343 research outputs found
X ray imaging microscope for cancer research
The NASA technology employed during the Stanford MSFC LLNL Rocket X Ray Spectroheliograph flight established that doubly reflecting, normal incidence multilayer optics can be designed, fabricated, and used for high resolution x ray imaging of the Sun. Technology developed as part of the MSFC X Ray Microscope program, showed that high quality, high resolution multilayer x ray imaging microscopes are feasible. Using technology developed at Stanford University and at the DOE Lawrence Livermore National Laboratory (LLNL), Troy W. Barbee, Jr. has fabricated multilayer coatings with near theoretical reflectivities and perfect bandpass matching for a new rocket borne solar observatory, the Multi-Spectral Solar Telescope Array (MSSTA). Advanced Flow Polishing has provided multilayer mirror substrates with sub-angstrom (rms) smoothnesss for the astronomical x ray telescopes and x ray microscopes. The combination of these important technological advancements has paved the way for the development of a Water Window Imaging X Ray Microscope for cancer research
Methodology and Results of the Near-Earth Object (NEO) Human Space Flight (HSF) Accessible Targets Study (NHATS)
Near-Earth Asteroids (NEAs) have been identified by the Administration as potential destinations for human explorers during the mid-2020s. Planning such ambitious missions requires selecting potentially accessible targets from the growing known population of 8,008 NEAs. NASA is therefore conducting the Near-Earth Object (NEO) Human Space Flight (HSF) Accessible Targets Study (NHATS), in which the trajectory opportunities to all known NEAs are being systematically evaluated with respect to a set of defined constraints. While the NHATS algorithms have identified hundreds of NEAs which satisfy purposely inclusive trajectory constraints, only a handful of them offer truly attractive mission opportunities in the time frame of greatest interest. In this paper we will describe the structure of the NHATS algorithms and the constraints utilized in the study, present current study results, and discuss various mission design considerations for future human space flight missions to NEAs
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Application of Soft X-Ray Lasers for Probing High Density Plasmas
The reliability and characteristics of collisionally pumped soft x-ray lasers make them ideal for a wide variety of plasma diagnostics. These systems now operate over a wavelength range extending from 35 to 400 {Angstrom} and have output energies as high as 10 mJ in 150 ps pulses. The beam divergence of these lasers is less than 15 mrad and they have a typical linewidth of {Delta}{lambda}/{lambda} {approximately} 10{sup -4} making them the brightest xuv sources available. In this paper we will describe the use of x-ray lasers to probe high density plasmas using a variety of diagnostic techniques. Using an x-ray laser and a multilayer mirror imaging system we have studied hydrodynamic imprinting of laser speckle pattern on directly driven thin foils with 1-2 {mu}m spatial resolution. Taking advantage of recently developed multilayer beamsplitters we have constructed and used a Mach-Zehnder interferometer operating at 155 {Angstrom} to probe 1-3 mm size laser produced plasmas with peak electron densities of 4 x 10{sup 21} cm{sup -3}. A comparison of our results with computer simulations will be presented
Observation and Modeling of the Solar Transition Region: II. Solutions of the Quasi-Static Loop Model
In the present work we undertake a study of the quasi-static loop model and
the observational consequences of the various solutions found. We obtain the
most general solutions consistent with certain initial conditions. Great care
is exercised in choosing these conditions to be physically plausible (motivated
by observations). We show that the assumptions of previous quasi-static loop
models, such as the models of Rosner, Tucker and Vaiana (1978) and Veseckey,
Antiochos and Underwood (1979), are not necessarily valid for small loops at
transition region temperatures. We find three general classes of solutions for
the quasi-static loop model, which we denote, radiation dominated loops,
conduction dominated loops and classical loops. These solutions are then
compared with observations. Departures from the classical scaling law of RTV
are found for the solutions obtained. It is shown that loops of the type that
we model here can make a significant contribution to lower transition region
emission via thermal conduction from the upper transition region.Comment: 30 pages, 3 figures, Submitted to ApJ, Microsoft Word File 6.0/9
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Reconstruction of Quasi-Monochromatic Images for Multispectral X-ray Imaging with a Pinhole Array and a Flat Bragg Mirror
We have developed a software package for reconstruction of quasi-monochromatic images from a multiple monochromatic x-ray imager for inertial confinement fusion implosions. The instrument consists of a pinhole array, a multi-layer Bragg mirror, and a image detector. The pinhole array projects hundreds of images onto the detector after reflection off the multi-layer Bragg mirror, which introduces spectral dispersion along the reflection axis. The quasi-monochromatic images of line emissions and continuum emissions can be used for measurement of temperature and density maps of implosion plasmas. In this paper, we describe a computer-aided processing technique for systematic reconstruction of quasi-monochromatic images from raw data. This technique provides flexible spectral bandwidth selection, and allows systematic subtraction of continuum emission from line emission images
High-Pressure Amorphous Nitrogen
The phase diagram and stability limits of diatomic solid nitrogen have been
explored in a wide pressure--temperature range by several optical spectroscopic
techniques. A newly characterized narrow-gap semiconducting phase has
been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational
and optical properties of the phase produced under these conditions
indicate that it is largely amorphous and back transforms to a new molecular
phase. The band gap of the phase is found to decrease with pressure
indicating possible metallization by band overlap above 280 GPa.Comment: 5 pages, 4 figure
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Multilayer Thin Film Thermoelectrics Produced by Sputtering
In this work we explore the possibility of achieving bulk electrical properties in single layer sputter deposited films grown epitaxially on (111) oriented BaF{sub 2} substrates. There are a number of sputter deposition parameters that can be varied in order to optimize the film quality. It is important to understand the effect of varying the deposition temperature, Ar sputtering gas pressure, and the substrate bias. We will consider only Bi and Bi{sub 0.86}Sb{sub 0.14} films in this paper. These materials were chosen since they have the same simple structure, two different band gaps and do not change significantly either in physical or electrical properties with small amounts of cross contamination. We will also present our work on multilayer thermoelectrics made of Bi and Bi{sub 0.86}Sb{sub 0.14} layers. There has been considerable interest in this multilayer structure in the literature. Theoretical calculations of the band structure and interface states of these multilayer structures have been made by Mustafaev and Agassi et al. respectively [6,7]. Experimentally Yoshida et al. have examined similar multilayer structures grown by MBE as well as Bi/Sb multilayer samples in which report an anomalous thermoelectric power [8]
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Multilayer Thermoelectric Films: A Strategy for the Enhancement of Zt
The relative efficiency of a thermoelectric material is measured in terms of a dimensionless figure of merit, ZT. Although all known thermoelectric materials are believed to have ZT {le} 1, recent theoretical results predict that thermoelectric devices fabricated as two-dimensional quantum wells (2D QWs) could have ZT {ge} 3. Multilayers with the dimensions of 2D QWs have been synthesized by alternately sputtering Bi{sub 0.9}Sb{sub 0.1} and PbTe{sub 0.8}Se{sub 0.2} onto a moving substrate from a pair of magnetron sources. These materials have been synthesized to test the thermoelectric quantum-well concept and gain insight into relevant transport mechanisms. This work focuses primarily on the scientific issues involved in producing the materials necessary to examine the possibility of enhancing ZT using quantum confinement. The techniques needed to measure the relevant electrical parameters of thermoelectric thin films are developed in this paper. Ultimately, if a quantum well enhancement of thermoelectrics is experimentally observed, devices based on this technology could be used to greatly expand the role of thermoelectrics in power generation and refrigeration
The Mission Accessibility of Near-Earth Asteroids
The population of near-Earth asteroids (NEAs) that may be accessible for human space flight missions is defined by the Near-Earth Object Human Space Flight Accessible Targets Study (NHATS). The NHATS is an automated system designed to monitor the accessibility of, and particular mission opportunities offered by, the NEA population. This is analogous to systems that automatically monitor the impact risk posed to Earth by the NEA population. The NHATS system identifies NEAs that are potentially accessible for future round-trip human space flight missions and provides rapid notification to asteroid observers so that crucial follow-up observations can be obtained following discovery of accessible NEAs. The NHATS was developed in 2010 and was automated by early 2012. NHATS data are provided via an interactive web-site, and daily NHATS notification emails are transmitted to a mailing list; both resources are available to the public
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