271 research outputs found
Deep Chandra Survey of the Small Magellanic Cloud. III. Formation Efficiency of High-mass X-Ray Binaries
We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to similar to 40-60 Myr, and then gradually decreases. The formation efficiency peaks at similar to 30-40 Myr with average rates of N(HMXB)/SFR = 339(-83)(+78) (M-circle dot/yr)(-1), and N(HMXB)/M-* = (8.74(-0.92)(+1.0)) x 10(-6) M-circle dot(-1,) in good agreement with previous estimates of the average formation efficiency in the broad similar to 20-60 Myr age range
Direct high-precision measurement of the magnetic moment of the proton
The spin-magnetic moment of the proton is a fundamental property of
this particle. So far has only been measured indirectly, analysing the
spectrum of an atomic hydrogen maser in a magnetic field. Here, we report the
direct high-precision measurement of the magnetic moment of a single proton
using the double Penning-trap technique. We drive proton-spin quantum jumps by
a magnetic radio-frequency field in a Penning trap with a homogeneous magnetic
field. The induced spin-transitions are detected in a second trap with a strong
superimposed magnetic inhomogeneity. This enables the measurement of the
spin-flip probability as a function of the drive frequency. In each measurement
the proton's cyclotron frequency is used to determine the magnetic field of the
trap. From the normalized resonance curve, we extract the particle's magnetic
moment in units of the nuclear magneton . This
measurement outperforms previous Penning trap measurements in terms of
precision by a factor of about 760. It improves the precision of the forty year
old indirect measurement, in which significant theoretical bound state
corrections were required to obtain , by a factor of 3. By application
of this method to the antiproton magnetic moment the fractional
precision of the recently reported value can be improved by a factor of at
least 1000. Combined with the present result, this will provide a stringent
test of matter/antimatter symmetry with baryons.Comment: published in Natur
Galactic and Extragalactic Samples of Supernova Remnants: How They Are Identified and What They Tell Us
Supernova remnants (SNRs) arise from the interaction between the ejecta of a
supernova (SN) explosion and the surrounding circumstellar and interstellar
medium. Some SNRs, mostly nearby SNRs, can be studied in great detail. However,
to understand SNRs as a whole, large samples of SNRs must be assembled and
studied. Here, we describe the radio, optical, and X-ray techniques which have
been used to identify and characterize almost 300 Galactic SNRs and more than
1200 extragalactic SNRs. We then discuss which types of SNRs are being found
and which are not. We examine the degree to which the luminosity functions,
surface-brightness distributions and multi-wavelength comparisons of the
samples can be interpreted to determine the class properties of SNRs and
describe efforts to establish the type of SN explosion associated with a SNR.
We conclude that in order to better understand the class properties of SNRs, it
is more important to study (and obtain additional data on) the SNRs in galaxies
with extant samples at multiple wavelength bands than it is to obtain samples
of SNRs in other galaxiesComment: Final 2016 draft of a chapter in "Handbook of Supernovae" edited by
Athem W. Alsabti and Paul Murdin. Final version available at
https://doi.org/10.1007/978-3-319-20794-0_90-
The Teleost Retina as a Model for Developmental and Regeneration Biology
Retinal development in teleosts can broadly be divided into three epochs. The first is the specification of cellular domains in the larval forebrain that give rise to the retinal primordia and undergo early morphogenetic movements. The second is the neurogenic events within the retina proper—proliferation, cell fate determination, and pattern formation—that establish neuronal identities and form retinal laminae and cellular mosaics. The third, which is unique to teleosts and occurs in the functioning eye, is stretching of the retina and persistent neurogenesis that allows the growth of the retina to keep pace with the growth of the eye and other tissues. The first two events are rapid, complete by about 3 days postfertilization in the zebrafish embryo. The third is life-long and accounts for the bulk of retinal growth and the vast majority of adult retinal neurons. In addition, but clearly related to the retina's developmental history, lesions that kill retinal neurons elicit robust neuronal regeneration that originates from cells intrinsic to the retina. This paper reviews recent studies of retinal development in teleosts, focusing on those that shed light on the genetic and molecular regulation of retinal specification and morphogenesis in the embryo, retinal neurogenesis in larvae and adults, and injury-induced neuronal regeneration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63365/1/zeb.2004.1.257.pd
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
Genetic Predisposition of Donors Affects the Allograft Outcome in Kidney Transplantation; Polymorphisms of Stromal-Derived Factor-1 and CXC Receptor 4
Genetic interaction between donor and recipient may dictate the impending
responses after transplantation. In this study, we evaluated the role of the
genetic predispositions of stromal-derived factor-1 (SDF1) [rs1801157
(G>A)] and CXC receptor 4 (CXCR4) [rs2228014 (C>T)] on
renal allograft outcomes. A total of 335 pairs of recipients and donors were
enrolled. Biopsy-proven acute rejection (BPAR) and long-term graft survival were
traced. Despite similar allele frequencies between donors and recipients, minor
allele of SDF1 rs1801157 (GA+AA) from donor, not from recipients, has a
protective effect on the development of BPAR compared to wild type donor (GG)
(P = 0.005). Adjustment for multiple
covariates did not affect this result (odds ratio 0.39, 95% C.I
0.20–0.76, P = 0.006). CXCR4
rs2228014 polymorphisms from donor or recipient did not affect the incidence of
acute rejection. SDF1 was differentially expressed in renal tubular epithelium
with acute rejection according to genetic variations of donor rs1801157 showing
higher expressions in the grafts from GG donors. Contrary to the development of
BPAR, the presence of minor allele rs1801157 A, especially homozygocity,
predisposed poor graft survival
(P = 0.001). This association was
significant after adjusting for several risk factors (hazard ratio 3.01;
95% C.I = 1.19–7.60;
P = 0.020). The allelic variation of
recipients, however, was not associated with graft loss. A donor-derived genetic
polymorphism of SDF1 has influenced the graft outcome. Thus, the genetic
predisposition of donor should be carefully considered in transplantation
Getting Acquainted with Kant
My question here concerns whether Kant claims that experience has
nonconceptual content, or whether, on his view, experience is
essentially conceptual. However there is a sense in which this debate
concerning the content of intuition is ill-conceived. Part of this has
to do with the terms in which the debate is set, and part to do with
confusion over the connection between Kant’s own views and contemporary
concerns in epistemology and the philosophy of mind. However, I think
much of the substance of the debate concerning Kant’s views on the
content of experience can be salvaged by reframing it in terms of a
debate about the dependence relations, if any, that exist between
different cognitive capacities. Below, in Section 2, I clarify the
notion of ‘content’ I take to be at stake in the interpretive debate.
Section 3 presents reasons for thinking that intuition cannot have
content in the relevant sense. I then argue, in Section 4, that the
debate be reframed in terms of dependence. We should distinguish between
Intellectualism, according to which all objective representation
(understood in a particular way) depends on acts of synthesis by the
intellect, and Sensibilism, according to which at least some forms of
objective representation are independent of any such acts (or the
capacity for such acts). Finally, in Section 5, I further elucidate the
cognitive role of intuition. I articulate a challenge which Kant
understands alethic modal considerations to present for achieving
cognition, and argue that a version of Sensibilism that construes
intuition as a form of acquaintance is better positioned to answer this
challenge than Intellectualism
Proteomic and Phospho-Proteomic Profile of Human Platelets in Basal, Resting State: Insights into Integrin Signaling
During atherogenesis and vascular inflammation quiescent platelets are activated to increase the surface expression and ligand affinity of the integrin αIIbβ3 via inside-out signaling. Diverse signals such as thrombin, ADP and epinephrine transduce signals through their respective GPCRs to activate protein kinases that ultimately lead to the phosphorylation of the cytoplasmic tail of the integrin αIIbβ3 and augment its function. The signaling pathways that transmit signals from the GPCR to the cytosolic domain of the integrin are not well defined. In an effort to better understand these pathways, we employed a combination of proteomic profiling and computational analyses of isolated human platelets. We analyzed ten independent human samples and identified a total of 1507 unique proteins in platelets. This is the most comprehensive platelet proteome assembled to date and includes 190 membrane-associated and 262 phosphorylated proteins, which were identified via independent proteomic and phospho-proteomic profiling. We used this proteomic dataset to create a platelet protein-protein interaction (PPI) network and applied novel contextual information about the phosphorylation step to introduce limited directionality in the PPI graph. This newly developed contextual PPI network computationally recapitulated an integrin signaling pathway. Most importantly, our approach not only provided insights into the mechanism of integrin αIIbβ3 activation in resting platelets but also provides an improved model for analysis and discovery of PPI dynamics and signaling pathways in the future
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