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PubMed2003

Investigation of the diffusion coefficient of polymers and micelles in aqueous solutions using the Soret effect in cw-laser thermal lens spectrometry.

The concentration gradient (Soret effect) induced in cw-laser thermal lens spectrometry subsequently to the formation of the thermal gradient (thermal lens effect) has been investigated in aqueous solutions of various macromolecular species including micelles, mixed micelles and polymers. It is shown that the build-up of the concentration gradient is much shorter than that in classical Soret experiments, reaching steady-state values in less than 1 min. The time evolution of the Soret signal has been used to derive mass-diffusion times from which mass-diffusion coefficients were calculated. Our data are in agreement with previous results obtained from quasi-elastic light scattering studies for the micellar solutions and calculated from a known molecular weight-dependent power law for polymer solutions.

Diffusion↗
PubMed2004

Luminescence emission spectra in the temperature range of the structural phase transitions of Na2SO4.

The spectral properties of Na2SO4 have been studied by means of infrared stimulated luminescence (IRSL), thermoluminescence (TL) and radioluminescence (RL) in the range of 200-800 nm. The observed changes in the RL emission spectra after an annealing treatment (400 degrees C for 1 h) could be linked to thermal phase transformations and alkali self-diffusion through the lattice of this salt. Despite the complexity of the luminescence spectra structure, five emission bands peaked at 330, 345, 385, 460 and 630 nm could be distinguished. The UV-blue TL emission of this material exhibits a maximum peaked at 230 degrees C which is well correlated with the differential thermal analysis (DTA) and can be associated with the thermal transformation of the orthorhombic sodium sulphate (Na2SO4) V (thenardite) phase into Na2SO4 III, II and I phases. Taking into account the observed changes on the structural phase transition by X-ray diffraction (XRD) from 16 degrees C onwards, this material does not show satisfactory features for radiation dosimetry, but could be employed for temperature calibration of TL readers.

Crystallization↗
PubMed2005

Exact dynamics of a reaction-diffusion model with spatially alternating rates.

We present the exact solution for the full dynamics of a nonequilibrium spin chain and its dual reaction-diffusion model, for arbitrary initial conditions. The spin chain is driven out of equilibrium by coupling alternating spins to two thermal baths at different temperatures. In the reaction-diffusion model, this translates into spatially alternating rates for particle creation and annihilation, and even negative "temperatures" have a perfectly natural interpretation. Observables of interest include the magnetization, the particle density, and all correlation functions for both models. Two generic types of time dependence are found: if both temperatures are positive, the magnetization, density, and correlation functions decay exponentially to their steady-state values. In contrast, if one of the temperatures is negative, damped oscillations are observed in all quantities. They can be traced to a subtle competition of pair creation and annihilation on the two sublattices. We comment on the limitations of mean-field theory and propose an experimental realization of our model in certain conjugated polymers and linear chain compounds.

Journal Article↗
PubMed2003

Localization properties of the anomalous diffusion phase in the directed trap model and in the Sinai diffusion with a bias.

We study the localization properties of the anomalous diffusion phase x approximately t(micro) with 0 0 and corresponds to the Golosov localization. For finite micro we thus generalize the usual real space renormalization method to allow for the spreading of the thermal packet over many renormalized valleys. Our construction allows one to compute exact series expansions in micro for all observables: to compute observables at order micro (n), it is sufficient to consider in each sample a spreading of the thermal packet onto at most (1+n) traps. So our approach provides a description of the structure of the thermal packet sample by sample, and a full statistical characterization of the important traps at a given order in micro. For the directed trap model, we show explicitly up to order micro(2) how to recover the exact expressions for the diffusion front, the thermal width, and the localization parameter Y2. We then use our method to derive exact results for the localization parameters Y(k) for arbitrary k, the correlation function of two particles, and the generating function of thermal cumulants. We then explain how these results apply to the Sinai diffusion with bias by deriving the quantitative mapping between the large-scale renormalized descriptions of the two models. Finally we study the internal structure of the effective "traps" for the Sinai model via path-integral methods.

Journal Article↗
PubMed2002

Alteration of pore properties of Escherichia coli OmpF induced by mutation of key residues in anti-loop 3 region.

The Escherichia coli OmpF pore is governed by an internal constriction consisting of the negatively charged loop 3 folded into the lumen and the positively charged barrel wall located on the opposite side across the pore, 'anti-loop 3'. To investigate the role of anti-loop 3 in solute diffusion, four site-directed mutations, K16A, K16D, R132A and R132D, were introduced into this eyelet region. The mutant porins were expressed efficiently and inserted into the outer membrane, and the thermal stabilities of the resulting trimers were determined. Diffusion of cefepime, a recently developed cephalosporin, was analysed in vivo. In vitro studies were performed on purified porins reconstituted in planar lipid bilayers to measure conductance, selectivity and voltage closure, as well as in liposomes for patch-clamp and sugar-swelling assays. All substitutions modified the ion-channel parameters, and minor conformational changes in the OmpF eyelet region were predicted from modelling studies. Our data show that Lys-16, and to a lesser extent Arg-132, are involved in voltage-gating and pore selectivity via their side-chain charges. Substitution K16D, which causes a severe decrease in critical voltage (V(c)), may generate a channel susceptible to membrane potential, which perturbs cefepime diffusion. These results suggest that the Lys-16 residue plays an important role in the process of diffusion through the OmpF lumen.

Arginine↗
PubMed1984

The relationship of lining thickness and thermal insulating efficiency.

The minimum thickness of a lining material that must be inserted into a cavity in order to afford protection to the dental pulp from thermal trauma has never been determined. By taking the diffusivity ratios of the hard dental tissues, amalgam and lining materials and equating them with the situations incurred in the transmission of thermal energy by the unfilled, as against the restored tooth, it becomes possible to produce a simple table from which measurements serving as guidelines for adequate protection can be taken. An experimental method of confirmation of the hypothesis is described.

Dental Cavity Lining↗
PubMed2002

Water diffusion in the rabbit lens in vivo.

PURPOSE: To examine water diffusion in the crystalline lens and sugar cataracts in the rabbits in vivo. MATERIALS AND METHODS: Water self-diffusion in the lens cortices of alloxan-diabetic and galactosemic rabbits was examined with magnetic resonance imaging (MRI). The animals were positioned in a 4.7-tesla animal system in conjunction with a 1-inch surface coil for the eye. Diffusion-weighted MRI was conducted using a pulsed-gradient spin-echo sequence with a gradient strength of 0-6 Gs/cm in the primary and secondary coordinates. Other MRI parameters included TR (repetition time)/TE (echo time) = 2,000/10 ms, a field of view of 4 cm, and a 256 x 128 matrix. RESULTS: There appeared an increase in water relaxation resulting in an increase of % (equatorial cortex depth)/(lens long axis) from 18 in the lenses of normal rabbits to 30.4 and 39.9 in the lenses of galactosemic and diabetic rabbits, respectively. In addition, water diffusion changed in the lens of the diabetic rabbit with an increasing intracellular fluidity along the long axis of the cortical fibers, for example, the diffusion coefficient changed from a normal of 0.48 to 0.96 x 10(-5) cm2 s-1 in the lens of the diabetic rabbit. These results showed altered water mobility due to subcellular disturbances occurring before any apparent lens opacities. Further, there also was an increase in the water diffusivity in the aqueous humor from a normal of 1.77 to 2.67 x 10(-5) cm2 s-1 in the galactosemic rabbit eye suggesting an increase in either free water proportion or thermal convection. CONCLUSIONS: Resistance to water self-diffusion appeared to relate to lens fiber orientation and intracellular protein order. Diffusion imaging therefore can be used to examine water self-diffusion to detect early osmotic alteration of lens fibers.

Animals↗
PubMedDate not supplied

The effects of random directional distributed flow in nuclear magnetic resonance imaging.

Capillary flow or microscopic random directional coherent flow as a model of perfusion is investigated both theoretically and experimentally. In the model, we assumed that molecular motion within a finite resolvable volume element (voxel) is a superposition of flow of randomly oriented small capillaries. In such a case, the observed signal from the capillary flow within a voxel will be attenuated in signal amplitude without any change in phase. Although this attenuation effect is similar to the diffusion phenomenon, it differs basically in the following aspects: since the motion in each capillary segment is coherent, phase cancellation occurs at even echoes due to spin rephasing, while the diffusion phenomenon is a purely random Brownian motion of the thermally agitated molecules, changing both in direction and speed during the measurement period. Because of the random character of diffusion, even-echo rephasing cannot be observed. Thus capillary flow or perfusionlike microscopic flow can be measured based on the above distinct flow characteristics, i.e., signal restoration at even echoes versus signal amplitude attenuation at odd echoes. By applying a suitable mathematical algorithm, information on the capillary flow alone can be extracted from the two separate distinct measurements, i.e., one with a single echo and the other with a double echo. Both a theoretical calculation of the capillary flow, as well as the experimental results with a human volunteer by a 0.6-T nuclear magnetic resonance imager, are presented.

Algorithms↗
PubMed1989

Fluorescence digital microscopy of interstitial macromolecular diffusion in burn injury.

Computer vision techniques implemented on an IBM PC/AT have been applied to the study of microvascular permeability and interstitial diffusion in dorsal skin flap chamber preparations of hamsters. Experimental data was obtained for the leakage of fluorescent labelled dextran (70,000 daltons) after a precisely controlled mild degree of localized thermal trauma and compared with control data acquired prior to burn injury. Computer vision analysis techniques were applied to convert the fluorescent images into two-dimensional concentration maps. Interstitial diffusion coefficient values were computed from measured extravascular concentration profiles around a vessel of interest, assuming cylindrical or rectangular geometry, and optimally fitting a diffusion model to the data. An increase in the apparent diffusivity after mild thermal trauma was observed. Novel techniques were applied to solve hardware problems related to data acquisition and analysis, and a new library of software was developed to handle specific image processing requirements.

Animals↗
PubMed2000

Local hyperthermia with MR-guided focused ultrasound: spiral trajectory of the focal point optimized for temperature uniformity in the target region.

The objective of hyperthermia treatment is to deliver a similar therapeutic thermal dose throughout the target volume within a minimum amount of time. We describe a noninvasive approach to this goal based on magnetic resonance imaging (MRI)-guided focused ultrasound (FUS) with a spherical transducer that can be moved along two directions inside the bed of a clinical MR imager and that has an adjustable focal length in the third dimension. Absorption of FUS gives rise to a highly localized thermal buildup, which then spreads by heat diffusion and blood perfusion. A uniform temperature within a large target volume can be obtained using a double spiral trajectory of the transducer focal point together with constant and maximum FUS power. Differences between the real and target temperatures during the first spiral are evaluated in real time with temperature MRI and corrected for during the second spiral trajectory employing FUS focal point velocity modulation. Once a uniform temperature distribution is reached within the entire volume, FUS heating is applied only at the region's boundaries to maintain the raised temperature levels. Heat conduction, together with the design and timing of the trajectories, therefore ensures a similar thermal dose for the entire target region. Good agreement is obtained between theory and experimental results in vitro on gel phantoms, ex vivo on meat samples, and in vivo on rabbit thigh muscle. Edema in muscle was visible 1 hour after hyperthermia as a spatially uniform rise of the signal intensity in T(2)-weighted images.

Animals↗
PubMed1982

Underestimation of thermal lung water volume in patients with high cardiac output.

When utilizing the intravascular double-indicator dilution technique to measure extravascular lung water, blood flow may be so high that diffusion equilibrium of the diffusible indicator fails to occur and the water distribution space is underestimated during the first 7 days after thermal injury. We serially measured cardiac index and lung water in five severely burned patients (mean age 24 years, range 18 to 33 years; mean burn size 56% total body surface, range 43% to 80%) by a rebreathing method utilizing two gases of differing solubility and by the thermal-indocyanine green dye (ICG) double-indicator dilution technique. Rebreathing lung water, determined by a time- and blood flow-insensitive method, increased significantly over the study period, from 6.6 ml/kg on admission to the hospital 11.3 ml/kg on postburn day 6 (+70%, P less than 0.01). Thermal-ICG lung water decreased slightly as blood flow rose. Rebreathing lung water correlated with clinical data in a patient with pulmonary edema, while thermal-ICG lung water changed in the opposite direction. Our data suggest that the thermal-ICG technique may be diffusion limited by short transit times at the high flows characteristic of burned and other critically ill patients with hyperdynamic circulations. Additionally, segmented redistribution of pulmonary blood flow known to occur in burn patients may contribute to underestimation of lung water.

Adolescent↗
PubMed2005

A finite difference thermal model of a cylindrical microwave heating applicator using locally conformal overlapping grids: part I--theoretical formulation.

In this paper, we present a versatile mathematical formulation of a newly developed 3-D locally conformal Finite Difference (FD) thermal algorithm developed specificallyfor coupled electromagnetic (EM) and heat diffusion simulations utilizing Overlapping Grids (OGFD) in the Cartesian and cylindrical coordinate systems. The motivation for this research arises from an attempt to characterize the dominant thermal transport phenomena typically encountered during the process cycle of a high-power, microwave-assisted material processing system employing a geometrically composite cylindrical multimode heating furnace. The cylindrical FD scheme is only applied to the outer shell of the housing cavity whereas the Cartesian FD scheme is used to advance the temperature elsewhere including top and bottom walls, and most of the inner region of the cavity volume. The temperature dependency of the EM constitutive and thermo-physical parameters of the material being processed is readily accommodated into the OGFD update equations. The time increment, which satisfies the stability constraint of the explicit OGFD time-marching scheme, is derived. In a departure from prior work, the salient features of the proposed algorithm are first, the locally conformal discretization scheme accurately describes the diffusion of heat and second, significant heat-loss mechanisms usually encountered in microwave heating problems at the interfacial boundary temperature nodes have been considered. These include convection and radiation between the surface of the workload and air inside the cavity, heat convection and radiation between the inner cavity walls and interior cavity volume, and free cooling of the outermost cavity walls.

Algorithms↗
PubMed2005

Potentiometric, spectroscopic and thermal studies on the metal chelates of 1-(2-thiazolylazo)-2-naphthalenol.

The synthesis and characterization of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pd(II) and UO2(II) chelates of 1-(2-thiazolylazo)-2-naphthalenol (TAN) were reported. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 degrees C and 0.1 M ionic strength. The solid complexes were characterized by elemental and thermal analyses, molar conductance, IR, magnetic and diffuse reflectance spectra. The complexes were found to have the formulae [M(L)2] for M = Mn(II), Co(II), Ni(II), Zn(II) and Cd(II); [M(L)X].nH2O for M = Cu(II) (X = AcO, n = 3), Pd(II) (X = Cl, n = 0) and UO2(II) (X = NO3, n = 0), and [Fe(L)Cl2(H2O)].2H2O. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the ligand is coordinated to the metal ions in a terdentate manner with ONN donor sites of the naphthyl OH, azo N and thiazole N. An octahedral structure is proposed for Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II) and UO2(II) complexes and a square planar structure for Cu(II) and Pd(II) complexes. The thermal behaviour of these chelates shows that water molecules (coordinated and hydrated) and anions are removed in two successive steps followed immediately by decomposition of the ligand molecule in the subsequent steps. The relative thermal stability of the chelates is evaluated. The final decomposition products are found to be the corresponding metal oxides. The thermodynamic activation parameters, such as E*, delta H*, delta S* and delta G* are calculated from the TG curves.

Azo Compounds↗
PubMed1998

Dynamics of the Lens culinaris agglutinin-lactotransferrin and serotransferrin complexes, followed by fluorescence intensity quenching of fluorescein (FITC) with iodide and temperature.

Dynamics of the fluorescent Lens culinaris agglutinin-fluorescein complex (LCA-FITC) are studied in absence and in presence of two glycoproteins, lactotransferrin (LTF) and serotransferrin (STF). Glycans of the serotransferrin are not fucosylated, while those of the lactotransferrin have an alpha-1,6-fucose bound to the N-acetylglucosamine residue linked to the peptide chain, and an alpha-1,3-fucose bound to the N-acetyllactosamine residues. Interaction between the lectin and the two glycoproteins occurs via the carbohydrate residues. Affinity between LCA and LTF is 50 times higher than that between LCA and STF, as a result of the alpha-1, 6-fucose-LCA linkage. In the present work, we studied the effect of the tight bond between the alpha-1,6-fucose and LCA on the dynamics of the amino acids of the lectin, by fluorescence intensity quenching with iodide and by thermal intensity quenching. Fluorescence intensity quenching with iodide indicates that the bimolecular diffusion constant of iodide is 2.402+/-0.068x109 and 1. 160+/-0.090x109 M-1 s-1, when the interaction occurs with free fluorescein and with fluorescein bound to LCA, respectively. Binding of STF or LTF to the LCA-FITC complex yields a bimolecular diffusion constant of 1.675+/-0.06x109 and 1.155+/-0.087x109 M-1 s-1, respectively. Thermal intensity quenching does not occur for fluorescein free in solution while it is linear with temperature with a relative change of 0.656%, 0.889% and 0.488% for FITC-LCA, FITC-LCA-LTF and FITC-LCA-STF complexes, respectively. Fluorescence intensity quenching with iodide and thermal quenching experiments indicate that the dynamics of LCA increase as the result of the flexibility of the carbohydrate residues (case of STF-LCA complex), and the presence of the alpha-1,6-fucose inhibits the effect of the other carbohydrate residues as the result of the tight bond that exists between the fucose and the lectin (case of LTF-LCA complex).

Fluorescein-5-isothiocyanate↗
PubMed2006

In vivo assessment of radio frequency induced thermal damage of kidney using optical spectroscopy.

PURPOSE: Radio frequency ablation is a promising modality for treating small renal tumors. Several studies have been published showing its efficacy. A major drawback in the current management of renal tumors with radio frequency ablation is the lack of an effective modality to accurately monitor the progress of the ablation zone in real-time fashion. Previous studies have demonstrated the feasibility of using optical spectroscopy to assess tissue thermal damage, especially in hepatic lesions. We examined the feasibility of this technology in the setting of renal radio frequency ablation. MATERIALS AND METHODS: A portable spectroscopic system was used to acquire in vivo fluorescence and diffuse reflectance spectra from porcine renal tissue undergoing radio frequency ablation in real-time fashion with simultaneous temperature recordings. Fluorescence and diffuse reflectance spectral data were then correlated with various degrees of thermal damage and temperature recordings. RESULTS: The most noticeable change in fluorescence characteristics of renal tissue resulting from thermal coagulation was a strong decrease in fluorescence intensity between 400 and 550 nm. When fully coagulated, a significant increase in diffuse reflectance intensity was observed between 500 and 800 nm. CONCLUSIONS: Optical spectroscopy, specifically fluorescence and diffuse reflectance spectroscopy, differs significantly in porcine renal tissues with varying degrees of thermal damage from radio frequency ablation in an in vivo setting. Future clinical studies with sufficient sample size are required to validate the potential of these findings. Optical diagnostics may prove to be a rapid, noninvasive, low cost option for monitoring the tumor response to radio frequency based ablative techniques. It may be integrated into future radio frequency ablation probes.

Animals↗
PubMed2005

Length dependence of carbon nanotube thermal conductivity and the "problem of long waves".

We present the first calculations of finite length carbon nanotube thermal conductivity that extend from the ballistic to the diffusive regime, throughout a very wide range of lengths and temperatures. The long standing problem of vanishing scattering of the "long wavelength phonf dramatically here, making the thermal conductivity diverge as the nanotube length increases. We show that the divergence disappears if 3-phonon scattering processes are considered to second or higher order. Nevertheless, for defect free nanotubes, the thermal conductivity keeps increasing up to very large lengths (10 gm at 300 K). Defects in the nanotube are also able to remove the long wavelength divergence.

Computer Simulation↗
PubMed2005

RESTORE: robust estimation of tensors by outlier rejection.

Signal variability in diffusion weighted imaging (DWI) is influenced by both thermal noise and spatially and temporally varying artifacts such as subject motion and cardiac pulsation. In this paper, the effects of DWI artifacts on estimated tensor values, such as trace and fractional anisotropy, are analyzed using Monte Carlo simulations. A novel approach for robust diffusion tensor estimation, called RESTORE (for robust estimation of tensors by outlier rejection), is proposed. This method uses iteratively reweighted least-squares regression to identify potential outliers and subsequently exclude them. Results from both simulated and clinical diffusion data sets indicate that the RESTORE method improves tensor estimation compared to the commonly used linear and nonlinear least-squares tensor fitting methods and a recently proposed method based on the Geman-McClure M-estimator. The RESTORE method could potentially remove the need for cardiac gating in DWI acquisitions and should be applicable to other MR imaging techniques that use univariate or multivariate regression to fit MRI data to a model.

Algorithms↗