458,017 research outputs found
Possibility of long-range order in clean mesoscopic cylinders
A microscopic Hamiltonian of the magnetostatic interaction is discussed. This
long-range interaction can play an important role in mesoscopic systems leading
to an ordered ground state.
The self-consistent mean field approximation of the magnetostatic interaction
is performed to give an effective Hamiltonian from which the spontaneous,
self-sustaining currents can be obtained.
To go beyond the mean field approximation the mean square fluctuation of the
total momentum is calculated and its influence on self-sustaining currents in
mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then,
by the use of the microscopic Hamiltonian of the magnetostatic interaction for
a set of stacked rings, the problem of long-range order is discussed. The
temperature below which the system is in an ordered state is
determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.
Estimating Self-Sustainability in Peer-to-Peer Swarming Systems
Peer-to-peer swarming is one of the \emph{de facto} solutions for distributed
content dissemination in today's Internet. By leveraging resources provided by
clients, swarming systems reduce the load on and costs to publishers. However,
there is a limit to how much cost savings can be gained from swarming; for
example, for unpopular content peers will always depend on the publisher in
order to complete their downloads. In this paper, we investigate this
dependence. For this purpose, we propose a new metric, namely \emph{swarm
self-sustainability}. A swarm is referred to as self-sustaining if all its
blocks are collectively held by peers; the self-sustainability of a swarm is
the fraction of time in which the swarm is self-sustaining. We pose the
following question: how does the self-sustainability of a swarm vary as a
function of content popularity, the service capacity of the users, and the size
of the file? We present a model to answer the posed question. We then propose
efficient solution methods to compute self-sustainability. The accuracy of our
estimates is validated against simulation. Finally, we also provide closed-form
expressions for the fraction of time that a given number of blocks is
collectively held by peers.Comment: 27 pages, 5 figure
Experimental and numerical study on self-sustaining performance of a 30-kW micro gas turbine generator system during startup process
The safe startup of micro gas turbine (MGT) generator system is the premise of normal operation. The whole start-up process contains motor startup, ignition, speed acceleration, motor switching to generator and power acceleration. Motor switching to generator happens at the self-sustaining state, which is significant to safe start-up process. However, characteristics of MGT generator system at self-sustaining state are hardly to investigate due to the lack of performance maps and complete experiments. Therefore, this work analyzed start-up schedule and presented a theoretical and experimental study on the self-sustaining performance of MGT generator system, based on the self-designed 30 kW MGT generator system built in Jiangjin Turbocharger Plant, China. The self-sustaining speed boundary and fuel consumption area is determined from the aspects of safe startup. A novel principle for determining the self-sustaining point (SSP) is proposed. Results show that the self-sustaining state can be achieved only when speed is over 26,750 rpm, and the SSP is determined at the speed of 30,750 rpm based on the proposed principle. Finally, the self-sustaining TIT and natural gas flow are compared with the experimental data, with two relative errors both almost within 4%. This method is instructive to the MGT generator system startup process
Self-sustained hydrodynamic oscillations in a natural-circulation two-phase-flow boiling loop
Results of an experimental and theoretical study of factors affecting self-sustaining hydrodynamic oscillations in boiling-water loops are reported. Data on flow variables, and the effects of geometry, subcooling and pressure on the development of oscillatory behavior in a natural-circulation two-phase-flow boiling loop are included
On self-sustaining processes in Rayleigh-stable rotating plane Couette flows and subcritical transition to turbulence in accretion disks
Subcritical transition to turbulence in Keplerian accretion disks is still a
controversial issue and some theoretical progress is required in order to
determine whether or not this scenario provides a plausible explanation for the
origin of angular momentum transport in non-magnetized accretion disks.
Motivated by the recent discoveries of exact nonlinear steady self-sustaining
solutions in linearly stable non-rotating shear flows, we attempt to compute
similar solutions in Rayleigh-stable rotating plane Couette flows and to
identify transition mechanisms in such flows by combining nonlinear
continuation methods and asymptotic theory. We obtain exact nonlinear solutions
for Rayleigh-stable cyclonic regimes but show that it is not possible to
compute solutions for Rayleigh-stable anticyclonic regimes, including Keplerian
flow, using similar techniques. We also present asymptotic descriptions of
these various problems at large Reynolds numbers that provide some insight into
the differences between the non-rotating and Rayleigh-stable anticyclonic
regimes and derive some necessary conditions for mechanisms analogous to the
non-rotating self-sustaining process to be present in flows on the Rayleigh
line. Our results demonstrate that subcritical transition mechanisms cannot be
identified in wall-bounded Rayleigh-stable anticyclonic shear flows by
transposing directly the phenomenology of subcritical transition in cyclonic
and non-rotating wall-bounded shear flows. Asymptotic developments, however,
leave open the possibility that nonlinear self-sustaining solutions may exist
in unbounded or periodic flows on the Rayleigh line. These could serve as a
starting point to discover solutions in Rayleigh-stable flows, but the
nonlinear stability of Keplerian accretion disks remains to be determined.Comment: 16 pages, 12 figures. Accepted for publication in A&
A review of landscape rehabilitation frameworks in ecosystem engineering for mine closure
Mining causes changes to the environment and rehabilitation is necessary at mine closure. There is a lack of appropriate frameworks for mine site rehabilitation. In most cases, restoring the mine to previous conditions
is challenging. Alternatively, mining companies can engineer ecosystems to suit new site conditions and aim for a self-sustaining and resilient ecosystem. In ecosystem design there should be consideration of the four key dimensions of any ecosystem; landscape, function, structure and composition (LFSC). Alcoa’s Bauxite mines and Barrick (Cowal) Limited’s Gold Mine have considered LFSC in their rehabilitation practices. From this, a framework based on LFSC is proposed as a means of planning, undertaking and monitoring
mine rehabilitation, which together aim for a self-sustaining and resilient ecosystem. Elements of this framework are being utilised in the industry, and are supported by research. The framework could be used
as an industry standard, utilised by regulatory bodies and potentially used in conjunction with other models and in other rehabilitation environments
Management framework of on going self-sustaining agricultural extension system and training of farmer promoters and farmers in Rwanda
This study reviews the organizational setting of the self-sustaining agricultural extension system adopted by the Ministry of Agriculture and Animal Resources in Rwanda. The main objective of the self-sustaining agricultural extension system is to make the farmers themselves to act as the resource persons without having to depend on people from outside. This report deals about the strengthening of the different aspects of self-sustaining agricultural extension systems like Institutional development of self-sustaining agricultural extension system Improving the supply of relevant services to respond to the farmers, Capacity Building of FFS farmers and FP farmers, Evaluation of performance of farmer groups, Capacity development of critical mass of frontline extension and Extension Methods used. The self-sustaining system was provided with stakeholder’s collaboration with sound purposes, which resulted in meeting the expected results like crop productivity. Stakeholders offered 74.2% of information to farmers through training of farmers. It was found that 40.8% of the training mode was village mobilization meeting. Stakeholders used 83.9% of the training by group meeting and 42.9% was done by the Farmers Field School (FFS) plots. The survey identified that 87.2% farmer promoters were in groups while 65.3% of the farmers were in self-sustaining extension groups. The study revealed that 75.6% farmers were attending the regular meetings conducted and 34% farmers attended the regular monthly group meetings. The Local Government Extension staff trained 64.6% of Farmer Promoters in extension systems among them 72% of the trained Farmer promoters established the demo plots. The success of the self-sustaining extension system in Rwanda is mainly due to its 91% of the farmers visited the demo plots at least one time in the season and 82% of the farmers used improved seeds.Keywords: Self-sustaining– agriculture – extension system – Training Farmers – Rwand
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