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PubMed2005

The influence of potential softness on the transport coefficients of simple fluids.

This study explores the effects of interaction softness on the transport properties of simple fluids. The transport coefficients of soft-sphere fluids in which the particles interact via the potential, phi(r)=epsilon(rsigma)(-n), with n in the range from 6 to 1152, have been calculated by molecular-dynamics computer simulation. The self-diffusion coefficient D shear viscosity eta(s), bulk viscosity eta(b), and thermal conductivity lambda were computed over a wide packing fraction range. It was found that the Batschinski-Hildebrand expressions, in which D, eta(s) (-1), eta(b) (-1), and lambda(-1) are assumed to have a linear dependence on the molar volume, represent the data quite well for all n, although least well for the thermal conductivity. The density for which, on extrapolation, each of these quantities is zero, increases with the softness of the interaction (or approximately n(-1)), suggesting that the effective hard-sphere diameter decreases with increasing softness in the small n limit. This treatment leads to simple empirical formulas for the effect of density and n on the effective hard-sphere diameter and packing fraction (in an intermediate range) and the four transport coefficients of these fluids.

Colloids↗
PubMed2006

Friction and diffusion of matter-wave bright solitons.

We consider the motion of a matter-wave bright soliton under the influence of a cloud of thermal particles. In the ideal one-dimensional system, the scattering process of the quasiparticles with the soliton is reflectionless; however, the quasiparticles acquire a phase shift. In the realistic system of a Bose-Einstein condensate confined in a tight waveguide trap, the transverse degrees of freedom generate an extra nonlinearity in the system which gives rise to finite reflection and leads to dissipative motion of the soliton. We calculate the velocity and temperature-dependent frictional force and diffusion coefficient of a matter-wave bright soliton immersed in a thermal cloud.

Journal Article↗
PubMed2001

Relationship between penile thermal sensory threshold measurement and electrophysiologic tests to assess neurogenic impotence.

OBJECTIVES: Erectile function is usually assessed by neurophysiologic tests such as the bulbocavernosus reflex or pudendal nerve somatosensory evoked potentials. These tests investigate only large nerve fibers, although erection depends on autonomic nerve fibers, which are of small diameter. Warm and cold sensory fibers have similar calibers as the autonomic nerve fibers, and their integrity can be reliably evaluated by the measurement of thermal sensory thresholds. We studied penile thermal sensory testing in parallel with standard electrophysiologic tests to assess their sensitivity in the diagnosis of penile neuropathy. METHODS: Twenty-five normal male subjects without erectile dysfunction or evidence of diffuse neuropathy (group 1) and 35 diabetic patients who complained of impotence (group 2) were studied. Erectile function was quantitated using the erectile dysfunction symptom score. Warm, cold, and vibratory sensory thresholds were assessed on the dorsal aspect of the penis. In addition, penile sympathetic skin responses and pudendal nerve somatosensory evoked potentials were recorded. RESULTS: We found a significant difference between the two groups in the erectile dysfunction symptom score (P <0.0001), cold threshold (P = 0.0007), and warm threshold (P = 0.0025), but not for the other parameters. The erectile dysfunction symptom score correlated with the penile warm and cold thresholds (P = 0.0006 and 0.002, respectively). CONCLUSIONS: Thermal thresholds assess small nerve fiber damage, which can indirectly reflect autonomic disturbances, particularly in the context of a diffuse neuropathy such as diabetic polyneuropathy. Penile thermal sensory testing correlated strongly with the clinical evaluation of erectile function and is a new and promising tool for the diagnosis of neurogenic impotence.

Adult↗
PubMed2006

New linear-parabolic rate equation for thermal oxidation of silicon.

We propose a new oxidation rate equation for silicon supposing only a diffusion of oxidizing species but not including any rate-limiting step by interfacial reaction. It is supposed that diffusivity is suppressed in a strained oxide region near SiO(2)/Si the interface. The expression of a parabolic constant in the new equation is the same as that of the Deal-Grove model, while a linear constant makes a clear distinction with that of the model. The estimated thickness using the new expression is close to 1 nm, which compares well with the thickness of the structural transition layers.

Journal Article↗
PubMed2005

Anomalous heat conduction and anomalous diffusion in nonlinear lattices, single walled nanotubes, and billiard gas channels.

We study anomalous heat conduction and anomalous diffusion in low-dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is sigma(2)(t)=2Dt(alpha) (0 1) implies an anomalous heat conduction with a divergent thermal conductivity (beta>0), and more interestingly, a subdiffusion (alpha<1) implies an anomalous heat conduction with a convergent thermal conductivity (beta<0), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our theoretical prediction.

Carbon↗
PubMed1995

Intrauterine light delivery for photodynamic therapy of the human endometrium.

Photodynamic therapy is currently being evaluated as a minimally invasive procedure for endometrial ablation not requiring anaesthesia. Light penetration depths at 630, 660 and 690 nm and the optimal configuration of intrauterine light-diffusing fibres were determined in 14 human uteri to assist in the design of a light intrauterine device. Post-menopausal ex-vivo uteri showed a significantly lower light penetration depth than pre-menopausal uteri. With a single central diffusing fibre inserted, the fluence rate measured in the uterine wall at the most remote point of the cavity decreased to 1.1 +/- 0.4% of that measured at closest proximity, whereas it decreased to only 40.0 +/- 9.0% with three fibres. Distension of the uterine cavity with 2 ml of an optically clear fluid increased the fluence rate at the fundus between the fibres at a depth of 2 mm by a factor of 4. We conclude that in normal-sized pre-menopausal uterine cavities, three diffusing fibres will deliver an optical dose above the photodynamic threshold level at a depth of 4 mm, even in the most remote areas, in < 30 min without causing thermal damage. For distorted and elongated cavities, either slight distension of the cavity or the insertion of a fourth diffusing fibre is required.

Adult↗
PubMed2004

Diffusion on a solid surface: anomalous is normal.

We present a numerical study of classical particles diffusing on a solid surface. The particles' motion is modeled by an underdamped Langevin equation with ordinary thermal noise. The particle-surface interaction is described by a periodic or a random two-dimensional potential. The model leads to a rich variety of different transport regimes, some of which correspond to anomalous diffusion such as has recently been observed in experiments and Monte Carlo simulations. We show that this anomalous behavior is controlled by the friction coefficient and stress that it emerges naturally in a system described by ordinary canonical Maxwell-Boltzmann statistics.

Journal Article↗
PubMed2006

Modeling transient absorption and thermal conductivity in a simple nanofluid.

Molecular dynamics simulations are used to simulate the thermal properties of a model fluid containing nanoparticles (nanofluid). By modeling transient absorption experiments, we show that they provide a reliable determination of interfacial resistance between the particle and the fluid. The flexibility of molecular simulation allows us to consider separately the effect of confinement, particle mass, and Brownian motion on the thermal transfer between fluid and particle. Finally, we show that in the absence of collective effects, the heat conductivity of the nanofluid is well described by the classical Maxwell Garnet equation model.

Absorption↗
PubMed2005

Coverage dependent desorption dynamics of deuterium on Si(100) surfaces: interpretation with a diffusion-promoted desorption model.

We studied coverage dependence of time-of-flight (TOF) spectra of D2 molecules thermally desorbed from the D/Si(100) surface. The mean translational energies Et of desorbed D2 molecules were found to increase from 0.20+/-0.05 eV to 0.40+/-0.04 eV as the desorption coverage window was decreased from 1.0 ML> or =thetaD> or =0.9 ML to 0.2 ML> or =thetaD> or =0 ML, being consistent with the kinetics switch predicted in the interdimer mechanism. The measured TOF spectra were deconvoluted into 2H, 3H, and 4H components by a curve fitting method along the principle of detailed balance. As a result, it turned out that the desorption kinetics changes from the 4H to the 3H situation at high coverage above thetaD=0.9 ML, while the 2H desorption is dominant for a quite wide coverage region up to thetaD=0.8 ML. A dynamic desorption mechanism by which the desorption is promoted by D-atom diffusion to dangling bonds was proposed.

Journal Article↗
PubMed1993

A facility for biomedical experiments with thermal neutrons.

The Studsvik thermal-neutron facility was originally designed for neutron capture radiography (NCR) at high thermal-neutron fluence and low fast-neutron contamination. It has now been modified to permit irradiation of living cells and animals without the need for stopping and restarting the R2-0 reactor. Previous calculations of the thermal-neutron intensity at the NCR position were performed using the two-dimensional diffusion theory code DIXY. In this report the Monte Carlo program MCNP 3B is used to calculate the neutron fluence at the radiography position, and neutron and photon fluences at the positions of the cell specimens. The normalized neutron fluences from the calculations agree well with measured values and show that the contamination with high-energy neutrons is low. The agreement between measured and calculated photon doses was reasonable. The thermal-neutron fluence rate is (2.3 +/- 0.1) x 10(9) cm-2 s-1 at 100 kW at the NCR position and (0.96 +/- 0.03 x 10(9) cm-2 s-1 at 100 kW at the front plate of the loading tube. The photon dose is about (1.6 +/- 0.2) x 10(-12) Gy per neutron. Survival curves of V79 cells grown as monolayers and irradiated in the thermal neutron beam, with and without boron, are presented.

Animals↗
PubMed2005

Growth of crystalline rubrene films with enhanced stability.

The growth of well-oriented crystalline films of rubrene (C42H28) on SiO2 and Au111 substrates is achieved by employing "hot wall" deposition whereas organic molecular beam deposition (OMBD) only yields rather amorphous layers or poly-crystalline dendritic networks at elevated temperature. This pronounced difference in film growth is related to the conformational change of rubrene molecules involving a loss of chirality upon crystallization and the enhanced diffusion which becomes possible at high temperature and large vapor pressure. Moreover, it is demonstrated that the crystalline rubrene films reveal an enhanced thermal and chemical stability as compared to the OMBD grown films.

Crystallization↗
PubMed1993

Validity of thermal dilution technique for measurement of cardiac output in rats.

The validity of the thermal dilution technique for the measurement of cardiac output was verified in experiments on a circulation model and on anesthetized rats under open- and closed-chest conditions. In the circulation model thermal dilution was compared with direct (Fdir) and electromagnetic (F(elm)) flowmetry. Flow values measured in the circulation model with the thermal dilution (Fth) technique correspond well with direct flowmetry (Fth = 0.92 Fdir + 7.0; r = 0.888) and with electromagnetic flowmetry (Fth = 0.95 F(elm) + 1.2; r = 0.990). In the anesthetized rat cardiac output was determined with thermal dilution and simultaneously with Fick's method and/or with electromagnetic flowmetry. Fick's method and electromagnetic flowmetry resulted in identical cardiac output values (COFick = 0.95 COelm; r = 0.865), whereas the thermal dilution technique yielded unequivocally higher values. The extent of overestimation is much more pronounced at low cardiac output than at a high output. The study clearly demonstrates that this overestimation is due to heat diffusion, which is obviously of greater significance in small animals than in large animals or humans. Therefore, the thermal dilution technique is not appropriate for the measurement of cardiac output in the rat.

Animals↗
PubMed2006

Evolving technology in bipolar perfused radiofrequency ablation: assessment of efficacy, predictability and safety in a pig liver model.

Bipolar radiofrequency (RF) ablation, especially with perfusion of saline, has been shown to increase volume over monopolar conventional methods. The aims of this study are to study whether this method is linked to too flattened thermal lesions and premature rise of impedance and to elucidate some safety concerns. Eighteen RF ablations were performed using a 1.8-mm-diameter bipolar applicator in the liver of nine healthy pigs through laparotomy with or without temporary vascular occlusion [the Pringle maneuver (PGM)]: group A (n=9), without PGM; group B (n=9), with PGM. Hypertonic saline solutions (3% and 20 %) were injected through the applicator at a rate of 400 ml/h during the procedure. The pigs were followed up and they were euthanased on the 15th day. Impedance, current, power output, energy output, temperatures, diameters of thermal lesion, volume, sphericity ratio of thermal lesion were correlated among groups. Impedance at the end of the procedure (50.00 Omega+/-28.39 and 52.88 Omega+/-26.77, for groups A and B, respectively) was very similar to the starting impedance (50 Omega). In a median of 1 (range, 0-6) time per RF ablation procedure a reduction of 30 W from the selected power supply was observed during the RF ablation procedure linked to a slight increase of impedance. Volume and short diameter of thermal lesion were 21.28 cm3+/-11.78 and 2.85 cm+/-0.87 for group A, 87.51 cm3+/-25.20 and 4.31 cm+/-0.65 for group B. Continuous thermal between both electrodes were described with a global sphericity ratio of 1.91. One major complication (thermal injury to the stomach) was encountered in a case of cross-sectional necrosis of the targeted liver and attributed to heat diffusion after the procedure. This method has been shown to determine: (1) the relative control of impedance during the procedure; (2) ovoid and relatively large thermal lesions with less dependence upon closest vessels.

Analysis of Variance↗
PubMed2006

Improvement of port wine stain laser therapy by skin preheating prior to cryogen spray cooling: a numerical simulation.

BACKGROUND AND OBJECTIVES: Although cryogen spray cooling (CSC) in conjunction with laser therapy has become the clinical standard for treatment of port wine stain (PWS) birthmarks, the current approach does not produce complete lesion blanching in the vast majority of patients. The objectives of this study are to: (1) experimentally determine the dynamic CSC heat flux when a skin phantom is preheated, and (2) numerically study the feasibility of using skin preheating prior to CSC to improve PWS laser therapeutic outcome. STUDY DESIGN/MATERIALS AND METHODS: A fast-response thin-foil thermocouple was used to measure the surface temperature and thus heat flux of an epoxy skin phantom during CSC. Using the heat flux as a boundary condition, PWS laser therapy was simulated with finite element heat diffusion and Monte Carlo light distribution models. Epidermal and PWS blood vessel thermal damage were calculated with an Arrhenius-type kinetic model. RESULTS: Experimental results show that the skin phantom surface can be cooled to a similar minimum temperature regardless of the initial temperature. Numerical simulation indicates that upon laser irradiation, the epidermal temperature increase is virtually unaffected by preheating, while higher PWS blood vessel temperatures can be achieved. Based on the damage criterion we assumed, the depth and maximum diameter of PWS vessels that can be destroyed irreversibly with skin preheating are greater than those without. CONCLUSIONS: Skin preheating prior to CSC can maintain epidermal cooling while increasing PWS blood vessel temperature before laser irradiation. Numerical models have been developed to show that patients may benefit from the skin preheating approach, depending on PWS vessel diameter and depth.

Cryotherapy↗
PubMed1981

Effect of naloxone upon diffuse noxious inhibitory controls (DNIC) in the rat.

Twenty-eight convergent neurones, responding to both noxious and innocuous stimuli applied to their cutaneous receptive fields were recorded at the lumbar level in anaesthetized intact rats. These cells received Aa and C fibre inputs as shown by electrical stimulation of their receptive fields, and were located in the medial part of the dorsal horn. (a) For 15 units, Diffuse Noxious Inhibitory Controls (DNCI)67,68 were investigated by applying noxious thermal stimuli (52 degrees C) to the distal two-thirds of the tail. This conditioning stimulus induced strong inhibition of the responses to both Aa (28%) and C (71%) fibres. Post-effects of long duration were commonly observed after cessation of the conditioning stimulus. The systemic injection of naloxone (0.3 mg/kg, i.v.) resulted in a partial reduction in these inhibitory effects with a decrease of about 50% for both Aa and C fibre response 10 min after naloxone administration. This was followed by a progressive recovery lasting 30 min. (b) 28 convergent units, including the 15 reported above, were recorded to investigate the effect of naloxone upon the unconditioned response. Responses to Aa fibre were unaffected, whereas the responses to C fibre were slightly (17%) but significantly increased by naloxone.

Afferent Pathways↗
PubMed1993

Temperature rise in tumor tissue during high-dose-rate photoradiation.

The bioheat transfer equation and optical diffusion theory are used to develop a mathematical model for describing the thermal field in a spherical tumor and its surrounding normal tissue resulting from photoradiation. Analytical solutions to the model equations are presented for determining both the steady-state and transient temperature profiles. The effect of the optical and thermal properties of the surrounding normal tissue on the thermal field generated within the tumor is explored.

Body Temperature↗
PubMed2005

ESR study of Gd3+ and Mn2+ ions sorbed on hydroxyapatite.

Adsorption of Gd3+ and Mn2+ into hydroxyapatite (HAP (Ca5(PO4)3(OH)2) was studied by ESR, ion chromatography and ICP-AES to investigate the U-uptake model. HAP absorbed Gd3+ via a cation exchange reaction and resulted in a signal width of 240 mT. The growth of the thermally stable Gd3+ signal in HAP was also fitted by saturation and diffusion equations. The ESR signals of Gd3+ and Mn2+ were observed overlapping the CO2- signals, however, the dose-response curves of the CO2- signal were similar to that of control HAP.

Journal Article↗
PubMed2006

Numerical estimation of real and apparent integral neutron parameters used in nuclear borehole geophysics.

The semi-empirical method of neutron logging tool calibration developed by Prof. J.A. Czubek uses the real and so-called apparent integral neutron parameters of geological formations. To this end, Czubek proposed a few separated calculation methods commonly based on analytical solutions of the neutron transport problem. A new calculation method for the neutron integral parameters is proposed. Quantities like slowing-down length, diffusion and migration lengths, probability to avoid absorption during slowing down, and thermal neutron absorption cross section can be easily approximated using Monte Carlo simulations. A comparison with the results of the analytical method developed by Czubek has been performed for many cases and the observed differences have been explained.

Journal Article↗