1,501 research outputs found
Humanitarianism's Contested Culture in War Zones
Humanitarians are no longer simply seen as selfless angels. Their motivations and mastery, their principles and products are questioned from within and from without. Understanding the ongoing transformations in contemporary humanitarianism requires examining the nature and evolution of humanitarian culture away from an agreed culture of cooperation to a contested one of competition. The latter reflects militarization, politicization, and marketization. What is required is a learning culture for practitioners and a consequentialist ethics more oriented to responsible reflection than rapid reaction
Exact and approximate solutions for elastic interactions in a nematic liquid crystal
Anisotropic fluids appear in a diverse array of systems, from liquid-crystal
displays to bacterial swarms, and are characterized by orientational order.
Large colloidal particles immersed in such environments disturb the medium's
orientational order, however, resulting in a stored elastic energy within the
bulk. As a consequence, multiple immersed bodies interact at equilibrium
through fluid-mediated forces and torques, which depend on the bodies'
positions, orientations, and shapes. We provide the equilibrium configuration
of a model nematic liquid crystal with multiple immersed bodies or inclusions
in two-dimensions, as well as the associated body forces, torques, and surface
tractions. A complex variables approach is taken which leans on previous work
by Crowdy (2020) for describing solutions with multiply-connected domains. Free
periods of a complex director field, which correspond to topological defect
positioning and net topological charge, are determined numerically to minimize
a global stored elastic energy, including a contribution of a weak (finite)
anchoring strength on the body surfaces. Finally, a general, analytical
description of two-body far-field interactions is provided, along with examples
using two cylindrical inclusions of arbitrary position and size, and two
triangles of arbitrary position and orientation.Comment: 33 pages, 6 figure
Dietary assimilation of cadmium associated with bacterial exopolymer sediment coatings by the estuarine amphipod \u3cem\u3eLeptocheirus plumulosus\u3c/em\u3e: effects of Cd concentration and salinity
Bacterial extracellular substances (also known as exopolysaccharides, or EPS) may serve as vectors for trophic transfer of metals in benthic systems because these ubiquitous sediment coatings can sorb high concentrations of toxic metals, and because many benthic invertebrates assimilate EPS sediment coatings upon ingestion. We conducted 3 sets of experiments to determine the assimilative bioavailability of EPS-associated Cd to the benthic amphipod Leptocheirus plumulosus as a function of Cd concentration and salinity. Bioavailability was measured as L. plumulosus Cd assimilation efficiency (AE) from EPS-coated silica (EPSâSi) and from uncoated silica (NCâSi) using modified pulse-chase methods with the gamma-emitting radioisotope 109Cd. Cd AE was significantly greater from NCâSi than from EPSâSi at 7.5%, but not at 2.5 or 25%. Overall, Cd AE from EPSâSi was between 15.1 and 21.5%. Because EPSâSi sorbed more Cd than NCâSi, EPS coatings magnified the amount of Cd amphipods accumulated at each salinity by up to a factor of 10. Salinity did not directly affect Cd AE from EPSâSi, but because CdâEPS partitioning increased with decreasing salinity, amphipods accumulated more Cd from EPS at the lowest CdâEPS incubation salinity (2.5%) than at higher salinities (7.5 and 25%). Finally, Cd concentration in EPS exhibited an inverse relationship with Cd AE at 2.5%, but not at 25%. Specifically, Cd AE was 12 times greater at 1 compared with 10”g Cd ”g-1 EPS. Together, these results show that estuarine benthos can accumulate Cd from EPS sediment coatings, but that the degree to which this phenomenon occurs is dependent upon seawater salinity and Cd concentration in EPS
Non-intuitive rotational reorientation in collisions of NO(A <sup>2</sup>ÎŁ<sup>+</sup>) with Ne from direct measurement of a four-vector correlation
Microbial biopesticides for integrated crop management : an assessment of environmental and regulatory sustainability
Herbivorous insects and mites, plant diseases and weeds are major impediments to the production of food crops and are increasingly difficult to control with conventional chemicals. This paper focuses on microbial control agents with an emphasis on augmentation. There are marked differences in the availability of products in different countries which can be explained in terms of differences in their regulatory systems. Regulatory failure arises from the application of an inappropriate synthetic pesticides model. An understanding of regulatory innovation is necessary to overcome these problems. Two attempts at remedying regulatory failure in the UK and the Netherlands are assessed. Scientific advances can feed directly into the regulatory process and foster regulatory innovation
Long-term benthic foraminiferal culture: strategies for carbonate-system control and experimentation
Abstrac
Correction of misaligned slices in multi-slice cardiovascular magnetic resonance using slice-to-volume registration
A popular technique to reduce respiratory motion for cardiovascular magnetic resonance is to perform a multi-slice acquisition in which a patient holds their breath multiple times during the scan. The feasibility of rigid slice-to-volume registration to correct for misalignments of slice stacks in such images due to differing breath-hold positions is explored. Experimental results indicate that slice-to-volume registration can compensate for the typical misalignments expected. Correction of slice misalignment results in anatomically more correct images, as well as improved left ventricular volume measurements. The interstudy reproducibility has also been improved reducing the number of samples needed for cardiac MR studies
Exact quantum statistics for electronically nonadiabatic systems using continuous path variables
We derive an exact, continuous-variable path integral (PI) representation of
the canonical partition function for electronically nonadiabatic systems.
Utilizing the Stock-Thoss (ST) mapping for an N-level system, matrix elements
of the Boltzmann operator are expressed in Cartesian coordinates for both the
nuclear and electronic degrees of freedom. The PI discretization presented here
properly constrains the electronic Cartesian coordinates to the physical
subspace of the mapping. We numerically demonstrate that the resulting PI-ST
representation is exact for the calculation of equilibrium properties of
systems with coupled electronic and nuclear degrees of freedom. We further show
that the PI-ST formulation provides a natural means to initialize semiclassical
trajectories for the calculation of real-time thermal correlation functions,
which is numerically demonstrated in applications to a series of nonadiabatic
model systems.Comment: 10 pages, 6 figure
A Comprehensive Survey of Hydrogen Chloride in the Galaxy
We report new observations of the fundamental transition of HCl (at
625.918GHz) toward a sample of 25 galactic star-forming regions, molecular
clouds, and evolved stars, carried out using the Caltech Submillimeter
Observatory. Fourteen sources in the sample are also observed in the
corresponding H\tscl\ transition (at 624.978GHz). We have obtained
clear detections in all but four of the targets, often in emission. Absorptions
against bright background continuum sources are also seen in nine cases,
usually involving a delicate balance between emission and absorption features.
From RADEX modeling, we derive gas densities and HCl column densities for
sources with HCl emission. HCl is found in a wide range of environments, with
gas densities ranging from to ~cm. The HCl abundance
relative to H is in the range of . Comparing with the
chlorine abundance in the solar neighborhood, this corresponds to a chlorine
depletion factor of up to 400, assuming that HCl accounts for one third
of the total chlorine in the gas phase. The [\tfcl]/[\tscl] isotopic ratio is
rather varied, from unity to 5, mostly lower than the terrestrial value
of 3.1. Such variation is highly localized, and could be generated by the
nucleosynthesis in supernovae, which predicts a \tscl\ deficiency in most
models. The lower ratios seen in W3IRS4 and W3IRS5 likely confine the
progenitors of the supernovae to stars with relatively large mass
(\ga25M_\sun) and high metallicity (Z0.02).Comment: 11 pages, 5 figures, accepted by Ap
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