6,278 research outputs found
Surface temperatures and temperature gradient features of the US Gulf Coast waters
Satellite thermal infrared data on the Gulf of Mexico show that a seasonal cycle exists in the horizontal surface temperature structure. In the fall, the surface temperatures of both coastal and deep waters are nearly uniform. With the onset of winter, atmospheric cold fronts, which are accompanied by dry, low temperature air and strong winds, draw heat from the sea. A band of cooler water forming on the inner shelf expands, until a thermal front develops seaward along the shelf break between the cold shelf waters and the warmer deep waters of the Gulf. Digital analysis of the satellite data was carried out in an interactive mode using a minicomputer and software. A time series of temperature profiles illustrates the temporal and spatial changes in the sea-surface temperature field
Data-Discriminants of Likelihood Equations
Maximum likelihood estimation (MLE) is a fundamental computational problem in
statistics. The problem is to maximize the likelihood function with respect to
given data on a statistical model. An algebraic approach to this problem is to
solve a very structured parameterized polynomial system called likelihood
equations. For general choices of data, the number of complex solutions to the
likelihood equations is finite and called the ML-degree of the model. The only
solutions to the likelihood equations that are statistically meaningful are the
real/positive solutions. However, the number of real/positive solutions is not
characterized by the ML-degree. We use discriminants to classify data according
to the number of real/positive solutions of the likelihood equations. We call
these discriminants data-discriminants (DD). We develop a probabilistic
algorithm for computing DDs. Experimental results show that, for the benchmarks
we have tried, the probabilistic algorithm is more efficient than the standard
elimination algorithm. Based on the computational results, we discuss the real
root classification problem for the 3 by 3 symmetric matrix~model.Comment: 2 table
Reaper is regulated by IAP-mediated ubiquitination
In most cases, apoptotic cell death culminates in the activation of the caspase family of cysteine proteases, leading to the orderly dismantling and elimination of the cell. The IAPs (inhibitors of apoptosis) comprise a family of proteins that oppose caspases and thus act to raise the apoptotic threshold. Disruption of IAP-mediated caspase inhibition has been shown to be an important activity for pro-apoptotic proteins in Drosophila (Reaper, HID, and Grim) and in mammalian cells (Smac/DIABLO and Omi/HtrA2). In addition, in the case of the fly, these proteins are able to stimulate the ubiquitination and degradation of IAPs by a mechanism involving the ubiquitin ligase activity of the IAP itself. In this report, we show that the Drosophila RHG proteins (Reaper, HID, and Grim) are themselves substrates for IAP-mediated ubiquitination. This ubiquitination of Reaper requires IAP ubiquitin-ligase activity and a stable interaction between Reaper and the IAP. Additionally, degradation of Reaper can be blocked by mutating its potential ubiquitination sites. Most importantly, we also show that regulation of Reaper by ubiquitination is a significant factor in determining its biological activity. These data demonstrate a novel function for IAPs and suggest that IAPs and Reaper-like proteins mutually control each other's abundance
Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O
Thermodynamic critical field curves have been measured for
over the full range of carrier concentrations
where superconductivity occurs in order to determine changes in the normal
state density of states with carrier concentration. There is a substantial
window in the plane where the measurements are possible because the
samples are both thermodynamically reversible and the temperature is low enough
that vortex fluctuations are not important. In this window, the data fit
Hao-Clem rather well, so this model is used to determine and
for each temperature and carrier concentration. Using N(0) and the ratio of the
energy gap to transition temperature, , as fitting
parameters, the curves give over the
whole range of . Values of N(0) remain rather constant in the optimum-doped
and overdoped regime, but drops quickly toward zero in the underdoped regime.
The Drosophila caspase Ice is important for many apoptotic cell deaths and for spermatid individualization, a nonapoptotic process
Caspase family proteases play important roles in the regulation of apoptotic cell death. Initiator caspases are activated in response to death stimuli, and they transduce and amplify these signals by cleaving and thereby activating effector caspases. In Drosophila, the initiator caspase Nc (previously Dronc) cleaves and activates two short-prodomain caspases, Dcp-1 and Ice (previously Drice), suggesting these as candidate effectors of Nc killing activity. dcp-1-null mutants are healthy and possess few defects in normally occurring cell death. To explore roles for Ice in cell death, we generated and characterized an Ice null mutant. Animals lacking Ice show a number of defects in cell death, including those that occur during embryonic development, as well as during formation of adult eyes, arista and wings. Ice mutants exhibit subtle defects in the destruction of larval tissues, and do not prevent destruction of salivary glands during metamorphosis. Cells from Ice animals are also markedly resistant to several stresses, including X-irradiation and inhibition of protein synthesis. Mutations in Ice also suppress cell death that is induced by expression of Rpr, Wrinkled (previously Hid) and Grim. These observations demonstrate that Ice plays an important non-redundant role as a cell death effector. Finally, we demonstrate that Ice participates in, but is not absolutely required for, the non-apoptotic process of spermatid differentiation
Update of axion CDM energy density
We improve the estimate of the axion CDM energy density by considering the
new values of current quark masses, the QCD phase transition effect and a
possible anharmonic effect.Comment: 7 pages, 6 figures. References are added. A factor is correcte
Modulated structures in electroconvection in nematic liquid crystals
Motivated by experiments in electroconvection in nematic liquid crystals with
homeotropic alignment we study the coupled amplitude equations describing the
formation of a stationary roll pattern in the presence of a weakly-damped mode
that breaks isotropy. The equations can be generalized to describe the planarly
aligned case if the orienting effect of the boundaries is small, which can be
achieved by a destabilizing magnetic field. The slow mode represents the
in-plane director at the center of the cell. The simplest uniform states are
normal rolls which may undergo a pitchfork bifurcation to abnormal rolls with a
misaligned in-plane director.We present a new class of defect-free solutions
with spatial modulations perpendicular to the rolls. In a parameter range where
the zig-zag instability is not relevant these solutions are stable attractors,
as observed in experiments. We also present two-dimensionally modulated states
with and without defects which result from the destabilization of the
one-dimensionally modulated structures. Finally, for no (or very small)
damping, and away from the rotationally symmetric case, we find static chevrons
made up of a periodic arrangement of defect chains (or bands of defects)
separating homogeneous regions of oblique rolls with very small amplitude.
These states may provide a model for a class of poorly understood stationary
structures observed in various highly-conducting materials ("prechevrons" or
"broad domains").Comment: 13 pages, 13 figure
Cellular Programming of Plant Gene Imprinting
Gene imprinting, the differential expression of maternal and paternal alleles, independently evolved in mammals and in flowering plants. A unique feature of flowering plants is a double-fertilization event in which the sperm fertilize not only the egg, which forms the embryo, but also the central cell, which develops into the endosperm (an embryo-supporting tissue). The distinctive mechanisms of gene imprinting in the endosperm, which involve DNA demethylation and histone methylation, begin in the central cell and sperm prior to fertilization. Flowering plants might have coevolved double fertilization and imprinting to prevent parthenogenetic development of the endosperm
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The catalytic core of DEMETER guides active DNA demethylation in Arabidopsis.
The Arabidopsis DEMETER (DME) DNA glycosylase demethylates the maternal genome in the central cell prior to fertilization and is essential for seed viability. DME preferentially targets small transposons that flank coding genes, influencing their expression and initiating plant gene imprinting. DME also targets intergenic and heterochromatic regions, but how it is recruited to these differing chromatin landscapes is unknown. The C-terminal half of DME consists of 3 conserved regions required for catalysis in vitro. We show that this catalytic core guides active demethylation at endogenous targets, rescuing dme developmental and genomic hypermethylation phenotypes. However, without the N terminus, heterochromatin demethylation is significantly impeded, and abundant CG-methylated genic sequences are ectopically demethylated. Comparative analysis revealed that the conserved DME N-terminal domains are present only in flowering plants, whereas the domain architecture of DME-like proteins in nonvascular plants mainly resembles the catalytic core, suggesting that it might represent the ancestral form of the 5mC DNA glycosylase found in plant lineages. We propose a bipartite model for DME protein action and suggest that the DME N terminus was acquired late during land plant evolution to improve specificity and facilitate demethylation at heterochromatin targets
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