728 research outputs found
Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry
Results are presented from a long-term astrometry program on PSR B0919+06
using the NRAO Very Long Baseline Array. With ten observations (seven epochs)
between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA,
86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68%
confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc,
making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has
been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s.
Combining the distance estimate with interstellar scintillation data spanning
20 years, we infer the existence of a patchy or clumpy scattering screen along
the line of sight in addition to the distributed electron density predicted by
models for the Galaxy, and constrain the location of this scattering region to
within about 250 parsecs of the Sun. Comparison with the lines of sight towards
other pulsars in the same quadrant of the Galaxy permits refinement of our
knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included);
ApJ submitte
Parallax of PSR J1744-1134 and the Local Interstellar Medium
We present the annual trigonometric parallax of PSR J1744-1134 derived from
an analysis of pulse times of arrival. The measured parallax, pi = 2.8+/-0.3
mas ranks among the most precisely determined distances to any pulsar. The
parallax distance of 357+/-39 pc is over twice that derived from the dispersion
measure using the Taylor & Cordes model for the Galactic electron distribution.
The mean electron density in the path to the pulsar, n_e = (0.0088 +/- 0.0009)
cm^{-3}, is the lowest for any disk pulsar. We have compared the n_e for PSR
J1744-1134 with those for another 11 nearby pulsars with independent distance
estimates. We conclude that there is a striking asymmetry in the distribution
of electrons in the local interstellar medium. The electron column densities
for pulsars in the third Galactic quadrant are found to be systematically
higher than for those in the first. The former correlate with the position of
the well known local HI cavity in quadrant three. The excess electrons within
the cavity may be in the form of HII clouds marking a region of interaction
between the local hot bubble and a nearby superbubble.Comment: revised version accepted for publication in ApJ Letters; reanalysis
of uncertainty in parallax measure and changes to fig
Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
We analyze high-resolution UV spectra of the Mg II h and k lines for 18
members of the Hyades Cluster to study inhomogeneity along these proximate
lines of sight. The observations were taken by the Space Telescope Imaging
Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). Three
distinct velocity components are observed. All 18 lines of sight show
absorption by the Local Interstellar Cloud (LIC), ten stars show absorption by
an additional cloud, which we name the Hyades Cloud, and one star exhibits a
third absorption component. The LIC absorption is observed at a lower radial
velocity than predicted by the LIC velocity vector derived by Lallement &
Bertin (1992) and Lallement et al. (1995), (v(predicted LIC) - v(observed LIC)
= 2.9 +/- 0.7 km/s), which may indicate a compression or deceleration at the
leading edge of the LIC. We propose an extention of the Hyades Cloud boundary
based on previous HST observations of other stars in the general vicinity of
the Hyades, as well as ground-based Ca II observations. We present our fits of
the interstellar parameters for each absorption component. The availability of
18 similar lines of sight provides an excellent opportunity to study the
inhomogeneity of the warm, partially ionized local interstellar medium (LISM).
We find that these structures are roughly homogeneous. The measured Mg II
column densities do not vary by more than a factor of 2 for angular separations
of < 8 degrees, which at the outer edge of the LIC correspond to physical
separations of < 0.6 pc.Comment: 35 pages, 11 figures, AASTEX v.5.0 plus EPSF extensions in mkfig.sty;
accepted by Ap
Synthesis and characterization of dual-functionalized core-shell fluorescent microspheres for bioconjugation and cellular delivery
The efficient transport of micron-sized beads into cells, via a non-endocytosis mediated mechanism, has only recently been described. As such there is considerable scope for optimization and exploitation of this procedure to enable imaging and sensing applications to be realized. Herein, we report the design, synthesis and characterization of fluorescent microsphere-based cellular delivery agents that can also carry biological cargoes. These core-shell polymer microspheres possess two distinct chemical environments; the core is hydrophobic and can be labeled with fluorescent dye, to permit visual tracking of the microsphere during and after cellular delivery, whilst the outer shell renders the external surfaces of the microspheres hydrophilic, thus facilitating both bioconjugation and cellular compatibility. Cross-linked core particles were prepared in a dispersion polymerization reaction employing styrene, divinylbenzene and a thiol-functionalized co-monomer. These core particles were then shelled in a seeded emulsion polymerization reaction, employing styrene, divinylbenzene and methacrylic acid, to generate orthogonally functionalized core-shell microspheres which were internally labeled via the core thiol moieties through reaction with a thiol reactive dye (DY630-maleimide). Following internal labeling, bioconjugation of green fluorescent protein (GFP) to their carboxyl-functionalized surfaces was successfully accomplished using standard coupling protocols. The resultant dual-labeled microspheres were visualized by both of the fully resolvable fluorescence emissions of their cores (DY630) and shells (GFP). In vitro cellular uptake of these microspheres by HeLa cells was demonstrated conventionally by fluorescence-based flow cytometry, whilst MTT assays demonstrated that 92% of HeLa cells remained viable after uptake. Due to their size and surface functionalities, these far-red-labeled microspheres are ideal candidates for in vitro, cellular delivery of proteins, as described in the accompanying paper
Capillary filling with wall corrugations] Capillary filling in microchannels with wall corrugations: A comparative study of the Concus-Finn criterion by continuum, kinetic and atomistic approaches
We study the impact of wall corrugations in microchannels on the process of
capillary filling by means of three broadly used methods - Computational Fluid
Dynamics (CFD), Lattice-Boltzmann Equations (LBE) and Molecular Dynamics (MD).
The numerical results of these approaches are compared and tested against the
Concus-Finn (CF) criterion, which predicts pinning of the contact line at
rectangular ridges perpendicular to flow for contact angles theta > 45. While
for theta = 30, theta = 40 (no flow) and theta = 60 (flow) all methods are
found to produce data consistent with the CF criterion, at theta = 50 the
numerical experiments provide different results. Whilst pinning of the liquid
front is observed both in the LB and CFD simulations, MD simulations show that
molecular fluctuations allow front propagation even above the critical value
predicted by the deterministic CF criterion, thereby introducing a sensitivity
to the obstacle heigth.Comment: 25 pages, 8 figures, Langmuir in pres
Dynamics of Fluid Vesicles in Oscillatory Shear Flow
The dynamics of fluid vesicles in oscillatory shear flow was studied using
differential equations of two variables: the Taylor deformation parameter and
inclination angle . In a steady shear flow with a low viscosity
of internal fluid, the vesicles exhibit steady tank-treading
motion with a constant inclination angle . In the oscillatory flow
with a low shear frequency, oscillates between or
around for zero or finite mean shear rate ,
respectively. As shear frequency increases, the vesicle
oscillation becomes delayed with respect to the shear oscillation, and the
oscillation amplitude decreases. At high with , another limit-cycle oscillation between and
is found to appear. In the steady flow, periodically rotates
(tumbling) at high , and and the vesicle shape
oscillate (swinging) at middle and high shear rate. In the
oscillatory flow, the coexistence of two or more limit-cycle oscillations can
occur for low in these phases. For the vesicle with a fixed shape,
the angle rotates back to the original position after an oscillation
period. However, it is found that a preferred angle can be induced by small
thermal fluctuations.Comment: 11 pages, 13 figure
Modelling the sigma phase
39th Edition of the Joint European Days on Equilibrium between Phases (JEEP), Nancy, FRANCE, MAR 19-21, 2013International audienceno abstrac
Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids
In this review, we describe and analyze a mesoscale simulation method for
fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now
called multi-particle collision dynamics (MPC) or stochastic rotation dynamics
(SRD). The method consists of alternating streaming and collision steps in an
ensemble of point particles. The multi-particle collisions are performed by
grouping particles in collision cells, and mass, momentum, and energy are
locally conserved. This simulation technique captures both full hydrodynamic
interactions and thermal fluctuations. The first part of the review begins with
a description of several widely used MPC algorithms and then discusses
important features of the original SRD algorithm and frequently used
variations. Two complementary approaches for deriving the hydrodynamic
equations and evaluating the transport coefficients are reviewed. It is then
shown how MPC algorithms can be generalized to model non-ideal fluids, and
binary mixtures with a consolute point. The importance of angular-momentum
conservation for systems like phase-separated liquids with different
viscosities is discussed. The second part of the review describes a number of
recent applications of MPC algorithms to study colloid and polymer dynamics,
the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of
viscoelastic fluids
Commentary on the WHO classification of tumors of lymphoid tissues (2008): aggressive B-cell lymphomas
In the novel WHO classification 2008, the classification of aggressive B-cell lymphoma has been revised for several categories with the aim to define âcleanâ entities. Within large B-cell lymphoma, a few distinct clinico-pathological entities have been recognized with more clinically defined entities than pathologically defined ones. The majority of known morphological variations were not considered to merit more than classification as a variant of DLBCL, not otherwise specified. Specifically, a biological subgrouping of DLBCL on the basis of molecular (activated B-cell versus germinal center B-cell) or immunophenotypic (CD5+) features was felt to be too immature to include at this stage. The role of EBV in aggressive B-cell lymphoma has been explored in more depth with the recognition of several novel and re-defined clinico-pathological entities. Also, in these diseases, clinical definitions play a very dominant role in the WHO classification 2008
Lichen planus and Hepatitis C: a case-control study
BACKGROUND: The association of lichen planus with hepatitis C (HCV) has been widely reported in the literature. However, there are wide geographical variations in the reported prevalence of HCV infection in patients with lichen planus. This study was conducted to determine the frequency of hepatitis C in Iranian patients with lichen planus at Razi hospital, Tehran. METHODS: During the years 1997 and 1998, 146 cases of lichen planus, 78 (53.1%) women and 69 (46.9%) men were diagnosed. They were diagnosed on the basis of the usual clinical features and, if necessary, typical histological findings. The patients were screened for the presence of anti-HCV antibodies by third generation ELISA and liver function tests. We used the results from screening of blood donors for anti HCV (carried out by Iranian Blood Transfusion Organization) for comparison as the control group. RESULTS: Anti-HCV antibodies were detected in seven cases (4.8%). This was significantly higher than that of the blood donors' antibodies (p < 0.001). The odds ratio was 50.37(21.45â112.24). A statistically significant association was demonstrated between erosive lichen planus and HCV infection. Liver function tests were not significantly different between HCV infected and non-infected patients. CONCLUSION: HCV apears to have an etiologic role for lichen planus in Iranian patients. On the other hand, liver function tests are not good screening means for HCV infection
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