Biomedical subjects

R Roth

Publications and source records attributed to R Roth.

At least 19 recordsLinked to original sources

PubMed2006

Depletion forces between nonspherical objects.

We extend the insertion approach for calculating depletion potentials to the case of nonspherical solutes. We suggest to employ the recently developed curvature expansion of density profiles close to complexly shaped walls. The approximations introduced in the calculation by the use of the curvature expansion and of weight functions for nonspherical objects can be tested independently. As an application for our approach we calculate and discuss the depletion potential between two hard oblate ellipsoids in a solvent of hard spheres. For this system we calculate the entropic force and torque acting on the objects.

Journal Article↗

PubMed2005

General methods for free-volume theory.

Free-volume theory for understanding depletion phenomena in mixtures of two species is generally derived using scaled-particle theory for those specific entities. Here we first give a general scaled-particle method for convex bodies in terms of the characteristic geometrical measures of the depletion agent, i.e., its volume, surface area, and integrated mean curvature, in mixtures with hard spheres. Second, we show that similar results can be derived from fundamental-measure theory. This different approach allows us to get a deep insight into the meaning of the various contributions to the theory from a geometrical point of view. From these two methods we arrive at a generalized "recipe" to free-volume theory. This recipe can be based on a desired equation of state for any convex shape of the depletion agents and is also valid for (polydisperse) mixtures of those. This is illustrated by mixtures of spheres with ellipsoids, spheres with several geometries as models for disklike mesogens, e.g., gibbsite, as well as depletion of spheres due to bar-shaped colloids, e.g., goethite.

Journal Article↗

PubMed2005

Solvent mediated interactions close to fluid-fluid phase separation: microscopic treatment of bridging in a soft-core fluid.

Using density functional theory we calculate the density profiles of a binary solvent adsorbed around a pair of big solute particles. All species interact via repulsive Gaussian potentials. The solvent exhibits fluid-fluid phase separation, and for thermodynamic states near to coexistence the big particles can be surrounded by a thick adsorbed "wetting" film of the coexisting solvent phase. On reducing the separation between the two big particles we find there can be a "bridging" transition as the wetting films join to form a fluid bridge. The effective (solvent mediated) potential between the two big particles becomes long ranged and strongly attractive in the bridged configuration. Within our mean-field treatment the bridging transition results in a discontinuity in the solvent mediated force. We demonstrate that accounting for the phenomenon of bridging requires the presence of a nonzero bridge function in the correlations between the solute particles when our model fluid is described within a full mixture theory based upon the Ornstein-Zernike equations.

Journal Article↗

PubMed2005

Inactivation of swmA results in the loss of an outer cell layer in a swimming synechococcus strain.

The mechanism of nonflagellar swimming of marine unicellular cyanobacteria remains poorly understood. SwmA is an abundant cell surface-associated 130-kDa glycoprotein that is required for the generation of thrust in Synechococcus sp. strain WH8102. Ultrastructural comparisons of wild-type cells to a mutant strain in which the gene encoding SwmA has been insertionally inactivated reveal that the mutant lacks a layer external to the outer membrane. Cryofixation and freeze-substitution are required for the preservation of this external layer. Freeze fracturing and etching reveal that this additional layer is an S-layer. How the S-layer might function in motility remains elusive; however, this work describes an ultrastructural component required for this unique type of swimming. In addition, the work presented here describes the envelope structure of a model swimming cyanobacterium.

Bacterial Proteins↗

PubMed2004

Nonanalytic curvature contributions to solvation free energies: influence of drying.

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.

Journal Article↗

PubMed2004

Decay of correlation functions in hard-sphere mixtures: structural crossover.

We investigate the decay of pair correlation functions in a homogeneous (bulk) binary mixture of hard spheres. At a given state point the asymptotic decay r-->infinity of all three correlation functions is governed by a common exponential decay length and a common wavelength of oscillations. Provided the mixture is sufficiently asymmetric, size ratios q less than or approximately 0.7, we find that the common wavelength reflects either the size of the small or that of the big spheres. By analyzing the (complex) poles of the partial structure factors we find a sharp structural crossover line in the phase diagram. On one side of this line the common wavelength is approximately the diameter of the smaller sized spheres whereas on the other side it is approximately the diameter of the bigger ones; the wavelength of the longest ranged oscillations changes discontinuously at the structural crossover line. Using density functional theory and Monte Carlo simulations we show that structural crossover also manifests itself in the intermediate range behavior of the pair correlation functions and we comment on the relevance of this observation for real (colloidal) mixtures. In highly asymmetric mixtures, q< or =0.1, where there is metastable fluid-fluid transition, we find a Fisher-Widom line with two branches. This line separates a region of the phase diagram where the decay of pair correlations is oscillatory from one in which it is monotonic.

Journal Article↗

PubMed2004

Morphological thermodynamics of fluids: shape dependence of free energies.

We examine the dependence of a thermodynamic potential of a fluid on the geometry of its container. If motion invariance, continuity, and additivity of the potential are satisfied, only four morphometric measures are needed to describe fully the influence of an arbitrarily shaped container on the fluid. These three constraints can be understood as a more precise definition for the conventional term extensive and have as a consequence that the surface tension and other thermodynamic quantities contain, aside from a constant term, only contributions linear in the mean and Gaussian curvature of the container and not an infinite number of curvatures as generally assumed before. We verify this numerically in the entropic system of hard spheres bounded by a curved wall.

Journal Article↗

PubMed2004

[Pulmonary embolism caused by PMMA in percutaneous vertebroplasty. Case report and review of the literature].

We report on an 80-year-old female patient with osteoporotic collapse of the L1 vertebra who developed absolute stenosis of the spinal canal. During preoperative vertebra augmentation with PMMA (polymethylmethacrylate), pulmonary embolism developed due to perivertebral leakage of acrylic cement. According to the literature, leakage of PMMA during (percutaneous) vertebroplasty is a more frequent complication than assumed so far. In view of the favorable prognosis of osteoporotic vertebral compression fractures with noninvasive management, we emphasize the need for clear and individual indications and adequate technical settings.

Aged↗

PubMed2004

Psychological impact of childhood islet autoantibody testing in families participating in the BABYDIAB study.

AIMS: To determine anxiety in parents of children undergoing testing for islet autoantibodies. SUBJECTS AND METHODS: Children of parents with Type 1 diabetes (T1DM) were tested at birth, age 9 months, 2 years and 5 years for islet autoantibodies. Families were informed about islet autoantibody status in the child after each visit. The psychological impact of islet autoantibody testing was assessed in parents before and after the 5 years visit. Anxiety was measured using a subscale of the State-Trait-Anxiety Inventory (STAI) and structured single-item questions. Four hundred and sixty-three parents were evaluated before blood drawing and 317 parents at notification of islet autoantibody status. RESULTS: Before blood withdrawal, anxiety was increased in mothers and in particular in mothers of islet autoantibody-positive offspring compared with a normative control group. At notification of islet antibody status, anxiety significantly decreased in parents of islet autoantibody-negative offspring, and increased in parents of islet autoantibody-positive offspring. Blood withdrawal was considered a burden for parents and offspring (15% and 48%, respectively). Most parents from islet autoantibody-negative and -positive offspring wished to know the diabetes risk of their child (95% and 100%, respectively) and were glad to be informed about their child's islet antibody status (97% and 87%). CONCLUSIONS: Overall, islet autoantibody testing in early childhood reduces anxiety in T1DM families. The increased anxiety associated with islet autoantibody-positive status suggests, however, that testing should be performed in centres which can provide accurate risk information and counselling if required.

Anxiety↗

PubMed2003

Hard-sphere fluids in contact with curved substrates.

The properties of a hard-sphere fluid in contact with hard-spherical and cylindrical walls are studied. Rosenfeld's density functional theory (DFT) is applied to determine the density profile and surface tension gamma for wide ranges of radii of the curved walls and densities of the hard-sphere fluid. Particular attention is paid to investigate the curvature dependence and the possible existence of a contribution to gamma which is proportional to the logarithm of the radius of curvature. Moreover, by treating the curved wall as a second component at infinite dilution, we provide an analytical expression for the surface tension of a hard-sphere fluid close to arbitrary hard convex walls. The agreement between the analytical expression and DFT is good. Our results show no signs for the existence of a logarithmic term in the curvature dependence of gamma.

Journal Article↗

PubMed2003

Direct measurement of entropic forces induced by rigid rods.

We present the first direct depletion potential measurements for a single colloidal sphere close to a wall in a suspension of rigid colloidal rods. Since all particle interactions are as good as hard-core-like, the depletion potentials are of entirely entropic origin. We developed a density functional theory approach that accurately accounts for this experimental situation. The depletion potentials calculated for different rod number densities are in very good quantitative agreement with the experimental results.

Colloids↗

PubMed2002

Entropic torque.

Quantitative predictions are presented of a depletion-induced torque and force acting on a single colloidal hard rod immersed in a solvent of hard spheres close to a planar hard wall. This torque and force, which are entirely of entropic origin, may play an important role for the key-lock principle, according to which a biological macromolecule (the key) is functional only in a particular orientation with respect to a cavity (the lock).

Journal Article↗

PubMed2002

Effective forces in colloidal mixtures: from depletion attraction to accumulation repulsion.

Computer simulations and theory are used to systematically investigate how the effective force between two big colloidal spheres in a sea of small spheres depends on the basic (big-small and small-small) interactions. The latter are modeled as hardcore pair potentials with a Yukawa tail which can be either repulsive or attractive. For a repulsive small-small interaction, the effective force follows the trends as predicted by a mapping onto an effective nonadditive hardcore mixture: both a depletion attraction and an accumulation repulsion caused by small spheres adsorbing onto the big ones can be obtained depending on the sign of the big-small interaction. For repulsive big-small interactions, the effect of adding a small-small attraction also follows the trends predicted by the mapping. But a more subtle "repulsion through attraction" effect arises when both big-small and small-small attractions occur: upon increasing the strength of the small-small interaction, the effective potential becomes more repulsive. We have further tested several theoretical methods against our computer simulations: The superposition approximation works best for an added big-small repulsion, and breaks down for a strong big-small attraction, while density functional theory is very accurate for any big-small interaction when the small particles are pure hard spheres. The theoretical methods perform most poorly for small-small attractions.

Journal Article↗

PubMed2002

Women's sexual behavior, body image and satisfaction with surgical outcomes after hysterectomy: a comparison of vaginal and abdominal surgery.

The aim of this study was to investigate the impact of vaginal and abdominal hysterectomy on women's sexual behavior, sexual dysfunction, body image and satisfaction with surgery. A prospective study was conducted on 90 women to evaluate the outcomes of hysterectomy. Data were collected prior to surgery, three months and two years after surgery, using self-report questionnaires. The results showed significant differences in women's sexual behavior and sexual dysfunction before and after hysterectomy, independent of the surgical procedure performed. Women in both groups reported improvements in sexual desire, sexual activity and sexual intercourse three months and two years after surgery. Sexual dysfunction such as dyspareunia, vaginismus, lack of orgasm and loss of sexual interest diminished significantly after surgery. Regression analyses revealed that postmenopausal status, severity of gynecological complaints and frequency of sexual intercourse were the most important factors for improved sexual outcomes. Women in the abdominal group were dissatisfied with their body image because of the abdominal scar, experienced more pain and had a longer period of recovery from surgery compared to women in the vaginal group. According to the results, sexual behavior alone is not an important factor in choosing vaginal or abdominal hysterectomy. However, sexual behavior was important in both groups when evaluating outcomes after hysterectomy.

Abdomen↗

PubMed2001

Theory of asymmetric nonadditive binary hard-sphere mixtures.

It is shown that the formal procedure of integrating out the degrees of freedom of the small spheres in a binary hard-sphere mixture works equally well for nonadditive as it does for additive mixtures. For highly asymmetric mixtures (small size ratios) the resulting effective Hamiltonian of the one-component fluid of big spheres, which consists of an infinite number of many-body interactions, should be accurately approximated by truncating after the term describing the effective pair interaction. Using a density functional treatment developed originally for additive hard-sphere mixtures the zero, one, and two-body contribution to the effective Hamiltonian are determined. It is demonstrated that even small degrees of positive or negative nonadditivity have significant effect on the shape of the depletion potential. The second virial coefficient B2, corresponding to the effective pair interaction between two big spheres, is found to be a sensitive measure of the effects of nonadditivity. The variation of B2 with the density of the small spheres shows significantly different behavior for additive, slightly positive and slightly negative nonadditive mixtures. Possible repercussions of these results for the phase behavior of binary hard-sphere mixtures are discussed and it is suggested that measurements of B2 might provide a means of determining the degree of nonadditivity in real colloidal mixtures.

Journal Article↗

PubMed2001

Intragenic recombination generated two distinct Cf genes that mediate AVR9 recognition in the natural population of Lycopersicon pimpinellifolium.

Resistance gene Cf-9 of cultivated tomato (Lycopersicon esculentum) confers recognition of the AVR9 elicitor protein of the fungal pathogen Cladosporium fulvum. The Cf-9 locus, containing Cf-9 and four homologs (Hcr9s), originates from Lycopersicon pimpinellifolium (Lp). We examined naturally occurring polymorphism in Hcr9s that confer AVR9 recognition in the Lp population. AVR9 recognition occurs frequently throughout this population. In addition to Cf-9, we discovered a second gene in Lp, designated 9DC, which also confers AVR9 recognition. Compared with Cf-9, 9DC is more polymorphic, occurs more frequently, and is more widely spread throughout the Lp population, suggesting that 9DC is older than Cf-9. The sequences of Cf-9 and 9DC suggest that Cf-9 evolved from 9DC by intragenic recombination between 9DC and another Hcr9. The fact that the 9DC and Cf-9 proteins differ in 61 aa residues, and both mediate recognition of AVR9, shows that in nature Hcr9 proteins with the same recognitional specificity can vary significantly.

Amino Acid Sequence↗

PubMed2001

Transmembrane orientation and topology of the NADH:quinone oxidoreductase putative quinone binding subunit NuoH.

NADH:quinone oxidoreductase, or Complex I, is a multi-subunit membrane-bound enzyme in the respiratory chain of many pro- and eukaryotes. The enzyme catalyzes the oxidation of NADH and donates electrons to the quinone pool, coupled to proton translocation across the membrane, but the mechanism of energy transduction is not understood. In bacteria the enzyme consists of 14 subunits, seven membrane spanning and seven protruding from the membrane. The hydrophobic NuoH (NQO8, ND1, NAD1, NdhA) subunit is seemingly involved in quinone binding. A homologous, structurally and most likely functionally similar subunit is also found in F(420)H2 oxidoreductases and in complex membrane-bound hydrogenases. We have made theoretical analyses of NuoH and NuoH-like polypeptides and experimentally analyzed the transmembrane topology of the NuoH subunit from Rhodobacter capsulatus by constructing and analyzing alkaline phosphatase fusion proteins. This demonstrated that the NuoH polypeptide has eight transmembrane segments, and four highly conserved hydrophilic sequence motifs facing the inside, bacterial cytoplasm. The N-terminal and C-terminal ends are located on the outside of the membrane. A topology model of NuoH based on these results is presented, and implications from the model are discussed.

Alkaline Phosphatase↗

PubMed2001

Survey of staphylococcal enterotoxin genes, exfoliative toxin genes, and toxic shock syndrome toxin 1 gene in non-Staphylococcus aureus species.

The aim of this study was to analyze the presence of staphylococcal exotoxin genes in staphylococci other than Staphylococcus aureus. Whereas for Staphylococcus aureus a large spectrum of different exotoxins responsible for toxin-mediated diseases has been described, only few and conflicting data are available regarding toxin production in all other staphylococcal species. A collection of clinical non-Staphylococcus aureus staphylococcal isolates were systematically screened for the presence of genes for toxic shock syndrome toxin 1, exfoliative toxins, and classical enterotoxins by using multiplex polymerase chain reaction enzyme immunoassays. In a total of 461 isolates of 18 different (sub)species derived from clinical specimens, no toxin gene sequences were amplified. The results indicate that the occurrence of toxin genes involved in staphylococcal toxin-mediated diseases is at least very rare in human-derived isolates of non-Staphylococcus aureus species.

Bacterial Toxins↗