624 research outputs found
The Optical Polarisation of the Vela Pulsar revisited
In this work we present a revised measurement of the phase-averaged optical
polarisation of the Vela pulsar (PSR B0833-45), for which only one value has
been published so far (Wagner & Seifert 2000). Our measurement has been
obtained through an accurate reanalysis of archival polarisation observations
obtained with the FORS instrument at the VLT. We have measured a phase-averaged
linear polarisation degree P=9.4% +/- 4% and a position angle 146 +/- 11 deg,
very close to the ones of the axis of symmetry of the X-ray arcs and jets
detected by Chandra and of the pulsar proper motion.We have compared the
measured phase-averaged optical polarisation with the expectations of different
pulsars' magnetosphere models. We have found that all models consistently
predict too large values of the phase-averaged linear polarization with respect
to the observed one. This is probably a consequence of present models'
limitations which neglect the contributions of various depolarisation effects.
Interestingly, for the outer gap model we have found that, assuming synchrotron
radiation for the optical emission, the observed polarisation position angle
also implies an alignment between the pulsar rotational axis and the axis of
symmetry of the X-ray arcs and jets.Comment: 8 pages, 4 figure
Self-organization of (001) cubic crystal surfaces
Self-organization on crystal surface is studied as a two dimensional spinodal
decomposition in presence of a surface stress. The elastic Green function is
calculated for a cubic crystal surface taking into account the crystal
anisotropy. Numerical calculations show that the phase separation is driven by
the interplay between domain boundary energy and long range elastic
interactions. At late stage of the phase separation process, a steady state
appears with different nanometric patterns according to the surface coverage
and the crystal elastic constants
Optical polarisation of the Crab pulsar: precision measurements and comparison to the radio emission
The linear polarisation of the Crab pulsar and its close environment was
derived from observations with the high-speed photo-polarimeter OPTIMA at the
2.56-m Nordic Optical Telescope in the optical spectral range (400 - 750 nm).
Time resolution as short as 11 microseconds, which corresponds to a phase
interval of 1/3000 of the pulsar rotation, and high statistics allow the
derivation of polarisation details never achieved before. The degree of optical
polarisation and the position angle correlate in surprising details with the
light curves at optical wavelengths and at radio frequencies of 610 and 1400
MHz. Our observations show that there exists a subtle connection between
presumed non-coherent (optical) and coherent (radio) emissions. This finding
supports previously detected correlations between the optical intensity of the
Crab and the occurrence of giant radio pulses. Interpretation of our
observations require more elaborate theoretical models than those currently
available in the literature.Comment: 21 pages, 13 figures, uses AMS.sty, mn2e.cls, mn2e.bst and
natbib.sty, submitted to MNRA
Stability of periodic domain structures in a two-dimensional dipolar model
We investigate the energetic ground states of a model two-phase system with
1/r^3 dipolar interactions in two dimensions. The model exhibits spontaneous
formation of two kinds of periodic domain structure. A striped domain structure
is stable near half filling, but as the area fraction is changed, a transition
to a hexagonal lattice of almost-circular droplets occurs. The stability of the
equilibrium striped domain structure against distortions of the boundary is
demonstrated, and the importance of hexagonal distortions of the droplets is
quantified. The relevance of the theory for physical surface systems with
elastic, electrostatic, or magnetostatic 1/r^3 interactions is discussed.Comment: Revtex (preprint style, 19 pages) + 4 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#ng_do
Evidence for alignment of the rotation and velocity vectors in pulsars
We present strong observational evidence for a relationship between the
direction of a pulsar's motion and its rotation axis. We show carefully
calibrated polarization data for 25 pulsars, 20 of which display linearly
polarized emission from the pulse longitude at closest approach to the magnetic
pole. Such data allow determination of the position angle of the linear
polarisation which in turn reflects the position angle of the rotation axis. Of
these 20 pulsars, 10 show an offset between the velocity vector and the
polarisation position angle which is either less than 10\degr or more than
80\degr, a fraction which is very unlikely by random chance. We believe that
the bimodal nature of the distribution arises from the presence of orthogonal
polarisation modes in the pulsar radio emission. In some cases this orthogonal
ambiguity is resolved by observations at other wavelengths so that we conclude
that the velocity vector and the rotation axis are aligned at birth.
Strengthening the case is the fact that 4 of the 5 pulsars with ages less than
3 Myr show this relationship, including the Vela pulsar. We discuss the
implications of these findings in the context of the Spruit & Phinney
(1998)\nocite{sp98} model of pulsar birth-kicks. We point out that, contrary to
claims in the literature, observations of double neutron star systems do not
rule out aligned kick models and describe a possible observational test
involving the double pulsar system.Comment: MNRAS, In Pres
Altered versican cleavage in ADAMTS5 deficient mice : a novel etiology of myxomatous valve disease
AbstractIn fetal valve maturation the mechanisms by which the relatively homogeneous proteoglycan-rich extracellular matrix (ECM) of endocardial cushions is replaced by a specialized and stratified ECM found in mature valves are not understood. Therefore, we reasoned that uncovering proteases critical for ‘remodeling’ the proteoglycan rich (extracellular matrix) ECM may elucidate novel mechanisms of valve development. We have determined that mice deficient in ADAMTS5, (A Disintegrin-like And Metalloprotease domain with ThromboSpondin-type 1 motifs) which we demonstrated is expressed predominantly by valvular endocardium during cardiac valve maturation, exhibited enlarged valves. ADAMTS5 deficient valves displayed a reduction in cleavage of its substrate versican, a critical cardiac proteoglycan. In vivo reduction of versican, in Adamts5−/− mice, achieved through Vcan heterozygosity, substantially rescued the valve anomalies. An increase in BMP2 immunolocalization, Sox9 expression and mesenchymal cell proliferation were observed in Adamts5−/− valve mesenchyme and correlated with expansion of the spongiosa (proteoglycan-rich) region in Adamts5−/− valve cusps. Furthermore, these data suggest that ECM remodeling via ADAMTS5 is required for endocardial to mesenchymal signaling in late fetal valve development. Although adult Adamts5−/− mice are viable they do not recover from developmental valve anomalies and have myxomatous cardiac valves with 100% penetrance. Since the accumulation of proteoglycans is a hallmark of myxomatous valve disease, based on these data we hypothesize that a lack of versican cleavage during fetal valve development may be a potential etiology of adult myxomatous valve disease
Synthesis, crystal structure, and DFT study of two new dinuclear copper(I) complexes bearing Ar-BIAN ligands functionalized with NO2 groups
Two new bis(aryl-imino)-acenaphthene, Ar-BIAN (Ar = 2,4,6-trimethylphenyl = mes) ligands, bearing the NO2
group in the naphthalene moiety of the iminoacenaphthene at para- (5-NO2) and meta- (4-NO2) position, of formulations 1,2-bis(mes-imino)-5-nitroacenaphthene, 1, and 1,2-bis(mes-imino)-4-nitroacenaphthene, 2, were synthesized. Their respective dinuclear iodide bridged copper(I) complexes [Cu2(μ-I)2(mes-BIAN-5-NO2)2], 3 and [Cu2(μ-I)2(mes-BIAN-4-NO2)2], 4, were obtained in good yields by treatment with an equimolar amount
of CuI. All compounds were characterized by elemental analysis, single-crystal X-ray diffraction, 1H-NMR, 13C-NMR, FTIR, UV/Vis spectroscopy. DFT calculations helped to understand the different molecular structure observed in the crystals of 3 and 4 and the determining role of packing forces. TDDFT revealed that the
absorption bands in the visible were essentially MLCT (Metal to Ligand Charge Transfer), with some n→π* character (intra ligand). The shift to the red compared to the spectrum of the Cu(I) complex analogue without the NO2 group, [Cu2(μ-I)2](mes-BIAN)2], 6, could be explained by the stabilization of the ligand unoccupied π* orbitals in the presence of NO2.info:eu-repo/semantics/publishedVersio
Influence of test parameters on in vitro fracture resistance of post-endodontic restorations: a structured review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75093/1/j.1365-2842.2009.01940.x.pd
Humoral and Cellular CMV Responses in Healthy Donors; Identification of a Frequent Population of CMV-Specific, CD4+ T Cells in Seronegative Donors
CMV status is an important risk factor in immune compromised patients. In hematopoeitic cell transplantations (HCT), both donor and recipient are tested routinely for CMV status by serological assays; however, one might argue that it might also be of relevance to examine CMV status by cellular (i.e., T lymphocyte) assays. Here, we have analyzed the CMV status of 100 healthy blood bank donors using both serology and cellular assays. About half (56%) were found to be CMV seropositive, and they all mounted strong CD8+ and/or moderate CD4+ T cell responses ex vivo against the immunodominant CMV protein, pp65. Of the 44 seronegative donors, only five (11%) mounted ex vivo T cell responses; surprisingly, 33 (75%) mounted strong CD4+ T cell responses after a brief in vitro peptide stimulation culture. This may have significant implications for the analysis and selection of HCT donors
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