1,425 research outputs found
Software-implemented fault insertion: An FTMP example
This report presents a model for fault insertion through software; describes its implementation on a fault-tolerant computer, FTMP; presents a summary of fault detection, identification, and reconfiguration data collected with software-implemented fault insertion; and compares the results to hardware fault insertion data. Experimental results show detection time to be a function of time of insertion and system workload. For the fault detection time, there is no correlation between software-inserted faults and hardware-inserted faults; this is because hardware-inserted faults must manifest as errors before detection, whereas software-inserted faults immediately exercise the error detection mechanisms. In summary, the software-implemented fault insertion is able to be used as an evaluation technique for the fault-handling capabilities of a system in fault detection, identification and recovery. Although the software-inserted faults do not map directly to hardware-inserted faults, experiments show software-implemented fault insertion is capable of emulating hardware fault insertion, with greater ease and automation
Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC
The band structures of 6H and 4H SiC calculated by means of the FP-LMTO
method are used to determine the effective mass tensors for their
conduction-band minima. The results are shown to be consistent with recent
optically detected cyclotron resonance measurements and predict an unusual band
filling dependence for 6H-SiC.Comment: 5 pages including 4 postscript figures incorporated with epsfig figs.
available as part 2: sicfig.uu self-extracting file to appear in Phys. Rev.
B: Aug. 15 (Rapid Communications
Fault-free performance validation of fault-tolerant multiprocessors
A validation methodology for testing the performance of fault-tolerant computer systems was developed and applied to the Fault-Tolerant Multiprocessor (FTMP) at NASA-Langley's AIRLAB facility. This methodology was claimed to be general enough to apply to any ultrareliable computer system. The goal of this research was to extend the validation methodology and to demonstrate the robustness of the validation methodology by its more extensive application to NASA's Fault-Tolerant Multiprocessor System (FTMP) and to the Software Implemented Fault-Tolerance (SIFT) Computer System. Furthermore, the performance of these two multiprocessors was compared by conducting similar experiments. An analysis of the results shows high level language instruction execution times for both SIFT and FTMP were consistent and predictable, with SIFT having greater throughput. At the operating system level, FTMP consumes 60% of the throughput for its real-time dispatcher and 5% on fault-handling tasks. In contrast, SIFT consumes 16% of its throughput for the dispatcher, but consumes 66% in fault-handling software overhead
Raman frequency shift in oxygen functionalized carbon nanotubes
In terms of lattice dynamics theory, we study the vibrational properties of
the oxygen-functionalized single wall carbon nanotubes (O-SWCNs). Due to the
C-O and O-O interactions, many degenerate phonon modes are split and even some
new phonon modes are obtained, different from the bare SWCNs. A distinct Raman
shift is found in both the radial breathing mode and G modes, depending not
only on the tube diameter and chirality but also on oxygen coverage and
adsorption configurations. With the oxygen coverage increasing, interesting, a
nonmonotonic up- and down-shift is observed in G modes, which is contributed to
the competition between the bond expansion and contraction, there coexisting in
the functionalized carbon nanotube.Comment: 4 pages, 3 figures, 1 tabl
Health-related quality of life as a predictor of pediatric healthcare costs: A two-year prospective cohort analysis
BACKGROUND: The objective of this study was to test the primary hypothesis that parent proxy-report of pediatric health-related quality of life (HRQL) would prospectively predict pediatric healthcare costs over a two-year period. The exploratory hypothesis tested anticipated that a relatively small group of children would account for a disproportionately large percent of healthcare costs. METHODS: 317 children (157 girls) ages 2 to 18 years, members of a managed care health plan with prospective payment participated in a two-year prospective longitudinal study. At Time 1, parents reported child HRQL using the Pediatric Quality of Life Inventory™ (PedsQL™ 4.0) Generic Core Scales, and chronic health condition status. Costs, based on health plan utilization claims and encounters, were derived for 6, 12, and 24 months. RESULTS: In multiple linear regression equations, Time 1 parent proxy-reported HRQL prospectively accounted for significant variance in healthcare costs at 6, 12, and 24 months. Adjusted regression models that included both HRQL scores and chronic health condition status accounted for 10.1%, 14.4%, and 21.2% of the variance in healthcare costs at 6, 12, and 24 months. Parent proxy-reported HRQL and chronic health condition status together defined a 'high risk' group, constituting 8.7% of the sample and accounting for 37.4%, 59.2%, and 62% of healthcare costs at 6, 12, and 24 months. The high risk group's per member per month healthcare costs were, on average, 12 times that of other enrollees' at 24 months. CONCLUSIONS: While these findings should be further tested in a larger sample, our data suggest that parent proxy-reported HRQL can be used to prospectively predict healthcare costs. When combined with chronic health condition status, parent proxy-reported HRQL can identify an at risk group of children as candidates for proactive care coordination
Coherent Control for a Two-level System Coupled to Phonons
The interband polarizations induced by two phase-locked pulses in a
semiconductor show strong interference effects depending on the time tau_1
separating the pulses. The four-wave mixing signal diffracted from a third
pulse delayed by tau is coherently controlled by tuning tau_1. The four-wave
mixing response is evaluated exactly for a two-level system coupled to a single
LO phonon. In the weak coupling regime it shows oscillations with the phonon
frequency which turn into sharp peaks at multiples of the phonon period for a
larger coupling strength. Destructive interferences between the two
phase-locked pulses produce a splitting of the phonon peaks into a doublet. For
fixed tau but varying tau_1 the signal shows rapid oscillations at the
interband-transition frequency, whose amplitude exhibits bursts at multiples of
the phonon period.Comment: 4 pages, 4 figures, RevTex, content change
Do bilinguals have different concepts? The case of shape and material in Japanese L2 users of English
An experiment investigated whether Japanese speakers’ categorisation of objects and substances as shape or material is influenced by acquiring English, based on Imai and Gentner (1997). Subjects were presented with an item such as a cork pyramid and asked to choose between two other items that matched it for shape (plastic pyramid) or for material (piece of cork). The hypotheses were that for simple objects the number of shape-based categorisations would increase according to experience of English and that the preference for shape and material-based categorisations of Japanese speakers of English would differ from mono¬lingual speakers of both languages. Subjects were 18 adult Japanese users of English who had lived in English-speaking countries between 6 months and 3 years (short-stay group), and 18 who had lived in English-speaking countries for 3 years or more (long-stay group). Both groups achieved above criterion on an English vocabulary test. Results were: both groups preferred material responses for simple objects and substances but not for complex objects, in line with Japanese mono¬linguals, but the long-stay group showed more shape preference than the short-stay group and also were less different from Americans. These effects of acquiring a second language on categorisation have implications for conceptual representation and methodology
Band gap engineering by functionalization of BN sheet
From first principles calculations, we investigate the stability and physical
properties of single layer h-BN sheet chemically functionalized by various
groups viz. H, F, OH, CH3, CHO, CN, NH2 etc. We find that full
functionalization of h-BN sheet with these groups lead to decrease in its
electronic band gap, albeit to different magnitudes varying from 0.3 eV to 3.1
eV, depending upon the dopant group. Functionalization by CHO group, in
particular, leads to a sharp decrease in the electronic band gap of the
pristine BN sheet to ~ 0.3 eV, which is congenial for its usage in transistor
based devices. The phonon calculations on these sheets show that frequencies
corresponding to all their vibrational modes are real (positive), thereby
suggesting their inherent stability. The chemisorption energies of these groups
to the B and N atoms of the sheet are found to lie in the range of 1.5 -6 eV.Comment: 15 pages, 2 figures PRB(submitted
Spin-dependent resonant tunneling through semimetallic ErAs quantum wells
Resonant tunneling through semimetallic ErAs quantum wells embedded in GaAs
structures with AlAs barriers was recently found to exhibit an intriguing
behavior in magnetic fields which is explained in terms of tunneling selection
rules and the spin-polarized band structure including spin-orbit coupling.Comment: 4 pages, figures supplied as self-unpacking figures.uu, uses
epsfig.sty to incorporate figures in preprin
Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum
This manuscript explores the apparent discrepancy between experimental data
and theoretical calculations of the lattice resistance of bcc tantalum. We
present the first results for the temperature dependence of the Peierls stress
in this system and the first ab initio calculation of the zero-temperature
Peierls stress to employ periodic boundary conditions, which are those best
suited to the study of metallic systems at the electron-structure level. Our ab
initio value for the Peierls stress is over five times larger than current
extrapolations of experimental lattice resistance to zero-temperature. Although
we do find that the common techniques for such extrapolation indeed tend to
underestimate the zero-temperature limit, the amount of the underestimation
which we observe is only 10-20%, leaving open the possibility that mechanisms
other than the simple Peierls stress are important in controlling the process
of low temperature slip.Comment: 12 pages and 9 figure
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