24,539 research outputs found
Controls, Astrophysics, and Structures Experiment in Space (CASES)
As the size and performance requirements of future NASA and DOD spacecrafts and payloads tend to increase, the associated control systems that must effect these requirements tend to interact with the vehicle's structural dynamics. Some of the Control Structure Interaction (CSI) issues are being addressed in a flight experiment which is entitled CASES (Controls, Astrophysics and Structures Experiment in Space). As one of the first CSI flight experiments, the main emphasis for CASES is to provide a test bed for validating CSI developments and simultaneously, to pave the way for subsequent CSI experiments and science missions by establishing precedents for flight qualifying Large Space Structures (LSS)-class spacecraft. In addition, CASES provides an opportunity to obtain data bases for in-space controls and structures experiments and, at the same time, to gather hard x ray data from pertinent galactic sources
Carbocations and the Complex Flavor and Bouquet of Wine: Mechanistic Aspects of Terpene Biosynthesis in Wine Grapes.
Computational chemistry approaches for studying the formation of terpenes/terpenoids in wines are presented, using five particular terpenes/terpenoids (1,8-cineole, α-ylangene, botrydial, rotundone, and the wine lactone), volatile compounds (or their precursors) found in wine and/or wine grapes, as representative examples. Through these examples, we show how modern computational quantum chemistry can be employed as an effective tool for assessing the validity of proposed mechanisms for terpene/terpenoid formation
Fractional Fokker-Planck Equations for Subdiffusion with Space-and-Time-Dependent Forces
We have derived a fractional Fokker-Planck equation for subdiffusion in a
general space-and- time-dependent force field from power law waiting time
continuous time random walks biased by Boltzmann weights. The governing
equation is derived from a generalized master equation and is shown to be
equivalent to a subordinated stochastic Langevin equation.Comment: 5 page
Distributed control using linear momentum exchange devices
MSFC has successfully employed the use of the Vibrational Control of Space Structures (VCOSS) Linear Momentum Exchange Devices (LMEDs), which was an outgrowth of the Air Force Wright Aeronautical Laboratory (AFWAL) program, in a distributed control experiment. The control experiment was conducted in MSFC's Ground Facility for Large Space Structures Control Verification (GF/LSSCV). The GF/LSSCV's test article was well suited for this experiment in that the LMED could be judiciously placed on the ASTROMAST. The LMED placements were such that vibrational mode information could be extracted from the accelerometers on the LMED. The LMED accelerometer information was processed by the control algorithms so that the LMED masses could be accelerated to produce forces which would dampen the vibrational modes of interest. Experimental results are presented showing the LMED's capabilities
Alpha Element Abundances in a Large Sample of Galactic Planetary Nebulae
We present emission line strengths, abundances, and element ratios (X/O for
Ne, S, Cl, and Ar) for a sample of 38 Galactic disk planetary nebulae (PNe)
consisting primarily of Peimbert classification Type I. Spectrophotometry for
these PNe incorporates an extended optical/near-IR range of 3600-9600 angstroms
including the [S III] lines at 9069 and 9532. We have utilized Emission Line
Spectrum Analyzer, a five-level atom abundance routine, to determine T_e, N_e,
ionization correction factors, and total element abundances. With a compilation
of data from >120 Milky Way PNe, we present results from our most recent
analysis of abundance patterns in Galactic disk PNe. We have examined the alpha
elements against H II regions and blue compact galaxies (H2BCG) to discern
signatures of depletion or enhancement in PNe progenitor stars, particularly
the destruction or production of O and Ne. We present evidence that many PNe
have higher Ne/O and lower Ar/Ne ratios compared to H2BCGs within the range of
8.5-9.0 for 12 + log(O/H). This suggests that Ne is being synthesized in the
low- and intermediate-mass progenitors. Sulfur abundances in PNe continue to
show great scatter and are systematically lower than those found in H2BCG at a
given metallicity. Although we find that PNe do show some distinction in alpha
elements when compared to H2BCG, within the Peimbert classification types
studied, PNe do not show significant differences in alpha elements amongst
themselves, at least to an extent that would distinguish in situ
nucleosynthesis from the observed dispersion in abundance ratios.Comment: 12 pages, 18 figures, 7 tables (note: tables 2-5 are available online
only in machine-readable form
Climigration? Population and climate change in Arctic Alaska
Residents of towns and villages in Arctic Alaska live on “the front line of climate change.” Some communities face immediate threats from erosion and flooding associated with thawing permafrost, increasing river flows, and reduced sea ice protection of shorelines. The term climigration, referring to migration caused by climate change, originally was coined for these places. Although initial applications emphasized the need for government relocation policies, it has elsewhere been applied more broadly to encompass unplanned migration as well. Some historical movements have been attributed to climate change, but closer study tends to find multiple causes, making it difficult to quantify the climate contribution. Clearer attribution might come from comparisons of migration rates among places that are similar in most respects, apart from known climatic impacts. We apply this approach using annual 1990–2014 time series on 43 Arctic Alaska towns and villages. Within-community time plots show no indication of enhanced out-migration from the most at-risk communities. More formally, there is no significant difference between net migration rates of at-risk and other places, testing several alternative classifications. Although climigration is not detectable to date, growing risks make either planned or unplanned movements unavoidable in the near future
Computing NodeTrix Representations of Clustered Graphs
NodeTrix representations are a popular way to visualize clustered graphs;
they represent clusters as adjacency matrices and inter-cluster edges as curves
connecting the matrix boundaries. We study the complexity of constructing
NodeTrix representations focusing on planarity testing problems, and we show
several NP-completeness results and some polynomial-time algorithms. Building
on such algorithms we develop a JavaScript library for NodeTrix representations
aimed at reducing the crossings between edges incident to the same matrix.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Oxidation = group theory
Dimensional reduction of theories involving (super-)gravity gives rise to
sigma models on coset spaces of the form G/H, with G a non-compact group, and H
its maximal compact subgroup. The reverse process, called oxidation, is the
reconstruction of the possible higher dimensional theories, given the lower
dimensional theory. In 3 dimensions, all degrees of freedom can be dualized to
scalars. Given the group G for a 3 dimensional sigma model on the coset G/H, we
demonstrate an efficient method for recovering the higher dimensional theories,
essentially by decomposition into subgroups. The equations of motion, Bianchi
identities, Kaluza-Klein modifications and Chern-Simons terms are easily
extracted from the root lattice of the group G. We briefly discuss some aspects
of oxidation from the E_{8(8)}/SO(16) coset, and demonstrate that our formalism
reproduces the Chern-Simons term of 11-d supergravity, knows about the
T-duality of IIA and IIB theory, and easily deals with self-dual tensors, like
the 5-tensor of IIB supergravity.Comment: LaTeX, 8 pages, uses IOP style files; Talk given at the RTN workshop
``The quantum structure of spacetime and the geometric nature of fundamental
interactions'', Leuven, September 200
Evaluation of an advanced directionally solidified gamma/gamma'-alpha Mo eutectic alloy
An attempt was made to improve on the properties of the candidate jet engine turbine blade material AG-60, a gamma/gamma prime-alpha Mo eutectic composite. Alloy 38 (AG-170) was evaluated in the greatest detail. This alloy, Ni-5.88 A1-29.74 Mo-1.65 V-1.2C Re (weight percent), represents an improvement beyond AG-60, based on mechanical testing of the transverse and/or longitudinal orientations over a range of temperatures in tension, shear, rupture, and rupture after thermal exposure. It is likely that other alloys in the study represent a similar improvement
The topology of U-duality (sub-)groups
We discuss the topology of the symmetry groups appearing in compactified
(super-)gravity, and discuss two applications. First, we demonstrate that for 3
dimensional sigma models on a symmetric space G/H with G non-compact and H the
maximal compact subgroup of G, the possibility of oxidation to a higher
dimensional theory can immediately be deduced from the topology of H. Second,
by comparing the actual symmetry groups appearing in maximal supergravities
with the subgroups of SL(32,R) and Spin(32), we argue that these groups cannot
serve as a local symmetry group for M-theory in a formulation of de Wit-Nicolai
type.Comment: 18 pages, LaTeX, 1 figure, 2 table
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