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PubMed2003

Heat transfer from protein crystals: implications for flash-cooling and X-ray beam heating.

Three problems involving heat transfer from a protein crystal to a cooling agent are analyzed: flash-cooling in a cold nitrogen- or helium-gas stream, plunge-cooling into liquid nitrogen, propane or ethane and crystal heating in a cold gas stream owing to X-ray absorption. Heat transfer occurs by conduction inside the crystal and by convection from the crystal's outer surface to the cooling fluid. For flash-cooling in cold gas streams, heat transfer is limited by the rate of external convection; internal temperature gradients and crystal strains during cooling are very small. Helium gas provides only a threefold improvement in cooling rates relative to nitrogen because its much larger thermal conductivity is offset by its larger kinematic viscosity. Characteristic cooling times vary with crystal size L as L(3/2) and theoretical estimates of these times are consistent with experiments. Plunge-cooling into liquid cryogens, which can give much smaller convective thermal resistances provided that surface boiling is eliminated, can increase cooling rates by more than an order of magnitude. However, the internal conduction resistance is no longer negligible, producing much larger internal temperature gradients and strains that may damage larger crystals. Based on this analysis, factors affecting the success of flash-cooling experiments can be ordered from most to least important as follows: (1) crystal solvent content and solvent composition, (2) crystal size and shape, (3) amount of residual liquid around the crystal, (4) cooling method (liquid plunge versus gas stream), (5) choice of gas/liquid and (6) relative speed between cooling fluid and crystal. Crystal heating by X-ray absorption on present high-flux beamlines should be small. For a fixed flux and illuminated area, heating can be reduced by using crystals with areas normal to the beam that are much larger than the beam area.

Algorithms↗
PubMed2005

Fingering of exothermic reaction-diffusion fronts in Hele-Shaw cells with conducting walls.

We consider the influence of heat losses through the walls of a Hele-Shaw cell on the linear stability and nonlinear dynamics of exothermic chemical fronts whose solutal and thermal contributions to density changes have the same signs. Our analysis is based on the reaction-diffusion-convection equations obtained from the Darcy-Boussinesq approximation. The parameters governing the equations are the Damkohler number, a kinetic parameter d, the Lewis number Le, the thermal-expansion coefficient gammaT, and a heat-transfer coefficient alpha which measures heat losses through the walls. We show that for thermally insulating walls, the temperature profile is a front that follows the concentration profile, while in the presence of heat losses, the temperature profile becomes a pulse that leads to a nonmonotonic density profile which in turn may lead to a destabilization of an otherwise stable front.

Journal Article↗
PubMed2001

Transport properties in a two-temperature plasma: theory and application.

An alternate derivation of transport properties in a two-temperature plasma has been performed. Indeed, recent works have shown that the simplified theory of transport properties out of thermal equilibrium introduced by Devoto and then Bonnefoi, very often used in two-temperature modeling, is questionable and particularly does not work when calculating the combined diffusion coefficients of Murphy. Thus, in this paper, transport properties are derived without Bonnefoi's assumptions in a nonreactive two-temperature plasma, assuming chemical equilibrium is achieved. The electron kinetic temperature T(e) is supposed to be different from that of heavy species T(h). Only elastic processes are considered in a collision-dominated plasma. The resolution of Boltzmann's equation, thanks to the Chapman-Enskog method, is used to calculate transport coefficients from sets of linear equations. The solution of these systems allows transport coefficients to be written as linear combinations of collision integrals, which take into account the interaction potential for a collision between two particles. These linear combinations are derived by extending the definition and the calculation of bracket integrals introduced by Chapman et al. to the thermal nonequilibrium case. The obtained results are rigorously the same as those of Hirschfelder et al. at thermal equilibrium. The derivation of diffusion velocity and heat flux shows the contribution of a new gradient, that of the temperature ratio straight theta=T(e)/T(h). An application is presented for a two-temperature argon plasma. First, it is shown that the two-temperature linear combinations of collision integrals are drastically modified with respect to equilibrium. Secondly, the two-temperature simplified theory of transport coefficients of Devoto and Bonnefoi underestimates the electron thermal conductivity with respect to the accurate value at T(e)=20 000 K. Lastly, contrary to the simplified theory of transport coefficients, the diffusion coefficients satisfy the symmetry conditions. An example is given at T(e)=6000 K for different values of straight theta for the diffusion coefficient between electrons and heavy species D(e-Ar) as well as for that between argon atoms and argon ions D(Ar-Ar+).

Journal Article↗
PubMed1978

[Physicochemical studies of Pharmachem's tylosin].

Studied is the effect of high temperature, light, moisture, the type of the solvent and the reaction in the medium on the chemical stability and biological activity of the tylosine base, tylosine tartarate and tylosine phosphate, produced by the "PHARMACHIM" State Economic Corporation. The evaluation of the effect is carried out by using the spectrophotometric (in the UV-region) and microbiological methods (diffusion in agar with Sarcina lutea A. T. C. C. 7341 as a test microorganism). It is found that tylosine is stable thermally both as substance and as solution, yet it loses a large part of its activity when the solutions are exposed to ultraviolet or direct sun light. This calls the solutions of the antibiotics in the course of their preparation, storage and application to be protected from the direct effect of light and that they should be packed in light-proof material. Depending on the air moisture (72--98 per cent), the tylosine base absorbs water from 4 to 11 per cent, the tartarate--from 9 to 37.5 per cent, the phosphate--from 8 to 28.5 per cent, the tylosine tartarate (water-soluble form)--from 7 to 32 per cent, and the tylosine phosphate (granules)--from 12 to 39 per cent of their weights. This requires their storage to be limited to dry, airy premises or they should be hermetically packed. Water, ethanol, methanol, phosphate buffers with pH 6--10.0, dimethylformamide and dimethylsulphoxide do not affect the activity of tylosine, but the last two solvents inhibit the diffusion of the antibiotic in agar and are unsuitable for biological tests. The tylosine base, manufactured by the "Elanco" Company, manifests similar properties in relation to thermal stability, light sensitivity, hygroscopicity and diffusions in agar.

Anti-Bacterial Agents↗
PubMed2006

Digital thermal hyperaemia impairment does not relate to skin fibrosis or macrovascular disease in systemic sclerosis.

OBJECTIVES: Thermal hyperaemia is impaired in patients with systemic sclerosis (SSc). The objective of these studies was to determine whether this was consecutive to skin fibrosis, microangiopathy or macroangiopathy. METHODS: Using laser Doppler flowmetry, we first compared the thermal hyperaemia on the third left finger pad and on the left forearm in 21 patients with non-diffuse systemic sclerosis (SSc), in comparison with primary Raynaud's phenomenon and healthy volunteers. Second, we tested whether the altered thermal hyperaemia correlated to the digital pressure index at baseline, and following the thermal challenge. RESULTS: In the first study, thermal hyperaemia of the finger pad was impaired in terms of both amplitude and kinetics, but not on the forearm in patients with SSc. In the seven SSc patients without cutaneous fibrosis, the response was similarly altered in terms of amplitude and kinetics. In the second study, we observed a weak correlation between the digital systolic blood pressure index. However, in the 15 SSc patients tested at 44 degrees C, the median digital systolic blood pressure index was 1.04 (0.84-1.24) at baseline vs 1.08 (0.87-1.29) at 44 degrees C (NS), while seven of them had an abnormal response in terms of kinetic. Furthermore, only one patient showed a clear-cut decrease in digital systolic blood pressure at 44 degrees C. CONCLUSION: In patients with SSc, digital thermal hyperaemia is impaired, but does not relate to the skin fibrosis or to an associated macroangiopathy in most cases. Further studies are required to determine whether its impairment reflects a functional or structural microvascular damage.

Adult↗
PubMed2004

Sorption rate and thermal barriers in a gas-zeolite system: investigation of n-hexane sorption in MFI-type zeolite.

The nonequilibrium gravimetric sorption method was used to determine diffusion coefficient values for n-hexane in MFI-type materials. Improvements in the measurement device and experimental conditions resulted in high values of the corrected diffusion coefficient, which are comparable to the literature data obtained by the methods of pulsed field gradient nuclear magnetic resonance (PFG NMR) and frequency response (FR). The results indicate that thermal effects of sorption affect practically neither the rate of the sorption nor the diffusion coefficient.

Journal Article↗
PubMed2004

Correlation of the thermal stability of phospholipid-based emulsions and the microviscosity measurements using fluorescence polarization.

The fluorescence polarization technique was used to measure the microviscosity of a series of phospholipid-based emulsions. Fourteen different oil-in-water emulsions containing 20% medium chain length triglycerides, various concentrations and types of phospholipids, and 2.2% glycerin were prepared by microfluidization and pH-adjusted to 4.0 or 7.4. Microviscosity was measured by determining the anisotropy of a fluorophore probe (1,6-phenyl 1,3,5-hexatriene) which was found to obey Perrin's equation as has been previously reported for liposomes and membrane bilayers. Moreover the method was validated by comparing viscosities of phospholipid-oil mixtures measured by rheometry and fluorescence polarization. The viscosities determined by fluorescence polarization were within 6% of the values obtained by classic rheometry. Emulsions were also subjected to thermal stress at 121 degrees C. The droplet growth rate was estimated by measuring the time-dependent mean droplet diameter using photon correlation spectroscopy. The logarithm of the droplet growth rate was found to be directly proportional to the interfacial rigidity (i.e., the inverse microviscosity) which suggested that coalescence rather than molecular diffusion is the primary mechanism of droplet growth under these conditions of thermal stress.

Diphenylhexatriene↗
PubMed1988

Influence of flow and diffusion on protein separation in a continuous flow electrophoresis cell: computation procedure.

Continuous flow zone electrophoresis is an efficient method for the non-destructive separation of biological materials in a flowing film of buffer solution in which the constituents of a sample are separated according to their electrophoretic mobilities, under the influence of an electric field. This paper deals with modeling of flow structure of the buffer solution taking into account the effect of electroosmosis, Joule heating and thermal free convection and the forced convection of axial flow. Modeling of diffusion is examined in a second part. The modeling equations and the corresponding boundary conditions are solved by finite difference methods. The various parameters affecting the quality of the fractionation are analyzed.

Diffusion↗
PubMed1998

Lung function following thermal injury in children--an 8-year follow up.

INTRODUCTION: despite the frequency of pulmonary complications and the reports of abnormal lung function as a sequela of severe thermal injury, most of the lung function studies following thermal injury have been directed at the immediate post-burn period. This investigation is designed to evaluate late residual respiratory impairment in patients with severe thermal injury. METHODS: spirometry and lung volumes were completed on 17 children with severe thermal injury 8 years post-injury. None of the patients had pre-existing lung disease prior to injury. RESULTS: the patient demographic data was as follows: nine male, eight female patients; mean TBSB=67+/-29%; mean third degree=62+/-32%; 13 patients had inhalation injury diagnosed by bronchoscopy. Spirometry and lung volumes at examination as a percentage of predicted values were: [see table in text]. Spirometry and lung volumes show: two patients had an obstructive disease process; nine patients had an obstructive and restrictive disease process; five patients had a purely restrictive process; and one patient had a diffusion defect. CONCLUSION: the data indicate that children who survive severe thermal injury may not regain normal lung function.

Adolescent↗
PubMed2006

Prescriptions for optimizing intensities of short-lived RIBs at ISOL based research facilities.

In order to generate useful intensities of short-lived radioactive species at Isotope Separator On-Line (ISOL) based research facilities, species of interest must be diffused from the interior of the production target-material, effusively transported to an ion source, ionized, extracted, mass-analyzed, and accelerated to research energies in times commensurate with their lifetimes. The intensities at such facilities are principally limited by decay losses associated with times required for diffusion-release from target materials and transport from the target to the ion source and by the maximum permissible primary beam power depositional density that can be tolerated without deleteriously affecting target integrity or ion source efficiency. Consequently, it is imperative to minimize delay times associated with the independent diffusion and effusive-flow processes by choosing small dimensioned (short-diffusion length) highly refractory target materials and formatting them in highly permeable mechanically and thermally robust structures that can withstand high-power beam irradiation for extended periods of time. This article provides basic information on methods, procedures and principles for selecting target materials; for designing fast diffusion-release targets; for designing fast effusive-flow vapor transport systems; and introduces methods for controlling target temperatures as required for optimizing intensities of short-lived radioactive ion beams at ISOL based research facilities.

Journal Article↗
PubMed1996

High lipid content enhances the rate of oxygen diffusion through fish skeletal muscle.

The diffusion coefficient for O2 (Do2) and the solubility constant for O2 (alpha O2) were measured at 15 degrees C in oxidative muscle from striped bass (Morone saxatilis) that had been acclimated to 5 degrees and 25 degrees C. This design allowed us to test the hypothesis that changes in composition of the tissue that are known to occur during thermal acclimation may affect O2 movement. Our measurements permitted calculation of the diffusion constant for O2 (Ko2) through the tissue, which is a primary determinant of capacity for O2 flux. Under isothermal conditions, alpha O2 was 3.59 +/- 0.20 x 10(-2) and 6.64 +/- 0.27 x 10(-2) ml O2.cm-3.atm-1 in tissues from 25 degrees- and 5 degrees C-acclimated animals, respectively. Because O2 is more soluble in lipid than aqueous phase, higher alpha O2 in tissues from cold-acclimated animals can be accounted for by the 13-fold increase in lipid content that is known to occur in oxidative muscle of striped bass during acclimation from 25 degrees to 5 degrees C. When measured under similar isothermal conditions, Do2 showed no significant difference between animals acclimated to warm or cold temperature; Do2 through tissues from 25 degrees- and 5 degrees C-acclimated animals was 2.50 +/- 0.18 and 2.57 +/- 0.40 cm2/s, respectively. Because alpha O2 increases, the calculated KO2 (DO2. alpha O2) is greater in tissue from cold- than from warm-acclimated fish. At physiological temperature, elevated lipid content in oxidative muscle of cold-acclimated striped bass should result in enhanced intracellular movement of O2 and at least partially offset the expected decrease in DO2 at cold temperature.

Acclimatization↗
PubMed2005

Noninvasive MR thermometry using paramagnetic lanthanide complexes of 1,4,7,10-tetraazacyclodoecane-alpha,alpha',alpha'',alpha'''-tetramethyl-1,4,7,10-tetraacetic acid (DOTMA4-).

Noninvasive techniques to monitor temperature have numerous useful biomedical applications. However, MR thermometry techniques based on the chemical shift, relaxation rates, and molecular diffusion rate of the water 1H signal suffer from poor thermal resolution. The feasibility of MR thermometry based on the strong temperature dependence of the hyperfine-shifted 1H signal from the paramagnetic lanthanide complex thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA-) was recently demonstrated. The use of paramagnetic lanthanide complexes for MR thermometry can be further enhanced by improving the signal-to-noise ratio (SNR) of the observed signal. In this study, the use of lanthanide complexes of a methyl-substituted analog of DOTA4-, 1,4,7,10-tetramethyl 1,4,7,10-tetra azacyclodoecane-1,4,7,10-tetraacetic acetate (DOTMA4-) was evaluated. DOTMA4- complexes have 12 magnetically equivalent methyl protons, which provide an intense and sharper resonance compared to the corresponding DOTA- complexes. Experiments with paramagnetic Pr3+, Yb3+, Tb3+, Dy3+, and Tm3+ complexes of DOTMA4- showed that the Tm3+ complex is most favorable for MR thermometery because of the high temperature dependence of its chemical shift and its relatively narrow linewidth. The chemical shift of the methyl 1H signal from TmDOTMA- was approximately 60 times more sensitive to temperature than the water 1H shift and was insensitive to changes in concentration, pH, [Ca2+], or the presence of other ions and macromolecules. The application of TmDOTMA- for measuring temperature in a subcutaneously implanted tumor model was demonstrated. Lastly, the feasibility of obtaining 3D images from the methyl 1H resonance of TmDOTMA- was demonstrated in phantom and live animal experiments. Overall, TmDOTMA- appears to be a promising probe for MR thermometry in vivo.

Algorithms↗
PubMed2004

Experimental investigation of the mammary gland tumour phantom for multifrequency microwave radio-thermometers.

Microwave radiometry is a spectral measurement technique for resolving the electromagnetic radiation of matter when its temperature is above absolute zero. The radio-thermometer utilises this technique and consequently can provide temperature distributions in subcutaneous biological tissues. A new phantom was proposed that imitates a mammary gland tumour, and the brightness temperature was observed using radio-thermometers operated at different frequencies, 1.75GHz and 3GHz. The proposed phantom, simulating heat diffusion propagated by tissues around real tumours, revealed that the thermal characteristics of the tumour imitator were well matched to the heat transfer properties of a real tumour and a proportional linear relationship between the location of the tumour imitator and the brightness temperature in a homogenous medium was established. From experiments using the proposed mammary gland tumour phantom and a clinical trial on patients with breast cancer, it could be concluded that a radio-thermometer with a short wavelength (lambda = 10cm, i.e. f= 3GHz) is useful to resolve a thermal anomaly at a shallow depth in an homogenous medium such as a breast.

Adult↗
PubMed2004

Reorganizational dynamics of multilamellar lipid bilayer assemblies using continuously scanning Fourier transform infrared spectroscopic imaging.

We employ an implementation of rapid-scan Fourier transform infrared (FT-IR) microspectroscopic imaging to acquire time-resolved images for assessing the non-repetitive reorganizational dynamics of aqueous dispersions of multilamellar lipid vesicles (MLVs) derived from distearoylphosphatidylcholine (DSPC). The spatially and temporally resolved images allow direct and simultaneous determinations of various physical and chemical properties of the MLVs, including the main thermal gel to liquid crystalline phase transition, comparisons of vesicle diffusion rates in both phases and the variation in lipid bilayer packing properties between the inner and outer lamellae defining the vesicle. Specifically, in the lipid liquid crystalline phase, the inner bilayers of the MLVs are more intermolecularly ordered than the outer regions, while the intramolecular acyl chain order/disorder parameters, reflecting the overall characteristics of the fluid phase, remain uniform across the vesicle diameter. In contrast, the lipid vesicle gel phase displays no intermolecular or intramolecular dependence as a function of distance from the MLV center.

Diffusion↗
PubMed2004

Preparation and characterization of a p-tert-butyl-calix[6]-1,4-benzocrown-4-bonded silica gel stationary phase for liquid chromatography.

A p-tert-butyl-calix[6]-1,4-benzocrown-4-bonded silica gel stationary phase (CR6BS) was first prepared via 3-glycidoxypropyltrimethoxysilane as coupling reagent for high performance liquid chromatography. The structure of the new stationary phase was characterized by diffuse reflectance infrared fourier transform spectroscopy (DRIFT), elemental analysis and thermal analysis. The chromatographic performance of the bonded-stationary phase was evaluated by using neutral, acidic and basic solutes as probes. Meanwhile, comparative study of the new stationary phase with a p-tert-butyl-calix[6]arene-bonded silica gel stationary phase (C6BS, the parent) and ODS was done under the same chromatographic conditions. The results show that the new stationary phase has an excellent reversed-phase property, which is similar to C6BS and ODS. However, the selectivities for some aromatic compounds are different from the parent phase (C6BS) and ODS, especially the latter. In one hand, as hybrid of calixarene and crown ether, CR6BS with the oxygen atoms of ether-bridge can provide the complexation sites for the solutes, lacking of C6BS. On the other hand, the rigid conformation of CR6BS may be responsible to the different performance partially. CR6BS exhibits high selectivity in the separation of alkylated aromatics from their parents as compared with C6BS.

Aniline Compounds↗
PubMed1981

NMR relaxation of protein and water protons in methemoglobin solutions.

Hemoglobin (Hb) proton spins rapidly equilibrate among themselves after an initial excitation, and relax toward thermal equilibrium as a unit. In the diamagnetic form, spin diffusion to nearby methyl relaxation sinks can account for this. For metHb, four strong heme relaxation centers dominate, and spin diffusion must occur over long distances. A sizeable difference in protein T1 is found between H2O and D2O solutions, much more than for diamagnetic Hb, consistent with internal H2O acting as a spin carrier to the heme.

Heme↗
PubMed2005

Evaluation of novel techniques for measurement of air-water exchange of persistent bioaccumulative toxicants in Lake Superior.

We report initial measurements of concentrations and net air-water exchange fluxes of target persistent bioaccumulative toxicants (PBTs) in Lake Superior utilizing techniques not previously applied for this purpose. Gaseous PBTs are collected in diffusion denuders containing sections of commercial chromatography columns and subsequently thermally extracted into the cooled injection inlet of a high-resolution gas chromatograph. The PBT sampling/analytical methods enable accurate determination of gas-phase PBT concentration and micrometeorological measurement of fluxes to be carried out. PBT fluxes are measured by the modified Bowen ratio technique in which sensible heat flux is related to PBT flux, with the assumption of identical transfer velocities of heat and PBTs between two heights in the atmospheric surface layer. Micrometeorological measurement of flux accounts for all sources of resistance to mass transfer, including atmospheric stability effects, surface films, waves, sea spray, and bubbles. The sensible heatflux, PBT concentration, and PBT flux measurements carried out in 14 2- or 3-h periods during seven sampling events in Lake Superior in summer and fall 2002 and spring 2003 demonstrate advantages under the constraints of the techniques. The uncertainty of the flux measurements was typically in the range from 1% to 160%. Gaseous concentrations of a-hexachlorocyclohexane (alpha-HCH) and hexachlorobenzene (HCB) over Lake Superior were in the range from 6 to 170 and 12-95 pg/m3, respectively. Fluxes out of Lake Superior were measurable in 75% of the cases in which a concentration gradient was measured, and were in the range from -0.17 to +0.064 ng/m2 x h for alpha-HCH and from -0.60 to -0.093 ng/m2 x h for HCB.

Air↗
PubMed1998

New Lanthanide Selenophosphates. Influence of Flux Composition on the Distribution of [PSe(4)](3)(-)/[P(2)Se(6)](4)(-) Units and the Stabilization of the Low-Dimensional Compounds A(3)REP(2)Se(8), and A(2)(RE)P(2)Se(7) (A = Rb, Cs; RE = Ce, Gd).

The reaction of Ce or Gd with a molten mixture of A(2)Se/P(2)Se(5)/Se (A = Rb, Cs) produced the quaternary compounds Rb(3)CeP(2)Se(8) (I) and Cs(3)GdP(2)Se(8) (II), as well as Rb(2)CeP(2)Se(7) (III) and Rb(2)GdP(2)Se(7) (IV). The orange crystals of I, II and the red crystals of III, IV are air- and water-sensitive. Compounds I, II crystallize in the monoclinic space group P2(1)/c, and for I, a = 9.6013(2) Å, b = 18.0604(1) Å, c = 10.0931(1) Å, beta = 90.619(1) degrees, and Z = 4. Compounds III, IV crystallize in the monoclinic space group P2(1)/n, and for IV, a = 10.137(2) Å, b = 7.212(1) Å, c = 20.299(2) Å, beta = 98.23(1) degrees, and Z = 4. Compounds I, II have a 1-D structure with [(RE)P(2)Se(8)](n)()(3)(n)()(-) chains separated by A(+) cations. The RE(3+) lanthanide cation is in a bicapped trigonal prismatic coordination with four tridentate [PSe(4)](3)(-) ligands. Compounds III, IV possess a 2-D structure. Each layer consists of [RE(PSe(4))](x)() "chains" interstitched in two dimensions by hexadentate [P(2)Se(6)](4)(-) ligands. The trivalent RE cation is in a square antiprismatic coordination. The compounds were characterized with differential thermal analysis, far-IR, and solid-state UV/vis diffuse reflectance spectroscopy. Magnetic measurements indicate that the compounds obey the Curie law with &mgr;(eff) values close to those of the free RE(3+) ions.

Journal Article↗