29,932 research outputs found
The fundamental group and torsion group of Beauville surfaces
We give a survey on the fundamental group of surfaces isogenous to a higher
product. If the surfaces are regular, e.g. if they are Beauville surfaces, the
first homology group is a finite group. We present a MAGMA script which
calculates the first homology groups of regular surfaces isogenous to a
product.Comment: 14 pages; MAGMA script included; v2: minor corrections, final version
to appear in the Proceedings of the Conference "Beauville Surfaces and
Groups", Newcastle University (UK), 7-9th June 201
Neutron matter under strong magnetic fields: a comparison of models
The equation of state of neutron matter is affected by the presence of a
magnetic field due to the intrinsic magnetic moment of the neutron. Here we
study the equilibrium configuration of this system for a wide range of
densities, temperatures and magnetic fields. Special attention is paid to the
behavior of the isothermal compressibility and the magnetic susceptibility. Our
calculation is performed using both microscopic and phenomenological approaches
of the neutron matter equation of state, namely the Brueckner--Hartree--Fock
(BHF) approach using the Argonne V18 nucleon-nucleon potential supplemented
with the Urbana IX three-nucleon force, the effective Skyrme model in a
Hartree--Fock description, and the Quantum Hadrodynamic formulation with a mean
field approximation. All these approaches predict a change from completely spin
polarized to partially polarized matter that leads to a continuous equation of
state. The compressibility and the magnetic susceptibility show characteristic
behaviors, which reflect that fact. Thermal effects tend to smear out the
sharpness found for these quantities at T=0. In most cases a thermal increase
of 10 MeV is enough to hide the signals of the change of polarization. The set
of densities and magnetic field intensities for which the system changes it
spin polarization is different for each model. However, there is an overall
agreement between the three theoretical descriptions.Comment: updated to correspond with the published versio
Charge Density Wave Ratchet
We propose to operate a locally-gated charge density wave as an electron
pump. Applying an oscillating gate potential with frequency causes equally
spaced plateaux in the sliding charge density wave current separated by where is the number of parallel chains. The effects of thermal
noise are investigated.Comment: To be published in Applied Physics Letter
Quality Assessment of Summer and Autumn Carrots from a Biodynamic Breeding Project and Correlations of Physico-Chemical Parameters and Features Determined by Picture Forming Methods
Introduction:
Assessment of product quality is of special significance in organic farming and includes the supervision of crop quality in different growing systems (e.g., Fleck et al. 1998) and the characterisation of different cultivars. Several methods have been developed and applied for this purpose, e.g., the physico-chemical analysis of crops, picture forming methods (PFMs) and plant observation. So far only limited information is available on the comparability of these methods. This contribution aims to compare the results of the analysis of physico-chemical parameters of summer and autumn carrots with features determined by PFMs by means of correlation analysis.
Conclusions:
High and significant correlation coefficients were found between quality parameters of summer and autumn carrots from a biodynamical breeding project determined by physico-chemical analysis and PFMs. This indicates close relationships between the two quality approaches which should be investigated further in future work
The X-ray Properties of the Cometary Blue Compact Dwarf galaxies Mrk 59 and Mrk 71
We present XMM-Newton and Chandra observations of two low-metallicity
cometary blue compact dwarf (BCD) galaxies, Mrk 59 and Mrk 71. The first BCD,
Mrk 59, contains two ultraluminous X-ray (ULX) sources, IXO 72 and IXO 73, both
associated with bright massive stars and H II complexes, as well as one fainter
extended source associated with a massive H II complex at the head of the
cometary structure. The low-metallicity of Mrk 59 appears to be responsible for
the presence of the two ULXs. IXO 72 has varied little over the last 10 yr,
while IXO 73 has demonstrated a variability factor of ~4 over the same period.
The second BCD, Mrk 71, contains two faint X-ray point sources and two faint
extended sources. One point source is likely a background AGN, while the other
appears to be coincident with a very luminous star and a compact H II region at
the "head" of the cometary structure. The two faint extended sources are also
associated with massive H II complexes. Although both BCDs have the same
metallicity, the three sources in Mrk 71 have X-ray luminosities ~1-2 orders of
magnitude fainter than those in Mrk 59. The age of the starburst may play a
role.Comment: 14 pages, 7 figures, accepted for publication in MNRA
Shot noise in magnetic tunnel junctions from first principles
We compute the shot noise in ballistic and disordered Fe/MgO/Fe tunnel
junctions by a wave function-matching method. For tunnel barriers with no more
than 5 atomic layers we find a suppression of the Fano factor as a function of
the magnetic configuration. For thicker MgO barriers the shot noise is
suppressed up to a threshold bias indicating the onset of resonant tunneling.
We find excellent agreement with recent experiments when interface disorder is
taken into accountComment: 5 pages,5 figure
Nuclear Magnetic Relaxation Rate in a Noncentrosymmetric Superconductor
For a noncentrosymmetric superconductor such as CePt3Si, we consider a Cooper
pairing model with a two-component order parameter composed of spin-singlet and
spin-triplet pairing components.
We demonstrate that such a model on a qualitative level accounts for
experimentally observed features of the temperature dependence of the nuclear
spin-lattice relaxation rate 1/T1, namely a peak just below Tc and a line-node
gap behavior at low temperatures.Comment: 4 page
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The effect of network topology on optimal exploration strategies and the evolution of cooperation in a mobile population
We model a mobile population interacting over an underlying spatial structure using a Markov movement model. Interactions take the form of public goods games, and can feature an arbitrary group size. Individuals choose strategically to remain at their current location or to move to a neighbouring location, depending upon their exploration strategy and the current composition of their group. This builds upon previous work where the underlying structure was a complete graph (i.e. there was effectively no structure). Here, we consider alternative network structures and a wider variety of, mainly larger, populations. Previously, we had found when cooperation could evolve, depending upon the values of a range of population parameters. In our current work, we see that the complete graph considered before promotes stability, with populations of cooperators or defectors being relatively hard to replace. By contrast, the star graph promotes instability, and often neither type of population can resist replacement. We discuss potential reasons for this in terms of network topology
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