1,386 research outputs found
Genomic function during the lampbrush chromosome stage of amphibian oogenesis
Throughout its lengthy developmental history the disposition of the genetic material in the amphibian oocyte nucleus differs from that in other cell types. The chromosomes in the oocyte nucleus, arrested for the whole of oogenesis at the prophase of the first meiotic division, are known to contain at least the tetraploid amount of DNA.(1,2) Oogenesis in amphibia requires months or even years to complete, depending on the species
Exponentiation of the Drell-Yan cross section near partonic threshold in the DIS and MSbar schemes
It has been observed that in the DIS scheme the refactorization of the
Drell-Yan cross section leading to exponentiation of threshold logarithms can
also be used to organize a class of constant terms, most of which arise from
the ratio of the timelike Sudakov form factor to its spacelike counterpart. We
extend this exponentiation to include all constant terms, and demonstrate how a
similar organization may be achieved in the MSbar scheme. We study the
relevance of these exponentiations in a two-loop analysis.Comment: 20 pages, JHEP style, no figure
Universal Power Law in the Noise from a Crumpled Elastic Sheet
Using high-resolution digital recordings, we study the crackling sound
emitted from crumpled sheets of mylar as they are strained. These sheets
possess many of the qualitative features of traditional disordered systems
including frustration and discrete memory. The sound can be resolved into
discrete clicks, emitted during rapid changes in the rough conformation of the
sheet. Observed click energies range over six orders of magnitude. The measured
energy autocorrelation function for the sound is consistent with a stretched
exponential C(t) ~ exp(-(t/T)^{b}) with b = .35. The probability distribution
of click energies has a power law regime p(E) ~ E^{-a} where a = 1. We find the
same power law for a variety of sheet sizes and materials, suggesting that this
p(E) is universal.Comment: 5 pages (revtex), 10 uuencoded postscript figures appended, html
version at http://rainbow.uchicago.edu/~krame
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
Analisi scientifiche sulle tempere murali di Villa Pace
International audienceThe morphology, mineralogy, and solid-liquid phase separation of the Cu and Zn precipitates formed with sulfide produced in a sulfate-reducing bioreactor were studied at pH 3, 5, and 7. The precipitates formed at pH 7 display faster settling rates, better dewaterability, and higher concentrations of settleable solids as compared to the precipitates formed at pH 3 and 5. These differences were linked to the agglomeration of the sulfidic precipitates and coprecipitation of the phosphate added to the bioreactor influent. The Cu and Zn quenched the intensity of the dissolved organic matter peaks identified by fluorescence-excitation emission matrix spectroscopy, suggesting a binding mechanism that decreases supersaturation, especially at pH 5. X-ray absorption fine structure spectroscopy analyses confirmed the precipitation of Zn-S as sphalerite and Cu-S as covellite in all samples, but also revealed the presence of Zn sorbed on hydroxyapatite. These analyses further showed that CuS structures remained amorphous regardless of the pH, whereas the ZnS structure was more organized at pH 5 as compared to the ZnS formed at pH 3 and 7, in agreement with the cubic sphalerite-type structures observed through scanning electron microscopy at pH 5
Hamiltonian approach for the wave packet dynamics: Beyond Gaussian wave functions
It is well known that the Gaussian wave packet dynamics can be written in
terms of Hamilton equations in the extended phase space that is twice as large
as in the corresponding classical system. We construct several generalizations
of this approach that include non-Gausssian wave packets. These generalizations
lead to the further extension of the phase space while retaining the Hamilton
structure of the equations of motion. We compare the Gaussian dynamics with
these non-Gaussian extensions for a particle with the quartic potential.Comment: 5 pages, 3 figure
Towards Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)
We describe ZStreak, a semi-real-time pipeline specialized in detecting
small, fast-moving near-Earth asteroids (NEAs) that is currently operating on
the data from the newly-commissioned Zwicky Transient Facility (ZTF) survey.
Based on a prototype originally developed by Waszczak et al. (2017) for the
Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an
improved machine-learning model that can cope with the data rate
increment between PTF and ZTF. Since its first discovery on 2018 February 5
(2018 CL), ZTF/ZStreak has discovered confirmed new NEAs over a total of
232 observable nights until 2018 December 31. Most of the discoveries are small
NEAs, with diameters less than m. By analyzing the discovery
circumstances, we find that objects having the first to last detection time
interval under 2 hr are at risk of being lost. We will further improve
real-time follow-up capabilities, and work on suppressing false positives using
deep learning.Comment: PASP in pres
Large Scale Cross-Correlations in Internet Traffic
The Internet is a complex network of interconnected routers and the existence
of collective behavior such as congestion suggests that the correlations
between different connections play a crucial role. It is thus critical to
measure and quantify these correlations. We use methods of random matrix theory
(RMT) to analyze the cross-correlation matrix C of information flow changes of
650 connections between 26 routers of the French scientific network `Renater'.
We find that C has the universal properties of the Gaussian orthogonal ensemble
of random matrices: The distribution of eigenvalues--up to a rescaling which
exhibits a typical correlation time of the order 10 minutes--and the spacing
distribution follow the predictions of RMT. There are some deviations for large
eigenvalues which contain network-specific information and which identify
genuine correlations between connections. The study of the most correlated
connections reveals the existence of `active centers' which are exchanging
information with a large number of routers thereby inducing correlations
between the corresponding connections. These strong correlations could be a
reason for the observed self-similarity in the WWW traffic.Comment: 7 pages, 6 figures, final versio
Auxin transport through non-hair cells sustains root-hair development.
The plant hormone auxin controls root epidermal cell development in a concentration-dependent manner. Root hairs are produced on a subset of epidermal cells as they increase in distance from the root tip. Auxin is required for their initiation and continued growth, but little is known about its distribution in this region of the root. Contrary to the expectation that hair cells might require active auxin influx to ensure auxin supply, we did not detect the auxin-influx transporter AUX1 in root-hair cells. A high level of AUX1 expression was detected in adjacent non-hair cell files. Non-hair cells were necessary to achieve wild-type root-hair length, although an auxin response was not required in these cells. Three-dimensional modelling of auxin flow in the root tip suggests that AUX1-dependent transport through non-hair cells maintains an auxin supply to developing hair cells as they increase in distance from the root tip, and sustains root-hair outgrowth. Experimental data support the hypothesis that instead of moving uniformly though the epidermal cell layer, auxin is mainly transported through canals that extend longitudinally into the tissue
Numerical study of one-dimensional and interacting Bose-Einstein condensates in a random potential
We present a detailed numerical study of the effect of a disordered potential
on a confined one-dimensional Bose-Einstein condensate, in the framework of a
mean-field description. For repulsive interactions, we consider the
Thomas-Fermi and Gaussian limits and for attractive interactions the behavior
of soliton solutions. We find that the disorder average spatial extension of
the stationary density profile decreases with an increasing strength of the
disordered potential both for repulsive and attractive interactions among
bosons. In the Thomas Fermi limit, the suppression of transport is accompanied
by a strong localization of the bosons around the state k=0 in momentum space.
The time dependent density profiles differ considerably in the cases we have
considered. For attractive Bose-Einstein condensates, a bright soliton exists
with an overall unchanged shape, but a disorder dependent width. For weak
disorder, the soliton moves on and for a stronger disorder, it bounces back and
forth between high potential barriers.Comment: 13 pages, 13 figures, few typos correcte
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