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PubMed2000

Continuous time dynamics of the thermal minority game

We study the continuous time dynamics of the thermal minority game. We find that the dynamical equations of the model reduce to a set of stochastic differential equations for an interacting disordered system with nontrivial random diffusion. This is the simplest microscopic description which accounts for all the features of the system. Within this framework, we study the phase structure of the model and find that its macroscopic properties strongly depend on the initial conditions.

Journal Article↗

PubMed2005

Microrheology of cross-linked polyacrylamide networks.

Experiments investigating the local viscoelastic properties of a chemically cross-linked polymer are performed on polyacrylamide solutions in the sol and the gel regimes using polystyrene beads of varying sizes and surface chemistry as probes. The thermal motions of the probes are measured to obtain the elastic and viscous moduli of the sample. Probe dynamics are measured using two different dynamic light scattering techniques, diffusing wave spectroscopy (DWS) and quasielastic light scattering (QELS) as well as video-based particle tracking. Diffusing wave spectroscopy probes the short-time dynamics of the scatterers while QELS measures the dynamics at larger times. Video-based particle tracking provides a way to investigate the local environment of the individual probe particles. A combination of all the techniques results in a larger range of frequencies that can be probed compared to conventional bulk measurements while providing local information at the level of individual probes. A modified algebraic form of the generalized Stokes-Einstein equation is used to calculate the frequency-dependent moduli. A comparison of microrheological measurements with bulk rheology exhibits striking similarity, confirming the applicability of microrheology for chemically cross-linked polymeric systems.

Journal Article↗

PubMed2000

Finite thermal conductivity in 1D lattices

We discuss the thermal conductivity of a chain of coupled rotators, showing that it is the first example of a 1D nonlinear lattice exhibiting normal transport properties in the absence of an on-site potential. Numerical estimates obtained by simulating a chain in contact with two thermal baths at different temperatures are found to be consistent with those based on linear response theory. The dynamics of the Fourier modes provides direct evidence of energy diffusion. The finiteness of the conductivity is traced back to the occurrence of phase jumps. Our conclusions are confirmed by the analysis of two variants of this model.

Journal Article↗

PubMed1989

Effect of peripheral temperature on the formation of venous gas bubbles.

Temperature of the tissue affects the many components involved in the formation of tissue gas phase formation: diffusion, perfusion, and inert gas solubility. Since the effects of perfusion and inert gas solubility may be counteracting in terms of enhancing growth of gas bubbles, the optimal thermal status of divers throughout a dive remains unresolved. To elucidate the role of peripheral body temperature on gas phase formation, four subjects were exposed to a 10 degree and 40 degree C environment for 3 h on two separate occasions, after a no-stop decompression from a 12-h dive to 9.14 m (30 fsw) on air. The 3-hour exposures to either a cold or warm air environment resulted in a significant difference in mean skin temperature (P less than or equal to 0.01) with no alteration in rectal temperature. Total peripheral resistance during the 10 degree C exposure was 13.8 +/- 1.9 mmHg.liter-1.min-1 and significantly higher than that observed during the 40 degree C exposure (10.4 +/- 3.5 mmHg.liter-1.min-1). Gas bubbles in the venous return were monitored with a Doppler ultrasonic transducer placed in the precordial region, both at rest and after a deep knee bend. Venous bubbles were only detected in 1 subject following the warm air exposure, whereas 3 of the 4 subjects developed Doppler-detectable bubbles during the cold air exposure. Although both the cold and warm air exposures (3 h postdecompression) were uneventful, a hot shower taken by the subjects on completion of the cold air exposure (6 h postdecompression) precipitated mild type I symptoms of decompression sickness. These symptoms were not present after a hot shower following the warm air exposure. The present results indicate that despite the assumed greater inert gas solubility of tissues expected during cold air exposure, the decrease in the perfusion may have played a more significant role in the observed levels of detectable venous gas bubbles. Development of type I symptoms following a 12-h saturation, a 3-h cold exposure, and a subsequent hot shower suggests that a rapid rise in peripheral temperature may cause a significant rise in tissue gas tension. This increase in tension does not seem to be sufficiently reduced by increased perfusion to the tissues to prevent bubble formation.

Adult↗

PubMed1995

Mechanisms of stimulus transmission across dentin--a review.

Several investigators have demonstrated that intradental A-type (A beta and A delta) nerve fibers are responsible for the sensitivity of dentin and that the endings of the responding fibers are located in the pulp-dentin area of the tooth. The exact mode of transmission of stimuli (e.g., thermal, chemical, mechanical, etc.) across dentin, however, is still unclear, although several hypotheses have been proposed. These include direct nerve stimulation, dentinal receptor (transducer/modulation), hydrodynamic, and direct ionic diffusion hypotheses. Currently, the most accepted mechanism of intradental nerve activation associated with dentin sensitivity appears to be hydrodynamic in nature, although alternative mechanisms of transmission (e.g., direct ionic diffusion) cannot be ruled out. Recent investigations (in the cat), however, appear to provide evidence substantiating the hydrodynamic hypothesis.

Animals↗

PubMed2006

Design and evaluation of colon specific drug delivery system containing flurbiprofen microsponges.

The purpose of this study was to design novel colon specific drug delivery system containing flurbiprofen (FLB) microsponges. Microsponges containing FLB and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. Additionally, FLB was entrapped into a commercial Microsponge 5640 system using entrapment method. Afterwards, the effects of drug:polymer ratio, inner phase solvent amount, stirring time and speed and stirrer type on the physical characteristics of microsponges were investigated. The thermal behaviour, surface morphology, particle size and pore structure of microsponges were examined. The colon specific formulations were prepared by compression coating and also pore plugging of microsponges with pectin:hydroxypropylmethyl cellulose (HPMC) mixture followed by tabletting. In vitro dissolution studies were done on all formulations and the results were kinetically and statistically evaluated. The microsponges were spherical in shape, between 30.7 and 94.5microm in diameter and showed high porosity values (61-72%). The pore shapes of microsponges prepared by quasi-emulsion solvent diffusion method and entrapment method were found as spherical and cylindrical holes, respectively. Mechanically strong tablets prepared for colon specific drug delivery were obtained owing to the plastic deformation of sponge-like structure of microsponges. In vitro studies exhibited that compression coated colon specific tablet formulations started to release the drug at the 8th hour corresponding to the proximal colon arrival time due to the addition of enzyme, following a modified release pattern while the drug release from the colon specific formulations prepared by pore plugging the microsponges showed an increase at the 8th hour which was the time point that the enzyme addition made. This study presents a new approach based on microsponges for colon specific drug delivery.

Algorithms↗

PubMed2006

Novel biobased nanocomposites from soybean oil and functionalized organoclay.

Novel biobased nanocomposites have been prepared by the cationic polymerization of conjugated soybean oil (CSOY) or conjugated LoSatSoy oil (CLS) with styrene (ST) and divinylbenzene (DVB), and a reactive organomodified montmorillonite (VMMT) clay as a reinforcing phase. This filler has been prepared by the cationic exchange of sodium montmorillonite with (4-vinylbenzyl)triethylammonium chloride in aqueous solution. The nanostructures of the nanocomposites have been determined by using wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM), respectively. The results from WAXD and TEM indicate that a heterogeneous structure consisting of intercalation and partial exfoliation or an intercalation structure exists in the nanocomposites, depending on the amount of VMMT in the polymer matrix. The thermal, mechanical, and organic vapor barrier properties of the nanocomposites have been evaluated by dynamic thermal analysis, thermogravimetric analysis, mechanical testing, and toluene absorption. A significant improvement is observed in the thermal stability, the dynamic bending storage modulus, the compressive modulus, the compressive strength, the compressive strain at failure, and the vapor barrier performance for the CSOY-- and CLS-based nanocomposites with 1-2 wt % VMMT loading, where some individual exfoliated silicate platelets occur. For example, the CLS-based nanocomposite with 1-2 wt % VMMT exhibits increases of 100-128%, 86-92%, and 5-7% in compressive modulus, compressive strength, and compressive strain at failure, respectively. CLS with higher unsaturation and reactivity affords nanocomposites with higher thermal stability and higher mechanical properties than CSOY.

Aluminum Silicates↗

PubMed2003

Structure and thermal behavior of a layered silver hydroxyalkanecarboxylate.

The structure and thermal behavior of silver 16-hydroxyhexadecanoate (Ag-HHDA) have been investigated by using various analytical tools. The X-ray diffraction pattern was composed of a series of peaks that could be indexed to (0k0) reflections of a layered structure. Diffuse reflectance infrared Fourier transform spectroscopy revealed that the alkyl chains in Ag-HHDA as prepared were in an all-trans conformational state. Upon heating the sample, noticeable structural changes took place particularly in two temperature regions. The first structural change occurring at approximately 380 K was a partially irreversible one in which the binding state of carboxylate to silver converted from bridging into unidentate. A second dramatic structural change occurring at approximately 480 K was a totally irreversible process that could be associated with the decomposition of Ag-HHDA. All of these thermal characteristics of Ag-HHDA are comparable to those of silver stearate (Ag-STA). Separately, we have endeavored without success to intercalate polar molecules into the OH-group terminated layers in Ag-HHDA; the exfoliation of Ag-HHDA in various polar solvents was also unsuccessful. This is indicative of the presence of a rather stronger H-bond in Ag-HHDA, but the comparable thermal characteristics of Ag-HHDA and Ag-STA dictate that the thermal behavior of silver alkanoate is determined exclusively by the silver-to-carboxylate group interaction. This is in sharp contrast to the case of two-dimensional self-assembled monolayers for which the terminal functionalities play a crucial role in determining the structure and thermal stability of entire monolayers.

Journal Article↗

PubMed2006

Diffusive sampling of methylene chloride with solid phase microextraction.

This study examined the characteristics of a solid phase microextraction (SPME) assembly as a passive sampler to determine the short-term exposure level (STEL) of methylene chloride. Two types of SPME fibers and six sampling-related factors were chosen and nested in an L(18) Taguchi's orthogonal array. Samples were thermally desorpted and analyzed by gas chromatograph equipped with an electron capture detector (GC/ECD). The use of 85-mum Carboxen/polydimethylsiloxane (Car/PDMS) fibers resulted in greater adsorbed mass, which was highly correlated with the product of concentration and sampling time (r>0.99, p<0.0001), than 85-microm polyacrylate fibers. The sampling rate (SR) of the 85-microm Carboxen/polydimethylsiloxane fibers was not significantly affected by variations in relative humidity (0-80%) and coexistent toluene (none to 100 ppm). Variance of sampling rate was predominantly attributed to the diffusive path length (86.4%) and sampling time (5.7%). With diffusive paths of 3, 10 and 15 mm, the sampling rates of 85-microm Carboxen/polydimethylsiloxane fibers for methylene chloride were 1.4 x 10(-2), 7.7 x 10(-3) and 5.1 x1 0(-3)mL min(-1), respectively. The measured sampling rates were greater than the theoretical values, and decreased with increment of sampling time until they came to constant.

Chromatography, Gas↗

PubMed1976

Mixed vascular deformities of the lower limbs, with particular reference to lymphography and surgical treatment.

A series of patients with congenital blood and lymph anomalies of the lower limb investigated and treated at St Thomas's Hospital, London, are reviewed. They fell into three classes: (1) those in which the venous element predominated (Klippel and other syndromes), (2) those with arteriovenous shunts and (3) those with angiomas of blood or lymph vessels scattered through the limb (diffuse mixed angiomas). Most of the patients were investigated by angiography (of blood or lymph systems) as well as by plethysmography, dermal temperature measurements and other techniques in the thermal laboratory. Phlebography showed most abnormalities in the Klippel group and was useful in delineating them before operation. The importance of confirming the existence of an adequate deep venous circulation prior to ablation of abnormal superficial vessels is emphasized. Arteriography showed most abnormalities in the group with suspected arteriovenous shunts. The most commonly performed operations in this group were for control of overgrowth of the limb or for ulceration. Lymphography showed many of the Klippel group to suffer from insufficiency of the main pathways, either aplasia or hypoplasia. In addition many had vesicles, fistulas and lymph cysts. Patients in the arteriovenous shunt group had large hyperplastic lymph pathways, which were possibly either congenital or a hypertrophic response. One hundred and thirty-eight operations were performed in 46 patients for a variety of lesions and disabilities. These are reviewed. The scope and benefit of surgery in these children are greater than has been accepted in the past. Three patients required amputation of a limb. There were 5 deaths in the series, 4 of these being in the scattered angioma group and in patients in whom the deformities extended beyond the limb into the trunk.

Adolescent↗

PubMed2006

Field-flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies.

This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.

Fractionation, Field Flow↗

PubMed2002

Direct analysis of volatile organic compounds in human breath using a miniaturized cylindrical ion trap mass spectrometer with a membrane inlet.

Membrane introduction mass spectrometry (MIMS) coupled to a miniature mass spectrometer equipped with a cylindrical ion trap (CIT) analyzer was used to monitor the flavor components, 3-phenyl-2-propenal and methyl salicylate, found in cinnamon and wintergreen candies, respectively, directly from human breath. The poly(dimethylsiloxane) (PDMS) membrane was operated in a trap-and-release mode, where the temperature of the membrane was cycled during the experiments, which permitted temporal resolution of the two compounds of interest, facilitating their observation in the complex sample. Under these thermally driven conditions, the 10-90% rise times for both compounds are similar (15 s for methyl salicylate, 17 s for 3-phenyl-2-propenal), but the difference in diffusivity means that the signal for 3-phenyl-2-propenal is delayed and the 10% point occurs 6 s later than that for wintergreen. Additional specificity needed for complex samples was gained by using tandem mass spectrometry.

Acrolein↗

PubMed2000

Selective extraction and purification of a mycobacterial outer membrane protein.

MspA forms water-filled channels in the mycolic acid layer of Mycobacterium smegmatis thereby allowing the diffusion of hydrophilic solutes through this permeability barrier into the periplasm. MspA is the first member of a new family of porins and is extremely stable against chemical and thermal denaturation. We developed a purification procedure based on selective extraction of MspA with detergents from whole cells of M. smegmatis at high temperatures. Anion-exchange and size-exclusion chromatography yielded about 230 microg apparently pure and highly active MspA per liter of culture. This was a 20-fold increased yield compared to previous purification protocols. Similar amounts of pure MspA were obtained with the detergents isotridecylpolyethyleneglycolether, lauryldimethylamine oxide, and octylpolyethylene oxide indicating that this purification procedure is not restricted to a specific detergent. This study will promote the structural and functional analysis of MspA and might be valuable for the isolation of porins from other mycolic acid-containing bacteria.

Chromatography, Ion Exchange↗

PubMed2000

Separation of metal chelates and organometallic compounds by SFC and SFE/GC.

Supercritical fluid chromatography (SFC) combines the high diffusion coefficients of gas chromatography (GC) and the solubility properties of liquid chromatography (LC). SFC generally requires lower temperatures for chromatographic separations and thus is more suitable for analyzing thermally labile compounds including a number of metal chelates and organometallic compounds. SFC also allows interfacing between supercritical fluid extraction (SFE) and chromatographic analysis of metal-containing compounds. A large number of metal chelates and organometallic compounds can be separated by SFC. This article summarizes SFC separation of various chelates of transition metals, heavy metals, lanthanides and actinides as well as organometallic compounds of lead, mercury, and tin reported in the recent literature. This article also discusses SFC detection systems and the determination of solubility of organometallic compounds by SFC.

Actinoid Series Elements↗

PubMed2004

Adsorption, desorption, and clustering of H2O on Pt111.

The adsorption, desorption, and clustering behavior of H2O on Pt111 has been investigated by specular He scattering. The data show that water adsorbed on a clean Pt111 surface undergoes a structural transition from a random distribution to clustered islands near 60 K. The initial helium scattering cross sections as a function of temperature are found to be insensitive to the incident H2O flux over a range of 0.005 monolayers (ML)/s-0.55 ML/s indicating that the clustering process is more complex than simple surface diffusion. The coarsening process of an initially random distribution of water deposited at 25 K is found to occur over a broad temperature range, 60<T<140 K, during thermal annealing. The desorption kinetics for submonolayer water are determined to be zero order for surface coverages greater than 0.05 ML and temperatures between 145 and 172 K. The zero-order desorption kinetics are consistent with a two-dimensional two-phase coexistence between a high-density H2O condensed phase (islands) and a low-density two-dimensional gaslike phase on the Pt surface.

Journal Article↗

PubMed2004

Libration induced stretching mode excitation for pump-probe spectroscopy in pure liquid water.

We developed an experimental approach to study pure liquid water in the infrared and avoid thermal effects. This technique is based on libration induced stretching excitation of water molecules. A direct correspondence between frequencies within the libration and OH stretching bands is demonstrated. Energy diffusion is studied in pure liquid water by measuring wave packet dynamics of OH stretching vibrator with infrared femtosecond spectroscopy. Wave packet dynamics reveals ultrafast energy dynamics and reflects 130 fs intermolecular energy transfer between water vibrators. Energy diffusion is almost two orders of magnitude faster than self diffusion in water.

Energy Transfer↗

PubMed2005

Surface diffusion of Cr adatoms on Au(111) by quantum tunneling.

The low-temperature surface diffusion of isolated Cr adatoms on Au(111) has been determined using nonperturbing x rays. Changes in the x-ray magnetic circular dichroism spectral line shape together with Monte Carlo calculations demonstrate that adatom nucleation proceeds via quantum tunneling diffusion rather than over-barrier hopping for temperatures <40K. The jump rates are shown to be as much as 35 orders of magnitude higher than that expected for thermal over-barrier hopping at 10 K.

Journal Article↗

PubMedDate not supplied

Synthesis and characterization of fluoro-substituted polyaniline.

Poly(2-fluoroaniline) was prepared by both chemical and electrochemical polymerization in acidic medium. Characterization of poly(2-fluoroaniline) was accomplished experimentally using ultraviolet-visible, Fourier transform infrared, differential scanning calorimetry, thermal gravimetric analysis, and X-ray diffraction techniques, respectively. Scanning electron microscopy studies revealed globular morphology of chemically synthesized poly(2-fluoroaniline). The cyclic voltammetric studies revealed diffusion-controlled phenomenon in electrochemically synthesized poly(2-fluoroaniline).

Aniline Compounds↗