284 research outputs found
Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale
We investigate what could be learned about the absolute scale of neutrino
masses from comparisons among the patterns within quark and lepton mass
hierarchies. First, we observe that the existing information on neutrino masses
fits quite well to the unexplained, but apparently present regularities in the
quark and charged lepton sectors. Second, we discuss several possible mass
patterns, pointing out that this quite generally leads towards hierarchical
neutrino mass patterns especially disfavoring the vacuum solution.Comment: final version to be published in PRD, 5 pages, 2 figures, RevTe
Trematode Infections inLittorina littoreaon the New Hampshire Coast
The prevalence of parasite infections in Littorina littorea (Common Periwinkle) was examined at 16 rocky intertidal sites along the New Hampshire coastline over three summers (2006 to 2008). We sampled over a relatively small spatial scale (21 km) and expected that the prevalence of infections in L. littorea would be similar between sites over this sampling area. In total, 1983 snails were collected from areas at mean low water during spring tides. Snail size (mm), gender, and type of parasitic infection were noted for all snails. Eleven percent of snails collected were infected with rediae and cercariae of the trematodes Cryptocotyle lingua or Cercaria parvicaudata; one snail had a double infection of both trematodes. The prevalence of infection at sites ranged from 1.9% to 30.1%. At all sites, female snails outnumbered male snails, and a greater proportion of females were infected than males. Large snails were more likely to be infected with trematodes at 3 sites, while a higher level of infection was found in small snails at 1 site. Snails at wave-protected sites were more likely to be infected than snails at wave-exposed sites. No relationship was found between the number of gulls at a site and the prevalence of infection. Although temporal variation in levels of prevalence in parasitic infections may explain some of our site-to-site differences, our data show large spatial variation of parasite prevalence in L. littorea over a minimum distance of 0.5 km and provide a foundation to test hypotheses concerning the susceptibility of female and immature (small) snails to infection
Measuring proper motions of isolated neutron stars with Chandra
The excellent spatial resolution of the Chandra observatory offers the
unprecedented possibility to measure proper motions at X-ray wavelength with
relatively high accuracy using as reference the background of extragalactic or
remote galactic X-ray sources. We took advantage of this capability to
constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and
lacking an optical counterpart. In this paper, we present results from a
preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and
138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022
respectively. We use these values together with those of other ROSAT discovered
INSs to constrain the origin, distance and evolutionary status of this
particular group of objects. We find that the tangential velocities of radio
quiet ROSAT neutron stars are probably consistent with those of 'normal'
pulsars. Their distribution on the sky and, for those having accurate proper
motion vectors, their possible birth places, all point to a local population,
probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
Strange Stars with a Density-Dependent Bag Parameter
We have studied strange quark stars in the framework of the MIT bag model,
allowing the bag parameter B to depend on the density of the medium. We have
also studied the effect of Cooper pairing among quarks, on the stellar
structure. Comparison of these two effects shows that the former is generally
more significant. We studied the resulting equation of state of the quark
matter, stellar mass-radius relation, mass-central-density relation,
radius-central-density relation, and the variation of the density as a function
of the distance from the centre of the star. We found that the
density-dependent B allows stars with larger masses and radii, due to
stiffening of the equation of state. Interestingly, certain stellar
configurations are found to be possible only if B depends on the density. We
have also studied the effect of variation of the superconducting gap parameter
on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in
Phys. Rev. (D
Constructive and destructive use of compilers in elliptic curve cryptography
Although cryptographic software implementation is often performed by expert programmers, the range of performance and security driven options, as well as more mundane software engineering issues, still make it a challenge. The use of domain specific language and compiler techniques to assist in description and optimisation of cryptographic software is an interesting research challenge. In this paper we investigate two aspects of such techniques, focusing on Elliptic Curve Cryptography (ECC) in particular. Our constructive results show that a suitable language allows description of ECC based software in a manner close to the original mathematics; the corresponding compiler allows automatic production of an executable whose performance is competitive with that of a hand-optimised implementation. In contrast, we study the worrying potential for naĂŻve compiler driven optimisation to render cryptographic software insecure. Both aspects of our work are set within the context of CACE, an ongoing EU funded project on this general topic
Inter- and intragrain currents in bulk melt-grown YBaCuO rings
A simple contactless method suitable to discern between the intergrain
(circular) current, which flows in the thin superconducting ring, and the
intragrain current, which does not cross the weakest link, has been proposed.
At first, we show that the intergrain current may directly be estimated from
the magnetic flux density measured by the Hall sensor positioned
in the special points above/below the ring center. The experimental
and the numerical techniques to determine the value are discussed. Being
very promising for characterization of a current flowing across the joints in
welded YBaCuO rings (its dependencies on the temperature and the external
magnetic field as well as the time dissipation), the approach has been applied
to study corresponding properties of the intra- and intergrain currents flowing
across the -twisted grain boundaries which are frequent in bulk
melt-textured YBaCuO samples. We present experimental data related to the flux
penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin
state and during the field reversal. The shielding properties and their
dependence on external magnetic fields are also studied. Besides, we consider
the flux creep effects and their influence on the current re-distribution
during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version,
corrections to perturbing effects near the weak links are introduced, one
more figure is added. lin
Montgomery Multiplication on the Cell
A technique to speed up Montgomery multiplication targeted at the Synergistic Processor Elements (SPE) of the Cell Broadband Engine is proposed. The technique consists of splitting a number into four consecutive parts. These parts are placed one by one in each of the four element positions of a vector, representing columns in a 4-SIMD organization. This representation enables arithmetic to be performed in a 4-SIMD fashion. An implementation of the Montgomery multiplication using this technique is up to 2.47 times faster compared to an unrolled implementation of Montgomery multiplication, which is part of the IBM multi-precision math library, for odd moduli of length 160 to 2048 bits. The presented technique can also be applied to speed up Montgomery multiplication on other SIMD-architectures
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