23,652 research outputs found
Revealing New Physical Structures in the Supernova Remnant N63A through Chandra Imaging Spectroscopy
We present Chandra X-ray observations of the supernova remnant (SNR) N63A in
the Large Magellanic Cloud (LMC). N63A, one of the brightest LMC remnants, is
embedded in an H II region and probably associated with an OB association. The
optical remnant consists of three lobes of emission contained within the
approximately three times larger X-ray remnant. Our Chandra data reveal a
number of new physical structures in N63A. The most striking of these are the
several ``crescent''-shaped structures located beyond the main shell that
resemble similar features seen in the Vela SNR. In Vela, these have been
interpreted as arising from high speed clumps of supernova ejecta interacting
with the ambient medium. Another distinct feature of the remnant is a roughly
triangular ``hole'' in the X-ray emission near the location of the optical
lobes and the brightest radio emission. X-ray spectral analysis shows that this
deficit of emission is a result of absorption by an intervening dense cloud
with a mass of ~450 M_sun that is currently being engulfed by the remnant's
blast wave. We also find that the rim of the remnant, as well as the
crescent-shaped features, have considerably softer X-ray spectra than the
interior. Limits on hard X-ray emission rule out a young, energetic pulsar in
N63A, but the presence of an older or less active one, powering a wind nebula
with a luminosity less than ~4e10^34 erg/s, is allowed.Comment: 18 pages, 5 figures (2 color), accepted for publication in Ap
In pursuit of causality in leadership training research: A review and pragmatic recommendations
Although research shows a reliable association between leadership training and positive organizational outcomes, a range of research design issues mean we do not know to what degree the former causes the later. Accordingly, the paper has two main aims. First, to describe the conditions necessary to determine causality in leadership training research and the ability of different research designs to achieve this. Six important, but often ignored, issues associated with determining causality are described (control conditions, sample representation, condition randomization, condition independence, temporal design, and author involvement). Second, to review the extent to which the leadership training literature is able to demonstrate causality. The review shows that the majority of studies do not meet many of the criteria, even the most basic criteria, required to establish causality. Finally, we provide guidelines for designing future research to improve causal identification and is capable of generating meaningful theory and policy recommendations
Wake Flows in Coastal Oceans: An Experimental Study of Topographic Effects
We consider the effects of coastal topography on the wake of an idealised headland model in a laboratory flume. Under a range of Reynolds numbers relevant to coastal oceans, we find that coherent eddies interact strongly with the headland shear layer and wake, affecting the width of the shear layer and the length of the wake. A preliminary investigation of turbulence statistics indicates that topography upstream of a headland can lead to a wider shear layer, a headland wake that extends further downstream, and enhanced horizontal diffusion out of the wake relative to the case with unperturbed oncoming flow
Intermittent exploration on a scale-free network
We study an intermittent random walk on a random network of scale-free degree
distribution. The walk is a combination of simple random walks of duration
and random long-range jumps. While the time the walker needs to cover all
the nodes increases with , the corresponding time for the edges displays a
non monotonic behavior with a minimum for some nontrivial value of . This
is a heterogeneity-induced effect that is not observed in homogeneous
small-world networks. The optimal increases with the degree of
assortativity in the network. Depending on the nature of degree correlations
and the elapsed time the walker finds an over/under-estimate of the degree
distribution exponent.Comment: 12 pages, 3 figures, 1 table, published versio
Residual mean first-passage time for jump processes: theory and applications to L\'evy flights and fractional Brownian motion
We derive a functional equation for the mean first-passage time (MFPT) of a
generic self-similar Markovian continuous process to a target in a
one-dimensional domain and obtain its exact solution. We show that the obtained
expression of the MFPT for continuous processes is actually different from the
large system size limit of the MFPT for discrete jump processes allowing
leapovers. In the case considered here, the asymptotic MFPT admits
non-vanishing corrections, which we call residual MFPT. The case of L/'evy
flights with diverging variance of jump lengths is investigated in detail, in
particular, with respect to the associated leapover behaviour. We also show
numerically that our results apply with good accuracy to fractional Brownian
motion, despite its non-Markovian nature.Comment: 13 pages, 8 figure
Low-angle misorientation dependence of the optical properties of InGaAs/InAlAs quantum wells
We investigate the dependence of the low-temperature photoluminescence
linewidths from InP-lattice-matched InGaAs/InAlAs quantum wells on the
low-angle misorientation from the (100) surface of the host InP substrate.
Quantum wells were grown on InP substrates misorientated by 0, 0.2, 0.4 and 0.6
degrees; 0.4 degrees was found to consistently result in the narrowest peaks,
with the optimal spectral purity of ~4.25 meV found from a 15nm quantum well.
The width of the emission from the 15nm quantum well was used to optimize the
growth parameters. Thick layers of Si-doped InGaAs were then grown and found to
have bulk, low temperature (77 K), electron mobilities up to \mu ~ 3.5 x 10^4
cm2/Vs with an electron concentration of ~1 x 10^16
Sustainable Multipurpose Biorefineries for Third-Generation Biofuels and Value-Added Co-Products
Averaged residence times of stochastic motions in bounded domains
Two years ago, Blanco and Fournier (Blanco S. and Fournier R., Europhys.
Lett. 2003) calculated the mean first exit time of a domain of a particle
undergoing a randomly reoriented ballistic motion which starts from the
boundary. They showed that it is simply related to the ratio of the volume's
domain over its surface. This work was extended by Mazzolo (Mazzolo A.,
Europhys. Lett. 2004) who studied the case of trajectories which start inside
the volume. In this letter, we propose an alternative formulation of the
problem which allows us to calculate not only the mean exit time, but also the
mean residence time inside a sub-domain. The cases of any combinations of
reflecting and absorbing boundary conditions are considered. Lastly, we
generalize our results for a wide class of stochastic motions.Comment: 7 pages, 3 figure
Avaliação e predição da asma e sua gravidade na comunidade pediátrica
Seventy four asthmatic children aged 7 to 11 years were examined along with controls matched by age and sex. Clinical and laboratory investigations preceded a 28-day follow-up where data about morning and evening peak expiratory flow rate (PEF), symptoms and treatment were recorded. The coefficient of variation of PEF was found to be an objective measurement of asthma severity that has statistically significant correlation with both symptoms (r s= .36) and treatment (r s= .60). Moreover, it separates mild and severe asthmatics, as confirmed by statistically significant differences (p= .008 or less) in symptoms, treatment, skin allergy and airways response to exercise. Skin allergy and airways responsiveness to exercise were found to be predictors of both disease and severity. By means of logistic regression analysis it was possible to establish the probabilities for both asthma and severe asthma when children presenting and not presenting these characteristics are compared. One single positive skin test represent a probability of 88% for the development of asthma and a probability of 70% for severe disease. A PEF reduction of 10% after an exercise test implies a probability of 73% for disease and a probability of 64% for severe disease. Increases in these variables imply geometrically increased risks and their presence together have a multiplicative effect in the final risk.Foram submetidas a exames, juntamente com grupos controle segundo idade e sexo,74 crianças asmáticas, com idade de 7 a 11 anos. Exames clínicos e laboratoriais precederam um acompanhamento de 28 dias, quando foram registrados dados sobre a taxa de pico do fluxo respiratório (PEF), sintomas e tratamento. Observou-se que o coeficiente de variação do PEF é uma medida objetiva do grau de gravidade da asma, que tem uma correlação estatística significativa, tanto com os sintomas (r s = .036), quanto com o tratamento (r s = .60). Além disso, separa os asmáticos graves e leves, como foi confirmado pelas diferenças estatisticamente significantes (p = 008 ou menos) nos sintomas, tratamentos, alergias da pele e resposta das vias aéreas ao exercício. Estas duas últimas foram consideradas elementos prognosticadores tanto da doença como do grau de gravidade. Pela regressão logística foi possível estabelecer a probabilidade para a asma grave quando as crianças, apresentando ou não essas características, foram comparadas. Um único teste de pele positivo representa uma probabilidade de 88% para o desenvolvimento de asma, e de 70% para doença grave. A redução do PEF de 10%, depois de um teste de exercício, leva a uma probabilidade de 73% de doença e de 64% para doença grave. Aumentos nessas variáveis implicam riscos aumentados geométricamente, cuja presença conjunta tem efeito multiplicativo no risco final
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