39,755 research outputs found
A Model of Low-lying States in Strongly Interacting Electroweak Symmetry-Breaking Sector
It is proposed that, in a strongly-interacting electroweak sector, besides
the Goldstone bosons, the coexistence of a scalar state () and vector
resonances such as [)], [] and
[] is required by the proper Regge behavior of the
forward scattering amplitudes. This is a consequence of the following
well-motivated assumptions: (a). Adler-Weisberger-type sum rules and the
superconvergence relations for scattering amplitudes hold in this strongly
interacting sector; (b). the sum rules at are saturated by a minimal set
of low-lying states with appropriate quantum numbers. It therefore suggests
that a complete description should include all these resonances. These states
may lead to distinctive experimental signatures at future colliders.Comment: revised version, to appear in Modern Physics Letters A; file also
available via anonymous ftp at ftp://ucdhep.ucdavis.edu/han/sews/lowlying.p
Atrocalopteryx melli orohainani ssp. nov. on the Island of Hainan, China (Zygoptera: Calopterygidae)
The new sp. is described from the mountain core of Hainan, southern China, where it usually occurs at altitudes not lower than 300 m asl. It lives on the same type of small, shaded rivers as the nominate ssp. on the continent, and is distinguished by its larger size, slightly less enfumed wings, and a 2.6% difference in the sequence of the barcoding portion of the mitochodrial DNA-cytochrome c oxidase subunit I gene (COI). Holotype male: Diaoluoshan mountain, 6-VIII-2011; deposited in the Inst. Hydrobiol., Jinan Univ., Guanghou. It is argued that this geographically defined ssp. evolved because of persistent poor gene flow with continental populations, caused by the lowland "panhandle" between Hainan and the continent. This barrier was probably functioning equally well during interglacials (like at present) as during pleniglacials (when Hainan was connected to the mainland), because lack of suitable environments (small sized running waters), and dry and cold conditions continued to limit the contact with A. melli of the mainland
Nuclear Spin Relaxation Rate of Disordered -wave Superconductors
Based on an effective Hamiltonian with the binary alloy disorder model
defined in the triangular lattice, the impurity scattering effects on the
density of states and especially on the spin-lattice relaxation rate of
-wave superconductors are studied by solving numerically the
Bogoliubov-de Gennes equations. In the clean limit, the coherence peak of
is observed as expected. More intriguingly, for strong scattering
potential, the temperature dependence of exhibits the two different
power law behaviors near and at low temperatures, respectively,
which is in good agreement with the nuclear quadrupolar resonance measurement.Comment: 4 pages, 3 figure
Coauthor prediction for junior researchers
Research collaboration can bring in different perspectives and generate more productive results. However, finding an appropriate collaborator can be difficult due to the lacking of sufficient information. Link prediction is a related technique for collaborator discovery; but its focus has been mostly on the core authors who have relatively more publications. We argue that junior researchers actually need more help in finding collaborators. Thus, in this paper, we focus on coauthor prediction for junior researchers. Most of the previous works on coauthor prediction considered global network feature and local network feature separately, or tried to combine local network feature and content feature. But we found a significant improvement by simply combing local network feature and global network feature. We further developed a regularization based approach to incorporate multiple features simultaneously. Experimental results demonstrated that this approach outperformed the simple linear combination of multiple features. We further showed that content features, which were proved to be useful in link prediction, can be easily integrated into our regularization approach. © 2013 Springer-Verlag
Approximate input physics for stellar modelling
We present a simple and efficient, yet reasonably accurate, equation of
state, which at the moderately low temperatures and high densities found in the
interiors of stars less massive than the Sun is substantially more accurate
than its predecessor by Eggleton, Faulkner & Flannery. Along with the most
recently available values in tabular form of opacities, neutrino loss rates,
and nuclear reaction rates for a selection of the most important reactions,
this provides a convenient package of input physics for stellar modelling. We
briefly discuss a few results obtained with the updated stellar evolution code.Comment: uuencoded compressed postscript. The preprint are also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Subdwarf B stars from the common envelope ejection channel
From the canonical binary scenario, the majority of sdBs are produced from
low-mass stars with degenerate cores where helium is ignited in a way of
flashes. Due to numerical difficulties, the models of produced sdBs are
generally constructed from more massive stars with non-degenerate cores,
leaving several uncertainties on the exact characteristics of sdB stars.
Employing MESA, we systematically studied the characteristics of sdBs produced
from the common envelope (CE) ejection channel, and found that the sdB stars
produced from the CE ejection channel appear to form two distinct groups on the
effective temperature-gravity diagram. One group (the flash-mixing model)
almost has no H-rich envelope and crows at the hottest temperature end of the
extremely horizontal branch (EHB), while the other group has significant H-rich
envelope and spreads over the whole canonical EHB region. The key factor for
the dichotomy of the sdB properties is the development of convection during the
first helium flash, which is determined by the interior structure of the star
after the CE ejection. For a given initial stellar mass and a given core mass
at the onset of the CE, if the CE ejection stops early, the star has a
relatively massive H-rich envelope, resulting in a canonical sdB generally. The
fact of only a few short-orbital-period sdB binaries being in the flash-mixing
sdB region and the lack of He-rich sdBs in short-orbital-period binaries
indicate that the flash mixing is not very often in the products of the CE
ejection. A falling back process after the CE ejection, similar to that
happened in nova, is an appropriate way of increasing the envelope mass, then
prevents the flash mixing.Comment: accepted by A&A 12 pages, 11 figure
Birthrates and delay times of Type Ia supernovae
Type Ia supernovae (SNe Ia) play an important role in diverse areas of
astrophysics, from the chemical evolution of galaxies to observational
cosmology. However, the nature of the progenitors of SNe Ia is still unclear.
In this paper, according to a detailed binary population synthesis study, we
obtained SN Ia birthrates and delay times from different progenitor models, and
compared them with observations. We find that the Galactic SN Ia birthrate from
the double-degenerate (DD) model is close to those inferred from observations,
while the birthrate from the single-degenerate (SD) model accounts for only
about 1/2-2/3 of the observations. If a single starburst is assumed, the
distribution of the delay times of SNe Ia from the SD model is a weak
bimodality, where the WD + He channel contributes to the SNe Ia with delay
times shorter than 100Myr, and the WD + MS and WD + RG channels to those with
age longer than 1Gyr.Comment: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30,
2009
The C-flash and the ignition conditions of type Ia supernovae
Thanks to a stellar evolution code able to compute through the
C-flash we link the binary population synthesis of single degenerate
progenitors of type Ia supernovae (SNe Ia) to their physical condition at the
time of ignition. We show that there is a large range of possible ignition
densities and we detail how their probability distribution depends on the
accretion properties. The low density peak of this distribution qualitatively
reminds of the clustering of the luminosities of Branch-normal SNe Ia. We
tighten the possible range of initial physical conditions for explosion models:
they form a one-parameter family, independent of the metallicity. We discuss
how these results may be modified if we were to relax our hypothesis of a
permanent Hachisu wind or if we were to include electron captures.Comment: 10 pages, 14 figures, MNRAS accepte
Vortex State in Na_xCoO_2.yH_2O: p_x\pm ip_y-wave versus d_{x^2-y^2}\pm id_{xy}-wave Pairing
Based on an effective Hamiltonian specified in the triangular lattice with
possible - or -wave pairing, which has
close relevance to the newly discovered NaCoOHO, the
electronic structure of the vortex state is studied by solving the
Bogoliubov-de Gennes equations. It is found that -wave is favored
for the electron doping as the hopping integral . The lowest-lying vortex
bound states are found to have respectively zero and positive energies for
- and -wave superconductors, whose vortex
structures exhibit the intriguing six-fold symmetry. In the presence of strong
on-site repulsion, the antiferromagnetic and ferromagnetic orders are induced
around the vortex cores for the former and the latter, respectively, both of
which cause the splitting of the LDOS peaks due to the lifting of spin
degeneracy. STM and NMR measurements are able to probe the new features of
vortex states uncovered in this work.Comment: 4 pages, 4 figures, The slightly shorter version was submitted to PR
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