56,936 research outputs found
A survey of comet missions
Comet mission design - interception, earth based observation, simulated phenomena, physics, and artificial orbiting come
Exposing the dressed quark's mass
This snapshot of recent progress in hadron physics made in connection with
QCD's Dyson-Schwinger equations includes: a perspective on confinement and
dynamical chiral symmetry breaking (DCSB); a pre'cis on the physics of
in-hadron condensates; results on the hadron spectrum, including
dressed-quark-core masses for the nucleon and Delta, their first radial
excitations, and the parity-partners of these states; an illustration of the
impact of DCSB on the electromagnetic pion form factor, thereby exemplifying
how data can be used to chart the momentum-dependence of the dressed-quark mass
function; and a prediction that F_1^{p,d}/F_1^{p,u} passes through zero at
Q^2\approx 5m_N^2 owing to the presence of nonpointlike scalar and axial-vector
diquark correlations in the nucleon.Comment: 10 pages, 4 figures, 2 tables. Contribution to the Proceedings of the
4th Workshop on Exclusive Reactions at High Momentum Transfer, Thomas
Jefferson National Accelerator Facility Newport News, Virginia, 18-21 May
201
Laser apparatus for removing material from rotating objects Patent
Laser device for removing material from rotating object for dynamic balancin
Dressed-quarks and the Roper resonance
A Dyson-Schwinger equation calculation of the light hadron spectrum, which
correlates the masses of meson and baryon ground- and excited-states within a
single framework, produces a description of the Roper resonance that
corresponds closely with conclusions drawn recently by EBAC. Namely, the Roper
is a particular type of radial excitation of the nucleon's dressed-quark core
augmented by a material meson cloud component. There are, in addition, some
surprises.Comment: 4 pages, 3 figures. Contribution to the Proceedings of "NSTAR2011 -
The 8th International Workshop on the Physics of Excited Nucleons," Thomas
Jefferson National Accelerator Facility, Newport News, Virginia USA, 17-20
May 201
Impact of dynamical chiral symmetry breaking on meson structure and interactions
We provide a glimpse of recent progress in meson physics made via QCD's
Dyson-Schwinger equations with: a perspective on confinement and dynamical
chiral symmetry breaking (DCSB); a pre'cis on the physics of in-hadron
condensates; results for the masses of the \pi, \sigma, \rho, a_1 mesons and
their first-radial excitations; and an illustration of the impact of DCSB on
the pion form factor.Comment: 6 pages, 3 figures, 1 table. Contribution to Proceedings of the 11th
International Workshop on Meson Production, Properties and Interaction,
Uniwersytet Jagiellonski, Instytut Fizyki, Krakow, Poland, 10-15 June 201
Fishing and the impact of marine reserves in a variable environment
We use discrete-time models to investigate the impact of marine reserve establishment on fishery catch and biomass levels in open-access and quota-regulated fisheries under conditions of recruitment variability and natural mortality events. We find that under the conditions of variability tested, reserves can increase the probability of achieving target levels of biomass (60%, 35%, and 5% of carrying capacity) and can reduce catch variability in neighbouring fisheries, making future planning in the fishery more efficient. The size of the reserve required to meet each objective will depend on the initial condition of the stock and the exploitation rate in the fishery. Reserve coverage of between 20% and 40% prevent stock collapse in most cases. In heavily exploited fisheries, reserves are also likely to enhance mean catches, particularly in highly variable systems. If the stock has previously been heavily exploited, large reserves (greater than or equal to60%) may be required to significantly increase the probability of achieving target biomass levels. However, once stocks have recovered, reserve coverage may be reduced without a reduction in this probability of success
Radar exploration of Venus
Spacecraft radar systems for exploration of Venu
Force on a moving point impurity due to quantum fluctuations in a Bose-Einstein condensate
An analytic expression is derived for a force on a weak point impurity
arising from the scattering of quantum fluctuations in a slow-moving, weakly
interacting, three-dimensional Bose-Einstein condensate at zero temperature. In
an infinitely extended geometry, this force is shown to exist at any
arbitrarily small flow velocity below Landau's critical velocity. Furthermore,
this force is shown to be directly proportional to the flow speed.Comment: v2: corrected notation and other minor change
Water velocity meter
Simple, inexpensive drag sphere velocity meter with a zero to 6 ft/sec range measures steady-state flow. When combined with appropriate data acquisition system, it is suited to applications where large numbers of simultaneous measurements are needed for current mapping or velocity profile determination
Understanding Algorithm Performance on an Oversubscribed Scheduling Application
The best performing algorithms for a particular oversubscribed scheduling
application, Air Force Satellite Control Network (AFSCN) scheduling, appear to
have little in common. Yet, through careful experimentation and modeling of
performance in real problem instances, we can relate characteristics of the
best algorithms to characteristics of the application. In particular, we find
that plateaus dominate the search spaces (thus favoring algorithms that make
larger changes to solutions) and that some randomization in exploration is
critical to good performance (due to the lack of gradient information on the
plateaus). Based on our explanations of algorithm performance, we develop a new
algorithm that combines characteristics of the best performers; the new
algorithms performance is better than the previous best. We show how hypothesis
driven experimentation and search modeling can both explain algorithm
performance and motivate the design of a new algorithm
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