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At least 649 records · Page 36Linked to original sources
PubMed2006

Behavior of the GABIE, 3M 3500, PerkinElmer Tenax TA, and RADIELLO 145 diffusive samplers exposed over a long time to a low concentration of VOCs.

Diffusive sampling is particularly suited to determine time-weighted average volatile organic compound (VOC) concentration in occupational hygiene and environmental air monitoring. The purpose of this study was to measure the sampling rate variation of four different samplers in a special use--the exposure to a low concentration of volatile organic compound (10 to 200 ppb) for a long period (1 to 14 days). PerkinElmer tube-type adsorbent was packed with Tenax TA and RADIELLO cartridge packed with Carbograph 4. Badge-type activated carbon diffusive samplers 3M 3500 and GABIE were exposed to the same controlled atmospheres of benzene as meta-xylene (BTX) during the same exposure times. Performance samplers were observed for variability of uptake rates according to concentration levels, exposure duration, back diffusion, and competition phenomena at the adsorption sites. Particular benzene behavior has been noted for the thermally desorbable tube-type diffusive sampler: the measured sampling rates decrease with time following an exponential profile. With badge-type active charcoal diffusive samplers, the uptake rates were found to be highly stable and unaffected by time exposure. Overall, in the region of a few tens of ppb, for long-time exposure and for the lightest compounds, 3M 3500 and GABIE diffusive samplers seem the most appropriate diffusive sampling technique in terms of performance and facility in use.

Adsorption↗
PubMed1985

[Evaluation of the thermal technic for the quantitative measurement of extravascular lung water].

To evaluate the accuracy of the method, sequential measurements (n = 159) of extravascular lung water (EVLW) using the thermo-dye double-indicator dilution technique were performed in 22 critically surgical ill patients. Radiographic grading of lung water content served as clinical standard. Normal mean EVLW defined radiographically without evidence of pulmonary edema was 4.8 +/- 1.1 ml/kg. Early interstitial fluid accumulation was quite accurately detected with 6.9 +/- 2.1 ml/kg EVLW (p less than 0.001 vs normal lung water content). The mean EVLW present with definitive interstitial and alveolar edema was 11.5 +/- 3.8 ml/kg and 19.1 +/- 4.5 ml/kg, respectively. Despite some objections to the method (diffusion limitation of the thermal indicator, uneven regional lung perfusion), this technique for measuring EVLW reliably assesses the degree of pulmonary edema. Even when properly performed, chest roentgenograms only confirm gross changes in the lung water content.

Adolescent↗
PubMed2004

Bi-directional flow sensor with a wide dynamic range for medical applications.

This paper describes a novel three-wire thermal flow sensor for medical applications. The present innovation for low-frequency measurements involves the use of a pulsed-wire anemometer with a comparatively large wire diameter (12.5 microm and larger) together with a novel signal processing approach. A small wire is heated using a sinusoidal alternating current, and two sensing wires, acting as resistance thermometers, are set parallel to, and at a small distance on either side of, the pulsed wire. The thermal wake of the pulsed wire is convected downstream to one of the two receiving wires which detect its delayed arrival. This arrangement allows the sensing of both the direction and the flow velocity component normal to the three probes. By appropriate signal processing, the present sensor can be operated such that the phase shift between the periodic current that drives the central wire and the detected signal by either the upstream or downstream wire takes into account a combination of convection, diffusion and the finite thermal response time of both the pulsed wire and the receiving wire. Because the time constants increase as the flow velocity decreases, the time lag due to thermal inertia supplements the time lag due to the true time of flight, thus yielding an effective operating range of 0.05 m/s <or= U <or= 25 m/s , which corresponds to a dynamic range of 500:1. This wide velocity range is an order of magnitude larger than that for the traditional time-of-flight pulsed-wire anemometers. An important application of the bi-directional thermal flowmeter is the measurement of human respiration, e.g. for early diagnostics of asthmatic attacks. The main advantage of the present sensor is its low sensitivity to variations in temperature and also to the composition of the flowing gas. Also, a calibration will be not needed for each density and gas used in addition to that for velocity. The resultant design work aimed at developing a sensor that can be mass-produced at low cost.

Asthma↗
PubMedDate not supplied

Ethyl acetate as a dispersing solvent in the production of poly(DL-lactide-co-glycolide) microspheres: effect of process parameters and polymer type.

This study deals with the production of poly(DL-lactide-co-glycolide) (PLGA) microspheres using ethyl acetate as a dispersing solvent, a partially water soluble and less toxic solvent, by using emulsification and solvent diffusion/ evaporation techniques. PLGA 50 : 50 was used, having molecular weights, 12000 and 34000 with the end group capped (RG502, 503) and uncapped (RG502H, 503H) biodegradable polymers. The microspheres were loaded with nifedipine (NFD) as a model drug. Solvent removal from the embryonic microspheres was manipulated by adopting different techniques. These methods have shown a significant effect on the physicochemical and release characteristics of the microspheres. Rapid removal of the solvent resulted in microspheres with a loose matrix and large size. Use of higher molecular weight polymers increased the size of the microspheres as well as delayed release of the drug. The uncapped polymer has given a higher rate of diffusion when compared to the capped polymers. Thermal analyses showed a uniform molecular distribution of the drug in the polymer matrix. The mechanism of drug release from the PLGA microspheres followed the Fickian diffusion.

Acetates↗
PubMed1988

Effects of emboli, positive-pressure ventilation, and airway water on lung water measurements.

We tested the effects of microemboli, continuous positive-pressure ventilation (CPPV), and aspirated airway water on measurements of extravascular lung water by use of the technique of thermal indicator dilution (ETVL). A control group of dogs and a group of dogs in which dextran was infused created all levels of pulmonary edema. In an emboli group 0.125 g/kg of starch microemboli (63-74 micron diam) were infused. In groups with emboli and CPPV, starch emboli were infused and CPPV was then applied at 15 cmH2O. In an airway saline group measured amounts of saline were poured into the airway. In all groups postmortem pulmonary extravascular tissue weight (PETW) was determined and compared with the last ETVL. Emboli created an increased scatter when the last ETVL is compared with PETW because 1) blood trapped distal to emboli was included in the ETVL measurement, and/or 2) diffusion limitations for the thermal indicator were exceeded. Emboli and CPPV decreased ETVL/PETW. Airway saline (80 +/- 5%) was measured by ETVL. In conclusion, the ETVL technique is reliable in well-perfused lungs but loses accuracy in measuring lung water after emboli of any size or with large amounts of airway fluid.

Algorithms↗
PubMed1993

Thermoreactive water-soluble polymers, nonionic surfactants, and hydrogels as reagents in biotechnology.

Thermoprecipitating polymers such as poly (N-isopropylacrylamide), poly(N-vinyl caprolactam), and some ethylene oxide-containing surfactants appear to be suitable for developing new separation systems to complement traditional precipitation, chromatography, and extraction of biological molecules. The nature of thermally induced phase separation of polymers and nonionic surfactants is discussed and examples are given. Covalent coupling of an enzyme to a thermoprecipitable polymer results in a biocatalyst which combines the qualities of soluble and immobilized enzymes. Biocatalysts of this type can be separated from reaction media by precipitation after temperature increase. The use of thermoprecipitating polymer-protein conjugates in immunoassays overcomes one of the shortcomings of traditional methods with solid sorbent-linked antigen or antibody-diffusional limitations. Thermoreactive hydrogels produced by crosslinking of thermoprecipitating polymers can be successfully used for concentrating macromolecules or microbe-rich slurries. Alternate volume changes of hydrogels on heating and cooling produce a "hydraulic pump" which can enhance the productivity of an immobilized biocatalyst. Hydrogels could be used to control reaction or diffusion rates by a thermal feedback mechanism.

Biotechnology↗
PubMed1996

Ablation of neural tissue by short-pulsed lasers--a technical report.

The basis for most laser applications in neurosurgery is the conversion of laser light into heat when the incident laser beam is absorbed by the tissue. Irradiation of neural tissue with laser light therefore leads to its thermal damage. However, due to the diffusion of heat energy into the surrounding tissue, often there is thermal damage to neural tissue outside the area of the target volume. These are the characteristics of thermal laser/tissue interaction. In this paper we discuss how we used three different short-pulsed lasers to achieve non-thermal ablation of neural tissue. Three different short-pulsed lasers were used to generate ultrashort laser pulses in the picosecond to femtosecond range. The interaction of such laser pulses with tissue was predicted to be nonthermal. The short-pulsed lasers were used for the ablation of neural tissue using an in vitro calf brain model. The histopathological examination of the lesions revealed that the neural tissue had been removed very precisely without any sign of thermal damage to the surrounding tissue.

Animals↗
PubMedDate not supplied

Effect of adding non-volatile oil as a core material for the floating microspheres prepared by emulsion solvent diffusion method.

Eudragit microspheres, to float in the gastrointestinal tract, were prepared to prolong a gastrointestinal transit time. To enhance their buoyancy, non-volatile oil was added to the dispersed phase. When an oil component was not miscible with water, over 90% was entrapped within the microspheres and prolonged the floating time of the microspheres. Depending on the solvent ratio, the morphologies of the microspheres were different and the best result was obtained when the ratio of dichloromethane:ethanol:isopropanol was 5:6:4. As the isopropanol portion increased, the time to form microspheres was delayed and the amount of fibre-like substance produced was decreased, due to the slow diffusion rate of the solvent. Compared with microspheres prepared without non-volatile oil, the release rate of the drug from microspheres was faster in all cases tested, except the microspheres containing mineral oil. The solubility of the drug in the non-volatile oil affected the release profiles of the drugs. The non-volatile oil tends to decrease the glass transition temperature of prepared microspheres and change the release profile. The internal morphology of the microspheres was slightly different depending on the entrapped oil phase used. Tiny spherical objects were present at the inner surface of microspheres and the inside of the shell.

Acrylates↗
PubMed1994

Kinetics of water vapor sorption in porcine stratum corneum.

The kinetics of water vapor absorption-desorption was studied in the porcine stratum corneum (sc) at 25 degrees C. Dry sc samples were exposed to several relative humidities followed by exposure to dry air, and the change in weight was monitored over time by use of a thermal gravimetric analysis technique. Diffusion coefficients were estimated by simulation and data fit optimization to modifications of the non-steady-state solution of Fick's law. Very good fits of experimental data to theoretical equations were obtained. The stratum corneum-water absorption isotherm was characterized by a linear increase from the origin, extending to about 55% relative humidity (10% water gain), followed by an upward curve where water gain increased further by increasing relative humidity. Water absorption and water desorption in the porcine sc were asymmetrical processes, desorption being the slower one. Water diffusivity for the absorption process was related to sc water content in two phases. In the first (water gain < 9%) diffusion coefficients increased as water concentration increased. In the second (water gain > 9%) diffusion coefficients were independent of water concentration, equal to 1.17 x 10(-10) cm2/s. Water diffusivity in the desorption phase was shown to decrease linearly as sc water content decreased. Analysis of the absorption isotherm and of the derived diffusion coefficients suggested at least two forms of water associated with the sc. The first, termed "firmly bound water" and characterized by low diffusion coefficients, was most apparent with dry sc and with a sc water gain of up to 10%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Synthesis, Characterization, and Catalytic Uses of Mg(3)(PO(4))(2)/MgO Systems.

Various Mg(3)(PO(4))(2)/MgO systems containing different proportions of both components were synthesized. The solids were characterized in structural terms by X-ray diffraction, thermal gravimetric analysis, and diffuse reflectance infrared spectroscopy; also, their surface properties were determined from N(2) adsorption-desorption isotherms and their chemical properties were measured with various titrants. An increasing P content in the solids was found to result in decreasing specific surface area and basicity. The solids were used as catalysts for the transformation of 2-hexanol and the alkylation of aniline with methanol. Dehydrogenation selectivity in the former was found to be highly correlated with basicity of the solid; also, alkylation activity and selectivity toward N,N'-dimethylaniline in the latter were found to increase with increasing P content. Copyright 1999 Academic Press.

Journal Article↗
PubMed1991

Effect of temperature on the myoglobin-facilitated transport of oxygen in skeletal muscle.

An analysis of thermal effects on the facilitative transport of oxygen in skeletal muscle fibers is presented. Steady-state mass and energy transport balances are written and solved analytically or numerically using a finite-difference procedure. It is shown that no significant spatial thermal gradients exist due to internal reactions or bulk conduction effects across a muscle fiber. At typical muscle conditions, it is predicted that increased global temperature reduces the fraction of oxygenated myoglobin, increases local oxygen concentrations, and increases the percentage of oxygen flux attributed to oxy-myoglobin. The maximum supportable oxygen consumption rate, mO2max, is defined as the highest consumption rate sustainable without developing anoxic regions at the center of the fiber. By considering only temperature sensitive effects within fibers, mO2max is found to increase slightly with temperature at low temperatures. This increase is due to thermal effects on the diffusion coefficients as opposed to effects associated with the kinetics of the myoglobin-oxygen reaction. If the simulations include the temperature effect associated with oxygen solubility in blood plasma, mO2max decreases with temperature. A sensitivity analysis was performed by varying the values of relevant parameters. The maximum consumption rate was least affected by parameters associated with the kinetic and equilibrium constants and most affected by the diffusion coefficients and the concentration of myoglobin.

Animals↗
PubMed2004

Low-temperature mobility and structure formation of a prochiral aromatic thiol (2,5-dichlorothiophenol) on Cu(111).

We present a low-temperature scanning tunneling microscopy study of increasing coverages of 2,5-dichlorothiophenol, an asymmetrically halo-substituted aromatic thiol, on Cu(111). At low coverage, deprotonation of the thiol occurs spontaneously upon adsorption at 80 K. Albeit the low deposition temperature, we find the formation of adsorbate islands at low coverage, which coalesce into a well-ordered film of horizontally adsorbed molecules at increasing coverage. This behavior indicates (i) significant mobility of the thiols on Cu(111) even at low temperatures and (ii) attractive adsorbate-adsorbate interactions. At higher coverages intermolecular interactions prevent long-range diffusion of adsorbates and thermal activation of the S-H bond becomes necessary. A close analysis of the molecular films reveals chiral recognition between neighboring molecules, which leads to the formation of enantiopure areas on the surface. Upright orientation of individual molecules starts at the boundaries between such phases and can be induced by scanning tunneling microscopy.

Journal Article↗
PubMed2004

Influence of strain on transport in dense Lennard-Jones systems.

We study the shear stress relaxation and temperature dependence of the diffusion coefficient, viscosity, and thermal conductivity along a high-density Lennard-Jones isochore of the reduced density of 1.0, as it crosses the freezing and melting lines, in equilibrium and under constant strain.

Journal Article↗
PubMedDate not supplied

Cyclophosphamide-loaded nanospheres: analysis of the matrix structure by thermal and spectroscopic methods.

This study reports on the preparation and evaluation of cyclophosphamide loaded-polyalkylcyanoacrylate nanospheres obtained by emulsion polymerization. Characterization by differential scanning calorimetry, infrared spectroscopy and X-ray diffraction can reveal state dispersion of the drug inside the nanospheres. Such information predicts the stability of the particles and the drug release behaviour. The study has indicated the prescence of a molecular dispersed system. The drug release behaviour was also studied.

Antineoplastic Agents, Alkylating↗
PubMed2002

Kinetic parameters of lithium and aluminium doped quartz from thermoluminescence glow curves.

The thermoluminescence (TL) glow curves of irradiated annealed and non-annealed synthetic beta-quartz (Li0.73Al0.73Si1.27O4) synthesised using the ceramic method have been studied. Annealed samples (1200 degrees C for 12 h) exhibit some changes of shape and intensity in the TL glow curves when compared to non-annealed samples in the range of 0.1-5 Gy. These changes can be attributed mainly to thermal alkali self-diffusion through the lattice interfaces involving modifications in the components of the luminescent traps. In non-annealed samples six groups of components at about 100 degrees C, 130 degrees C, 160 degrees C, 210 degrees C, 330 degrees C and 450 degrees C can be found, whereas annealed samples only display one very intense peak at a lower temperature (deconvoluted into three peaks at 90 degrees C, 105 degrees C and 130 degrees C) and a lower intensity second wide broad emission at approximately 240 degrees C. In this paper, a computerised curve-fitting based on general order kinetics has been used to characterise the glow curve structure resolving trapping parameters for each glow peak: trap depth (E), frequency factor (s) and the order of the kinetics (b). The dose dependence of the individual components of the glow curve has been also studied. These data allow us to select the most stable component for use in dosimetric purposes.

Aluminum↗
PubMed2003

Gibbs-Bogolyubov inequality and transport properties for strongly coupled Yukawa fluids.

The Gibbs-Bogolyubov inequality is used to establish a mapping between the Yukawa system and both the hard-sphere and the one-component reference systems. The transport coefficients of self-diffusion, shear viscosity, and thermal conductivity are computed for the Yukawa fluid using known properties of the reference systems. Comparisons are made with simulation results. For sufficiently strong screening, the hard-sphere reference system yields a lower upper bound of the Yukawa Helmholtz free energy and a better estimate of the Yukawa transport coefficients.

Journal Article↗
PubMed2006

One-dimensional fluctuating nanodomains in the charge-transfer molecular system TTF-CA and their first-order crystallization.

We report on the direct observation by x-ray diffuse scattering measurements of thermally induced one-dimensional nanoscale ordered fluctuations in the mixed-stack charge-transfer molecular system tetrathiafulvalene-p chloranil (TTF-CA), the prototype for the neutral-ionic phase transition. The unusual physical properties of this compound are considered to be driven by such one-dimensional excitations. The results are discussed in relation to previous experimental and theoretical experiments both at thermal equilibrium and under light irradiation.

Journal Article↗
PubMed2006

Ultrafast vibrational dynamics at water interfaces.

Time-resolved sum-frequency vibrational spectroscopy permits the study of hitherto neglected ultrafast vibrational dynamics of neat water interfaces. Measurements on interfacial bonded OH stretch modes revealed relaxation behavior on sub-picosecond time scales in close resemblance to that of bulk water. Vibrational excitation is followed by spectral diffusion, vibrational relaxation, and thermalization in the hydrogen-bonding network. Dephasing of the excitation occurs in </=100 femtoseconds. Population relaxation of the dangling OH stretch was found to have a time constant of 1.3 picoseconds, the same as that for excitation transfer between hydrogen-bonded and unbonded OH stretches of water molecules surrounded by acetone.

Journal Article↗