264 research outputs found
Natural connection with totally skew-symmetric torsion on almost contact manifolds with B-metric
A natural connection with totally skew-symmetric torsion on almost contact
manifolds with B-metric is constructed. The class of these manifolds, where the
considered connection exists, is determined. Some curvature properties for this
connection, when the corresponding curvature tensor has the properties of the
curvature tensor for the Levi-Civita connection and the torsion tensor is
parallel, are obtained.Comment: 17 page
Specific function of a plastid sigma factor for ndhF gene transcription
The complexity of the plastid transcriptional apparatus (two or three different RNA polymerases and numerous regulatory proteins) makes it very difficult to attribute specific function(s) to its individual components. We have characterized an Arabidopsis T-DNA insertion line disrupting the nuclear gene coding for one of the six plastid sigma factors (SIG4) that regulate the activity of the plastid-encoded RNA polymerase PEP. This mutant shows a specific diminution of transcription of the plastid ndhF gene, coding for a subunit of the plastid NDH [NAD(P)H dehydrogenase] complex. The absence of another NDH subunit, i.e. NDHH, and the absence of a chlorophyll fluorescence transient previously attributed to the activity of the plastid NDH complex indicate a strong down-regulation of NDH activity in the mutant plants. Results suggest that plastid NDH activity is regulated on the transcriptional level by an ndhF-specific plastid sigma factor, SIG4
Physics Results from RICH Detectors
RICH detectors have become extraordinarily useful. Results include
measurement of solar neutrino rates, evidence for neutrino oscillations,
measurement of TeV gamma-rays from gravitational sources, properties of QCD,
charm production and decay, and measurement of the CKM matrix elements Vcs, Vcb
and Vub. A new value |Vub/Vcb|=0.087+/-0.012 is determined.Comment: Invited talk at ``The 3rd International Workshop on Ring Imaging
Cherenkov Detectors," Ein-Gedi, Dead-Sea, Israel, Nov. 15-20, 1998, 21 pages,
22 fig
Revisiting pseudo-Dirac neutrinos
We study the pseudo-Dirac mixing of left and right-handed neutrinos in the
case where the Majorana masses M_L and M_R are small when compared with the
Dirac mass, M_D. The light Majorana masses could be generated by a
non-renormalizable operator reflecting effects of new physics at some high
energy scale. In this context, we obtain a simple model independent closed
bound for M_D. A phenomenologically consistent scenario is achieved with
M_L,M_R ~ 10^{-7} eV and M_D ~ 10^{-5}-10^{-4} eV. This precludes the
possibility of positive mass searches in the planned future experiments like
GENIUS or in tritium decay experiments. If on the other hand, GENIUS does
observe a positive signal for a Majorana mass \geq 10^{-3} eV, then with very
little fine tuning of neutrino parameters, the scale of new physics could be in
the TeV range, but pseudo-Dirac scenario in that case is excluded. We briefly
discuss the constraints from cosmology when a fraction of the dark matter is
composed of nearly degenerate neutrinos.Comment: 17 pages, no figures, references added, to be published in PL
Absolute Branching Fraction Measurements of Exclusive D^0 Semileptonic Decays
With the first data sample collected by the CLEO-c detector at the psi(3770)
resonance we have studied four exclusive semileptonic decays of the D0 meson.
Our results include the first observation and absolute branching fraction
measurement for D0 --> rho- e+ nu_e and improved measurements of the absolute
branching fractions for D0 decays to K- e+ nu_e, pi- e+ nu_e, and K*- e+ nu_e.Comment: 9 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2005/, submitted to PR
Plasma Sex Steroid Levels and Steroidogenesis in the Gonad of the Self-fertilizing Fish Rivulus marmoratus
The mangrove killifish, Rivulus marmoratus, is the only known self-fertilizing vertebrate. This species is sexually dimorphic; sexually mature individuals are either hermaphrodite or primary and secondary males. Although the mangrove killifish has a unique reproductive strategy, there has been no study on the reproductive endocrinology of this species. Thus we investigated plasma sex steroid hormone levels and steroidogenesis in the gonads of R. marmoratus by enzyme linked immunosorbent assay (ELISA). Plasma 17β-estradiol (E2) and 11-ketotestosterone (11-KT) were detected both in hermaphrodite and in primary male. Ovarian follicles (follicle-enclosed oocytes) from hermaphrodites, which were categorized into early yolk stage and late yolk stage, and testis tissue of primary males were cultured with different concentrations of 17α-hydroxyprogesterone (OHP) or testosterone (T) for 24 h. Production of T, E2, 11-KT and 17α-20 β-dihydroxy-4-pregnen-3-one (17α,20β-P) in the medium from tissue culture were measured by ELISA. Early and late ovarian follicles of hermaphrodites and testis pieces of primary males synchronously secreted E2, 11-KT, and 17α,20β-P following incubation with OHP or T. We conclude that both hermaphrodite and primary male of the mangrove killifish secrete estrogen, androgen, and progestin synchronously
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