PubMed Health⌕ Search

Biomedical subjects

S Dietrich

Publications and source records attributed to S Dietrich.

At least 19 recordsLinked to original sources
PubMed2006

Microscopic theory for interface fluctuations in binary liquid mixtures.

Thermally excited capillary waves at fluid interfaces in binary liquid mixtures exhibit simultaneously both density and composition fluctuations. Based on a density functional theory for inhomogeneous binary liquid mixtures we derive an effective wavelength dependent Hamiltonian for fluid interfaces in these systems beyond the standard capillary-wave model. Explicit expressions are obtained for the surface tension, the bending rigidities, and the coupling constants of compositional capillary waves in terms of the profiles of the two number densities characterizing the mixture. These results lead to predictions for grazing-incidence x-ray scattering experiments at such interfaces.

Journal Article↗
PubMed2006

Surface properties of fluids of charged platelike colloids.

Surface properties of mixtures of charged platelike colloids and salt in contact with a charged planar wall are studied within density functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model [J. Chem. Phys. 39, 1714 (1963)] and the charges of the particles are concentrated at their centers. The density functional applied is an extension of a recently introduced functional for charged platelike colloids. It provides a qualitative approach because it does not determine the relation between the actual and the effective charges entering into the model. Technically motivated approximations, such as using the Zwanzig model, are expected not to influence the results qualitatively. Analytically and numerically calculated bulk and surface phase diagrams exhibit first-order wetting for sufficiently small macroion charges and isotropic bulk order as well as first-order drying for sufficiently large macroion charges and nematic bulk order. The asymptotic wetting and drying behaviors are investigated by means of effective interface potentials which turn out to be asymptotically the same as for a suitable neutral system governed by isotropic nonretarded dispersion forces. Wetting and drying points as well as predrying lines and the corresponding critical points have been located numerically. A crossover from monotonic to nonmonotonic electrostatic potential profiles upon varying the surface charge density has been observed. Nonmonotonic electrostatic potential profiles are equivalent to the occurrence of charge inversion. Due to the presence of both the Coulomb interactions and the hard-core repulsions, the surface potential and the surface charge do not vanish simultaneously, i.e., the point of zero charge and the isoelectric point of the surface do not coincide.

Journal Article↗
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↗
PubMed2006

Complete wetting of nanosculptured substrates.

Complete wetting of geometrically structured substrates by one-component fluids with long-ranged interactions is studied theoretically. We consider periodic arrays of rectangular or parabolic grooves and lattices of cylindrical or parabolic pits. We show that the midpoint interfacial heights within grooves and pits are related in the same way as for complete wedge and cone filling. For sufficiently deep cavities with vertical walls and small undersaturation, an effective planar scaling regime emerges. The scaling exponent is -1/3 in all cases studied, and only the amplitudes depend on the geometrical features. We find quantitative agreement with recent experimental data for such systems.

Journal Article↗
PubMed2006

Lateral and normal forces between patterned substrates induced by nematic fluctuations.

We consider a nematic liquid crystal confined by two parallel flat substrates whose anchoring conditions vary periodically in one lateral direction. Within the Gaussian approximation, we study the effective forces between the patterned substrates induced by the thermal fluctuations of the nematic director. The shear force oscillates as a function of the lateral shift between the patterns on the lower and the upper substrates. We compare the strength of this fluctuation-induced lateral force with the lateral van der Waals force arising from chemically structured adsorbed monolayers. The fluctuation-induced force in the normal direction is either repulsive or attractive, depending on the model parameters.

Journal Article↗
PubMed2006

Forces between chemically structured substrates mediated by critical fluids.

We consider binary liquid mixtures close to their critical points confined by two parallel, geometrically flat, and chemically structured substrates. Universal order parameter profiles are calculated within mean field theory for periodic patterns of stripes with alternating preferences for the two species of the mixture and with different relative positions of the two substrates. From the order parameter profiles the effective forces between the two plates are derived. The tuning of Casimir amplitudes is discussed.

Journal Article↗
PubMed2006

[Attention and executive functions in patients with severe obesity. A controlled study using the Attention Network Test].

In this paper, attention and temperament are compared between 41 severely obese patients with psychiatric comorbidity and 45 control persons. Networks of attention were assessed by the Attention Network Test: alerting (ability to achieve and maintain an alert state), orienting (ability to orient to a stimulus), and executive attention (ability to resolve conflict). According to hypotheses, obese patients show reduced executive attention, more effortful control, and higher negative affectivity than controls. The concept of attention networks is related to cognitive mechanisms of self-regulation, opening new perspectives for understanding psychiatric disorders.

Adolescent↗
PubMed2006

Proliferation-based T-cell selection for immunotherapy and graft-versus-host-disease prophylaxis in the context of bone marrow transplantation.

Graft-versus-host disease (GvHD) caused by alloreactive T cells within the graft is a major drawback of allogeneic BMT, but depletion of T cells leads to higher rates of relapse, opportunistic infections and graft failure. Therefore, selective removal of GvHD-inducing alloreactive T cells might be beneficial. We describe here the separation of alloresponsive T cells, based on carboxyfluorescein succimidyl ester labeling, in vitro allostimulation and FACS-sorting. In vivo effects of the separated cell populations were investigated in the context of allogeneic BMT in murine models: in vitro resting T cells were shown to survive in the allogeneic host and retain immunoreactivity against 'third-party' antigens. As demonstrated in two different transplantation models, elimination of proliferating cells significantly reduces GvHD but offers no advantages to using T-cell-depleted bone marrow alone concerning engraftment and tumor control. Transplanting T cells that proliferate in response to tumor antigens in vitro may narrow down the spectrum of antigens recognized by T cells and therefore reduce GvHD while maintaining graft-facilitating function and tumor control. Therefore, selecting tumor-reactive T cells on the basis of their proliferative response in vitro may be beneficial for the recipient, less time consuming than T-cell cloning and still reduce the extent of GvHD.

Animals↗
PubMed2006

Public beliefs about and attitudes towards people with mental illness: a review of population studies.

OBJECTIVE: To provide a review of population-based attitude research in psychiatry during the past 15 years. METHOD: An electronic search using PubMed, Medline, and Academic Search Premier plus a hand search of the literature was carried out for studies on public beliefs about mental illness and attitudes towards the mentally ill published between 1990 and 2004. RESULTS: Thirty-three national studies and 29 local and regional studies were identified, mostly from Europe. Although the majority are of descriptive nature, more recent publications include studies testing theory-based models of the stigmatization of mentally ill people, analyses of time trends and cross-cultural comparisons, and evaluations of antistigma interventions. CONCLUSION: Attitude research in psychiatry made considerable progress over the past 15 years. However, there is still much to be done to provide an empirical basis for evidence-based interventions to reduce misconceptions about mental illness and improve attitudes towards persons with mental illness.

Attitude to Health↗
PubMed2005

Free isotropic-nematic interfaces in fluids of charged platelike colloids.

Bulk properties and free interfaces of mixtures of charged platelike colloids and salt are studied within the density-functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model. The charges of the particles are concentrated in their center. The density functional is derived by functional integration of an extension of the Debye-Hückel pair distribution function with respect to the interaction potential. For sufficiently small macroion charges, the bulk phase diagrams exhibit one isotropic and one nematic phase separated by a first-order phase transition. With increasing platelet charge, the isotropic and nematic binodals are shifted to higher densities. The Donnan potential between the coexisting isotropic and nematic phases is inferred from bulk structure calculations. Nonmonotonic density and nematic order parameter profiles are found at a free interface interpolating between the coexisting isotropic and nematic bulk phases. Moreover, electrically charged layers form at the free interface leading to monotonically varying electrostatic potential profiles. Both the widths of the free interfaces and the bulk correlation lengths are approximately given by the Debye length. For fixed salt density, the interfacial tension decreases upon increasing the macroion charge.

Journal Article↗
PubMed2005

Critical adsorption at chemically structured substrates.

We consider binary liquid mixtures near their critical consolute points and exposed to geometrically flat but chemically structured substrates. The chemical contrast between the various substrate structures amounts to opposite local preferences for the two species of the binary liquid mixtures. Order parameter profiles are calculated for a chemical step, for a single chemical stripe, and for a periodic stripe pattern. The order parameter distributions exhibit frustration across the chemical steps which heals upon approaching the bulk. The corresponding spatial variation of the order parameter and its dependence on temperature are governed by universal scaling functions which we calculate within mean field theory. These scaling functions also determine the universal behavior of the excess adsorption relative to suitably chosen reference systems.

Journal Article↗
PubMed2005

Effective capillary interaction of spherical particles at fluid interfaces.

We present a detailed analysis of the effective force between two smooth spherical colloids floating at a fluid interface due to deformations of the interface in an inhomogeneous pressure field. The results hold in general and are applicable independently of the source of the deformation provided the capillary deformations are small so that a superposition approximation for the deformations is valid. We conclude that an effective long-ranged attraction is possible if the net force on the system does not vanish. Otherwise, the interaction is short ranged and cannot be computed reliably based on the superposition approximation. As an application, we consider the case of like-charged, smooth nanoparticles and electrostatically induced capillary deformation. The resulting long-ranged capillary attraction can be easily tuned by a relatively small external electrostatic field, but it cannot explain recent experimental observations of attraction if these experimental systems were indeed isolated.

Journal Article↗
PubMed2005

Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets.

Density functional theory is used to study binary colloidal fluids consisting of hard spheres and thin platelets in their bulk and near a planar hard wall. This system exhibits liquid-liquid coexistence of a phase that is rich in spheres (poor in platelets) and a phase that is poor in spheres (rich in platelets). For the mixture near a planar hard wall, we find that the phase rich in spheres wets the wall completely upon approaching the liquid demixing binodal from the sphere-poor phase, provided the concentration of the platelets is smaller than a threshold value which marks a first-order wetting transition at coexistence. No layering transitions are found, in contrast to recent studies on binary mixtures of spheres and nonadsorbing polymers or thin hard rods.

Journal Article↗
PubMed2005

Matrix metalloproteinase 19 processes the laminin 5 gamma 2 chain and induces epithelial cell migration.

In this study we analyzed the proteolytic activity of MMP-19 and its impact on keratinocyte migration. In the HaCaT keratinocyte cell line overexpressing wild-type MMP-19 (HaCaT-WT), transmigration through fibrin and type IV collagen matrices was significantly increased compared to cells harboring a catalytically inactive mutant (HaCaT-EA). Studying the expression of MMP-19 in early stages of squamous cell cancer (SCC), we found co-localization of MMP-19 and laminin 5 at the invading tumor front but not in suprabasal epidermis of the tumor. Examination of laminin 5 processing revealed increased processing of the gamma2 chain in the medium and matrix of HaCaT-WT cells and degradation by recombinant human MMP-19 to 105-kDa and 80-kDa fragments. Parental HaCaT grown on the matrix of HaCaT-WT and HaCaT-EA cells displayed differential tyrosine phosphorylation. Using integrin blocking and stimulating antibodies we could attribute these differences to a shift from beta4-integrin-dependent signaling on the HaCaT-EA matrix toward alpha3-integrin-dependent signaling on the HaCaT-WT matrix. As a consequence, parental HaCaT showed increased migration on the matrix of HaCaT-WT cells. These data suggest that the MMP-19-dependent processing of the gamma2 chains leads to the integrin switch favoring epithelial migration and that MMP-19 actively participates in the early stages of SCC invasion.

Cell Movement↗
PubMed2005

Media consumption and desire for social distance towards people with schizophrenia.

There is ample evidence for a distorted presentation of the mentally ill in the media. However, only little is known about its impact on attitudes towards people with mental disorders. Therefore, we investigated the relationship between watching TV and reading the newspaper on the one hand, and the desire for social distance towards people with schizophrenia on the other. In 2001, a representative population survey was conducted in Germany, using a fully structured personal interview. We found that the desire for social distance towards people with schizophrenia increases almost continuously with the amount of TV consumption. The association between reading the newspaper and social distance is less pronounced and depends on the type of newspaper people read. Since, obviously, there is a relationship between media consumption and attitudes towards people with schizophrenia, inaccurate and one-sided messages about mental disorders should be replaced by accurate and more balanced messages.

Adolescent↗
PubMed2004

Critical adsorption and Casimir torque in wedges and at ridges.

Geometrical structures of confining surfaces profoundly influence the adsorption of fluids upon approaching a critical point T(c) in their bulk phase diagram, i.e., for t= (T- T(c) ) / T(c) -->+/-0 . Guided by general scaling considerations, we calculate, within the mean-field theory, the temperature dependence of the order parameter profile in a wedge with opening angle gamma pi) for T>< T(c) and in the presence of surface fields. For a suitably defined reduced excess adsorption Gamma (+/-) (gamma,t-->+/-0) approximately Gamma (+/-) (gamma) mid R:tmid R:(beta-2nu) we compute the universal amplitudes Gamma (+/-) (gamma) , which diverge as Gamma (+/-) (gamma-->0) approximately 1/gamma for small opening angles, vary linearly close to gamma=pi for gamma 2pi . There is evidence that, within the mean-field theory, the ratio Gamma (+) (gamma) / Gamma (-) (gamma) is independent of gamma . We also discuss the critical Casimir torque acting on the sides of the wedge as a function of the opening angle and temperature.

Journal Article↗