1,078 research outputs found
Precision Pointing Control System (PPCS) system design and analysis
The precision pointing control system (PPCS) is an integrated system for precision attitude determination and orientation of gimbaled experiment platforms. The PPCS concept configures the system to perform orientation of up to six independent gimbaled experiment platforms to design goal accuracy of 0.001 degrees, and to operate in conjunction with a three-axis stabilized earth-oriented spacecraft in orbits ranging from low altitude (200-2500 n.m., sun synchronous) to 24 hour geosynchronous, with a design goal life of 3 to 5 years. The system comprises two complementary functions: (1) attitude determination where the attitude of a defined set of body-fixed reference axes is determined relative to a known set of reference axes fixed in inertial space; and (2) pointing control where gimbal orientation is controlled, open-loop (without use of payload error/feedback) with respect to a defined set of body-fixed reference axes to produce pointing to a desired target
Control landscapes for two-level open quantum systems
A quantum control landscape is defined as the physical objective as a
function of the control variables. In this paper the control landscapes for
two-level open quantum systems, whose evolution is described by general
completely positive trace preserving maps (i.e., Kraus maps), are investigated
in details. The objective function, which is the expectation value of a target
system operator, is defined on the Stiefel manifold representing the space of
Kraus maps. Three practically important properties of the objective function
are found: (a) the absence of local maxima or minima (i.e., false traps); (b)
the existence of multi-dimensional sub-manifolds of optimal solutions
corresponding to the global maximum and minimum; and (c) the connectivity of
each level set. All of the critical values and their associated critical
sub-manifolds are explicitly found for any initial system state. Away from the
absolute extrema there are no local maxima or minima, and only saddles may
exist, whose number and the explicit structure of the corresponding critical
sub-manifolds are determined by the initial system state. There are no saddles
for pure initial states, one saddle for a completely mixed initial state, and
two saddles for other initial states. In general, the landscape analysis of
critical points and optimal manifolds is relevant to the problem of explaining
the relative ease of obtaining good optimal control outcomes in the laboratory,
even in the presence of the environment.Comment: Minor editing and some references adde
The Map is Not Which Territory?: Speculating on the Geo-Spatial Diffusion of Ideas in the Arab Spring of 2011
The process by which social movements move through time and space can be understood as a process of innovation diffusion of memes or ideas. This process of diffusion may be traceable through computational linguistics and map geocoding of the linguistic memes employed by such movements. A Visualizing Information Space In Ontological Networks (VISION) method is described and illustrated with web-based search results of keywords relevant to Arab Spring. Using map algebra, and with the potential for using computational linguistics, the intent is to demonstrate the feasibility of both the theoretical model of diffusion, as well as the relevance of the geospatial dimension in understanding another dimension of diffusionâthe meaning space of ideas as they spread through new media. Such methodology holds substantial promise for understanding the communicative dynamics of social movements and social influence
A Nonabelian Yang-Mills Analogue of Classical Electromagnetic Duality
The classic question of a nonabelian Yang-Mills analogue to electromagnetic
duality is here examined in a minimalist fashion at the strictly 4-dimensional,
classical field and point charge level. A generalisation of the abelian Hodge
star duality is found which, though not yet known to give dual symmetry,
reproduces analogues to many dual properties of the abelian theory. For
example, there is a dual potential, but it is a 2-indexed tensor
of the Freedman-Townsend type. Though not itself functioning as such,
gives rise to a dual parallel transport, , for the
phase of the wave function of the colour magnetic charge, this last being a
monopole of the Yang-Mills field but a source of the dual field. The standard
colour (electric) charge itself is found to be a monopole of .
At the same time, the gauge symmetry is found doubled from say to
. A novel feature is that all equations of motion,
including the standard Yang-Mills and Wong equations, are here derived from a
`universal' principle, namely the Wu-Yang (1976) criterion for monopoles, where
interactions arise purely as a consequence of the topological definition of the
monopole charge. The technique used is the loop space formulation of Polyakov
(1980).Comment: We regret that, due to a technical hitch, parts of the reference list
were mixed up. This is the corrected version. We apologize to the authors
whose papers were misquote
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Overview of the results of the organics PET Study of the cometary samples returned from comet Wild 2 by the Stardust mission
This presenation will provide an overview of the efforts and results produced by the Organics Preliminary Examination Team during their studies of the samples returned from comet Wild 2 by the Stardust spacecraft
Cognitive impairment induced by delta9-tetrahydrocannabinol occurs through heteromers between cannabinoid CB1 and serotonin 5-HT2A receptors
Delta-9-tetrahydrocannabinol (THC), the main psychoactive compound of marijuana, induces numerous undesirable effects, including memory impairments, anxiety, and dependence. Conversely, THC also has potentially therapeutic effects, including analgesia, muscle relaxation, and neuroprotection. However, the mechanisms that dissociate these responses are still not known. Using mice lacking the serotonin receptor 5-HT2A, we revealed that the analgesic and amnesic effects of THC are independent of each other: while amnesia induced by THC disappears in the mutant mice, THC can still promote analgesia in these animals. In subsequent molecular studies, we showed that in specific brain regions involved in memory formation, the receptors for THC and the 5-HT2A receptors work together by physically interacting with each other. Experimentally interfering with this interaction prevented the memory deficits induced by THC, but not its analgesic properties. Our results highlight a novel mechanism by which the beneficial analgesic properties of THC can be dissociated from its cognitive side effects
Implementable Strategies and Exploratory Considerations to Reduce Costs Associated with Anti-TNF Therapy in Inflammatory Bowel Disease:
A health care system is needed where care is based on the best available evidence and is delivered reliably, efficiently, and less expensively (best care at lower cost). In gastroenterology, anti-tumor necrosis factor (anti-TNF) agents represent the most effective medical therapeutic option for patients with moderate-to-severe inflammatory bowel disease (IBD), but are very expensive and account for nearly a quarter of the cost of IBD care, representing a major area of present and future impact in direct health care costs. The ImproveCareNow Network, consisting of over 55 pediatric IBD centers, seeks ways to improve the value of care in IBD â curtailing unnecessary costs and promoting better health outcomes through systematic and incremental quality improvement initiatives. This report summarizes the key evidence to facilitate the cost-effective use of anti-TNF agents for patients with IBD. Our review outlines the scientific rationale for initiating cost-reducing measures in anti-TNF use and focuses on three implementable strategies and four exploratory considerations through practical clinical guidelines, as supported by existing evidence. Implementable strategies can be readily integrated into todayâs daily practice, while exploratory considerations can guide research to support future implementation
Control of daughter centriole formation by the pericentriolar material
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Cell Biology 10 (2008): 322-328, doi:10.1038/ncb1694.Controlling the number of its centrioles is vital for the cell as supernumerary
centrioles result in multipolar mitosis and genomic instability. Normally, just one
daughter centriole forms on each mature (mother) centriole; however, a mother
centriole can produce multiple daughters within a single cell cycle. The
mechanisms that prevent centriole âoverduplicationâ are poorly understood. Here we
use laser microsurgery to test the hypothesis that attachment of the daughter
centriole to the wall of the mother inhibits formation of additional daughters. We
show that physical removal of the daughter induces reduplication of the mother in Sarrested
cells. Under conditions when multiple daughters simultaneously form on a
single mother, all of these daughters must be removed to induce reduplication.
Intriguingly, the number of daughter centrioles that form during reduplication does
not always match the number of ablated daughter centrioles. We also find that
exaggeration of the pericentriolar material (PCM) via overexpression of the PCM
protein pericentrin in S-arrested CHO cells induces formation of numerous daughter
centrioles. We propose that that the size of the PCM cloud associated with the
mother centriole restricts the number of daughters that can form simultaneously.This work was supported
by grants from the National Institutes of Health (GM GM59363) and the Human Frontiers
Science Program (RGP0064). Construction of our laser microsurgery workstation was
supported in part by a fellowship from Nikon/Marine Biological Laboratory (A.K.)
âDoggedâ Search of Fresh Nakhla Surfaces Reveals New Alteration Textures
Special Issue: 74th Annual Meeting of the Meteoritical Society, August 8-12, 2011, London, U.K.International audienceCarbonaceous chondrites are considered as amongst the most primitive Solar System samples available. One of their primitive characteristics is their enrichment in volatile elements.This includes hydrogen, which is present in hydrated and hydroxylated minerals. More precisely, the mineralogy is expected to be dominated by phyllosilicates in the case of CM chondrites, and by Montmorillonite type clays in the case of CI. Here, in order to characterize and quantify the abundance of lowtemperature minerals in carbonaceous chondrites, we performed thermogravimetric analysis of matrix fragments of Tagish Lake, Murchison and Orgueil
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