14,383 research outputs found
Modeling and Analysis of Power Processing Systems (MAPPS), initial phase 2
The overall objective of the program is to provide the engineering tools to reduce the analysis, design, and development effort, and thus the cost, in achieving the required performances for switching regulators and dc-dc converter systems. The program was both tutorial and application oriented. Various analytical methods were described in detail and supplemented with examples, and those with standardization appeals were reduced into computer-based subprograms. Major program efforts included those concerning small and large signal control-dependent performance analysis and simulation, control circuit design, power circuit design and optimization, system configuration study, and system performance simulation. Techniques including discrete time domain, conventional frequency domain, Lagrange multiplier, nonlinear programming, and control design synthesis were employed in these efforts. To enhance interactive conversation between the modeling and analysis subprograms and the user, a working prototype of the Data Management Program was also developed to facilitate expansion as future subprogram capabilities increase
The Einstein Ring 0047-2808 Revisited: A Bayesian Inversion
In a previous paper, we outlined a new Bayesian method for inferring the
properties of extended gravitational lenses, given data in the form of resolved
images. This method holds the most promise for optimally extracting information
from the observed image, whilst providing reliable uncertainties in all
parameters. Here, we apply the method to the well studied optical Einstein ring
0047-2808. Our results are in broad agreement with previous studies, showing
that the density profile of the lensing galaxy is aligned within a few degrees
of the light profile, and suggesting that the source galaxy (at redshift 3.6)
is a binary system, although its size is only of order 1-2 kpc. We also find
that the mass of the elliptical lensing galaxy enclosed by the image is
(2.910.01) M_{\sun}. Our method is able to achieve
improved resolution for the source reconstructions, although we also find that
some of the uncertainties are greater than has been found in previous analyses,
due to the inclusion of extra pixels and a more general lens model.Comment: Accepted for publication in Ap
The lens and source of the optical Einstein ring gravitational lens ER 0047-2808
(Abridged) We perform a detailed analysis of the optical gravitational lens
ER 0047-2808 imaged with WFPC2 on the Hubble Space Telescope. Using software
specifically designed for the analysis of resolved gravitational lens systems,
we focus on how the image alone can constrain the mass distribution in the lens
galaxy. We find the data are of sufficient quality to strongly constrain the
lens model with no a priori assumptions about the source. Using a variety of
mass models, we find statistically acceptable results for elliptical
isothermal-like models with an Einstein radius of 1.17''. An elliptical
power-law model (Sigma \propto R^-beta) for the surface mass density favours a
slope slightly steeper than isothermal with beta = 1.08 +/- 0.03. Other models
including a constant M/L, pure NFW halo and (surprisingly) an isothermal sphere
with external shear are ruled out by the data. We find the galaxy light profile
can only be fit with a Sersic plus point source model. The resulting total
M/L_B contained within the images is 4.7 h_65 +/-0.3. In addition, we find the
luminous matter is aligned with the total mass distribution within a few
degrees. The source, reconstructed by the software, is revealed to have two
bright regions, with an unresolved component inside the caustic and a resolved
component straddling a fold caustic. The angular size of the entire source is
approx. 0.1'' and its (unlensed) Lyman-alpha flux is 3 x 10^-17 erg/s/cm^2.Comment: 13 pages, 5 figures. Revised version accepted for publication in
MNRA
A Deep Multicolor Survey I. Imaging Observations and Catalog of Stellar Objects
We have used the KPNO 4-meter Mayall telescope to image 0.83 square degrees
of sky in six fields at high galactic latitude in six filters spanning
3000-10000\AA\ to magnitude limits ranging from 22.1 to 23.8. We have assembled
a catalog of 21,375 stellar objects detected in the fields for use primarily in
conducting a multicolor search for quasars. This paper describes the data
reduction techniques used on the CCD data, the methods used to construct the
stellar object catalog, and the simulations performed to understand its
completeness and contamination.Comment: To Appear in ApJ Supplement, 1996. 168k uuencoded gunzipped tarred
tex file (requires aas2pp4.sty and tighten.sty) and 4 PostScript figures.
Also available at http://astro.as.arizona.edu/~pathall/astro.html#preprint
Tunable fibre-coupled multiphoton microscopy with a negative curvature fibre
Negative curvature fibre (NCF) guides light in its core by inhibiting the coupling of core and cladding modes. In this work, an NCF was designed and fabricated to transmit ultrashort optical pulses for multiphoton microscopy with low group velocity dispersion (GVD) at 800 nm. Its attenuation was measured to be <0.3 dB m(-1) over the range 600-850 nm and the GVD was -180 ± 70 fs(2) m(-1) at 800 nm. Using an average fibre output power of ∼20 mW and pulse repetition rate of 80 MHz, the NCF enabled pulses with a duration of <200 fs to be transmitted through a length of 1.5 m of fibre over a tuning range of 180 nm without the need for dispersion compensation. In a 4 m fibre, temporal and spectral pulse widths were maintained to within 10% of low power values up to the maximum fibre output power achievable with the laser system used of 278 mW at 700 nm, 808 mW at 800 nm and 420 mW at 860 nm. When coupled to a multiphoton microscope, it enabled imaging of ex vivo tissue using excitation wavelengths from 740 nm to 860 nm without any need for adjustments to the set-up
Stellar Collisions and the Interior Structure of Blue Stragglers
Collisions of main sequence stars occur frequently in dense star clusters. In
open and globular clusters, these collisions produce merger remnants that may
be observed as blue stragglers. Detailed theoretical models of this process
require lengthy hydrodynamic computations in three dimensions. However, a less
computationally expensive approach, which we present here, is to approximate
the merger process (including shock heating, hydrodynamic mixing, mass
ejection, and angular momentum transfer) with simple algorithms based on
conservation laws and a basic qualitative understanding of the hydrodynamics.
These algorithms have been fine tuned through comparisons with the results of
our previous hydrodynamic simulations. We find that the thermodynamic and
chemical composition profiles of our simple models agree very well with those
from recent SPH (smoothed particle hydrodynamics) calculations of stellar
collisions, and the subsequent stellar evolution of our simple models also
matches closely that of the more accurate hydrodynamic models. Our algorithms
have been implemented in an easy to use software package, which we are making
publicly available (see http://vassun.vassar.edu/~lombardi/mmas/). This
software could be used in combination with realistic dynamical simulations of
star clusters that must take into account stellar collisions.Comment: This revised version has 37 pages, 13 figures, 4 tables; submitted to
ApJ; for associated software package, see
http://vassun.vassar.edu/~lombardi/mmas/ This revised version presents
additional comparisons with SPH results and slightly improved merger recipe
Bostonia. Volume 15
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
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