29,150 research outputs found
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
Tracking and data systems support for the Helios project. Volume 3: DSN support of Project Helios May 1976 - June 1977
Spacecraft extended mission coverage does not generally carry a high priority, but Helios was fortunate in that a combination of separated viewperiods and unique utilization of the STDN Goldstone antenna have provided a considerable amount of additional science data return, particularly at key times such a perihelion and/or solar occultation
Analytic Criteria for Power Exhaust in Divertors due to Impurity Radiation
Present divertor concepts for next step experiments such ITER and TPX rely
upon impurity and hydrogen radiation to transfer the energy from the edge
plasma to the main chamber and divertor chamber walls. The efficiency of these
processes depends strongly on the heat flux, the impurity species, and the
connection length. Using a database for impurity radiation rates constructed
from the ADPAK code package, we have developed criteria for the required
impurity fraction, impurity species, connection length and electron temperature
and density at the mid-plane. Consistent with previous work, we find that the
impurity radiation from coronal equilibrium rates is, in general, not adequate
to exhaust the highest expected heating powers in present and future
experiments. As suggested by others, we examine the effects of enhancing the
radiation rates with charge exchange recombination and impurity recycling, and
develop criteria for the minimum neutral fraction and impurity recycling rate
that is required to exhaust a specified power. We also use this criteria to
find the optimum impurity for divertor power exhaust.Comment: Preprint for the 11th PSI meeting, Adobe pdf with 14 figures, 15
page
Investigation of resonant and transient phenomena in Josephson junction flux qubits
We present an analytical and computational study of resonances and transient
responses in a classical Josephson junction system. A theoretical basis for
resonances in a superconducting loop with three junctions is presented,
outlining both the direct relationship between the dynamics of single- and
multi-junction systems, and the direct relationships between observations of
the classical counterparts to Rabi oscillations, Ramsey fringes, and spin echo
oscillations in this class of systems. We show simulations data along with
analytical analyses of the classical model, and the results are related to
previously reported experiments conducted on three junction loops. We further
investigate the effect of off-resonant microwave perturbations to, e.g., the
Rabi-type response of the Josephson system, and we relate this response back to
the nonlinear and multi-valued resonance behavior previously reported for a
single Josephson junction. The close relationships between single and
multi-junction behavior demonstrates the underlying dynamical mechanism for a
whole class of classical counterparts to expected quantum mechanical
observations in a variety of systems; namely the resonant and transient
behavior of a particle in an anharmonic potential well with subsequent escape.Comment: 11 pages, seven figure
KINETIC RESPONSES DURING LANDINGS OF PLYOMETRIC EXERCISES
The objective of the current study was to compare landing impulse and peak ground reaction force (GRF) during a variety of plyometric exercises. Eight Division-I athletes who routinely trained plyometric exercises performed a single repetition each of countermovement jump (CMJ), drop jumps from 30 and 60 cm (DJ30 and DJ60), cone hop (CH), tuck jump (TJ), single leg CMJ (SLJ), and squat jump with 30% 1 RM dumbbell squat (SJ30). Landing impulses and peak GRF were evaluated on an AMTI force plate.
One-way ANOVA indicated mean and total impulses and peak GRF differed across exercises, with CH and SLJ displaying lower values and DJ30 and SJ30 having higher values. Results indicate that when landing from various plyometric exercises landing impulses and GRF are different across the exercises
High Q Cavity Induced Fluxon Bunching in Inductively Coupled Josephson Junctions
We consider fluxon dynamics in a stack of inductively coupled long Josephson
junctions connected capacitively to a common resonant cavity at one of the
boundaries. We study, through theoretical and numerical analysis, the
possibility for the cavity to induce a transition from the energetically
favored state of spatially separated shuttling fluxons in the different
junctions to a high velocity, high energy state of identical fluxon modes.Comment: 8 pages, 5 figure
Finite-dimensional states and entanglement generation for a nonlinear coupler
We discuss a system comprising two nonlinear (Kerr-like) oscillators coupled
mutually by a nonlinear interaction. The system is excited by an external
coherent field that is resonant to the frequency of one of the oscillators. We
show that the coupler evolution can be closed within a finite set of -photon
states, analogously as in the \textit{nonlinear quantum scissors} model.
Moreover, for this type of evolution our system can be treated as a
\textit{Bell-like states} generator. Thanks to the nonlinear nature of both:
oscillators and their internal coupling, these states can be generated even if
the system exhibits its energy dissipating nature, contrary to systems with
linear couplings.Comment: Accepted for publication in Physical Review
Competition between Diffusion and Fragmentation: An Important Evolutionary Process of Nature
We investigate systems of nature where the common physical processes
diffusion and fragmentation compete. We derive a rate equation for the size
distribution of fragments. The equation leads to a third order differential
equation which we solve exactly in terms of Bessel functions. The stationary
state is a universal Bessel distribution described by one parameter, which fits
perfectly experimental data from two very different system of nature, namely,
the distribution of ice crystal sizes from the Greenland ice sheet and the
length distribution of alpha-helices in proteins.Comment: 4 pages, 3 figures, (minor changes
Fish schooling as a basis for vertical axis wind turbine farm design
Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the
high power coefficient (mechanical power output divided by the power of the
free-stream air through the turbine cross-sectional area) of an isolated
turbine. However when in close proximity to neighbouring turbines, HAWTs suffer
from a reduced power coefficient. In contrast, previous research on vertical
axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience
only small decreases (or even increases) in an individual turbine's power
coefficient when placed in close proximity to neighbours, thus yielding much
higher power outputs for a given area of land. A potential flow model of
inter-VAWT interactions is developed to investigate the effect of changes in
VAWT spatial arrangement on the array performance coefficient, which compares
the expected average power coefficient of turbines in an array to a
spatially-isolated turbine. A geometric arrangement based on the configuration
of shed vortices in the wake of schooling fish is shown to significantly
increase the array performance coefficient based upon an array of 16x16 wind
turbines. Results suggest increases in power output of over one order of
magnitude for a given area of land as compared to HAWTs.Comment: Submitted for publication in BioInspiration and Biomimetics. Note:
The technology described in this paper is protected under both US and
international pending patents filed by the California Institute of Technolog
- …