2,098 research outputs found
A swollen phase observed between the liquid-crystalline phase and the interdigitated phase induced by pressure and/or adding ethanol in DPPC aqueous solution
A swollen phase, in which the mean repeat distance of lipid bilayers is
larger than the other phases, is found between the liquid-crystalline phase and
the interdigitated gel phase in DPPC aqueous solution. Temperature, pressure
and ethanol concentration dependences of the structure were investigated by
small-angle neutron scattering, and a bending rigidity of lipid bilayers was by
neutron spin echo. The nature of the swollen phase is similar to the anomalous
swelling reported previously. However, the temperature dependence of the mean
repeat distance and the bending rigidity of lipid bilayers are different. This
phase could be a precursor to the interdigitated gel phase induced by pressure
and/or adding ethanol.Comment: 7 pages, 6 figure
Intermediate states at structural phase transition: Model with a one-component order parameter coupled to strains
We study a Ginzburg-Landau model of structural phase transition in two
dimensions, in which a single order parameter is coupled to the tetragonal and
dilational strains. Such elastic coupling terms in the free energy much affect
the phase transition behavior particularly near the tricriticality. A
characteristic feature is appearance of intermediate states, where the ordered
and disordered regions coexist on mesoscopic scales in nearly steady states in
a temperature window. The window width increases with increasing the strength
of the dilational coupling. It arises from freezing of phase ordering in
inhomogeneous strains. No impurity mechanism is involved. We present a simple
theory of the intermediate states to produce phase diagrams consistent with
simulation results.Comment: 16 pages, 14 figure
Silicon-based resonant-cavity-enchanced photodiode with a buried SiO2 reflector
We report on a silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry-Perot oscillations. Resonant peaks and antiresonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 and 709 nm. The leakage current density is 85 pA/mm(2) at -5 V, and the average zero-bias capacitance is 12 pF/mm(2). We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response. (C) 1999 American Institute of Physics. (DOI: 10.1063/1.123499)
Measuring velocity of sound with nuclear resonant inelastic x-ray scattering
Nuclear resonant inelastic x-ray scattering is used to measure the projected
partial phonon density of states of materials. A relationship is derived
between the low-energy part of this frequency distribution function and the
sound velocity of materials. Our derivation is valid for harmonic solids with
Debye-like low-frequency dynamics. This method of sound velocity determination
is applied to elemental, composite, and impurity samples which are
representative of a wide variety of both crystalline and noncrystalline
materials. Advantages and limitations of this method are elucidated
Thermoelectric properties of lead chalcogenide core-shell nanostructures
We present the full thermoelectric characterization of nanostructured bulk
PbTe and PbTe-PbSe samples fabricated from colloidal core-shell nanoparticles
followed by spark plasma sintering. An unusually large thermopower is found in
both materials, and the possibility of energy filtering as opposed to grain
boundary scattering as an explanation is discussed. A decreased Debye
temperature and an increased molar specific heat are in accordance with recent
predictions for nanostructured materials. On the basis of these results we
propose suitable core-shell material combinations for future thermoelectric
materials of large electric conductivities in combination with an increased
thermopower by energy filtering.Comment: 12 pages, 8 figure
Exactly solvable model for cosmological perturbations in dilatonic brane worlds
We construct a model where cosmological perturbations are analytically solved
based on dilatonic brane worlds. A bulk scalar field has an exponential
potential in the bulk and an exponential coupling to the brane tension. The
bulk scalar field yields a power-law inflation on the brane. The exact
background metric can be found including the back-reaction of the scalar field.
Then exact solutions for cosmological perturbations which properly satisfy the
junction conditions on the brane are derived. These solutions provide us an
interesting model to understand the connection between the behavior of
cosmological perturbations on the brane and the geometry of the bulk. Using
these solutions, the behavior of an anisotropic stress induced on the
inflationary brane by bulk gravitational fields is investigated.Comment: 30 pages, typos corrected, reference adde
Restructuring of colloidal aggregates in shear flow: Coupling interparticle contact models with Stokesian dynamics
A method to couple interparticle contact models with Stokesian dynamics (SD)
is introduced to simulate colloidal aggregates under flow conditions. The
contact model mimics both the elastic and plastic behavior of the cohesive
connections between particles within clusters. Owing to this, clusters can
maintain their structures under low stress while restructuring or even breakage
may occur under sufficiently high stress conditions. SD is an efficient method
to deal with the long-ranged and many-body nature of hydrodynamic interactions
for low Reynolds number flows. By using such a coupled model, the restructuring
of colloidal aggregates under stepwise increasing shear flows was studied.
Irreversible compaction occurs due to the increase of hydrodynamic stress on
clusters. Results show that the greater part of the fractal clusters are
compacted to rod-shaped packed structures, while the others show isotropic
compaction.Comment: A simulation movie be found at
http://www-levich.engr.ccny.cuny.edu/~seto/sites/colloidal_aggregates_shearflow.htm
Weakly coupled states on branching graphs
We consider a Schr\"odinger particle on a graph consisting of links
joined at a single point. Each link supports a real locally integrable
potential ; the self--adjointness is ensured by the type
boundary condition at the vertex. If all the links are semiinfinite and ideally
coupled, the potential decays as along each of them, is
non--repulsive in the mean and weak enough, the corresponding Schr\"odinger
operator has a single negative eigenvalue; we find its asymptotic behavior. We
also derive a bound on the number of bound states and explain how the
coupling constant may be interpreted in terms of a family of
squeezed potentials.Comment: LaTeX file, 7 pages, no figure
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