789 research outputs found
Finite Temperature QCD Interfaces Out of Equilibrium
The properties of interfaces in non-equilibrium situations are studied by
constructing a density matrix with a space-dependent temperature. The
temperature gradient gives rise to new terms in the equation for the order
parameter. Surface terms induced in effective actions by abrupt temperature
changes provide a natural theoretical framework for understanding the occurence
of both continuous and discontinuous behavior in the order parameter. Monte
Carlo simulation of pure QCD shows both kinds of interfacial behavior.
Perturbation theory predicts a universal profile in the high temperature phase,
which can be tested by Monte Carlo simulation.Comment: 3 pages, contribution to Lattice '94 conference, self-extracting
(revised only to include heplat number in line below
Bundles of Interacting Strings in Two Dimensions
Bundles of strings which interact via short-ranged pair potentials are
studied in two dimensions. The corresponding transfer matrix problem is solved
analytically for arbitrary string number N by Bethe ansatz methods. Bundles
consisting of N identical strings exhibit a unique unbinding transition. If the
string bundle interacts with a hard wall, the bundle may unbind from the wall
via a unique transition or a sequence of N successive transitions. In all
cases, the critical exponents are independent of N and the density profile of
the strings exhibits a scaling form that approaches a mean-field profile in the
limit of large N.Comment: 8 pages (latex) with two figure
Shape fluctuations and elastic properties of two-component bilayer membranes
The elastic properties of two-component bilayer membranes are studied using a
coarse grain model for amphiphilic molecules. The two species of amphiphiles
considered here differ only in their length. Molecular Dynamics simulations are
performed in order to analyze the shape fluctuations of the two-component
bilayer membranes and to determine their bending rigidity. Both the bending
rigidity and its inverse are found to be nonmonotonic functions of the mole
fraction of the shorter B-amphiphiles and, thus, do not satisfy a
simple lever rule. The intrinsic area of the bilayer also exhibits a
nonmonotonic dependence on and a maximum close to .Comment: To appear on Europhysics Letter
Collective Molecular Dynamics in Proteins and Membranes
The understanding of dynamics and functioning of biological membranes and in
particular of membrane embedded proteins is one of the most fundamental
problems and challenges in modern biology and biophysics. In particular the
impact of membrane composition and properties and of structure and dynamics of
the surrounding hydration water on protein function is an upcoming hot topic,
which can be addressed by modern experimental and computational techniques.
Correlated molecular motions might play a crucial role for the understanding
of, for instance, transport processes and elastic properties, and might be
relevant for protein function. Experimentally that involves determining
dispersion relations for the different molecular components, i.e., the length
scale dependent excitation frequencies and relaxation rates. Only very few
experimental techniques can access dynamical properties in biological materials
on the nanometer scale, and resolve dynamics of lipid molecules, hydration
water molecules and proteins and the interaction between them. In this context,
inelastic neutron scattering turned out to be a very powerful tool to study
dynamics and interactions in biomolecular materials up to relevant nanosecond
time scales and down to the nanometer length scale. We review and discuss
inelastic neutron scattering experiments to study membrane elasticity and
protein-protein interactions of membrane embedded proteins
Lateral phase separation of confined membranes
We consider membranes interacting via short, intermediate and long stickers.
The effects of the intermediate stickers on the lateral phase separation of the
membranes are studied via mean-field approximation. The critical potential
depth of the stickers increases in the presence of the intermediate sticker.
The lateral phase separation of the membrane thus suppressed by the
intermediate stickers. Considering membranes interacting with short and long
stickers, the effect of confinement on the phase behavior of the membranes is
also investigated analytically
Prävalenz und Morphologie überzähliger Zähne in der Bevölkerung einer Schweizer Gemeinde: Short communication
Ziel der Studie war die Ermittlung der aktuellen Prävalenz überzähliger Zähne in der Bevölkerung einer Schweizer Gemeinde.
Als Grundlage dienten 3004 routinemässig angefertigte Orthopantomogramme aus dem
alljährlichen Schuluntersuch der Stadt Winterthur während der Jahre 1990–2005 (Durchschnittsalter 9,45 Jahre, 1391 Mädchen, 1613 Knaben bei einer Streuung von 6 bis 15 Jahren).
Die Studie fand 44 überzählige Zähne. Dieser Anteil ergibt eine Prävalenz von 1,5%. Die Prävalenz bei den Knaben lag mit 1,1% höher als bei den Mädchen, die mit 0,4% davon
betroffen waren. Der grösste Teil überzähliger Zähne war in der oberen Front zu finden (38 von 44 Zähnen, 86%). Davon waren 33 aufgrund ihrer Lage als Mesiodentes zu bezeichnen.
Fünf überzählige Zähne hatten die gleiche Form wie die eines oberen lateralen Schneidezahnes. In der Unterkieferfront fanden sich 5 überzählige Zähne mit gleicher Form wie die bleibenden unteren Inzisiven.
Die überzähligen Zähne hatten zu 70% eine konische Zahnform.
Die Prävalenz überzähliger Zähne ist mit 1,5% niedrig und vergleichbar mit ähnlichen Studien in der Literatur. Die meisten überzähligen Zähne (86%) sind in der Oberkieferfront angesiedelt.Bei Retentionen und Durchbruchsstörungen von Zähnen in dieser Region sollte
in Betracht gezogen werden, dass überzählige Zähne Ursache dafür sein könnten
Collective dynamics in phospholipid bilayers investigated by inelastic neutron scattering: Exploring the dynamics of biological membranes with neutrons
We present the first inelastic neutron scattering study of the short
wavelength dynamics in a phospholipid bilayer. We show that inelastic neutron
scattering using a triple-axis spectrometer at the high flux reactor of the ILL
yields the necessary resolution and signal to determine the dynamics of model
membranes. The results can quantitatively be compared to recent Molecular
Dynamics simulations. Reflectivity, in-plane correlations and the corresponding
dynamics can be measured simultaneously to gain a maximum amount of
information. With this method, dispersion relations can be measured with a high
energy resolution. Structure and dynamics in phospholipid bilayers, and the
relation between them, can be studied on a molecular length scale
Counterion density profiles at charged flexible membranes
Counterion distributions at charged soft membranes are studied using
perturbative analytical and simulation methods in both weak coupling
(mean-field or Poisson-Boltzmann) and strong coupling limits. The softer the
membrane, the more smeared out the counterion density profile becomes and
counterions pentrate through the mean-membrane surface location, in agreement
with anomalous scattering results. Membrane-charge repulsion leads to a
short-scale roughening of the membrane.Comment: 4 pages, 4 figure
Two-dimensional Vesicle dynamics under shear flow: effect of confinement
Dynamics of a single vesicle under shear flow between two parallel plates is
studied using two-dimensional lattice-Boltzmann simulations. We first present
how we adapted the lattice-Boltzmann method to simulate vesicle dynamics, using
an approach known from the immersed boundary method. The fluid flow is computed
on an Eulerian regular fixed mesh while the location of the vesicle membrane is
tracked by a Lagrangian moving mesh. As benchmarking tests, the known vesicle
equilibrium shapes in a fluid at rest are found and the dynamical behavior of a
vesicle under simple shear flow is being reproduced. Further, we focus on
investigating the effect of the confinement on the dynamics, a question that
has received little attention so far. In particular, we study how the vesicle
steady inclination angle in the tank-treading regime depends on the degree of
confinement. The influence of the confinement on the effective viscosity of the
composite fluid is also analyzed. At a given reduced volume (the swelling
degree) of a vesicle we find that both the inclination angle, and the membrane
tank-treading velocity decrease with increasing confinement. At sufficiently
large degree of confinement the tank-treading velocity exhibits a
non-monotonous dependence on the reduced volume and the effective viscosity
shows a nonlinear behavior.Comment: 12 pages, 8 figure
Lateral phase separation in mixtures of lipids and cholesterol
In an effort to understand "rafts" in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid-cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. The phase diagrams for binary mixtures of saturated/unsaturated lipids and lipid/cholesterol are in semi-quantitative agreement with the experiments. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems
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