5,571 research outputs found
Large area Czochralski silicon
The overall cost effectiveness of the Czochralski process for producing large-area silicon was determined. The feasibility of growing several 12 cm diameter crystals sequentially at 12 cm/h during a furnace run and the subsequent slicing of the ingot using a multiblade slurry saw were investigated. The goal of the wafering process was a slice thickness of 0.25 mm with minimal kerf. A slice + kerf of 0.56 mm was achieved on 12 cm crystal using both 400 grit B4C and SiC abrasive slurries. Crystal growth experiments were performed at 12 cm diameter in a commercially available puller with both 10 and 12 kg melts. Several modifications to the puller hoz zone were required to achieve stable crystal growth over the entire crystal length and to prevent crystallinity loss a few centimeters down the crystal. The maximum practical growth rate for 12 cm crystal in this puller design was 10 cm/h, with 12 to 14 cm/h being the absolute maximum range at which melt freeze occurred
The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE J1810--197
(Abridged) We present a multi-epoch spectral study of the Transient Anomalous
X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four
observations taken over the course of a year reveal strong spectral evolution
as the source fades from outburst. The origin of this is traced to the
individual decay rates of the pulsar's spectral components. A 2-T fit at each
epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the
component luminosities decrease exponentially with tau=900 & 300d,
respectively. One possible interpretation is that the slowly decaying cooler
component is the radiation from a deep heating event that affected a large
fraction of the crust, while the hotter component is powered by external
surface heating at the foot-points of twisted magnetic field lines, by
magnetospheric currents that are decaying more rapidly. The energy-dependent
pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a
sine and triangle function. These profiles peak at the same phase, suggesting a
concentric surface emission geometry. The spectral and pulse evolution together
argue against the presence of a significant ``power-law'' contribution to the
X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the
historic quiescent level, characterized by an even cooler blackbody spectrum,
by the year 2007.Comment: 12 pages, 6 Figures, Latex, emulateapj. To appear in the
Astrophysical Journa
Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL
We report on a multi-band high-energy observing campaign aimed at studying
the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS
J170849.0-400910, one of the magnetar candidates. We observed 1RXS
J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in
the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy
range. Furthermore, we also reanalyzed, using the latest calibration and
software, all the publicly available INTEGRAL data since 2002, and the soft
X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and
Swift/XRT, in order to study the soft and hard X-ray spectral variability of
1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux,
extending the hardness-intensity correlation proposed for this source over 2
orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics main journa
VLT observations of the magnetar CXO J164710.2-455216 and the detection of a candidate infrared counterpart
We present deep observations of the field of the magnetar CXOJ164710.2-455216
in the star cluster Westerlund 1, obtained in the near-infrared with the
adaptive optics camera NACO@VLT. We detected a possible candidate counterpart
at the {\em Chandra} position of the magnetar, of magnitudes , , and . The K-band measurements available for two epochs (2006 and
2013) do not show significant signs of variability but only a marginal
indication that the flux varied (at the 2 level), consistent with the
fact that the observations were taken when CXOJ164710.2-455216 was in
quiescence. At the same time, we also present colour--magnitude and
colour--colour diagrams in the J, H, and K bands from the 2006 epoch
only, the only one with observations in all three bands, showing that the
candidate counterpart lies in the main bulk of objects describing a relatively
well--defined sequence. Therefore, based on its colours and lack of
variability, we cannot yet associate the candidate counterpart to
CXOJ164710.2-455216. Future near-infrared observations of the field,
following-up a source outburst, would be crucial to confirm the association
from the detection of near-infrared variability and colour evolution.Comment: 5 pages, 3 figures, accepted for publication in MNRA
Robotic-Like Formulation of the Approximated Body-Guidance Problem
A classical problem in the mechanics of mechanisms is the body-guidance synthesis. As first formulated by Burmester, the problem consists of finding the dimensions of a planar four-bar linkage whose coupler link attains a prescribed set of finitely separated poses. The problem is solved either in exact, up to five prescribed poses, or in approximate forms by several methods. Many of them rely on the algebraic geometry to find center- and circle-point loci of the RR dyads composing the mechanism. The method was also used to find the circle-point locus of the PR dyad. In this paper a different approach was followed. We propose a formulation of the problem by using the vector loop equations, usually employed in robotics for kinematic analysis, to obtain the set of nonlinear synthesis equations then solved by advanced and stabilized algorithms. The method allows us to achieve the approximate solution of the body-guidance problem either with RR or PR dyads with high accuracy also including prescribed timing
Heartbreak, Spirit, and Hope: Leading a School in the Throes and Aftermath of a School Crisis.
Ed.D. Thesis. University of HawaiÊ»i at MÄnoa 2017
Hybrid Inspection Robot for Indoor and Outdoor Surveys
In this paper, simulation and experimental tests are reported for a hybrid robot being used for indoor and outdoor inspections. Automatic or tele-operated surveys can be performed by mobile robots, which represent the most efficient solution in terms of power consumption, control, robustness, and overall costs. In the context of structures and infrastructure inspection, robots must be able to move on horizontal or sloped surfaces and overpass obstacles. In this paper, the mechatronic design, simulations, and experimental activity are proposed for a hybrid robot being used for indoor and outdoor inspections, when the environmental conditions do not allow autonomous navigation. In particular, the hybrid robot is equipped with external and internal sensors to acquire information on the main structural elements, avoiding the need for experienced personnel being directly inside the inspection site, taking information from the environment and aiding the pilot to understand the best maneuvers/decisions to take. Given the current state of research and shortcomings worldwide, this paper discusses inspection robots taking into account the main issues in their use, functionality and standard systems, and how internal sensors can be set in order to improve inspection robotsâ performances. On this basis, an illustrative study case is proposed
Design and Development of an Inspection Robotic System for Indoor Applications
The inspection and monitoring of industrial sites, structures, and infrastructure are important issues for their sustainability and further maintenance. Although these tasks are repetitive and time consuming, and some of these environments may be characterized by dust, humidity, or absence of natural light, classical approach relies on large human activities. Automatic or robotic solutions can be considered useful tools for inspection because they can be effective in exploring dangerous or inaccessible sites, at relatively low-cost and reducing the time required for the relief. The development of a paradigmatic system called Inspection Robotic System (IRS) is the main objective of this paper to demonstrate the feasibility of mechatronic solutions for inspection of industrial sites. The development of such systems will be exploited in the form of a tool kit to be flexible and installed on a mobile system, in order to be used for inspection and monitoring, possibly introducing high efficiency, quality and repetitiveness in the related sector. The interoperability of sensors with wireless communication may form a smart sensors tool kit and a smart sensor network with powerful functions to be effectively used for inspection purposes. Moreover, it may constitute a solution for a broad range of scenarios spacing from industrial sites, brownfields, historical sites or sites dangerous or difficult to access by operators. First experimental tests are reported to show the engineering feasibility of the system and interoperability of the mobile hybrid robot equipped with sensors that allow real-time multiple acquisition and storage
Cholesterol metabolism in the endoplasmic reticulum of rat liver
In work directed towards the purification of a liver microsomal
cytochrome P-450 species capable of supporting cholesterol 7a-hydroxylase
activity in a reconstituted system, the use of the detergent Renex 690
for the solubilisation of microsomal protein resulted in an unacceptable
inhibition of cholesterol 7ct-hydroxylation. This confirmed previous
work, showing that Nonidet P42 is the optimum choice of solubilising
agent for this purpose. DEAE-cellulose chromatography of microsomal
protein solubilised with Nonidet P42 was confirmed to be a suitable
first step in the purification of liver microsomal cytochrome P-450,
since there is a good separation of this species from NADPH cytochrome c
reductase activity. However, the recovery and purification of total
cytochrome P-450 was low. Dithiothreitol, 4-phenyl-imidazole, diethyldithiocarbamate
and glycerol, by themselves or in combination with each
other, were shown to be useful agents in liver microsomal cytochrome
P-450 purification. It was further demonstrated that increasing the
recovery of cytochrome P-450 gave a concomitant improvement in its
purification. Chromatography on quaternary aminoethyl-Sephadex or on
carboxymethylcellulose did not result in any purification of cytochrome
P-450. Hydroxyapatite chromatography of cytochrome P-450 - containing
fractions from the DEAE-cellulose eluate gave a further small purification
of cytochrome P-450. The use of chemical donors of "active oxygen"
in the reconstitution of cholesterol 7a-hydroxylase activity with liver
microsomal cytochrome P-450 was shown to be limited by the rapid
destruction of the cytochrome by these agents
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