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PubMed2004

Transient temperature rise due to ultrasound absorption at a bone/soft-tissue interface.

Thermal effects due to high ultrasound absorption in bone pose an ongoing safety issue. Of considerable concern is the heating of the soft tissue adjacent to the bone surface. Mathematical models can be useful in predicting the transient temperature near the interface during insonation. This paper develops a model that provides the temperature field in terms of simple expressions that convey the functional dependence of the material properties, and are easily incorporated into standards and ultrasound machine software, yet are able to incorporate the material properties of both bone and soft tissue. The model contains an asymptotic theory based upon a "high-attenuation" assumption: the distance diffused by heat over the time of interest is large compared to the ultrasound attenuation length. Model predictions of temperature rise and location of maximum temperature were in close agreement with finite-element calculations, using parameters appropriate for radiation-force imaging and focused-ultrasound surgery.

Animals↗
PubMed2004

Partitioning of evaporative water loss in white-winged doves: plasticity in response to short-term thermal acclimation.

We investigated changes in the relative contributions of respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) to total evaporative water loss (TEWL) in response to short-term thermal acclimation in western white-winged doves Zenaida asiatica mearnsii. We measured REWL, CEWL, oxygen consumption and carbon dioxide production in a partitioned chamber using flow-through respirometry. In doves housed for 2-4 weeks in a room heated to ca. 43 degrees C during the day, TEWL increased from 5.5+/-1.3 mg g(-1) h(-1) at an air temperature (T(a)) of 35 degrees C to 19.3+/-2.5 mg g(-1) h(-1) at T(a)=45 degrees C. In doves housed at room temperature for the same period, TEWL increased from 4.6+/-1.1 mg g(-1) h(-1) at T(a)=35 degrees C to 16.1+/-4.6 mg g(-1) h(-1) at T(a)=45 degrees C. The CEWL of heat-acclimated doves increased from 3.6+/-1.2 mg g(-1) h(-1) (64% of TEWL) at 35 degrees C to 15.0+/-2.1 mg g(-1) h(-1) (78% of TEWL) at T(a)=45 degrees C. Cool-acclimated doves exhibited more modest increases in CEWL, from 2.7+/-0.7 mg g(-1) h(-1) at T(a)=35 degrees C to 7.8+/-3.4 mg g(-1) h(-1) at T(a)=45 degrees C, with the contribution of CEWL to TEWL averaging 53% over this T(a) range. Cool-acclimated doves became mildly hyperthermic (body temperature T(b)=42.9+/-0.4 degrees C) and expended 35% more energy relative to heat-acclimated doves (T(b)=41.9+/-0.6 degrees C) at T(a)=45 degrees C, even though TEWL in the two groups was similar. In each of the two groups, metabolic rate did not vary with T(a), and averaged 7.1+/-0.5 mW g(-1) in cool-acclimated doves and 6.3+/-0.8 mW g(-1) in heat-acclimated doves. The differences in TEWL partitioning we observed between the two experimental groups resulted from a consistently lower skin water vapour diffusion resistance (r(v)) in the heat-acclimated doves. At T(a)=45 degrees C, r(v) in the cool-acclimated doves was 120+/-81 s cm(-1), whereas r(v) in the heat-acclimated doves was 38+/-8 s cm(-1). Our data reveal that in Z. a. mearnsii, TEWL partitioning varies in response to short-term thermal acclimation.

Acclimatization↗
PubMed2004

The use of 19F spectroscopy and diffusion-weighted MRI to evaluate differences in gene-dependent enzyme prodrug therapies.

To evaluate noninvasive measures of gene expression and tumor response in a gene-dependent enzyme prodrug therapy (GDEPT), a bifunctional fusion gene between Saccharomyces cerevisiae cytosine deaminase (CD) and Haemophilus influenzae uracil phosphoribosyltransferase (UPRT) was constructed. CD deaminates 5-fluorocytosine (5FC) to 5-fluorouracil (5FU), and UPRT subsequently converts 5FU to fluorouridine monophosphate, and both of these reactions can be monitored noninvasively in vitro and in vivo using 19F magnetic resonance spectroscopy (MRS). Following transient transfection the CD-UPRT fusion protein exhibited both UPRT and CD enzymatic activities as documented by 19F MRS. In addition, an increase in CD activity and thermal stability was witnessed for the fusion protein compared to native CD. Stable expression of CD-UPRT in 9L glioma cells increased both 5FC and 5FU sensitivity in vitro compared to CD-expressing and wild-type 9L cells. Noninvasive 19F MRS of both CD and UPRT gene function in vivo demonstrated that in animals bearing CD-expressing tumors there was limited conversion of 5FC to 5FU with no measurable accumulation of cytotoxic fluorinated nucleotides (F-nucs). In contrast, CD-UPRT-expressing tumors had increased CD gene activity with a threefold higher intratumoral accumulation of 5FU and significant generation of F-nucs. Finally, CD-UPRT yielded increased efficacy in an orthotopic animal model of high-grade glioma. More importantly, early changes in cellular water mobility, which are felt to reflect cellular death, as measured by diffusion-weighted MRI, were predictive of both durable response and increased animal survival. These results demonstrate the increased efficacy of the CD-UPRT GDEPT compared to CD alone both biochemically and in a preclinical model and validate both 19F MRS and diffusion-weighted MRI as tools to assess gene function and therapeutic efficacy.

Animals↗
PubMed1987

Quantitative cryomicroscopic analysis of intracellular freezing of granulocytes without cryoadditive.

Purified human granulocytes were frozen in isotonic saline at different constant cooling rates down to -60 degrees C and subsequently thawed on the thermally defined cryostage of a cryomicroscope. Cells monitored on videotape were examined with respect to cooling rate threshold, type, and temperature of intracellular ice formation during cooling and recrystallization during warming. Two apparently different mechanisms of intracellular ice formation (iif) were distinguished during cooling, i.e., "twitching" (no visible ice front) and "darkening" (diffuse ice front). Both types of iif are related to cooling rate and hence also to dehydration. Cooling rate thresholds and temperatures of intracellular recrystallization were determined. It was found that twitching iif occurs just about 6.3 to 7.4 degrees C above the homogeneous nucleation temperature, suggesting that it might be catalyzed by nucleators present within the cells. Darkening iif, on the other hand, was observed at much higher temperatures, i.e., 23.4 to 28.3 degrees C above the homogeneous nucleation temperature, which could possibly indicate a nucleation induced by extracellular ice crystals (at a cooling rate of 30 degrees K/min, however, darkening iif was observed to occur at a temperature lower than that required for twitching iif). The proposed mechanisms of cryoinjury are related to membrane integrity measurements presented in M. W. Scheiwe, Ch. Körber, and S. Englich, Cryo-Letters, 5, 300-306, 1984.

Blood Preservation↗
PubMed2005

Preparation of organic-inorganic composite anion-exchange membranes via aqueous dispersion polymerization and their characterization.

Organic-inorganic composite membranes based on poly(vinyl alcohol)/SiO(2) were prepared via an aqueous dispersion polymerization route and anion-exchange groups were introduced in the membrane matrix by the chemical grafting of 4-vinylpyridine with the desired content. These membranes were extensively characterized for their surface morphology, thermal stability, water content, and surface-charge properties using SEM, TEM, FTIR, TGA, water uptake, and ion-exchange capacity measurements. Counterion transport numbers across these membranes were estimated from membrane potential data. Membrane conductance measurements were also performed and these data were used for the estimation of values of counterion diffusion coefficients in the membrane phase. Physicochemical and electrochemical properties of these membranes and equivalent pore radius (estimated from electroosmotic flux measurements) were found to be highly dependent on the 4-vinylpyridine (4-VP) content in the membrane phase. It was also observed that for better selectivity and membrane conductivity of anion-exchange membranes complete optimization of the loading of 4-VP in the membrane phase is necessary. Furthermore, among these, membrane with 25% loading with 4-VP exhibited very good selectivity, water content, and ion-exchange capacity along with moderate membrane conductivity, which may be used for their application in electro-driven separation at elevated temperatures or for other electrochemical processes.

Journal Article↗
PubMed1999

Controlled release of vancomycin from poloxamer 407 gels.

The purpose of this study was to investigate Poloxamer 407 25% (w/w) formulations aimed at prolonging the residence time of vancomycin, a time-dependent antibiotic, in a body site with a high infectious risk. Reversible thermal gelation of the formulations permitted their local injection in liquid form and in situ gelation as they warmed to body temperature. Neither the rheological properties of the Poloxamer matrices nor the antibacterial activity of vancomycin was altered by their combination. In vitro, the dispersed form exhibited prolonged release, with a lower diffusion coefficient of vancomycin compared to the solubilized form (4.7x10(-8) vs 2. 1x10(-7) cm(2) s(-1)131 mg l(-1) for the solubilized form), followed by lower but effective antibacterial levels for at least 8 days. Controlled-release profiles, good preservation of vancomycin activity, good tolerability in rats, and ease of administration suggest that Poloxamer 407 may be useful as a vancomycin delivery vehicle for local prophylaxis of infections, especially in prosthetic surgery.

Animals↗
PubMed2000

Integration of a microextraction system on a glass chip: ion-pair solvent extraction of Fe(II) with 4,7-diphenyl-1,10-phenanthrolinedisulfonic acid and tri-n-octylmethylammonium chloride

An ion-pair solvent extraction was performed in a microchannel fabricated in a quartz glass chip. the aqueous solution of Fe-bathophenanthrolinedisulfonic acid complex and the chloroform solution of tri-n-octylmethylammonium chloride were introduced into the microchannel, and a parallel two-phase laminar flow was formed. The ion-pair product extracted in chloroform was monitored by the thermal lens microscope. The ion-pair product was gradually extracted from aqueous solution into chloroform when the flow was very slow or stopped, while nothing was extracted into chloroform when the flow was fast. The time for extraction in the present 250 microns microchannel, 45 s, roughly coincided with the molecular diffusion time, and the extraction time was at least 1 order shorter compared with the ordinary extraction time using a separatory funnel and mechanical shaking. The microspace in the microchannel was characterized by the large specific interface area and short diffusion distance, and these characteristics may contribute to highly efficient extraction without mechanical shaking. The success of this molecular transport may lead to the integration of more complicated separation and chemical operations on a microchip and more applications.

Journal Article↗
PubMed2006

Scaling and the Smoluchowski equations.

The Smoluchowski equations, which describe coalescence growth, take into account combination reactions between a j-mer and a k-mer to form a (j+k)-mer, but not breakup of larger clusters to smaller ones. All combination reactions are assumed to be second order, with rate constants K(jk). The K(jk) are said to scale if K(lambda j,gamma k) = lambda(mu)gamma(nu)K(jk) for j < or = k. It can then be shown that, for large k, the number density or population of k-mers is given by Ak(a)e(-bk), where A is a normalization constant (a function of a, b, and time), a = -(mu+nu), and b(mu+nu-1) depends linearly on time. We prove this in a simple, transparent manner. We also discuss the origin of odd-even population oscillations for small k. A common scaling arises from the ballistic model, which assumes that the velocity of a k-mer is proportional to 1/square root of m(k) (Maxwell distribution), i.e., thermal equilibrium. This does not hold for the nascent distribution of clusters produced from monomers by reactive collisions. By direct calculation, invoking conservation of momentum in collisions, we show that, for this distribution, velocities are proportional to m(k)(-0.577). This leads to mu+nu = 0.090, intermediate between the ballistic (0.167) and diffusive (0.000) results. These results are discussed in light of the existence of systems in the experimental literature which apparently correspond to very negative values of mu+nu.

Journal Article↗
PubMed1988

Theoretical and practical considerations of measuring extravascular lung water.

The volume of extravascular lung water is currently measured in vivo from the difference in mean transit times of the extrapolated first-pass dilution curves of two indicators, one diffusible and the other confined to the intravascular space. To overcome the limitations of this method, one can prolong the measurement interval, introduce a highly diffusible indicator, or both. In the first case, recirculating indicators are measured and included in the computation by deconvolution of the mean transit time through the lung. In the second case, heat is used as the water indicator. In the third case, not yet explored, recirculating heat would be measured and long thermal transit times uncovered. In view of the complexity of the deconvolution method and the pitfalls of the thermal dilution method, a radiographic score of pulmonary edema may be more useful clinically to assess the volume of extravascular lung water in patients with heart disease or adult respiratory distress syndrome.

Animals↗
PubMed2000

Thermal lattice boltzmann simulation for multispecies fluid equilibration

The equilibration rate for multispecies fluids is examined using thermal lattice Boltzmann simulations. Two-dimensional free-decay simulations are performed for effects of velocity shear layer turbulence on sharp temperature profiles. In particular, parameters are so chosen that the lighter species is turbulent while the heavier species is laminar-and so its vorticity layers would simply decay and diffuse in time. With species coupling, however, there is velocity equilibration followed by the final relaxation to one large co- and one large counter-rotating vortex. The temperature equilibration proceeds on a slower time scale and is in good agreement with the theoretical order of magnitude estimate of Morse [Phys. Fluids 6, 1420 (1963)].

Journal Article↗
PubMed2026

Experimental evolution reveals contrasting adaptive landscapes in lab and field environments.

Experimental evolution is widely used to infer microbial responses to environmental change, yet most laboratory studies impose constant, well-mixed conditions that differ fundamentally from fluctuating, spatially structured field environments. We compared genomic evolution in the leaf litter-associated bacterium Curtobacterium strain MMLR14_002 under control and warming treatments in laboratory culture and in a complementary field experiment. Laboratory-derived isolates accumulated more mutations per genome and exhibited stronger locus-level parallelism, with mutations recurring in a small number of coding loci. Field-derived isolates accumulated fewer mutations per genome, and these mutations rarely occurred in the same coding loci across replicate populations. Instead, field isolates exhibited a higher proportion of intergenic mutations, with mutations recurring in the same intergenic regions across independent field deployments. When coding mutations were detected in the field, they were distributed across functionally diffuse targets and more often involved metabolic pathways than the core cellular processes repeatedly targeted during laboratory evolution. Warming itself did not consistently influence mutation accumulation or the genomic distribution of mutations; instead, laboratory and field contexts primarily shaped the accumulation, targets, and repeatability of genomic change. These results suggest that laboratory thermal evolution identifies adaptive routes favored under sustained selection but may overestimate coding-level parallelism under heterogeneous field conditions. Bridging laboratory and field evolution will likely require experimental designs that incorporate temporal variability and spatial heterogeneity characteristic of natural systems.IMPORTANCEA central goal of experimental evolution is to infer how microbes evolve in nature from laboratory studies. Here, we evaluate this assumption by comparing genomic evolution of a leaf litter-associated Curtobacterium strain in laboratory and field warming experiments to identify broad patterns rather than isolate the contribution of any single environmental factor. We find that the strong parallelism at coding loci observed under laboratory conditions is reduced in the field, while mutations recurring in the same intergenic regions across field deployments suggest that parallel evolution in nature may more often involve regulatory noncoding regions rather than coding targets. These results show that environmental context reshapes adaptive landscapes and may limit the parallelism of coding-level genomic responses inferred from homogeneous laboratory conditions.

experimental evolution↗
PubMedDate not supplied

[Premenstrual mastodynia: objective signs (author's transl)].

Mammary congestion is mainly a painful syndrome, principally related to diffuse edema of the gland, the radiological signs of which are described in this report. Excellent validity can be obtained by a trained observer of these signs. In contrast, however, thermographic signs are of less value, probably due to the presence of a more or less abundant superficial edema. This interferes with thermal propagation towards the skin covering, and could be the cause of the superficial hypothermia which is recorded in one third of patients with definite clinical congestion. Hormonal disturbances are observed frequently enough in this syndrome for them to be considered responsible for a large proportion of the congestive and edemaotus phenomena. Observation of these signs enables a choice of therapy to be made, but this is not discussed in this report.

Adult↗
PubMed1994

Uracil DNA N-glycosylase distributively interacts with duplex polynucleotides containing repeating units of either TGGCCAAGCU or TGGCCAAGCTTGGCCAAGCU.

Uracil DNA N-glycosylase (UDG) has been used as a model enzyme to test a novel universal approach to discriminate between two possible enzymatic mechanisms of specific site location in DNA, processive (DNA-scanning mechanism) and distributive (random diffusion-mediated mechanism). Two double-stranded concatemeric polynucleotides of defined length (440-480 nucleotides) containing deoxyuridine at either every 10th or 20th nucleotide in the DNA chain were prepared by the ligation of self-complementary 10- or 20-mer oligodeoxyribonucleotides. Incubation of these polynucleotides with Escherichia coli UDG, followed by thermal breakage of the abasic sites, formed fragments that were multiples of either the 10- or the 20-mer. Since the processive and distributive mechanisms of uracil removal by UDG would be very different, the fragment distribution, generated at each time interval during the UDG reaction, should be unique. To show this, we developed a computer model illustrating both possible mechanisms of UDG functioning. The distribution of DNA fragments experimentally generated during the time course of the UDG reaction was compared with the results of the computer programs that modeled the distributive and processive mechanisms. The data indicated that uracil removal, catalyzed by UDG, is consistent with a distributive model.

Base Sequence↗
PubMed1987

Extravascular lung water.

Extravascular lung water (idQw1) is measured in vivo from the difference in mean transit times, computed by extrapolating the dilution curves, of two indicators, one freely diffusible, the other confined to the intravascular space. Using 3H2O it has been shown that idQw1 is smaller than the amount of extravascular water obtained from the difference between wet and dry lung weight (Qw1). Extrapolation allows one to use dilution curves for a short time, i.e., up to onset of obvious recirculation. Clearing the dilution curves or recirculation by deconvolution extends the observation time, which then becomes limited by sampling duration rather than onset of recirculation. This procedure entails recording recirculating tracers in the pulmonary artery (PA). Dilutions of tracers at input in PA and output in a systemic artery must be related to each other as continuous time functions. This is accomplished by means of a convolution integral. Deconvolution yields the frequency function of water molecule transit time in the extravascular lung space, l(t). In dogs and men, in both normal and edematous lungs, l(t) exhibits a knee and a fairly long tail. Extravascular lung water computed from l(t), idcQw1, agrees with Qw1 and correlates with data on the extravascular thermal volume of the lung and with radiographic findings of lung edema. A radiographic score of pulmonary edema may be used clinically to assess extravascular lung water in cardiac patients and in patients with adult respiratory distress syndrome.

Capillary Permeability↗
PubMed2004

Application of heated electrodes operating in a non-isothermal mode for interference elimination with amperometric biosensors.

Heated electrodes were applied for the non-isothermal operation of amperometric glucose biosensors based on glucose oxidase immobilised on the electrode surface by entrapment within a polymer layer. The localised deposition of the polymer film under simultaneous entrapment of the enzyme was achieved by an electrochemically induced pH-modulation in the diffusion zone in front of the electrode, thus altering the solubility of the polymer chains. This non-manual sensor preparation protocol could be successfully used for the modification of a novel indirectly heated electrode. The non-isothermal operating mode allows working at the optimum temperature of the enzyme sensors without any thermal distortion of the bulk solution. Increased surface temperature of the sensor thus accelerates transport as well as kinetic processes, resulting in an enhanced amperometric signal. In the presence of interfering compounds such as ascorbic acid, the proposed technique allows use of the diverging thermal impact on the sensing process, for different electrochemically active compounds, for a deconvolution of the amperometric signal at different electrode temperatures. A calculation method for determination of glucose in the presence of one interfering compound is presented as a basis for a calculative interference elimination.

Journal Article↗
PubMed2002

Ultra-relativistic electrons in Jupiter's radiation belts.

Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20[?]MeV. Although most radiation belt models predict electrons at higher energies, adiabatic diffusion theory can account only for energies up to around 20[?]MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8[?]GHz synchrotron emission that confirm the presence of electrons with energies up to 50[?]MeV; the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20[?]MeV are more numerous than previously believed.

Journal Article↗
PubMed2004

Power requirement of the geodynamo from ohmic losses in numerical and laboratory dynamos.

In the Earth's fluid outer core, a dynamo process converts thermal and gravitational energy into magnetic energy. The power needed to sustain the geomagnetic field is set by the ohmic losses (dissipation due to electrical resistance). Recent estimates of ohmic losses cover a wide range, from 0.1 to 3.5 TW, or roughly 0.3-10% of the Earth's surface heat flow. The energy requirement of the dynamo puts constraints on the thermal budget and evolution of the core through Earth's history. Here we use a set of numerical dynamo models to derive scaling relations between the core's characteristic dissipation time and the core's magnetic and hydrodynamic Reynolds numbers--dimensionless numbers that measure the ratio of advective transport to magnetic and viscous diffusion, respectively. The ohmic dissipation of the Karlsruhe dynamo experiment supports a simple dependence on the magnetic Reynolds number alone, indicating that flow turbulence in the experiment and in the Earth's core has little influence on its characteristic dissipation time. We use these results to predict moderate ohmic dissipation in the range of 0.2-0.5 TW, which removes the need for strong radioactive heating in the core and allows the age of the solid inner core to exceed 2.5 billion years.

Journal Article↗
PubMed2005

Cloning, purification, crystallization and preliminary X-ray diffraction analysis of nitrile hydratase from the themophilic Bacillus smithii SC-J05-1.

Nitrile hydratase (NHase) converts nitriles to the corresponding amides and is recognized as having important industrial applications. Purification, cloning, crystallization and initial crystallographic studies of the NHase from Bacillus smithii SC-J05-1 (Bs NHase) were conducted to analyze the activity, specificity and thermal stability of this hydrolytic enzyme. Bs NHase was purified to homogeneity from microbial cells of B. smithii SC-J05-1 and the nucleotide sequences of both the alpha- and beta-subunits were determined. Purified Bs NHase was used for crystallization and several crystal forms were obtained by the vapour-diffusion method. Microseeding and the addition of magnesium ions were essential components to obtain crystals suitable for X-ray diffraction analysis.

Bacillus↗