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PubMed2003

Dynamic roughening of tetrahedral amorphous carbon.

The roughness of tetrahedral amorphous carbon (ta-C) films grown at room temperature is measured as a function of film thickness by atomic force microscopy, to extract roughness and growth exponents of alpha approximately 0.39 and beta approximately 0-0.1, respectively. This extremely small growth exponent shows that some form of surface diffusion and relaxation operates at a homologous temperature of 0.07, much lower than in any other material. This is accounted for by a Monte Carlo simulation, which assumes a smoothening during a thermal spike, following energetic ion deposition. The low roughness allows ta-C to be used as an ultrathin protective coating on magnetic disk storage systems with approximately 1 Tbit/in.(2) storage density.

Journal Article↗
PubMed2005

Light-induced protein-matrix uncoupling and protein relaxation in dry samples of trehalose-coated MbCO at room temperature.

In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal side) heme pocket, experiencing averaged protein heme pocket structures, as a result of the presence of Brownian motions. At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme pocket side probing in nonaveraged structures. We revisit here the flash photolysis data by Librizzi et al. (2002) and report on new, room temperature experiments in MbCO-trehalose samples, shortly illuminated prior the laser pulse. In dry samples, pre-illumination increased the diffusion of CO from the distal to the proximal heme pocket side, which resulted in less structure than in non-pre-illuminated samples. Such an effect, which is absent in humid samples, stems from a decoupling of the protein internal degrees of freedom from those of the external water-sugar matrix. We suggest that such a decoupling can be brought about by the continuous attempts performed by the protein during pre-illumination to undergo relaxation toward the photodissociated deoxy state. This, in turn, causes a collapse in the hydrogen bond network, which connects the protein surface to the water-sugar matrix, as reported by Cottone et al. (2002) and Giuffrida et al. (2003). In the conclusion section, we discuss the possible involvement of the processes invoked to rationalize the present data, in the function of macromolecules and interactions in living cells.

Animals↗
PubMed1978

Measurement of heated skin O2 diffusion conductance and PO2 sensor induced O2 gradient.

A large cathode heated transcutaneous PO2 electrode was used to measure the resistance of skin to diffusion of O2 from the capillary bed to the surface. With a non-O2-consuming tcPO2 electrode, one would read ideal tcPO2, Pi, which approximates PaO2 between 50 and 100 mmHg due to approximate cancellation of the rise by heating and the fall by skin O2 consumption. When a large cathode tcPO2 electrode is used, its O2 consumption causes a PO2 gradient across skin resistance, Rs, which depends on electrode membrane resistance RM (with Mylar), or RT (with Telfon). Surface PO2 will fall below Pi, and assuming no change in capillary PO2: PT/Pi = RT/(RT + Rs) and PM/Pi = RM/(RM + Rs) (1) 12 micrometer Telfon is 50 times as permeable to O2 as 6 micrometer Myler. When an electrode, covered alternately with these two membranes, was mounted on the same skin site in six subjects, the mean observed PT/PM was about 0.3. Substituting in equation (1) yields RT/Rs = 0.4, Rm/Rs = 20, and PM/Pi = 0.95. Using the known O2 permeability of Teflon, we computed skin O2 conductance to be 6.6 pmol O2/(cm2 .s .kPa), or 15 nl O2/(cm2 .s .atm). This method thus provides a way of determining ideal tc PO2 and stirring effect, phi, of other electrodes and various membranes.

Blood Gas Analysis↗
PubMed1978

Current noise around steady states in discrete transport systems.

Subject of this paper is the transport noise in discrete systems. The transport systems are given by a number (n) of binding sites separated by energy barriers. These binding sites may be in contact outer reservoirs. The state of the systems is characterized by the occupation numbers of particles (current carriers) at these binding sites. The change in time of the occupation numbers is generated by individual "jumps" of particles over the energy barriers, building up the flux matter (for charged particles: the electric current). In the limit n leads to infinity continuum processes as e.g. usual diffusion are included in the transport model. The fluctuations in occupation numbers and other quantities linearly coupled to the occupation numbers may be treated with the usual master equation approach. The treatment of the fluctuation in fluxes (current) makes necessary a different theoretical approach which is presented in this paper under the assumption of vanishing interactions between the particles. This approach may be applied to a number of different transport systems in biology and physics (ion transport through porous channels in membranes, carriers mediated ion transport through membranes, jump diffusion e.g. in superionic conductors). As in the master equation approach the calculation of correlations and noise spectra may be reduced to the solution of the macroscopic equations for the occupation numbers. This result may be regarded as a generalization to non-equilibrium current fluctuations of the usual Nyquist theorem relating the current (voltage) noise spectrum in thermal equilibrium to the macroscopic frequency dependent admittance. The validity of the general approach is demonstrated by the calculation of the autocorrelation function and spectrum of current noise for a number of special examples (e.g. pores in membranes, carrier mediated ion transport).

Binding Sites↗
PubMedDate not supplied

Solubility and diffusion of nitrogen in maltodextrin/protein tablets.

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history-dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.

Diffusion↗
PubMed1996

Wear-resistant, hemocompatible Ti-Nb-Zr and Zr-Nb alloys to improve blood pump design and performance.

Over the past several years, we have developed novel titanium-niobium-zirconium (Ti-Nb-Zr) alloys to address the long-term performance needs of orthopedic implants. The unique properties of these alloys also render them promising candidates for blood pumps. These properties include excellent biocompatibility in combination with high strength and toughness, and low elastic modulus (low stiffness). Additionally, these metal alloys are readily hot or cold worked into complex shapes including wire, foil, tubing and bar. They are readily machined and polished, and they can be surface oxidized to form a hard, wear-resistant, low-friction ceramic surface layer. In this diffusion-hardened condition, oxygen also hardens the underlying metal to optimize the bone between the ceramic oxide surface and the tough metal substrate. Unlike metal surfaces, oxidative wear, which can alter surface energy, friction, and hemocompatibility, does not occur. Consequently, the combined benefits of a stable, wear-resistant, low-friction ceramic surface layer with the toughness, strength, formability, and thermal conductivity of metal may provide improvements in the design and performance of blood pumps and peripheral graft and percutaneous (power) components of the pump.

Alloys↗
PubMed1992

Excimer laser coronary angioplasty.

Recent experience with excimer laser coronary angioplasty (ELCA) has shown the safety and efficacy of the technique in the treatment of coronary stenosis, with results similar to percutaneous transluminal coronary angioplasty (PTCA). Several advantages of the excimer laser for intravascular use have been identified by the ELCA Registry, a group of 15 institutions nationally that have pooled data on their cooperative experience with ELCA. Advantages include the ability of the laser to ablate atheroma with microscopic precision without thermal injury and the ability of vessel surfaces to heal without scarring. The initial results of the multicenter investigation of ELCA in 958 patients indicate that ELCA may be indicated particularly for long, diffuse lesions. With the advent of larger diameter catheters, ELCA is a viable alternative to PTCA. Restenosis was seen as a significant problem, and it remained problematic at 6-month follow-up. In comparison with conventional balloon angioplasty, ELCA may eliminate that component of restenosis due to inadequate dilation or elastic recoil, but it does not appear to affect restenosis caused by smooth muscle proliferation. Catheter design and energy delivery continue to evolve and may affect future results of laser coronary angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed1992

Nucleotide- and temperature-induced changes in myosin subfragment-1 structure.

The effects of nucleotide binding and temperature on the internal structural dynamics of myosin subfragment 1 (S1) were monitored by intrinsic tryptophan phosphorescence lifetime and fluorescence anisotropy measurements. Changes in the global conformation of S1 were monitored by measuring its rate of rotational diffusion using transient electric birefringence techniques. At 5 degrees C, the binding of MgADP, MgADP,P and MgADP,V (vanadate) progressively reduce the rotational freedom of S1 tryptophans, producing what appear to be increasingly more rigidified S1-nucleotide structures. The changes in the luminescence properties of the tryptophans suggest that at least one is located at the interface of two S1 subdomains. Increasing the temperature from 0 to 25 degrees C increases the apparent internal mobility of S1 tryptophans in all cases and, in addition, a reversible temperature-dependent transition centered near 15 degrees C was observed for S1, S1-MgADP and S1-MgADP,P, but not for S1-MgADP,V. The rotational diffusion constants of S1 and S1-MgADP were measured at temperatures between 0 and 25 degrees C. After adjusting for the temperature and viscosity of the solvent, the data indicate that the thermally induced transition at 15 degrees C comprises local conformational changes, but no global conformational change. Structural features of S1-MgADP,P, which may relate to its role in force generation while bound to actin, are presented.

Adenine Nucleotides↗
PubMed1997

A new molecular model for collagen elasticity based on synchrotron X-ray scattering evidence.

Collagen is the most abundant structural protein in vertebrates. The specific shape of its stress-strain curve is crucial for the function of a number of organs. Although the macroscopic mechanical behavior of collagen is well known, there is still no explanation of the elastic process at the supramolecular level. We have performed in situ synchrotron x-ray scattering experiments, which show that the amount of lateral molecular order increases upon stretching of collagen fibers. In strain cycling experiments the relation between strain and diffuse equatorial scattering was found to be linear in the "heel" region of the stress-strain curve. A new molecular model for collagen elasticity is proposed, which, based on the existence of thermally activated molecular kinks, reproduces this linearity and gives a simple explanation for the form of the stress-strain curve of collagen.

Animals↗
PubMed2000

Integration of a microextraction system solvent extraction of a Co-2-nitroso-5-dimethylaminophenol complex on a microchip.

A newly designed microchannel for solvent extraction was fabricated in a quartz glass chip and applied to solvent extraction of a Co-2-nitroso-5-dimethylaminophenol complex. The aqueous solution of Co complex and toluene were introduced into the microchannel, and the Co complex extracted in toluene was detected by thermal lens microscopy (TLM). The Co complex was quickly extracted into toluene when the flow was stopped. The observed extraction time, ca. 50 s, was almost equivalent to the value calculated using the diffusion distance and diffusion coefficient. The dependence of the TLM signal on the concentration of the Co complex showed good linearity in the range of 1 x 10(-7) - 1 x 10(-6) M.

Cobalt↗
PubMed2006

Nanomechanical detection of DNA melting on microcantilever surfaces.

We observe surface stress changes in response to thermal dehybridization, or melting, of double-stranded DNA (dsDNA) oligonucleotides that are grafted on one side of a microcantilever beam. Changes in surface stress occur when one complementary DNA strand melts and diffuses away from the other, resulting in alterations of the electrostatic, counterionic, and hydration interaction forces between the remaining neighboring surface-grafted DNA molecules. We have been able to distinguish changes in the melting temperature of dsDNA as a function of salt concentration and oligomer length. This technique also highlights differences between surface immobilized and solution DNA melting dynamics, which allows us to better understand the stability of DNA on surfaces. The transduction of phase transitions into a mechanical signal is ubiquitous for DNA, making cantilever-based detection a widely useful and complementary alternative to calorimetric and fluorescence measurements.

DNA↗
PubMed2004

Reply to "Comment on 'Collective dynamics in liquid lithium, sodium, and aluminum' ".

Phys. Rev. E 70, 013201 (2004)]] have raised certain objections to physical interpretation of the parameters of the model proposed by us earlier [Phys. Rev. E 67, 012201 (2003)]]. We have found that heat diffusion term enters into processes which are responsible for the quasielastic peak of the dynamical structure factor. An attempt has been made to study the role played by atomic and electronic contributions to thermal conductivity for studying atomic density-density correlation function.

Journal Article↗
PubMed1997

Comets as porous aggregates of interstellar dust.

A comet model is derived based on the interstellar dust chemical composition in dense molecular and diffuse clouds resulting from their subsequent chemical interactions and UV photoprocessing. The collapsing presolar nebula leads to a porous aggregate model for comet nuclei, from which is derived certain physical properties that include thermal conductivity and tensile strength. The porous morphological structure is also shown to imply anomalous (expansion rather than contraction) behavior when subjected to strong shock waves, which is supported by recent shock experiments on (porous) carbonaceous chondrite material.

Cosmic Dust↗
PubMed2006

Design of a rotating facility for extracorporal treatment of an explanted liver with disseminated metastases by boron neutron capture therapy with an epithermal neutron beam.

In 2001, at the TRIGA reactor of the University of Pavia (Italy), a patient suffering from diffuse liver metastases from an adenocarcinoma of the sigmoid was successfully treated by boron neutron capture therapy (BNCT). The procedure involved boron infusion prior to hepatectomy, irradiation of the explanted liver at the thermal column of the reactor, and subsequent reimplantation. A complete response was observed. This encouraging outcome stimulated the Essen/Petten BNCT group to investigate whether such an extracorporal irradiation could be performed at the BNCT irradiation facility at the HFR Petten (The Netherlands), which has very different irradiation characteristics than the Pavia facility. A computational study has been carried out. A rotating PMMA container with a liver, surrounded by PMMA and graphite, is simulated using the Monte Carlo code MCNP. Due to the rotation and neutron moderation of the PMMA container, the initial epithermal neutron beam provides a nearly homogeneous thermal neutron field in the liver. The main conditions for treatment as reported from the Pavia experiment, i.e. a thermal neutron fluence of 4 x 10(12) +/- 20% cm(-2), can be closely met at the HFR in an acceptable time, which, depending on the defined conditions, is between 140 and 180 min.

Computer Simulation↗
PubMed1999

Histopathologic changes of the soft palate after laser-assisted uvulopalatoplasty.

OBJECTIVE: To assess late histopathologic changes of the soft palate after laser-assisted uvulopalatoplasty in patients with snoring and mild obstructive sleep apnea. DESIGN: A nonrandomized, histopathologic controlled study. SUBJECTS AND INTERVENTIONS: Palatal surgical specimens were removed from 10 patients with snoring and obstructive sleep apnea in whom laser-assisted uvulopalatoplasty was not successful and who subsequently underwent uvulopalatopharyngoplasty. The mean interval between the last laser treatment and uvulopalatopharyngoplasty was 24 months. The patients' specimens were compared with those of a control group consisting of 12 palates and uvulae excised during uvulopalatopharyngoplasty. RESULTS: After laser-assisted uvulopalatoplasty, all soft palates displayed marked and progressive pathologic changes that increased with every additional treatment and extended far beyond the point of laser beam application. The loose connective tissue present in the lamina propria was replaced by diffuse fibrosis, which also extended to the central layer, on the expanse of seromucous glands and muscle fibers. Other changes included ulceration of the oral epithelium and a patchy inflammatory reaction. CONCLUSIONS: Extensive thermal-induced changes, involving the 3 layers of the organ, were found. They are compatible with clinical observations reported elsewhere and are probably responsible for the worsening of the obstructive sleep apnea status and the sensation of the pharyngeal dryness that developed months after the laser-assisted uvulopalatoplasty. Although it has immediate benefits, the procedure is still relatively new and all its implications are as yet unknown.

Adult↗
PubMed2004

Physicochemical properties and mechanism of drug release from ethyl cellulose matrix tablets prepared by direct compression and hot-melt extrusion.

The objective of this research project was to determine the physicochemical properties and investigate the drug release mechanism from ethyl cellulose (EC) matrix tablets prepared by either direct compression or hot-melt extrusion (HME) of binary mixtures of water soluble drug (guaifenesin) and the polymer. Ethyl cellulose was separated into "fine" or "coarse" particle size fractions corresponding to 325-80 and 80-30 mesh particles, respectively. Tablets containing 30% guaifenesin were prepared at 10, 30, or 50 kN compaction forces and extruded at processing temperatures of 80-90 and 90-110 degrees C. The drug dissolution and release kinetics were determined and the tablet pore characteristics, tortuosity, thermal properties and surface morphologies were studied using helium pycnometry, mercury porosimetry, differential scanning calorimetry and scanning electron microscopy. The tortuosity was measured directly by a novel technique that allows for the calculation of diffusion coefficients in three experiments. The Higuchi diffusion model, Percolation Theory and Polymer Free Volume Theory were applied to the dissolution data to explain the release properties of drug from the matrix systems. The release rate was shown to be dependent on the ethyl cellulose particle size, compaction force and extrusion temperature.

Cellulose↗
PubMed1993

Calorimetric studies of freeze-induced dehydration of phospholipids.

Differential scanning calorimetry (DSC) was used to determine the amount of water that freezes in an aqueous suspension of multilamellar dipalmitoylphosphatidylcholine (DPPC) liposomes. The studies were performed with dehydrated suspensions (12-20 wt% water) and suspensions containing an excess of water (30-70 wt% water). For suspensions that contained > or = 18 wt% water, two ice-formation events were observed during cooling. The first was attributed to heterogeneous nucleation of extraliposomal ice; the second was attributed to homogeneous nucleation of ice within the liposomes. In suspensions with an initial water concentration between 13 and 16 wt%, ice formation occurred only after homogeneous nucleation at temperatures below -40 degrees C. In suspensions containing < 13 wt% water, ice formation during cooling was undetectable by DSC, however, an endotherm resulting from ice melting during warming was observed in suspensions containing > or = 12 wt% water. In suspensions containing < 12 wt% water, an endotherm corresponding to the melting of ice was not observed during warming. The amount of ice that formed in the suspensions was determined by using an improved procedure to calculate the partial area of the endotherm resulting from the melting of ice during warming. The results show that a substantial proportion of water associated with the polar headgroup of phosphatidylcholine can be removed by freeze-induced dehydration, but the amount of ice depends on the thermal history of the samples. For example, after cooling to -100 degrees C at rates > or = 10 degrees C/min, a portion of water in the suspension remains supercooled because of a decrease in the diffusion rate of water with decreasing temperature. A portion of this supercooled water can be frozen during subsequent freeze-induced dehydration of the liposomes under isothermal conditions at subfreezing storage temperature Ts. During isothermal storage at Ts > or = -40 degrees C, the amount of unfrozen water decreased with decreasing Ts and increasing time of storage. After 30 min of storage at Ts = -40 degrees C and subsequent cooling to -100 degrees C, the amount of water associated with the polar headgroups was < 0.1 g/g of DPPC. At temperatures > -50 degrees C, the amount of unfrozen water associated with the polar headgroups of DPPC decreased with decreasing temperature in a manner predicted from the desorption isotherm of DPPC. However, at lower temperatures, the amount of unfrozen water remained constant, in large part, because the unfrozen water underwent a liquid-to-glass transformation at a temperature between -50 degrees and -140 degrees C.

1,2-Dipalmitoylphosphatidylcholine↗