2,188 research outputs found
Starquake-induced Magnetic Field and Torque Evolution in Neutron Stars
The persistent increases in spin-down rate offsets seen to accompany glitches
in the Crab and other pulsars suggest increases in the spin-down torque. We
interpret these offsets as due to starquakes occurring as the star spins down
and the rigid crust becomes less oblate. We study the evolution of strain in
the crust, the initiation of starquakes, and possible consequences for magnetic
field and torque evolution. Crust cracking occurs as equatorial material shears
under the compressive forces arising from the star's decreasing circumference,
and matter moves to higher latitudes along a fault inclined to the equator. A
starquake is most likely to originate near one of the two points on the
rotational equator farthest from the magnetic poles. The material breaks along
a fault approximately aligned with the magnetic poles. We suggest that the
observed offsets come about when a starquake perturbs the star's mass
distribution, producing a misalignment of the angular momentum and spin axes.
Subsequently, damped precession to a new rotational state increases the angle
alpha between the rotation and magnetic axes. The resulting increase in
external torque appears as a permanent increase in the spin-down rate. Repeated
starquakes would continue to increase alpha, making the pulsar more of an
orthogonal rotator.Comment: 16 pages, 6 postscript figures, uses AASTeX macros, submitted to ApJ
Letter
Detecting the dark matter annihilation at the ground EAS detectors
In this paper we study the possibility of detecting gamma rays from dark
matter annihilation in the subhalos of the Milky Way by the ground based EAS
detectors within the frame of the minimal supersymmetric standard model. Based
on the Monte Carlo simulation we also study the properties of two specific EAS
detectors, the ARGO and HAWC, and the sensitivities of these detectors on the
detection of dark matter annihilation. We find the ground EAS detectors have
the possibility to observe such signals. Conversely if no signal observed we
give the constraints on the supersymmetric parameter space, which however
depends on the subhalos properties.Comment: 23 pages, 9 figures, accepted by NP
Pharmacologic inhibition of S-nitrosoglutathione reductase protects against experimental asthma in BALB/c mice through attenuation of both bronchoconstriction and inflammation
BACKGROUND: S-nitrosoglutathione (GSNO) serves as a reservoir for nitric oxide (NO) and thus is a key homeostatic regulator of airway smooth muscle tone and inflammation. Decreased levels of GSNO in the lungs of asthmatics have been attributed to increased GSNO catabolism via GSNO reductase (GSNOR) leading to loss of GSNO- and NO- mediated bronchodilatory and anti-inflammatory actions. GSNOR inhibition with the novel small molecule, N6022, was explored as a therapeutic approach in an experimental model of asthma. METHODS: Female BALB/c mice were sensitized and subsequently challenged with ovalbumin (OVA). Efficacy was determined by measuring both airway hyper-responsiveness (AHR) upon methacholine (MCh) challenge using whole body plethysmography and pulmonary eosinophilia by quantifying the numbers of these cells in the bronchoalveolar lavage fluid (BALF). Several other potential biomarkers of GSNOR inhibition were measured including levels of nitrite, cyclic guanosine monophosphate (cGMP), and inflammatory cytokines, as well as DNA binding activity of nuclear factor kappa B (NFκB). The dose response, onset of action, and duration of action of a single intravenous dose of N6022 given from 30 min to 48 h prior to MCh challenge were determined and compared to effects in mice not sensitized to OVA. The direct effect of N6022 on airway smooth muscle tone also was assessed in isolated rat tracheal rings. RESULTS: N6022 attenuated AHR (ED(50) of 0.015 ± 0.002 mg/kg; Mean ± SEM) and eosinophilia. Effects were observed from 30 min to 48 h after treatment and were comparable to those achieved with three inhaled doses of ipratropium plus albuterol used as the positive control. N6022 increased BALF nitrite and plasma cGMP, while restoring BALF and plasma inflammatory markers toward baseline values. N6022 treatment also attenuated the OVA-induced increase in NFκB activation. In rat tracheal rings, N6022 decreased contractile responses to MCh. CONCLUSIONS: The significant bronchodilatory and anti-inflammatory actions of N6022 in the airways are consistent with restoration of GSNO levels through GSNOR inhibition. GSNOR inhibition may offer a therapeutic approach for the treatment of asthma and other inflammatory lung diseases. N6022 is currently being evaluated in clinical trials for the treatment of inflammatory lung disease
A Bayesian approach to the semi-analytic model of galaxy formation: methodology
We believe that a wide range of physical processes conspire to shape the
observed galaxy population but we remain unsure of their detailed interactions.
The semi-analytic model (SAM) of galaxy formation uses multi-dimensional
parameterisations of the physical processes of galaxy formation and provides a
tool to constrain these underlying physical interactions. Because of the high
dimensionality, the parametric problem of galaxy formation may be profitably
tackled with a Bayesian-inference based approach, which allows one to constrain
theory with data in a statistically rigorous way. In this paper we develop a
SAM in the framework of Bayesian inference. We show that, with a parallel
implementation of an advanced Markov-Chain Monte-Carlo algorithm, it is now
possible to rigorously sample the posterior distribution of the
high-dimensional parameter space of typical SAMs. As an example, we
characterise galaxy formation in the current CDM cosmology using the
stellar mass function of galaxies as an observational constraint. We find that
the posterior probability distribution is both topologically complex and
degenerate in some important model parameters, suggesting that thorough
explorations of the parameter space are needed to understand the models. We
also demonstrate that because of the model degeneracy, adopting a narrow prior
strongly restricts the model. Therefore, the inferences based on SAMs are
conditional to the model adopted. Using synthetic data to mimic systematic
errors in the stellar mass function, we demonstrate that an accurate
observational error model is essential to meaningful inference.Comment: revised version to match published article published in MNRA
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
STAGES: the Space Telescope A901/2 Galaxy Evolution Survey
We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey
(STAGES). STAGES is a multiwavelength project designed to probe physical
drivers of galaxy evolution across a wide range of environments and luminosity.
A complex multi-cluster system at z~0.165 has been the subject of an 80-orbit
F606W HST/ACS mosaic covering the full 0.5x0.5 (~5x5 Mpc^2) span of the
supercluster. Extensive multiwavelength observations with XMM-Newton, GALEX,
Spitzer, 2dF, GMRT, and the 17-band COMBO-17 photometric redshift survey
complement the HST imaging. Our survey goals include simultaneously linking
galaxy morphology with other observables such as age, star-formation rate,
nuclear activity, and stellar mass. In addition, with the multiwavelength
dataset and new high resolution mass maps from gravitational lensing, we are
able to disentangle the large-scale structure of the system. By examining all
aspects of environment we will be able to evaluate the relative importance of
the dark matter halos, the local galaxy density, and the hot X-ray gas in
driving galaxy transformation. This paper describes the HST imaging, data
reduction, and creation of a master catalogue. We perform Sersic fitting on the
HST images and conduct associated simulations to quantify completeness. In
addition, we present the COMBO-17 photometric redshift catalogue and estimates
of stellar masses and star-formation rates for this field. We define galaxy and
cluster sample selection criteria which will be the basis for forthcoming
science analyses, and present a compilation of notable objects in the field.
Finally, we describe the further multiwavelength observations and announce
public access to the data and catalogues.Comment: 29 pages, 22 figures; accepted to MNRAS. Full data release available
at http://www.nottingham.ac.uk/astronomy/stage
Identifying the science and technology dimensions of emerging public policy issues through horizon scanning
Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security.Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security
First-level trigger systems for LHC experiments
We propose to carry out a broad-based programme of R&D on level-1 trigger systems for LHC experiments. We will consider the overall level-1 which coordinates different subtriggers and which interacts with the front end electronics and with the level-2 system. Careful attention will be paid to systems aspects and problems of synchronization within the pipelined processor system. Trigger algorithms for selecting events with high-pt electrons, photons, muons, jets and large missing Et will be evaluated by physics simulation studies. We will study possible implementations of such trigger algorithms in fast electronics by making conceptual design studies and using behavioural simulation models. For critical areas more detailed design studies will be made, and prototypes of some key elements will be constructed and tested. The proposed R&D project builds on existing studies and will complement other R&D projects already funded by the DRDC
Integrating organizational, social, and individual perspectives in Web 2.0-based workplace e-learning
From the issue entitled 'Special Issue: Emerging Social and Legal Aspect'E-learning is emerging as a popular approach of education in the workplace by virtue of its flexibility to access, just-in-time delivery, and cost-effectiveness. To improve social interaction and knowledge sharing in e-learning, Web 2.0 is increasingly utilized and integrated with e-learning applications. However, existing social learning systems fail to align learning with organizational goals and individual needs in a systemic way. The dominance of technology-oriented approaches makes elearning applications less goal-effective and poor in quality and design. To solve the problem, we address the requirement of integrating organizational, social, and individual perspectives in the development of Web 2.0 elearning systems. To fulfill the requirement, a key performance indicator (KPI)-oriented approach is presented in this study. By integrating a KPI model with Web 2.0 technologies, our approach is able to: 1) set up organizational goals and link the goals with expertise required for individuals; 2) build a knowledge network by linking learning resources to a set of competences to be developed and a group of people who learn and contribute to the knowledge network through knowledge creation, sharing, and peer evaluation; and 3) improve social networking and knowledge sharing by identifying each individual's work context, expertise, learning need, performance, and contribution. The mechanism of the approach is explored and elaborated with conceptual frameworks and implementation technologies. A prototype system for Web 2.0 e-learning has been developed to demonstrate the effectiveness of the approach. © Springer Science + Business Media, LLC 2009.postprin
- …