1,337 research outputs found
Instrument technology for remote-surface exploration, prospecting and assaying, part 2
The capability to specify new instrument/mechanism technology needs, for effective remote surface exploration, prospecting and assaying (EPA), requires first, an understanding of the functions or major elements of such a task, and second an understanding of the scientific instruments and support mechanisms that may be involved. An analog or task model was developed from which the various functions, operational procedures, scientific instruments, and support mechanisms for an automated mission could be derived. The task model led to the definition of nine major functions or categories of discrete operational elements that may have to be accomplished on a mission of this type. Each major function may stand alone as an element of an EPA mission, but more probably a major function will require the support of other functions, so they are inter-related
Discussion meeting on Gossamer spacecraft (ultralightweight spacecraft)
Concepts, technology, and application of ultralightweight structures in space are examined. Gossamer spacecraft represented a generic class of space vehicles or structures characterized by a low mass per unit area (approximately 50g/m2). Gossamer concepts include the solar sail, the space tether, and various two and three dimensional large lightweight structures that were deployed or assembled in space. The Gossamer Spacecraft had a high potential for use as a transportation device (solar sail), as a science instrument (reflecting or occulting antenna), or as a large structural component for an enclosure, manned platform, or other human habitats. Inflatable structures were one possible building element for large ultralightweight structures in space
Venus - Preliminary science objectives and experiments for use in advanced mission studies
Scientific objectives and supporting experiments for Mariner-type spacecraft missions to Venu
Topological Entanglement of Polymers and Chern-Simons Field Theory
In recent times some interesting field theoretical descriptions of the
statistical mechanics of entangling polymers have been proposed by various
authors. In these approaches, a single test polymer fluctuating in a background
of static polymers or in a lattice of obstacles is considered. The extension to
the case in which the configurations of two or more polymers become non-static
is not straightforward unless their trajectories are severely constrained. In
this paper we present another approach, based on Chern--Simons field theory,
which is able to describe the topological entanglements of two fluctuating
polymers in terms of gauge fields and second quantized replica fields.Comment: 16 pages, corrected some typos, added two new reference
Quantum state preparation in semiconductor dots by adiabatic rapid passage
Preparation of a specific quantum state is a required step for a variety of
proposed practical uses of quantum dynamics. We report an experimental
demonstration of optical quantum state preparation in a semiconductor quantum
dot with electrical readout, which contrasts with earlier work based on Rabi
flopping in that the method is robust with respect to variation in the optical
coupling. We use adiabatic rapid passage, which is capable of inverting single
dots to a specified upper level. We demonstrate that when the pulse power
exceeds a threshold for inversion, the final state is independent of power.
This provides a new tool for preparing quantum states in semiconductor dots and
has a wide range of potential uses.Comment: 4 pages, 4 figure
Mission to a comet - Preliminary scientific objectives and experiments for use in advanced mission studies
Scientific objectives and experiments for comet missio
Venus/Mercury swingby with Venus capsule. Preliminary science objectives and experiments for use in advanced mission studies
Venus/Mercury swingby with Venus capsule - preliminary science objectives and experiments for use in advanced mission studie
Experimental and Theoretical Investigation of Regioselectivity for a Series of Ketoimines with Nuclear Magnetic Resonance Spectroscopy and Density Functional Theory
A series of ketoimines bearing pendant quinolyl substituents were prepared by Schiff base condensation of 1,3-diketones with two different substituents: trifluoromethyl and an alkyl/aryl group (e.g., Me, Et, iPr,tBu, Ph. Synthetic reactions of ketoimines with varying alkyl/aryl substituents altered the distribution of regioisomers as measured in isolated yields and detected by 1H and 19F NMR spectroscopy of crude reaction mixtures. Reaction with the least sterically encumbered diketone (CF3with Me) resulted in mixture of ketoimines with virtually quantitative formation of the ketoimine resulting from quinolyl addition to the carbonyl adjacent to the alkyl substituent. As the steric bulk of the hydrocarbon substituent increased (CF3with Et, iPr, or Ph), a mixture of regioisomers continued, which favored quinolyl addition adjacent to the trifluoromethyl substituent. Only a single ketoimine was isolated or observed with CF3and tBu substituents with quinolyl addition adjacent to CF3. In order to investigate the role of steric and electronic influence of differing alkyl/aryl substitution, Density Functional Theory (DFT) calculation were employed to determine probable transition state structures as well an quantify differences in activation energy between the two regioisomers. Transition state structures were calculated using QST3 calculations verified with IRC calculations at the B3LYP level of theory. Comparisons between DDG‡ determined by DFT agreed well with those calculated experimentally and supported steric driven regioselectivity for the series of ketoimines
Topological interactions in systems of mutually interlinked polymer rings
The topological interaction arising in interlinked polymeric rings such as
DNA catenanes is considered. More specifically, the free energy for a pair of
linked random walk rings is derived where the distance between two segments
each of which is part of a different ring is kept constant. The topology
conservation is imposed by the Gauss invariant. A previous approach (M.Otto,
T.A. Vilgis, Phys.Rev.Lett. {\bf 80}, 881 (1998)) to the problem is refined in
several ways. It is confirmed, that asymptotically, i.e. for large
where is average size of single random walk ring, the effective
topological interaction (free energy) scales .Comment: 16 pages, 3 figur
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