10,477 research outputs found
A Design Strategy for Deadlock-Free Concurrent Systems
When building concurrent systems, it would be useful to have a collection of reusable processes
to perform standard tasks. However, without knowing certain details of the inner workings of
these components, one can never be sure that they will not cause deadlock when connected to
some particular network.
Here we describe a hierarchical method for designing complex networks of communicating
processeswhich are deadlock-free.We use this to define a safe and simple method for specifying
the communication interface to third party software components. This work is presented using
the CSP model of concurrency and the occam2.1 programming language
Deuteron and proton NMR study of D₂, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases
The solutes dideuterium, 1,3,5-trichlorobenzene and p-dichlorobenzene (pdcb) are co-dissolved in a 61/39 wt% mixture of CBC9CB/5CB, a bimesogenic liquid crystal with two nematic phases. NMR spectra are collected for each solute. The local electric field gradient (FZZ) is obtained from the dideuterium spectrum. A double Maier-Saupe potential (MSMS) is used to rationalize the order parameters of pdcb. The liquid-crystal fields G₁ and G₂ are taken to be due to size and shape interactions and interactions between the solute molecular quadrupole and the mean FZZ of the medium. The FZZ’s obtained from D₂ and G₂ (from pdcb) are compared and discussed
A technique for optimal temperature estimation for modeling sunrise/sunset thermal snap disturbance torque
A predictive temperature estimation technique which can be used to drive a model of the Sunrise/Sunset thermal 'snap' disturbance torque experienced by low Earth orbiting spacecraft is described. The twice per orbit impulsive disturbance torque is attributed to vehicle passage in and out of the Earth's shadow cone (umbra), during which large flexible appendages undergo rapidly changing thermal conditions. Flexible members, in particular solar arrays, experience rapid cooling during umbra entrance (Sunset) and rapid heating during exit (Sunrise). The thermal 'snap' phenomena has been observed during normal on-orbit operations of both the LANDSAT-4 satellite and the Communications Technology Satellite (CTS). Thermal 'snap' has also been predicted to be a dominant source of error for the TOPEX satellite. The fundamental equations used to model the Sunrise/Sunset thermal 'snap' disturbance torque for a typical solar array like structure will be described. For this derivation the array is assumed to be a thin, cantilevered beam. The time varying thermal gradient is shown to be the driving force behind predicting the thermal 'snap' disturbance torque and therefore motivates the need for accurate estimates of temperature. The development of a technique to optimally estimate appendage surface temperature is highlighted. The objective analysis method used is structured on the Gauss-Markov Theorem and provides an optimal temperature estimate at a prescribed location given data from a distributed thermal sensor network. The optimally estimated surface temperatures could then be used to compute the thermal gradient across the body. The estimation technique is demonstrated using a typical satellite solar array
NMR study of a bimesogenic liquid crystal with two nematic phases
Recent interest in bimesogenic liquid crystals showing two nematic phases has led us to investigate the nematic mean-field interactions in these nematic phases by using rigid solutes as probes. The nematic potential that is modelled by two independent Maier-Saupe terms is successful in fitting the observed dipolar couplings (order parameters) of para-, meta- and ortho-dichlorobenzene solutes in both the nematic phases of 39 wt% of 4-n-pentyl-4′-cyanobiphenyl (5CB) in α,ω-bis(4-4′-cyanobiphenyl)nonane (CB_C9_CB) to better than the 5% level. The derived liquid-crystal potential parameters G₁ and G₂ for each solute in the N and Ntb phases will be discussed. The most interesting observation is that G1 (associated with size and shape interactions) is almost constant in the Ntb phase, whereas G₂ (associated with longer-range electrostatic interactions) has large variation, even changing sign
Applied regional monitoring of the vernal advancement and retrogradation (Green wave effect) of natural vegetation in the Great Plains corridor
The author has identified the following significant results. LANDSAT 2 has shown that digital data products can be effectively employed on a regional basis to monitor changes in vegetation conditions. The TV16 was successfully applied to an extended test site and the Great Plains Corridor in tests of the ability to assess green forage biomass on rangelands as an index to vegetation condition. A strategy for using TV16 on a regional basis was developed and tested. These studies have shown that: (1) for rangelands with good vegetative cover, such as most of the Great Plains, and which are not heavily infested with brush or undesirable weed species, the LANDSAT digital data can provide a good estimate (within 250 kg/ha) of the quantity of green forage biomass, and (2) at least five levels of pasture and range feed conditions can be adequately mapped for extended regions
Alternative model for the administration and analysis of research-based assessments
Research-based assessments represent a valuable tool for both instructors and
researchers interested in improving undergraduate physics education. However,
the historical model for disseminating and propagating conceptual and
attitudinal assessments developed by the physics education research (PER)
community has not resulted in widespread adoption of these assessments within
the broader community of physics instructors. Within this historical model,
assessment developers create high quality, validated assessments, make them
available for a wide range of instructors to use, and provide minimal (if any)
support to assist with administration or analysis of the results. Here, we
present and discuss an alternative model for assessment dissemination, which is
characterized by centralized data collection and analysis. This model provides
a greater degree of support for both researchers and instructors in order to
more explicitly support adoption of research-based assessments. Specifically,
we describe our experiences developing a centralized, automated system for an
attitudinal assessment we previously created to examine students'
epistemologies and expectations about experimental physics. This system
provides a proof-of-concept that we use to discuss the advantages associated
with centralized administration and data collection for research-based
assessments in PER. We also discuss the challenges that we encountered while
developing, maintaining, and automating this system. Ultimately, we argue that
centralized administration and data collection for standardized assessments is
a viable and potentially advantageous alternative to the default model
characterized by decentralized administration and analysis. Moreover, with the
help of online administration and automation, this model can support the
long-term sustainability of centralized assessment systems.Comment: 7 pages, 1 figure, accepted in Phys. Rev. PE
Contribution of cod liver oil-related nutrients (vitamins A, D, E and eicosapentaenoic acid and docosahexaenoic acid) to daily nutrient intake and their associations with plasma concentrations in the EPIC-Norfolk cohort
Total nutrient intake (TNI) is intake from food and supplements. This provides an assessment of nutrient adequacy and the prevalence of excessive intake, as well as the response with respect to biomarkers. Cod liver oil (CLO) is the most frequently consumed supplement in the UK, containing nutrients that might have varying influences on health. We calculated TNI for vitamins A, D and E, as well as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and assessed associations with the respective blood concentrations
Quality engineering of a traction alternator by robust design
Robust design is an engineering methodology for improving productivity during research and development so that high-quality products can be developed and produced quickly and at low cost. A large electrical company was developing traction alternators for a diesel electrical engine. Customer requirement was to obtain very high efficiency which, in turn, was influenced by several design parameters. The usual approach of the 'design-build-test' cycle was considered time-consuming and costly; it used to take anywhere from 4 months to 1 year before finalizing the product design parameters as it involved physical assembly and also testing. Instead, the authors used Taguchi's parameter design approach. This approach took about 8 weeks to arrive at optimum design parameter values; clearly demonstrating the cutting edge of this methodology over the traditional design-build-test approach. The prototype built and tested accordingly gave satisfactory overall performance, meeting and even exceeding customer requirements
A High-Mass Protobinary System in the Hot Core W3(H2O)
We have observed a high-mass protobinary system in the hot core W3(H2O) with
the BIMA Array. Our continuum maps at wavelengths of 1.4mm and 2.8mm both
achieve sub-arcsecond angular resolutions and show a double-peaked morphology.
The angular separation of the two sources is 1.19" corresponding to 2.43X10^3
AU at the source distance of 2.04 kpc. The flux densities of the two sources at
1.4mm and 2.8mm have a spectral index of 3, translating to an opacity law of
kappa ~ nu. The small spectral indices suggest that grain growth has begun in
the hot core. We have also observed 5 K components of the CH3CN (12-11)
transitions. A radial velocity difference of 2.81 km/s is found towards the two
continuum peaks. Interpreting these two sources as binary components in orbit
about one another, we find a minimum mass of 22 Msun for the system. Radiative
transfer models are constructed to explain both the continuum and methyl
cyanide line observations of each source. Power-law distributions of both
density and temperature are derived. Density distributions close to the
free-fall value, r^-1.5, are found for both components, suggesting continuing
accretion. The derived luminosities suggest the two sources have equivalent
zero-age main sequence (ZAMS) spectral type B0.5 - B0. The nebular masses
derived from the continuum observations are about 5 Msun for source A and 4
Msun for source C. A velocity gradient previously detected may be explained by
unresolved binary rotation with a small velocity difference.Comment: 38 pages, 9 figures, accepted by The Astrophysical Journa
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