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PubMed2004

Synthesis and properties of plasma-polymerized polypyrrole/Au composite nanofibers.

Nanostructured composites have a wide variety of potential applications in microelectronics, chemical sensors, and electrochemical energy production. Here, we report the chemical, structural, and electrochemical characteristics of a nanostructured composite material formed from plasma-polymerized polypyrrole-coated Au fibers. The properties of the plasma-polymerized polypyrrole (PPPy) films were characterized by FTIR, X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy, as well as cyclic voltammetry (CV), and scanning electron microscopy (SEM). These spectroscopy analyses suggest that thermal treatment of the materials results in elimination of loosely-bound, low mass oligomers in the films. Mass spectral analysis of the plasma phase suggests that plasma polymerization of the pyrrole takes place on the substrate surface as a result of diffusion of radicals produced in the plasma. In addition, thermal treatment enhances the electrochemical properties of the PPPy films because of changes in the surface morphology and bulk structure of the films. However, as-deposited PPPy films coated on Au nanotubes demonstrate better electrochemical properties than as-deposited PPPy films coated on flat ITO electrodes as a result of the increase in surface area and decrease in film thickness.

Crystallization↗
PubMed2004

Thermal effects of a laser beam tube consisting of a window and nonflowing gas.

High-energy laser systems include an optical train and a gas medium that must be capable of transporting and directing the beam. The optical train is termed a laser beam tube. Because of the finite absorption of laser energy, the thermal effects of the beam tube make the beam diffuse and cause degradation of the laser beam's quality. We study systematically a beam tube consisting of a laser window made from white bijou (i.e., Al2O3) or fused silica and a tube of nonflowing nitrogen or helium gas. The results show that the thermal effects of the window and the gas on the beam neutralize each other; in particular, in some cases they compensate for each other completely, such that the beam tube has no effect on the beam quality in spite of the fact that separately each has a severe effect. We explain how to acquire the specific cases.

Journal Article↗
PubMedDate not supplied

[Experimental study on efficacy of thermal muds of Ischia Island combined with balneotherapy in the treatment of psoriasis vulgaris with plaques].

A lot of studies show the efficacy of thermal therapy in psoriasis. The main indications concern all forms of psoriasis (except for pustolosa and eritrodermic) especially diffuse psoriasis, intensive itchy, artropatic psoriasis and gutted psoriasis child. Benefit effects of thermal water and muds, which are important parameters in psoriasis' treatment, they are excellent to reduce inflammation, scaling, and erythema. In this study we evaluated the clinical efficacy of thermal bath plus muds in patients affected by psoriasis. 18 patients has been examined and randomly divided in 3 group (A-B-C). All the patients received thermal therapy for 4 weeks. To evaluate the behaviour of the disease we performed (corneometry, sebometry, phmetry), as well as evaluation of P.A.S.I. At the end of the study, values of P.A.S.I. showed a reduction from 10 to 6 unites P.A.S.I. for patients belong to group A, more 12 to less 10 for patients belong to group C e no significant variations for group B (because represent control group). Results obtained can be considered useful, considering that thermal treatment was used alone in the treatment of all patients.

Adult↗
PubMed2006

Family of tunable spherically symmetric potentials that span the range from hard spheres to waterlike behavior.

We investigate the equation of state, diffusion coefficient, and structural order of a family of spherically symmetric potentials consisting of a hard core and a linear repulsive ramp. This generic potential has two characteristic length scales: the hard and soft core diameters. The family of potentials is generated by varying their ratio, lambda. We find negative thermal expansion (thermodynamic anomaly) and an increase of the diffusion coefficient upon isothermal compression (dynamic anomaly) for 0< or =lambda<6/7. As in water, the regions where these anomalies occur are nested domes in the (T, p) or (T, P) planes , with the thermodynamic anomaly dome contained entirely within the dynamic anomaly dome. We calculate translational and orientational order parameters (t and Q6), and project equilibrium state points onto the (t, Q6) plane, or order map. The order map evolves from waterlike behavior to hard-sphere-like behavior upon varying lambda between 4/7 and 6/7. Thus, we traverse the range of liquid behavior encompassed by hard spheres (lanbda=1) and waterlike (lambda approximately 4/7) with a family of tunable spherically symmetric potentials by simply varying the ratio of hard to soft-core diameters. Although dynamic and thermodynamic anomalies occur almost across the entire range 0< or=lambda< or=1, waterlike structural anomalies (i.e., decrease in both t and Q6 upon compression and strictly correlated T and Q6 in the anomalous region) occur only around lambda=4/7. Waterlike anomalies in structure, dynamics and thermodynamics arise solely due to the existence of two length scales, with their ratio lambda being the single control parameter, orientation-dependent interactions being absent by design.

Journal Article↗
PubMed2003

Dynamic fluorescence microscopy as a feasible technique for estimating the diffusion coefficients of small particles in the presence of additives.

The Brownian motion of carboxylated polystyrene latex, labeled with fluorescent probe molecules, at low concentrations in aqueous solutions was investigated by dynamic fluorescence microscopy. For all three latex radii, i.e., 0.5, 0.265, and 0.1 mum, the estimated diffusion coefficients correspond well with the theoretical predictions if thermal and electrostatic contributions are included in the discussions. It was also possible to discriminate latex interactions with an added polymer. Added polyethylene glycol showed no or very weak interaction with the latex until the polymer overlap concentration was reached, at which the formation of a polymer network slowed down the latex diffusion. Polyvinylpyrrolidone, on the other hand, had a more pronounced interaction with the polystyrene latex and slowed down the diffusion even at polymer concentrations in the ppm range. The overall conclusion is that fluorescence microscopy is a feasible method for the study of the dynamic behavior of small particles in solution.

Journal Article↗
PubMed2002

Localization of thermal packets and metastable states in the Sinai model.

We consider the Sinai model describing a particle diffusing in a one-dimensional random force field. As shown by Golosov, this model exhibits a strong localization phenomenon for the thermal packet: all thermal trajectories starting from the same initial condition in the same sample remain within a finite distance of each other even in the limit of infinite time. More precisely, he has proved that the disorder average P(t)(y) of the distribution of the relative distance y=x(t)-m(t) with respect to the (disorder-dependent) most probable position m(t), converges in the limit t--> infinity, towards a distribution P(G)(y) defined as a functional of two independent Bessel processes. In this paper, we revisit this question of the localization of the thermal packet. We first generalize the result of Golosov by computing explicitly the joint distribution P( infinity )(y,u) of relative position y=x(t)-m(t) and relative energy u=U(x(t))-U(m(t)) for the thermal packet. Next, we compute the localization parameters Y(k), representing the disorder-averaged probabilities that k particles of the thermal packet are at the same place in the infinite-time limit, and the correlation function C(l) representing the disorder-averaged probability density that two particles of the thermal packet are at a distance l from each other. We, moreover, prove that our results for Y(k) and C(l) exactly coincide with the thermodynamic limit L--> infinity of the analog quantities computed for independent particles at equilibrium in a finite sample of length L. So even if the Sinai dynamics on the infinite line is always out-of-equilibrium since it consists in jumps in deeper and deeper wells, the particles of the same thermal packet can nevertheless be considered asymptotically as if they were at thermal equilibrium in a Brownian potential. Finally, we discuss the properties of the finite-time metastable states that are responsible for the localization phenomenon and compare with the general theory of metastable states in glassy systems, in particular as a test of the Edwards conjecture.

Journal Article↗
PubMedDate not supplied

Equilibrium temperature distributions in uniform phantoms for superficial microwave applicators: implications for temperature-based standards of applicator adequacy.

Equilibrium temperature distributions are computed using measured SAR distributions for five different superficial microwave (915 MHz) applicators. We assume a model with uniform conduction and blood flow. A Green's function approach is used to calculate equilibrium solutions which identically obey boundary conditions at the surface of the phantom and at infinite depth. The equilibrium solutions are categorized by surface temperature (TS), maximum allowed temperature (TM), and by a parameter (referred to as the diffusion length, lambda) which characterizes the contributions of thermal conduction relative to blood flow. The computed equilibrium temperature distribution at depths of 2 and 3 cm is strongly dependent on lambda and on TM. It is not strongly dependent on surface temperature for TS below 35 degrees C. In previous work we compared the SAR distribution with local control of 53 superficial tumours with over 1 year of follow-up. As an alternative to an SAR-based description of applicator adequacy we consider a temperature-based standard. Tumours are categorized by the minimum value of lambda that would allow full coverage of the tumour volume by the 42 degrees C contour, assuming a TM of 47.5 degrees C and a TS of 35 degrees C. Eighteen of 27 lesions (67%) were locally controlled for lambda less than 1 cm. The local control in 26 lesions with lambda greater than or equal to 1 cm was 31% (p = 0.016). The lesions with the best results were those with both good coverage in theory (lambda less than 1 cm) and with all monitored catheter tracks achieving at least one session with 30 min at or above 43 degrees C. We found that the temperature-based standard of applicator adequacy was not independent of an SAR-based standard, and in this cohort of patients either a minimum SAR criterion or a maximum diffusion length criterion would serve equally well as a screen for inappropriate applicators.

Body Temperature↗
PubMed2001

Particle-scale investigation of PAH desorption kinetics and thermodynamics from sediment.

Dredged sediment from Milwaukee Harbor showed two primary classes of particles in the <2 mm size range: a lighter-density coal- and wood-derived fraction with 62% of total PAHs and a heavier-density sand, silt, and clay fraction containing the remaining 38% of the PAHs. Room-temperature PAH desorption kinetic studies on separated sediment fractions revealed slow desorption rates for the coal-derived particles and fast desorption rates for the clay/silt particles. The effect of temperature on PAH release was measured by thermal program desorption mass spectrometry to investigate the desorption activation energies for PAHs on the different sediment particles. Three activated diffusion-based models and an activated first-order rate model were used to describe the thermal desorption of PAHs for four molecular weight classes. PAH binding with the coal-derived particles was associated with high activation energies, typically in the range of 115-139 kJ/mol. PAHs bound to the clay/silt material had much lower activation energy, i.e., in the range of 37-41 kJ/ mol for molecular weight 202. Among the desorption models tested, a spherical diffusion model with PAHs located like a rind on the outer 1-3 microm region best described the PAH thermal desorption response for coal-derived particles. This internal PAH distribution pattern on coalderived particles is based on prior direct measurement of PAH locations at the subparticle scale. These studies reveal that heterogeneous particle types in sediment exhibit much different amounts and binding of PAHs. PAHs associated with coal-derived particles aged over several decades in the field appear to be far from reaching an equilibrium sorption state due to the extremely slow diffusivities through the polymer-like coal matrix. These results provide an improved mechanistic perspective for the understanding of PAH mobility and bioavailability in sediments.

Adsorption↗
PubMed2006

Reaction driven convection around a stably stratified chemical front.

A vertical stratification of a light and hot fluid over a heavy and cold one is expected to be stable with regard to buoyancy-driven convection. Here we show that chemical reactions can trigger convection around chemical fronts even in cases where concentration and heat both contribute to a stable density stratification. The balance between intrinsic thermal and solutal density gradients initiated by a spatially localized reaction zone and double diffusive mechanisms are at the origin of a new convective instability, the mechanism of which is explained by a displaced particle argument. Linear stability analysis of a reaction-diffusion-convection model confirmed by nonlinear simulations delimits the instability region in the parameter space spanned by the thermal and solutal Rayleigh numbers. Experimental systems in which to test our theoretical predictions are proposed.

Journal Article↗
PubMed1985

Lung water measurements with the mean transit time approach.

The potential usefulness and limitations of the double-indicator mean transit time approach for measuring lung water are evaluated from both theoretical and empirical points of view. It is concluded that poor tissue perfusion is the most serious factor that can compromise the reliability of this approach. Replacement of the conventional water isotopes with a thermal signal enhances indicator delivery to ischemic areas but the diffusion of heat is not sufficiently rapid to permit measurements of water in macroscopic collections of fluid which remain unperfused. The frequency of pulmonary vascular obstruction in patients with pulmonary edema related to lung injury suggests that interpretation of transit time data will be complicated by uncertainties concerning perfusion. Thermal-dye measurements of lung water may prove more helpful in situations where pulmonary blood flow remains relatively uniform.

Animals↗
PubMed1992

Transient thermal and mechanical response of water subject to ionizing radiation.

The ultrafast transient (10(-14) to 10(-12)S) thermal and mechanical response of water subject to ionizing radiations of different linear energy transfers has been investigated in order to understand the initial events which lead to cell mutation and lethality. Based on computational fluid dynamics, the production of a "thermal spike" around the trajectory of a charged particle and subsequent diffusion of deposited heart are calculated for particles with linear energy transfer (LET) of 4, 40, and 400 keV/microns. A radiation damage region (that is, the so-called "thermal core") is identified, and the transient behavior of the thermal core is studied. The local and transient environment has a dimension of nanometers, a scale which is of critical interest in understanding mechanisms of radiation damage in cells. The radius of the thermal core, Dd, at temperatures (or internal energy density) of up to 1,000 K, is observed to increase with LET, L, as Dd (in nanometers) = C4.L (in keV/microns)0.6, where, for example, C4 = 0.50 for T = 800 degrees C.

Energy Transfer↗
PubMed1991

Real-time magnetic resonance imaging of laser heat deposition in tissue.

We applied diffusion-sensitive echo planar (Instascan) imaging to study thermal changes caused by a Nd:YAG laser. Images of phantom materials and normal rabbit brain tissue in vivo, acquired in 150 ms, every 2s, clearly showed the dynamics of temperature-related signal intensity changes in the regions irradiated by the laser.

Animals↗
PubMed2006

Modulation of nano-hydroxyapatite size via formation on chitosan-gelatin network film in situ.

Natural bone is actually an inorganic/organic composite mainly make up of nano-hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2), nHA) and collagen fibers. It is most important to form nHA/polymer composites in order to provide good biocompatibility and integration with bone tissue. In this work, nHA was formed in-situ on the surface of chitosan-gelatin (CG) network films in tris-buffer solution containing Ca(NO(3))(2)-Na(3)PO(4). The interaction between CG network film and nHA crystalline were studided using the diffuse reflectance FT-IR (ATR-FTIR), thermal analysis (TGA) and X-ray diffraction analysis (XRD), and the influence the nHA size factors, e.g. the ratio of chitosan (CS) and gelatin (Gel), concentration of calcium ions and reaction temperature, were elucidated by XRD and transmission electron microscope (TEM). Results suggested that carboxyl groups, CO and amino groups play crucial roles for HA formatting on the surface of CG network films and the average size of nHA crystalline decreasing with enhancing Gel content and increase with the increasing calcium and phosphate concentration, and when the reaction temperature below 50 degrees C the nHA crystalline size is almost fixedness (range from 17.2 to 19.2 nm) but when the temperature arrived at 70 degrees C it increase to 52.3 nm.

Animals↗
PubMed1989

Treatment of combined subglottic and critically low tracheal stenoses secondary to burn inhalation injury.

We report a case of combined severe subglottic and lower tracheobronchial stenoses after an inhalation burn injury. The patient was successfully treated by the insertion of a bifurcated silicone rubber stent. The proximal limb of the silicone tube was used to stent the subglottic stenosis after it had been resected, a treatment option not previously reported. It is speculated that the diffuse airway damage resulted from a combination of thermal injury, mechanical trauma and infection. The relatively late symptomatic presentation of the lower tracheal stricture is stressed and the treatment options discussed.

Burns, Inhalation↗
PubMed2005

Magnetically actuated complementary metal oxide semiconductor resonant cantilever gas sensor systems.

In the present paper, an electromagnetically actuated resonant cantilever gas sensor system is presented that features piezoresistive readout by means of stress-sensitive MOS transistors. The monolithic gas sensor system includes a polymer-coated resonant cantilever and the necessary oscillation feedback circuitry, both monolithically integrated on the same chip. The fully differential feedback circuit allows for operating the device in self-oscillation with the cantilever constituting the frequency-determining element of the feedback loop. The combination of magnetic actuation and transistor-based readout entails little power dissipation on the cantilever and reduces the temperature increase in the sensitive polymer layer to less than 1 degrees C, whereas previous designs with thermally actuated cantilevers showed a temperature increase of up to 19 degrees C. The lower temperature of the sensitive polymer layer on the cantilever directly improves the sensitivity of the sensor system as the extent of analyte physisorption decreases with increasing temperature. The electromagnetic sensor design shows an almost 2 times larger gas sensitivity than the earlier design, which is thermally actuated and read out using p-diffused resistors. The gas sensor is fabricated using an industrial complementary metal oxide semiconductor (CMOS) process and post-CMOS micromachining.

Journal Article↗
PubMed2004

The dynamics of noble metal atom penetration through methoxy-terminated alkanethiolate monolayers.

We have studied the interaction of vapor-deposited Al, Cu, Ag, and Au atoms on a methoxy-terminated self-assembled monolayer (SAM) of HS(CH(2))(16)OCH(3) on polycrystalline Au[111]. Time-of-flight secondary ion mass spectrometry, infrared reflection spectroscopy, and X-ray photoelectron spectroscopy measurements at increasing coverages of metal show that for Cu and Ag deposition at all coverages the metal atoms continuously partition into competitive pathways: penetration through the SAM to the S/substrate interface and solvation-like interaction with the -OCH(3) terminal groups. Deposited Au atoms, however, undergo only continuous penetration, even at high coverages, leaving the SAM "floating" on the Au surface. These results contrast with earlier investigations of Al deposition on a methyl-terminated SAM where metal atom penetration to the Au/S interface ceases abruptly after a approximately 1:1 Al/Au layer has been attained. These observations are interpreted in terms of a thermally activated penetration mechanism involving dynamic formation of diffusion channels in the SAM via hopping of alkanethiolate-metal (RSM-) moieties across the surface. Using supporting quantum chemical calculations, we rationalized the results in terms of the relative heights of the hopping barriers, RSAl > RSAg, RSCu > RSAu, and the magnitudes of the metal-OCH(3) solvation energies.

Journal Article↗
PubMed2000

Influence of thermal treatments on Ag Sn Cu powders in order to reduce mercury contents in dental amalgam.

The mercury content of dental amalgams is a controversial subject with regard to the biological properties of these materials. The object of this study is to optimize the thermal treatments performed on an experimental powder in order to obtain a low mercury ratio (41% by weight) while preserving the desirable clinical qualities of the material. Using atomized powder, two types of thermal treatments are performed: A1, to obtain a partially annealed structure and A2, to obtain a complete homogenization. The kinetics of the amalgamation reaction is mainly evaluated by X-ray diffraction to identify the newly formed phases as a function of setting time. Mechanical properties are evaluated according to the ISO norms at 37 degrees C. Metallographical examination of the amalgams shows a Ag-Hg phase which acts as a matrix incorporating the Cu-Sn and Ag-Sn compounds. The setting kinetics of the A1 amalgams is linear and slightly more rapid than that of the A2 amalgam. The mechanical properties of the amalgams are significantly improved regarding the higher mercury content commercial amalgams. A specific thermal treatment permits us to slow down the diffusion of mercury between the different intermetallic compounds into the powder. The final amalgam composition, thus, most approaches the stoechiometric ratio calculated from a quaternary diagram.

Journal Article↗
PubMedDate not supplied

Low cycle fatigue behavior of Ti6Al4V thermochemically nitrided for its use in hip prostheses.

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Besides, titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes difficult the use of titanium and Ti6Al4V in some biomedical applications, like articulating components of prostheses. Some surface treatments are available in order to correct these problems, like thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Low cycle fatigue behavior in air of Ti6Al4V alloy has been studied. Results show a reduction of low cycle fatigue life up to 10% compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

Journal Article↗