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Anomalous temperature-induced volume contraction in GeTe
The recent surge of interest in phase change materials GeTe,
GeSbTe, and related compounds motivated us to revisit the
structural phase transition in GeTe in more details than was done before.
Rhombohedral-to-cubic ferroelectric phase transition in GeTe has been studied
by high resolution neutron powder diffraction on a spallation neutron source.
We determined the temperature dependence of the structural parameters in a wide
temperature range extending from 309 to 973 K. Results of our studies clearly
show an anomalous volume contraction of 0.6\% at the phase transition from the
rhombohedral to cubic phase. In order to better understand the phase transition
and the associated anomalous volume decrease in GeTe we have performed phonon
calculations based on the density functional theory. Results of the present
investigations are also discussed with respect to the experimental data
obtained for single crystals of GeTe
Spectroscopic studies on the denaturation of papain solubilized and triton X-100 - solubilized glucoamylase from rabbit small intestine
Intestinal brush border proteins consist of an enzymatically active hydrophilic moiety attached to a hydrophobic tail. Papain dissociates the hydrophilic part by cleaving off the hydrophobic tail, whereas the detergentTriton X-100 solubilizes the whole molecule. Denaturation by 8 M urea or 4 M guanidinium chloride does not alter the structure of the papain-solubilized enzyme. An appreciable alteration of the structure of detergent-solubilized enzyme was observed on denaturation. The difference spectra of Triton X-100 (1%)-solubilized enzyme and its urea denatured form shifts and intensifies, with increase in the concentration of the denaturant with an isobestic point at 252 nm. A new band at 280 nm also appears at 4 M urea concentration. Papain-solubilized glucoamylase has an ∝ -helical conformation in solution unlike the detergentsolubilized fraction. An elongated structure for the papain solubilized enzyme is inferred from the urea denaturation studies and from molecular weight determinations
Comments on the Martingale Convergence Theorem Technical Report No. 21
Proofs of generality of martingale convergence theore
Magnetoelastic effects in Jahn-Teller distorted CrF and CuF studied by neutron powder diffraction
We have studied the temperature dependence of crystal and magnetic structures
of the Jahn-Teller distorted transition metal difluorides CrF and CuF
by neutron powder diffraction in the temperature range 2-280 K. The lattice
parameters and the unit cell volume show magnetoelastic effects below the
N\'eel temperature. The lattice strain due to the magnetostriction effect
couples with the square of the order parameter of the antiferromagnetic phase
transition. We also investigated the temperature dependence of the Jahn-Teller
distortion which does not show any significant effect at the antiferromagnetic
phase transition but increases linearly with increasing temperature for CrF
and remains almost independent of temperature in CuF. The magnitude of
magnetovolume effect seems to increase with the low temperature saturated
magnetic moment of the transition metal ions but the correlation is not at all
perfect
Conformational and ion-binding properties of cyclolinopeptide A isolated from linseed
The conformation of the cyclic nonapeptide from linseed, cyclolinopeptide A in
methanol and in acetonitrile has been elucidated by one- and two-dimensional nuclear
magnetic resonance. The molecule is folded in a ß-turn conformation. Cyclolinopeptide A
interacts and weakly complexes with Tb3+ (a Ca2+ mimic ion) with the metal ion
positioned proximally to the Phe residue, but with no substantial structural alteration upon
metal binding. Cyclolinopeptide A is also seen to aid the translocation of Pr3+ (another
Ca2+ mimic) across unilamellar liposomes. However, cyclolinopeptide A does not phase
transfer or act as an ionophore of calcium ion myself. Experiments using lanthanide ions thus
do not necessarily indicate any ionophoretic ability of the complexone towards calcium
ions
Combining Molecular Dynamics with Lattice-Boltzmann: A Hybrid Method for the Simulation of (Charged) Colloidal Systems
We present a hybrid method for the simulation of colloidal systems, that
combines molecular dynamics (MD) with the Lattice-Boltzmann (LB) scheme. The LB
method is used as a model for the solvent in order to take into account the
hydrodynamic mass and momentum transport through the solvent. The colloidal
particles are propagated via MD and they are coupled to the LB fluid by viscous
forces. With respect to the LB fluid, the colloids are represented by uniformly
distributed points on a sphere. Each such point (with a velocity V(r) at any
off-lattice position r is interacting with the neighboring eight LB nodes by a
frictional force F=\xi_0(V(r)-u(r)) with \xi_0 being a friction force and u(r)
being the velocity of the fluid at the position r. Thermal fluctuations are
introduced in the framework of fluctuating hydrodynamics. This coupling scheme
has been proposed recently for polymer systems by Ahlrichs and D"unweg [J.
Chem. Phys. 111, 8225 (1999)]. We investigate several properties of a single
colloidal particle in a LB fluid, namely the effective Stokes friction and long
time tails in the autocorrelation functions for the translational and
rotational velocity. Moreover, a charged colloidal system is considered
consisting of a macroion, counterions and coions that are coupled to a LB
fluid. We study the behavior of the ions in a constant electric field. In
particular, an estimate of the effective charge of the macroion is yielded from
the number of counterions that move with the macroion in the direction of the
electric field.Comment: 37 pages, 12 figure
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