41,232 research outputs found
Effective equidistribution of primitive rational points on expanding horospheres
We prove an effective version of a result due to Einsiedler, Mozes, Shah and
Shapira who established the equidistribution of primitive rational points on
expanding horospheres in the space of unimodular lattices in at least
dimensions. Their proof uses techniques from homogeneous dynamics and relies in
particular on measure-classification theorems --- an approach which does not
lend itself to effective bounds. We implement a strategy based on spectral
theory, Fourier analysis and Weil's bound for Kloosterman sums in order to
quantify the rate of equidistribution for a specific horospherical subgroup in
any dimension. We apply our result to provide a rate of convergence to the
limiting distribution for the appropriately rescaled diameters of random
circulant graphs.Comment: 21 pages, incorporates the referee's comments and correction
Outage analysis of superposition modulation aided network coded cooperation in the presence of network coding noise
We consider a network, where multiple sourcedestination pairs communicate with the aid of a half-duplex relay node (RN), which adopts decode-forward (DF) relaying and superposition-modulation (SPM) for combining the signals transmitted by the source nodes (SNs) and then forwards the composite signal to all the destination nodes (DNs). Each DN extracts the signals transmitted by its own SN from the composite signal by subtracting the signals overheard from the unwanted SNs. We derive tight lower-bounds for the outage probability for transmission over Rayleigh fading channels and invoke diversity combining at the DNs, which is validated by simulation for both the symmetric and the asymmetric network configurations. For the high signal-to-noise ratio regime, we derive both an upperbound as well as a lower-bound for the outage performance and analyse the achievable diversity gain. It is revealed that a diversity order of 2 is achieved, regardless of the number of SN-DN pairs in the network. We also highlight the fact that the outage performance is dominated by the quality of the worst overheated link, because it contributes most substantially to the network coding noise. Finally, we use the lower bound for designing a relay selection scheme for the proposed SPM based network coded cooperative communication (SPM-NC-CC) system.<br/
Progressive collapse analysis of steel structures under fire conditions
This is the post-print version of the final paper published in Engineering Structures. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2011 Elsevier B.V.In this paper a robust static-dynamic procedure has been developed. The development extends the capability of the Vulcan software to model the dynamic and static behaviour of steel buildings during both local and global progressive collapse of the structures under fire conditions. The explicit integration method was adopted in the dynamic procedure. This model can be utilized to allow a structural analysis to continue beyond the temporary instabilities which would cause singularities in the full static analyses. The automatic switch between static and dynamic analysis makes the Vulcan a powerful tool to investigate the mechanism of the progressive collapse of the structures generated by the local failure of components. The procedure was validated against several practical cases. Some preliminary studies of the collapse mechanism of steel frame due to columns’ failure under fire conditions are also presented. It is concluded that for un-braced frame the lower loading ratio and bigger beam section can give higher failure temperature in which the global structural collapse happens. However, the localised collapse of the frame with the higher loading ratio and smaller beam section can more easily be generated. The bracing system is helpful to prevent the frame from progressive collapse. The higher lateral stiffness of the frame can generate the smaller vertical deformation of the failed column at the re-stable position. However, the global failure temperature of the frame is not sensitive to the lateral stiffness of the frame
Two Body Relaxation in Simulated Cosmological Haloes
This paper aims at quantifying discreetness effects, born of finite particle
number, on the dynamics of dark matter haloes forming in the context of
cosmological simulations. By generalising the standard calculation of two body
relaxation to the case when the size and mass distribution are variable, and
parametrising the time evolution using established empirical relations, we find
that the dynamics of a million particle halo is noise-dominated within the
inner percent of the final virial radius. Far larger particle numbers (~ 10^8)
are required for the RMS perturbations to the velocity to drop to the 10 %
level there. The radial scaling of the relaxation time is simple and strong:
t_relax ~ r^2, implying that numbers >> 10^8 are required to faithfully model
the very inner regions; artificial relaxation may thus constitute an important
factor, contributing to the contradictory claims concerning the persistence of
a power law density cusp to the very centre. The cores of substructure haloes
can be many relaxation times old. Since relaxation first causes their expansion
before recontraction occurs, it may render them either more difficult or easier
to disrupt, depending on their orbital parameters. It may thus modify the
characteristics of the subhalo distribution and effects of interactions with
the parent. We derive simple closed form formulas for the characteristic
relaxation times, as well as for the weak N-scaling reported by Diemand et al.
when the main contribution comes from relaxing subhaloes (abridged).Comment: 11 Pages, 7 figs, Monthly Notices styl
Detecting events and key actors in multi-person videos
Multi-person event recognition is a challenging task, often with many people
active in the scene but only a small subset contributing to an actual event. In
this paper, we propose a model which learns to detect events in such videos
while automatically "attending" to the people responsible for the event. Our
model does not use explicit annotations regarding who or where those people are
during training and testing. In particular, we track people in videos and use a
recurrent neural network (RNN) to represent the track features. We learn
time-varying attention weights to combine these features at each time-instant.
The attended features are then processed using another RNN for event
detection/classification. Since most video datasets with multiple people are
restricted to a small number of videos, we also collected a new basketball
dataset comprising 257 basketball games with 14K event annotations
corresponding to 11 event classes. Our model outperforms state-of-the-art
methods for both event classification and detection on this new dataset.
Additionally, we show that the attention mechanism is able to consistently
localize the relevant players.Comment: Accepted for publication in CVPR'1
Extending the gaia methodology for the design and development of agent-based software systems
Over the past decade, agent-based computing has emerged as a new and popular paradigm for design, implementation and analysis of distributed information systems. In this paper, the participant researchers in Health Care Computing Group at University of Westminster concentrate on the agent-oriented methodology for the analysis and design of agentbased systems and identify how methodology can support both the levels of "agent structure" and of "agent society" in the agent-oriented software design and development process. The research reported here takes one leading agent-oriented methodology-Gaia, and then extended it by the creation of innovative design tools which aimed at better supporting application to real-world domains. In discussion section, agent-oriented methodology and AUML approaches are compared and evaluated in great detail; the strengths and weaknesses of the current agent-oriented methodology are explored and discussed; the importance of effectively using methodology to improve agents and their productivity potential also is emphasized. Finally, we draw conclusions from the work presented and the experience gained in this research and look into the future possible improvements on agent-oriented software engineering in the agent technology research field
Efficient Alternating Minimization Solvers for Wyner Multi-View Unsupervised Learning
In this work, we adopt Wyner common information framework for unsupervised
multi-view representation learning. Within this framework, we propose two novel
formulations that enable the development of computational efficient solvers
based on the alternating minimization principle. The first formulation,
referred to as the {\em variational form}, enjoys a linearly growing complexity
with the number of views and is based on a variational-inference tight
surrogate bound coupled with a Lagrangian optimization objective function. The
second formulation, i.e., the {\em representational form}, is shown to include
known results as special cases. Here, we develop a tailored version from the
alternating direction method of multipliers (ADMM) algorithm for solving the
resulting non-convex optimization problem. In the two cases, the convergence of
the proposed solvers is established in certain relevant regimes. Furthermore,
our empirical results demonstrate the effectiveness of the proposed methods as
compared with the state-of-the-art solvers. In a nutshell, the proposed solvers
offer computational efficiency, theoretical convergence guarantees (local
minima), scalable complexity with the number of views, and exceptional accuracy
as compared with the state-of-the-art techniques. Our focus here is devoted to
the discrete case and our results for continuous distributions are reported
elsewhere
Agent-based models for community care systems analysis and design
In recent years, the providers of public and private sector health care services have been faced with some radical changes in the society they serve, and more importantly, development in the way that traditional health care is delivered to Information Technology (I.T) based communities. It is widely believed by health care professionals that the better health care results really come from the improved healthcare systems and more effective health care services' management. This paper focuses on using an agnet-based software engineering approach and design models to the development of an appropriate agent-based healthcare software system is described in which software researchers collaborate with environment builders to enhance the levels of cooperation and support provided within an integrated agent-based community healthcare system
Magnetic phase transition and magnetocaloric effect in PrCo9Si4 and NdCo9Si4
The compounds, PrCo9Si4 and NdCo9Si4, have been recently reported to exhibit
first-order ferromagnetic transitions near 24 K. We have subjected this
compound for further characterization by magnetization, heat-capacity and
electrical resistivity measurements at low temperatures in the presence of
magnetic fields, particularly to probe magnetocaloric effect and
magnetoresistance. The compounds are found to exhibit rather modest
magnetocaloric effect at low temperatures peaking at Curie temperature,
tracking the behavior of magnetoresistance. The magnetic transition does not
appear to be first order in its character.Comment: In pres
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New method for nonparaxial beam propagation
A new method for solving the wave equation is presented that is nonparaxial and can be applied to wide-angle beam propagation. It shows very good stability characteristics in the sense that relatively larger step sizes can be taken. An implementation by use of the collocation method is presented in which only simple matrix multiplications are involved and no numerical matrix diagonalization or inversion is needed. The method is hence faster and is also highly accurate
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