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At least 1,333 records · Page 74Linked to original sources
PubMed1997

Ultrasonic liposculpturing: extrapolations from the analysis of in vivo sonicated adipose tissue.

The ultrasonic liposculpturing technique is currently gaining increasing popularity. Although ultrasound is an accepted part of our diagnostic medical practice, the way in which it interacts with solid living tissue is still a complex and unsolved biophysical problem. Very few studies, if any, have followed the effects of diffusion of this intriguing technique on the fields of biosafety and interaction mechanisms. We evaluate the results of our standard ultrasound liposculpturing technique in order to recognize the physical mechanism-thermal, cavitational, or "direct"-involved in the damaging process. Our microscopic analysis of sonicated adipose tissue confirms that ultrasound is highly selective in its action, producing disruption of macromolecules and cellular structures probably through microstreaming tissue movement. The results of ultrasonic liposculpturing and standard suction lipoplasty are compared. The main advantages of this new technique are the possibility of a very selective destruction of adipose tissue and the prospective solution to such delicate problems as the irregularity of cellulite.

Adipose Tissue↗
PubMed1999

Droplet vaporization at critical conditions: long-time convective-diffusive profiles along the critical isobar.

The heating of a cold fluid package introduced, at critical conditions, in a hotter environment of the same fluid at the critical pressure is analyzed. Critical anomalies of the fluid transport properties as well as an arbitrary equation of state are taken into account. In unconfined microgravity conditions and for times much longer than the characteristic acoustic time, the heat transfer becomes a convective-diffusive isobaric transient process. An asymptotic theory valid in the limit of very small ratio between the fluid densities in the hot and cold regions is developed. The divergency of the thermal conductivity kappa at the critical temperature controls the heat transfer to the cold region. In the present model it is shown that there exists a well defined border, denoted by R(t), delimiting two distinguishable regions. The outer region extends from the far field down to R(t) where the critical temperature T(c) is reached. There, the temperature gradient vanishes due to the divergency of kappa. Thus, heat does not penetrate in the inner cold region where the temperature remains equal to T(c). The heating of the initially cold fluid package takes place by the recession of the border R(t). The model predicts a temperature profile in the outer region which is quasisteady in a reference system receding with R(t). It is shown that R2(t) decreases linearly with time. The recession velocity and thus the vaporization time are obtained as a function of the geometry and of the far-field conditions. Furthermore, the restrictions imposed by the long-time isobaric hypothesis are analyzed.

Journal Article↗
PubMed1999

Application of liquid dynamics theory to the glass transition.

In monatomic liquid dynamics theory, the system moves among a large number of intersecting nearly harmonic valleys in the many-particle potential energy surface. The same potential surface underlies the motion of atoms in the supercooled liquid. As temperature is decreased below the melting temperature, the motion among the potential valleys will begin to freeze out, and the system will pass out of equilibrium. It is therefore necessary to develop a nonequilibrium theory, based on the Hamiltonian motion. The motion is separated into two distinct parts, and idealized as follows: (a) the vibrational motion within a single valley is assumed to be purely harmonic, and remaining in equilibrium; and (b) the transit motion, which carries the system from one valley to another, is assumed to be instantaneous, and energy and momentum conserving. This idealized system is capable of exhibiting a glass transition behavior. An elementary model, incorporating the idealized motion, is the independent atom model, originally developed to treat self diffusion in monatomic liquids. For supercooled liquids, in the independent atom model, the vanishing of self diffusion at a finite temperature implies the same property for the transit probability. The vanishing of the transit probability at a finite temperature supports the view that transits are not merely thermally activated, but are controlled by phase-space correlations. For supercooled liquid sodium, the transit probability has Vogel-Tamann-Fulcher temperature dependence. The independent atom model is shown to be capable of exhibiting all the essential glass transition properties, including rate dependence of the glass transition temperature, and both exponential and nonexponential relaxation.

Journal Article↗
PubMed2002

Aging effects in the quantum dynamics of a dissipative free particle: non-Ohmic case.

We report the results related to the two-time dynamics of the coordinate of a quantum free particle, damped through its interaction with a fractal thermal bath (non-Ohmic coupling approximately omega(delta) with 0<delta <1 or 1<delta <2). When the particle is localized, its position does not age. When it undergoes anomalous diffusion, only its displacement may be defined. It is shown to be an aging variable. The finite temperature aging regime is self-similar. It is described by a scaling function of the ratio t(w)/tau of the waiting time to the observation time, as characterized by an exponent directly linked to delta.

Journal Article↗
PubMed2002

A silver-free, single-sheet imaging medium based on acid amplification.

We describe a photographic medium that uses acid-amplified imaging (AAI) rather than silver halide development to amplify a latent image. The latent image is captured when small amounts of superacid are generated by the photolysis of iodonium salts sensitized by cationic dyes. During thermal processing, the quantity of acid is multiplied in a process catalyzed by strong acid, resulting in a much larger amount of a weaker acid. Acid-sensitive indicator dyes that diffuse into regions where acid has been produced form a colored image. The AAI system is not sufficiently sensitive for direct use in cameras but is suitable for many printing applications.

Journal Article↗
PubMed2006

Periodic hyperthermia and abnormal circadian temperature rhythm in a patient with multiple sclerosis.

Disturbances of the central thermoregulation in patients with multiple sclerosis (MS) are not often reported. We describe a 45-year old patient with a 13-year history of MS, who developed a clinical picture of recurrent hyperthermia. MRI showed a bilateral involvement of the hypothalamus in the setting of diffuse white matter disease. Serial body temperature measurement for five consecutive months disclosed an inversion of the circadian temperature rhythm. The clinical presentation and MRI findings suggested abnormalities of the central thermal control in relation to MS widespread involvement of the central nervous system (CNS).

Body Temperature Regulation↗
PubMed1979

[Ultrastructural analysis of the morphological changes in the lungs and heart in experimental thermal burns of the skin].

The experimental results showed that in severe thermal burns of the skin marked disorders of microcirculation in all parts of the tissue in the lungs and myocardium or rabbits, disorders in permeability of capillary and cell membranes, increased diffusion and filtration processes developed. Alongside with these processes, dystrophic changes of some organoids were observed in cells. Most of these changes were reversible which was conducive to subsequent restoration of the ultrastructure of the affected cells as a result of intracellular compensatory processes.

Animals↗
PubMed2004

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.

Colloids↗
PubMedDate not supplied

Alginate-diltiazem hydrochloride beads: optimization of formulation factors, in vitro and in vivo availability.

Alginate beads containing diltiazem hydrochloride (DTZ) were prepared by the ionotropic gelation method. The effects of various factors (alginate concentration, additives type, calcium chloride concentration and curing time) on the efficiency of drug loading were investigated. The formulation containing a mixture of 0.8% methylcellulose (MC) and 4% alginate cured in 2% calcium chloride for 6 h was chosen as the best formula regarding the loading efficiency. The release rate of DTZ from various beads formulations was investigated. The release of drug from alginate beads followed two mechanisms; by diffusion and relaxation of the polymer at pH 1.2, whilst diffusion and erosion are at pH 6.8. The in vitro release of DTZ from MC-alginate beads showed an extended release pattern which was compared with that from commercially available sustained-release (Dilzem SR) and fast release tablets (Dilzem). Thermal analysis revealed that the drug was molecularly dispersed in the beads matrix. Although the release characteristics of DTZ from Dilzem SR and MC-alginate beads were completely different, the bioavailability of DTZ in dogs was comparable as measured by AUC, MRT and relative bioavailability. The absolute bioavailability of MC-alginate beads and Dilzem SR was 88 and 93%, respectively.

Alginates↗
PubMed2002

Structural change of site-directed mutants of PYP: new dynamics during pR state.

The energetics, protein dynamics, and diffusion coefficients of three mutants of photoactive yellow protein, R52Q, P68A, and W119G, were studied by the transient grating and pulsed laser-induced photoacoustic method. We observed a new dynamics with a lifetime of approximately 1 micro s in the transient grating signal, which is silent by the light absorption technique. This fact indicates that, after the structure change around the chromophore is completed (pR(1)), the protein part located far from the chromophore is still moving to finally create another pR (pR(2)) species, which can transform to the next intermediate, pB. Although the kinetics of pR(2)-->pB-->pG are very different depending on the mutants, the enthalpies of the first long-lived (in micro seconds, 100-micro s range) intermediate species (pR(2)) are similar and very high for all mutants. The diffusion coefficients of the parent (pG) and pB species of the mutants are also similar to that of the wild-type photoactive yellow protein. From the temperature dependence of the volume change, the difference in the thermal expansion coefficients taken as indicator of the flexibility of the structure between pG and pR(2) is measured. They are also similar to that of the wild-type photoactive yellow protein. These results suggest that the protein structures of pR(2) and pB in these mutants are globally different from that of pG, and this structural change is not altered so much by the single amino acid residue mutation. This is consistent with the partially unfolded nature of these intermediate species. On the other hand, the volume changes during pR(1)-->pR(2) are sensitive to the mutations, which may suggest that the volume change reflects a rather local character of the structure, such as the chromophore-protein interaction.

Acoustics↗
PubMed1977

Temperature sensitivity of the erythrocyte membrane potential as determined by cyanine dye fluorescence.

We have used the cyanine dye fluorescence technique to measure the membrane potential of human erythrocytes as a function of temperature. With erythrocytes starved of glucose, there is an abrupt decrease in membrane potential centered at 38 degrees which is reversible up to 41 degrees, and irreversible at higher temperatures. With erythrocytes supplemented with glucose, the thermally induced transition is centered at 41 degrees and is reversible up to the highest temperature measured, 45 degrees. These results extend previous spectroscopic studies with erythrocyte membranes which demonstrated a thermally induced transition in protein tertiary or quaternary structure that is irreversible above 42 degrees.

Diffusion↗
PubMed2004

Local atomic structures of palladium nanowire.

In this paper, investigation of the structure of palladium nanowire has been performed by using genetic algorithm simulation based on the molecular dynamics. Our calculation employs a well-fitted, tight-binding many-body potential for Pd atoms. Some local atomic structures and defects in nanowires have been reported. The melting behavior of palladium nanowire has also been investigated. An interesting result is that the diffusion of the central atoms results in the beginning of the melting. The moving central atoms build up a monostrand atomic chain during the melting process. The single atomic chain is very stable which can exist in a wide temperature region (800-950 K). The formation of the single atomic chain causes some new defects in the nanowire. And the new defects result in the decrease of the thermal stability of the nanowire. Interestingly, the liquid from the nanowire melting has a supercooled feature because the splitting of the second peak of pair correlation function is observed. The curves of the internal energy and the local cluster are used to monitor the phase transition. The melting of the nanowire is not only due to the single atomic diffusion, but also the diffusion of the local clusters.

Journal Article↗
PubMed1980

Application of cryosectioning to x-ray microanalysis of biological tissue.

Cryosectioning biological tissue is a critical and difficult step when applied to x-ray microanalysis of diffusible elements. Conventional metal machining theory can explain and predict results obtained by cryosectioning more consistantly than a freeze-thaw model. Temperature of a critical zone where shearing occurs is probably the most important factor for cryosectioning. This is presumed to be a result of thermally induced changes in tissue brittleness. Two other factors which may change effective cutting temperature are section thickness and cutting speed. Tissue brittleness also depends upon the extent of ice crystal damage from initial freezing which is largely determined by heat removal rate (freezing rate), water content, size, and composition. Antiroll plates are effective devices for counteracting bending forces which occur as the section is sheared from the block. Cryosectioning does not appear to affect elemental distribution or tissue morphology in either bounded or unbounded systems. Thus cryosectioning appears to be a predictable and controllable step which is suitable for x-ray microanalysis of diffusible elements in biological tissue. Deterioration of spatial and analytical resolution does not appear to occur through the process of cryosectioning; rather these limits are set by initial freezing.

Electron Probe Microanalysis↗
PubMed1994

Modeling and observation of temperature changes in vivo using MRI.

Models have been developed for the signal changes occurring in human peripheral muscle after thermal stress for some methods of measuring temperature in vivo. These include the dependency of T1 on temperature, observed by both direct, and magnetization transfer, experiments, and the temperature sensitivity of the diffusion coefficient and the chemical shift of the water proton line. Results show the relative complexity of the T1-dependent models when there are significant variations in, possibly amongst other things, tissue perfusion, and how the predictions made using them match the behavior of the practical values quite well. Using changes in the diffusion coefficient appears less problematic, although there can still be significant errors in temperature calibrations. The problems with this approach are likely to be due to the consequences of anisotropy in tissue.

Adipose Tissue↗
PubMed2003

Chemometric investigation of the efficiency of different TiO(2)-based catalysts as principal components of TOC photochemical sensors under development.

There is an increasing demand for measurement of organic carbon in solutions both in industry and in environmental research for the purpose of continuous water-quality monitoring. Practically all the methods used are based on a catalytic system in which metal oxides play a major role. The development of a new TOC/DOC measurement system, in our work, uses a mixed anatase-rutile form of TiO(2 )as catalyst of the mineralisation process, and direct measurement of the CO(2) produced, by a gaseous diffusion electrode. The entire research is based on heterogeneous catalysis using an immobilised catalyst, which can offer considerable advantages over other methods of catalysis. Four different catalytic systems were analysed. Three involved thermal immobilisation of TiO(2) on glass supports (glass spheres and glassy particulates) or on an Al metal grid. One further system consisted of direct oxidation of a Ti grid at high temperatures. The system was illuminated using a 350 nm UV source (350 mW cm(-2)) contained in a home-made measurement cell. Five molecules-malic acid, pentachlorophenol, sodium dodecylsulfate, hydroquinone, and citric acid-which were deemed to be representative and had been investigated in several previous studies, were used as photodegradation targets. However, it was not possible to obtain a direct expression of "catalytic efficiency" simply by reading the data obtained, nor any indirect molecular "recalcitrancy" scale. Chemometric analysis, by principal components analysis, allows the five used catalytic systems to be easily compared each other and a single PC component is able to perform classification.

Journal Article↗
PubMed1988

Effects of heterotopic conditioning stimuli on first and second pain: a psychophysical evaluation in humans.

Psychophysical experiments were carried out on 7 human participants to determine the extent to which experimentally produced first or second pain is reduced by concomitant nociceptive stimulation of body regions remote from those at which test stimuli are presented. This form of pain reduction has been termed diffuse noxious inhibitory controls (DNIC). Test stimuli used to evoke first and second pain consisted of intense electrical pulses delivered to the ankle area by subepithelial electrodes. Conditioning stimuli were 10 sec thermal stimuli (43, 47, 51 degrees C) applied to 1 cm2 areas of skin of either the dorsal surface of the contralateral foot or the abdominal region. The perceived magnitudes of first and second pains evoked by test stimuli were rated on visual analogue scales (VAS). Frankly noxious conditioning thermal stimuli (47 and 51 degrees C), but not innocuous thermal stimuli (43 degrees C), applied to the contralateral foot or abdomen reliably inhibited both first and second pain. However, the degree of inhibition was significantly greater for second pain that for first pain. In addition, the inhibitory effects did not outlast the duration of the conditioning stimulus. All of these results closely parallel electrophysiological observations about DNIC in primates. Since the extent of reduction of first pain is relatively weak and the durations of all inhibitory effects are very brief, it is unlikely that DNIC subserves the functions of relieving pain or providing a mechanism of coding pain. The spatial and temporal pattern of DNIC indicates that it may be a phenomenon associated more with the organization and production of withdrawal reflexes than with the relief of pain or pain coding.

Adult↗
PubMed2003

Age-related differences in endogenous pain modulation: a comparison of diffuse noxious inhibitory controls in healthy older and younger adults.

Despite decades of research, hundreds of studies, and a number of recent reviews, the effects of aging on the experience of pain remain poorly understood. Many prior investigators have reported increases in persistent pain conditions and diminished tolerance for certain types of laboratory-induced pain among the elderly. While explanations for these effects often propose senescent decrements in endogenous analgesic systems as a possible contributory mechanism, almost no direct empirical evidence for this hypothesis has yet emerged in human studies. The present investigation was designed to evaluate the existence and nature of these putative age-related differences in endogenous pain inhibition. Groups of healthy younger (n=45, mean age=21.6 years, range=18-25) and older (n=48, mean age=63.1 years, range=55-67) adults participated in a controlled, two-session laboratory assessment of diffuse noxious inhibitory controls (DNIC), a measure of endogenous pain inhibition. In this study, we examined age differences in the effects of concurrent cold pain on ratings of heterotopically presented repetitive noxious thermal stimuli. Interestingly, older adults demonstrated facilitation rather than inhibition of thermal pain during concurrent noxious cold stimulation while younger adults demonstrated some expected DNIC effects (i.e. a reduction in thermal pain ratings during heterotopic stimulation with noxious cold). Collectively, the findings of the present study suggest age-associated decrements in at least one form of endogenous analgesic response. If replicated, such findings of reduced pain-modulatory capacity in the elderly may partially explain age-related differences in the prevalence, severity, and impact of chronic pain.

Adult↗
PubMed2003

Anomalous heat conduction and anomalous diffusion in one-dimensional systems.

We establish a connection between anomalous heat conduction and anomalous diffusion in one-dimensional systems. It is shown that if the mean square of the displacement of the particle is =2Dt(alpha)(0 1) implies anomalous heat conduction with a divergent thermal conductivity (beta>0). More interestingly, subdiffusion (alpha<1) implies anomalous heat conduction with a convergent thermal conductivity (beta<0), and, consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our results.

Journal Article↗