Measurement and numerical analysis of flammability limits of halogenated hydrocarbons

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.     

A study on flammability limits of fuel mixtures

Flammability limit measurements were made for various binary and ternary mixtures prepared from nine different compounds. The compounds treated are methane, propane, ethylene, propylene, methyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. The observed values of lower flammability limits of mixtures were found to be in good agreement to the calculated values by Le Chatelier's formula. As for the upper limits, however, some are close to the calculated values but some are not. It has been found that the deviations of the observed values of upper flammability limits from the calculated ones are mostly to lower concentrations. Modification of Le Chatelier's formula was made to better fit to the observed values of upper flammability limits. This procedure reduced the average difference between the observed and calculated values of upper flammability limits to one-third of the initial value.     

Optical and electronic properties of some semiconductors from energy gaps

II-VI and III-V tetrahedral semiconductors have significant potential for novel optoelectronic applications. In the present work, some of the optical and electronic properties of these groups of semiconductors have been studied using a recently proposed empirical relationship for refractive index from energy gap. The calculated values of these properties are also compared with those calculated from some well known relationships. From an analysis of the calculated electronic polarisability of these tetrahedral binary semiconductors from different formulations, we have proposed an empirical relation for its calculation. The predicted values of electronic polarisability of these semiconductors agree fairly well with the known values over a wide range of energy gap. The proposed empirical relation has also been used to calculate the electronic polarisability of some ternary compounds.     

Quantum computation of photoelastic properties of ionic crystals

A general scheme for computation of photoelastic properties has been proposed using the well-established quantum ion dependent theory. The families under consideration are I–VII type ionic crystals and AB ₂ type cross compounds. The calculated values of strain polarisability constant (λ) for the crystals in these families are compared with the predicted values by some other workers as well as with the available experimental ones. The results of the present work are in much better agreement with the available experimental data than the earlier estimated ones. This formulation is proposed to extend for other families of similar nature and theoretical analysis of the properties of nano materials. The industrial applications are also suggested.     

Diffusion of tin in lead tin telluride epitaxial layers grown by liquid phase epitaxy

The distribution of tin in epitaxial layers of lead tin telluride grown by liquid phase epitaxy on lead telluride substrates has been determined by electron probe microanalysis. The diffusion coefficients calculated from the experimental data agree approximately with the literature values.     

The relationship between indentation hardness of organic solids and their molecular structure

A model has been developed relating the indentation hardness of organic molecular solids to their cohesive energy density, the length of the Burgers vector, the weakest plane from the crystal structure and crystal structural parameters. Whilst the described model is pragmatic, calculated indentation values for a variety of materials based on the weakest plane using specific Burgers vectors agree well with those from literature data.     

Prediction of permeability coefficients of compounds through caco-2 cell monolayer using artificial neural network analysis

Artificial neural network (ANN) analysis was used to predict the permeability of selected compounds through Caco-2 cell monolayers. Previously reported models, which were shown to be useful in the prediction of permeability values, use many structural parameters. More complex equations have also been proposed using both linear and non-linear relationships, including ANN analysis and various structural parameters. But proposed models still need to be developed using different neuron patterns for more precise predictions and a better understanding of which factors affect the permeation. To develop a simple and useful model or method for easy prediction is also a general need. Permeability coefficients (log k_p) were obtained from various literature sources. Some structural parameters were calculated using computer programs. Multiple linear regression analysis (MLRA) was used to predict Caco-2 cell permeability for the set of 50 compounds (r² = 0.403). A successful ANN model was developed, and the ANN produced log kp values that correlated well with the experimental ones (r² = 0.952). The permeability of a compound, famotidine, which has not previously been studied, through the Caco-2 cell monolayer was investigated, and its permeability coefficient determined. It was then possible to compare the experimental data with that predicted using the trained ANN with previously determined Caco-2 cell permeability values and structural parameters of compounds. The model was also tested using literature values. The developed and described ANN model in this publication does not require any experimental parameters; it could potentially provide useful and precise prediction of permeability for new drugs or other penetrants.     

Recent analytical applications of nanoparticle sensitized lucigenin and luminol chemiluminescent reactions

There is an ever-increasing demand for rapid, sensitive, cost effective and selective detection methods for the analysis of many essential compounds. When chemiluminescence has been introduced to analytical chemistry as a detection technique, it has been shown to meet many of these requirements. This method has become a powerful tool for the determination of many compounds. Using this method, low detection limits can be obtained with simple and inexpensive instrumentation. Coupled with flow injection technique the method has become more popular for wider applications. Since many excellent reviews on the chemiluminogenic techniques have appeared in the literature in recent years, the present paper does not intend to cover the exhaustive studies in this area, but will selectively describe the analytical applications of nanoparticle sensitized lucigenin and luminol chemiluminescent reactions and evaluate their recent progress together with our present work.     

Dose-area product measurements in panoramic dental radiology

In this study, dose-area product (DAP) measurements in panoramic dental radiology have been performed in Germany. The results obtained in this study were proposed as diagnostic reference levels (DRLs). A representative number of dental panoramic units, both with digital and conventional image receptors, have been chosen. Common statistical parameters such as mean, standard deviation and 3rd quartile have been calculated. For four different standard programmes, 'large adult', 'adult male', 'adult female' and 'child', the proposed DRLs are 101, 87, 84 and 75 mGy cm(2), respectively. No clear tendency to a generalised dose reduction from the transition to digital techniques has been observed. Effective doses have been calculated from E/DAP conversion factors published in literature. Even though these values differ by a factor of approximately 3, upper limits of 15.8-21.2 microSv for the four different exposure settings were derived from the data.     

Ideal-gas specific heat and second virial coefficient of HFC-125 based on sound-velocity measurements

The sound velocity in gaseous pentafluoroethane (HFC-125, CF₃CHF₂) has been measured by means of a spherical acoustic resonator, Seventy-two sound-velocity values were measured with an uncertainty of ±0.01% at temperatures from 273 to 343 K and pressures from 101 to 250 kPa. The ideal-gas specific heats and the second acoustic-virial coefficients have been determined on the basis of the Sound-velocity measurements. The second virial coefficients calculated from the present sound-velocity measurements agree with literature values which were determined fromPVT measurements by means of a Burnett method.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24 1994, Boulder, Colorado, U.S.A.     

On the fracture pressure of liquid metals

Fracture pressure of six liquid metals, Pb, Al, Cu, Ni, Ti and Fe have been calculated at their melting points in three different ways; (i) by extrapolating molecular dynamic (MD) data reported in the literature for various temperatures to their melting points, (ii) by using the fracture pressure equation developed by Fisher and (iii) by using the work of nucleation suggested by Fletcher. Results have shown that the Fisher equation and MDs estimates agree closely, whereas the ones based on the work of nucleation are systematically lower than the other two. In all cases, calculated fracture pressures are several orders of magnitude different from those assumed in the literature, emphasizing the extent of weakening by extrinsic factors in liquid metals.     

Calculation of yield stresses and plastic strain ratios

Yield stresses and plastic strain ratios of aluminium, copper, brass and steel sheets having various textures, which are characterized by the orientation distribution functions, have been calculated as a function of angle to the rolling direction using the Bunge method based on Taylor's minimum energy theory and another method suggested by the present authors. The calculated results are compared with the measured ones. For steels, the two methods yield almost identical yield stress results. The Bunge method yields higher average plastic strain ratios than the measured data, while their variation with the angle to the rolling direction agrees very well with the measured values. The plastic strain ratios calculated by the second method are in very good agreement with the measured data in their average values but show smaller variations with the angle to the rolling direction than the measureD. Therefore, combination of the two methods can yield very good agreement between calculated and measured plastic strain ratios. For the f c c metals, the calculated yield stresses and plastic strain ratios are in good agreement with measured data, regardless of the calculation method.     

Prediction of Permeability Coefficients of Compounds Through Caco-2 Cell Monolayer Using Artificial Neural Network Analysis

Artificial neural network (ANN) analysis was used to predict the permeability of selected compounds through Caco-2 cell monolayers. Previously reported models, which were shown to be useful in the prediction of permeability values, use many structural parameters. More complex equations have also been proposed using both linear and non-linear relationships, including ANN analysis and various structural parameters. But proposed models still need to be developed using different neuron patterns for more precise predictions and a better understanding of which factors affect the permeation. To develop a simple and useful model or method for easy prediction is also a general need. Permeability coefficients (log k_p) were obtained from various literature sources. Some structural parameters were calculated using computer programs. Multiple linear regression analysis (MLRA) was used to predict Caco-2 cell permeability for the set of 50 compounds (r² = 0.403). A successful ANN model was developed, and the ANN produced log kp values that correlated well with the experimental ones (r² = 0.952). The permeability of a compound, famotidine, which has not previously been studied, through the Caco-2 cell monolayer was investigated, and its permeability coefficient determined. It was then possible to compare the experimental data with that predicted using the trained ANN with previously determined Caco-2 cell permeability values and structural parameters of compounds. The model was also tested using literature values. The developed and described ANN model in this publication does not require any experimental parameters; it could potentially provide useful and precise prediction of permeability for new drugs or other penetrants.     

On the determination of Oxide Formation Rate for tantalum in chromate bath from cell voltage

Anodic oxide growth has been followed on Ta in chromate solutions by measuring the cell voltage/time relations at current densities between 200 and 700 m?A/cm². It is demonstrated here that the reference electrode can be dispensed with for technical studies, and estimates for the parameters of oxide growth can be calculated from cell voltage/time relations. Results are given for the formation rate, electric field strength, reciprocal capacity and increase of oxide thickness. The formation rate has been found to depend on current density following the empirical relation previously established for valve metals from the results of anodic charging curves. The empirical constants calculated here agree with the values in the literature, thus showing that cell voltage measurements can be used successfully to estimate growth parameters.     

Estimation of the Heat Capacity of Some Semiconductor Compounds Using <Emphasis Type="Italic">n</Emphasis>-Dimensional Debye Functions

In the present study, a simple and efficient expression for the accurate and quick calculation of the specific heat capacity of semiconductor compounds is presented on the basis of n-dimensional Debye functions using binomial coefficients. As will be seen, the present formulation yields compact, closed-form expressions which enable the straightforward calculation of the heat capacity of solids for arbitrary temperature values. As an example of the application, the calculation is performed for the specific heat capacity of semiconductor compounds. The calculated results have been compared with those reported in the literature and are found to be in good agreement with those of other studies.     

First-Principle Investigation of V and Cr Doping on the Dilute Magnetic Semiconducting Properties of Rutile SnO<Subscript>2</Subscript>: a Modified Becke-Johnson (TB-mBJ) Exchange Potential Study

Theoretical investigations on rutile SnO₂ doped with V and Cr were performed by using recently implemented Tran and Blaha’s modified Becke-Johnson exchange potential model (TB-mBJ) based on density functional theory. The electronic, magnetic, dielectric and optical properties of V and Cr-doped tin oxide have been calculated by full-potential linearized augmented plane wave method (FP-LAPW) by WIEN2k code. The present works demonstrate accurate prediction of band structures and properties using the TB-mBJ model. The calculated values of magnetic moment, dielectric constant and refractive index of doped and undoped compounds agree well with the experimental results. The TB-mBJ model is a direct method without using empirical corrections and hence, the furnished data are useful in material modelling for spintronics applications.     

Leveraging Values in Global Organizations: Premises,Paradoxes and Progress

In this focused issue on the theme of “Leveraging Values in Global Organizations”, we highlight several prevalent themes on national, organizational and individual values in the literature. We argue that many premises in the literature have been accepted as fact; yet there are still many avenues open to exploration. We present several paradoxes that are often overlooked or lead to inconsistencies in the literature on values. The five articles in this focused issue address these premises and paradoxes, presenting new challenges and opportunities, providing progress and paving the way for future research on leveraging values in global organizations. The selected articles explore values with respect to international alliances and subsidiaries of multinational organizations at the organizational level, among global managers at the group level, and among employees and inpatriates at the individual level of analysis. We trust that readers of this issue will agree that the articles provide novel insights into key issues in the established, yet dynamic, field of research on values in the context of global organizations.     

Tacticity in shocked polymer hydrocarbons

There is a recent interest in the response of thermoplastics to shock. Previous work on three simple hydrocarbons has indicated that the shear strength increases with the complexity of the side group. Strength values have been calculated using lateral stress measurements with manganin gauges that have been recalibrated for use in the low stress regime. The present work aims to investigate the effect of the configuration of the thermoplastic’s chain when side groups are added. In particular, whether steric effects are present when the groups become larger. Results show that whilst polyethylene has the lowest shear strength, polypropylene and polystyrene have similar values. In all cases the strength of polymer increases with time after the shock has passed. As the applied stress increases, polystyrene and polypropylene strengthen to a higher degree when compared with polyethylene. Explanations are offered in terms of microstructure and tacticity of the chain.     

Modelling of plate finned tube evaporators and condensers working with R134A

A model to predict the behaviour of finned tube evaporators and condensers working with R134a has been developed. For modelling of the refrigerant phase change, evaporation or condensation, the heat transfer and the pressure drop for the two-phase flow have to be calculated. Therefore, a number of correlations, the most recommended ones in the reviewed literature, have been analysed and compared. The results of this comparison are presented for the evaporation and condensation heat transfer coefficients and for the evaporator frictional pressure drop. Once the correlations have been implemented in the model and compared with the experimental results, the ones that work best for the studied heat exchangers have been ultimately selected.The experimental study to validate the model has been carried out in a small airconditioning unit with cross-flow air-refrigerant type heat exchangers. The results are compared with model predictions for thermal capacity, refrigerant superheat or subcooling, and tube-side pressure drop.     

Planar limit-assisted structural interpretation of saturates/aromatics/resins/asphaltenes fractionated crude oil compounds observed by Fourier transform ion cyclotron resonance mass spectrometry

Planar limits, defined as lines generated by connecting maximum double-bond equivalence (DBE) values at given carbon numbers, are proposed as a means of predicting and understanding the molecular structure of compounds in crude oil. The slopes and y-intercepts of the lines are determined by the DBE/carbon number ratios of functional groups defining the planar limits. For example, the planar limit generated by a serial addition of saturated cyclic rings has a slope of 0.25. The planar limit formed by the linear and nonlinear addition of benzene rings yields lines with slopes of 0.75 and 1, respectively. The y-intercepts of these lines were determined by additional functional groups added within a series of molecules. Plots of DBE versus carbon number for S(1) class compounds observed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) showed that saturates/aromatics/resins/asphaltenes (SARA) fractions exhibited unique slopes and y-intercepts. The slope of the planar limit observed from a saturates fraction matched well with the slope of a planar limit generated by the serial addition of saturated cyclic rings. The slopes of planar limits of aromatics and resins fractions were very similar to that obtained from the linear addition of benzene rings. Finally, the slope of the asphaltenes fraction was almost identical to the slope obtained from the nonlinear addition of benzene rings. Simulated and experimental data show that SARA fractions exhibit different molecular structure characteristics. On the basis of the slope and y-intercept of the planar limit, the structures of molecules in SARA fractions were predicted and suggested. The use of planar limits for structural interpretation is not limited to crude oil compounds but can also be used to study other organic mixtures such as humic substances or metabolites.