3,461 research outputs found
Integrated health monitoring and controls for rocket engines
Current research in intelligent control systems at the Lewis Research Center is described in the context of a functional framework. The framework is applicable to a variety of reusable space propulsion systems for existing and future launch vehicles. It provides a 'road map' technology development to enable enhanced engine performance with increased reliability, durability, and maintainability. The framework hierarchy consists of a mission coordination level, a propulsion system coordination level, and an engine control level. Each level is described in the context of the Space Shuttle Main Engine. The concept of integrating diagnostics with control is discussed within the context of the functional framework. A distributed real time simulation testbed is used to realize and evaluate the functionalities in closed loop
An improved cell-volume analyzer
Design and operation of cell-volume analyzer friction, glaze ice, and studded tire effects on highway
Magnetic reversals in a simple model of MHD
We study a simple magnetohydrodynamical approach in which hydrodynamics and
MHD turbulence are coupled in a shell model, with given dynamo constrains in
the large scales. We consider the case of a low Prandtl number fluid for which
the inertial range of the velocity field is much wider than that of the
magnetic field. Random reversals of the magnetic field are observed and it
shown that the magnetic field has a non trivial evolution linked to the nature
of the hydrodynamics turbulence.Comment: 4 pages, submitted to PR
\u3cem\u3eDe Novo\u3c/em\u3e [PSI\u3csup\u3e+\u3c/sup\u3e] Prion Formation Involves Multiple Pathways to Form Infectious Oligomers
Prion and other neurodegenerative diseases are associated with misfolded protein assemblies called amyloid. Research has begun to uncover common mechanisms underlying transmission of amyloids, yet how amyloids form in vivo is still unclear. Here, we take advantage of the yeast prion, [PSI +], to uncover the early steps of amyloid formation in vivo. [PSI +] is the prion form of the Sup35 protein. While [PSI +] formation is quite rare, the prion can be greatly induced by overexpression of the prion domain of the Sup35 protein. This de novo induction of [PSI +] shows the appearance of fluorescent cytoplasmic rings when the prion domain is fused with GFP. Our current work shows that de novoinduction is more complex than previously thought. Using 4D live cell imaging, we observed that fluorescent structures are formed by four different pathways to yield [PSI +] cells. Biochemical analysis of de novo induced cultures indicates that newly formed SDS resistant oligomers change in size over time and lysates made from de novo induced cultures are able to convert [psi −] cells to [PSI +] cells. Taken together, our findings suggest that newly formed prion oligomers are infectious
Recommended from our members
The relative stabilities of the reverse and normal polarity states of the earth's magnetic field
Recent analyses of the geomagnetic reversal sequence have led to different conclusions regarding the important question of whether there is a discernible difference between the properties of the two polarity states. The main differences between the two most recent studies are the statistical analyses and the possibility of an additional 57 reversal events in the Cenozoic. These additional events occur predominantly during reverse polarity time, but it is unlikely that all of them represent true reversal events. Nevertheless the question of the relative stabilities of the polarity states is examined in detail, both for the case when all 57 "events" are included in the reversal chronology and when they are all excluded. It is found that there is not a discernible difference between the stabilities of the two polarity states in either case. Inclusion of these short events does, however, change the structure of the non-stationarity in reversal rate, but still allows a smooth non-stationarity. Only 7 of the 57 short events are pre-38 Ma, but the evidence suggests that this is a real geomagnetic phenomenon rather than degradation of the magnetic recording or a bias in observation. This could be tested by detailed magnetostratigraphic and oceanic magnetic surveys of the Paleogene and Late Cretaceous. Overall it would appear that the present geomagnetic polarity timescale for 0–160 Ma is probably a very good representation of the actual history, and that different timescales and additional events now represent only changes in detail
Asymmetric polarity reversals, bimodal field distribution, and coherence resonance in a spherically symmetric mean-field dynamo model
Using a mean-field dynamo model with a spherically symmetric helical
turbulence parameter alpha which is dynamically quenched and disturbed by
additional noise, the basic features of geomagnetic polarity reversals are
shown to be generic consequences of the dynamo action in the vicinity of
exceptional points of the spectrum. This simple paradigmatic model yields long
periods of constant polarity which are interrupted by self-accelerating field
decays leading to asymmetric polarity reversals. It shows the recently
discovered bimodal field distribution, and it gives a natural explanation of
the correlation between polarity persistence time and field strength. In
addition, we find typical features of coherence resonance in the dependence of
the persistence time on the noise.Comment: 5 pages, 7 figure
Osteopontin Expression during Early Cerebral Ischemia-Reperfusion in Rats: Enhanced Expression in the Right Cortex Is Suppressed by Acetaminophen
Osteopontin (OPN) is a pleiotropic protein implicated in various inflammatory responses including ischemia-reperfusion (I-R) injury. Two distinct forms of the protein have been identified: an extensively studied secreted form (sOPN) and a less-well-known intracellular form (iOPN). Studies have shown that increased OPN expression parallels the time course of macrophage infiltration into injured tissue, a late event in the development of cerebral infarcts. sOPN has been suggested to promote remodeling of the extracellular matrix in the brain; the function of iOPN may be to facilitate certain signal transduction processes. Here, we studied OPN expression in adult male Sprague-Dawley rats subjected to global forebrain I-R injury. We found iOPN in the cytoplasm of both cortices and the hippocampus, but unexpectedly only the right cortex exhibited a marked increase in the iOPN level after 45 min of reperfusion. Acetaminophen, a drug recently shown to decrease apoptotic incidence, caspase-9 activation, and mitochondrial dysfunction during global I-R, significantly inhibited the increase in iOPN protein in the right cortex, suggesting a role for iOPN in the response to I-R injury in the right cortex
Construction of Parseval wavelets from redundant filter systems
We consider wavelets in L^2(R^d) which have generalized multiresolutions.
This means that the initial resolution subspace V_0 in L^2(R^d) is not singly
generated. As a result, the representation of the integer lattice Z^d
restricted to V_0 has a nontrivial multiplicity function. We show how the
corresponding analysis and synthesis for these wavelets can be understood in
terms of unitary-matrix-valued functions on a torus acting on a certain vector
bundle. Specifically, we show how the wavelet functions on R^d can be
constructed directly from the generalized wavelet filters.Comment: 34 pages, AMS-LaTeX ("amsproc" document class) v2 changes minor typos
in Sections 1 and 4, v3 adds a number of references on GMRA theory and
wavelet multiplicity analysis; v4 adds material on pages 2, 3, 5 and 10, and
two more reference
- …