An analytical expression for the total band absorptance of infrared-radiating gases

It is shown that an exact closed form expression for the total band absorptance of infrared-radiating gases can be obtained by employing the Malkmus narrow band model and the Edwards and Menard wide band approximation. Comparisons with other approximate analytical expressions are presented.     

An approximate band model for radiative transfer in semitransparent solids

A simplified model for the spectral refractive index and absorption coefficient of semitransparent solids is developed from solid state lattice vibrational theory. This model accurately predicts the total band absorptance and total internal emittance for long pathlengths and selected solids. Total band absorptance is shown to be proportional to the square root of the pathlength when the pathlength is large. Comparison to exact results for α-quartz and lithium fluoride demonstrates that the total radiative transfer properties are accurately predicted by the model when the pathlength exceeds one millimeter.     

A band absorptance formulation for Doppler broadening

An expression is presented for the total band absorptance of vibration—rotation bands having Doppler-broadened lines. The result is similar in form to corresponding expressions for pressure broadening, in that the total band absorptance is expressed in terms of a dimensionless pressure path length, a bandwidth parameter, and a line-structure parameter.The band absorptance formulation is employed to estimate pressure levels at which Dopple broadening dominates over pressure broadening for CO₂ bands within the atmospheres of Venus and Mars, and for CH₄ bands within the atmospheres of Jupiter and Saturn.     

Narrow band model parameters for the CO2 4·3 μm band

The narrow band model parameters of the carbon dioxide 4·3 μm band have been obtained from absorption experiments with four broadening gases, namely CO, N₂, O₂, and Ar. The temperature and wave number dependence of the parameters are discussed. The experiments were performed at temperatures of about 303, 598 and 1185°K, with CO₂ partial pressures between 0·01 and 1·0 atm, at a total pressure of 1·0 atm. The Elsasser and the statistical models were applied to thebands in order to obtain applicable parameters and to determine a suitable model for the band at each temperature. It has been found that the Elsasser model is an adequate representation of the band at low temperatures whereas the statistical model is preferred at elevated temperatures. The effect on the line half-widths of the broadening gases is discussed. Good agreement is obtained between absorptance calculated with the present parameters and experimental results obtained by other authors.     

Slab band absorptance for molecular gas radiation

Nongray molecular gas radiation can be formulated in terms of slab band absorptance, which can be calculated from correlations of laboratory-measured values of band absorption. Slab-band absorptance is not only useful for obtaining the emissivity or mean beam length but also for the formulation of the radiant flux in a nonisothermal gas. Effects of nongray self-absorption by cold boundary layers can then be readily estimated. Illustrative results are presented for gas in a channel with simple straight-line boundary layer profiles at the walls and constant temperature in the center.     

An analytical model for total absorption of a band

A theoretical model for total absorption of a band is developed based on the Elsasser band model and considering the effects of spectral band contour and low-intensity lines in the spectral band. This model yields a simple and analytical expression and has the correct asymptotic forms. Comparisons with other models are presented.     

Comparison of an analytical model with approximate models for total band absorptions and their derivatives

The introduction of the total band absorption concept has greatly reduced the mathematical complexity of integrating the spectral function in determining the i.r. radiation by nongrey molecular gases due to vibration-rotation bands.A number of simple but approximate equations for total band absorption have been developed for the investigations of i.r. radiation by nongrey gases. Most of these equations are, however, limited to completely overlapped lines and are not applicable to the strong-line cases. Others, which account for the line effects, have been developed empirically and are not directly related to the spectral narrow-band models. Analytical equations for total band absorption and its derivative were derived directly from a spectral narrow-band model and they are universally applicable to all line strengths.Presented in this paper is the comparison of the analytical model with the approximate wide-band models. Also presented is the comparison of the foregoing models with a spectral function integrated to give total band absorption.     

Radiative decay time of a nongray medium with arbitrary configurations

Based on the principle of conservation of energy, a simple analytical expression is presented for the radiative decay time of a nongray medium with arbitrary configurations. It is expressed explicity in terms of the mean beam length and the total band absorptance. In the high-pressure limit, where the decay time based on the harmonic thermal perturbation is available for two configurations, comparison is made with the present decay time. Good agreement is found.     

Radiative heat transfer in a cylindrical mixture of non-gray particulates and molecular gases

The interaction between particulate clouds and molecular gases with respect to radiative heat transfer in a one-dimensional cylindrical medium with black walls is investigated. The particulates are assumed to have a non-gray absorption coefficient with a power-law dependence on wavenumber. The absorption coefficient of the molecular gases is described by the exponential wide-band model. Heat transfer rates are found through the evaluation of internal and external total hemispherical emissivities of the particulate cloud and through evaluation of total band absorptances for the molecular gases, modified to account for the interaction with the particles. Simple, closed-form expressions for the total hemispherical emissivities and total band absorptance are also presented, resulting in good accuracy.     

Intensity,radiative flux and flux divergence of an exponential-wide band

Exact and asymptotic results are obtained for the total intensity, forward radiative flux and forward radiative flux divergence in a plane-parallel layer of a homogeneous medium whose absorption coefficient is given by the envelope of the exponential-wide band model. These are compared to an empirical correlation.     

Infrared radiation properties of methane at elevated temperatures

The spectral absorptivity of the v₃ and v₄ fundamental and the v₁ + v₄ combination bands of methane have been measured at low resolution for temperatures between 290 and 850 K. Spectral mean (narrow-band) parameters for the fundamental bands have been correlated from the Elsasser model, while total band absorptance data for all three bands have been correlated using the Edwards exponential wide band model. A total emissivity chart has been developed, based on the wide band absorption models.     

A dynamic approach to the sudden jump model in single molecule spectroscopy

Various theories that use the sudden jump model to explain the time dependence of the optical band of a single molecule in a fluctuating environment are analyzed. It is shown that the dynamic theory of the optical band, based on the Hamiltonian of the system, should necessarily include the initial conditions for the quantum system. We show how these initial conditions should be chosen for the dynamic theory to properly describe the quantum jumps of the optical band of a single molecule. Unlike stochastic theories based on the sudden jump model, the dynamic theory predicts several absorptances of a single molecule and directly connects the absorptance fluctuations with this fact. The theory is used to account for the time dependence of the broadening of experimentally measured lines of individual molecules.     

Universal absorption of two-dimensional materials within k ⋅ p method

The universal optical absorption is a fascinating property existing in certain two-dimensional (2D) materials. By introducing a general two-band $\mathbf{k}?\mathbf{p}$ effective Hamiltonian, we demonstrate that the absorptance can manifest an universal value at the direct band-edge of 2D materials in three specific cases. However, for general 2D materials, the absorptance becomes nonuniversal. We investigate the dependency of absorptance on the band parameters of general 2D materials. The influences of band-anisotropy and band warping are also considered. Interestingly, we find that the coherent interband coupling and the band warping are responsible for the occurrence of the saddle-point type of Van Hove singularity, which leads to strong light-matter interactions in 2D materials.     

Dynamic analysis of clamp band joint system subjected to axial vibration

Clamp band joints are commonly used for connecting circular components together in industry. Some of the systems jointed by clamp band are subjected to dynamic load. However, very little research on the dynamic characteristics for this kind of joint can be found in the literature. In this paper, a dynamic model for clamp band joint system is developed. Contact and frictional slip between the components are accommodated in this model. Nonlinear finite element analysis is conducted to identify the model parameters. Then static experiments are carried out on a scaled model of the clamp band joint to validate the joint model. Finally, the model is adopted to study the dynamic characteristics of the clamp band joint system subjected to axial harmonic excitation and the effects of the wedge angle of the clamp band joint and the preload on the response. The model proposed in this paper can represent the nonlinearity of the clamp band joint and be used conveniently to investigate the effects of the structural and loading parameters on the dynamic characteristics of this type of joint system.     

Exponential wide band parameters for the pure rotational band of water vapor

New exponential wide band parameters are provided for the pure rotational band of water vapor. These wide band correlations are in good agreement with available spectral and total emissivity data. Calculated overlap correction factors for CO₂-H₂O mixtures based on these new parameters are in good agreement with Hottel's overlap corrections at 400 K and with the calculations of Penner and Varanasi at 811 K. On the other hand, comparisons with Hottel's overlap corrections at 811 and 1200 K show maximum discrepancies of 57 and 46%, respectively. Recognizing the preliminary nature of Hottel's overlap corrections, this discrepancy would probably be best resolved by new experimental data.     

Numerical analysis of a temperature sensor based on the photonic band gap effect in a photonic crystal fiber

In this paper we investigate, by the plane wave expansion method and an analytical model, the temperature effect on the photonic band gap fiber, and we report on a numerical demonstration of a temperature sensor based on the photonic band gap (PBG) shift in a solid core photonic crystal fiber (PCF) infiltrated with a high refractive index oil. The bandwidth and the position of the central wavelength of the band gap are the parameters of interests for our temperature sensing purpose. Simulation results were found to be in excellent agreement with the refractive index scaling law and the highest sensitivity of 3.21?nm/°C was achieved, and it will be even higher than the grating based sensors written in PCFs with similar structure.     

Influence of line interference on the vibration-rotation band shapes

The shapes of the CO, v₃, CO₂, and v₃ N₂O fundamental vibration-rotation bands have been studied at various temperatures and in the presence of several perturbing gases. Also the half-widths of CO vibration-rotation lines have been measured at 78 K. In the region of line wings, the measured absorption coefficients deviate from those given by the superposition of Lorentzian profiles. These deviations are explained by the collision-induced line interference that causes redistribution of absorption inside the band. A theory of line mixing is formulated which is based on Markov approximation and on the strong collision model. Simple analytical expressions are obtained for the band shape. The computed shapes are in satisfactory agreement with the experimental results. The deviations from the Lorentz absorption observed in pure CO and in CO-N₂ at low temperature are partially ascribed to the formation of van der Waals dimers.     

A narrow band pattern-matching model of vowel perception

The purpose of this paper is to propose and evaluate a new model of vowel perception which assumes that vowel identity is recognized by a template-matching process involving the comparison of narrow band input spectra with a set of smoothed spectral-shape templates that are learned through ordinary exposure to speech. In the present simulation of this process, the input spectra are computed over a sufficiently long window to resolve individual harmonics of voiced speech. Prior to template creation and pattern matching, the narrow band spectra are amplitude equalized by a spectrum-level normalization process, and the information-bearing spectral peaks are enhanced by a "flooring" procedure that zeroes out spectral values below a threshold function consisting of a center-weighted running average of spectral amplitudes. Templates for each vowel category are created simply by averaging the narrow band spectra of like vowels spoken by a panel of talkers. In the present implementation, separate templates are used for men, women, and children. The pattern matching is implemented with a simple city-block distance measure given by the sum of the channel-by-channel differences between the narrow band input spectrum (level-equalized and floored) and each vowel template. Spectral movement is taken into account by computing the distance measure at several points throughout the course of the vowel. The input spectrum is assigned to the vowel template that results in the smallest difference accumulated over the sequence of spectral slices. The model was evaluated using a large database consisting of 12 vowels in /hVd/ context spoken by 45 men, 48 women, and 46 children. The narrow band model classified vowels in this database with a degree of accuracy (91.4%) approaching that of human listeners.     

Broad band enhanced infrared light absorption of a femtosecond laser microstructured silicon

Absorptive properties of surface-structured silicon prepared by femtosecond laser pulses irradiating in SF₆ or N₂ are measured in a wide wavelength range of 0.3–16.0 μm. The SF₆-prepared surface-structured silicon shows enhanced light absorptance up to 80% or more in the entire measured wavelength range. The absorptance for N₂_prepared surface-structured silicon in the wavelength range of 9–14 µm is similar to that of a SF₆-prepared sample, although it decreases to about 30% in the wavelength range of 2–7 µm. Light absorption varies with the height and density of the spikes formed on silicon surfaces.