3,294 research outputs found
Dynamical clustering of counterions on flexible polyelectrolytes
Molecular dynamics simulations are used to study the local dynamics of
counterion-charged polymer association at charge densities above and below the
counterion condensation threshold. Surprisingly, the counterions form
weakly-interacting clusters which exhibit short range orientational order, and
which decay slowly due to migration of ions across the diffuse double layer.
The cluster dynamics are insensitive to an applied electric field, and
qualitatively agree with the available experimental data. The results are
consistent with predictions of the classical theory only over much longer time
scales
Residual stress development and evolution in two-phase crystalline material: a discrete dislocation study
Crystalline materials undergo heterogeneous deformation upon the application of external load, which results in the development of incompatible elastic strains in the material as soon as the load is removed. The presence of heterogeneous distribution of elastic strains in the absence of any form of external load results in the building up of stresses referred to as residual stresses. The heterogeneity of strain is attributed either to the presence of multiple phases or to the orientation gradients across the sample volume. This paper is an endeavour to model the presence of second phase in a two-dimensional discrete dislocation dynamics framework, which already contains constitutive rules to include three-dimensional mechanisms, such as line tension and dynamic junction formation. The model is used to investigate residual stress development in single crystals subjected to plane strain loading and then subsequently unloaded to study residual stresses. The dislocation accumulation around the second phase and its effect on the mechanical properties is studied. The orientation dependence of residual stresses as a function of the underlying defect substructure has also been explored. A variety of results are obtained. In particular, the development of stresses as a function of underlying defect substructure is also presented and found to depend upon the orientation of the crystal
Rituximab treatment in rheumatoid arthritis: how does it work?
Treatment with the chimerical monoclonal antibody rituximab results in CD20-directed B cell depletion. Although this depletion is almost complete in the peripheral blood of nearly all patients with rheumatoid arthritis, a proportion of patients does not exhibit a clinical response. The paper by Nakou and colleagues suggests that a decrease in CD19+CD27+ memory B cells in both peripheral blood and bone marrow precedes the clinical response to rituximab. This finding adds to the emerging evidence that lack of response to rituximab is associated with persistence of B lineage cells in specific body compartments
Chemokine blockade: a new era in the treatment of rheumatoid arthritis?
Blockade of chemokines or chemokine receptors is emerging as a new potential treatment for various immune-mediated conditions. This review focuses on the therapeutic potential in rheumatoid arthritis, based on studies in animal models and patients. Several knockout models as well as in vivo use of chemokine antagonists are discussed. Review of these data suggests that this approach might lead to novel therapeutic strategies in rheumatoid arthritis and other chronic inflammatory disorders
Measuring the geographic coverage of methadone maintenance programme in Hong Kong by using geographic information system (GIS)
<p>Abstract</p> <p>Objective</p> <p>While access and utilization form core components in assessing the effectiveness of a health service, the concept of coverage is often neglected. In this study we propose to develop a GIS-based methodological framework for the measurement of district-based geographic coverage to examine the service effectiveness of methadone treatment programme (MTP) in Hong Kong on a regular basis.</p> <p>Methods</p> <p>To overcome the incompatibility of spatial units, population data and data of heroin addiction of the year 2001 are interpolated by population-weighted and area-weighted algorithms. Standard overlay and proximity analytical functions are used to delineate altogether 20 accessible zones around each methadone clinic at a fixed 1.5 km Euclidean distance. Geographic coverage here is defined as the percentage of heroin addicts covered by a methadone clinic within the accessible zone by district.</p> <p>Results</p> <p>A total of 6413 out of 11000 reported heroin addicts are found geographically covered. The average geographic coverage in Hong Kong is 44.6%, with the figure varying from 0% to 96% by district. One district having no clinic results in 0% coverage whereas another without a clinic yields 15.3% coverage from the clinic in adjacent district. Maps illustrating district-based geographic coverage are generated.</p> <p>Conclusion</p> <p>As continuous data collection is required for a monitoring system, the simplified approach facilitates the handling of large volume data and relevant data analysis. It is concluded that the number of methadone clinics is as important as their locations. Geographic coverage could become an important consideration for monitoring harm reduction.</p
Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591
CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes
around young stellar objects is predicted to vary greatly with far-UV and X-ray
irradiation by the central star. Aim We search for molecular tracers of
high-energy irradiation by the protostar in the hot inner envelope. METHODS:
The Submillimeter Array (SMA) has observed the high-mass star forming region
AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at
350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc.
The SMA observations are compared with the predictions of a chemical model
fitted to previous single-dish observations. RESULTS: The CS and SO main peaks
are extended in space at the FWHM level, as predicted in the model assuming
protostellar X-rays. However, the main peak sizes are found smaller than
modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and
HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500
AU that are not predicted. All lines except SO show a secondary peak within the
approaching outflow cone. A dip or null in the visibilities caused by a sharp
decrease in abundance with increasing radius is not observed in CS and only
tentatively in SO. CONCLUSIONS: The emission of protostellar X-rays is
supported by the good fit of the modeled SO and CS amplitude visibilities
including an extended main peak in CS. The broad pedestals can be interpreted
by far-UV irradiation in a spherically non-symmetric geometry, possibly
comprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SO
main peaks suggest sulfur evaporation near the 100 K temperature radius.Comment: Astronomy and Astrophysics, in pres
- …