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PubMed2005

Smoothed particle hydrodynamics model for phase separating fluid mixtures. II. Diffusion in a binary mixture.

A previously formulated smoothed particle hydrodynamics model for a phase separating mixture is tested for the case when viscous processes are negligible and only mass and energy diffusive processes take place. We restrict ourselves to the case of a binary mixture that can exhibit liquid-liquid phase separation. The thermodynamic consistency of the model is assessed and the potential of the model to study complex pattern formation in the presence of various thermal boundaries is illustrated.

Journal Article↗
PubMedDate not supplied

Analysis of release data in the evaluation of the physical state of progesterone in matrix systems.

Ethylene-vinyl acetate microspheres were prepared by an emulsion solvent-evaporation method as sustained delivery carriers of progesterone. Physical state of the drug in the microspheres was affected by drug loading level. As thermal analysis and mathematical release models showed, low payloads of the matrix supported the molecularly dispersed drug. Crystalline drug appeared only as the drug loading level increased. The release process of the crystalline drug produced a porosity increase in the polymeric system; thus, the drug could diffuse through pores and channels. Hence, the porosity of the matrix structure was affected by the payload. This hypothesis could justify the increasing goodness-of-fit of the release data to the square-root model as the drug loading level of the microspheres increased.

Calorimetry, Differential Scanning↗
PubMed2004

Verteporfin: new indication. In certain age-related macular degeneration: too little evidence.

(1) The standard treatment for neovascular forms of age-related macular degeneration is thermal coagulation by argon or krypton laser, but it is only suitable for patients with juxtafoveal or extrafoveal neovascularisation. (2) Verteporfin, a photosensitising agent, is injected intravenously 15 minutes before non thermal red laser activation. This protocol was initially restricted to patients with predominantly visible neovascularisation in the subfoveal choroidal region. In Europe (but not in the United States), this treatment has now been approved for patients with occult subfoveal neovascularisation, i.e. poorly defined zones of fluorescein diffusion. (3) Use in this indication is supported by a single double-blind trial comparing red laser + verteporfin with red laser + placebo. After one year's treatment there was no difference between the groups in the number of patients whose loss of visual acuity had stabilised. One of the several statistical analyses showed that red laser + verteporfin was significantly more effective than red laser + placebo at two years, after five treatment sessions on average. Only a minority of patients benefited, however, and these cannot yet be identified before treatment. It is unclear whether efficacy persists in the long term. (4) Some patients experienced a transient visual deterioration. Verteporfin infusion can provoke local reactions and thoracic or lumbar pain. Cutaneous photosensitisation can occur for 48 hours after treatment. (5) Treatment with verteporfin is expensive. (6) In practice, there is currently no reason to use red laser + verteporfin in patients with age-related macular degeneration and occult neovascularisation, other than in clinical trials.

Choroidal Neovascularization↗
PubMed2006

First-principles study of the diffusion of hydrogen in ZnO.

Zinc oxide, a wide-gap semiconductor, typically exhibits n-type conductivity even when nominally undoped. The nature of the donor is contentious, but hydrogen is a prime candidate. We present ab initio calculations of the migration barrier for H, yielding a barrier of less than approximately 0.5 eV. This indicates isolated hydrogen is mobile at low temperature and that thermally stable H-related donors must logically be trapped at other defects. We argue this is also true for other oxides where H is a shallow donor.

Journal Article↗
PubMed2001

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results.

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Brønsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Brønsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes.

Journal Article↗
PubMed2004

Spatial summation of heat pain within and across dermatomes in fibromyalgia patients and pain-free subjects.

The mechanisms of spatial summation of pain (SSP) include pain coding dependent on impulse frequency and the number of recruited central neurons. However, SSP may also be influenced by pain inhibitory mechanisms, such as diffuse noxious inhibitory controls. Abnormal interactions between pain inhibitory mechanisms and SSP may be relevant for chronic pain conditions such as fibromyalgia (FM) and may help explain why widespread pain is characteristic for this chronic pain syndrome. The present study was designed to determine the difference of thermal SSP in the upper extremities between FM and normal control (NC) subjects, particularly within and across dermatomes of the hand. Fourteen NC and 19 FM subjects were enrolled in this study. SSP testing sessions involved immersion of each individual fingertip as well as stepwise immersion of the fingers, hands, and forearms in a hot water bath (46 degrees Celsius) for 5s and 20s. In addition, immersion of several fingertips across dermatome C(7)-C(8) was compared to progressive immersion of the index finger (dermatome C(7)). These experiments demonstrated significant spatial summation of heat-induced pain in both FM and NC subjects. SSP was most extensive within the fingers, and became negligible as the stimulus area increased above the hand. Furthermore, SSP was more pronounced within one dermatome such as that of the index finger than across several dermatomes of the hand. These results were similar for both FM and NC subjects. Thus, mechanisms of SSP, including possible inhibitory factors that limit this relevant pain mechanism, appear to be similar for both FM and NC subjects.

Adult↗
PubMed2006

A new technique to assess dermal absorption of volatile chemicals in vitro by thermal gravimetric analysis.

Potential health hazards of dermal exposure, variability in reported dermal absorption rates and potential losses from the skin by evaporation indicate a need for a simple, inexpensive and standardized procedure to measure dermal absorption and desorption of chemical substances. The aim of this study was to explore the possibility to measure dermal absorption and desorption of volatile chemicals using a new gravimetric technique, namely thermal gravimetric analysis (TGA), and trypsinated stratum corneum from pig. Changes in skin weight were readily detected before, during and after exposure to vapours of water, 2-propanol, methanol and toluene. The shape and height of the weight curves differed between the four chemicals, reflecting differences in diffusivity and partial pressure and skin:air partitioning, respectively. As the skin weight is highly sensitive to the partial pressure of volatile chemicals, including water, this technique requires carefully controlled conditions with respect to air flow, temperature, chemical vapour generation and humidity. This new technique may help in the assessment of dermal uptake of volatile chemicals. Only a small piece of skin is needed and skin integrity is not necessary, facilitating the use of human samples. The high resolution weight-time curves obtained may also help to elucidate the characteristics of absorption, desorption and diffusion of chemicals in skin.

2-Propanol↗
PubMed2006

Hydrothermal synthesis of Zn2SnO4 nanorods in the diameter regime of sub-5 nm and their properties.

Single crystalline Zn(2)SnO(4) (ZTO) nanorods 2-4 nm in diameter and around 20 nm in length were successfully synthesized by a simple hydrothermal process with use of hydrazine hydrate as an alkaline mineralizer instead of NaOH or NH(3).H(2)O. By analyzing the UV-vis diffuse reflectance spectrum, the optical band gap (E(g)) of the nanorods was found to be 3.87 eV, which indicates a blue shift of 0.27 eV from that of bulk ZTO (3.6 eV). In situ high-temperature X-ray diffraction was employed to study the thermal expansion coefficient and the variation of lattice parameter with temperature of the product. Furthermore, we discussed the chemical mechanism and key factors to the hydrothermal formation of the sub-5 nm ZTO nanorods.

Journal Article↗
PubMed2002

Somatosensory perception in a remote pain-free area and function of diffuse noxious inhibitory controls (DNIC) in patients suffering from long-term trapezius myalgia.

In patients with localized musculoskeletal pain, spread of pain and tenderness outside the primarily painful area and sometimes even generalization of pain have been reported, the latter possibly indicating a dysfunction of endogenous pain modulatory systems. The purpose of the study was to use patients with long-term trapezius myalgia as a model to investigate the possible influence of a localized muscle pain on somatosensory processing in a remote pain-free area and the effect of heterotopic noxious conditioning stimulation (HNCS) on 'diffuse noxious inhibitory controls' (DNIC) related mechanisms. Altered somatosensory processing may indicate subclinical derangement of endogenous modulatory systems. Ten patients with long-term (> or = 1 year) trapezius myalgia and 10 age- and sex-matched healthy controls participated. Pressure pain sensitivity, low threshold mechanoreceptive function and thermal sensitivity, including thermal pain, were assessed at the right thigh before, during and following HNCS. Pain was induced in the forearm by the tourniquet test. At rest allodynia to pressure was found at the thigh in conjunction with hypoaesthesia to cold (p<0.03 and p<0.01 respectively), in patients compared with controls. During HNCS, the sensitivity to pressure pain and suprathreshold heat pain decreased in patients and controls alike (p<0.02 and p<0.04 respectively) and returned to baseline following HNCS. In conclusion, in a remote non-painful area allodynia to pressure and hypoaesthesia to cold were found in conjunction with preserved function of DNIC-related mechanisms. Whether altered central somatosensory processing at rest may indicate a predisposition for further spread of pain is at present unclear.

Blood Pressure↗
PubMed2006

Multidimensional infrared spectroscopy of water. I. Vibrational dynamics in two-dimensional IR line shapes.

In this and the following paper, we describe the ultrafast structural fluctuations and rearrangements of the hydrogen bonding network of water using two-dimensional (2D) infrared spectroscopy. 2D IR spectra covering all the relevant time scales of molecular dynamics of the hydrogen bonding network of water were studied for the OH stretching absorption of HOD in D2O. Time-dependent evolution of the 2D IR line shape serves as a spectroscopic observable that tracks how different hydrogen bonding environments interconvert while changes in spectral intensity result from vibrational relaxation and molecular reorientation of the OH dipole. For waiting times up to the vibrational lifetime of 700 fs, changes in the 2D line shape reflect the spectral evolution of OH oscillators induced by hydrogen bond dynamics. These dynamics, characterized through a set of 2D line shape analysis metrics, show a rapid 60 fs decay, an underdamped oscillation on a 130 fs time scale induced by hydrogen bond stretching, and a long time decay constant of 1.4 ps. 2D surfaces for waiting times larger than 700 fs are dominated by the effects of vibrational relaxation and the thermalization of this excess energy by the solvent bath. Our modeling based on fluctuations with Gaussian statistics is able to reproduce the changes in dispersed pump-probe and 2D IR spectra induced by these relaxation processes, but misses the asymmetry resulting from frequency-dependent spectral diffusion. The dynamical origin of this asymmetry is discussed in the companion paper.

Journal Article↗
PubMed2006

Heterogeneous dynamics, ageing, and rejuvenating in van der Waals liquids.

It has been shown over the past ten years that the dynamics close to the glass transition is strongly heterogeneous: fast domains coexist with domains three or four decades slower, the size of these regions being about 3 nm at T(g). The authors extend here a model that has been proposed recently for the glass transition in van der Waals liquids. The authors describe in more details the mechanisms of the alpha relaxation in such liquids. It allows then to interpret physical ageing in van der Waals liquids as the evolution of the density fluctuation distribution towards the equilibrium one. The authors derive the expression of macroscopic quantities (volume, compliance, etc.). Numerical results are compared with experimental data (shape, times to reach equilibrium) for simple thermal histories (quenches, annealings). The authors explain the existence of a "Kovacs memory effect" and the temporal asymmetry between down jump and up jump temperatures experiments, even for systems for which there is no energy barriers. Their model allows also for calculating the evolution of small probe diffusion coefficients during ageing.

Journal Article↗
PubMed2005

Direct observation of nondiffusive motion of a Brownian particle.

The thermal position fluctuations of a single micron-sized sphere immersed in a fluid were recorded by optical trapping interferometry with nanometer spatial and microsecond temporal resolution. We find, in accord with the theory of Brownian motion including hydrodynamic memory effects, that the transition from ballistic to diffusive motion is delayed to significantly longer times than predicted by the standard Langevin equation. This delay is a consequence of the inertia of the fluid. On the shortest time scales investigated, the sphere's inertia has a small, but measurable, effect.

Journal Article↗
PubMed2004

Pattern formation during T-cell adhesion.

T cells form intriguing patterns during adhesion to antigen-presenting cells. The patterns are composed of two types of domains, which either contain short TCR/MHCp receptor-ligand complexes or the longer LFA-1/ICAM-1 complexes. The final pattern consists of a central TCR/MHCp domain surrounded by a ring-shaped LFA-1/ICAM-1 domain, whereas the characteristic pattern formed at intermediate times is inverted with TCR/MHCp complexes at the periphery of the contact zone and LFA-1/ICAM-1 complexes in the center. Several mechanisms have been proposed to explain the T-cell pattern formation. Whereas biologists have emphasized the role of active cytoskeletal processes, previous theoretical studies suggest that the pattern evolution may be caused by spontaneous self-assembly processes alone. Some of these studies focus on circularly symmetric patterns and propose a pivot mechanism for the formation of the intermediate inverted pattern. Here, we present a statistical-mechanical model which includes thermal fluctuations and the full range of spatial patterns. We confirm the observation that the intermediate inverted pattern may be formed by spontaneous self-assembly. However, we find a different self-assembly mechanism in which numerous TCR/MHCp microdomains initially nucleate throughout the contact zone. The diffusion of free receptors and ligands into the contact zone subsequently leads to faster growth of peripheral TCR/MHCp microdomains and to a closed ring for sufficiently large TCR/MHCp concentrations. At smaller TCR/MHCp concentrations, we observe a second regime of pattern formation with characteristic multifocal intermediates, which resemble patterns observed during adhesion of immature T cells or thymozytes. In contrast to other theoretical models, we find that the final T-cell pattern with a central TCR/MHCp domain is only obtained in the presence of active cytoskeletal transport processes.

Animals↗
PubMed2004

Mechanical measurement of single-molecule binding rates: kinetics of DNA helix-destabilization by T4 gene 32 protein.

Bacteriophage T4 gene 32 protein (gp32) is a single-stranded DNA (ssDNA) binding protein, and is essential for DNA replication, recombination and repair. While gp32 binds preferentially and cooperatively to ssDNA, it has not been observed to lower the thermal melting temperature of natural double-stranded DNA (dsDNA). However, in single-molecule stretching experiments, gp32 significantly destabilizes lambda DNA. In this study, we develop a theory of the effect of the protein on single dsDNA stretching curves, and apply it to the measured dependence of the DNA overstretching force on pulling rate in the presence of the full-length and two truncated forms of the protein. This allows us to calculate the rate of cooperative growth of single clusters of protein along ssDNA that are formed as the dsDNA molecule is stretched, as well as determine the site size of the protein binding to ssDNA. The rate of cooperative binding (ka) of both gp32 and of its proteolytic fragment *I (which lacks 48 residues from the C terminus) varies non-linearly with protein concentration, and appears to exceed the diffusion limit. We develop a model of protein association with the ends of growing clusters of cooperatively bound protein enhanced by 1-D diffusion along dsDNA, under the condition of protein excess. Upon globally fitting ka versus protein concentration, we determine the binding site size and the non-cooperative binding constants to dsDNA for gp32 and I. Our experiment mimics the growth of clusters of gp32 that likely exist at the DNA replication fork in vivo, and explains the origin of the "kinetic block" to dsDNA melting by gene 32 protein observed in thermal melting experiments.

Bacteriophage T4↗
PubMed2003

Isoflurane depresses diffuse noxious inhibitory controls in rats between 0.8 and 1.2 minimum alveolar anesthetic concentration.

UNLABELLED: Diffuse noxious inhibitory control (DNIC) occurs when the response to a noxious stimulus is inhibited by a second, spatially remote noxious stimulus. The minimum alveolar anesthetic concentration (MAC) to suppress movement is not altered by a second remote noxious stimulus. We hypothesized that DNIC would be depressed in the peri-MAC range. Rats were anesthetized with isoflurane, and MAC was measured. We recorded dorsal horn neuronal responses to noxious thermal stimulation of the hindpaw, with or without concomitant supramaximal noxious mechanical stimulation of the tail or contralateral hindpaw. At 0.8 MAC, the tail clamp decreased neuronal responses 70% compared with control heat-evoked responses (from 1032 +/- 178 impulses per minute to 301 +/- 135 impulses per minute; P < 0.05). The tail clamp had no significant effect on neuronal responses at 1.2 MAC (from 879 +/- 139 impulses per minute to 825 +/- 191 impulses per minute; P > 0.05). Similarly, 1.2 MAC isoflurane significantly depressed DNIC elicited by hindpaw clamping. In another group, the cervical spinal cord was reversibly blocked by cooling to determine whether the inhibition was mediated supraspinally. With spinal cord cooling, the counterstimulus-evoked inhibition was not observed at 0.8 MAC. These results suggest that DNIC involves supraspinal structures and is present at sub-MAC isoflurane concentrations but is depressed at more than 1 MAC. IMPLICATIONS: Diffuse noxious inhibitory control (DNIC) occurs when a noxious stimulus is perceived as being less painful when a second noxious stimulus is applied elsewhere on the body. DNIC is present in anesthetized animals, although how anesthesia affects it is unknown. We found that isoflurane depressed DNIC in the transition from 0.8 to 1.2 minimum alveolar anesthetic concentration, suggesting that DNIC is depressed in the anesthetic range needed to suppress movement.

Action Potentials↗
PubMed1999

1H DNP at 1.4 T of water doped with a triarylmethyl-based radical.

Recently a triarylmethyl-based (TAM) radical has been developed for research in biological and other aqueous systems, and in low magnetic fields, 10 mT or less, large (1)H dynamic nuclear polarization (DNP) enhancements have been reported. In this paper the DNP properties of this radical have been investigated in a considerably larger field of 1.4 T, corresponding to proton and electron Larmor frequencies of 60 MHz and 40 GHz, respectively. To avoid excessive microwave heating of the sample, an existing DNP NMR probe was modified with a screening coil, wound around the sample capillary and with its axis perpendicular to the electric component of the microwave field. It was found that with this probe the temperature increase in the sample after 4 s of microwave irradiation with an incident power of 10 W was only 16 degrees C. For the investigations, 10 mM of the TAM radical was dissolved in deionized, but not degassed, water and put into a 1-mm i.d. and 6-mm long capillary tube. At 26 degrees C the following results were obtained: (I) The relaxivity of the radical is 0.07 (mMs)(-1), in accordance with the value extrapolated from low-field results; (II) The leakage factor is 0.63, the saturation factor at maximum power is 0.85, and the coupling factor is -0.0187. It is shown that these results agree very well with an analysis where the electron-dipolar interactions are the dominant DNP mechanism, and where the relaxation transitions resulting from these interactions are governed by translational diffusion of the water molecules. Finally, the possibilities of combining DNP with magnetic resonance microscopy (MRM) are discussed. It is shown that at 26 degrees C the overall DNP-enhanced proton polarization should become maximal in an external field of 0.3 T and become comparable to the thermal equilibrium polarization in a field of 30 T, considerably larger than the largest high-resolution magnet available to date. It is concluded that DNP MRM in this field, which corresponds to a standard microwave frequency of 9 GHz, has the potential to significantly increase the sensitivity in NMR and MRI experiments of small aqueous samples doped with the TAM radical.

Chemical Phenomena↗
PubMed1995

Molecular dynamics of alamethicin transmembrane channels from open-channel current noise analysis.

Conductance noise measurement of the open states of alamethicin transmembrane channels reveals excess noise attributable to cooperative low-frequency molecular dynamics that can generate fluctuations approximately 1 A rms in the effective channel pore radius. Single-channel currents through both persistent and nonpersistent channels with multiple conductance states formed by purified polypeptide alamethicin in artificial phospholipid bilayers isolated onto micropipettes with gigaohm seals were recorded using a voltage-clamp technique with low background noise (rms noise < 3 pA up to 20 kHz). Current noise power spectra between 100 Hz and 20 kHz of each open channel state showed little frequency dependence. Noise from undetected conductance state transitions was insignificant. Johnson and shot noises were evaluated. Current noise caused by electrolyte concentration fluctuation via diffusion was isolated by its dependence on buffer concentration. After removing these contributions, significant current noise remains in all persistent channel states and increases in higher conductance states. In nonpersistent channels, remaining noise occurs primarily in the lowest two states. These fluctuations of channel conductance are attributed to thermal oscillations of the channel molecular conformation and are modeled as a Langevin translational oscillation of alamethicin molecules moving radially from the channel pore, damped mostly by lipid bilayer viscosity.

Alamethicin↗
PubMed1998

Growth factor release from thermally reversible tissue culture substrates.

Thermally reversible poly(N-isopropylacrylamide) (PIPAAm) was covalently grafted onto tissue culture dishes to allow detachment of cultured cells upon temperature change from physiological to room temperature. In addition the grafted polymer matrix was used to entrap biomolecules such as growth factors either to be released by diffusion early in cell cultures, or remain entrapped and be reversibly exposed to cell receptors. Experiments with model proteins trypsin and insulin show that amount loaded and released depends upon the PIPAAm grafting density. Dishes grafted with 2.5 microgram/cm2 PIPAAm released approximately four times more model protein over 4 h than dishes grafted with 1.8 microgram/cm2. This in vitro drug delivery system can be used to deliver factors to the basal side of cells early in cell culture by providing high local concentrations without high bulk concentration. Cultures of human retinal pigmented epithelium showed higher growth rate on insulin loaded dishes than on controls containing a similar bulk solution concentration. These cultures retained the ability to detach singly or as confluent sheets from the loaded surfaces.

Adult↗