10,255 research outputs found
Effective Confinement as Origin of the Equivalence of Kinetic Temperature and Fluctuation-Dissipation Ratio in a Dense Shear Driven Suspension
We study response and velocity autocorrelation functions for a tagged
particle in a shear driven suspension governed by underdamped stochastic
dynamics. We follow the idea of an effective confinement in dense suspensions
and exploit a time-scale separation between particle reorganization and
vibrational motion. This allows us to approximately derive the
fluctuation-dissipation theorem in a "hybrid" form involving the kinetic
temperature as an effective temperature and an additive correction term. We
show numerically that even in a moderately dense suspension the latter is
negligible. We discuss similarities and differences with a simple toy model, a
single trapped particle in shear flow
Towards an English-Spanish version of the Comprehensive Transboundary International Water Quality Management Agreement
The aim of this communication is to discuss strategies for, and progress achieved in transboundary water quality management. The Comprehensive Transboundary Water Quality Management Agreement with Guidelines for Development of a Management Plan, Standards, and Criteria. (ASCE/EWRI 33-09). The purpose of this Agreement is to provide a framework for governments to adopt or modify comprehensive water quality planning and management mechanisms of shared water resources.
The Spanish version of the Agreement, completed by the ASCE/EWRI Border International Water Quality Standards Committee (BIWQ SC) Translation Ad Hoc Group, allows the scope of this Framework along and across Spanish speaking political boundaries. This version includes some updates balloted by the Committee to ensure that all factors involved in the sharing and management of water resources are considered in the development of the Agreement, so that it can accommodate the current realities of the boundary governments. The original version of the Agreement (ASCE/EWRI 33-09) is being revised and will be replaced in the coming months by the ASCE/EWRI 33-16.
The ASCE/EWRI 33-16 contains the most current model for comprehensive water quality planning and management of shared water resources. It underlines the importance of governmental cooperation to alleviate causes of present and future disagreement and promotes the development of common strategies to use, manage and protect shared water resources. The ASCE/EWRI 33-16 is an agreement to be used, modified, and enhanced through every government on an international scale and in a variety of geopolitical settings
Robust formation of morphogen gradients
We discuss the formation of graded morphogen profiles in a cell layer by
nonlinear transport phenomena, important for patterning developing organisms.
We focus on a process termed transcytosis, where morphogen transport results
from binding of ligands to receptors on the cell surface, incorporation into
the cell and subsequent externalization. Starting from a microscopic model, we
derive effective transport equations. We show that, in contrast to morphogen
transport by extracellular diffusion, transcytosis leads to robust ligand
profiles which are insensitive to the rate of ligand production
When it Pays to Rush: Interpreting Morphogen Gradients Prior to Steady-State
During development, morphogen gradients precisely determine the position of
gene expression boundaries despite the inevitable presence of fluctuations.
Recent experiments suggest that some morphogen gradients may be interpreted
prior to reaching steady-state. Theoretical work has predicted that such
systems will be more robust to embryo-to-embryo fluctuations. By analysing two
experimentally motivated models of morphogen gradient formation, we investigate
the positional precision of gene expression boundaries determined by
pre-steady-state morphogen gradients in the presence of embryo-to-embryo
fluctuations, internal biochemical noise and variations in the timing of
morphogen measurement. Morphogens that are direct transcription factors are
found to be particularly sensitive to internal noise when interpreted prior to
steady-state, disadvantaging early measurement, even in the presence of large
embryo-to-embryo fluctuations. Morphogens interpreted by cell-surface receptors
can be measured prior to steady-state without significant decrease in
positional precision provided fluctuations in the timing of measurement are
small. Applying our results to experiment, we predict that Bicoid, a
transcription factor morphogen in Drosophila, is unlikely to be interpreted
prior to reaching steady-state. We also predict that Activin in Xenopus and
Nodal in zebrafish, morphogens interpreted by cell-surface receptors, can be
decoded in pre-steady-state.Comment: 18 pages, 3 figure
Magnetic Excitations in NpCoGa5
We report the results of inelastic neutron scattering experiments on
NpCoGa, an isostructural analogue of the PuCoGa superconductor. Two
energy scales characterize the magnetic response in the antiferromagnetic
phase. One is related to a non-dispersive excitation between two crystal field
levels. The other at lower energies corresponds to dispersive fluctuations
emanating from the magnetic zone center. The fluctuations persist in the
paramagnetic phase also, although weaker in intensity. This supports the
possibility that magnetic fluctuations are present in PuCoGa, where
unconventional d-wave superconductivity is achieved in the absence of magnetic
order.Comment: 4 pages, 5 figure
Relationship between neuronal migration and cell-substratum adhesion: laminin and merosin promote olfactory neuronal migration but are anti-adhesive.
Regulation by the extracellular matrix (ECM) of migration, motility, and adhesion of olfactory neurons and their precursors was studied in vitro. Neuronal cells of the embryonic olfactory epithelium (OE), which undergo extensive migration in the central nervous system during normal development, were shown to be highly migratory in culture as well. Migration of OE neuronal cells was strongly dependent on substratum-bound ECM molecules, being specifically stimulated and guided by laminin (or the laminin-related molecule merosin) in preference to fibronectin, type I collagen, or type IV collagen. Motility of OE neuronal cells, examined by time-lapse video microscopy, was high on laminin-containing substrata, but negligible on fibronectin substrata. Quantitative assays of adhesion of OE neuronal cells to substrata treated with different ECM molecules demonstrated no correlation, either positive or negative, between the migratory preferences of cells and the strength of cell-substratum adhesion. Moreover, measurements of cell adhesion to substrata containing combinations of ECM proteins revealed that laminin and merosin are anti-adhesive for OE neuronal cells, i.e., cause these cells to adhere poorly to substrata that would otherwise be strongly adhesive. The evidence suggests that the anti-adhesive effect of laminin is not the result of interactions between laminin and other ECM molecules, but rather an effect of laminin on cells, which alters the way in which cells adhere. Consistent with this view, laminin was found to interfere strongly with the formation of focal contacts by OE neuronal cells
Structural properties of epitaxial {\alpha}-U thin films on Ti, Zr, W and Nb
Thin layers of orthorhombic uranium ({\alpha}-U) have been grown onto
buffered sapphire substrates by d.c. magnetron sputtering, resulting in the
discovery of new epitaxial matches to Ti(00.1) and Zr(00.1) surfaces. These
systems have been characterised by X-ray diffraction and reflectivity and the
optimal deposition temperatures have been determined. More advanced structural
characterisation of the known Nb(110) and W(110) buffered {\alpha}-U systems
has also been carried out, showing that past reports of the domain structures
of the U layers are incomplete. The ability of this low symmetry structure to
form crystalline matches across a range of crystallographic templates
highlights the complexity of U metal epitaxy and points naturally toward
studies of the low temperature electronic properties of {\alpha}-U as a
function of epitaxial strain
An Enhanced Reservation-Based MAC Protocol for IEEE 802.15.4 Networks
The IEEE 802.15.4 Medium Access Control (MAC) protocol is an enabling standard for wireless sensor networks. In order to support applications requiring dedicated bandwidth or bounded delay, it provides a reservation-based scheme named Guaranteed Time Slot (GTS). However, the GTS scheme presents some drawbacks, such as inefficient bandwidth utilization and support to a maximum of only seven devices. This paper presents eLPRT (enhanced Low Power Real Time), a new reservation-based MAC protocol that introduces several performance enhancing features in comparison to the GTS scheme. This MAC protocol builds on top of LPRT (Low Power Real Time) and includes various mechanisms designed to increase data transmission reliability against channel errors, improve bandwidth utilization and increase the number of supported devices. A motion capture system based on inertial and magnetic sensors has been used to validate the protocol. The effectiveness of the performance enhancements introduced by each of the new features is demonstrated through the provision of both simulation and experimental results
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