2,762 research outputs found
Modeling heat transfer from quench protection heaters to superconducting cables in Nb3Sn magnets
We use a recently developed quench protection heater modeling tool for an
analysis of heater delays in superconducting high-field Nb3Sn accelerator
magnets. The results suggest that the calculated delays are consistent with
experimental data, and show how the heater delay depends on the main heater
design parameters.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet,
Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva,
Switzerlan
Active Aging: Motives and Barriers
Both the successful aging and productive aging literatures attach great importance to activity. In the successful aging paradigm, activity contributes positively to both physical health and psychological well being. In the productive aging paradigm, older people make contributions to society through certain types of activities, notably gainful employment, community service volunteering, informal assistance usually within their families, and political participation.
Less attention has been given to the relationships among various forms of productive activity. Various forms of activity may be complementary or competitive. In other words, participation in one form of productive activity may open doors to other forms of productive activity. On the other hand, under some circumstances participation in one form of activity because of its time demands may tend to crowd out participation in other activities. From the healthy aging perspective, questions can be asked about the implications of type of activity for well being. Does one form of activity readily substitute for another? In other words, do all kinds of activity contribute equally to well being? Does variety in activity matter? In other words, do elders maximize their well being when they engage in a variety of forms of activity
Measuring the Contributions of Motives and Perceived Barriers to Active Aging
General motivation to be active and general perceived barriers to activity may help to explain the overall activity patterns of older persons in the second half of the life course. We report on a project designed to develop and refine measures of motivation and perceived barriers that can be used to examine the relationships between activity motivation, activity barriers, and several forms of actual activities. Four specific activities were considered: working, volunteering, exercising, and taking classes. An opportunity sample of 192 middle-aged and older persons from eastern Massachusetts responded to a questionnaire concerned with motivation, perceived barriers, and activities. Reliable measures of both general and activity-specific motivation and perceived barriers to activity were developed. The measures were examined for construct validity purposes. This analysis demonstrates that general activity motivation and perceived barriers are helpful in understanding patterns of activity among older people
Elder Activities: Patterns, Motives, and Interpretation. Massachusetts Lifestyles Study III
We are engaged in a continuing effort to understand the scope of elder activity and the implications of activity for well-being. We are particularly interested in the forces that encourage or inhibit multiple forms of activity, the ways in which participation in some activities influences participation in other activities, and the cumulative implications of activities for well being. Our interest in multiple forms of activities sets us somewhat apart from Gerontologists who focus on single forms of activity such as volunteering, taking classes, caring for grandchildren, working, or exercising
Rewriting Logic Semantics of a Plan Execution Language
The Plan Execution Interchange Language (PLEXIL) is a synchronous language
developed by NASA to support autonomous spacecraft operations. In this paper,
we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance
logical engine. The rewriting logic semantics is by itself a formal interpreter
of the language and can be used as a semantic benchmark for the implementation
of PLEXIL executives. The implementation in Maude has the additional benefit of
making available to PLEXIL designers and developers all the formal analysis and
verification tools provided by Maude. The formalization of the PLEXIL semantics
in rewriting logic poses an interesting challenge due to the synchronous nature
of the language and the prioritized rules defining its semantics. To overcome
this difficulty, we propose a general procedure for simulating synchronous set
relations in rewriting logic that is sound and, for deterministic relations,
complete. We also report on two issues at the design level of the original
PLEXIL semantics that were identified with the help of the executable
specification in Maude
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Fourth generation electron cyclotron resonance ion sources.
The concepts and technical challenges related to developing a fourth generation electron cyclotron resonance (ECR) ion source with a rf frequency greater than 40 GHz and magnetic confinement fields greater than twice B(ECR) will be explored in this article. Based on the semiempirical frequency scaling of ECR plasma density with the square of operating frequency, there should be significant gains in performance over current third generation ECR ion sources, which operate at rf frequencies between 20 and 30 GHz. While the third generation ECR ion sources use NbTi superconducting solenoid and sextupole coils, the new sources will need to use different superconducting materials, such as Nb(3)Sn, to reach the required magnetic confinement, which scales linearly with rf frequency. Additional technical challenges include increased bremsstrahlung production, which may increase faster than the plasma density, bremsstrahlung heating of the cold mass, and the availability of high power continuous wave microwave sources at these frequencies. With each generation of ECR ion sources, there are new challenges to be mastered, but the potential for higher performance and reduced cost of the associated accelerator continues to make this a promising avenue for development
The First Passage Probability of Intracellular Particle Trafficking
The first passage probability (FPP), of trafficked intracellular particles
reaching a displacement L, in a given time t or inverse velocity S = t/L, can
be calculated robustly from measured particle tracks, and gives a measure of
particle movement in which different types of motion, e.g. diffusion, ballistic
motion, and transient run-rest motion, can readily be distinguished in a single
graph, and compared with mathematical models. The FPP is attractive in that it
offers a means of reducing the data in the measured tracks, without making
assumptions about the mechanism of motion: for example, it does not employ
smoothing, segementation or arbitrary thresholds to discriminate between
different types of motion in a particle track. Taking experimental data from
tracked endocytic vesicles, and calculating the FPP, we see how three molecular
treatments affect the trafficking. We show the FPP can quantify complicated
movement which is neither completely random nor completely deterministic,
making it highly applicable to trafficked particles in cell biology.Comment: Article: 13 pages, 8 figure
Technical assistance, neo-colonialism or mutual trade? The experience of an Anglo/Ukrainian/Russian social work practice learning project
Since the collapse of the Soviet Union there has been a steady stream of Western consultants ready to work in Eastern Europe and Russia and share professional and academic expertise and experience. Social work, unknown as a discrete discipline or profession in the Soviet Union, has been a growth area with funding from a variety of sources to help promote East-West partnerships.Social work theory and practice emphasises critical appraisal of policy and embraces issues of power, discrimination and oppression. Social work educators should therefore be especially alert to the complex ethical questions which these kinds of collaborations raise, and adept at finding practical solutions or workable compromises. This article explores these ethical and political issues with reference to a project to develop social work practice learning in a Russian oblast' (region). The project was an ambitious partnership of British, Ukrainian and Russian educators, involving numerous Russian social work and related agencies, and four Russian universities and colleges in one oblast'. The authors use a series of vignettes to help the reader achieve insights into these East-West transactions. The article concludes with a discussion of different interpretations of these dealings, using three prisms: technical assistance, neo-colonialism and mutual trade
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