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PubMed1998

Survival of Listeria monocytogenes in sea water and effect of exposure on thermal resistance.

Survival, recoverability and sublethal injury of two strains of Listeria monocytogenes, Scott A and an environmental strain KM, on exposure to sea water at 12.8 or 20.8 degrees C was determined using in situ diffusion chambers. Plate counts were used to assess recoverability and injury while 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) reduction was used to determine respiratory activity. T90 values (times for 10-fold decreases in numbers of recoverable cells) on non-selective medium (trypticase soya agar with 0.6% yeast extract) at 12.8 and 20.8 degrees C were 61.7 and 69.2 h for L. monocytogenes Scott A, and 103.0 and 67.0 h for L. monocytogenes KM, respectively. On selective medium (Oxford agar), T90 values at 12.8 and 20.8 degrees C were 60.6 and 56.9 h for L. monocytogenes Scott A, and 83.0 and 65.9 h for L. monocytogenes KM, respectively. With Scott A, the percentage of sublethally injured cells at 12.8 and 20.8 degrees C was 1.7 and 17.7%, respectively, while for KM the values were 19.0 and 1.6%, respectively. The fraction of cells reducing CTC but which were not recoverable on plating progressively increased on exposure to sea water. Listeria monocytogenes KM challenged at 58 degrees C showed an apparent increase in heat resistance after exposure to sea water at 20.8 degrees C for 7 d (D58 = 2.64 min) compared with before exposure (D58 = 1.24). This increase in thermal resistance was not apparent at temperatures greater than 63 degrees C, and analysis of the best-fit regression lines fitted to the thermal data obtained from the two cell populations indicated that their thermal resistance was not significantly different (P > 0.05) over the temperature range tested (58-62 degrees C).

Heating↗
PubMed2006

Percolative transport and cluster diffusion near and below the percolation threshold of a porous polymeric matrix.

PURPOSE: The purpose of this research was to develop a quantitative mass transport model to describe the release of a drug from a porous inert matrix dosage form near and below the percolation threshold for the system. METHODS: Cumulative release profiles were generated for a series of tablets composed of a binary mixture of varying amounts of non-conducting (poly(vinyl stearate)) and conducting (benzoic acid) components. The porous microstructure was analyzed using re-constructed three-dimensional images of leached microtomed tablet sections. Poly(vinyl stearate) was characterized for transport properties, molecular weight and thermal properties. RESULTS: Based on percolation theory, the binary matrix was determined to have a percolation threshold of 0.09 +/- 0.02. Transport, which could not be explained by "classical" percolation theory or surface diffusion alone, was observed below the percolation threshold for the system. CONCLUSIONS: A model describing transport near and below the percolation threshold in matrices composed of two phases, polymer and drug, was developed. The percolation model developed accounts for diffusion within the porous structure and through the inert, insoluble polymeric amorphous regions of the matrix. The low percolation threshold and subsequently high coordination was concluded to be due to the biphasic classical porous and nonclassical polymeric diffusional transport mechanisms associated with the system studied.

Algorithms↗
PubMed1984

Characteristics of drug-phospholipid coprecipitates I: Physical properties and dissolution behavior of griseofulvin-dimyristoylphosphatidylcholine systems.

Solid dispersions of griseofulvin and dimyristoylphosphatidylcholine (lecithin) have been prepared as both coprecipitates and physical mixtures, and their physical characteristics and dissolution behavior compared with pure griseofulvin. The dissolution of the physical mixtures was similar to pure drug, but the coprecipitates yielded a 3.5-fold greater initial dissolution rate and a limiting concentration after 60 min which was 72% greater at a griseofulvin-lecithin weight ratio of 19:1. Increasing the lecithin content to 1.5:1 compositions resulted in only a further 50% increase in the initial dissolution rate and a further 12% increase in the limiting concentration. The effect of the pH of the medium on dissolution was slight, but varied with the composition of the system. The phase diagram indicated that these systems have no significant eutectic or solid solution formation. X-ray diffraction spectra further showed that freshly prepared or aged coprecipitates contained griseofulvin crystals, and photomicrographs showed that the crystals essentially retained their characteristic shapes and sizes in all systems. Differential thermal analysis yielded heats of fusion that gave a good linear correlation with the percent of griseofulvin dissolved from coprecipitates at all time intervals, but not with physical mixtures. Furthermore, aged coprecipitates underwent a slower rate of dissolution compared with fresh samples. The results are interpreted to suggest that griseofulvin undergoes improved dissolution from coprecipitates due to the formation of crystals of lower stability. In addition, the rapid dispersion of lecithin in the aqueous medium (as seen microscopically) entraps griseofulvin in myelinic structures and liposomes and effectively increases the saturation concentration of drug in the diffusion layer during the dissolution process.

Chemical Phenomena↗
PubMed2000

[The latest development of the research on Chinese medicine by molecular vibrational spectroscopy].

The latest development of the molecular vibrational spectroscopy (Fourier Transform Raman Spectroscopy and Fourier Transform Infraed Spectroscopy) and the latest application of the non-destructive identification, quantitative analysis, thermal-stability monitoring and Chinese medicine optimizing were described in this paper. Some Chinese crude herbs can be directly and quickly identified by Fourier Transform Raman spectroscopy (FT - Raman) and Diffused Reflection Fourier Transform Infrared Spectroscopy (DR-FTIR). The content of Chinese herbs, medicine and medicament can be quantified without destruction by Diffused Reflection Fourier Transform and Near Infrared Spectroscopy (DR-NIR-FTIR). The mechanism of interaction between the Chinese medicine and some cells or bacteria can be in situ monitored by FT-Raman and HATR-FTIR. Best medicine could be selected and medicament could be optimized according to the injury degree of the cell or bacteria. The decomposing and degenerating process of medicines can also be timely monitored by FT-Raman and the temperature controlled FTIR. These are the latest use of molecular spectroscopy in Chinese medicine. The fast indentification, quantitative analysis monitoring, thermal stability predicting and the optimizing of Chinese herbs, medicine and medicament can be guided by the above mentioned methods. It is proved that these methods are nondestructive to samples, fast accurate, and easy to use.

Drug Stability↗
PubMed1986

The uptake of manganese ions and the apparent thermal transition of the erythrocyte membranes.

The nuclear magnetic resonance manganese doping technique is currently used for the determination of the water diffusional exchange time through human erythrocyte membranes. An apparent thermal transition at 26 degrees C was noticed at 18-30 mM manganese doping in the suspending solution. An analysis in terms of a two-phase nuclear spin exchanging system revealed that apparent thermal transitions are expected to occur in the upper and lower temperature regions. They represent a shift from intermediate exchange rates where water diffusion through the membrane is dominant to either fast or slow exchange rates where proton relaxation is the controlling process. The lower temperature apparent transition may be altered by the intracellular manganese concentration; the lower the Mn2+ concentration the lower the transition. Also according to this interpretation only a fraction of the erythrocytes are significantly permeated by Mn2+. The upper transition depends on the Mn2+ concentration in the extracellular volume; it decreases with decreasing Mn2+ concentration.

Chemical Phenomena↗
PubMed2001

Combining membrane extraction with mobile gas chromatography for the field analysis of volatile organic compounds in contaminated waters.

A mobile gas chromatographic device (Airmobtx HC 1000 monitor manufactured by Airmotec, Germany), originally designed for the analysis of benzene, toluene, ethylbenzene and xylenes (BTEX) in air, was connected to a flow cell for dynamic membrane extraction. Volatile organic compounds (VOCs) diffuse out of a water stream through a hollow fibre, are enriched onto sorption tubes integrated in the mobile device, and are then thermally desorbed and analysed by gas chromatography-flame ionisation detection. Battery operation of the device enables continuous on-site analysis of VOCs. Influences of the water flow-rate on system response and memory effects were investigated. The linear range of the method depends on the flow-rate of the water sample and did not exceed two orders of magnitude. The detection limits for trichloroethene, chlorobenzene and the BTEX compounds were found to be between 0.1 and 1.0 microg/l using a water flow-rate of 30 ml/min. Dynamic membrane extraction combined with the mobile gas chromatographic device was used for the on-site analysis of contaminated waters in the area of Leipzig.

Benzene↗
PubMed2001

The physics of molecular motors.

Molecular motors convert chemical energy into mechanical force and movement. Operating at energies just above those of the thermal bath, these motors experience large fluctuations, and their physical description must be necessarily stochastic. Here, motor operation is described as a biased diffusion on a potential energy surface defined by the interactions of the motor with its track and its fuel. These ideas are illustrated with a model of the rotary movement of the F(o) motor.

Animals↗
PubMed2000

Vortex-like excitations and the onset of superconducting phase fluctuation in underdoped La(2-x)Sr(x)CuO4

Two general features of a superconductor, which appear at the critical temperature, are the formation of an energy gap and the expulsion of magnetic flux (the Meissner effect). In underdoped copper oxides, there is strong evidence that an energy gap (the pseudogap) opens up at a temperature significantly higher than the critical temperature (by 100-220 K). Certain features of the pseudogap suggest that it is closely related to the gap that appears at the critical temperature (for example, the variation of the gap magnitudes around the Fermi surface and their maximum amplitudes are very similar). However, the Meissner effect is absent in the pseudogap state. The nature of the pseudogap state, and its relation (if any) to the superconducting state are central issues in understanding copper oxide superconductivity. Recent evidence suggests that, in the underdoped regime, the Meissner state is destroyed above the critical temperature by strong phase fluctuations (as opposed to a vanishing of the superfluid density). Here we report evidence for vortices (or vortex-like excitations) in La(2-x)Sr(x)CuO4 at temperatures significantly above the critical temperature. A thermal gradient is applied to the sample in a magnetic field. Vortices are detected by the large transverse electric field produced as they diffuse down the gradient (the Nernst effect). We find that the Nernst signal is anomalously enhanced at temperatures as high as 150 K.

Journal Article↗
PubMed2001

Transmyocardial laser revascularization.

Low-powered lasers were first used in the early 1980s to produce transventricular channels as an adjunct to coronary artery bypass graft surgery (CABG). Early results were encouraging, but because of the combined procedure, could not be attributed directly to use of the laser [1]. High-powered lasers were introduced into clinical practice in 1990 [2]. These lasers are powerful enough to create a transmyocardial channel with minimal thermal damage to surrounding tissues [3]. Clinical studies, using transmyocardial laser revascularization (TMR) as the sole operative therapy for patients with severe and diffuse coronary artery disease (CAD) who have Class III or IV angina, and are on medical therapy, have been conducted since 1993. Based on the results of these studies, the FDA granted approval for the use of TMR as a sole therapy. Clinical studies are currently underway to assess the results of combined TMR and CABG [4]. Results of four controlled randomized studies have been published [5-8]. The data from two of these studies formed the basis for FDA approval of two different types of laser systems. The results of these studies have not provided any additional insights into the mechanism of action of TMR, which remains the Achilles' heel of this procedure. In this review, background information about the TMR procedure will be discussed along with an analysis of the recently published randomized studies.

Angina Pectoris↗
PubMed2002

Electronically excited states and transport properties of thermal plasmas: the reactive thermal conductivity.

The role of excited states in affecting the transport of ionization energy in thermal plasmas in the temperature range 10,000 < or = T < or = 25,000 K is discussed by taking into account the dependence of diffusion cross sections on principal quantum number. The results show a strong effect at high pressure, while compensation effects reduce the role of excited states at atmospheric pressure. Extension of the results to nonequilibrium situations is discussed by presenting calculations of effective multicomponent diffusion coefficients. In this case also the presence of excited states dramatically affects these coefficients.

Journal Article↗
PubMed2004

Anomalous transport in unbound and ratchet potentials.

A non-Markovian Langevin equation with a broadband noise is proposed to describe anomalous transport of a particle passing over a potential saddle or moving in a ratchet potential. In the presence of thermal broadband noise, the asymptotic mean square displacement of a free particle is proportional to the square of time; this is called ballistic diffusion. The passing probability of a particle driven by this broadband noise over the saddle of an inverted harmonic potential is obtained analytically. It is shown that the passing probability increases with the kinetic energy, which is slower than that of normal case. The mechanisms of ballistic diffusion and mobility are also applied to the rocking (a square-wave driving force acting on the potential) and flashing (the potential fluctuating between on and off) ratchets. Phenomena such as acceleration and double-peak mean velocity are observed.

Journal Article↗
PubMed2005

Relaxation of the distribution function tails for systems described by Fokker-Planck equations.

We study the formation and the evolution of velocity distribution tails for systems with weak long-range interactions. In the thermal bath approximation, the evolution of the distribution function of a test particle is governed by a Fokker-Planck equation where the diffusion coefficient depends on the velocity. We extend the theory of Potapenko et al [Phys. Rev. E 56, 7159 (1997)] developed for power-law diffusion coefficients to the case of an arbitrary form of diffusion coefficient and friction force. We study how the structure and the progression of the front depend on the behavior of the diffusion coefficient and friction force for large velocities. Particular emphasis is given to the case where the velocity dependence of the diffusion coefficient is Gaussian. This situation arises in Fokker-Planck equations associated with one dimensional systems with long-range interactions such as the Hamiltonian mean field (HMF) model and in the kinetic theory of two-dimensional point vortices in hydrodynamics. We show that the progression of the front is extremely slow (logarithmic) in that case so that the convergence towards the equilibrium state is peculiar. Our general formalism can have applications for other physical systems such as optical lattices.

Journal Article↗
PubMed2004

Nuclear spin dynamics in the quantum regime of a single-molecule magnet.

We show that the nuclear spin dynamics in the single-molecule magnet Mn12-ac below 1 K is governed by quantum tunneling fluctuations of the cluster spins, combined with intercluster nuclear spin diffusion. We also obtain the first experimental proof that-surprisingly-even deep in the quantum regime the nuclear spins remain in good thermal contact with the lattice phonons. We propose a simple model for how T-independent tunneling fluctuations can relax the nuclear polarization to the lattice that may serve as a framework for more sophisticated theories.

Journal Article↗
PubMed2005

The allosteric transition in DnaK probed by infrared difference spectroscopy. Concerted ATP-induced rearrangement of the substrate binding domain.

The biological activity of DnaK, the bacterial representative of the Hsp70 protein family, is regulated by the allosteric interaction between its nucleotide and peptide substrate binding domains. Despite the importance of the nucleotide-induced cycling of DnaK between substrate-accepting and releasing states, the heterotropic allosteric mechanism remains as yet undefined. To further characterize this mechanism, the nucleotide-induced absorbance changes in the vibrational spectrum of wild-type DnaK was characterized. To assign the conformation sensitive absorption bands, two deletion mutants (one lacking the C-terminal alpha-helical subdomain and another comprising only the N-terminal ATPase domain), and a single-point DnaK mutant (T199A) with strongly reduced ATPase activity, were investigated by time-resolved infrared difference spectroscopy combined with the use of caged-nucleotides. The results indicate that (1) ATP, but not ADP, binding promotes a conformational change in both subdomains of the peptide binding domain that can be individually resolved; (2) these conformational changes are kinetically coupled, most likely to ensure a decrease in the affinity of DnaK for peptide substrates and a concomitant displacement of the lid away from the peptide binding site that would promote efficient diffusion of the released peptide to the medium; and (3) the alpha-helical subdomain contributes to stabilize the interdomain interface against the thermal challenge and allows bidirectional transmission of the allosteric signal between the ATPase and substrate binding domains at stress temperatures (42 degrees C).

Adenosine Diphosphate↗
PubMed1975

Heat transport in laminar flow of erythrocyte suspensions.

Measurements of thermal conductivity were made in laminar flow of dog and turkey erythrocyte suspensions in a stainless stell tube of about 1 mm ID. These measurements were independent of the shear rate, showing that the red cell motion relative to plasma in flowing blood had no effect on the heat transfer. Measurements of thermal conductivity were further made in suspensions of polystyrene spheres of 100 mum and were found to be dependent upon the shear rate. The Graetz solution corresponding to uniform wall temperature was used for determining the value of thermal conductivity in an apparatus calibrated with tap water. The overall accuracy of the results is within 10%. A model based on the particle rotation with the entrained fluid is proposed. It is pointed out that the diffusion of platelets, red cells, and possibly plasma proteins (such as fibrinogen) will be augmented if they happen to be in the hydrodynamic field of rotating erythrocytes.

Animals↗
PubMed2001

A qualitative and quantitative study of the lung of an ostrich, Struthio camelus.

The ostrich lung, with its lack of interparabronchial septa, the presence of very shallow atria and exceptional morphometric refinement, structurally resembles those of small, energetic flying birds, whereas it also displays features characteristic of the flightless ratites in which the neopulmo is relatively poorly developed and a segmentum accelerans may be generally lacking. The large size of the bronchial system of the ostrich may help explain the unique shifts in the airflow pathways that must occur from resting to panting breathing, explaining its insensitivity to acid-base imbalance of the blood during sustained panting under thermal stress. The mass-specific volume of the lung is 39.1 cm(3)kg(-1) and the volume density of the exchange tissue is remarkably high (78.31%). The blood-gas (tissue) barrier is relatively thick (0.56 microm) but the plasma layer is very thin (0.14 microm). In this flightless ratite bird, the mass-specific surface area of the tissue barrier (30.1 cm(2)g(-1)), the mass-specific anatomical diffusing capacity of the tissue barrier for oxygen (0.00 22 ml O(2) s(-1) Pa(-1) kg(-1)), the mass-specific volume of pulmonary capillary blood (6.25 cm(3)kg(-1)) and the mass-specific total anatomical diffusing capacity for oxygen (0.00073 ml O(2) s(-1) Pa(-1) kg(-1)) are equivalent to or exceed those of much smaller highly aerobic volant birds. The distinctive morphological and morphometric features that seem to occur in the ostrich lung may explain how it achieves and maintains high aerobic capacities and endures long thermal panting without experiencing respiratory alkalosis.

Animals↗
PubMed1993

Dynamic light scattering of aqueous solutions of linear aggregates induced by thermal denaturation of ovalbumin.

Dynamic light scattering measurements were performed on dilute aqueous solutions of native ovalbumin (OA) and on those of linear OA aggregates induced by thermal denaturation at low ionic strength and neutral pH. The weight-average molecular weight MW of four aggregates tested ranged from 1,700,000 to 5,500,000. The translational diffusion coefficient D0 of native OA at infinite dilution was estimated as 8.70 x 10(-7) cm2/s, which gave 56.0 A as the diameter of the rigid spherical particle. The intensity autocorrelation function of linear OA polymers was analyzed with the cumulant method to obtain the first cumulant gamma e. The dependence of gamma e on the scattering vector q at very low polymer concentration was found intermediate between those of a flexible chain and a rigid rod. The translational diffusion coefficient Dtr [identical to (gamma e/q2)q-->0] was in proportion to M-0.55W, and the magnitude was in good agreement with a value calculated from the wormlike cylinder model with values of three parameters determined in an earlier study, ML = 1600 A-1, d = 120 A, and Q = 230 A, where ML, d, and Q are the molecular weight per unit length, diameter, and persistence length, respectively. Based on these results, a new model, to be called as the dimer model, was proposed to interpret the formation mechanism of linear OA polymers induced by thermal denaturation.

Animals↗
PubMed1990

Multiple breath washout of He and SF6 in panting dogs.

Pulmonary gas transport mechanisms in panting were studied by multiple breath washout of two poorly soluble inert gases of similar solubility but different diffusivity (He and SF6). The experiments were performed in 6 chronically tracheotomized conscious dogs (mean body weight 31.0 kg) which, upon exposure to elevated room temperature, were enforced to thermal panting (mean breathing frequency 288/min). After equilibration of lung gas with 1% He and 1% SF6 followed by changeover to test gas-free air, end-tidal gas concentrations during multiple breath washout were recorded by mass spectrometry. The washout time course was analyzed into 3 exponential components. The initial fast component was considered to be in part determined by the transient response of the measuring system, whereas the intermediate and the slow component could be attributed to lung washout. The mean He/SF6 ratio of medium and slow rate constants was 1.06 and 1.13, respectively (both values differing from 1.0 at P less than 0.001). It is concluded that gas transport in dog lungs during panting was mainly determined by convection, diffusion-dependent processes being discernible but playing a minor role.

Animals↗