29,620 research outputs found
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online
A Parallax-based Distance Estimator for Spiral Arm Sources
The spiral arms of the Milky Way are being accurately located for the first
time via trigonometric parallaxes of massive star forming regions with the
BeSSeL Survey, using the Very Long Baseline Array and the European VLBI
Network, and with the Japanese VERA project. Here we describe a computer
program that leverages these results to significantly improve the accuracy and
reliability of distance estimates to other sources that are known to follow
spiral structure. Using a Bayesian approach, sources are assigned to arms based
on their (l,b,v) coordinates with respect to arm signatures seen in CO and HI
surveys. A source's kinematic distance, displacement from the plane, and
proximity to individual parallax sources are also considered in generating a
full distance probability density function. Using this program to estimate
distances to large numbers of star forming regions, we generate a realistic
visualization of the Milky Way's spiral structure as seen from the northern
hemisphere.Comment: 25 pages with 16 figures; to appear in Ap
Computation of Casimir Interactions between Arbitrary 3D Objects with Arbitrary Material Properties
We extend a recently introduced method for computing Casimir forces between
arbitrarily--shaped metallic objects [M. T. H. Reid et al., Phys. Rev.
Lett._103_ 040401 (2009)] to allow treatment of objects with arbitrary material
properties, including imperfect conductors, dielectrics, and magnetic
materials. Our original method considered electric currents on the surfaces of
the interacting objects; the extended method considers both electric and
magnetic surface current distributions, and obtains the Casimir energy of a
configuration of objects in terms of the interactions of these effective
surface currents. Using this new technique, we present the first predictions of
Casimir interactions in several experimentally relevant geometries that would
be difficult to treat with any existing method. In particular, we investigate
Casimir interactions between dielectric nanodisks embedded in a dielectric
fluid; we identify the threshold surface--surface separation at which
finite--size effects become relevant, and we map the rotational energy
landscape of bound nanoparticle diclusters
New broadband square-law detector
Compact device has wide dynamic range, accurate square-law response, good thermal stability, high-level dc output with immunity to ground-loop problems, ability to insert known time constants for radiometric applications, and fast response times compatible with computer systems
A precision DC-potentiometer microwave insertion-loss test set
Precision dc potentiometer microwave insertion loss test set for calibrating low noise microwave receiving systems used in space communication
Thereās just huge anxiety: ontological security, moral panic, and the decline in young peopleās mental health and well-being in the UK
This study aims to critically discuss factors associated with a recent dramatic rise in recorded mental health issues amongst UK youth. It draws from interviews and focus groups undertaken with young people, parents and professionals. We offer valuable new insights into significant issues affecting young peopleās mental health and well-being that are grounded in their lived experiences and in those who care for and work with them. By means of a thematic analysis of the data, we identified an increase in anxiety related to: future orientation, social media use, education, austerity, and normalization of mental distress and self-harm. We apply the notion of ontological security in our interpretation of how socio-cultural and political changes have increased anxiety amongst young people and consequent uncertainty about the self, the world and the future, leading to mental health problems. There are also problems conceptualizing and managing adolescent mental health, including increased awareness, increased acceptance of these problems, and stigmatisation. We relate this to the tendency for moral panic and widespread dissemination of problems in a risk society. In our conclusion, we highlight implications for future research, policy and practice
Trigonometric Parallaxes of Massive Star Forming Regions: G012.88+0.48 and W33
We report trigonometric parallaxes for water masers in the G012.88+0.48
region and in the massive star forming complex W33 (containing G012.68--0.18,
G012.81--0.19, G012.90--0.24, G012.90--0.26), from the Bar and Spiral Structure
Legacy (BeSSeL) survey using the Very Long Baseline Array. The parallax
distances to all these masers are consistent with kpc,
which locates the W33 complex and G012.88+0.48 in the Scutum spiral arm. Our
results show that W33 is a single star forming complex at about two-thirds the
kinematic distance of 3.7 kpc. The luminosity and mass of this region, based on
the kinematic distance, have therefore been overestimated by more than a factor
of two. The spectral types in the star cluster in W33\,Main have to be changed
by 1.5 points to later types.Comment: 9 pages, 11 figures, 2 tables; accepted for publication at A&
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Beyond recurrent costs: an institutional analysis of the unsustainability of donor-supported reforms in agricultural extension
International donors have spent billions of dollars over the past four decades in developing and/or reforming the agricultural extension service delivery arrangements in developing countries. However, many of these reforms, supported through short-term projects, became unsustainable once aid funding had ceased. The unavailability of recurrent funding has predominantly been highlighted in the literature as the key reason for this undesirable outcome, while little has been written about institutional factors. The purpose of this article is to examine the usefulness of taking an institutional perspective in explaining the unsustainability of donor-supported extension reforms and derive lessons for improvement. Using a framework drawn from the school of institutionalism in a Bangladeshi case study, we have found that a reform becomes unsustainable because of poor demands for extension information and advice; missing, weak, incongruent, and perverse institutional frameworks governing the exchange of extension goods (services); and a lack of institutional learning and change during the reform process. Accordingly, we have argued that strategies for sustainable extension reforms should move beyond financial considerations and include such measures as making extension goods (services) more tangible and monetary in nature, commissioning in-depth studies to learn about local institutions, crafting new institutions and/or reforming the weak and perverse institutions prevailing in developing countries. We emphasize the need to address three categories of institutions ā regulative, normative, and cultural-cognitive ā and call for an alignment among them. We further argue that, in order to be sustainable, a reform should take a systemic approach in institutional capacity building and, for this to be possible, adopt a long-term program approach, as opposed to a short-term project approach
Comparison of predictive scores of symptomatic intracerebral haemorrhage after stroke thrombolysis in a single centre
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