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PubMed2007

Quantum surface diffusion of vibrationally excited molecular dimers.

We consider the thermally activated quantum diffusion of a molecular dimer in a periodic surface potential by means of a time-dependent wave packet method. We show that the potential energy surface resulting from the interplay of intradimer and dimer-surface interactions can lead to resonant states and predict high tunneling probabilities at specific, below barrier, energies that depend also on the initial vibrational state of the dimer. For soft molecular bonds, we show that the chaotic dynamical regime of classical dimers is mirrored, in the quantum case, by the tunneling induced mixing of vibrational states. The knowledge of the transmission coefficient is used to formulate an approximate description of quantum thermal diffusion by defining an effective temperature-dependent activation energy that can be compared to the classical case.

Journal Article↗
PubMed1991

Computational studies of ligand diffusion in globins: I. Leghemoglobin.

The thermally assisted diffusion of a small ligand (carbon monoxide) through a protein matrix (lupine leghemoglobin) is investigated computationally. The diffusion paths are calculated by a variant of the time-dependent Hartree approximation which we call LES (locally enhanced sampling). The variant which was recently introduced by Elber and Karplus is based on the classical TDSCF approximation of Gerber et al. The simulation enables more significant search for diffusion pathways than was possible before. This is done by increasing the number of ligand trajectories using a single trajectory for the protein. We compare qualitatively diffusion rates in leghemoglobin and in myoglobin. The calculation shows that the diffusion in leghemoglobin is much faster than the diffusion in myoglobin, in agreement with experiment. The gate in leghemoglobin is opened by fluctuations at a close contact between the B/C and the G helices. The most relevant fluctuation is the rigid shift of the C helix with respect to the G helix. This path is not observed in a comparable calculation for myoglobin. This finding is rationalized by the lack of the D helix in leghemoglobin and a significantly more flexible CE loop. Supporting experimental evidence for the importance of the CE loop in leghemoglobin can be found in the kinetics studies of Gibson et al.

Amino Acid Sequence↗
PubMed2004

Technical developments for cerebral thermal treatment: water-cooled diffusing laser fibre tips and temperature-sensitive MRI using intersecting image planes.

The aim was to determine if water-cooled diffusing tips could produce larger and safer (better controlled) thermal lesions than non-cooled diffusing tips at 980 nm. Thermal lesions were induced in beef myocardium in vitro with and without water cooling using a 980 nm diode laser at various power levels. Seven intracerebral treatments were performed in six canines using water-cooled diffusing tips with four animals having intracerebral transmissible venereal tumours grown from inoculate. Magnetic resonance thermal imaging (MRTI)-based feedback software using a fast, radio frequency-spoiled gradient echo acquisition with two intersecting image planes was used for on-line monitoring and control of treatment and for the evaluation of in vivo laser lesion production. In cases where two-plane MRTI was employed, the maximum calculated temperature was compared in each plane. Using water-cooled tips and 400 micro m core diameter laser diffusing fibres in in vitro beef myocardium, power of up to 9.5 W was applied for 8 min without tip failure. Without cooling, tip failure occurred in under 4 min at 6 W, in under 2 min at 7 W and instantaneously at 8 W. Additionally, char accompanied lesions made with uncooled tips while cooled application resulted in only minimal char at only the highest thermal dose. Achieved lesion cross-sectional diameters in in vitro samples were up to 26.5 x 23.3 mm when water cooling was used. In canine brain and transmissible venereal tumours, up to 18.1 x 21.4 mm lesions were achieved. It is concluded that water cooling allows safe application of higher power to small core diameter diffusing tip fibres, which results in larger thermal lesions than can be achieved without cooling. Two-plane MRTI enhances on-line monitoring and feedback of thermal treatment.

Animals↗
PubMed1975

Acute gastric disease after cutaneous thermal injury.

Diffuse erosive "gastritis" was discovered as early as five hours postinjury in 45 of 54 burn patients (83.5%) evaluated by gastroduodenoscopy. Acute ulcers were identified in 14 patients (26%); concomitant duodenal disease was present in 34 patients (76%). Microvascular fibrin thrombi were not demonstrated even though five patients had disseminated intravascular coagulation. Seven patients were examined before nasogastric intubation; four, with a mean burn size of 59.6% total body surface, had diffuse "gastritis." Low total serum protein levels were measured in 81% of tested patients, but were not predictive of mucosal disease. Hemorrhage followed the clinical deterioration of six patients (11.1%); one ulcer perforated. Whereas coagulation abnormalities, nasogastric intubation, and hypoproteinemia may augment mucosal injury, the morphologic and histologic examinations of the lesions suggested a primary ischemic cause resulting from the opening of submucosal shunts or local vasoconstriction.

Blood Proteins↗
PubMed2002

Simulating the swelling and deformation behaviour in soft tissues using a convective thermal analogy.

BACKGROUND: It is generally accepted that cartilage adaptation and degeneration are mechanically mediated. Investigating the swelling behaviour of cartilage is important because the stress and strain state of cartilage is associated with the swelling and deformation behaviour. It is well accepted that the swelling of soft tissues is associated with mechanical, chemical, and electrical events. METHOD: The purpose of the present study was to implement the triphasic theory into a commercial finite element tool (ABAQUS) to solve practical problems in cartilage mechanics. Because of the mathematical identity between thermal and mass diffusion processes, the triphasic model was transferred into a convective thermal diffusion process in the commercial finite element software. The problem was solved using an iterative procedure. RESULTS: The proposed approach was validated using the one-dimensional numerical solutions and the experimental results of confined compression of articular cartilage described in the literature. The time-history of the force response of a cartilage specimen in confined compression, which was subjected to swelling caused by a sudden change of saline concentration, was predicted using the proposed approach and compared with the published experimental data. CONCLUSION: The advantage of the proposed thermal analogy technique over previous studies is that it accounts for the convective diffusion of ion concentrations and the Donnan osmotic pressure in the interstitial fluid.

Adaptation, Physiological↗
PubMed2005

Noise thermal impedance of a diffusive wire.

The current noise density S2 of a conductor in equilibrium, the Johnson noise, is determined by its temperature T: S2 = 4k(B)TG, with G the conductance. The sample's noise temperature T(N) = S2/(4k(B)G) generalizes T for a system out of equilibrium. We introduce the "noise thermal impedance" of a sample as the ratio deltaT(N)omega/deltaP(J)omega of the amplitude deltaT(N)omega of the oscillation of T(N) when heated by an oscillating power deltaP(J)omega at frequency omega. For a macroscopic sample, it is the usual thermal impedance. We show for a diffusive wire how this (complex) frequency-dependent quantity gives access to the electron-phonon interaction time in a long wire and to the diffusion time in a shorter one, and how its real part may also give access to the electron-electron inelastic time. These times are not simply accessible from the frequency dependence of S2 itself.

Journal Article↗
PubMed2003

Ballistic diffusion induced by a thermal broadband noise.

We present a thermal broadband noise from the difference between two Ornstein-Uhlenbeck noises, which can induce a ballistic diffusion, i.e., long-time mean square displacement of a free particle driven by this noise reads proportional to t(2). We apply this noise to a flashing ratchet and the mean velocity of the particle is calculated via Langevin simulation. The results show that a double peak of the mean velocity and flux reversal appears for the ratchet with large and small asymmetries, respectively; the inertia effect induces a large mean velocity and multireversal of flux. These rich and interesting phenomena are explained.

Journal Article↗
PubMed1993

Simultaneous temperature and regional blood volume measurements in human muscle using an MRI fast diffusion technique.

The thermal dependence of the translational diffusion coefficient and of the regional blood volume was investigated in vivo by using a special MR pulsed gradient technique with reduced sensitivity to bulk tissue motion. Measurements were done at 0.5 T, using a small gradient insert. The diffusion coefficient of muscle water was calibrated against thermocouple-measured temperature in vitro, both with the muscle fibers parallel and perpendicular to the diffusion gradient. The maximum muscle temperature variation obtained by percutaneous conduction was -8.8 +/- 1.6 degrees C under cooling and +3.7 +/- 1.6 degrees C under heating, from basal state. Simultaneously the fractional regional blood volume decreased by a factor of 3.5 under cooling and increased by a factor of 2.7 under heating. Due to the interdependence of microcirculation and tissue temperature, this technique may be used to follow heat production or deposition in living tissue (muscle exercise, electromagnetic irradiation, etc.).

Artifacts↗
PubMed2000

Optical and thermal properties of nasal septal cartilage.

BACKGROUNDS AND OBJECTIVES: The aim of the study was to measure the spectral dependence of optical absorption and reduced scattering coefficients and thermal conductivity and diffusivity of porcine nasal septal cartilage. Values of optical and thermal properties determined in this study may aid in determining laser dosimetry and allow selection of an optical source wavelength for noninvasive diagnostics for laser-assisted reshaping of cartilage. MATERIALS AND METHODS: The diffuse reflectance and transmittance of ex vivo porcine nasal septal cartilage were measured in the 400- to 1,400-nm spectral range by using a spectrophotometer. The reflectance and transmittance data were analyzed by using an inverse adding-doubling algorithm to obtain the absorption (mu(a)) and reduced scattering (mu(a)') coefficients. A multichannel thermal probe controller system and infrared imaging radiometer methods were applied to measure the thermal properties of cartilage. The multichannel thermal probe controller system was used as an invasive technique to measure thermal conductivity and diffusivity of cartilage at three temperatures (27, 37, 50 degrees C). An infrared imaging radiometer was used as a noninvasive method to measure the thermal diffusivity of cartilage by using a CO(2) laser source (lambda = 10.6 microm) and an infrared focal plane array (IR-FPA) camera. RESULTS: The optical absorption peaks at 980 nm and 1,180 nm in cartilage were observed and corresponded to known absorption bands of water. The determined reduced scattering coefficient gradually decreased at longer wavelengths. The thermal conductivity values of cartilage measured by using an invasive probe at 27, 37, and 50 degrees C were 4.78, 5.18, and 5.76 mW/cm degrees C, respectively. The corresponding thermal diffusivity values were 1.28, 1.31, and 1.40x 10(-3) cm(2)/sec. Because no statistically significant difference in thermal diffusivity values with increasing temperature is found, the average thermal diffusivity is 1.32 x 10(-3) cm(2)/sec. The numerical estimate for thermal diffusivity obtained from infrared radiometry measurements was 1.38 x 10(-3) cm(2)/sec. CONCLUSION: Values of the spectral dependence of the optical absorption and reduced scattering coefficients, and thermal conductivity and diffusivity of cartilage were measured. The invasive and noninvasive diffusivity measurements were consistent and concluded that the infrared imaging radiometric technique has an advantage to determine thermal properties, because damage to the cartilage sample may be avoided. The measured values of absorption and reduced scattering coefficients can be used for predicting the optical fluence distribution in cartilage and determining optical source wavelengths for the laser-assisted cartilage reshaping studies. The thermal conductivity and diffusivity values can play role in understanding thermal-dependent phenomenon in cartilage during laser irradiation and determining laser dosimetry for the laser-assisted cartilage reshaping studies.

Animals↗
PubMed2002

On the emergence of the Green's function in the correlations of a diffuse field: pulse-echo using thermal phonons.

It is shown that a diffuse field is not devoid of phase information, but has a correlation function equal to the Green's function. More specifically, the cross-correlation between diffuse signals in two transducers is very nearly equal to the direct response of one transducer to an impulse applied to the other. This is true whether the diffuse field is one that was created by a distant source, or (if the detectors are sufficiently sensitive) created by thermal fluctuations in the specimen. Here we outline and review proofs, and laboratory demonstrations, from three recent archival publications.

Journal Article↗
PubMed1987

[Rate of evaporation of tear fluid in the human compared with a physical model].

Evaporation of tears occurs by diffusion, free (thermal), and forced convection. Under resting conditions only diffusion and free convection play a role. Therefore, a device should be applied with only these two parameters working. Creating a stationary known pressure gradient of water vapor over the eye, the evaporation rate was found to be 24.8 +/- 6.8 mg cm-2 h-1 in 21 test persons (no spectacle or contact lens wearers, no known general or eye disease, average age 25.6 years). The same test arrangement over a water surface of 1.7 cm2 gave a value of 43 mg cm-2 h-1 and simplified calculation, applying Fick's law of diffusion, 54 mg cm-2 h-1. These results suggest that there is a water vapor pressure of less than half the saturation water vapor pressure of less than half the saturation water vapor pressure corresponding to 32 degree C over the surface of the eye. Calculation yields a value of 230 mg per eye per 16 hours, corresponding to 32 degrees C (50% air humidity) over the surface of the eye and 22 degrees C (50% air humidity) room temperature. Assuming a tear secretion of 0.6 g per eye per 16 hours (Schirmer), about 40% of this amount evaporates under normal conditions.

Adolescent↗
PubMed2002

A random walk model of skin permeation.

A new mathematical model for permeability of chemicals in aqueous vehicle through skin is presented. The rationale for this model is to represent diffusion by its fundamental molecular mechanism, i.e., random thermal motion. Diffusion is modeled as a two-dimensional random walk through the biphasic (lipid and corneocyte) stratum corneum (SC). This approach permits calculations of diffusion phenomena in a morphologically realistic SC structure. Two concepts are key in the application of the model to the prediction of steady-state skin permeability coefficients: "effective diffusivity" and "effective path length," meaning the diffusivity and thickness of a homogeneous membrane having identical permeation properties as the stratum corneum. Algebraic expressions for these two variables are developed as functions of the molecular weight and octanol-water partition coefficient of the diffusing substance. Combining these with expressions for membrane-vehicle partition coefficient and permeability of the aqueous epidermis enables the calculation of steady-state skin permeability coefficients. The resulting four-parameter algebraic model was regressed against the "Flynn data base" with excellent results (R2 = 0.84: SE = 0.0076; F = 154; N = 94). The model provides insight into the contributions of stratum corneum diffusivity and effective path lengths to overall skin permeability and may prove useful in the prediction of non-steady-state diffusion phenomena.

Diffusion↗
PubMed1989

Treatment of children with port-wine stains using the flashlamp-pulsed tunable dye laser.

Thirty-five children, three months to 14 years of age, with disfiguring port-wine stains were treated with a flashlamp-pulsed tunable dye laser. All had complete clearing of the stains after an average of 6.5 laser treatments to each lesional area; skin over bony prominences required approximately half as many sessions as skin on the cheek. Children less than seven years old required fewer sessions (mean +/- SD, 5.8 +/- 1.1) than older children (7.1 +/- 1.1; P less than 0.05). Treated skin was identical in texture and color to adjacent normal skin in 33 (94.3 percent) of the children, whereas 2 (5.7 percent) had small, isolated, depressed scars in areas accidentally traumatized soon after laser treatment. The only other side effect was transient hyperpigmentation, which occurred in 20 patients (57 percent). These results can be attributed to two distinguishing characteristics of the flashlamp-pulsed tunable dye laser: an emission wavelength of 577 nm, theoretically ideal for selective absorption by the intravascular target oxyhemoglobin, and a pulse duration of 360 microseconds, which closely matches the thermal relaxation time for dermal blood vessels and hence avoids diffuse nonspecific thermal necrosis with subsequent scarring of the treated skin.

Adolescent↗
PubMed2002

Frequency-domain theory of laser infrared photothermal radiometric detection of thermal waves generated by diffuse-photon-density wave fields in turbid media.

A three-dimensional theory of the frequency-domain thermal-wave field generated inside a turbid medium with optical and thermal properties of human tissue is presented. The optical source is treated as a three-dimensional harmonically modulated diffuse-photon-density wave (DPDW) field in the diffusion approximation of the radiative transfer theory. Unlike earlier Green-function-based theoretical models, exact boundary conditions are used based on the requirement that there should be no diffuse photon intensity entering the turbid medium from the outside. Explicit analytical expressions for the DPDW field and for the dependent thermal-wave field are obtained in the spatial Hankel-transform domain. The formalism is further extended to the calculation of the infrared photothermal radiometric signal arising from the nonradiatively generated thermal-wave distribution in turbid media with instantaneous nonradiative deexcitation as well as in media with nonzero fluorescence relaxation lifetimes. Numerical inversions have been performed and presented as examples of selected special cases of the theory. It is found that the present theory with exact DPDW-field boundary conditions is valid throughout the entire domain of the turbid medium, with the exception of the very near-surface ballistic photon "skin layer" (7-50 microm). Photothermal radiometric signals were found to be more reliably predicted than DPDW signals within this layer, due to the depth-integration nature of this detection methodology.

Biophysical Phenomena↗
PubMed2005

Band-broadening in capillary zone electrophoresis with axial temperature gradients.

It is widely accepted that Joule heating effects yield radial temperature gradients in capillary zone electrophoresis (CZE). The resultant parabolic profile of electrophoretic velocity of analyte molecules is believed to increase the band-broadening via Taylor-Aris dispersion. This typically insignificant contribution, however, cannot explain the decrease in separation efficiency at high electric fields. We show that the additional band-broadening due to axial temperature gradients may provide the answer. These axial temperature variations result from the change of heat transfer condition along the capillary, which is often present in CZE with thermostating. In this case, the electric field becomes nonuniform due to the temperature dependence of fluid conductivity, and hence the induced pressure gradient is brought about to meet the mass continuity. This modification of the electroosmotic flow pattern can cause significant band-broadening. An analytical model is developed to predict the band-broadening in CZE with axial temperature gradients in terms of the theoretical plate height. We find that the resultant thermal plate height can be very high and even comparable to that due to molecular diffusion. This thermal plate height is much higher than that due to radial temperature gradients alone. The analytical model explains successfully the phenomena observed in previous experiments.

Electrophoresis, Capillary↗
PubMed1998

Ultrafast DNA analysis by capillary electrophoresis/laser-induced fluorescence detection.

The limits of ultrafast DNA analysis by CE were determined by investigating the influence of the effective capillary length and the electric field strength on the analysis time for a given peak resolution (10 bp). In accordance with theory, the use of a fast ramp power supply for narrow plug electrokinetic injection was found to be essential to minimize the extra column effects on peak dispersion. Two major column dispersion factors, longitudinal diffusion and thermal dispersion, were determined experimentally, as well as the influence of the electric field strength on the electrophoretic mobilities and diffusion coefficients of DNA. It was found that higher field strengths can be applied with lower thermal dispersion than predicted by classical CE models. This was attributed to the faster mass transport in the radial direction due to field-induced DNA orientation. Short capillaries (approximately 3-7 cm effective length) and moderate to high electric field strengths (approximately 600-800 V/cm) were used to perform a series of fast DNA separations. The dsDNA fragment standards phiX174/HaeIII and pBR322/HaeIII were separated within 30 s. The possibility for fast mutation detection was demonstrated using constant denaturant capillary electrophoresis (CDCE) for the analysis of a single base mutation in mitochondrial DNA in 72 s. The potential for fast DNA sequencing was illustrated by separating 300 ssDNA fragments within 180 s.

DNA↗