12,716 research outputs found
High-contrast Imaging from Space: Speckle Nulling in a Low Aberration Regime
High-contrast imaging from space must overcome two major noise sources to
successfully detect a terrestrial planet angularly close to its parent star:
photon noise from diffracted star light, and speckle noise from star light
scattered by instrumentally-generated wavefront perturbation. Coronagraphs
tackle only the photon noise contribution by reducing diffracted star light at
the location of a planet. Speckle noise should be addressed with
adaptative-optics systems. Following the tracks of Malbet, Yu and Shao (1995),
we develop in this paper two analytical methods for wavefront sensing and
control that aims at creating dark holes, i.e. areas of the image plane cleared
out of speckles, assuming an ideal coronagraph and small aberrations. The first
method, speckle field nulling, is a fast FFT-based algorithm that requires the
deformable-mirror influence functions to have identical shapes. The second
method, speckle energy minimization, is more general and provides the optimal
deformable mirror shape via matrix inversion. With a NxN deformable mirror, the
size of matrix to be inverted is either N^2xN^2 in the general case, or only
NxN if influence functions can be written as the tensor product of two
one-dimensional functions. Moreover, speckle energy minimization makes it
possible to trade off some of the dark hole area against an improved contrast.
For both methods, complex wavefront aberrations (amplitude and phase) are
measured using just three images taken with the science camera (no dedicated
wavefront sensing channel is used), therefore there are no non-common path
errors. We assess the theoretical performance of both methods with numerical
simulations, and find that these speckle nulling techniques should be able to
improve the contrast by several orders of magnitude.Comment: 31 pages, 8 figures, 1 table. Accepted for publication in ApJ (should
appear in February 2006
Excess mortality during heat waves in Ireland
Ireland is not known for having extreme high temperatures, with values above 30C uncommon. Ireland has significant excess winter mortality compared to summer. The objective of this study is to estimate the impact of nation-wide heat waves on the total, cardiovascular and respiratory relationship, for the period 1981â2003, to determine if there are any periods of excess summer mortality
Circuit approach to photonic heat transport
We discuss the heat transfer by photons between two metals coupled by a
linear element with a reactive impedance. Using a simple circuit approach, we
calculate the spectral power transmitted from one resistor to the other and
find that it is determined by the photon transmission coefficient, which
depends on the impedances of the metals and the coupling element. We study the
total photonic power flow for different coupling impedances, both in the linear
regime, where the temperature difference between the metals is small, and in
the non-linear regime of large temperature differences.Comment: 6 pages, 6 figure
Recanalization of the Chronically Occluded Internal Carotid Artery: Review of the Literature.
Introduction: We reviewed the literature on interventions for patients with medically refractory chronically occluded internal carotid artery (COICA) to assess the risks and/or benefits after recanalization via an endovascular technique (ET) or hybrid surgery (HS, i.e., ET plus carotid endarterectomy).
Methods: A systematic search of the electronic databases was performed. Patients with COICA were classified into 4 different categories according to Hasan et al classification.
Results: Eighteen studies satisfied the inclusion criteria. Only 6 studies involved an HS procedure. We identified 389 patients with COICA who underwent ET or HS; 91% were males. The overall perioperative complication rate was 10.1% (95% confidence interval [CI]: 7.4%-13.1%). For types A and B, the successful recanalization rate was 95.4% (95% CI: 86.5%-100%), with a 13.7% (95% CI: 2.3%-27.4%) complication rate. For type C, the success rate for ET was 45.7% (95% CI: 17.8%-70.7%), with a complication rate of 46.0% (95% CI: 20.0%-71.4%) for ET and for the HS technique 87.6% (95% CI: 80.9%-94.4%), with a complication rate of 14.0% (95% CI: 7.0%-21.8%). For type D, the success rate of recanalization was 29.8% (95% CI: 7.8%-52.8%), with a 29.8% (95% CI: 6.1%-56.3%) complication rate. Successful recanalization resulted in a symmetrical perfusion between both cerebral hemispheres, resolution of penumbra, normalization of the mean transit time, and improvement in Montreal Cognitive Assessment (MoCA) score (ÎMoCA = 9.80 points; P = 0.004).
Conclusions: Type A and B occlusions benefit from ET, especially in the presence of a large penumbra. Type C occlusions can benefit from HS. Unfortunately, we did not identify an intervention to help patients with type D occlusions. A phase 2b randomized controlled trial is needed to confirm these findings
THE EFFECTS OF ALTERNATIVE SEASONAL PRICE DIFFERENTIALS ON MILK PRODUCTION IN NEW YORK
Uneven monthly milk production (seasonality) is a major problem in the New York dairy industry. This article estimates expected monthly milk production response to a set of hypothetical seasonal price differentials designed to reduce the degree of seasonality. The analysis is based on a random mail survey and farm record data. The results indicate that a seasonal price differential of $1.12 per cwt. (over three times the current differential) would be necessary to completely balance spring and fall production in New York, based on the perceptions of farmers surveyed. Also, producers with better managerial skills are shown to be able to reduce their seasonality at a significantly lower price differential than less skilled farm managers.Livestock Production/Industries,
Nurturing the young shoots of talent: Using action research for exploration and theory building
This is an Author's Accepted Manuscript of an article published in European Early Childhood Education Research Journal, 19(4), 433-450, 2011, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/1350293X.2011.623515.This paper reports the outcomes of a set of action research projects carried out by teacher researchers in 14 local education authorities in England, working collaboratively with university tutors, over a period of three years. The common aim of all the projects was to explore practical ways of nurturing the gifts and talents of children aged fourâseven years. The project was funded by the Department of Education and Skills in England as part of the government's gifted and talented programme. The project teachers felt that their understanding of issues relating to nurturing the gifts and talents of younger children was enhanced through their engagement in the project. It was possible to map the findings of the projects to the English government's National Quality Standards for gifted and talented education which include: (1) identification; (2) effective provision in the classroom; (3) enabling curriculum entitlement and choice; (4) assessment for learning; (5) engaging with community, families and beyond. The findings are also analysed within the framework of good practice in educating children in the first years of schooling. Participating practitioners felt that action research offered them a suitable methodology to explore the complexity of the topic of giftedness through cycles of planning, action and reflection and personal theory building
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The APHEKOM Project: A literature review of air pollution interventions and their impact of public health
Intervention studies play an important role in supporting and complementing scientific validation of results of epidemiological non-intervention studies linking air pollution and health. In this paper a collection of existing published intervention studies is reviewed with the aim to give a summarized overview spanning a variety of approaches regarding the type of the intervention and findings with the main focus on studies that assessed interventions that improved air quality and the associated positive impact on public health. Air pollution interventions were defined as events aimed at reducing air pollution and also events where air pollution reductions occurred as a side effect
Finite dimensional quantizations of the (q,p) plane : new space and momentum inequalities
We present a N-dimensional quantization a la Berezin-Klauder or frame
quantization of the complex plane based on overcomplete families of states
(coherent states) generated by the N first harmonic oscillator eigenstates. The
spectra of position and momentum operators are finite and eigenvalues are
equal, up to a factor, to the zeros of Hermite polynomials. From numerical and
theoretical studies of the large behavior of the product of non null smallest positive and largest eigenvalues, we infer
the inequality (resp. ) involving, in suitable
units, the minimal () and maximal () sizes of
regions of space (resp. momentum) which are accessible to exploration within
this finite-dimensional quantum framework. Interesting issues on the
measurement process and connections with the finite Chern-Simons matrix model
for the Quantum Hall effect are discussed
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