3,089 research outputs found
Interfacial Magnetoelectric Coupling in Tri-component Superlattices
Using first-principles density functional theory, we investigate the
interfacial magnetoelectric coupling in a tri-component superlattice composed
of a ferromagnetic metal (FM), ferroelectric (FE), and normal metal (NM). Using
Fe/FE/Pt as a model system, we show that a net and cumulative interfacial
magnetization is induced in the FM metal near the FM/FE interface. A carefully
analysis of the magnetic moments in Fe reveals that the interfacial
magnetization is a consequence of a complex interplay of interfacial charge
transfer, chemical bonding, and spin dependent electrostatic screening. The
last effect is linear in the FE polarization, is switchable upon its reversal,
and yields a substantial interfacial magnetoelectric coupling.Comment: 5 pages, 6 figure
Mars mission solar array Semiannual progress report, period ending 31 Dec. 1969
Design and testing of beryllium-structure solar panel for Mars missio
Wang-Landau molecular dynamics technique to search for low-energy conformational space of proteins
Multicanonical molecular dynamics (MD) is a powerful technique for sampling
conformations on rugged potential surfaces such as protein. However, it is
notoriously difficult to estimate the multicanonical temperature effectively.
Wang and Landau developed a convenient method for estimating the density of
states based on a multicanonical Monte Carlo method. In their method, the
density of states is calculated autonomously during a simulation. In this paper
we develop a set of techniques to effectively apply the Wang-Landau method to
MD simulations. In the multicanonical MD, the estimation of the derivative of
the density of states is critical. In order to estimate it accurately, we
devise two original improvements. First, the correction for the density of
states is made smooth by using the Gaussian distribution obtained by a short
canonical simulation. Second, an approximation is applied to the derivative,
which is based on the Gaussian distribution and the multiple weighted histogram
technique. A test of this method was performed with small polypeptides,
Met-enkephalin and Trp-cage, and it is demonstrated that Wang-Landau MD is
consistent with replica exchange MD but can sample much larger conformational
space.Comment: 8 pages, 7 figures, accepted for publication in Physical Review
Direct optical observations of surface thermal motions at sub-shot noise levels
We measure spectral properties of surface thermal fluctuations of liquids,
solids, complex fluids and biological matter using light scattering methods.
The random thermal fluctuations are delineated from random noise at sub-shot
noise levels. The principle behind this extraction, which is quite general and
is not limited to surface measurements, is explained. An optical lever is used
to measure the spectrum of fluctuations in the inclinations of surfaces down to
at W optical intensity, corresponding
to in the vertical displacement, in the
frequency range . The dynamical evolution of the
surface properties is also investigated. The measurement requires only a short
amount of time and is essentially passive, so that it can be applied to a wide
variety of surfaces.Comment: 5pp, 5 figure
Domain Size Dependence of Piezoelectric Properties of Ferroelectrics
The domain size dependence of piezoelectric properties of ferroelectrics is
investigated using a continuum Ginzburg-Landau model that incorporates the
long-range elastic and electrostatic interactions. Microstructures with desired
domain sizes are created by quenching from the paraelectric phase by biasing
the initial conditions. Three different two-dimensional microstructures with
different sizes of the domains are simulated. An electric field is
applied along the polar as well as non-polar directions and the piezoelectric
response is simulated as a function of domain size for both cases. The
simulations show that the piezoelectric coefficients are enhanced by reducing
the domain size, consistent with recent experimental results of Wada and
Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered
Comment: submitted to Physical Review
Search for an exotic three-body decay of orthopositronium
We report on a direct search for a three-body decay of the orthopositronium
into a photon and two penetrating particles, o-Ps -> gamma + X1 + X2. The
existence of this decay could explain the discrepancy between the measured and
the predicted values of the orthopositronium decay rate. From the analysis of
the collected data a single candidate event is found, consistent with the
expected background. This allows to set an upper limit on the branching ratio <
4.4 \times 10^{-5} (at the 90% confidence level), for the photon energy in the
range from 40 keV < E_gamma< 400 keV and for mass values in the kinematical
range 0
gamma + X1 + X2 decay mode as the origin of the discrepancy.Comment: 9 pages, 3 figure
Nonchaotic Stagnant Motion in a Marginal Quasiperiodic Gradient System
A one-dimensional dynamical system with a marginal quasiperiodic gradient is
presented as a mathematical extension of a nonuniform oscillator. The system
exhibits a nonchaotic stagnant motion, which is reminiscent of intermittent
chaos. In fact, the density function of residence times near stagnation points
obeys an inverse-square law, due to a mechanism similar to type-I
intermittency. However, unlike intermittent chaos, in which the alternation
between long stagnant phases and rapid moving phases occurs in a random manner,
here the alternation occurs in a quasiperiodic manner. In particular, in case
of a gradient with the golden ratio, the renewal of the largest residence time
occurs at positions corresponding to the Fibonacci sequence. Finally, the
asymptotic long-time behavior, in the form of a nested logarithm, is
theoretically derived. Compared with the Pomeau-Manneville intermittency, a
significant difference in the relaxation property of the long-time average of
the dynamical variable is found.Comment: 11pages, 5figure
A new ultra high energy gamma ray telescope at Ohya mine
The search for ultra high energy gamma rays coming from point sources is one of the main experimental aims. A fast air shower timing system was constructed at ICRR for the study of the angular resolution of the system and operated approximately half a year. The characteristics of the surface array of Ohya air shower telescope is described
Background light measurements at the DUMAND site
Ambient light intensities at the DUMAND site, west of the island of Hawaii were measured around the one photoelectron level. Throughout the water column between 1,500m and 4,700m, a substantial amount of stimulateable bioluminescence is observed with a ship suspended detector. But non-stimulated bioluminescence level is comparable, or less than, K sup 40 background, when measured with a bottom tethered detector typical of a DUMAND optical module
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