2,255 research outputs found
Oxygen diffusion barrier coating
A method for coating a titanium panel or foil with aluminum and amorphous silicon to provide an oxygen barrier abrogating oxidation of the substrate metal is developed. The process is accomplished with known inexpensive procedures common in materials research laboratories, i.e., electron beam deposition and sputtering. The procedures are conductive to treating foil gage titanium and result in submicron layers which virtually add no weight to the titanium. There are no costly heating steps. The coatings blend with the substrate titanium until separate mechanical properties are subsumed by those of the substrate without cracking or spallation. This method appreciably increases the ability of titanium to mechanically perform in high thermal environments such as those witnessed on structures of space vehicles during re-entr
Surface effects on hydrogen permeation through Ti-14Al-21Nb alloy
Hydrogen transport through Ti-14Al-21Nb (wt percent) alloy is measured using ultrahigh vacuum permeation techniques over the temperature range of 500 to 900 C and hydrogen pressure range of 0.25 to 10 torr. Hydrogen permeability through the alloy can be described through two different mechanisms depending on th temperature of exposure. In the 675 to 900 C range, the process is diffusion-limited: the permeability has a weak temperature dependence, but the diffusivity has a strong temperature dependence. Below 675 C, the permeation rate of hydrogen is very sensitive to surface controlled processes such as the formation of a barrier layer from contaminants. A physical model explaining the role of surface films on the transport of hydrogen through Ti-14Al-21Nb alloy was described
Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics
Graphics Processing Units (GPUs) are having a transformational effect on
numerical lattice quantum chromodynamics (LQCD) calculations of importance in
nuclear and particle physics. The QUDA library provides a package of mixed
precision sparse matrix linear solvers for LQCD applications, supporting single
GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This
library, interfaced to the QDP++/Chroma framework for LQCD calculations, is
currently in production use on the "9g" cluster at the Jefferson Laboratory,
enabling unprecedented price/performance for a range of problems in LQCD.
Nevertheless, memory constraints on current GPU devices limit the problem sizes
that can be tackled. In this contribution we describe the parallelization of
the QUDA library onto multiple GPUs using MPI, including strategies for the
overlapping of communication and computation. We report on both weak and strong
scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in
excess of 4 Tflops.Comment: 11 pages, 7 figures, to appear in the Proceedings of Supercomputing
2010 (submitted April 12, 2010
Increasing the Efficiency of 6-DoF Visual Localization Using Multi-Modal Sensory Data
Localization is a key requirement for mobile robot autonomy and human-robot
interaction. Vision-based localization is accurate and flexible, however, it
incurs a high computational burden which limits its application on many
resource-constrained platforms. In this paper, we address the problem of
performing real-time localization in large-scale 3D point cloud maps of
ever-growing size. While most systems using multi-modal information reduce
localization time by employing side-channel information in a coarse manner (eg.
WiFi for a rough prior position estimate), we propose to inter-weave the map
with rich sensory data. This multi-modal approach achieves two key goals
simultaneously. First, it enables us to harness additional sensory data to
localise against a map covering a vast area in real-time; and secondly, it also
allows us to roughly localise devices which are not equipped with a camera. The
key to our approach is a localization policy based on a sequential Monte Carlo
estimator. The localiser uses this policy to attempt point-matching only in
nodes where it is likely to succeed, significantly increasing the efficiency of
the localization process. The proposed multi-modal localization system is
evaluated extensively in a large museum building. The results show that our
multi-modal approach not only increases the localization accuracy but
significantly reduces computational time.Comment: Presented at IEEE-RAS International Conference on Humanoid Robots
(Humanoids) 201
INVESTIGATING THE RELATIONSHIP BETWEEN YIELD RISK AND AGRI-ENVIRONMENTAL INDICATORS
Crop insurance provides risk reduction benefits yet may increase planted acres in risky areas. This paper investigates the relationship between environmental quality and crop insurance induced changes in cropping pattern. Results suggest that yield risk and soil erosion are positively correlated for the majority of acreage in the study area.Environmental Economics and Policy, Risk and Uncertainty,
Formal Semantics And Pragmatics Of Belief
It is argued that an adequate model-theoretic treatment of belief requires the devices of a two-dimensional intensional logic; a logic, that is, that can represent the relevant features of the epistemic situation of an agent in something like the way a logic of indexicals represents possible contexts of disourse. The general approach is illustrated by means of several examples, Kripke\u27s Puzzle About Belief among them. A model theory is developed for a formal language containing a belief operator, quantifiers, description operator and identity predicate, and a truth predicate and reference operator. Certain properties of the model theory are demonstrated, and the application to indexical belief is sketched
The Development of Andragogical Techniques of Instruction for Adult Education
AB the Twentieth Century began, there was a traditional posture evident in higher education in the United States. For those males whose families could afford it, beginning college immediately following high school provided a liberal arts education. For select 21 year old college graduates, specialization in a professional field was available in graduate school. For the remainder of America\u27s youth, and nearly all of its women, high school graduation was the highest academic pinnacle they might obtain for the remainder of their life
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