2,101 research outputs found
An analysis of the relationship of school entrance age to mental age and school achievement in grades I, III, V, and VIII
Thesis (Ed.M.)--Boston Universit
Analysis of multigrid methods on massively parallel computers: Architectural implications
We study the potential performance of multigrid algorithms running on massively parallel computers with the intent of discovering whether presently envisioned machines will provide an efficient platform for such algorithms. We consider the domain parallel version of the standard V cycle algorithm on model problems, discretized using finite difference techniques in two and three dimensions on block structured grids of size 10(exp 6) and 10(exp 9), respectively. Our models of parallel computation were developed to reflect the computing characteristics of the current generation of massively parallel multicomputers. These models are based on an interconnection network of 256 to 16,384 message passing, 'workstation size' processors executing in an SPMD mode. The first model accomplishes interprocessor communications through a multistage permutation network. The communication cost is a logarithmic function which is similar to the costs in a variety of different topologies. The second model allows single stage communication costs only. Both models were designed with information provided by machine developers and utilize implementation derived parameters. With the medium grain parallelism of the current generation and the high fixed cost of an interprocessor communication, our analysis suggests an efficient implementation requires the machine to support the efficient transmission of long messages, (up to 1000 words) or the high initiation cost of a communication must be significantly reduced through an alternative optimization technique. Furthermore, with variable length message capability, our analysis suggests the low diameter multistage networks provide little or no advantage over a simple single stage communications network
Human-robot visual interface for 3D steering of a flexible, bioinspired needle for neurosurgery
Robotic minimally invasive surgery has been a subject of intense research and development over the last three decades, due to the clinical advantages it holds for patients and doctors alike. Particularly for drug delivery mechanisms, higher precision and the ability to follow complex trajectories in three dimensions (3D), has led to interest in flexible, steerable needles such as the programmable bevel-tip needle (PBN). Steering in 3D, however, holds practical challenges for surgeons, as interfaces are traditionally designed for straight line paths. This work presents a pilot study undertaken to evaluate a novel human-machine visual interface for the steering of a robotic PBN, where both qualitative evaluation of the interface and quantitative evaluation of the performance of the subjects in following a 3D path are measured. A series of needle insertions are performed in phantom tissue (gelatin) by the experiment subjects. User could adequately use the system with little training and low workload, and reach the target point at the end of the path with millimeter range accuracy
Unconventional Wisdom: Estimating the Economic Impact of the Democratic and Republican National Political Conventions
We use daily hotel occupancy, price, and revenue data to analyze the economic impact of the 2008 and 2012 Democratic and Republican National Conventions. We find that political conventions generate approximately 29,000 room nights of lodging, though this figure is offset by lower hotel occupancy during the week before and, to a lesser extent, after conventions. Conventions increase hotel revenue by approximately 150 million or more may be implausible
Cyclic motion control for programmable bevel-tip needles 3D steering: a simulation study
Flexible, steerable, soft needles are desirable in Minimally Invasive Surgery to achieve complex trajectories while maintaining the benefits of percutaneous intervention compared to open surgery. One such needle is the multi-segment Programmable Bevel-tip Needle (PBN), which is inspired by the mechanical design of the ovipositor of certain wasps. PBNs can steer in 3D whilst minimizing the force applied to the surrounding substrate, due to the cyclic motion of the segments. Taking inspiration also from the control strategy of the wasp to perform insertions and lay their eggs, this paper presents the design of a cyclic controller that can steer a PBN to produce a desired trajectory in 3D. The performance of the controller is demonstrated in simulation in comparison to that of a direct controller without cyclic motion. It is shown that, while the same steering curvatures can be attained by both controllers, the time taken to achieve the configuration is longer for the cyclic controller, leading to issues of potential under-steering and longer insertion times
Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Four Years
We present the results of spectroscopic observations from the ESSENCE
high-redshift supernova (SN) survey during its first four years of operation.
This sample includes spectra of all SNe Ia whose light curves were presented by
Miknaitis et al. (2007) and used in the cosmological analyses of Davis et al.
(2007) and Wood-Vasey et al. (2007). The sample represents 273 hours of
spectroscopic observations with 6.5 - 10-m-class telescopes of objects detected
and selected for spectroscopy by the ESSENCE team. We present 174 spectra of
156 objects. Combining this sample with that of Matheson et al. (2005), we have
a total sample of 329 spectra of 274 objects. From this, we are able to
spectroscopically classify 118 Type Ia SNe. As the survey has matured, the
efficiency of classifying SNe Ia has remained constant while we have observed
both higher-redshift SNe Ia and SNe Ia farther from maximum brightness.
Examining the subsample of SNe Ia with host-galaxy redshifts shows that
redshifts derived from only the SN Ia spectra are consistent with redshifts
found from host-galaxy spectra. Moreover, the phases derived from only the SN
Ia spectra are consistent with those derived from light-curve fits. By
comparing our spectra to local templates, we find that the rate of objects
similar to the overluminous SN 1991T and the underluminous SN 1991bg in our
sample are consistent with that of the local sample. We do note, however, that
we detect no object spectroscopically or photometrically similar to SN 1991bg.
Although systematic effects could reduce the high-redshift rate we expect based
on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less
prevalent at high redshift.Comment: 21 pages, 17 figures, accepted to A
The Infrared Light Curve of SN 2011fe in M101 and the Distance to M101
We present near-infrared light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting 14 days before maximum brightness in the B band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera. When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch ofB-band maximum of 10.85 ± 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used
Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck-II Telescope
We report on the first observation of cosmologically distant field galaxies
with an high order Adaptive Optics (AO) system on an 8-10 meter class
telescope. Two galaxies were observed at 1.6 microns at an angular resolution
as high as 50 milliarcsec using the AO system on the Keck-II telescope. Radial
profiles of both objects are consistent with those of local spiral galaxies and
are decomposed into a classic exponential disk and a central bulge. A
star-forming cluster or companion galaxy as well as a compact core are detected
in one of the galaxies at a redshift of 0.37+/-0.05. We discuss possible
explanations for the core including a small bulge, a nuclear starburst, or an
active nucleus. The same galaxy shows a peak disk surface brightness that is
brighter than local disks of comparable size. These observations demonstrate
the power of AO to reveal details of the morphology of distant faint galaxies
and to explore galaxy evolution.Comment: 5 pages, Latex, 3 figures. Accepted for publication in P.A.S.
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