8,547 research outputs found
In-Suit Doppler Technology Assessment
The objective of this program was to perform a technology assessment survey of non-invasive air embolism detection utilizing Doppler ultrasound methodologies. The primary application of this technology will be a continuous monitor for astronauts while performing extravehicular activities (EVA's). The technology assessment was to include: (1) development of a full understanding of all relevant background research; and (2) a survey of the medical ultrasound marketplace for expertise, information, and technical capability relevant to this development. Upon completion of the assessment, LSR was to provide an overview of technological approaches and R&D/manufacturing organizations
Direct Measurement of the g-Factor of Composite Fermions
The activation gap of the fractional quantum Hall states at constant
fillings and 2/5 has been measured as a function of the
perpendicular magnetic field . A linear dependence of on is
observed while approaching the spin polarization transition. This feature
allows a direct measurement of the -factor of composite fermions which
appears to be heavily renormalized by interactions and strongly sensitive to
the electronic filling factor.Comment: 4 pages, 4 figures Changed content: Fokus more on g-factors (and less
on other details
Study of ecosystems in the context of global change
Journal ArticleGlobal change research requires not only knowledge of how individual species (e.g. pests) respond to climate and land-use change, but also an understanding of the responses of whole systems to their multiple and interacting drivers. An upscaling from single systems to landscapes and continents is an additional essential component of global change research. In contrast to the well-established research methodology in the ecophysiology of species (see Pearcy et al., 1989), the approaches to studying ecosystems as a whole, and the theory required to identify key parameters that drive the multiple interactions at the ecosystem level, are less developed (see Schulze, 1995a)
The orbit rigidity matrix of a symmetric framework
A number of recent papers have studied when symmetry causes frameworks on a
graph to become infinitesimally flexible, or stressed, and when it has no
impact. A number of other recent papers have studied special classes of
frameworks on generically rigid graphs which are finite mechanisms. Here we
introduce a new tool, the orbit matrix, which connects these two areas and
provides a matrix representation for fully symmetric infinitesimal flexes, and
fully symmetric stresses of symmetric frameworks. The orbit matrix is a true
analog of the standard rigidity matrix for general frameworks, and its analysis
gives important insights into questions about the flexibility and rigidity of
classes of symmetric frameworks, in all dimensions.
With this narrower focus on fully symmetric infinitesimal motions, comes the
power to predict symmetry-preserving finite mechanisms - giving a simplified
analysis which covers a wide range of the known mechanisms, and generalizes the
classes of known mechanisms. This initial exploration of the properties of the
orbit matrix also opens up a number of new questions and possible extensions of
the previous results, including transfer of symmetry based results from
Euclidean space to spherical, hyperbolic, and some other metrics with shared
symmetry groups and underlying projective geometry.Comment: 41 pages, 12 figure
Neural Deformable Cone Beam CT
In oral and maxillofacial cone beam computed tomography (CBCT), patient motion is frequently observed and, if not accounted
for, can severely affect the usability of the acquired images. We propose a highly flexible, data driven motion correction and
reconstruction method which combines neural inverse rendering in a CBCT setting with a neural deformation field. We jointly
optimize a lightweight coordinate based representation of the 3D volume together with a deformation network. This allows our
method to generate high quality results while accurately representing occurring patient movements, such as head movements,
separate jaw movements or swallowing. We evaluate our method in synthetic and clinical scenarios and are able to produce
artefact-free reconstructions even in the presence of severe motion. While our approach is primarily developed for maxillofacial
applications, we do not restrict the deformation field to certain kinds of motion. We demonstrate its flexibility by applying it to
other scenarios, such as 4D lung scans or industrial tomography settings, achieving state-of-the art results within minutes with
only minimal adjustments
The degradation of MgB2 under ambient environment
The superconductivities of samples prepared by several procedures were found
to degrade under ambient environment. The degradation mechanism was studied by
measuring the change of surface chemical composition of dense MgB2 pellets
(prepared by hot isostatic pressure, HIPed) under atmospheric exposure using
X-ray Photoelectron Spectroscopy (XPS). Results showed that samples with poor
connectivity between grains and with smaller grain sizes degrade with time when
exposed to ambient conditions. In these samples, the Tc did not change with
time, but the superconducting transition became broader and the Meissner
fraction decreased. In contrast, our well-sintered and the HIPed samples
remained stable for several months under ambient condition. The degradation was
found to be related to surface decomposition as observed by XPS. We observed
the formation of oxidized Mg, primarily in the form of a Mg hydroxide, the
increase of C and O contents, and the reduction of B concentration in the
surface layer of MgB2 samples.Comment: 15 pages, 3 figure
Altitude-wind-tunnel Investigation of Several Afterburner Configurations Having Moderately High Burner-inlet Velocities
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