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PubMed2002

Quantum Kramers equation for energy diffusion and barrier crossing dynamics in the low-friction regime.

Based on a true phase space probability distribution function and an ensemble averaging procedure we have recently developed [Phys. Rev. E 65, 021109 (2002)] a non-Markovian quantum Kramers equation to derive the quantum rate coefficient for barrier crossing due to thermal activation and tunneling in the intermediate to strong friction regime. We complement and extend this approach to weak friction regime to derive quantum Kramers equation in energy space and the rate of decay from a metastable well. The theory is valid for arbitrary temperature and noise correlation. We show that depending on the nature of the potential there may be a net reduction of the total quantum rate below its corresponding classical value, which is in conformity with earlier observation. The method is independent of path integral approaches and takes care of quantum effects to all orders.

Journal Article↗
PubMed1999

Crystallization and preliminary X-ray crystallographic analysis of spruce budworm antifreeze protein.

Antifreeze proteins have the ability to bind to ice with high affinity and inhibit further crystal growth. The insect antifreeze protein from spruce budworm exhibits very high thermal hysteresis activity and is implicated in the protection of overwintering larvae from freezing. This protein has been crystallized in 20-25% polyethylene glycol (Mr 6000), 0.4 M NaCl, 0.1 M Tris-HCl, pH 8.5, by vapor diffusion using the hanging drop method. The resulting crystals are very thin (typically <0.01 mm in the shortest dimension), and only after repeated seeding could crystals be grown large enough for data collection using synchrotron radiation. The crystals belong to the monoclinic space group C2, with cell dimensions a = 82.28 A, b = 62.29 A, c = 63.63 A, and beta = 113.7 degrees. Molecules in the asymmetric unit are related by a twofold axis of symmetry with two molecules present. Native data to a resolution of 2.6 A have been collected with 90.3% completeness and a Rsym of 6.9%.

Animals↗
PubMed2001

Activation of diffuse noxious inhibitory controls (DNIC) in rats with an experimental peripheral mononeuropathy.

Diffuse noxious inhibitory controls (DNIC), which involve supraspinal structures and modulate the transmission of nociceptive signals, were investigated in rats with chronic constriction injury of the sciatic nerve. Nerve-injured rats with increased sensitivity to mechanical and thermal stimulation on the operated side were anesthetized and recordings were made from trigeminal convergent neurons. Inhibitions of C-fiber-evoked neuronal responses during and after the application of nociceptive conditioning stimuli to the hindpaw, were measured to evaluate DNIC. The conditioning stimuli consisted of graded natural (pressure and heat) and electrical stimuli and were applied alternately to non-operated and operated hindpaws. Compared with the non-operated paw, inhibitions elicited by pressure on the operated hindpaw were increased significantly at all stimulus intensities. Albeit to a lesser extent, inhibitions elicited by thermal stimulation of the operated paw were also increased in the nerve-injured animals. Such exacerbation of DNIC-induced inhibitions produced by mechanical and thermal stimulation of the operated paw can be explained by an increase in the afferent input to the spinal cord. In contrast to the results obtained with natural stimulations, inhibitions evoked from the operated and non-operated paws were similar when graded electrical stimulation was used as the conditioning stimulus. This was true regardless of the intensity and frequency of stimulation and regardless of whether the stimuli were applied transcutaneously or directly to the sciatic nerve. The clear-cut difference between the results obtained with natural and electrical conditioning stimuli suggests that the nociceptive neurons involved in the triggering of DNIC may not be sensitized at the central level. Peripheral mechanisms such as the sensitization of nerve injured fibers and/or sprouting of nerve terminals may thus be the main causes of DNIC increase in this model of neuropathic pain.

Animals↗
PubMed1999

Dehydration and rehydration of a hydrate diclofenac salt at room temperature.

The salt diclofenac/N-(2-hydroxyethyl) pyrrolidine crystallizes from water as a dihydrate, while it precipitates from organic solvents anhydrously: the two salts have different crystal structures. Dehydration of the dihydrate salt was carried out in a desiccator over silica gel at room temperature: the process occurs with the retention of the crystal structure. Slight changes observed in the diffractograms suggest, that soon after dehydration, a phase transition starts, slowly due to the low temperature of the process. The reaction was followed determining the loss of weight as a function of time and by thermal analysis, since the dihydrate and the dehydrate forms have different thermograms, but similar diffractograms. The reaction was complete after 24 h. The analysis of the experimental data suggests a kinetic process related to a one-dimensional diffusion of the crystallization water molecules outwards the solid particles. At room temperature, the dehydrate material rapidly back-absorbs the two molecules of crystallization water from the atmosphere moisture. The interaction with water of the different forms of the salt was discussed as a function of their solid structures as well as of the complex equilibria present in aqueous solution: these can explain previous apparently anomalous results.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Electron photodetachment from aqueous anions. 3. Dynamics of Geminate pairs derived from photoexcitation of mono- vs polyatomic anions.

Photostimulated electron detachment from aqueous inorganic anions is the simplest example of solvent-mediated electron transfer reaction. As such, this photoreaction became the subject of many ultrafast studies. Most of these studied focused on the behavior of halide anions, in particular, iodide, that is readily accessible in the UV. In this study, we contrast the behavior of these halide anions with that of small polyatomic anions, such as pseudohalide anions (e.g., HS(-)) and common polyvalent anions (e.g., SO(3)(2-)). Geminate recombination dynamics of hydrated electrons generated by 200 nm photoexcitation of aqueous anions (I(-), Br(-), OH(-), HS(-), CNS(-), CO(3)(2-), SO(3)(2-), and Fe(CN)(6)(4-)) have been studied. Prompt quantum yields for the formation of solvated, thermalized electrons and quantum yields for free electrons were determined. Pump-probe kinetics for 200 nm photoexcitation were compared with kinetics obtained at lower photoexcitation energy (225 or 242 nm) for the same anions, where possible. Free diffusion and mean force potential models of geminate recombination dynamics were used to analyze these kinetics. These analyses suggest that for polyatomic anions (including all polyvalent anions studied) the initial electron distribution has a broad component, even at relatively low photoexcitation energy. There seems to be no well-defined threshold energy below which the broadening of this electron distribution does not occur, as is the case for halide anions. The constancy of (near-unity) prompt quantum yields vs the excitation energy as the latter is scanned across the lowest charge-transfer-to-solvent band of the anion is observed for halide anions but not for other anions: the prompt quantum yields are considerably less than unity and depend strongly on the excitation energy. Our study suggests that halide anions are in the class of their own; electron photodetachment from polyatomic, especially polyvalent, anions exhibits qualitatively different behavior.

Journal Article↗
PubMed2005

Thermal conductance and thermopower of an individual single-wall carbon nanotube.

We have observed experimentally that the thermal conductance of a 2.76-microm-long individual suspended single-wall carbon nanotube (SWCNT) was very close to the calculated ballistic thermal conductance of a 1-nm-diameter SWCNT without showing signatures of phonon-phonon Umklapp scattering for temperatures between 110 and 300 K. Although the observed thermopower of the SWCNT can be attributed to a linear diffusion contribution and a constant phonon drag effect, there could be an additional contact effect.

Journal Article↗
PubMed2004

Formation of thermal vacancies on the Si sublattice of the intermetallic compound MoSi2.

For a detailed understanding of high-temperature processes in complex solids the identification of the sublattice on which thermal defects are formed is of basic interest. Theoretical studies in intermetallic compounds favor a particular sublattice for thermal vacancy formation. In the present study we detect in ordered MoSi2 thermal vacancies with a low formation enthalpy of H(F)(V)=(1.6+/-0.1) eV, and we succeed in showing by experimental and theoretical efforts that they are preferentially formed on the Si sublattice. By these data self-diffusion in MoSi2 can be understood.

Journal Article↗
PubMed2005

Association between erectile dysfunction and coronary artery disease: a case report study.

Evidence is accumulating in favor of classifying erectile dysfunction (ED) as a vascular disorder. There are three main clinical scenarios in which ED and coronary artery disease (CAD) may coexist: the patient with ED who later develops CAD, the patient with overt CAD who is casually found to have ED, and the patient with acute coronary syndrome who has normal sexual function. This study presents three cases and discusses a "putative" pathophysiological mechanism underlying all these clinical presentations. Further studies, coupling functional and structural changes of coronary circulation with those of penile (i.e., dynamic penile test) circulation in each of these situations are mandatory to support this hypothesis.

Aged↗
PubMed1994

Diffuse noxious inhibitory control. Reappraisal by pain-related somatosensory evoked potentials following CO2 laser stimulation.

The effects of DNIC (diffuse noxious inhibitory control) in humans were evaluated by means of pain SEPs (somatosensory evoked potentials) and pain visual analogue scale (VAS) following CO2 laser stimulation applied to the left knee while conditioning stimuli (non-noxious and noxious thermal stimuli) applied to the right hand. Pain SEPs were recorded from scalp electrodes following laser stimulation applied to the left knee during various conditions as follows: (1) control (without any interference), (2) non-noxious (dipping the right hand in water at 41 degrees C for 3 min), (3) noxious (dipping the right hand in water at 46 degrees C for 3 min), and (4) after-effect (3-6 min after taking the hand from the water at 46 degrees C). The present pain SEPs findings confirmed the presence of DNIC in humans, and indicates: (1) degree of pain relief was significantly correlated with changes in pain SEPs, particularly a marked decrease in amplitude, and a decrease in VAS; (2) DNIC was more effective on the second pain than the first pain; (3) the effect of DNIC gradually increased over time, but it rapidly disappeared after the conditioning stimuli ceased; and (4) DNIC was not due merely to changes of attention. I propose that the site responsible for DNIC is the brainstem or the spinal cord rather than the cerebral hemisphere.

Adult↗
PubMed2005

Combination of ultrasound and discarded tire rubber: removal of Cr(III) from aqueous solution.

Ground discarded tire rubber is an interesting and inexpensive medium for the sorption of toxic metals, including chromium, from water. The batch sorption tests were conducted to investigate the sorption capacity of Cr(III) from aqueous solution by ground tire in the presence and absence of ultrasound. The research parameters included ultrasonic waves, solution temperature, aqueous chromium concentration, particle size of the ground tire, contact time, and others. The Langmuir model was applied to the sorption equilibrium to determine the maximum metal sorption capacity in the presence and absence of ultrasound. The Langmuir constants were also obtained from the isotherms under different conditions. The results indicated that the tire rubber was a more efficient sorbent for the removal of chromium in the presence of ultrasound. Because there are several stages in the sorption process, it is important to find out which step or steps control the rate of sorption. According to the results, the internal porous diffusion is the rate-controlling step. The diffusion coefficient of Cr(III) in ground tire rubber in the presence of ultrasound was about two times greater than that in the absence of ultrasound. The effect of ultrasound on the sorption process could be explained by the thermal and nonthermal properties of acoustic cavitation.

Absorption↗
PubMed2001

Cryosurgery of normal and tumor tissue in the dorsal skin flap chamber: Part I--thermal response.

Current research in cryosurgery is concerned with finding a thermal history that will definitively destroy tissue. In this study, we measured and predicted the thermal history obtained during freezing and thawing in a cryosurgical model. This thermal history was then compared to the injury observed in the tissue of the same cryosurgical model (reported in companion paper (Hoffmann and Bischof, 2001)). The dorsal skin flap chamber, implanted in the Copenhagen rat, was chosen as the cryosurgical model. Cryosurgery was performed in the chamber on either normal skin or tumor tissue propagatedfrom an AT-1 Dunning rat prostate tumor. The freezing was performed by placing a approximately 1 mm diameter liquid-nitrogen-cooled cryoprobe in the center of the chamber and activating it for approximately 1 minute, followed by a passive thaw. This created a 4.2 mm radius iceball. Thermocouples were placed in the tissue around the probe at three locations (r = 2, 3, and 3.8 mm from the center of the window) in order to monitor the thermal history produced in the tissue. The conduction error introduced by the presence of the thermocouples was investigated using an in vitro simulation of the in vivo case and found to be <10 degrees C for all cases. The corrected temperature measurements were used to investigate the validity of two models of freezing behavior within the iceball. The first model used to approximate the freezing and thawing behavior within the DSFC was a two-dimensional transient axisymmetric numerical solution using an enthalpy method and incorporating heating due to blood flow. The second model was a one-dimensional radial steady state analytical solution without blood flow. The models used constant thermal properties for the unfrozen region, and temperature-dependent thermal properties for the frozen region. The two-dimensional transient model presented here is one of the first attempts to model both the freezing and thawing of cryosurgery. The ability of the model to calculate freezing appeared to be superior to the ability to calculate thawing. After demonstrating that the two-dimensional model sufficiently captured the freezing and thawing parameters recorded by the thermocouples, it was used to estimate the thermal history throughout the iceball. This model was used as a basis to compare thermal history to injury assessment (reported in companion paper (Hoffmann and Bischof, 2001)).

Animals↗
PubMed1991

Kinetic aspects of human placental alkaline phosphatase enzyme membrane.

The crosslinking of alkaline phosphatase of human placenta with human serum albumin has been optimized. During the physico-chemical characterization of this immobilized biocatalyst, special attention was paid to attributes such as the irreversibility of the enzyme support bonding, the stability of the catalytic activity, and the effects of pH and temperature on this activity. Regarding stability, patterns of denaturation are proposed, to account for inactivation curves over time and under storage/operation conditions. These patterns, in some cases, indicate the existence of different populations of immobilized enzyme molecules, with a different degree of sensitivity to denaturation. The activity vs pH profiles are clearly modified by the immobilization process. This is because the pH of the free homogeneous solution, measurable with a pH-meter, differs from the real pH of the immediate microenvironment of the immobilized enzyme molecules due to the effects of proton accumulation in the microenvironment (in the reaction catalysed by alkaline phosphatase, protons are produced), to limitations to the free diffusion of H+ and to the possible partition effects of H+ due to polar interactions with residues or molecules of the enzyme membrane. In the experimental working conditions, the apparent optimum temperatures are centered at 40 degrees C, inactivation (thermal denaturation) occurring above this temperature. In the temperature range 10-40 degrees C, the kinetic control over the overall activity of the immobilized enzyme was observed, causing the Arrhenius profiles to be linear.

Alkaline Phosphatase↗
PubMed1979

[Experimental and clinical experiences with silicone catheters in fistulizing glaucoma surgery].

1. A historical revue of seton operations is presented, which were actually explored for the first time by Rollet in 1907. 2. The paramount importance of the selection of the appropriate material for the setons is stressed. 3. Ocular tolerance especially of silicone tubings has been investigated by animal experiments. Excellent tolerance of silicone intraocularly as well as subconjunctivally has been found. This fact confirms experimental investigations by other authors. 4. In animal experiments for the first time a surgical technique securing firm anchorage of a sole silicone tubing could be developed. Insertion of a silicone catheter was combined with thermal sclerostomy; ocular hypotony was not encountered. 5. A study exploring aqueous egress following the new surgical procedure has been conducted by means of injection of fluorescein into the anterior chamber. Various exit-sites of aqueous were recorded: diffuse outflow through the filtration cleft as well as the catheter lumen, and also via channels either within lymph vessels or secondary aqueous veins. 6. Aqueous outflow following the seton operation has also been studied by scintigraphic means; the first description of this method in glaucoma-operated eyes is presented. Applying this technique not only the existence of a filtering bleb is documented, but in addition the speed of aqueous transit through the filtering bleb was measured. This transit has been found to be a rapid one. 7. The clinical results of this type of seton operation do confirm the experimental evidence of excellent ocular tolerance of silicone tubings as well as the reliability of their firm anchorage. Postoperative tension with or without additional antiglaucomatous medication proved quite satisfactory. 8. The proposed surgical procedure is recommendable especially in patients exhibiting haemorrhagic glaucoma, were conventional methods are likely to fail in the majority of cases.

Adult↗
PubMed1984

Effect of hyperthermia on murine myeloid precursors.

Murine bone marrow was exposed to hyperthermia temperatures of 41.5 to 45.5 degrees C. The proliferation capacity of myeloid progenitor and committed precursors was assayed in vivo utilizing spleen colony formation and diffusion chamber (DC) techniques. The survival of both pluripotential (CFU-S) and committed myeloid (CFU-DG) stem cells decreased exponentially with an increase in the heating period. Progression from CFU-S to CFU-DG significantly altered thermal sensitivity in the temperature range examined. Proliferation of mature granulocyte-monocytes (G-M) in DC is more thermostable than their stem cell precursors. Heat inactivation energies (enthalpies) of CFU-S and CFU-DG were derived from the slope of the heating time survival curves. Enthalpy of CFU-S is 300 kcal/mole below 43 degrees and 105 kcal/mole above 43 degrees. The enthalpy of CFU-DG is 250 and 145 kcal/mole below and above 43 degrees, respectively.

Animals↗
PubMed2002

Kinetics of solubilization of n-decane and benzene by micellar solutions of sodium dodecyl sulfate.

We observed the diminishing of single microscopic oil drops to study the kinetics of solubilization of n-decane and benzene by micellar solutions of sodium dodecyl sulfate (SDS). Each drop is located in a horizontal glass capillary of inner diameter 0.06 cm filled with a thermostated surfactant solution; the small vertical dimension of the cell prevents the appearance of uncontrollable thermal convections. The experiments show that the radius of an n-decane drop decreases linearly with time, whereas for benzene this dependence is nonlinear. To interpret the data, a kinetic model of solubilization is developed. It accounts for the diffusion and capturing of dissolved oil molecules by the surfactant micelles, as well as for the finite rate of oil dissolution at the oil-water interface. By processing the data, we determined the rate constant of solubilization for a given oil and surfactant. It turns out that the elementary act of catching a dissolved oil molecule by a surfactant micelle occurs under a barrier (rather than diffusion) control. The effective rate of solubilization is greater for the oil, which exhibits a higher equilibrium solubility in pure water (benzene), despite the lower value of the solubilization rate constant for this oil.

Journal Article↗
PubMed1994

The effects of inhibitory controls triggered by heterotopic noxious stimuli on a jaw reflex evoked by perioral stimuli in man.

Electromyographic recordings (EMGs) were made from the active masseter muscle of the inhibitory reflex evoked by application of electrical stimuli to the skin of the upper lip in 11 human subjects. In control sequences, the reflex had a mean latency and duration of 41 +/- 1.7 and 44 +/- 2.6 ms, respectively. The magnitude of the reflex (measured by integration of the EMG) was significantly reduced by the application of cold (3 degrees C) or hot (47-48 degrees C) but not warm (38-46 degrees C) water to a hand or foot. The strongest stimuli (3 or 48 degrees C) produced mean reductions of the reflex magnitude in the range of 62-85%. These effects occurred regardless of whether the background activity in the masseter was raised or lowered during the application of the thermal stimuli. Thus, activity in nociceptive nerves from widespread areas of the body can modulate jaw reflexes in man by exerting an influence on the reflex pathway at a point before the motor neurones. This may involve the system of 'diffuse noxious inhibitory controls', which have been shown to depress limb flexion reflexes and neuronal activity in the spinal dorsal horn and trigeminal nuclear complex.

Cold Temperature↗
PubMed2005

Temperature-induced phase transitions of the ordered superlattice assembly of Au nanoclusters.

Superlattices of monolayer protected metallic and semiconducting nanoclusters have attracted significant attention due to their promising applications in nanotechnology. In this paper, we investigate the effect of temperature on the ordered superlattice structure of relatively larger sized Au nanoclusters passivated with dodecanethiol [ca. Au1415(RS)328] with the help of in situ temperature controlled X-ray diffraction (XRD) and infrared spectroscopy (IR) in conjunction with thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis. In brief, monolayer protected Au nanoclusters (AuMPC) were prepared by a modified Brust synthesis technique, where dodecanethiol itself acts as both phase transfer and simultaneous capping agent during the reduction process, generating an average particle size of 3.72 +/- 0.4 nm after repeated solvent extraction and careful fractionation experiments. These particles are characterized with the help of UV-vis, transmission electron microscopic (TEM), IR, and NMR techniques, where effective capping as well as the superlattice formation on the TEM grid is evident from the combined analysis of these results. In situ low-angle XRD analysis shows that the particles undergo an irreversible phase transition in the temperature range of 100-115 degrees C, which is also reflected in the data from in situ IR analysis. However, the DSC analysis does not account for this phase transition, although the reversible phase transition due to the alkyl chain dynamics is in good agreement with the previously reported results. These results indicate the formation of temperature-induced, diffusion-limited phase transition involving nonequilibrium fractal structures, which is in good agreement with the previous available theoretical studies. The determination of the temperature window for the stability of these ordered assemblies would be used to understand the effect of thermal stress for device applications.

Journal Article↗
PubMed1999

Stress-induced recrystallization of a protein crystal by electron irradiation.

Ordering of a system of particles into its thermodynamically stable state usually proceeds by thermally activated mass transport of its constituents. Particularly at low temperature, the activation barrier often hinders equilibration--this is what prevents a glass from crystallizing and a pile of sand from flattening under gravity. But if the driving force for mass transport (that is, the excess energy of the system) is increased, the activation barrier can be overcome and structural changes are initiated. Here we report the reordering of radiation-damaged protein crystals under conditions where transport is initiated by stress rather than by thermal activation. After accumulating a certain density of radiation-induced defects during observation by transmission electron microscopy, the distorted crystal recrystallizes. The reordering is induced by stress caused by the defects at temperatures that are low enough to suppress diffusive mass transport. We propose that this defect-induced reordering might be a general phenomenon.

Cryoelectron Microscopy↗