22,140 research outputs found
Design and Construction of the 3.2 Mev High Voltage Column for Darht II
A 3.2 MeV injector has been designed and built for the Darht II Project at
Los Alamos Lab. The installation of the complete injector system is nearing
completion at this time. The requirements for the injector are to produce a 3.2
MeV, 2000 ampere electron pulse with a flattop width of at least 2-microseconds
and emittance of less than 0.15 p cm-rad normalized. A large high voltage
column has been built and installed. The column is vertically oriented, is 4.4
meters long, 1.2 meters in diameter, and weights 5700 kilograms. A novel method
of construction has been employed which utilizes bonded mycalex insulating
rings. This paper will describe the design, construction, and testing completed
during construction. Mechanical aspects of the design will be emphasized.Comment: 3 pages, 4 figures, Linac 200
Spatial reasoning to determine stream network from LANDSAT imagery
In LANDSAT imagery, spectral and spatial information can be used to detect the drainage network as well as the relative elevation model in mountainous terrain. To do this, mixed information of material reflectance in the original LANDSAT imagery must be separated. From the material reflectance information, big visible rivers can be detected. From the topographic modulation information, ridges and valleys can be detected and assigned relative elevations. A complete elevation model can be generated by interpolating values for nonridge and non-valley pixels. The small streams not detectable from material reflectance information can be located in the valleys with flow direction known from the elevation model. Finally, the flow directions of big visible rivers can be inferred by solving a consistent labeling problem based on a set of spatial reasoning constraints
Non-genetic therapeutic approaches to Canavan disease
Canavan disease (CD) is a rare leukodystrophy characterized by diffuse spongiform white matter degeneration, dysmyelination and intramyelinic oedema with consequent impairment of psychomotor development and early death. The molecular cause of CD has been identified as being mutations of the gene encoding the enzyme aspartoacylase (ASPA) leading to its functional deficiency. The physiological role of ASPA is to hydrolyse N-acetyl-l-aspartic acid (NAA), producing l-aspartic acid and acetate; as a result, its deficiency leads to abnormally high central nervous system NAA levels. The aim of this article is to review what is currently known regarding the aetiopathogenesis and treatment of CD, with emphasis on the non-genetic therapeutic strategies, both at an experimental and a clinical level, by highlighting: (a) major related hypotheses, (b) the results of the available experimental simulatory approaches, as well as (c) the relevance of the so far examined markers of CD neuropathology. The potential and the limitations of the current non-genetic neuroprotective approaches to the treatment of CD are particularly discussed in the current article, in a context that could be used to direct future experimental and (eventually) clinical work in the field
When Nature Invades: Resident perceptions of the austerity-driven rewilding of an urban park in Rock Island, Illinois
In an era of rapid urbanization, changing climate, and increasing political division, parks represent increasingly important places for urban residents to interact with and feel connected to the natural environment and receive a number of mental and physical health benefits. Unfortunately, in an age of austerity politics, parks and recreation departments in Midwest Rust Belt cities often lack adequate funding to maintain such public spaces. Recently, the business-minded Rock Island, Illinois Department of Parks and Recreation has implemented a creative cost-saving management solution: “naturalizing” sections of its city parks. This interdisciplinary study uses a mixed methods approach to discover how the community members near two representative urban parks in Rock Island perceive this economically motivated accidental “rewilding” of long-manicured and domesticated urban nature. Resident reactions reveal enduring conceptions of a culture-nature divide, as well as the proper, upper class, white ideologies that have historically shaped park construction and use in the United States
Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian
The complete exact solution of the T=1 neutron-proton pairing Hamiltonian is
presented in the context of the SO(5) Richardson-Gaudin model with
non-degenerate single-particle levels and including isospin-symmetry breaking
terms. The power of the method is illustrated with a numerical calculation for
Ge for a model space which is out of reach of modern
shell-model codes.Comment: To be published by Physical Review Letter
Structural characteristics of positionally-disordered lattices: relation to the first sharp diffraction peak in glasses
Positional disorder has been introduced into the atomic structure of certain
crystalline lattices, and the orientationally-averaged structure factor S(k)
and pair-correlation function g(r) of these disordered lattices have been
studied. Analytical expressions for S(k) and g(r) for Gaussian positional
disorder in 2D and 3D are confirmed with precise numerical simulations. These
analytic results also have a bearing on the unsolved Gauss circle problem in
mathematics. As the positional disorder increases, high-k peaks in S(k) are
destroyed first, eventually leaving a single peak, that with the lowest-k
value. The pair-correlation function for lattices with such high levels of
positional disorder exhibits damped oscillations, with a period equal to the
separation between the furthest-separated (lowest-k) lattice planes. The last
surviving peak in S(k) is, for example for silicon and silica, at a wavevector
nearly identical to that of the experimentally-observed first sharp diffraction
peak (FSDP) in the amorphous phases of those materials. Thus, for these
amorphous materials at least, the FSDP can be regarded as arising from
scattering from atomic configurations equivalent to the single family of
positionally-disordered local Bragg planes having the furthest separation.Comment: v2: changes in response to referees' comments: Figure 2 made more
readable, improved discussion of height of peaks in S(k), other minor changes
4 pages, 3 figures, submitted to Physical Review
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