Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Effects on Heat Stress of a Flame-Retardant Ensemble for Aluminum Smelters
2000
A common belief is that a flame-retardant clothing ensemble will increase the level of heat stress over ordinary cotton work clothes. This is supported by bench tests on fabrics that indicate higher insulation and vapor resistance values for flame-retardant clothing. This research compared a flame-retardant clothing ensemble for an aluminum smelter (Zirpo wool shirt and FR8 denim pants) with typical cotton work clothing. Four young men walked on a treadmill at two work levels inside a climatic chamber under controlled conditions of heat stress. During each test, heart rate, core temperature, and skin temperatures were continuously monitored and recorded every 5 min. After a physiological st…
Mass Output and Particle Size Distribution of Glucocorticosteroids Emitted from Different Inhalation Devices Depending on Various Inspiratory Paramet…
2002
Efficient inhalation therapy depends on successful delivery of the drug to the lung. The efficacy of drug delivery is not only influenced by the characteristics of the inhalation device, but also by the patient's handling of the device and by the inspiratory maneuver achieved through the device. We analyzed the output characteristics of three different chlorofluorocarbon (CFC)-free breath-actuated inhalers for inhaled glucocorticosteroids (BUD Turbohaler, FP Diskus/Accuhaler and HFA-BDP Autohaler, respectively). Mass output and particle size distribution of drug aerosol delivered by the inhalers were determined depending on different inhalation parameters in vitro using an Andersen cascade …
In Vitro Percutaneous Penetration of Acyclovir from Solvent Systems and Carbopol 971-P Hydrogels: Influence of Propylene Glycol
2005
The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER = 10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increase…
Time-Varying Surrogate Data to Assess Nonlinearity in Nonstationary Time Series: Application to Heart Rate Variability
2009
We propose a method to extend to time-varying (TV) systems the procedure for generating typical surrogate time series, in order to test the presence of nonlinear dynamics in potentially nonstationary signals. The method is based on fitting a TV autoregressive (AR) model to the original series and then regressing the model coefficients with random replacements of the model residuals to generate TV AR surrogate series. The proposed surrogate series were used in combination with a TV sample entropy (SE) discriminating statistic to assess nonlinearity in both simulated and experimental time series, in comparison with traditional time-invariant (TIV) surrogates combined with the TIV SE discrimin…
Towards comprehensive non-target screening using heart-cut two-dimensional liquid chromatography for the analysis of organic atmospheric tracers in i…
2021
Abstract Non-target screening of secondary organic aerosol compounds in ice cores is used to reconstruct atmospheric conditions and sources and is a valuable tool to elucidate the chemical profiles of samples with the aim to obtain as much information as possible from one mass spectrometric measurement. The coupling of mass spectrometry to chromatography limits the results of a non-target screening to signals of compounds within a certain polarity range based on the utilized stationary phases of the columns. Comprehensive two-dimensional liquid chromatography (LCxLC) introduces a second column of different functionality to enable the analysis of a broader range of analytes. Conventional LCx…
MYCOTOXINS | Detection and Analysis by Classical Techniques
2014
This article is a revision of the previous edition article by Imad Ali Ahmed, volume 2, pp. 1526–1532, © 1999, Elsevier Ltd.
Effect of Stiffness on the Micellization Behavior of Model H4T4 Surfactant Chains
2006
The micellization behavior of a series of model surfactants, all with four head and tail groups (H4T4) but with different degrees of chain stiffness, was studied using grand canonical Monte Carlo simulations on a cubic lattice. The critical micelle concentration, micellar size, and thermodynamics of micellization were examined. In all cases investigated, the critical micelle concentration was found to increase with increasing temperature as observed for nonionic surfactants in apolar or slightly polar solvents. At a fixed reduced temperature and increasing chain stiffness, in agreement with previous observations, it was found that the critical micelle concentration decreased and the average…
Calorimetric investigation of water/lecithin/cyclohexane microemulsions
1997
The enthalpies of dilution of water/lecithin/cyclohexane microemulsion-gels at variousR values (R=[water]/[lecithin]) and molar enthalpies of solution of water in lecithin/cyclohexane at a fixed lecithin concentration were determined calorimetrically at 25°C. Through a description of the process of dilution of water/lecithin/cyclohexane microemulsion-gels as one involving mainly the scission of lecithin reversed micelles in to smaller ones, the concentration dependence of the enthalpy was rationalized. Surprisingly, in order to account for the dilution enthalpies, it was not necessary to hypothesize a thermal effect arising from the breakage of the micellar network present in the micremulsi…
Aminoacid zwitterions in solution : Geometric, energetic, and vibrational analysis using density functional theory-continuum model calculations
1998
Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of glycine and alanine zwitterions are studied at the B3PW91/6-31+G∗∗ level and the results compared with those obtained at the HF and MP2/6-31+G∗∗ levels. Solvents effects are incorporated by means of an ellipsoidal cavity model with a multipolar expansion (up to sixth order) of the solute’s electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the more favorable scaling behavior of density funct…