67,368 research outputs found
RW Aur A from the X-Wind Point of View: General Features
In this paper, the RW Aur A microjet is studied from the point of view of
X-wind models. The archived HST/STIS spectra of optical forbidden lines [O I],
[S II], and [N II] from RW Aur A, taken in Cycle 8 with seven parallel slits
along the jet axis, spaced at 0".07 apart, were analyzed. Images,
position-velocity diagrams, and line ratios among the species were constructed,
and compared with synthetic observations generated by selected solutions of the
X-wind. Prominent features arising in a steady state X-wind could be identified
within the convolved images, full-widths at half maxima and high-velocity peaks
on both of the redshifted and blueshifted jets. The well-known asymmetric
velocity profiles of the opposite jets are built into the selected models. We
discuss model selections within the existing uncertainties of stellar
parameters and inclination angle of the system. In this framework, the
mass-loss rates that were inferred to be decreasing along the jet axis in the
literature are the results of slowly decreasing excitation conditions and
electron density profiles. Despite the apparent asymmetry in terminal
velocities, line intensities and mass-loss rates, the average linear momenta
from the opposite sides of the jet are actually balanced. These previously
hard-to-explain features of the asymmetric RW Aur A jet system now find a
different but self-consistent interpretation within the X-wind framework.Comment: 31 pages, 9 figures, 5 tables; accepted for publication in ApJ (Send
correspondence to: [email protected]
Online cooperation learning environment : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Computer Science at Massey University, Albany, New Zealand
This project aims to create an online cooperation learning environment for students who study the same paper. Firstly, the whole class will be divided into several tutorial peer groups. One tutorial group includes five to seven students. The students can discuss with each other in the same study group, which is assigned by the lecturer. This is achieved via an online cooperation learning environment application (OCLE), which consists of a web based J2EE application and a peer to peer (P2P) java application, cooperative learning tool (CLT). It can reduce web server traffic significantly during online tutorial discussion time
An Upper Bound on the Convergence Time for Quantized Consensus of Arbitrary Static Graphs
We analyze a class of distributed quantized consensus algorithms for
arbitrary static networks. In the initial setting, each node in the network has
an integer value. Nodes exchange their current estimate of the mean value in
the network, and then update their estimation by communicating with their
neighbors in a limited capacity channel in an asynchronous clock setting.
Eventually, all nodes reach consensus with quantized precision. We analyze the
expected convergence time for the general quantized consensus algorithm
proposed by Kashyap et al \cite{Kashyap}. We use the theory of electric
networks, random walks, and couplings of Markov chains to derive an upper bound for the expected convergence time on an arbitrary graph of size
, improving on the state of art bound of for quantized consensus
algorithms. Our result is not dependent on graph topology. Example of complete
graphs is given to show how to extend the analysis to graphs of given topology.Comment: to appear in IEEE Trans. on Automatic Control, January, 2015. arXiv
admin note: substantial text overlap with arXiv:1208.078
Accurate and efficient splitting methods for dissipative particle dynamics
We study numerical methods for dissipative particle dynamics (DPD), which is
a system of stochastic differential equations and a popular stochastic
momentum-conserving thermostat for simulating complex hydrodynamic behavior at
mesoscales. We propose a new splitting method that is able to substantially
improve the accuracy and efficiency of DPD simulations in a wide range of the
friction coefficients, particularly in the extremely large friction limit that
corresponds to a fluid-like Schmidt number, a key issue in DPD. Various
numerical experiments on both equilibrium and transport properties are
performed to demonstrate the superiority of the newly proposed method over
popular alternative schemes in the literature
Generalized k-core percolation on correlated and uncorrelated multiplex networks
It has been recognized that multiplexes and interlayer degree correlations can play a crucial role in the resilience of many real-world complex systems. Here we introduce a multiplex pruning process that removes nodes of degree less than ki and their nearest neighbors in layer i for i=1,...,m, and establish a generic framework of generalized k-core (Gk-core) percolation over interlayer uncorrelated and correlated multiplex networks of m layers, where k=(k1,...,km) and m is the total number of layers. Gk-core exhibits a discontinuous phase transition for all k owing to cascading failures. We have unraveled the existence of a tipping point of the number of layers, above which the Gk-core collapses abruptly. This dismantling effect of multiplexity on Gk-core percolation shows a diminishing marginal utility in homogeneous networks when the number of layers increases. Moreover, we have found the assortative mixing for interlayer degrees strengthens the Gk-core but still gives rise to discontinuous phase transitions as compared to the uncorrelated counterparts. Interlayer disassortativity on the other hand weakens the Gk-core structure. The impact of correlation effect on Gk-core tends to be more salient systematically over k for heterogenous networks than homogeneous ones
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