Biomedical subjects
Publications and source records attributed to J R Henderson.
Recent work has raised serious doubts as to whether widely used current statistical mechanical methods are applicable to model colloidal systems. This Letter reports a simulation test strongly supporting a complex scenario that has important implications for the future development of theoretical colloidal physics.
The statistical geometry of hard-sphere mixtures, as defined by Speedy and Reiss, is found to lead to a sum rule that is identical in form to the fundamental equation of the generalized ensemble. This leads one to conjecture the specific form of a set of thermodynamic fields entirely defined by ensemble averages of geometric properties of the configurations. The potential for a direct physical understanding of these quantities is discussed and it is noted that they could, therefore, be of crucial significance to our future understanding of colloidal physics. In the presence of an ideal wall, an analogous sum rule is obtained in terms of interfacial geometric properties (the available surface area for insertions at the wall). For this case, which generalizes beyond hard-sphere models, there exists an obvious physical interpretation involving complete wetting at the ideal wall.
The physics of wetting transitions (stability of fluid films adsorbed at planar substrates) is reassessed in the context of the original theory of wetting known as Frumkin-Derjaguin theory [A. Frumkin, Zh. Fiz. Khim. 12, 337 (1938)]. In particular, the Russian School classify wetting phenomena in terms of the mean-field disjoining pressure. The integral of the mean-field disjoining pressure, with respect to film thickness, defines the interface potential accessible from density-functional theory (DFT). For wall-fluid models (substrate defined as an external field), the exact disjoining pressure of an adsorbed film can be expressed as a one-body sum rule. One of the aims of this work is to verify the internal consistency of the statistical thermodynamics of Frumkin-Derjaguin theory, by direct evaluation of the disjoining pressure sum rule, using DFT. For short-range models, the form of the interface potential (and hence disjoining pressure) is directly obtainable from liquid-state asymptotics. The second aim of this work is to verify from DFT that for standard short-range models there are three qualitatively different regimes, arising from competition between the correlation lengths predicted by asymptotic theory. A variety of related issues are also considered, including (i) crossover between the various regimes, (ii) incorporation of capillary-wave fluctuations (beyond mean-field), and (iii) qualitative changes induced by power-law dispersion interactions and the related prediction of two-stage wetting.
We report ellipsometrically obtained adsorption isotherms for a carefully chosen test liquid on block copolymer films of Kraton G1650, compared with adsorption isotherms on homogeneous films of the constituent polymers. Standard atomic force microscopy images imply the outer surface of Kraton G1650 is chemically patterned on the nanoscale, but this could instead be a reflection of structure buried beneath a 10 nm layer of the lower energy component. Our test liquid was chosen on the basis that it did not dissolve in either component and in addition that it was nonwetting on the lower energy polymer while forming thick adsorbed films on pure substrates of the higher energy component. Our ellipsometry data for Kraton G1650 rule out the presence of segregation by the lower energy constituent to the outer surface, implying a mixed surface consistent with Cassie's law. We discuss implications of our findings and related work for the outer surface structures of block copolymer films.
We investigate the solvation of a hard spherical cavity, of radius R, immersed in a fluid for which the interparticle forces are short ranged. For thermodynamic states lying close to the liquid binodal, where the chemical potential deviation deltamu is identical with mu-muco(T) is very small and positive, complete wetting by gas (drying) occurs and two regimes of interfacial behavior can be identified. These are characterized by the length scale Rc=2gamma(gl)infinity/(Deltarhodeltamu), where gamma(gl)infinity is the planar gas-liquid surface tension and Deltarho is the difference in coexisting densities at temperature T. For R>Rc, the interfacial free energy and the density profile of the fluid near the hard wall can be expanded in powers of the curvature R(-1), in keeping with the analysis of Stillinger and Cotter [J. Chem. Phys. 55, 3449 (1971)]. In the other regime, R 0, of the work of formation of a hard spherical cavity and of the Gibbs adsorption and the fluid density at contact with the wall. Our analysis, which is based on an effective interfacial Hamiltonian combined with exact statistical mechanical sum rules, is confirmed fully by the results of microscopic density functional calculations for a square-well fluid. We discuss the repercussions of our results for solvation phenomena, emphasizing that nonanalytic behavior equivalent to that we find for complete drying in solvophobic systems will also arise in the case of complete wetting, i.e. when liquid films are adsorbed on the surface of large (colloidal) particles or at curved substrates. We reassess various results in the important but neglected Stillinger-Cotter paper, where drying was not considered explicitly, in the light of our present analysis.
I consider the statistical mechanics of inhomogeneous fluids applied to fluids adsorbed in planar wedges. Exact results are described that belong to an infinite subset of models defined as the intersection of any two identical semi-infinite planar wall-fluid potentials. This geometry is interesting as a generic example of adsorption onto structured interfaces and of interfacial phase transitions controlled by the substrate geometry. Previously described virial theorems are extended to the case of a general wall-fluid model. This enables the consideration of wedge filling when Young's contact angle far from the wedge apex is finite. The virial theorems generate two important relations: the wedge sum rules. The first sum rule links the interfacial free energy far from the wedge apex to the structure induced at the apex. The second sum rule links the free energy of the apex region to the structure induced by the apex. When Young's contact angle at the wedge walls is finite these relations further yield an exact result for the macroscopic contact angle in terms of the nanoscopic structure at the three-phase contact line (the intersection of the liquid-vapor surface with a wedge wall): the contact angle sum rule. These exact results are of direct relevance to computer simulation studies of adsorbed films. In addition, they take on special significance in the vicinity of continuous interfacial phase transitions: an approach to complete filling and the filling transition at bulk liquid-vapor coexistence.
Metropolis Monte Carlo simulations are used to investigate the wetting of chemically nanopatterned surfaces, for the case of hexagonal disk patterns where liquid wishes to wet high-energy circular patches but not wet the background surface. We calculate the density profiles of saturated liquid adsorbed on a variety of such substrates, spanning the nanoscale to atomic scale patterns. In addition, statistical mechanical sum rules are used to obtain interfacial order parameters and interfacial free energies. We observe that Cassie's law is typically obeyed, together with an associated breakdown of the mechanical interpretation of Young's equation, for pattern wavelengths greater than 15 molecular diameters. Here, the adsorbed fluid exists as an array of hemi-drops. At about half this wavelength, the breakdown of Cassie's law lies within realistic energy scales and is associated with the unbending of the outer surface of adsorbed films. For atomic scale patterns, the usual interpretation of Young's equation is restored for films thicker than one monolayer. At high chemical contrast, when the monolayer in contact with high-energy regions would prefer to be crystalline, we observe a variety of exotic interfacial phenomena that may have technological significance.
An exact sum rule is derived that links the structure of fluids adsorbed in wedges and at edges to the interfacial free energy far from the wedge apex. By focusing on hard-wall models, one observes a correspondence between interfacial statistical mechanics and geometry. The physical necessity of this correspondence can be argued from the presence of complete drying at a hard wall. Invoking the potential distribution theorem generates yet another class of geometric results, this time concerning the excluded volume generated by a sphere rolling along the surface of the wedge. Direct proof of these latter geometric theorems is straightforward in two-dimensions. Acute wedges and the right-angled wedge, provide examples of models for which comparison with simulation data and density functional theory are available.
Wilhelmy plate measurements of contact angles with a series of test liquids are used to calculate the surface energies of two poly(ethylene-co-1-butene) random copolymers. Results from five methods of calculation are reported: one-liquid (Good-Girifalco and Neumann), two-liquid (harmonic mean and geometric mean), and three-liquid (Lifshitz-van der Waals acid-base) methods. We find that all five methods are sensitive to the choice of test liquids used for contact angle measurements, as previously reported, but consistent results are obtained if recommended combinations of liquids are used. The mean results of the three-liquid acid-base method are judged to be the most reliable and informative, leading to surface energies of 30.8 mJ/m2 for poly(ethylene-co-1-butene) copolymer composed of 92 mol% ethylene and 30.2 mJ/m2 for copolymer composed of 88 mol% ethylene.
Measurements of the diamagnetic susceptibility chi(a), the rotational viscosity coefficient gamma(1), and the micellar orientational order parameter S have been made as a function of temperature across the entire nematic phases of cesium pentadecafluorooctanoate (CsPFO)-D2O samples over the concentration range weight fraction CsPFO w from 0.350 to 0.500. This has been chosen so as to embrace the pseudo-nematic phase-lamellar tricritical point that has been purported to occur at w=0.43 (volume fraction phi=0.26). The values of gamma(1) vary from about 0.1 kg m(-1) s(-1) to 1000 kg m(-1) s(-1) as the temperature decreases across the nematic phase, covering a much larger range than those reported for thermotropic liquid crystals. Measurements of gamma(1) have been made much closer to the critical temperature T(LN) than have previously been reported [(T-T(LN))/T(LN)=2 x 10(-5) for the w=0.350 sample]. The rotational viscosity critical exponents x calculated from the divergence of gamma(1) on approaching the nematic-phase-to-lamellar transition are found to be constant at 2/3 independent of the concentration. These values differ from those of 1/3 and 1/2, respectively, predicted by the He-like three-dimensional XY and mean-field models, in combination with mean-field dynamical relaxation. However, the former would be supported if complete Fisher renormalization (at alpha=1/2) was appropriate over an extended concentration range. Alternatively, this could be an indication of the importance of coupling between the micellar rotational dynamics and critical fluctuations since the latter are seen to be predominant across the entire temperature range of the nematic phase as revealed in the temperature dependence of gamma(1).
Deuterium NMR spectroscopy of 2H2O has been used to monitor the magnetic-field-induced order on approaching a transition to a nematic phase in isotropic solutions of disklike micelles of cesium pentadecafluorooctanoate. Highly accurate data on the phase boundaries and spinodals have been obtained for solutions with volume fraction concentration straight phi between 0.078 and 0.201. The quantity TIN-T*, where T* is the spinodal limit of the isotropic phase and TIN is the temperature at which the nematic phase first appears on cooling, decreases linearly with decreasing concentration, extrapolating to zero only at zero concentration. Thus, there is no evidence to support the presence of a Landau point along the transition line as has previously been conjectured. The values for (TIN-T*)/TIN are in the range 10(-5)-10(-4), up to two orders of magnitude smaller than corresponding values reported for calamitic thermotropic nematics. The transition gap (phiNI-phiIN)/phiIN approximately 0.33% for phi<0.20 is also very small, although finite as required for a first-order phase transition. These data, when combined with previously measured properties, present an intriguing picture of the isotropic-to-nematic phase transition in a paradigmatic system of self-assembled diskotic particles. However, it is not completely clear, within the context of current theoretical understanding, whether the behavior of this system is explicable by hard-particle models, or if the self-assembly plays a crucial role in weakening the phase transition.
Entanglements of Hawaiian monk seals, Monachus schauinslandi, were documented in the northwestern Hawaiian Islands (NWHI) from 1982 to 1998, and debris which presented a threat of entanglement was inventoried and removed from 1987 to 1996. A total of 173 entanglements was documented. The number of entanglements did not change after implementation of MARPOL Annex V in 1989. Pups and juvenile seals were more likely to become entangled than older seals, and became entangled primarily in nets, whereas entanglement of subadults and adults was more likely to involve line. The subpopulation of seals at Lisianski Island experienced the most entanglements, although Lisianski did not accumulate the most debris. Localized high entanglement rates may gravely affect individual monk seal subpopulations. Accumulation of debris has not diminished since implementation of Annex V, nor has occurrence of derelict drift nets abated since a 1989 moratorium. Debris washing ashore has likely been circulating in the North Pacific Ocean for some time.
OBJECTIVE: To determine the efficacy and safety of the potassium channel blocker tedisamil versus placebo in the treatment of patients with stable angina. DESIGN: Prospective, double blind, placebo controlled study. 203 patients first completed a seven day placebo run in. They were then randomised to receive 50 mg, 100 mg or 150 mg tedisamil twice daily, or placebo. Treadmill exercise testing was carried out at baseline and after 14 days of double blind treatment. MAIN OUTCOME MEASURES: Primary efficacy parameters were an increase in total exercise duration and a reduction of the sum of ST segment depression using six ECG leads at maximum workload at trough (12 hours after last medication). Secondary aims included increase in exercise time to onset of 0.1 mV ST segment depression, increase in exercise time to onset of any anginal pain, and reduction in ST segment depression in any of the six specified leads at maximum workload. These were all at trough. The same parameters were also assessed at peak concentrations (two hours after administration). Overall attacks of angina and the use of short acting nitrates were assessed from patient diaries. RESULTS: Tedisamil led to a dose dependent prolongation of exercise duration (significant at all concentrations), an effect that was greater at peak than at trough. Treatment also led to a significant dose dependent reduction in the sum of ST segment depression at both trough and peak concentrations. Tedisamil also decreased (in a dose dependent way) the frequency of anginal attacks and the consumption of short acting nitrates, an improvement that became significant for all doses in the second treatment week. Adverse events with tedisamil were few. There was a pronounced rise in the incidence of diarrhoea with the 150 mg twice daily regimen. Bradycardic effects and increases in QT interval were dose dependent, but were no more evident at exercise than at rest. CONCLUSIONS: Tedisamil, at doses of 50-100 mg twice daily, was found to be an effective antianginal and anti-ischaemic agent. At doses above 100 mg twice daily its main side effect, diarrhoea, becomes pronounced; therefore the 50-100 mg twice daily regimen appears to be appropriate.
LIM domains are double zinc-finger motifs found in many proteins that play central roles in cell differentiation. Members of the cysteine-rich protein (CRP) family display two LIM domains and are implicated in muscle development. Here we describe the characterization of one member of this family, CRP1, in the mouse. We have isolated and sequenced murine cDNAs that encode CRP1. We have determined by Northern analysis and in situ hybridization that CRP1 expression is developmentally regulated in the embryonic mouse and displays organ specific regulation in adults. The gene encoding CRP1 is expressed in the smooth muscle cells (SMCs) of the dorsal aorta at E9.5, thus illustrating that CRP1 is an early marker for SMC differentiation at that site. As development proceeds, CRP1 transcripts are observed throughout the SMC lineage, with minimal, transient expression detected in skeletal and cardiac muscle. Interestingly, although several markers of mature smooth muscle are already expressed, CRP1 expression in the bladder is not upregulated until the onset of bladder expansion at embryonic day 16.5, at which time its expression becomes very prominent. CRP1 expression persists into adulthood with prominent expression observed in both vascular and visceral smooth muscle. The results reported here define CRP1 as a general marker of smooth muscle lineages.
BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors have an accepted place in the treatment of hypertension and heart failure. However, at present they have no specific role in the prevention or treatment of coronary artery disease: evidence from animal experiments and some of the large ACE inhibitor cardiac studies makes this effect well worth testing. OBJECTIVE: The objective of EUROPA is to assess the effects of perindopril (an ACE inhibitor) on outcome in patients with stable coronary artery disease, but no clinical heart failure. METHODS: This is a double-blind, placebo-controlled, multicentre study with a duration of 3.5 years. It is proposed to recruit 10500 patients from 24 countries in Europe. The primary end-point is a combined one: total mortality, non-fatal acute myocardial infarction, unstable angina pectoris and cardiac arrest with successful resuscitation are included; the outcome is studied in patients with proven coronary artery disease and no clinical heart failure. Secondary end-points consist of these events individually calculated. The first patient was recruited in October 1997, and it is planned to finish recruitment by the end of 1998.
Ganciclovir (Cymevene*) is an antiviral drug that shows efficacy against cytomegalovirus (CMV) infections. These are particularly important in patients with AIDS or iatrogenic immunosuppression. Ganciclovir is a virostatic agent that prevents viral DNA replication: it is effective in CMV retinitis, colitis and pneumonitis. Since the drug is particularly taken up by cells with a high rate of DNA replication, its adverse effects are most pronounced in bone marrow and testis; its present indications are therefore only for serious CMV disease.
The distribution of oxytocin and vasopressin in the adrenals of rat, cow, hamster and guinea pig has been studied by use of immunohistochemical techniques. In all the species studied the adrenal cortex contained both peptides; the staining in the zona glomerulosa being more intense than that in zona fasciculata or zona reticularis. The medulla, however, showed considerable species variation. In the cow, both peptides appear to be present in the adrenergic and noradrenergic cells, though staining was particularly prominent in cortical islands interspersed within the medullary tissue. In the rat, groups of medullary cells positive for both peptides were found, though it was not possible to associate these groups with particular chromaffin cell types. In the hamster oxytocin was present only in adrenaline-containing cells, whereas vasopressin was present in all medullary cells. The guinea pig medulla, which contains only adrenaline-secreting cells, was positive for both peptides. The possibilities that vasopressin and oxytocin have an autocrine or paracrine role in functioning of the adrenal gland is discussed.