59,264 research outputs found
NASA ground terminal communication equipment automated fault isolation expert systems
The prototype expert systems are described that diagnose the Distribution and Switching System I and II (DSS1 and DSS2), Statistical Multiplexers (SM), and Multiplexer and Demultiplexer systems (MDM) at the NASA Ground Terminal (NGT). A system level fault isolation expert system monitors the activities of a selected data stream, verifies that the fault exists in the NGT and identifies the faulty equipment. Equipment level fault isolation expert systems are invoked to isolate the fault to a Line Replaceable Unit (LRU) level. Input and sometimes output data stream activities for the equipment are available. The system level fault isolation expert system compares the equipment input and output status for a data stream and performs loopback tests (if necessary) to isolate the faulty equipment. The equipment level fault isolation system utilizes the process of elimination and/or the maintenance personnel's fault isolation experience stored in its knowledge base. The DSS1, DSS2 and SM fault isolation systems, using the knowledge of the current equipment configuration and the equipment circuitry issues a set of test connections according to the predefined rules. The faulty component or board can be identified by the expert system by analyzing the test results. The MDM fault isolation system correlates the failure symptoms with the faulty component based on maintenance personnel experience. The faulty component can be determined by knowing the failure symptoms. The DSS1, DSS2, SM, and MDM equipment simulators are implemented in PASCAL. The DSS1 fault isolation expert system was converted to C language from VP-Expert and integrated into the NGT automation software for offline switch diagnoses. Potentially, the NGT fault isolation algorithms can be used for the DSS1, SM, amd MDM located at Goddard Space Flight Center (GSFC)
Generation of spin current and polarization under dynamic gate control of spin-orbit interaction in low-dimensional semiconductor systems
Based on the Keldysh formalism, the Boltzmann kinetic equation and the drift
diffusion equation have been derived for studying spin polarization flow and
spin accumulation under effect of the time dependent Rashba spin-orbit
interaction in a semiconductor quantum well. The time dependent Rashba
interaction is provided by time dependent electric gates of appropriate shapes.
Several examples of spin manipulation by gates have been considered. Mechanisms
and conditions for obtaining the stationary spin density and the induced
rectified DC spin current are studied.Comment: 10 pages, 3 figures, RevTeX
Strain-Induced Coupling of Spin Current to Nanomechanical Oscillations
We propose a setup which allows to couple the electron spin degree of freedom
to the mechanical motions of a nanomechanical system not involving any of the
ferromagnetic components. The proposed method employs the strain induced
spin-orbit interaction of electrons in narrow gap semiconductors. We have shown
how this method can be used for detection and manipulation of the spin flow
through a suspended rod in a nanomechanical device.Comment: 4 pages, 1 figur
Comparing two financial crises: the case of Hong Kong real estate markets
Hong Kong is no stranger to bubbles or crisis. During the Asian Financial Crisis(AFC), the Hong Kong housing price index drops more than 50% in less than a year. The same market then experiences the Internet Bubble, the SARS attack, and recently the Global Financial Crisis (GFC). This paper attempts to provide some “stylized facts” of the real estate markets and the macroeconomy, and follow the event-study methodology to examine whether the markets behave differently in the AFC and GFC, and discuss the possible linkage to the change in government policies (“learning effect”) and the flow of Chinese consumers and investors to Hong Kong (“China factor”).regime switching, structural change, small open economy, bounded rationality, banking policy
A non-dispersive Raman D-band activated by well-ordered interlayer interactions in rotationally stacked bi-layer Graphene
Raman measurements on monolayer graphene folded back upon itself as an
ordered but skew-stacked bilayer (i.e. with interlayer rotation) presents new
mechanism for Raman scattering in sp2 carbons that arises in systems that lack
coherent AB interlayer stacking. Although the parent monolayer does not exhibit
a D-band, the interior of the skewed bilayer produces a strong two-peak Raman
feature near 1350 cm-1; one of these peaks is non-dispersive, unlike all
previously observed D-band features in sp2 carbons. Within a double-resonant
model of Raman scattering, these unusual features are consistent with a skewed
bilayer coupling, wherein one layer imposes a weak but well-ordered
perturbation on the other. The discrete Fourier structure of the rotated
interlayer interaction potential explains the unusual non-dispersive peak near
1350 cm-1
H2A.Z facilitates access of active and repressive complexes to chromatin in embryonic stem cell self-renewal and differentiation.
SummaryChromatin modifications have been implicated in the self-renewal and differentiation of embryonic stem cells (ESCs). However, the function of histone variant H2A.Z in ESCs remains unclear. We show that H2A.Z is highly enriched at promoters and enhancers and is required for both efficient self-renewal and differentiation of murine ESCs. H2A.Z deposition leads to an abnormal nucleosome structure, decreased nucleosome occupancy, and increased chromatin accessibility. In self-renewing ESCs, knockdown of H2A.Z compromises OCT4 binding to its target genes and leads to decreased binding of MLL complexes to active genes and of PRC2 complex to repressed genes. During differentiation of ESCs, inhibition of H2A.Z also compromises RA-induced RARα binding, activation of differentiation markers, and the repression of pluripotency genes. We propose that H2A.Z mediates such contrasting activities by acting as a general facilitator that generates access for a variety of complexes, both activating and repressive
Magnetic and the magnetocaloric properties of Ce1-xRxFe2 and Ce(Fe1-xMx)2 compounds
We have studied selected rare earth doped and transition metal doped CeFe2
compounds by examining their structural, magnetic and magneto-thermal
properties. With substitution of Ce by 5 and 10% Gd and 10% Ho, the Curie
temperature can be tuned to the range of 267-318 K. Localization of Ce 4f
electronic state with rare earth substitutions is attributed for the
enhancement of Curie temperature. On the other hand, with Ga and Al
substitution at the Fe site, system undergoes paramagnetic to ferromagnetic
transition and then to an antiferromagnetic phase on cooling. The
magnetocaloric effect across the transitions has been studied from both
magnetization isotherms and heat capacity data. It is shown that by choosing
the appropriate dopant and its concentration, the magnetocaloric effect around
room temperature can be tuned.Comment: 13 pages, 6 figures, 2 table
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