1,197 research outputs found
Modern mechanisms make manless Martian mission mobile: Spin-off spells stairclimbing self-sufficiency for earthbound handicapped
Concepts were developed for three wheel chairs from progressively improving designs of a proposed unmanned roving vehicle for the surface exploration of Mars; as a spin-off, a concept for a stair-climbing wheel chair was generated. The mechanisms employed in these are described. The Mars mission is envisioned using the booster rockets and aeroshell of the Viking missions
Electronic properties of ion-implanted yttria-stabilized zirconia
Ion implantation of iron and titanium has been applied to modify the surface properties of polycrystalline yttria-stabilized zirconia ((ZrO2)0.87(YO1.5)0.13 (YSZ)) discs in an attempt to prepare surfaces with a mixed conductivity and by this an enhanced surface oxygen exchange kinetics. Surface-sensitive spectroscopic techniques were applied to investigate the implanted layers as a function of different pretreatments such as oxidation, reduction and annealing. Depth profiles were recorded by Rutherford Backscattering Spectroscopy (RBS) and X-ray Photoelectron Spectroscopy (XPS) in combination with sputtering. Ion Scattering Spectroscopy (ISS) and XPS were used to investigate the surface composition and valency of implanted ions. Electronic properties like the band gap, the work function and the energy difference between the Fermi level and valence band edge (EF-EV) were obtained from Ultraviolet Photoelectron Spectroscopy (UPS) and Electron Energy Loss Spectroscopy (EELS). Overlayers of Fe2O3 or TiO2 are formed during oxidation of as-implanted samples. The Fe- and Ti-oxides could be reduced in hydrogen to the oxidation states Fe2+, Fe0 or Ti3+. Annealing of the samples leads to decreased surface concentrations of the implanted ions due to in-diffusion. At the surface of the annealed iron-implanted samples, Fe2+ and metallic Fe could be generated after further reduction whereas at the surface of the annealed Ti-implanted samples only Ti4+ was detectable.\u
Charter School Funding: Inequity’s Next Frontier
Of all the controversies swirling around the nation’s charter schools, none is more hotly contested than the debate over funding. Charter opponents charge that] these autonomous public schools are draining scarce resources from public school districts. Proponents, by contrast, complain that charter schools do not get their fair share of public education dollars
Multiplexed readout of kinetic inductance bolometer arrays
Kinetic inductance bolometer (KIB) technology is a candidate for passive
sub-millimeter wave and terahertz imaging systems. Its benefits include
scalability into large 2D arrays and operation with intermediate cryogenics in
the temperature range of 5 -- 10 K. We have previously demonstrated the
scalability in terms of device fabrication, optics integration, and cryogenics.
In this article, we address the last missing ingredient, the readout. The
concept, serial addressed frequency excitation (SAFE), is an alternative to
full frequency-division multiplexing at microwave frequencies conventionally
used to read out kinetic inductance detectors. We introduce the concept, and
analyze the criteria of the multiplexed readout avoiding the degradation of the
signal-to-noise ratio in the presence of a thermal anti-alias filter inherent
to thermal detectors. We present a practical scalable realization of a readout
system integrated into a prototype imager with 8712 detectors. This is used for
demonstrating the noise properties of the readout. Furthermore, we present
practical detection experiments with a stand-off laboratory-scale imager.Comment: 7 pages, 6 figure
A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. I. Testing Validity of Rate Equations in Molecular Clouds
In this study we demonstrate for the first time that the unified Monte Carlo
approach can be applied to model gas-grain chemistry in large reaction
networks. Specifically, we build a time-dependent gas-grain chemical model of
the interstellar medium, involving about 6000 gas-phase and 200 grain surface
reactions. This model is used to test the validity of the standard and modified
rate equation methods in models of dense and translucent molecular clouds and
to specify under which conditions the use of the stochastic approach is
desirable.
We found that at temperatures 25--30 K gas-phase abundances of HO,
NH, CO and many other gas-phase and surface species in the stochastic model
differ from those in the deterministic models by more than an order of
magnitude, at least, when tunneling is accounted for and/or diffusion energies
are 3x lower than the binding energies. In this case, surface reactions,
involving light species, proceed faster than accretion of the same species. In
contrast, in the model without tunneling and with high binding energies, when
the typical timescale of a surface recombination is greater than the timescale
of accretion onto the grain, we obtain almost perfect agreement between results
of Monte Carlo and deterministic calculations in the same temperature range. At
lower temperatures ( K) gaseous and, in particular, surface abundances
of most important molecules are not much affected by stochastic processes.Comment: 33 pages, 9 figures, 1 table. Accepted for publication in Ap
Single flux quantum circuits with damping based on dissipative transmission lines
We propose and demonstrate the functioning of a special Rapid Single Flux
Quantum (RSFQ) circuit with frequency-dependent damping. This damping is
achieved by shunting individual Josephson junctions by pieces of open-ended RC
transmission lines. Our circuit includes a toggle flip-flop cell, Josephson
transmission lines transferring single flux quantum pulses to and from this
cell, as well as DC/SFQ and SFQ/DC converters. Due to the desired
frequency-dispersion in the RC line shunts which ensures sufficiently low noise
at low frequencies, such circuits are well-suited for integrating with the
flux/phase Josephson qubit and enable its efficient control.Comment: 6 pages incl. 6 figure
Vluchten in bureaucratie: bureaucratische gehechtheid onder professionals in de jeugdhulpverlening
Characterization of the Ho Electron Capture Spectrum: A Step Towards the Electron Neutrino Mass Determination
The isotope Ho is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to Dy with an energy available to the decay, Q, of about 2.8 keV. According to the present knowledge, this is the lowest Q value for such transitions. Here we discuss a newly obtained spectrum of Ho, taken by cryogenic metallic magnetic calorimeters with Ho implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the Dy daughter atom following the capture of electrons from the 5s shell in Ho, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48 eV. In addition, a precise determination of the energy available for the decay Q=(2.858±0.010±0.05)  keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between Ho and Dy obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique
Elevated left and reduced right orbitomedial prefrontal fractional anisotropy in adults with bipolar disorder revealed by tract-based spatial statistics
Context - Diffusion tensor imaging (DTI) studies in adults with bipolar disorder (BD) indicate altered white matter (WM) in the orbitomedial prefrontal cortex (OMPFC), potentially underlying abnormal prefrontal corticolimbic connectivity and mood dysregulation in BD. Objective - To use tract-based spatial statistics (TBSS) to examine WM skeleton (ie, the most compact whole-brain WM) in subjects with BD vs healthy control subjects. Design - Cross-sectional, case-control, whole-brain DTI using TBSS. Setting - University research institute. Participants - Fifty-six individuals, 31 having a DSM-IV diagnosis of BD type I (mean age, 35.9 years [age range, 24-52 years]) and 25 controls (mean age, 29.5 years [age range, 19-52 years]). Main Outcome Measures - Fractional anisotropy (FA) longitudinal and radial diffusivities in subjects with BD vs controls (covarying for age) and their relationships with clinical and demographic variables. Results - Subjects with BD vs controls had significantly greater FA (t > 3.0, P = .05 corrected) in the left uncinate fasciculus (reduced radial diffusivity distally and increased longitudinal diffusivity centrally), left optic radiation (increased longitudinal diffusivity), and right anterothalamic radiation (no significant diffusivity change). Subjects with BD vs controls had significantly reduced FA (t > 3.0, P = .05 corrected) in the right uncinate fasciculus (greater radial diffusivity). Among subjects with BD, significant negative correlations (P < .01) were found between age and FA in bilateral uncinate fasciculi and in the right anterothalamic radiation, as well as between medication load and FA in the left optic radiation. Decreased FA (P < .01) was observed in the left optic radiation and in the right anterothalamic radiation among subjects with BD taking vs those not taking mood stabilizers, as well as in the left optic radiation among depressed vs remitted subjects with BD. Subjects having BD with vs without lifetime alcohol or other drug abuse had significantly decreased FA in the left uncinate fasciculus. Conclusions - To our knowledge, this is the first study to use TBSS to examine WM in subjects with BD. Subjects with BD vs controls showed greater WM FA in the left OMPFC that diminished with age and with alcohol or other drug abuse, as well as reduced WM FA in the right OMPFC. Mood stabilizers and depressed episode reduced WM FA in left-sided sensory visual processing regions among subjects with BD. Abnormal right vs left asymmetry in FA in OMPFC WM among subjects with BD, likely reflecting increased proportions of left-sided longitudinally aligned and right-sided obliquely aligned myelinated fibers, may represent a biologic mechanism for mood dysregulation in BD
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