1,187 research outputs found
Advancements in medicine from aerospace research
A program designed to find second applications for space technology in the medical field is described. Illustrative examples and clinical test results are included for prosthetic urethral devices, ear oximeter for monitoring leukemia patients, devices for measuring low level CO effects on automobile drivers, radiation dosimeter probe for detecting radiation levels in cancerous areas, and electromyographic muscle trainer
Comment on "On the negative value of dielectric permittivity of the water surface layer" [Appl. Phys. Lett. 83, 4506 (2003)]
The recent interpretation of the positive resonance frequency shift in
dielectric resonators loaded by water is reviewed. Instead of the invoked
negative dielectric constant of water surface layer, it is demonstrated that
the experimental results are fully reproduced by taking into account the
dielectric losses of the sample.Comment: PDF Acrobat 4.0 file, 2 pages, 2 figures, submitted to Appl. Phys.
Let
A Computer Simulation Model of Waterhyacinth and Weevil Interactions
A personal computer simulation model termed INSECT has been developed to evaluate biological control of waterhyacinth (Eichhornia crassipes (Mart.) Solms.) by two species of weevil (Neochetina eichhorniae Warner, and N. bruchi Hustache). The model results were compared with the data from three different locations. For each data set, the simulated plant biomass, adult and larva populations were plotted aqainst the 95% confidence intervals of the actual field observations. In many cases, the simulation results were within the 95% confidence intervals, and especially during the growing season, they indicated trends similar to those seen in the field data. However, there were discrepancies in both the magnitude and the trend for early and the late periods of the year. These initial results suggest that development of a model to simulate the impact of a biocontrol agent on waterhyacinth populations is a feasible approach to better understand the interactions within this control system
Wide-range optical studies on various single-walled carbon nanotubes: the origin of the low-energy gap
We present wide-range (3 meV - 6 eV) optical studies on freestanding
transparent carbon nanotube films, made from nanotubes with different diameter
distributions. In the far-infrared region, we found a low-energy gap in all
samples investigated. By a detailed analysis we determined the average
diameters of both the semiconducting and metallic species from the near
infrared/visible features of the spectra. Having thus established the
dependence of the gap value on the mean diameter, we find that the frequency of
the low energy gap is increasing with increasing curvature. Our results
strongly support the explanation of the low-frequency feature as arising from a
curvature-induced gap instead of effective medium effects. Comparing our
results with other theoretical and experimental low-energy gap values, we find
that optical measurements yield a systematically lower gap than tunneling
spectroscopy and DFT calculations, the difference increasing with decreasing
diameter. This difference can be assigned to electron-hole interactions.Comment: 9 pages, 8 figures, to be published in Physical Review B,
supplemental material attached v2: Figures 1, 7 and 8 replaced, minor changes
to text; v3: Figures 3, 4 and 5 replaced, minor changes to tex
The electron-boson spectral density function of underdoped BiSrCaCuO and YBaCuO
We investigate the electron-boson spectral density function,
, of CuO plane in underdoped
BiSrCaCuO (Bi-2212) and underdoped
YBaCuO (Y-123) using the Eliashberg formalism. We apply a new
(in-plane) pseudogap model to extract the electron-boson spectral function. For
extracting the spectral function we assume that the spectral density function
consists of two components: a sharp mode and the broad Millis-Monien-Pines
(MMP) mode. We observe that both the resulting spectral density function and
the intensity of the pseudogap show strong temperature dependences: the sharp
mode takes most spectral weight of the function and the peak position of the
sharp mode shifts to lower frequency and the depth of pseudogap,
, is getting deeper as temperature decreases. We observe also
that the total spectral weight of the electron-boson density and the mass
enhancement coefficient increase as temperature decreases. We estimate
fictitious (maximum) superconducting transition temperatures, , from
the extracted spectral functions at various temperatures using a generalized
McMillan formula. The estimated (maximum) also shows a strong temperature
dependence; it is higher than the actual at all measured temperatures and
decreases with temperature lowering. Since as lowering temperature the
pseudogap is getting stronger and the maximum is getting lower we propose
that the pseudogap may suppress the superconductivity in cuprates.Comment: 8 pages, 6 figure
Supermetallic conductivity in bromine-intercalated graphite
Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to
in-plane charge conductivities which increase monotonically with intercalation
time toward values (for ~6 at% Br) that are significantly higher than Cu at
temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic
susceptibility measurements confirm that the Br dopes the graphene sheets with
holes while simultaneously increasing the interplanar separation. The increase
of mobility (~ 5E4 cm^2/Vs at T=300 K) and resistance anisotropy together with
the reduced diamagnetic susceptibility of the intercalated samples suggests
that the observed supermetallic conductivity derives from a parallel
combination of weakly-coupled hole-doped graphene sheets.Comment: 5 pages, 4 figure
Medical Technology Transfer
The Biomedical Applications Team program sponsored by the National Aeronautics and Space Administration is an effective means for transferring aerospace technology to applications in medicine. A conceptual framework for medical technology transfer is presented to describe the transfer process in medicine and to supply a rationale for the Biomedical Applications Team methodology. Examples illustrate medical technology transfer at the material, design, and capacity levels. The roles of donor, recipient, and transfer agent are illustrated and factors essential to the success of medical technology transfer are summarized
Binary continuous random networks
Many properties of disordered materials can be understood by looking at
idealized structural models, in which the strain is as small as is possible in
the absence of long-range order. For covalent amorphous semiconductors and
glasses, such an idealized structural model, the continuous-random network, was
introduced 70 years ago by Zachariasen. In this model, each atom is placed in a
crystal-like local environment, with perfect coordination and chemical
ordering, yet longer-range order is nonexistent. Defects, such as missing or
added bonds, or chemical mismatches, however, are not accounted for. In this
paper we explore under which conditions the idealized CRN model without defects
captures the properties of the material, and under which conditions defects are
an inherent part of the idealized model. We find that the density of defects in
tetrahedral networks does not vary smoothly with variations in the interaction
strengths, but jumps from close-to-zero to a finite density. Consequently, in
certain materials, defects do not play a role except for being thermodynamical
excitations, whereas in others they are a fundamental ingredient of the ideal
structure.Comment: Article in honor of Mike Thorpe's 60th birthday (to appear in J.
Phys: Cond Matt.
Magneto-optical behaviour of EuIn_2P_2
We report results of a magneto-optical investigation of the Zintl-phase
compound EuInP. The compound orders magnetically at =24 K and
exhibits concomitant large magnetoresistance effects. For 50 K and
increasing magnetic fields we observe a transfer of spectral weight in
from energies above 1 eV into the low-energy metallic
component as well as into a mid-infrared signal centered at about 600
cm. This latter absorption is reminiscent to what has been seen in a
large variety of so-called Kondo materials and ascribed to excitations across
the hybridization gap. The observed gain of Drude weight upon increasing
magnetic field suggests an enhancement of the itinerant charge-carrier
concentration due to the increasing magnetization, a phenomenon that was
previously observed in other compounds which exhibit colossal magnetoresistive
effects.Comment: 13 pages, 4 figure
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