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PubMed1978

Photolysis in 131I, 35S or 14C labeled HgLSCN powders.

In 1938, S.V. Raghava Rao reported that a crystal of HgXSCN (X=halogen) has photropic properties and in 1955, the author reported the mechanism of the phototropy is identical with that of HgI2.2HgS. However, a behavior of S, I and C atoms in the crystals irradiated by sunlight was not known. Purpose of this paper is to clarify the behavior of these atoms by using radioactive tracer technique. The results obtained show that when electrons belonging to S2- or I- ions absorb photons and are excited to upper state, these electrons leave behind neutral S or I atoms, which diffuse thermally toward the crystal surface and escape into atmosphere. 14C atoms do not escape. S atoms are more sensitive to light than I or C atoms.

Carbon Radioisotopes↗
PubMed1995

[Induction of impaired hepatic microcirculation by in situ hilus preparation in liver explantation].

AIM: Usually, in-situ preparation of the hepatic hilar structures is performed prior to the perfusion with preservation solution. Aim of this study was to investigate mechanical effects of liver preparation on the hepatic microcirculation. METHODS: 16 pigs (German landrace) were randomized in two groups. In both groups, laparotomy was performed after intratracheal intubation. Subsequently, a thermal diffusion probe was implanted into the medial left liver lobe for quantification of microperfusion. In group A (n = 8), bile duct, hepatic artery, and portal vein were exposed and the lesser omentum transsected thereafter. Ultrasound-volume-probes were placed around the hepatic artery and portal vein. Simultaneous measurement of hepatic microperfusion and total liver blood flow was performed five minutes after the end of liver preparation. In group B (n = 8) hepatic microperfusion was quantified 45 minutes after laparotomy without further manipulations. RESULTS: By the preparation, liver perfusion was significantly reduced in group A from 78 +/- 13 ml/100g/min to 61 +/- 16 ml/100g/min. After preparation a total liver blood flow of 137 +/- 46 ml/100g/min was recorded indicating a shunt fraction of 51 +/- 21%. In contrast, hepatic microperfusion in group B remained at baseline during the whole observation period (79 +/- 3 ml/100g/min vs. 78 +/- 5 ml/100g/min). CONCLUSION: In-situ liver preparation induces a relevant disturbance of hepatic microcirculation. Preservation perfusion shortly after surgical manipulation could become ineffective because of an increase in shunt flow. If the regeneration period is too short, e.g. lack of heart explantation, the quality of the liver graft could be limited.

Animals↗
PubMed1998

In vitro and animal validation of bromine-76-bromodeoxyuridine as a proliferation marker.

UNLABELLED: The potential of 76Br-bromodeoxyuridine as a PET tracer for characterizing proliferation potential was investigated in multicellular tumor aggregates and in healthy rats and pigs. METHODS: Bromine-76-bromide was produced by proton irradiation of a 76Se-enriched target using a 17-MeV cyclotron and recovered by thermal diffusion. Bromine-76-BrdU was prepared from the corresponding trimethylstannate by an oxidative bromination. Multicellular aggregates from a carcinoid cell line and two bladder cancer cell lines were co-incubated with 76Br-BrdU and 3H-thymidine and the uptake and DNA incorporation analyzed. About 0.5 MBq 76Br-BrdU were injected in the tail vein of unanaesthetised Sprague-Dawley rats. Two to 36 hr later they were decapitated and the radioactivity concentration and fraction of radioactivity incorporated into DNA determined in five different organs and the blood. Parallel studies were performed in animals pretreated with hydroxyurea. In separate experiments, rats were given an injection of 76Br-bromide and organ uptake was evaluated after 20 hr. PET studies were performed in two pigs and the uptake in different organs was investigated after injection of 76Br-BrdU. In these studies, diuresis was induced by furosemide and mannitol and radioactivity in blood and organs was followed during 10 hr. RESULTS: In the cell aggregates, 30%-90% of the radioactivity was extracted in the DNA fraction. A good correlation was found between 76Br-BrdU and 3H-thymidine with respect to total uptake and DNA fraction. The DNA fraction increased from 2-10 hr after incubation. With in vivo injection in the rat, relatively high uptake of radioactivity was found in all organs, unrelated to the degree of DNA synthesis. However, inhibition by hydroxyurea occurred only in the spleen and intestines, organs which also showed a high degree of incorporation of 76Br-BrdU into DNA. In the pig, the highest in vivo uptake was observed in the red bone marrow and the intestines. In these organs, 70%-80% of the radioactivity was recovered in the DNA fraction. The concentration of radioactivity in the heart, liver and kidney was 3-10 times lower, and here the DNA fraction accounted for 10%-20% of the radioactivity. The decay-corrected radioactivity in blood and nonproliferating organs decreased with diuresis with a half-life of 13 and 16 hr, respectively. CONCLUSION: It is suggested that the radioactivity uptake as seen after the administration of 76Br-BrdU, is constituted by two parts: one relating to incorporation into DNA and one existing as free 76Br- or metabolites of 76Br-BrdU. If sufficient time has passed, 76Br- dominates other metabolites. A correct assessment of DNA-incorporated radioactivity using PET with 76Br-BrdU is not trivial and can only be made with due correction for 76Br-, using either a complementary investigation after hydroxyurea pretreatment (in animal studies) or a separate 76Br-bromide investigation. Alternatively, the free bromide can be eliminated partially through forced diuresis.

Animals↗
PubMed1998

Supramolecular receptor structures in the plasma membrane of lymphocytes revealed by flow cytometric energy transfer, scanning force- and transmission electron-microscopic analyses.

Receptors in the plasma membrane of blood cells in general and in that of lymphocytes in particular are supposed to move around in a random walk fashion relatively freely driven by thermal diffusion, as described by the Singer-Nicolson fluid mosaic membrane model. In this article we summarized data and techniques that indicated nonrandom codistribution patterns of receptor superstructures under conditions, where the generation of such molecular colocalizations by the methods themselves were excluded. Application of fluorescence energy transfer in a flow cytometer helped to analyze such codistribution patterns in cell populations. After normalizing energy transfer values for possible differences between labeling ratios of the targeting monoclonal antibodies and using the mean values of energy transfer distribution curves, two-dimensional receptor maps were generated from data obtained in a pair-wise fashion between receptors. Major histocompatibility complex (MHC) class I and II, intercellular adhesion molecule-1 (ICAM-1), TcR-CD3-CD4, tetraspan molecules (CD81, CD82, CD53), and the subunits of the multisubunit IL-2 receptor displayed nonrandom codistribution patterns sometimes with, but very frequently without induction by their ligand. Immunogold-bead "sandwich" labeling analyzed by atomic force microscopy has shown that such receptor "islands" existed also in "receptor-island-groups". This indicated the existence of nonrandom receptor distribution of MHC class I and II molecules also at an elevated hierarchical level. An analysis is given herein concerning a standardized approach. The apparent incompatibility of these supramolecular patterns with the Singer-Nicolson type "free-protein and lipid-mobility paradigm" was resolved by recommending an additional emphasis on the mosaicism of the membrane besides receptor mobility.

Antibodies, Monoclonal↗
PubMed2004

Theoretical and experimental comparison of the Soret coefficient for water-methanol and water-ethanol binary mixtures.

In multicomponent mixtures, a much richer variety of phenomena can occur than in simple (single-component) fluids. Natural convection in single-component fluids is due to buoyancy forces caused by temperature gradients. In multicomponent mixtures, buoyancy forces may also be caused by concentration gradients. Because natural convection, molecular diffusion, and thermal conduction have different relaxation time scales, a wide variety of resulting convective motions and heat and mass distributions might occur. In some fluid mixtures such as water-ethanol system, for instance, ethanol diffuses much more slowly than heat, and because of this difference in time scales oscillatory convection might occur. In a multicomponent mixture, the total molar flux consists of two parts: the convective molar flux and the diffusive molar flux (resulting from the difference between the component velocity and the bulk velocity). The diffusion molar flux of a component depends, not only on its own mole fraction gradient (Fickian diffusion), but also on the gradient of all the components present in the mixture (cross-molecular diffusion). The diffusion flux depends also on the pressure gradient (pressure diffusion; the so-called gravitational effect) and temperature gradient (thermal diffusion; the so-called Soret effect). Firoozabadi's thermal diffusion model was applied to calculate the Soret coefficient, as well as the thermal diffusion coefficient and molecular diffusion coefficient for methanol-water and ethanol-water mixtures at 310.65 K temperature and 1 bar pressure with 10% water mass fraction. The results were compared with experimental data (J.K. Platten, in Proceedings of the 5th International Meeting on Thermodiffusion (IMT5), Lyngby, Aug. 2002, Philos. Mag. 83, Nos. 17-18 (2003)), as well as theoretical predictions with other models. A better agreement with the experimental data using the Firoozabadi model was achieved.

Journal Article↗
PubMed2000

Direct observation of the quantum tunneling of single hydrogen atoms with a scanning tunneling microscope

Single hydrogen atoms were imaged on the Cu(001) surface by scanning tunneling microscopy (STM). The vibrations of individual H and D atoms against the surface were excited and detected by inelastic electron tunneling spectroscopy (STM-IETS). Variable temperature measurements of H atom diffusion showed a transition from thermally activated diffusion to quantum tunneling at 60 K. Regimes of phonon-assisted and electron-limited quantum tunneling were observed. The thermal diffusion rate of D atoms varied over 7 orders of magnitude between 80 and 50 K with no transition to quantum tunneling down to a thermal hopping rate of 4x10(-7) s(-1).

Journal Article↗
PubMed1985

Temperatures within comet nuclei.

We have performed a theoretical study of temperatures beneath the surface of a comet's nucleus. We solve the one-dimensional heat conduction equation for the outer portion of the comet. The upper boundary condition of the model is given by energy balance at the surface of the nucleus, including conduction of heat inward, radiation, insolation as modified by the coma, and sublimation. Our coma model assumes single scattering and includes attenuation of direct sunlight by dust grains, scattering of light onto the nucleus, and infrared radiation by dust grains. The lower boundary condition is zero net heat flux around an orbit. The thermal conductivity expression for the nucleus includes direct conduction at grain boundaries, radiative conduction, and Knudsen flow vapor diffusion. The thermal diffusivity of the nucleus and the resultant temperature profiles are shown to be strongly dependent on the physical properties of the material, including porosity, pore size, and compaction. The temperature profiles and the equilibrium temperature deep within the comet also depend on the functional relationship between thermal conductivity and temperature; the highest deep equilibrium temperatures are found for models where the thermal conductivity increases strongly with increasing temperature. The dependence of temperatures on the albedo and thermal emissivity of the nucleus is also calculated, as well as the variation of temperature with latitude for a variety of pole orientations. The effect of a dust mantle on subsurface temperatures is also investigated. All calculations are presented for short-period comets with orbits that make them accessible for exploration by spacecraft rendezvous. In situ measurements of the thermal profile in the upper meter of a comet nucleus can substantially constrain the thermal diffusivity of the material, which in turn can provide significant information about the physical properties of the nucleus.

Cosmic Dust↗
PubMed1989

Encoding of nociceptive thermal stimuli by diffuse noxious inhibitory controls in humans.

1. It has previously been shown that, in normal humans, heterotopic painful thermal conditioning stimuli induce parallel increase in the thresholds of a spinal nociceptive flexion reflex (RIII reflex) and the concurrent sensation of pain elicited by electrical stimulation of the sural nerve. On the basis of analogous animal studies, we proposed that such phenomena could be related to diffuse noxious inhibitory controls (DNIC), which have been described in the rat. The present study, which was carried out on normal volunteer subjects, was particularly concerned with the extent and temporal characteristics of the depressive effects of DNIC triggered by painful thermal stimuli on RIII reflex activity. In addition, because it was possible that these depressive effects could have resulted from a direct postsynaptic inhibition of motoneurons, a second part of the study was aimed at determining whether or not the heterotopic noxious thermal stimuli also affected the excitability of alpha-motoneurons, as monitored by the monosynaptic Hoffmann reflex (H reflex) technique. 2. In the 11 subjects under study, application of moderate, nonnoxious temperatures (40-44 degree C) to the contralateral hand (via a thermoregulated and agitated waterbath) did not modify the RIII reflex nor the associated sensation of pain. By contrast noxious temperatures clearly depressed the RIII reflex and the concurrent sensation of pain, both during and after the conditioning procedure (CP), in a direct linear relationship to the temperature of the waterbath in the 45-47 degree C range; the maximal depressive effect was observed with the highest conditioning temperature. A significant relationship was also found between the extent of the RIII depression during the CP and that during a 10-min period of post-CP observation. 3. The depressive effects observed on both the RIII reflex and pain were not associated with clear change in autonomic functions. Respiration remained stable during the sessions, with no significant relationship between the temperatures of the waterbath and respiratory rate. Heart rate was slightly but significantly increased during the immersion of the hand in the 46 or 47 degree C waterbaths; this increase, however, ceased with the end of CP. 4. Application of thermal conditioning stimuli produced a slight but nonsignificant increase of the monosynaptic H reflex during the first minute of CP, no matter what was the temperature of the waterbath. However, there were no subsequent variations during the 6-min period of post-CP observation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1981

The encoding of thermal stimuli by diffuse noxious inhibitory controls (DNIC).

The relationship between stimulus intensity and its efficacy in inducing diffuse noxious inhibitory controls (DNIC) was investigated in anaesthetized rats by using thermal stimulation of the tail for conditioning dorsal horn convergent neuronal responses to C fibres emanating from the hindpaw extremity. The threshold for obtaining inhibition of the neuronal responses ranged between 40 and 44 degrees C and there was a highly significant correlation between noxious temperatures (44-52 degrees C) and the degree of inhibition. These data provide support for the notion of an involvement of inhibitory processes (DNIC) in the signalling of pain by convergent neurones.

Animals↗
PubMed1999

Evaluation of two adsorbents for diffusive sampling and thermal desorption-gas chromatographic analysis of monoterpenes in air.

Tube type samplers with two different adsorbents, Chromosorb 106 and Tenax TA, were evaluated by laboratory experiments and field tests for simultaneous diffusive sampling of alpha-pinene, beta-pinene and delta 3-carene and subsequent thermal desorption-gas chromatographic analysis. No statistically significant effects of exposure time, concentrations of monoterpenes or relative humidity were found for samplers with Chromosorb 106 when running a factorial design, with the exception of the adsorption of delta 3-carene, for which some weak effects were noted. Samplers with Tenax TA were affected by the sampling time as well as the concentration for all terpenes, with a strong interaction effect between these two factors. The terpenes showed good storage stability on both adsorbents. No effect of back-diffusion was noted when using Chromosorb 106, while Tenax TA showed some back-diffusion effects. The uptake rates, in ml min-1, for the terpenes on Chromosorb 106 were 0.36 for alpha-pinene, 0.36 for beta-pinene and 0.40 for delta 3-carene. The corresponding average values on Tenax TA were 0.30 for alpha-pinene, 0.32 for beta-pinene and 0.38 for delta 3-carene. The field validation proved that diffusive sampling on Chromosorb 106 agreed well with pumped sampling on charcoal for stationary samples, while the personal samples indicated a discrepancy of 25% between Chromosorb 106 and charcoal samples. Tenax TA generally gave lower results than Chromosorb 106 in all field samples. Samplers packed with Chromosorb 106 could be used to monitor terpene levels in workplaces such as sawmills. The major advantages with this method are the sampling procedure, which is simple to perform compared to other techniques, the easily automated analysis procedure and the possibility to reuse the samplers.

Adsorption↗
PubMed2003

The application of diffusive sampling combined with thermal desorption in occupational exposure monitoring--field evaluation.

Diffusive sampling combined with thermal desorption (DSTD) is considered useful in monitoring workers' exposures to organic vapors, not only due to its simplicity of operation in the field but, also, its simplifying the sample treatment, eliminating the use of extracting solvent, and increasing analytical sensitivity. Herein, the feasibility of applying DSTD in field conditions was assessed through a comparison of the results with those from the well-accepted active/charcoal method. Side-by-side active and diffusive (tube-type, Tenax TA as the adsorbent) samples, both personal and area, were collected and analyzed for xylenes, ethyl acetate, styrene, and n-butyl acetate in four different industrial settings. Statistically significant correlations were found between the two methods in personal samples with the correlation coefficients of 0.92, 0.90, 0.83, 0.88, and 0.97 for m&p-xylenes, o-xylene, n-butyl acetate, styrene, and ethyl acetate, respectively. A paired t-test revealed significant difference between the two methods for n-butyl acetate and styrene. For area sampling, statistical differences (p < 0.05) were found between the two methods, except for xylenes. The DSTD method had, mostly, a lower concentration than the active method, with the bias ranging from 10.2 to -54.4 percent. The possible causes for the discrepancies are discussed. These results suggest that though DSTD protocols can be considered as a simple approach for screening workers' exposures to volatile organics, they should be applied with caution since diffusive sampling is potentially affected by various environmental conditions and adsorptive characteristics.

Adsorption↗
PubMed2006

Charge-transport regime of crystalline organic semiconductors: diffusion limited by thermal off-diagonal electronic disorder.

We propose that the electron transport in crystalline organic semiconductors at room temperature (RT) is neither polaronic nor a combination of thermally activated hopping and polaronic transport, as previously thought. Thermal molecular motions cause large fluctuations in the intermolecular transfer integrals that, in turn, localize the charge carrier. This effect destroys the translational symmetry of the electronic Hamiltonian and makes the band description inadequate for RT organic crystals. We used a one-dimensional semiclassical model to compute the (temperature dependent) charge carrier mobility in the presence of thermal fluctuations of the electronic Hamiltonian. This transport mechanism explains several contrasting experimental observations pointing sometimes to a delocalized "bandlike" transport and sometimes to the existence of strongly localized charge carriers.

Journal Article↗
PubMed1987

Interferometric technique for investigation of laser thermal retinal damage.

We describe a new technique for investigating laser-tissue interactions based on the use of an interferometric laser exposure pattern. A Michelson interferometer is used to generate a sinusoidal fringe exposure pattern. The periodicity of the fringe pattern may be adjusted from macroscopic dimensions to a scale of microns without the need for an imaging plane. Since fringe pattern periodicity is more adjustable and directly measureable than laser spot size, this technique offers significant advantages for studying the effects of thermal damage and diffusion in the irradiated tissue. In addition, the comparison of tissue response with theoretical models is simplified since the sinusoidal fringe pattern is itself an eigenfunction of the thermal diffusion equation. This technique is demonstrated for argon laser photocoagulation in the rabbit retina. Exposures at durations comparable to the thermal relaxation time produced spatially confined lesions, while those at much longer durations resulted in significant diffusion of the thermal damage beyond the primary targeted regions. The role of thermal diffusion can thus be assessed directly from the ophthalmoscopic and histologic appearances of the lesions. This technique can be employed to study thermal diffusion and other transport phenomena occurring in laser-tissue interactions for a variety of laser sources and tissue targets.

Animals↗
PubMed2006

Generation and detection of incoherent phonons in picosecond ultrasonics.

In picosecond ultrasonics experiments the absorption of a femtosecond laser pulse in a thin metallic transducer is used to generate very short acoustic pulses. These pulses are made of coherent longitudinal waves with a frequency spectrum that can reach 100-200 GHz. The laser pulse absorption gives rise to a heating of the film of a few Kelvin within a typical time of 1 ps. Later on, the heat goes in the substrate through an interface thermal resistance and is diffused by thermal conduction. At very low temperature and in pure crystals the thermal phonons emitted by the heated metallic film can propagate ballistically over large distances and produce a so-called heat pulse. We report on the experimental evidence of the coexistence of the coherent acoustic pulse and the incoherent heat pulse generated and detected by laser ultrasonics.

Journal Article↗