724 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
Spectromicroscopy of electronic phase separation in KFeSe superconductor
Structural phase separation in AFeSe system has been studied
by different experimental techniques, however, it should be important to know
how the electronic uniformity is influenced, on which length scale the
electronic phases coexist, and what is their spatial distribution. Here, we
have used novel scanning photoelectron microscopy (SPEM) to study the
electronic phase separation in KFeSe, providing a direct
measurement of the topological spatial distribution of the different electronic
phases. The SPEM results reveal a peculiar interconnected conducting
filamentary phase that is embedded in the insulating texture. The filamentary
structure with a particular topological geometry could be important for the
high T superconductivity in the presence of a phase with a large magnetic
moment in AFeSe materials.Comment: 14 pages,3 figure
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
Medical Treatment of Radiological Casualties: Current Concepts
The threat of radiologic or nuclear terrorism is increasing, yet many physicians are unfamiliar with basic treatment principles for radiologic casualties. Patients may present for care after a covert radiation exposure, requiring an elevated level of suspicion by the physician. Traditional medical and surgical triage criteria should always take precedence over radiation exposure management or decontamination. External contamination from a radioactive cloud is easily evaluated using a simple Geiger-Müller counter and decontamination accomplished by prompt removal of clothing and traditional showering. Management of surgical conditions in the presence of persistent radioactive contamination should be dealt with in a conventional manner with health physics guidance. To be most effective in the medical management of a terrorist event involving high-level radiation, physicians should understand basic manifestations of the acute radiation syndrome, the available medical countermeasures, and the psychosocial implications of radiation incidents. Health policy considerations include stockpiling strategies, effective use of risk communications, and decisionmaking for shelter-in-place versus evacuation after a radiologic incident
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
Spectroscopy of 13B via the 13C(t,3He) reaction at 115 AMeV
Gamow-Teller and dipole transitions to final states in 13B were studied via
the 13C(t,3He) reaction at Et = 115 AMeV. Besides the strong Gamow-Teller
transition to the 13B ground state, a weaker Gamow-Teller transition to a state
at 3.6 MeV was found. This state was assigned a spin-parity of 3/2- by
comparison with shell-model calculations using the WBP and WBT interactions
which were modified to allow for mixing between nhw and (n+2)hw configurations.
This assignment agrees with a recent result from a lifetime measurement of
excited states in 13B. The shell-model calculations also explained the
relatively large spectroscopic strength measured for a low-lying 1/2+ state at
4.83 MeV in 13B. The cross sections for dipole transitions up to Ex(13B)= 20
MeV excited via the 13C(t,3He) reaction were also compared with the shell-model
calculations. The theoretical cross sections exceeded the data by a factor of
about 1.8, which might indicate that the dipole excitations are "quenched".
Uncertainties in the reaction calculations complicate that interpretation.Comment: 11 pages, 6 figure
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