54,007 research outputs found
A New Young Diagrammatic Method For Kronecker Products of O(n) and Sp(2m)
A new simple Young diagrammatic method for Kronecker products of O(n) and
Sp(2m) is proposed based on representation theory of Brauer algebras. A general
procedure for the decomposition of tensor products of representations for O(n)
and Sp(2m) is outlined, which is similar to that for U(n) known as the
Littlewood rules together with trace contractions from a Brauer algebra and
some modification rules given by King.Comment: Latex, 11 pages, no figure
On several families of elliptic curves with arbitrary large Selmer groups
In this paper, we calculate the Selmer groups
S^{(\phi)} (E / \Q) and S^{(\hat{\varphi})} (E^{\prime} / \Q) of elliptic
curves via descent theory
(see [S, Chapter X]), in particular, we obtain that the Selmer groups of
several families of such elliptic curves can be arbitrary large.Comment: 22 page
In vitro Culture of Several Rice Cultivars
Tissue culture methods have been established to regenerate certain rice (Oryza sativa L) cultivars, but regeneration of the rice cultivars widely grown in Arkansas has not been reported. This study has established an in vitroculture for the rice cultivars \u27Nortai\u27, \u27Starbonnet\u27, \u27Mars\u27, Tebonnet\u27, \u27Newbonnet\u27, and \u27Lemont\u27. Callus was induced in the dark at either 20 or 28 C from dehusked seeds cultured on Murashige and Skoog (MS) medium (Murashige and Skoog, 1962) containing 40 g L^-1 sucrose, 10 g L^1 agar, 0.5, 1.0, or 2.0 mg L^-1 1 2,4-dichlorophenoxyacetic acid (2,4-D) and adjusted to pH 5.7. After four weeks the calli were weighed, transferred onto MS medium containing no 2,4-D, and maintained in a 1 2-h photoperiod (65 uE m^-2 s^-1) at 25 ± 2 C to induce plant regeneration. Callus production was best when cultured on a medium containing 1.0 mg L^-1 2,4-D and incubated at 28 C. Plant regeneration was observed two to four weeks later. The percentage of calli regenerating platlets varied with the cultivar and the callus induction treatment. Callus induction at 20 C on a medium with a 2,4-D level less than 2.0 mg L^-1 enhanced the regenerability of most cultivars. Regenerates were transplanted to soil and grow normally to maturity. This system can be helpful in improving rice cultivars with tissue culture techniques such as somaclonal variant selection and somatic hybridization
Observation of a push force on the end face of a nm fiber taper exerted by outgoing light
There are two different proposals for the momentum of light in a transparent
dielectric of refractive index n: Minkowski's version nE/c and Abrahm's version
E/(nc), where E and c are the energy and vacuum speed of light, respectively.
Despite many tests and debates over nearly a century, momentum of light in a
transparent dielectric remains controversial. In this Letter, we report a
direct observation of the inward push force on the end face of a free nm fiber
taper exerted by the outgoing light. Our results clearly support Abraham
momentum. Our experiment also indicates an inward surface pressure on a
dielectric exerted by the incident light, different from the commonly
recognized pressure due to the specular reflection. Such an inward surface
pressure by the incident light may be useful for precise design of the
laser-induced inertially-confined fusion.Comment: 9 pages, 3 figures;Accepted for publication as a Letter in Physical
Review Letters(CODE: LP11093
Hierarchical fragmentation and collapse signatures in a high-mass starless region
Aims: Understanding the fragmentation and collapse properties of the dense
gas during the onset of high-mass star formation. Methods: We observed the
massive (~800M_sun) starless gas clump IRDC18310-4 with the Plateau de Bure
Interferometer (PdBI) at sub-arcsecond resolution in the 1.07mm continuum
andN2H+(3-2) line emission. Results: Zooming from a single-dish low-resolution
map to previous 3mm PdBI data, and now the new 1.07mm continuum observations,
the sub-structures hierarchically fragment on the increasingly smaller spatial
scales. While the fragment separations may still be roughly consistent with
pure thermal Jeans fragmentation, the derived core masses are almost two orders
of magnitude larger than the typical Jeans mass at the given densities and
temperatures. However, the data can be reconciled with models using
non-homogeneous initial density structures, turbulence and/or magnetic fields.
While most sub-cores remain (far-)infrared dark even at 70mum, we identify weak
70mum emission toward one core with a comparably low luminosity of ~16L_sun,
re-enforcing the general youth of the region. The spectral line data always
exhibit multiple spectral components toward each core with comparably small
line widths for the individual components (in the 0.3 to 1.0km/s regime). Based
on single-dish C18O(2-1) data we estimate a low virial-to-gas-mass ratio
<=0.25. We discuss that the likely origin of these spectral properties may be
the global collapse of the original gas clump that results in multiple spectral
components along each line of sight. Even within this dynamic picture the
individual collapsing gas cores appear to have very low levels of internal
turbulence.Comment: 8 pages, 4 figures, A&A in pres
X-ray Shots of Cyg X-1
X-ray shots of Cyg X-1 in different energy bands and spectral states have
been studied with PCA/RXTE observations. The detailed shot structure is
obtained by superposing many shots with one millisecond time bin through
aligning their peaks with an improved algorithm. In general, the shots are
composed of a slow rise and fast decay. The shot structures in the different
states are different. The duration of shot in the high state is shorter than
that in the low and transition states. The shot profile in the high energy band
is more asymmetric and narrower than that in the low energy band. The average
hardness of shot is lower than that of steady emission in the transition and
low states but higher than that in the high state. The time lags between the
shots in higher and lower energy bands have been found in the different states.
In transition states, the time lag is the largest among the different states of
Cyg X-1, and it is the smallest in the low state. The implications of the
observed shot features for shot models are discussed.Comment: Latex, 20 pages, 12 figures(included), to be published in Ap
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