86,471 research outputs found
Amenability of Groupoids Arising from Partial Semigroup Actions and Topological Higher Rank Graphs
We consider the amenability of groupoids equipped with a group valued
cocycle with amenable kernel . We prove a general result
which implies, in particular, that is amenable whenever is amenable and
if there is countable set such that for all . We show that our result is applicable to groupoids arising from
partial semigroup actions. We explore these actions in detail and show that
these groupoids include those arising from directed graphs, higher rank graphs
and even topological higher rank graphs. We believe our methods yield a nice
alternative groupoid approach to these important constructions.Comment: Revised as suggested by a very helpful referee. In particular, a gap
in the proof of Theorem 5.13 has been repaired resulting in a much improved
version (with fewer hypotheses
State space collapse and diffusion approximation for a network operating under a fair bandwidth sharing policy
We consider a connection-level model of Internet congestion control,
introduced by Massouli\'{e} and Roberts [Telecommunication Systems 15 (2000)
185--201], that represents the randomly varying number of flows present in a
network. Here, bandwidth is shared fairly among elastic document transfers
according to a weighted -fair bandwidth sharing policy introduced by Mo
and Walrand [IEEE/ACM Transactions on Networking 8 (2000) 556--567] []. Assuming Poisson arrivals and exponentially distributed document
sizes, we focus on the heavy traffic regime in which the average load placed on
each resource is approximately equal to its capacity. A fluid model (or
functional law of large numbers approximation) for this stochastic model was
derived and analyzed in a prior work [Ann. Appl. Probab. 14 (2004) 1055--1083]
by two of the authors. Here, we use the long-time behavior of the solutions of
the fluid model established in that paper to derive a property called
multiplicative state space collapse, which, loosely speaking, shows that in
diffusion scale, the flow count process for the stochastic model can be
approximately recovered as a continuous lifting of the workload process.Comment: Published in at http://dx.doi.org/10.1214/08-AAP591 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Theory of Feshbach molecule formation in a dilute gas during a magnetic field ramp
Starting with coupled atom-molecule Boltzmann equations, we develop a
simplified model to understand molecule formation observed in recent
experiments. Our theory predicts several key features: (1) the effective
adiabatic rate constant is proportional to density; (2) in an adiabatic ramp,
the dependence of molecular fraction on magnetic field resembles an error
function whose width and centroid are related to the temperature; (3) the
molecular production efficiency is a universal function of the initial phase
space density, the specific form of which we derive for a classical gas. Our
predictions show qualitative agreement with the data from [Hodby et al, Phys.
Rev. Lett. {\bf{94}}, 120402 (2005)] without the use of adjustable parameters
The health state preferences and logistical inconsistencies of New Zealanders: a tale of two tariffs
Notwithstanding the proposed use of Cost-Utility Analysis (CUA) to inform health care priority setting in New Zealand, to date there has been no research into New Zealanders’ valuations of health-related quality of life. This paper reports the results of a study of the health state preferences of adult New Zealanders generated from a postal survey to which 1360 people responded (a 50% response rate). The survey employed a self-completed questionnaire in which a selection of health states were described using the EQ-5D health state classification system and respondents’ valuations were sought using a visual analogue scale (VAS). Close attention is paid to the quality of the data, in particular to the ‘logical inconsistencies’ in respondents’ valuations. Regression analysis is used to interpolate values over the 245 possible EQ-5D states. Two tariffs of health state preferences, arising from contrasting treatments of the logical inconsistencies, are reported.New Zealand, EuroQol, EQ-5D
Podiatry services for patients with arthritis: an unmet need
Foot problems are extremely common in patients with rheumatoid arthritis (RA).
There is ample evidence that foot pain, either alone or as a comorbidity, contributes
significantly to disability. Despite the high prevalence of foot disease in RA, this
problem is often trivialised or underappreciated. The inequity in foot health provision
for patients with rheumatic disorders in New Zealand has recently been highlighted.
Expertise in dealing with foot problems is often limited among healthcare
professionals, and it has been argued that better integration of podiatric services into
rheumatology services would be beneficial. The aim of this paper is to highlight the
major issues related to foot care for patients with arthritis and provide key
recommendations that should implemented to improve access to podiatric services in
New Zealand
Adaptive identification and control of structural dynamics systems using recursive lattice filters
A new approach for adaptive identification and control of structural dynamic systems by using least squares lattice filters thar are widely used in the signal processing area is presented. Testing procedures for interfacing the lattice filter identification methods and modal control method for stable closed loop adaptive control are presented. The methods are illustrated for a free-free beam and for a complex flexible grid, with the basic control objective being vibration suppression. The approach is validated by using both simulations and experimental facilities available at the Langley Research Center
Mercury accumulation in fishes from tropical aquatic ecosystems in the Niger Delta, Nigeria
Fishes are important biomarkers of trace elements in
aquatic ecosystems, and are used to evaluate the status
of water pollution by mercury in tropical aquatic ecosystems in Nigeria. Common fishes, Chrysichthys nigrodigitatus,Brycinus nurse, Hemichromis fasciatus,
Lutianus ava, Oreochromis nilotica, Pomadasys jubelini,
Stellifer stellifer and Tilapia guineensis were analysed
for Hg accumulation using the cold vapour atomic absorption spectrophotometry technique. The results
showed that Hg concentration in P. jubelini was relatively
the highest, with a mean concentration of 0.063 ± 0.03 mg kg–1. Other concentration values were 0.044 ± 0.031 mg kg–1 for O. nilotica, 0.026 ± 0.013 mg kg–1 for B. nurse, 0.034 ± 0.034 mg kg–1 for H. fasciatus, 0.023 ± 0.020 mg kg–1 for C. nigrodigitatus and 0.33 ± 0.016 mg kg–1 for L. ava. Concentrations of Hg accumulated by the fishes were low and within internationally accepted limit, not likely to cause mercury poisoning. Because of the high Hg accumulating potential of P. jubelini, it is recommended as a biomarker for assessment of Hg toxicity in a tropical aquatic environment
QUAGMIRE v1.3: a quasi-geostrophic model for investigating rotating fluids experiments
QUAGMIRE is a quasi-geostrophic numerical model for performing fast, high-resolution simulations of multi-layer rotating annulus laboratory experiments on a desktop personal computer. The model uses a hybrid finite-difference/spectral approach to numerically integrate the coupled nonlinear partial differential equations of motion in cylindrical geometry in each layer. Version 1.3 implements the special case of two fluid layers of equal resting depths. The flow is forced either by a differentially rotating lid, or by relaxation to specified streamfunction or potential vorticity fields, or both. Dissipation is achieved through Ekman layer pumping and suction at the horizontal boundaries, including the internal interface. The effects of weak interfacial tension are included, as well as the linear topographic beta-effect and the quadratic centripetal beta-effect. Stochastic forcing may optionally be activated, to represent approximately the effects of random unresolved features. A leapfrog time stepping scheme is used, with a Robert filter. Flows simulated by the model agree well with those observed in the corresponding laboratory experiments
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