611 research outputs found
Adaptive multibeam phased array design for a Spacelab experiment
The parametric tradeoff analyses and design for an Adaptive Multibeam Phased Array (AMPA) for a Spacelab experiment are described. This AMPA Experiment System was designed with particular emphasis to maximize channel capacity and minimize implementation and cost impacts for future austere maritime and aeronautical users, operating with a low gain hemispherical coverage antenna element, low effective radiated power, and low antenna gain-to-system noise temperature ratio
Study on successive superconducting transitions in TaSC from electrical resistivity and nonlinear AC magnetic susceptibility
TaSC compound undergoes superconducting transitions at K and K. The nature of successive
superconducting transitions has been studied from electrical resistivity,
linear and nonlinear AC magnetic susceptibilities. The resistivity at
= 0 shows a local maximum near , a kink-like behavior around
, and reduces to zero at below = 2.1 K. The dependence
of is observed at = 50 kOe at low temperatures, which is due to
two-dimensional weak-localization effect. Below a two-dimensional
superconducting phase occurs in each TaC layer. The linear and nonlinear
susceptibilities , ,
, and as well as the difference
() between the FC and ZFC
susceptibilities, start to appear below 6.0 K, the onset temperature of
irreversibility. A drastic growth of the in-plane superconducting coherence
length below 6.0 K gives rise to a three-dimensional superconducting phase
below , through interplanar Josephson couplings between adjacent TaC
layers. The oscillatory behavior of ,
, and below is
related to the nonlinear behavior arising from the thermally activated flux
flow.Comment: 11 pages, 10 figures, Physical Review B (accepted for publication
Focal Plane Detector System of SHARAQ Spectrometer
International audienceThis report describes the basic performance of the detector system installed in the final momentum-dispersive focal plane of the SHARAQ spectrometer
Fluctuating-friction molecular motors
We show that the correlated stochastic fluctuation of the friction
coefficient can give rise to long-range directional motion of a particle
undergoing Brownian random walk in a constant periodic energy potential
landscape. The occurrence of this motion requires the presence of two
additional independent bodies interacting with the particle via friction and
via the energy potential, respectively, which can move relative to each other.
Such three-body system generalizes the classical Brownian ratchet mechanism,
which requires only two interacting bodies. In particular, we describe a simple
two-level model of fluctuating-friction molecular motor that can be solved
analytically. In our previous work [M.K., L.M and D.P. 2000 J. Nonlinear Opt.
Phys. Mater. vol. 9, 157] this model has been first applied to understanding
the fundamental mechanism of the photoinduced reorientation of dye-doped liquid
crystals. Applications of the same idea to other fields such as molecular
biology and nanotechnology can however be envisioned. As an example, in this
paper we work out a model of the actomyosin system based on the
fluctuating-friction mechanism.Comment: to be published in J. Physics Condensed Matter
(http://www.iop.org/Journals/JPhysCM
Octupole strength in the neutron-rich calcium isotopes
Low-lying excited states of the neutron-rich calcium isotopes Ca
have been studied via -ray spectroscopy following inverse-kinematics
proton scattering on a liquid hydrogen target using the GRETINA -ray
tracking array. The energies and strengths of the octupole states in these
isotopes are remarkably constant, indicating that these states are dominated by
proton excitations.Comment: 15 pages, 3 figure
Molecular Chemical Engines: Pseudo-Static Processes and the Mechanism of Energy Transduction
We propose a simple theoretical model for a molecular chemical engine that
catalyzes a chemical reaction and converts the free energy released by the
reaction into mechanical work. Binding and unbinding processes of reactant and
product molecules to and from the engine are explicitly taken into account. The
work delivered by the engine is calculated analytically for infinitely slow
(``pseudo-static'') processes, which can be reversible (quasi-static) or
irreversible, controlled by an external agent. It is shown that the work larger
than the maximum value limited by the second law of thermodynamics can be
obtained in a single cycle of operation by chance, although the statistical
average of the work never exceeds this limit and the maximum work is delivered
if the process is reversible. The mechanism of the energy transductionis also
discussed.Comment: 8 pages, 3 figues, submitted to J. Phys. Soc. Jp
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