2,250 research outputs found
A stochastic differential equation for local times of super-Brownian motion
We show that local times of super-Brownian motion, or of Brownian motion
indexed by the Brownian tree, satisfy an explicit stochastic differential
equation. Our proofs rely on both excursion theory for the Brownian snake and
tools from the theory of superprocesses.Comment: 32 page
Quenched convergence of a sequence of superprocesses in R^d among Poissonian obstacles
We prove a convergence theorem for a sequence of super-Brownian motions
moving among hard Poissonian obstacles, when the intensity of the obstacles
grows to infinity but their diameters shrink to zero in an appropriate manner.
The superprocesses are shown to converge in probability for the law
of the obstacles, and -almost surely for a
subsequence, towards a superprocess with underlying spatial motion given by
Brownian motion and (inhomogeneous) branching mechanism of the form
, where depends on the density of the
obstacles. This work draws on similar questions for a single Brownian motion.
In the course of the proof, we establish precise estimates for integrals of
functions over the Wiener sausage, which are of independent interest.Comment: 22 page
Ferromagnetic order in U(Rh,Co)Ge
We report the variation of ferromagnetic order in the pseudo-ternary
compounds URh_{1-x}Co_{x}Ge (0 \leq x \leq 1). Magnetization and transport data
taken on polycrystalline samples show that the Curie temperature T_{C}
gradually increases with increasing Co content from a value of 9.5 K for URhGe
to a maximum value of 20 K for x = 0.6 and then steadily decreases to 3 K for
UCoGe. The magnetic interaction strength varies smoothly across the series. For
all samples the electrical resistivity for T < T_{C} follows the behaviour \rho
= \rho_{0} + AT^2. The A coefficient is dominated by scattering at spin waves
and is strongly enhanced for x = 0 and 1.Comment: 12 pages (4 figures), submitted to SS
Polymers and manifolds in static random flows: a renormalization group study
We study the dynamics of a polymer or a D-dimensional elastic manifold
diffusing and convected in a non-potential static random flow (the ``randomly
driven polymer model''). We find that short-range (SR) disorder is relevant for
d < 4 for directed polymers (each monomer sees a different flow) and for d < 6
for isotropic polymers (each monomer sees the same flow) and more generally for
d<d_c(D) in the case of a manifold. This leads to new large scale behavior,
which we analyze using field theoretical methods. We show that all divergences
can be absorbed in multilocal counter-terms which we compute to one loop order.
We obtain the non trivial roughness zeta, dynamical z and transport exponents
phi in a dimensional expansion. For directed polymers we find zeta about 0.63
(d=3), zeta about 0.8 (d=2) and for isotropic polymers zeta about 0.8 (d=3). In
all cases z>2 and the velocity versus applied force characteristics is
sublinear, i.e. at small forces v(f) f^phi with phi > 1. It indicates that this
new state is glassy, with dynamically generated barriers leading to trapping,
even by a divergenceless (transversal) flow. For random flows with long-range
(LR) correlations, we find continuously varying exponents with the ratio gL/gT
of potential to transversal disorder, and interesting crossover phenomena
between LR and SR behavior. For isotropic polymers new effects (e.g. a sign
change of zeta - zeta_0) result from the competition between localization and
stretching by the flow. In contrast to purely potential disorder, where the
dynamics gets frozen, here the dynamical exponent z is not much larger than 2,
making it easily accessible by simulations. The phenomenon of pinning by
transversal disorder is further demonstrated using a two monomer ``dumbbell''
toy model.Comment: Final version, some explications added and misprints corrected (69
pages latex, 40 eps-figures included
Mesoscale subduction at the Almeria-Oran front. Part 2: biophysical interactions.
This paper presents a detailed diagnostic analysis of hydrographic and current meter data from three, rapidly repeated, fine-scale surveys of the AlmeriaâOran front. Instability of the frontal boundary, between surface waters of Atlantic and Mediterranean origin, is shown to provide a mechanism for significant heat transfer from the surface layers to the deep ocean in winter. The data were collected during the second observational phase of the EU funded OMEGA project on RRS Discovery cruise 224 during December 1996. High resolution hydrographic measurements using the towed undulating CTD vehicle, SeaSoar, traced the subduction of Mediterranean Surface Water across the AlmeriaâOran front. This subduction is shown to result from a significant baroclinic component to the instability of the frontal jet. The Q-vector formulation of the omega equation is combined with a scale analysis to quantitatively diagnose vertical transport resulting from mesoscale ageostrophic circulation. The analyses are presented and discussed in the presence of satellite and airborne remotely sensed data; which provide the basis for a thorough and novel approach to the determination of observational error
Priorities for Pig Research in Southeast Asia and the Pacific to 2010
Livestock Production/Industries, Research and Development/Tech Change/Emerging Technologies,
Piwi induces piRNA-guided transcriptional silencing and establishment of a repressive chromatin state
In the metazoan germline, piwi proteins and associated piwi-interacting RNAs (piRNAs) provide a defense system against the expression of transposable elements. In the cytoplasm, piRNA sequences guide piwi complexes to destroy complementary transposon transcripts by endonucleolytic cleavage. However, some piwi family members are nuclear, raising the possibility of alternative pathways for piRNA-mediated regulation of gene expression. We found that Drosophila Piwi is recruited to chromatin, colocalizing with RNA polymerase II (Pol II) on polytene chromosomes. Knockdown of Piwi in the germline increases expression of transposable elements that are targeted by piRNAs, whereas protein-coding genes remain largely unaffected. Derepression of transposons upon Piwi depletion correlates with increased occupancy of Pol II on their promoters. Expression of piRNAs that target a reporter construct results in a decrease in Pol II occupancy and an increase in repressive H3K9me3 marks and heterochromatin protein 1 (HP1) on the reporter locus. Our results indicate that Piwi identifies targets complementary to the associated piRNA and induces transcriptional repression by establishing a repressive chromatin state when correct targets are found
Non-Hodgkin Lymphoma in Children and Adolescents: Progress Through Effective Collaboration, Current Knowledge, and Challenges Ahead
Non-Hodgkin lymphoma is the fourth most common malignancy in children, has an even higher incidence in adolescents, and is primarily represented by only a few histologic subtypes. Dramatic progress has been achieved, with survival rates exceeding 80%, in large part because of a better understanding of the biology of the different subtypes and national and international collaborations. Most patients with Burkitt lymphoma and diffuse large B-cell lymphoma are cured with short intensive pulse chemotherapy containing cyclophosphamide, cytarabine, and high-dose methotrexate. The benefit of the addition of rituximab has not been established except in the case of primary mediastinal B-cell lymphoma. Lymphoblastic lymphoma is treated with intensive, semi-continuous, longer leukemia-derived protocols. Relapses in B-cell and lymphoblastic lymphomas are rare and infrequently curable, even with intensive approaches. Event-free survival rates of approximately 75% have been achieved in anaplastic large-cell lymphomas with various regimens that generally include a short intensive B-like regimen. Immunity seems to play an important role in prognosis and needs further exploration to determine its therapeutic application. ALK inhibitor therapeutic approaches are currently under investigation. For all pediatric lymphomas, the intensity of induction/consolidation therapy correlates with acute toxicities, but because of low cumulative doses of anthracyclines and alkylating agents, minimal or no long-term toxicity is expected. Challenges that remain include defining the value of prognostic factors, such as early response on positron emission tomography/computed tomography and minimal disseminated and residual disease, using new biologic technologies to improve risk stratification, and developing innovative therapies, both in the first-line setting and for relapse
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