114,834 research outputs found
Apodized-pupil Lyot coronagraphs: multistage designs for extremely large telescopes
Earlier apodized-pupil Lyot coronagraphs (APLC) have been studied and
developed to enable high-contrast imaging for exoplanet detection and
characterization with present-day ground-based telescopes. With the current
interest in the development of the next generation of telescopes, the future
extremely large telescopes (ELTs), alternative APLC designs involving
multistage configuration appear attractive. The interest of these designs for
application to ELTs is studied. Performance and sensitivity of multistage APLC
to ELT specificities are analyzed and discussed, taking into account several
ineluctable coronagraphic telescope error sources by means of numerical
simulations. Additionally, a first laboratory experiment with a two-stages-APLC
in the near-infrared (H-band) is presented to further support the numerical
treatment. Multistage configurations are found to be inappropriate to ELTs. The
theoretical gain offered by a multistage design over the classical single-stage
APLC is largely compromised by the presence of inherent error sources occurring
in a coronagraphic telescope, and in particular in ELTs. The APLC remains an
attractive solution for ELTs, but rather in its conventional single-stage
configuration.Comment: A&A accepte
Coupling methods for multistage sampling
Multistage sampling is commonly used for household surveys when there exists
no sampling frame, or when the population is scattered over a wide area.
Multistage sampling usually introduces a complex dependence in the selection of
the final units, which makes asymptotic results quite difficult to prove. In
this work, we consider multistage sampling with simple random without
replacement sampling at the first stage, and with an arbitrary sampling design
for further stages. We consider coupling methods to link this sampling design
to sampling designs where the primary sampling units are selected
independently. We first generalize a method introduced by [Magyar Tud. Akad.
Mat. Kutat\'{o} Int. K\"{o}zl. 5 (1960) 361-374] to get a coupling with
multistage sampling and Bernoulli sampling at the first stage, which leads to a
central limit theorem for the Horvitz--Thompson estimator. We then introduce a
new coupling method with multistage sampling and simple random with replacement
sampling at the first stage. When the first-stage sampling fraction tends to
zero, this method is used to prove consistency of a with-replacement bootstrap
for simple random without replacement sampling at the first stage, and
consistency of bootstrap variance estimators for smooth functions of totals.Comment: Published at http://dx.doi.org/10.1214/15-AOS1348 in the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Multistage multiple-reentry turbine Patent
Multistage, multiple reentry, single rotor, axial flow turbin
Model equation for simulating flows in multistage turbomachinery
A steady, three-dimensional average-passage equation system is derived for use in simulating multistage turbomachinery flows. These equations describe a steady, viscous flow that is periodic from blade passage to blade passage. From this system of equations, various reduced forms can be derived for use in simulating the three-dimensional flow field within multistage machinery. It is suggested that a properly scaled form of the average-passage equation system would provide an improved mathematical model for simulating the flow in multistage machines at design and, in particular, at off-design conditions
Single action separation mechanism Patent
Separation mechanism for use between stages of multistage rocket vehicle
Multistage Switching Architectures for Software Routers
Software routers based on personal computer (PC) architectures are becoming an important alternative to proprietary and expensive network devices. However, software routers suffer from many limitations of the PC architecture, including, among others, limited bus and central processing unit (CPU) bandwidth, high memory access latency, limited scalability in terms of number of network interface cards, and lack of resilience mechanisms. Multistage PC-based architectures can be an interesting alternative since they permit us to i) increase the performance of single software routers, ii) scale router size, iii) distribute packet manipulation and control functionality, iv) recover from single-component failures, and v) incrementally upgrade router performance. We propose a specific multistage architecture, exploiting PC-based routers as switching elements, to build a high-speed, largesize,scalable, and reliable software router. A small-scale prototype of the multistage router is currently up and running in our labs, and performance evaluation is under wa
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