500 research outputs found
Proper Motions of PSRs B1757-24 and B1951+32: Implications for Ages and Associations
Over the last decade, considerable effort has been made to measure the proper
motions of the pulsars B1757-24 and B1951+32 in order to establish or refute
associations with nearby supernova remnants and to understand better the
complicated geometries of their surrounding nebulae. We present proper motion
measurements of both pulsars with the Very Large Array, increasing the time
baselines of the measurements from 3.9 yr to 6.5 yr and from 12.0 yr to 14.5
yr, respectively, compared to previous observations. We confirm the
non-detection of proper motion of PSR B1757-24, and our measurement of (mu_a,
mu_d) = (-11 +/- 9, -1 +/- 15) mas yr^{-1} confirms that the association of PSR
B1757-24 with SNR G5.4-1.2 is unlikely for the pulsar characteristic age of
15.5 kyr, although an association can not be excluded for a significantly
larger age. For PSR B1951+32, we measure a proper motion of (mu_a, mu_d) =
(-28.8 +/- 0.9, -14.7 +/- 0.9) mas yr^{-1}, reducing the uncertainty in the
proper motion by a factor of two compared to previous results. After correcting
to the local standard of rest, the proper motion indicates a kinetic age of ~51
kyr for the pulsar, assuming it was born near the geometric center of the
supernova remnant. The radio-bright arc of emission along the pulsar proper
motion vector shows time-variable structure, but moves with the pulsar at an
approximately constant separation ~2.5", lending weight to its interpretation
as a shock structure driven by the pulsar.Comment: LaTeX file uses emulateapj.cls; 7 pages, 4 figures, to be published
ApJ February 10, 2008, v674 p271-278. Revision reflects journal formatting;
there are no substantial revision
The pediatric asthma yardstick: Practical recommendations for a sustained step-up in asthma therapy for children with inadequately controlled asthma
Calculations of the A_1 phonon frequency in photoexcited Tellurium
Calculations of the A_1 phonon frequency in photoexcited tellurium are
presented. The phonon frequency as a function of photoexcited carrier density
and phonon amplitude is determined. Recent pump probe experiments are
interpreted in the light of these calculatons. It is proposed that, in
conjunction with measurements of the phonon period in ultra-fast pump-probe
reflectivity experiments, the calculated frequency shifts can be used to infer
the evolution of the density of photoexcited carriers on a sub-picosecond
time-scale.Comment: 15 pages Latex, 3 postscript figure
Quantum state engineering on an optical transition and decoherence in a Paul trap
A single Ca+ ion in a Paul trap has been cooled to the ground state of
vibration with up to 99.9% probability. Starting from this Fock state |n=0> we
have demonstrated coherent quantum state manipulation on an optical transition.
Up to 30 Rabi oscillations within 1.4 ms have been observed. We find a similar
number of Rabi oscillations after preparation of the ion in the |n=1> Fock
state. The coherence of optical state manipulation is only limited by laser and
ambient magnetic field fluctuations. Motional heating has been measured to be
as low as one vibrational quantum in 190 ms.Comment: 4 pages, 5 figure
Dirac-Foldy term and the electromagnetic polarizability of the neutron
We reconsider the Dirac-Foldy contribution to the neutron electric
polarizability. Using a Dirac equation approach to neutron-nucleus scattering,
we review the definitions of Compton continuum (), classical
static (), and Schr\"{o}dinger () polarizabilities
and discuss in some detail their relationship. The latter is the
value of the neutron electric polarizability as obtained from an analysis using
the Schr\"{o}dinger equation. We find in particular , where is the magnitude of the magnetic moment
of a neutron of mass . However, we argue that the static polarizability
is correctly defined in the rest frame of the particle, leading to
the conclusion that twice the Dirac-Foldy contribution should be added to
to obtain the static polarizability .Comment: 11 pages, RevTeX, to appear in Physical Review
Physical properties of misfit-layered (Bi,Pb)-Sr-Co-O system: Effect of hole doping into triangular lattice formed by low-spin Co ions
Pb-doping effect on physical properties of misfit-layered (Bi,Pb)-Sr-Co-O
system, in which Co ions form a two-dimensional triangular lattice, was
investigated in detail by electronic transport, magnetization and specific-heat
measurements. Pb doping enhances the metallic behavior, suggesting that
carriers are doped. Pb doping also enhances the magnetic correlation in this
system and increases the magnetic transition temperature. We found the
existence of the short-range magnetic correlation far above the transition
temperature, which seems to induce the spin-glass state coexisting with the
ferromagnetic long-range order at low temperatures. Specific-heat measurement
suggests that the effective mass of the carrier in (Bi,Pb)-Sr-Co-O is not
enhanced so much as reported in NaCoO. Based on these experimental
results, we propose a two-bands model which consists of narrow and
rather broad bands. The observed magnetic property and
magnetotransport phenomena are explained well by this model
Association of the infant gut microbiome with early childhood neurodevelopmental outcomes: An ancillary study to the VDAART randomized clinical trial
Importance: In animal models, the early life gut microbiome influences later neurodevelopment. Corresponding data in human populations are lacking.
Objective: To study associations between the gut microbiome in infants and development at preschool age measured by the Ages and Stages Questionnaire, third edition (ASQ-3).
Design, Setting, and Participants: This ancillary cohort study of the Vitamin D Antenatal Asthma Reduction Trial (VDAART) used data from 715 participants who had development assessed at 3 years of age by the ASQ-3, which included scores in 5 domains (gross motor skills, fine motor skills, problem solving, communication, and personal and social skills). A total of 309 stool samples were collected from infants aged 3 to 6 months for microbiome analysis using 16S rRNA gene sequencing.
Exposures: Infant gut microbiome.
Main Outcomes and Measures: Continuous ASQ-3 scores and typical vs potential delay in the 5 developmental domains. Factor scores for bacterial coabundance groups were used as predictors in regression models of continuous ASQ-3 scores. Logistic regression was used to examine bacterial coabundance scores and odds of scoring below the threshold for typical development. Multivariate analysis examined the abundance of individual taxa and ASQ-3 scores.
Results: The 309 participants (170 [55.0%] male) with ASQ-3 scores and stool samples were ethnically diverse (136 [44.0%] black, 41 [13.3%] Hispanic, 86 [27.8%] white, and 46 [14.9%] other race/ethnicity); the mean (SD) age at ASQ-3 assessment was 3.0 (0.07) years. Coabundance scores dominated by Clostridiales (Lachnospiraceae genera and other, unclassified Clostridiales taxa) were associated with poorer ASQ-3 communication (ÎČ, -1.12; 95% CI, -2.23 to -0.01; Pâ=â.05) and personal and social (ÎČ, -1.44; 95% CI, -2.47 to -0.40; Pâ=â.01) scores and with increased odds of potential delay for communication (odds ratio [OR], 1.69; 95% CI, 1.06 to 2.68) and personal and social skills (OR, 1.96; 95% CI, 1.22 to 3.15) per unit increase in coabundance score. The Bacteroides-dominated coabundance grouping was associated with poorer fine motor scores (ÎČ, -2.42; 95% CI, -4.29 to -0.55; Pâ=â.01) and with increased odds of potential delay for fine motor skills (OR, 1.52; 95% CI, 1.07 to 2.16) per unit increase in coabundance score. Multivariate analysis detected similar family-level and order-level associations.
Conclusions and Relevance: These findings suggest an association between infant gut microbiome composition and communication, personal and social, and fine motor skills at age 3 years. The majority of associations were driven by taxa within the order Clostridiales
Design and Tests of the Hard X-ray Polarimeter X-Calibur
X-ray polarimetry promises to give qualitatively new information bout high-energy astrophysical sources, such as binary black hole  systems, micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built and tested ahard X-ray polarimeter, X-Calibur, to be used in the focal plane of the InFOCuS grazing incidence hard X-ray telescope.X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 20â60 keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation; in principal, a similar space-borne experiment could be operated in the 5â100 keV regime. X-Calibur achieves a high detection efficiency of order unity
Young Women and Consumer Culture
This article is presented as an intervention in the field of feminist media and cultural studies with particular reference to consumer culture. It is concerned with the seeming evasion of critique which can be detected in a number of recent feminist responses to the way in which modalities of âpopular feminismâ have found themselves incorporated into women's genres of television, such as, in particular, the US series Sex in the City. This usage or instrumentalization of feminism (in its most conventionally liberal feminist guise) also provides corporate culture with the means of presenting itself to young women as their ally and even champion of âgirlsâ while at the same time earning seeming approval for adopting the mantle of social responsibility, which makes the concept of popular feminism more problematic than it first appeared. Such appropriation of popular feminist discourse by the commercial domain prompts a self-critique on the part of the author alongside an analysis of recent approaches toward consumer culture in cultural studies. The article continues by presenting a schematic account of how the commercial domain increasingly supplants state and public sector institutions in the intensity and dedication of its address to girls and young women. Whilst some may argue that the intersection of youthful femininity and the commercial sphere is not a new phenomenon, what is being explored here is the connection between this intensification of attention and the logic of current neo-liberal economic rationalities. The argument is, therefore, that it is by these means including the instrumentalization of a specific modality of âfeminismâ that there emerges into existence a neo-liberal culture, with global aspirations, which has as its ideal subject the category of âgirlâ
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