254,755 research outputs found
Plastic collapse of pipe bends under combined internal pressure and in-plane bending
Plastic collapse of pipe bends with attached straight pipes under combined internal pressure and in-plane closing moment is investigated by elastic–plastic finite element analysis. Three load histories are investigated, proportional loading, sequential pressure–moment loading and sequential moment–pressure loading. Three categories of ductile failure load are defined: limit load, plastic load (with associated criteria of collapse) and instability loads. The results show that theoretical limit analysis is not conservative for all the load combinations considered. The calculated plastic load is dependent on the plastic collapse criteria used. The plastic instability load gives an objective measure of failure and accounts for the effects of large deformations. The proportional and pressure–moment load cases exhibit significant geometric strengthening, whereas the moment–pressure load case exhibits significant geometric weakening
Effect of spin relaxations on the spin mixing conductances for a bilayer structure
The spin current can result in a spin-transfer torque in the
normal-metal(NM)|ferromagnetic-insulator(FMI) or
normal-metal(NM)|ferromagnetic-metal(FMM) bilayer. In the earlier study on this
issue, the spin relaxations were ignored or introduced phenomenologically. In
this paper, considering the FMM or FMI with spin relaxations described by a
non-Hermitian Hamiltonian, we derive an effective spin-transfer torque and an
effective spin mixing conductance in the non-Hermitian bilayer. The dependence
of the effective spin mixing conductance on the system parameters (such as
insulating gap, \textit{s-d} coupling, and layer thickness) as well as the
relations between the real part and the imaginary part of the effective spin
mixing conductance are given and discussed. We find that the effective spin
mixing conductance can be enhanced in the non-Hermitian system. This provides
us with the possibility to enhance the spin mixing conductance
Correlated Spectral and Temporal Variability in the High-Energy Emission from Blazars
Blazar flare data show energy-dependent lags and correlated variability
between optical/X-ray and GeV-TeV energies, and follow characteristic
trajectories when plotted in the spectral-index/flux plane. This behavior is
qualitatively explained if nonthermal electrons are injected over a finite time
interval in the comoving plasma frame and cool by radiative processes.
Numerical results are presented which show the importance of the effects of
synchrotron self-Compton cooling and plasmoid deceleration. The use of INTEGRAL
to advance our understanding of these systems is discussed.Comment: 8 pages, 5 figures, uses epsf.sty, rotate.sty Invited paper in "The
Extreme Universe," 3rd INTEGRAL Workshop, 14-18 September 1998, Taorimina,
Ital
When Both Transmitting and Receiving Energies Matter: An Application of Network Coding in Wireless Body Area Networks
A network coding scheme for practical implementations of wireless body area
networks is presented, with the objective of providing reliability under
low-energy constraints. We propose a simple network layer protocol for star
networks, adapting redundancy based on both transmission and reception energies
for data and control packets, as well as channel conditions. Our numerical
results show that even for small networks, the amount of energy reduction
achievable can range from 29% to 87%, as the receiving energy per control
packet increases from equal to much larger than the transmitting energy per
data packet. The achievable gains increase as a) more nodes are added to the
network, and/or b) the channels seen by different sensor nodes become more
asymmetric.Comment: 10 pages, 7 figures, submitted to the NC-Pro Workshop at IFIP
Networking Conference 2011, and to appear in the conference proceedings,
published by Springer-Verlag, in the Lecture Notes in Computer Science (LNCS)
serie
The IT performance evaluation in the construction industry
To date there has been limited published work in
the construction management and engineering
literature that has provided empirical evidence to
demonstrate that IT can improve organizational
performance. Without an explicit understanding
about how IT can be effectively used to improve
organizational performance, its justification will
remain to be weak for managers. To ensure the
continuous increase in IT based applications in the
construction industry, sufficient evidence has to be
provided for management in various professions of
the construction industry to evaluate, allocate and
utilize appropriate IT systems. In an attempt to
explore the relationship between IT and
productivity, an empirical investigation of 60
Professional Consulting Firms (PCF) from the
Hong Kong construction industry was undertaken.
A model for determining the organizational
productivity of IT is proposed, and the
methodology used to test the model is described.
The findings are analyzed and a cross-profession
comparison of the results indicated the differences
in the use of IT. The research findings are discussed
with similarities being drawn. The limitations of the
research are then presented and discussed. The
implications of the findings and conclusions then
fully presented
Non-fragile H∞ control with randomly occurring gain variations, distributed delays and channel fadings
This study is concerned with the non-fragile H∞ control problem for a class of discrete-time systems subject to randomly occurring gain variations (ROGVs), channel fadings and infinite-distributed delays. A new stochastic phenomenon (ROGVs), which is governed by a sequence of random variables with a certain probabilistic distribution, is put forward to better reflect the reality of the randomly occurring fluctuation of controller gains implemented in networked environments. A modified stochastic Rice fading model is then exploited to account for both channel fadings and random time-delays in a unified representation. The channel coefficients are a set of mutually independent random variables which abide by any (not necessarily Gaussian) probability density function on [0, 1]. Attention is focused on the analysis and design of a non-fragile H∞ outputfeedback controller such that the closed-loop control system is stochastically stable with a prescribed H∞ performance. Through intensive stochastic analysis, sufficient conditions are established for the desired stochastic stability and H∞ disturbance attenuation, and the addressed non-fragile control problem is then recast as a convex optimisation problem solvable via the semidefinite programme method. An example is finally provided to demonstrate the effectiveness of the proposed design method
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