10,742 research outputs found
Flow visualization in the Langley 0.3-meter Transonic Cryogenic Tunnel and preliminary plans for the National Transonic Facility
Design problems associated with the integration of flow visualization in cryogenic facilities are discussed. The possible effects from the cryogenic environment (i.e., window distortion due to thermal contraction both in the mounts and in the window material itself and turbulence in the flow due to injected LN2) are examined. The flow visualization techniques studied are schlieren, shadowgraph, moire deflectometry, and holographic interferometry. The test beds for this work are a Langley in-house cryogenic test chamber and the 0.3-Meter Transonic Cryogenic Tunnel
Hypothesis testing near singularities and boundaries
The likelihood ratio statistic, with its asymptotic distribution at
regular model points, is often used for hypothesis testing. At model
singularities and boundaries, however, the asymptotic distribution may not be
, as highlighted by recent work of Drton. Indeed, poor behavior of a
for testing near singularities and boundaries is apparent in
simulations, and can lead to conservative or anti-conservative tests. Here we
develop a new distribution designed for use in hypothesis testing near
singularities and boundaries, which asymptotically agrees with that of the
likelihood ratio statistic. For two example trinomial models, arising in the
context of inference of evolutionary trees, we show the new distributions
outperform a .Comment: 32 pages, 12 figure
Flow and thermal effects in continuous flow electrophoresis
In continuous flow electrophoresis the axial flow structure changes from a fully developed rectilinear form to one characterized by meandering as power levels are increased. The origin of this meandering is postulated to lie in a hydrodynamic instability driven by axial (and possibly lateral) temperature gradients. Experiments done at MSFC show agreement with the theory
Pyrotechnic shock at the orbiter/external tank forward attachment
During the initial certification test of the forward structural attachment of the space shuttle orbiter to the external tank, pyrotechnic shock from actuation of the separation device resulted in structural failure of the thermal protection tiles surrounding the attachment. Because of the high shock associated with the separation bolt, the development of alternative low shock separation designs was initiated. Two concepts that incorporate a 5.08 centimeter frangible nut as the release device were developed and tested
Tensor Rank, Invariants, Inequalities, and Applications
Though algebraic geometry over is often used to describe the
closure of the tensors of a given size and complex rank, this variety includes
tensors of both smaller and larger rank. Here we focus on the tensors of rank over , which has as a dense subset the orbit
of a single tensor under a natural group action. We construct polynomial
invariants under this group action whose non-vanishing distinguishes this orbit
from points only in its closure. Together with an explicit subset of the
defining polynomials of the variety, this gives a semialgebraic description of
the tensors of rank and multilinear rank . The polynomials we
construct coincide with Cayley's hyperdeterminant in the case , and thus
generalize it. Though our construction is direct and explicit, we also recast
our functions in the language of representation theory for additional insights.
We give three applications in different directions: First, we develop basic
topological understanding of how the real tensors of complex rank and
multilinear rank form a collection of path-connected subsets, one of
which contains tensors of real rank . Second, we use the invariants to
develop a semialgebraic description of the set of probability distributions
that can arise from a simple stochastic model with a hidden variable, a model
that is important in phylogenetics and other fields. Third, we construct simple
examples of tensors of rank which lie in the closure of those of rank
.Comment: 31 pages, 1 figur
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Development of a Rooftop Collaborative Experimental Space through Experiential Learning Projects
The Solar, Water, Energy, and Thermal Laboratory
(SWEAT Lab) is a rooftop experimental space at the
University of Texas at Austin built by graduate and
undergraduate students in the Cockrell School of
Engineering. The project was funded by the Texas State
Energy Conservation Office and the University’s Green
Fee Grant, a competitive grant program funded by UT
Austin tuition fees to support sustainability-related projects
and initiatives on campus. The SWEAT Lab is an on-going
experiential learning facility that enables engineering
education by deploying energy and water-related projects.
To date, the lab contains a full weather station tracking
weather data, a rainwater harvesting system and rooftop
garden.
This project presented many opportunities for students to
learn first hand about unique engineering challenges. The
lab is located on the roof of the 10 story Engineering
Teaching Center (ETC) building, so students had to design
and build systems with constraints such as weight
limitations and wind resistance. Students also gained
experience working with building facilities and
management for structural additions, power, and internet
connection for instruments.
With the Bird’s eye view of UT Austin campus, this unique
laboratory offers a new perspective and dimension to
applied student research projects at UT Austin.Cockrell School of Engineerin
Intrinsic carrier mobility of multi-layered MoS field-effect transistors on SiO
By fabricating and characterizing multi-layered MoS-based field-effect
transistors (FETs) in a four terminal configuration, we demonstrate that the
two terminal-configurations tend to underestimate the carrier mobility
due to the Schottky barriers at the contacts. For a back-gated two-terminal
configuration we observe mobilities as high as 125 cmVs which
is considerably smaller than 306.5 cmVs as extracted from the
same device when using a four-terminal configuration. This indicates that the
intrinsic mobility of MoS on SiO is significantly larger than the
values previously reported, and provides a quantitative method to evaluate the
charge transport through the contacts.Comment: 8 pages, 5 figures, typos fixed, and references update
Kato square root problem with unbounded leading coefficients
We prove the Kato conjecture for elliptic operators,
, with a
complex measurable bounded coercive matrix and a measurable
real-valued skew-symmetric matrix in with entries in
;\, i.e., the domain of is the Sobolev space
in any dimension, with the estimate
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