754 research outputs found
The Role of 5-quark Components on the Nucleon Form Factors
The covariant quark model is shown to allow a phenomenological description of
the neutron electric form factor, G_E^n(Q^2), in the impulse approximation,
provided that the wave function contains minor (~ 3 %) admixtures of the lowest
sea-quark configurations. While that form factor is not very sensitive to
whether the \bar q in the qqqq\bar q component is in the P-state or in the
S-state, the calculated nucleon magnetic form factors are much closer to the
empirical values in the case of the former configuration. In the case of the
electric form factor of the proton, G_E^p(Q^2), a zero appears in the impulse
approximation close to 9 GeV^2, when the \bar q is in the P-state. That
configuration, which may be interpreted as a pion loop ("cloud") fluctuation,
also leads to a clearly better description of the nucleon magnetic moments.
When the amplitude of the sea-quark admixtures are set so as to describe the
electric form factor of the neutron, the qqqq\bar q admixtures have the
phenomenologically desirable feature, that the electric form factor of the
proton falls at a more rapid rate with momentum transfer than the magnetic form
factor.Comment: To appear in Nuclear Physics
Orbital evolution of P\v{r}\'{i}bram and Neuschwanstein
The orbital evolution of the two meteorites P\v{r}\'{i}bram and
Neuschwanstein on almost identical orbits and also several thousand clones were
studied in the framework of the N-body problem for 5000 years into the past.
The meteorites moved on very similar orbits during the whole investigated
interval. We have also searched for photographic meteors and asteroids moving
on similar orbits. There were 5 meteors found in the IAU MDC database and 6
NEAs with currently similar orbits to P\v{r}\'{i}bram and Neuschwanstein.
However, only one meteor 161E1 and one asteroid 2002 QG46 had a similar orbital
evolution over the last 2000 years.Comment: 7 pages, 2 figures, 3 table
Effects of Methylene Blue and Polyethelene Glycol on Facial Nerve Axotomy Recovery
poster abstractInjury and disease are common factors affecting peripheral nerves and can lead to loss of function. Recovery time after an injury is slow and not very efficient in humans. Treatment methods involving methylene blue (MB) and polyethylene glycol (PEG) have shown combinational effects in sciatic nerve axotomies. We are using behavior analysis of eye blink reflex and vibrissae orientation and movement as a measurement of rate of functional recovery. We will have treatment groups of both cut and crush rats. For each group we will be testing the effect of PEG/MB or no treatment control groups. The results of these treatment groups are significant to finding treatment options for clinical use
Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO2
Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO2 is an earth abundant, cheaper alternative to In2O3 as a TCO. However, its performance in terms of mobilities and conductivities lags behind that of In2O3. On the basis of the recent discovery of mobility and conductivity enhancements in In2O3 from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy, and semiconductor statistics modeling to understand what is the optimal dopant to maximize performance of SnO2-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO2, as it is a resonant dopant which is readily incorporated into SnO2 with the Ta 5d states sitting ∼1.4 eV above the conduction band minimum. Experimentally, the band edge electron effective mass of Ta doped SnO2 was shown to be 0.23m0, compared to 0.29m0 seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities
Threshold Electrodisintegration of ^3He
Cross sections were measured for the near-threshold electrodisintegration of
^3He at momentum transfer values of q=2.4, 4.4, and 4.7 fm^{-1}. From these and
prior measurements the transverse and longitudinal response functions R_T and
R_L were deduced. Comparisons are made against previously published and new
non-relativistic A=3 calculations using the best available NN potentials. In
general, for q<2 fm^{-1} these calculations accurately predict the threshold
electrodisintegration of ^3He. Agreement at increasing q demands consideration
of two-body terms, but discrepancies still appear at the highest momentum
transfers probed, perhaps due to the neglect of relativistic dynamics, or to
the underestimation of high-momentum wave-function components.Comment: 9 pages, 7 figures, 1 table, REVTEX4, submitted to Physical Review
Effects of rapid prey evolution on predator-prey cycles
We study the qualitative properties of population cycles in a predator-prey
system where genetic variability allows contemporary rapid evolution of the
prey. Previous numerical studies have found that prey evolution in response to
changing predation risk can have major quantitative and qualitative effects on
predator-prey cycles, including: (i) large increases in cycle period, (ii)
changes in phase relations (so that predator and prey are cycling exactly out
of phase, rather than the classical quarter-period phase lag), and (iii)
"cryptic" cycles in which total prey density remains nearly constant while
predator density and prey traits cycle. Here we focus on a chemostat model
motivated by our experimental system [Fussmann et al. 2000,Yoshida et al. 2003]
with algae (prey) and rotifers (predators), in which the prey exhibit rapid
evolution in their level of defense against predation. We show that the effects
of rapid prey evolution are robust and general, and furthermore that they occur
in a specific but biologically relevant region of parameter space: when traits
that greatly reduce predation risk are relatively cheap (in terms of reductions
in other fitness components), when there is coexistence between the two prey
types and the predator, and when the interaction between predators and
undefended prey alone would produce cycles. Because defense has been shown to
be inexpensive, even cost-free, in a number of systems [Andersson and Levin
1999, Gagneux et al. 2006,Yoshida et al. 2004], our discoveries may well be
reproduced in other model systems, and in nature. Finally, some of our key
results are extended to a general model in which functional forms for the
predation rate and prey birth rate are not specified.Comment: 35 pages, 8 figure
The application of thin-plate spark chambers to high-energy [pi]-p experiments
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32259/1/0000321.pd
D-state configurations in the electromagnetic form factors of the nucleon and the Delta(1232) resonance
The electromagnetic transition form factors are calculated in the
Poincar\'e covariant quark model in three forms of relativistic kinematics.
Addition of state components to pure state model wave functions, chosen
so as to reproduce the empirical elastic electromagnetic nucleon form factors
with single constituent currents, brings the calculated ratio for the
transition closer to the empirical values in instant
and point form kinematics. The calculated ratio is insensitive to the
state component. In front form kinematics the substantial violation of the
angular condition for the spin 3/2 resonance transition amplitude in the
impulse approximation prevents a unique determination of and ,
both of which are very sensitive to state components. In no form of
kinematics do state deformations of the rest frame baryon wave functions
alone suffice for a description of the empirical values of these ratios.Comment: 11 figures, elsevier forma
Surface state atoms and their contribution to the surface tension of quantum liquids
We investigate the new type of excitations on the surface of liquid helium.
These excitations, called surfons, appear because helium atoms have discrete
energy level at the liquid surface, being attracted to the surface by the van
der Waals force and repulsed at a hard-core interatomic distance. The
concentration of the surfons increases with temperature. The surfons propagate
along the surface and form a two-dimensional gas. Basing on the simple model of
the surfon microscopic structure, we estimate the surfon activation energy and
effective mass for both helium isotopes. We also calculate the contribution of
the surfons to the temperature dependence of the surface tension. This
contribution explains the great and long-standing discrepancy between theory
and experiment on this temperature dependence in both helium isotopes. The
achieved agreement between our theory and experiment is extremely high. The
comparison with experiment allows to extract the surfon activation energy and
effective mass. The values of these surfon microscopic parameters are in a
reasonable agreement with the calculated from the proposed simple model of
surfon structure.Comment: 10 pages, 6 figure
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