4,353 research outputs found
System data communication structures for active-control transport aircraft, volume 2
The application of communication structures to advanced transport aircraft are addressed. First, a set of avionic functional requirements is established, and a baseline set of avionics equipment is defined that will meet the requirements. Three alternative configurations for this equipment are then identified that represent the evolution toward more dispersed systems. Candidate communication structures are proposed for each system configuration, and these are compared using trade off analyses; these analyses emphasize reliability but also address complexity. Multiplex buses are recognized as the likely near term choice with mesh networks being desirable for advanced, highly dispersed systems
System data communication structures for active-control transport aircraft, volume 1
Candidate data communication techniques are identified, including dedicated links, local buses, broadcast buses, multiplex buses, and mesh networks. The design methodology for mesh networks is then discussed, including network topology and node architecture. Several concepts of power distribution are reviewed, including current limiting and mesh networks for power. The technology issues of packaging, transmission media, and lightning are addressed, and, finally, the analysis tools developed to aid in the communication design process are described. There are special tools to analyze the reliability and connectivity of networks and more general reliability analysis tools for all types of systems
Polymerized alpha-antitrypsin is present on lung vascular endothelium. New insights into the biological significance of alpha-antitrypsin polymerization.
Compressed Data Structures for Dynamic Sequences
We consider the problem of storing a dynamic string over an alphabet
in compressed form. Our representation
supports insertions and deletions of symbols and answers three fundamental
queries: returns the -th symbol in ,
counts how many times a symbol occurs among the
first positions in , and finds the position
where a symbol occurs for the -th time. We present the first
fully-dynamic data structure for arbitrarily large alphabets that achieves
optimal query times for all three operations and supports updates with
worst-case time guarantees. Ours is also the first fully-dynamic data structure
that needs only bits, where is the -th order
entropy and is the string length. Moreover our representation supports
extraction of a substring in optimal time
Deconvolving Instrumental and Intrinsic Broadening in Excited State X-ray Spectroscopies
Intrinsic and experimental mechanisms frequently lead to broadening of
spectral features in excited-state spectroscopies. For example, intrinsic
broadening occurs in x-ray absorption spectroscopy (XAS) measurements of heavy
elements where the core-hole lifetime is very short. On the other hand,
nonresonant x-ray Raman scattering (XRS) and other energy loss measurements are
more limited by instrumental resolution. Here, we demonstrate that the
Richardson-Lucy (RL) iterative algorithm provides a robust method for
deconvolving instrumental and intrinsic resolutions from typical XAS and XRS
data. For the K-edge XAS of Ag, we find nearly complete removal of ~9.3 eV FWHM
broadening from the combined effects of the short core-hole lifetime and
instrumental resolution. We are also able to remove nearly all instrumental
broadening in an XRS measurement of diamond, with the resulting improved
spectrum comparing favorably with prior soft x-ray XAS measurements. We present
a practical methodology for implementing the RL algorithm to these problems,
emphasizing the importance of testing for stability of the deconvolution
process against noise amplification, perturbations in the initial spectra, and
uncertainties in the core-hole lifetime.Comment: 35 pages, 13 figure
Electronic structure and chemical bonding in Ti4SiC3 investigated by soft x-ray emission spectroscopy and first principle theory
The electronic structure in the new transition metal carbide Ti4SiC3 has been
investigated by bulk-sensitive soft x-ray emission spectroscopy and compared to
the well-studied Ti3SiC2 and TiC systems. The measured high-resolution Ti L, C
K and Si L x-ray emission spectra are discussed with ab initio calculations
based on density-functional theory including core-to-valence dipole matrix
elements. The detailed investigations of the Ti-C and Ti-Si chemical bonds
provide increased understanding of the physical properties of these
nanolaminates. A strongly modified spectral shape is detected for the buried Si
monolayers due to Si 3p hybridization with the Ti 3d orbitals. As a result of
relaxation of the crystal structure and the charge-transfer from Ti (and Si) to
C, the strength of the Ti-C covalent bond is increased. The differences between
the electronic and crystal structures of Ti4SiC3 and Ti3SiC2 are discussed in
relation to the number of Si layers per Ti layer in the two systems and the
corresponding change of materials properties.Comment: 12 pages, 7 figures, 1 tabl
A Note on Encodings of Phylogenetic Networks of Bounded Level
Driven by the need for better models that allow one to shed light into the
question how life's diversity has evolved, phylogenetic networks have now
joined phylogenetic trees in the center of phylogenetics research. Like
phylogenetic trees, such networks canonically induce collections of
phylogenetic trees, clusters, and triplets, respectively. Thus it is not
surprising that many network approaches aim to reconstruct a phylogenetic
network from such collections. Related to the well-studied perfect phylogeny
problem, the following question is of fundamental importance in this context:
When does one of the above collections encode (i.e. uniquely describe) the
network that induces it? In this note, we present a complete answer to this
question for the special case of a level-1 (phylogenetic) network by
characterizing those level-1 networks for which an encoding in terms of one (or
equivalently all) of the above collections exists. Given that this type of
network forms the first layer of the rich hierarchy of level-k networks, k a
non-negative integer, it is natural to wonder whether our arguments could be
extended to members of that hierarchy for higher values for k. By giving
examples, we show that this is not the case
Effect of a Cold Margin on Ice Flow at the Terminus of Storglaciaren, Sweden: Implications for Sediment Transfer
The cold-based termini of polythermal glaciers are usually assumed to adhere strongly to an immobile substrate and thereby supply significant resistance to the flow of warm-based ice upglacier. This compressive environment is commonly thought to uplift basal sediment to the surface of the glacier by folding and thrust faulting. We present model and field evidence from the terminus of Storglaciaren, Sweden, showing that the cold margin provides limited resistance to flow from up-glacier. Ice temperatures indicate that basal freezing occurs in this zone at 10−1 –10−2 ma−1, but model results indicate that basal motion at rates greater than 1ma−1 must, nevertheless, persist there for surface and basal velocities to be consistent with measurements. Estimated longitudinal compressive stresses of 20– 25 kPa within the terminus further indicate that basal resistance offered by the cold-based terminus is small. These results indicate that where polythermal glaciers are underlain by unlithified sediments, ice-flow trajectories and sediment transport pathways may be affected by subglacial topography and hydrology more than by the basal thermal regime
Macromolecular properties and end-group analysis of heparin isolated from bovine liver capsule
Rab17, a novel small GTPase, is specific for epithelial cells and is induced during cell polarization
The rab subfamily of small GTPases has been demonstrated to play an important role in the regulation of membrane traffic in eukaryotic cells. Compared with nonpolarized cells, epithelial cells have distinct apical and basolateral transport pathways which need to be separately regulated. This raises the question whether epithelial cells require specific rab proteins. However, all rab proteins identified so far were found to be equally expressed in polarized and nonpolarized cells. Here we report the identification of rab17, the first epithelial cell-specific small GTPase. Northern blot analysis on various mouse organs revealed that the rab17 mRNA is present in kidney, liver, and intestine but not in organs lacking epithelial cells nor in fibroblasts. To determine whether rab17 is specific for epithelial cells we studied its expression in the developing kidney. We found that rab17 is absent from the mesenchymal precursors but is induced upon their differentiation into epithelial cells. In situ hybridization studies on the embryonic kidney and intestine revealed that rab17 is restricted to epithelial cells. By immunofluorescence and immunoelectron microscopy on kidney sections, rab17 was localized to the basolateral plasma membrane and to apical tubules. Rab proteins associated with two distinct compartments have been found to regulate transport between them. Therefore, our data suggest that rab17 might be involved in transcellular transport
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