39,861 research outputs found
Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds
Large-scale homogeneous surveys of Galactic stars may indicate that the
elemental abundance gradient evolves with cosmic time, a phenomenon that was
not foreseen in existing models of Galactic chemical evolution (GCE). If the
phenomenon is confirmed in future studies, we show that this effect, at least
in part, is due to large-scale winds that once enriched the disk. These set up
the steep abundance gradient in the inner disk (R <14 kpc). At the close of the
wind phase, chemical enrichment through accretion of metal-poor material from
the halo onto the disk gradually reduced the metallicity of the inner region,
whereas a slow increase in the metallicity proceeded beyond the solar circle.
Our "wind+infall" model accounts for flattening of the abundance gradient in
the inner disk, in good agreement with observations. Accordingly, we propose
that enrichment by large-scale winds is a crucial factor for chemical evolution
in the disk. We anticipate that rapid flattening of the abundance gradient is
the hallmarks of disk galaxies with significant central bulges.Comment: 9 pages including 5 figures, accepted for publication in PAS
Investigation of the relation between solar variations and weather on earth as shown by study of simultaneous data from the sun, Mariner II, near-earth satellites and the atmosphere below the mesosphere
Relation of solar variations and wind to weather on earth shown by data from sun, Mariner II, ATMOSPHERE, and near-earth satellite
Aerodynamic characteristics of a powered tilt-proprotor wind tunnel model
An investigation was conducted in the Langley V/STOL tunnel to determine the performance, stability and control, and rotor-wake interaction effects of a powered tilt-proprotor aircraft model with gimbal-hub rotors. Tests were conducted at representative flight conditions for hover, helicopter, transition, and airplane flight. Force and moment data were obtained for the complete model and for each of the two rotors. In addition to wind-speed variation, the angle of attack, angle of sideslip, rotor speed, rotor collective pitch, longitudinal cyclic pitch, rotor pylon angle, and configuration geometry were varied. The results, presented in graphical form, are available in tabular form to facilitate the validation of analytical methods of defining the aerodynamic characteristics of tilt-proprotor configurations
Relaxation dynamics of the toric code in contact with a thermal reservoir: Finite-size scaling in a low temperature regime
We present an analysis of the relaxation dynamics of finite-size topological
qubits in contact with a thermal bath. Using a continuous-time Monte Carlo
method, we explicitly compute the low-temperature nonequilibrium dynamics of
the toric code on finite lattices. In contrast to the size-independent bound
predicted for the toric code in the thermodynamic limit, we identify a
low-temperature regime on finite lattices below a size-dependent crossover
temperature with nontrivial finite-size and temperature scaling of the
relaxation time. We demonstrate how this nontrivial finite-size scaling is
governed by the scaling of topologically nontrivial two-dimensional classical
random walks. The transition out of this low-temperature regime defines a
dynamical finite-size crossover temperature that scales inversely with the log
of the system size, in agreement with a crossover temperature defined from
equilibrium properties. We find that both the finite-size and
finite-temperature scaling are stronger in the low-temperature regime than
above the crossover temperature. Since this finite-temperature scaling competes
with the scaling of the robustness to unitary perturbations, this analysis may
elucidate the scaling of memory lifetimes of possible physical realizations of
topological qubits.Comment: 14 Pages, 13 figure
Robust CNOT gates from almost any interaction
There are many cases where the interaction between two qubits is not
precisely known, but single qubit operations are available. In this paper we
show how, regardless of an incomplete knowledge of the strength or form of the
interaction between two qubits, it is often possible to construct a CNOT gate
which has arbitrarily high fidelity. In particular, we show that oscillations
in the strength of the exchange interaction in solid state Si and Ge structures
are correctable.Comment: 5 pages, 2 figure
The Shape of Dark Matter Haloes II. The Galactus HI Modelling & Fitting Tool
We present a new HI modelling tool called \textsc{Galactus}. The program has
been designed to perform automated fits of disc-galaxy models to observations.
It includes a treatment for the self-absorption of the gas. The software has
been released into the public domain. We describe the design philosophy and
inner workings of the program. After this, we model the face-on galaxy NGC2403,
using both self-absorption and optically thin models, showing that
self-absorption occurs even in face-on galaxies. It is shown that the maximum
surface brightness plateaus seen in Paper I of this series are indeed signs of
self-absorption. The apparent HI mass of an edge-on galaxy can be drastically
lower compared to that same galaxy seen face-on. The Tully-Fisher relation is
found to be relatively free from self-absorption issues.Comment: Accepted for publication by Monthly Notices RAS. Hi-res. version
available at www.astro.rug.nl/~vdkruit/Petersetal-II.pd
Radiolysis of Macromolecular Organic Material in Mars-Relevant Mineral Matrices
The fate of organic material on Mars after deposition is crucial to interpreting the source of these molecules. Previous work has addressed how various organic compounds at millimeter depths in sediments respond to ultraviolet radiation. In contrast, this study addressed how highenergy particle radiation (200MeV protons, simulating the effect of galactic cosmic rays and solar wind at depths of <45 cm) inuences organic macromolecules in sediments. Specically, we report the generation of organicacid radiolysis products after exposure to radiation doses equivalent to geological time scales (17 Myr). We found that formate and oxalate were produced from a variety of organic starting materials and mineral matrices. Unlike ultravioletdriven reactions that can invoke Fenton chemistry to produce organic acids, our work suggests that irradiation of semiconductor surfaces, such as TiO2 or possible clay minerals found on Mars, forms oxygen and hydroxyl radical species, which can break down macromolecules into organic acids. We also investigated the metastability of benzoate in multiple mineral matrices. Benzoate was added to samples prior to irradiation and persisted up to 500 kGys of exposure. Our ndings suggest that organic acids are likely a major component of organic material buried at depth on Mars
Project for the analysis of technology transfer Annual report, 1969
Technology utilization of NASA programs and other research and development programs in Federal Government - project analysis results of technology transfe
Project for the analysis of technology transfer Quarterly evaluation report, 1 Jan. - 31 Mar. 1969
Technology transfer analysis project studying nonspace applications of NASA and AEC generated technolog
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