12,865 research outputs found
Fitting quotients of finitely presented abelian-by-nilpotent groups
We show that every finitely generated nilpotent group of class 2 occurs as
the quotient of a finitely presented abelian-by-nilpotent group by its largest
nilpotent normal subgroup.Comment: This second version takes into account the suggestions by the
referee; 11 page
Year-class formation in Pacific herring (Clupea pallasi) estimated from spawning-date distributions of juveniles in San Francisco Bay, California
Inter and intra-annual variation in year-class strength was analyzed for San Francisco Bay Pacific herring (Clupea pallasi) by using otoliths of juveniles. Juvenile herring
were collected from March through June in 1999 and 2000 and otoliths from subsamples of these collections were aged by daily otolith increment analysis. The composition of the year classes in 1999 and 2000 were determined by back-calculating the birth date distribution for surviving juvenile herring. In 2000, 729% more juveniles were captured than in 1999, even though an estimated 12% fewer
eggs were spawned in 2000. Spawning-date distributions show that survival for the 2000 year class was exceptionally good for a short (approximately 1 month) period of spawning,
resulting in a large abundance of juvenile recruits. Analysis of age at size shows that growth rate increased
significantly as the spawning season progressed both in 1999 and 2000. However, only in 2000 were the bulk of surviving juveniles a product of the fast growth period. In the two years examined, year-class strength was not predicted by the estimated number of eggs spawned, but rather appeared to depend on survival of eggs or larvae (or both) through the juvenile stage. Fast growth through the larval stage may have little effect on year-class strength if mortality during the egg stage is high and few larvae are available
Monte-Carlo simulations of photohadronic processes in astrophysics
A new Monte Carlo program for photohadronic interactions of relativistic
nucleons with an ambient photon radiation field is presented. The event
generator is designed to fulfil typical astrophysical requirements, but can
also be used for radiation and background studies at high energy colliders such
as LEP2 and HERA, as well as for simulations of photon induced air showers.
We consider the full photopion production cross section from the pion
production threshold up to high energies.
It includes resonance excitation and decay, direct single pion production and
diffractive and non-diffractive multiparticle production.
The cross section of each individual process is calculated by fitting
experimental data, while the kinematics is determined by the underlying
particle production process. We demonstrate that our model is capable of
reproducing known accelerator data over a wide energy range.Comment: 39 pages, 17 figures, submitted to Comp.Phys.Co
Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions
We report single-shot measurements of resistance versus time for thermally
assisted spin-torque-driven switching in magnetic tunnel junctions. We achieve
sufficient sensitivity to resolve the resistance signals leading up to
switching, including the variations between individual switching events.
Analyses of pre-switching thermal fluctuations allow detailed measurements of
coherence times and variations in magnetization precession amplitude. We find
that with a small in-plane hard-axis magnetic field the magnetization dynamics
are more spatially coherent than for the case of zero field.Comment: 13 pages, 4 figure
Giant Relaxation Oscillations in a Very Strongly Hysteretic SQUID ring-Tank Circuit System
In this paper we show that the radio frequency (rf) dynamical characteristics
of a very strongly hysteretic SQUID ring, coupled to an rf tank circuit
resonator, display relaxation oscillations. We demonstrate that the the overall
form of these characteristics, together with the relaxation oscillations, can
be modelled accurately by solving the quasi-classical non-linear equations of
motion for the system. We suggest that in these very strongly hysteretic
regimes SQUID ring-resonator systems may find application in novel logic and
memory devices.Comment: 7 pages, 5 figures. Uploaded as implementing a policy of arXiving old
paper
Measurements of strongly-anisotropic g-factors for spins in single quantum states
We have measured the full angular dependence, as a function of the direction
of magnetic field, for the Zeeman splitting of individual energy states in
copper nanoparticles. The g-factors for spin splitting are highly anisotropic,
with angular variations as large as a factor of five. The angular dependence
fits well to ellipsoids. Both the principal-axis directions and g-factor
magnitudes vary between different energy levels within one nanoparticle. The
variations agree quantitatively with random-matrix theory predictions which
incorporate spin-orbit coupling.Comment: 4 pages, 3 figures, 2 in colo
Fitting quotients of finitely presented abelian-by-nilpotent groups
We show that every finitely generated nilpotent group of class 2 occurs as the quotient of a finitely presented abelian-by-nilpotent group by its largest nilpotent normal subgrou
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