been developed. The technique includes inversion of the temperature profile from emission measurements when the CO 2 concentration distribution is known, inversion of the CO 2 concentration profile from transmittance measurements when the temperature distribution is known, and inversion of both temperature and CO 2 concentration profiles simultaneously from emission and transmittance data of the combustion-gas flow. The iteration technique is accurate, efficient, and effective even under structured temperature distributions. The effects of temperature, optical thickness, wave number, and band model parameters on the determined profiles are analyzed. It is found that a deviation of 40% in CO 2 concentration results in a difference of only about 5% in the determined temperature profile. This implies a possibility of passive scanning. The determined temperature profile of a laboratory combustion-gas flow agrees well with probe measurements.

Nonlinear Fracture Properties from Size Effect Tests

The previously derived size effect law for blunt fracture is exploited for determining the parameters of the R-curve of the crack band model, and of Hillerborg’s fictitious crack model. No measurements of the crack length or of the unloading compliance are needed. It suffices to measure only the maximum load values for a set of geometrically similar specimens of different sizes. The parameters of the size effect law can then be identified by linear regression. The inverse slope of the regression line yields the fracture energy. The regression also has a twofold benefit: it smoothes statistically scattered data, and it extends the range of the data, so that one can do with fewer tests. From the experimentally calibrated size effect law, the R-curve may then be obtained as the envelope of the family of fracture equilibrium curves for different specimen sizes. A simple algebraic formula for this envelope is presented. The size effect regression plot makes it also possible to determine crack band model parameters, particularly the fracture energy, the crack band width, and the strait-softening modulus. The same is made possible for Hillerborg’s model.

Validated infrared transmittance band model for methane in the atmosphere

A validated band model for atmospheric methane (CH4) in the 1085–1755- and 2370–3215-cm−1 wave-number regions is presented. Discussions of the transmittance data base used to create the model and of the band parameter determination scheme are given. Comparisons of the model vs methane transmittance are provided. Band model parameters at 5-cm−1 intervals for 20-cm−1 spectral resolution throughout the absorption bands are included for direct incorporation into the lowtran code. A vertical profile of methane’s volume mixing ratio is also proposed for use with the thirty-three-layer standard atmosphere.