6,602 research outputs found
Casting propellant in rocket engine
A method is described for casting a solid propellant in the casing of a rocket engine having a continuous wall with a single opening which is formed by leaves of a material which melt at a temperature of the propellant and with curved edges concentric to the curvature of the spherical casing. The leaves are inserted into the spherical casing through the opening forming a core having a greater width than the width of the single opening and with curved peripheral edges. The cast propellant forms a solid mass and then heated to melt the leaves and provide a central opening with radial projecting flutes
The Coming Boom in Computer Loads
Computers and other electronic equipment now consume as much electricity as electric steel furnaces, and their growth shows no signs of slowing. Utilities are active participants in the computer revolution. Northeast Utilities, for example, reports that 20% of electricity use in a typical new office building in its service area goes to computers. Given the expected growth in computers and computer loads, this technology deserves greater attention from utility planners and other energy analysts. It is shown that the commercial sector has been the largest contributor to kilowatt-hour (kwh) sales growth and that new uses within the commercial sector have accounted for the biggest portion of this growth. Confirming this conclusion are a 4-year Department of Energy-funded study of the Park Plaza Building office tower and a 1985 study of 181 office buildings by Northwest Utilities. A prospective study suggests that computers could account for as much as 150 billion kwh by the early 1990s
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Pattern-Based Parsing for Word-Sense Disambiguation
In the study of natural language understanding, the reductionist approach has been commonly used by A, I. researchers. Here we develop a technique for parsing based on this approach. W e use a set of semantic primitives to represent word meanings and utilize patterns of sentences for mapping sentences onto meaning structures. To assist the parsing process,w e develop semantic mappings for primitive sentences, semantic transformations for decomposing complex sentences using function word sand axioms that encode world knowledge. W e then explore the application of our approach to the word polysemy problem
Adaptation to implied tilt: extensive spatial extrapolation of orientation gradients
To extract the global structure of an image, the visual system must integrate local orientation estimates across space. Progress is being made toward understanding this integration process, but very little is known about whether the presence of structure exerts a reciprocal influence on local orientation coding. We have previously shown that adaptation to patterns containing circular or radial structure induces tilt-aftereffects (TAEs), even in locations where the adapting pattern was occluded. These spatially “remote” TAEs have novel tuning properties and behave in a manner consistent with adaptation to the local orientation implied by the circular structure (but not physically present) at a given test location. Here, by manipulating the spatial distribution of local elements in noisy circular textures, we demonstrate that remote TAEs are driven by the extrapolation of orientation structure over remarkably large regions of visual space (more than 20°). We further show that these effects are not specific to adapting stimuli with polar orientation structure, but require a gradient of orientation change across space. Our results suggest that mechanisms of visual adaptation exploit orientation gradients to predict the local pattern content of unfilled regions of space
Arterial Elastin as Seen with Scanning Electron Microscopy: A Review
All large arteries contain elastin, collagen, and muscle which can be seen with light microscopy and transmission electron microscopy. Elastin forms an internal elastic lamina (IEL) in all arteries, but also forms multiple fenestrated sheets in the media of the aorta and other large arteries. The fenestrations in the media are larger than those in the IEL. The adventitial elastin is more fibrous and often contains tubular elastin surrounding vasa vasorum when prepared by removing all non-elastin by placing the aorta in 0.1 N NaOH at 70-75°C for five hours. The fenestrations are larger near branches and in an experimentally created poststenotic dilatation. Atherosclerosis appears associated with both new elastin formation in early atherosclerosis and elastolysis in late disease
Kinetic instabilities that limit {\beta} in the edge of a tokamak plasma: a picture of an H-mode pedestal
Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak (MAST)
have sufficient resolution to capture plasma evolution during the short period
between edge-localized modes (ELMs). Immediately after the ELM steep gradients
in pressure, P, and density, ne, form pedestals close to the separatrix, and
they then expand into the core. Local gyrokinetic analysis over the ELM cycle
reveals the dominant microinstabilities at perpendicular wavelengths of the
order of the ion Larmor radius. These are kinetic ballooning modes (KBMs) in
the pedestal and microtearing modes (MTMs) in the core close to the pedestal
top. The evolving growth rate spectra, supported by gyrokinetic analysis using
artificial local equilibrium scans, suggest a new physical picture for the
formation and arrest of this pedestal.Comment: Final version as it appeared in PRL (March 2012). Minor improvements
include: shortened abstract, and better colour table for figures. 4 pages, 6
figure
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Aberrant activity in conceptual networks underlies N400 deficits and unusual thoughts in schizophrenia.
BackgroundThe N400 event-related potential (ERP) is triggered by meaningful stimuli that are incongruous, or unmatched, with their semantic context. Functional magnetic resonance imaging (fMRI) studies have identified brain regions activated by semantic incongruity, but their precise links to the N400 ERP are unclear. In schizophrenia (SZ), N400 amplitude reduction is thought to reflect overly broad associations in semantic networks, but the abnormalities in brain networks underlying deficient N400 remain unknown. We utilized joint independent component analysis (JICA) to link temporal patterns in ERPs to neuroanatomical patterns from fMRI and investigate relationships between N400 amplitude and neuroanatomical activation in SZ patients and healthy controls (HC).MethodsSZ patients (n = 24) and HC participants (n = 25) performed a picture-word matching task, in which words were either matched (APPLE→apple) by preceding pictures, or were unmatched by semantically related (in-category; IC, APPLE→lemon) or unrelated (out of category; OC, APPLE→cow) pictures, in separate ERP and fMRI sessions. A JICA "data fusion" analysis was conducted to identify the fMRI brain regions specifically associated with the ERP N400 component. SZ and HC loading weights were compared and correlations with clinical symptoms were assessed.ResultsJICA identified an ERP-fMRI "fused" component that captured the N400, with loading weights that were reduced in SZ. The JICA map for the IC condition showed peaks of activation in the cingulate, precuneus, bilateral temporal poles and cerebellum, whereas the JICA map from the OC condition was linked primarily to visual cortical activation and the left temporal pole. Among SZ patients, fMRI activity from the IC condition was inversely correlated with unusual thought content.ConclusionsThe neural networks associated with the N400 ERP response to semantic violations depends on conceptual relatedness. These findings are consistent with a distributed network underlying neural responses to semantic incongruity including unimodal visual areas as well as integrative, transmodal areas. Unusual thoughts in SZ may reflect impaired processing in transmodal hub regions such as the precuneus, leading to overly broad semantic associations
Glycogen and its metabolism: some new developments and old themes
Glycogen is a branched polymer of glucose that acts as a store of energy in times of nutritional sufficiency for utilization in times of need. Its metabolism has been the subject of extensive investigation and much is known about its regulation by hormones such as insulin, glucagon and adrenaline (epinephrine). There has been debate over the relative importance of allosteric compared with covalent control of the key biosynthetic enzyme, glycogen synthase, as well as the relative importance of glucose entry into cells compared with glycogen synthase regulation in determining glycogen accumulation. Significant new developments in eukaryotic glycogen metabolism over the last decade or so include: (i) three-dimensional structures of the biosynthetic enzymes glycogenin and glycogen synthase, with associated implications for mechanism and control; (ii) analyses of several genetically engineered mice with altered glycogen metabolism that shed light on the mechanism of control; (iii) greater appreciation of the spatial aspects of glycogen metabolism, including more focus on the lysosomal degradation of glycogen; and (iv) glycogen phosphorylation and advances in the study of Lafora disease, which is emerging as a glycogen storage disease
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