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PubMed2006

Balls and chains--a mesoscopic approach to tethered protein domains.

Many proteins contain regions of unstructured polypeptide chain that appear to be flexible and to undergo random thermal motion. In some cases the unfolded sequence acts as a flexible tether that restricts the diffusion of a globular protein domain for the purpose of catalysis or self-assembly. In this article, we present a stochastic model for tethered protein domains under various conditions and solve it numerically to deduce the general and dynamic properties of these systems. A critical domain size dependent on the length of the tether is presented, above which a spherical domain tethered to an impenetrable wall by a flexible chain displays a restricted localization between two concentric half-shells. Results suggest that the diffusion of such a spherical domain is effectively reduced in its dimensionality and able to explore the available space with high efficiency. It also becomes clear that the orientation of the ball is not independent of the distance from the tethering point but becomes more constrained as the linking tether is extended. The possible biological significance of these and other results is discussed.

Chemoreceptor Cells↗
PubMed2000

[Cold and warm thermoregulation by oropharynx area and esophagus].

UNLABELLED: After being ingested, food and liquids suffer a thermal regulation process, which adapts them immediately to the body temperature by means of the mucosa diffusion. We have not found bibliographical information about this matter yet. OBJECTIVES: 1) To describe the reaction of the oropharynx area and the esophagus by heat and coldness. 2) To compare both areas reaction. STUDY POPULATIONS: Six patients (three men, three women, Age: mean 42 years old, SD 11.8), healthy individuals without both gastrointestinal and systemic disease that could after microcirculation. MATERIALS & METHODS: Temperature measurement of liquid at mouth entrance and at 24 cm and 38 cm from dentary superior arcade using two thermocouples. Deglution of 40 ml of hot water (X 60 degrees C at entrance) or cold water (X 4 degrees C) in two draughts. Temperature measurement at both thermocouples at the end of deglution (time = 0 (zero)) and every 10 seconds. Random sequences every 30 minutes. RESULTS: Using water at 60 degrees C, the temperature descended to 42 degrees C in the distal end. The oropharynx region dissipated 45% of the initial temperature while the esophagus completed the other 55%. The esophagus itself dissipated 65.6% of the 12.2 degrees C in time = 0 (zero). After 40 seconds the temperature reached the normal body temperature. In the case of the iced water (4 degrees C), the total work consisted on increasing temperature 33.6 degrees C to the normal corporal temperature. The 68.45% of the difference between the initial and the final temperature was obtained by the oropharynx region and the rest by the esophagus. In time = 0 (zero) the temperature increased up to 30 degrees C and the esophagus only contributed with 28.3% of the total work. The normal corporal temperature was reached after 40 seconds. It was observed a significant difference in the heating capacity between the oropharynx region and esophagus (p > 0.001). There was also a significant difference in the oesophagus itself between heat and coldness in time = 0 (zero) ¿65.6% (heat) Vs. 28.3% (coldness), 0.02 > p > 0.01¿ and values between time = 0 (zero) and 10-40 seconds (p > 0.001). CONCLUSION: 1) The ability of cooling was similar in both regions. 2) In the oropharynx region the capacity of heating was higher (voluntary time of deglution) than in the esophagus region. 3) The esophagus initial response before coldness was slower than oropharynx region's one. The buccal retention was greater. 4) Before both stimulus, normal corporal temperature was reached after 40 seconds. COMMENTARY: The isothermation of coldness and heat would work through the same mechanism: the mucosa vasodilatation and the increase of blood flow. This hypothesis would be valid for all the mucosa of the digestive tract. This mechanism could be altered in inflammatory diseases. Iced water washings on bleeding wounds be counter-productive. The persistence of extreme temperatures in the environment modifies the structure of the esophagus mienteric plexus (Auerbach's plexus). Frequent ingestion of fluids above 60 degrees C would be a predisponent factor for esophagus cancer.

Adult↗
PubMed1989

Application of thermal dilution measurements for thermal treatment planning.

The use of thermal dilution measurements is demonstrated in quantifying effective thermal conductivity distributions through tumours. For focused acoustic sources these data are applied in the solution of the heat diffusion equation to estimate steady-state temperature distributions. The advantages and disadvantages of this approach are presented. The effective conductivity measurements are found to be useful in predicting the circumstances under which this simple model can be applied and in aiding the selection of the most appropriate heating modality.

Animals↗
PubMed2005

In situ discovery of an electrostatic potential, trapping electrons and mediating fast reconnection in the Earth's magnetotail.

Anisotropic electron phase space distributions, f, measured by the Wind spacecraft in a rare crossing of a diffusion region in Earth's far magnetotail (60 Earth radii), are analyzed. We use the measured f to probe the electrostatic and magnetic geometry of the diffusion region. For the first time, the presence of a strong electrostatic potential (1 kV) within the ion diffusion region is revealed. This potential has far reaching implications for the reconnection process; it accounts for the observed acceleration of the unmagnetized ions out of the reconnection region and it causes all thermal electrons be trapped electrostatically. The trapped electron motion implies that the thermal part of the electron distributions are symmetric around v( parallel)=0: f(v( parallel),v( perpendicular)) approximately f(-v( parallel),v( perpendicular)). It follows that the field aligned currents in the diffusion region are limited and fast magnetic reconnection is mediated.

Journal Article↗
PubMed2004

Fluctuation-response relation in a rocking ratchet.

The relationship between the positional fluctuation and mechanical response for a thermal ratchet at a nonequilibrium steady state was investigated experimentally and considered theoretically. We constructed a ratchet system using a scanning optical trapping system and microbeads (0.20 microm diameter), which is interpreted as a realization of a rocking ratchet [M. O. Magnasco, Phys. Rev. Lett. 71, 1477 (1993)]. In the experiment, an asymmetric periodic potential (2.5 microm period) was generated by optical trap scanning, which traps a bead. When the potential profile was rocked sinusoidally, diffusion of the bead was rectified in one direction. We confirmed that both the diffusion coefficient and the mobility increased with potential rocking with a positive correlation. To obtain better insight, we performed numerical and theoretical analyses of the corresponding Langevin system. Although there is a positive relationship between the diffusion coefficient and mobility, the diffusion coefficient is greater than the value given in the Einstein relation. This result means that the effective temperature of the thermal ratchet at a nonequilibrium steady state becomes greater than that of the environment. We propose that this elevation of the effective temperature causes a decrease in the energetic efficiency of the thermal ratchet through irreversible dissipation to the heat bath.

Journal Article↗
PubMed2006

Molecular theory of thermal conductivity of the Lennard-Jones fluid.

In this paper the thermal conductivity of the Lennard-Jones fluid is calculated by applying the combination of the density-fluctuation theory, the modified free volume theory of diffusion, and the generic van der Waals equation of state. A Monte Carlo simulation method is used to compute the equilibrium pair-correlation function necessary for computing the mean free volume and the coefficient in the potential-energy and virial contributions to the thermal conductivity. The theoretical results are compared with our own molecular dynamics simulation results and with those reported in the literature. They agree in good accuracy over wide ranges of density and temperature examined in molecular dynamics simulations. Thus the combined theory represents a molecular theory of thermal conductivity of the Lennard-Jones fluid and by extension simple fluids, which enables us to compute the nonequilibrium quantity by means of the Monte Carlo simulations for the equilibrium pair-correlation function.

Journal Article↗
PubMed2006

Automatic temperature controller for multielement array hyperthermia systems.

This paper concerns the optimization and performance analysis of an automatic control algorithm for managing power output of large multielement array hyperthermia applicators. Simulation and corresponding measurement of controller performance in a solid tissue equivalent phantom model is utilized for analysis of controller response to dynamically varying thermal load conditions that simulate clinical treatments. The analysis leads to an optimum controller which demonstrates the ability to achieve a uniform and stable temperature profile over a large surface area regardless of surrounding thermal load. This paper presents several advancements to the performance of a previously published control routine, including: 1) simplified simulation techniques for thorough characterization of controller performance; 2) an optimization procedure leading to an improved hybrid control algorithm for maintaining optimal performance during periods of both "rising" and "steady-state" temperature; 3) performance analysis of a control algorithm tailored for large area hyperthermia treatments with a mulitelement array applicator. The optimized hybrid controller is applied to the conformal microwave array (CMA) hyperthermia system previously developed for heating large area surface disease such as diffuse chestwall recurrence of breast carcinoma, and shown to produce stable, uniform temperatures under the multielement array applicator for all thermal load conditions.

Body Temperature Regulation↗
PubMed2001

Anisotropic thermal conductivity of Ge quantum-dot and symmetrically strained Si/Ge superlattices.

We report the first experimental results on the temperature dependent in-plane and cross-plane thermal conductivities of a symmetrically strained Si/Ge superlattice and a Ge quantum-dot superlattice measured by the two-wire 3 omega method. The measured thermal conductivity values are highly anisotropic and are significantly reduced compared to the bulk thermal conductivity of the structures. The results can be explained by using heat transport models based on the Boltzmann transport equation with partially diffusive scattering of the phonons at the superlattice interfaces.

Anisotropy↗
PubMedDate not supplied

Hair color changes caused by dyeing and thermal treatments.

The aim of this study was to show the effect of heat exposure, dyeing, and shampooing on hair color as measured by diffuse reflectance spectrophotometry. Successive dyeing of virgin hair with six permanent commercial formulations showed that color saturation was obtained after the first dyeing cycle. An unexpectedly high difference in hair color saturation, measured as DE* values, was obtained for virgin hair samples that differed only in cleansing history. After six sequential washings of the dyed hair samples, no difference was observed in color durability, indicating that the adhesion strength is similar to long-lasting and tone-up dyeing formulations. Exposure to a hot plate at 172 degrees C showed a significant darkening of the virgin hair samples after 2 min. On the other hand, virgin hair samples exposed to the gentler heat of a hand dryer (approximately 60 degrees C) showed partial disappearance of the hair medulla after 60 min. However, values of total color difference were near the error limit.

Hair↗
PubMed1994

Experimental nerve thermal injury.

Thermal injury to rat sciatic nerve was produced by local heating (47 and 58 degrees C) and studied physiologically and morphologically. Unmyelinated nerve fibres showed a greater direct vulnerability to hyperthermia; first manifest as a reversible conduction block of C fibre action potentials and at higher temperatures by immediate and selective axonal degeneration. By contrast, lower grade nerve thermal injury resulted in delayed, selective loss of myelinated fibres. Evidence from this study suggests that this is secondary to a heat-induced angiopathy, immediately and diffusely manifest in the vasa nervorum and giving rise to a progressive and ultimately severe reduction in nerve blood flow. The relative sparing of unmyelinated fibres is likely to be a result of their greater resistance to ischaemia. The pathological vulnerability of unmyelinated fibres to thermal injury, coupled with the susceptibility of large myelinated nerve fibres to secondary ischaemia, largely resolves previous contradictions in the literature.

Action Potentials↗
PubMed2006

The study of amorphous aggregation of tobacco mosaic virus coat protein by dynamic light scattering.

The kinetics of heat-induced and cetyltrimethylammonium bromide induced amorphous aggregation of tobacco mosaic virus coat protein in Na(+)/Na(+) phosphate buffer, pH 8.0, have been studied using dynamic light scattering. In the case of thermal aggregation (52 degrees C) the character of the dependence of the hydrodynamic radius (R(h)) on time indicates that at certain instant the population of aggregates is split into two components. The size of the aggregates of one kind remains practically constant in time, whereas the size of aggregates of other kind increases monotonously in time reaching the values characteristic of aggregates prone to precipitation (R(h)=900-1500 nm). The construction of the light scattering intensity versus R(h) plots shows that the large aggregates (the start aggregates) exist in the system at the instant the initial increase in the light scattering intensity is observed. For thermal aggregation the R(h) value for the start aggregates is independent of the protein concentration and equal to 21.6 nm. In the case of the surfactant-induced aggregation (at 25 degrees C) no splitting of the aggregates into two components is observed and the size of the start aggregates turns out to be much larger (107 nm) than on the thermal aggregation. The dependence of R(h) on time for both heat-induced aggregation and surfactant-induced aggregation after a lapse of time follows the power law indicating that the aggregation process proceeds in the kinetic regime of diffusion-limited cluster-cluster aggregation. Fractal dimension is close to 1.8. The molecular chaperone alpha-crystallin does not affect the kinetics of tobacco mosaic virus coat protein thermal aggregation.

Capsid Proteins↗
PubMed1999

Computer model for cryosurgery of the prostate.

The objective of this study was to devise an interactive tool to assist in cryoablation therapy through computer modeling, simulation, and visualization. CryoSim, a software package, accepts a set of acquired and processed three-dimensional ultrasound images, then models heat diffusion (formation of the iceball) based on numerical approximation of the heat equation and knowledge of the thermal properties of the underlying tissues. Results of cryoexperiments were found to be significantly similar to those generated by CryoSim. Therefore, CryoSim provides a viable technique for predicting the outcome of cryosurgery, and establishes a platform for future automation of cryosurgery.

Animals↗
PubMed1983

Permeation of skin and eschar by antiseptics I: baseline studies with phenol.

To assess how the permeability of phenol is altered by thermal injury, it was first necessary to have baselines of comparison on normal skin. Using in vitro diffusion cells and the skin of the hairless mouse, [14C]phenol was applied to skin in an aqueous medium with a reference copermeating species, [3H]methanol, and 37 degrees permeability coefficients of the pair were evaluated as functions of animal age, skin hydration, stripping of the skin, dermis isolation, and phenol concentration. Age proved to be of little consequence to permeability over a wide age range. Prolonged aqueous soaking of the skins was also without much effect. Stripping of the skin and isolating the dermis by soaking techniques allowed assessment of individual skin strata diffusion resistances. When applied to skin in trace radiochemical concentrations, phenol behaved diffusionally as an alkanol with a chain length of six. But at concentrations greater than 2% w/v, phenol facilitated the permeation rates of itself and methanol; the effect was markedly concentration sensitive and only fractionally reversible. Concentration studies using silicone rubber membranes proved that the effects on the skin were the results of destroyed barrier integrity. At 6% phenol concentration there was an essentially instantaneous, 10-fold increase in the phenol permeability coefficient, raising it to two-thirds that observed with fully stripped skin. Overall, the data suggest that the stratum corneum is proportionally impaired as the phenol concentration is increased.

Aging↗
PubMed1995

Interstellar water in meteorites?

D/H ratios of two meteorites (Renazzo CR and Semarkona LL3), which are known to exhibit the largest departures from the terrestrial hydrogen isotopic ratios, have been determined with the CRPG Nancy ion microprobe. Correlations between the D/H ratios and the chemical compositions (H2O, K, Si, C/H) of plausible hydrogen carriers were observed. From these correlations, it is possible to show that, contrary to previous interpretations, phyllosilicates are the carriers of the deuterium-rich hydrogen in Semarkona and Renazzo: 870 x 10(-6) > or = D/H > or = 670 x 10(-6) (+4600 > or = deltaD > or = 3300%) and > or = 320 x 10(-6) (deltaD > or = 1050%), respectively. Hydrogen is also present in the chondrules of these two deuterium-rich meteorites. The large differences in D/H ratios between matrix (up to 700 x 10(-6), deltaD up to +3500%) and chondrules (from 120 x 10(-6) (deltaD = -230%) to 230 x 10(-6) (deltaD = +475%)) show that hydrogen in chondrules cannot originate from the matrix by simple contamination or diffusion processes. The high D/H ratios measured in water-bearing minerals could not have been produced thermally within a dense solar nebula. Chemical reactions (i.e., involving ions or radicals), taking place in interstellar space or in the outer regions of the nebula at 110-140K are presently the only conceivable mechanisms capable of yielding such isotopic enrichments. Water in these meteorites should no longer be considered as a simple product of nebular condensation under equilibrium thermodynamic conditions at T > or = 160K.

Carbon↗
PubMed2000

Analysis of failure mechanisms in electrically stressed gold nanowires

An analysis of polycrystalline Au thin-film interconnects of widths ranging from 850 to 25 nm, and lengths ranging from 1 microm to 20 nm which have been electrically stressed to the point of failure is presented. A new method for testing failure of interconnects is proposed, based on a quantity we call the failure current density. The mean time to failure for fixed current density and also the failure current density are seen to decrease with decreasing wire width contrary to expectations. The failure current density for a given wire width increases as the length decreases. An analysis of the temperature and stress profiles based on calculations of a simple model is presented which shows that the length dependence is due to thermal stresses rather than electromigration, and the width dependence is due to enhanced electromigration due to surface diffusion.

Journal Article↗
PubMed2003

Frequency and phase synchronization in stochastic systems.

The phenomenon of frequency and phase synchronization in stochastic systems requires a revision of concepts originally phrased in the context of purely deterministic systems. Various definitions of an instantaneous phase are presented and compared with each other with special attention paid to their robustness with respect to noise. We review the results of an analytic approach describing noise-induced phase synchronization in a thermal two-state system. In this context exact expressions for the mean frequency and the phase diffusivity are obtained that together determine the average length of locking episodes. A recently proposed method to quantify frequency synchronization in noisy potential systems is presented and exemplified by applying it to the periodically driven noisy harmonic oscillator. Since this method is based on a threshold crossing rate pioneered by Rice the related phase velocity is termed the Rice frequency. Finally, we discuss the relation between the phenomenon of stochastic resonance and noise-enhanced phase coherence by applying the developed concepts to the periodically driven bistable Kramers oscillator.

Models, Theoretical↗
PubMed2000

Enhancing effects of fatty acids on piroxicam permeation through rat skins.

To increase the skin permeation of piroxicam from the Poloxamer 407 gel, fatty acid was added as a penetration enhancer to the Poloxamer 407 gel containing 1% piroxicam. The enhancing effects of the enhancer on the skin permeation of piroxicam were evaluated using Franz diffusion cells fitted with intact excised rat skins. To elucidate the modes of the action of enhancers, thermal analysis and histological examinations were conducted. Among fatty acids tested, linoleic acid showed the highest enhancing effects, with an enhancement factor (EF) of 1.76. From the thermal analysis results, fatty acids have fluidizing effects on the stratum corneum. The skin pretreated with the Poloxamer 407 gels containing piroxicam including linoleic acid showed a loosely layered stratum corneum and wide intercellular space.

Administration, Cutaneous↗
PubMed2005

Nanostructured systems for biological materials.

The sol-gel process is a chemical technique for immobilizing biomolecules in an inorganic, transparent matrix. The dopant biomolecules reside in an interconnected mesoporous network and become part of the nanostructured architecture of the entire material. In this chapter, we review the sol-gel immobilization approach and discuss how it leads to the stabilization of a number of proteins against aggressive chemical and thermal environments. We also review the sensor applications of this material that result from having analyte molecules diffuse through the matrix and reach the immobilized biomolecule.

Biosensing Techniques↗