On the rate of convergence to stationarity of the M/M/N queue in the Halfin-Whitt regime

We prove several results about the rate of convergence to stationarity, that is, the spectral gap, for the M/M/n queue in the Halfin-Whitt regime. We identify the limiting rate of convergence to steady-state, and discover an asymptotic phase transition that occurs w.r.t. this rate. In particular, we demonstrate the existence of a constant $B^*\approx1.85772$ s.t. when a certain excess parameter $B\in(0,B^*]$, the error in the steady-state approximation converges exponentially fast to zero at rate $\frac{B^2}{4}$. For $B>B^*$, the error in the steady-state approximation converges exponentially fast to zero at a different rate, which is the solution to an explicit equation given in terms of special functions. This result may be interpreted as an asymptotic version of a phase transition proven to occur for any fixed n by van Doorn [Stochastic Monotonicity and Queueing Applications of Birth-death Processes (1981) Springer]. We also prove explicit bounds on the distance to stationarity for the M/M/n queue in the Halfin-Whitt regime, when $B<B^*$. Our bounds scale independently of $n$ in the Halfin-Whitt regime, and do not follow from the weak-convergence theory.Comment: Published in at http://dx.doi.org/10.1214/12-AAP889 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

High levels of cyclic di-GMP in Klebsiella pneumoniae attenuate virulence in the lung

ABSTRACT The bacterial second messenger bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) has been shown to influence the expression of virulence factors in certain pathogenic bacteria, but little is known about its activity in the increasingly antibiotic-resistant pathogen Klebsiella pneumoniae . Here, the expression in K. pneumoniae of a heterologous diguanylate cyclase increased the bacterial c-di-GMP concentration and attenuated pathogenesis in murine pneumonia. This attenuation remained evident in mice lacking the c-di-GMP sensor STING, indicating that the high c-di-GMP concentration exerted its influence not on host responses but on bacterial physiology. While serum resistance and capsule expression were unaffected by the increased c-di-GMP concentration, both type 3 and type 1 pili were strongly upregulated. Importantly, attenuation of K. pneumoniae virulence by high c-di-GMP levels was abrogated when type 1 pilus expression was silenced. We conclude that increased type 1 piliation may hamper K. pneumoniae virulence in the respiratory tract and that c-di-GMP signaling represents a potential therapeutic target for antibiotic-resistant K. pneumoniae in this niche. </jats:p

Comment on "Superinstantons and the Reliability of Perturbation Theory in Non-Abelian Models"

In a recent letter (hep-lat/9311019) A. Patrascioiu and E. Seiler argued that when taking into account "superinstantons configurations" the perturbative expansion and the beta-function of the two-dimensional non-linear sigma-model are modified at two loops order. I point out that: (1) perturbation theory in a superinstanton background is infra-red singular beyond three loops; (2) the new infra-red singular terms, which change the two loop terms, come from singular operators - describing superinstanton insertions - in the OPE; (3) taking into account these operators, the beta-function is not modified. Therefore the results of Patrascioiu and Seiler do not contradict perturbation theory.Comment: 1 page, REVTeX, no figure

A Critical Examination of the FDA’s Efforts to Preempt Failure-to-Warn Claims

This article explores the legality and wisdom of the FDA’s effort to persuade courts to find most failure-to-warn claims preempted. The article first analyzes the FDA’s justifications for reversing its long-held views to the contrary and explains why the FDA’s position cannot be reconciled with its governing statute. The article then examines why the FDA’s position, if ultimately adopted by the courts, would undermine the incentives drug manufacturers have to change labeling to respond to newly-discovered risks. The background possibility of failure-to-warn litigation provides important incentives for drug companies to ensure that drug labels reflect accurate and up-to-date safety information. The article next explains why the agency’s view that it is capable of singlehandedly regulating the safety of drugs is unrealistic. The agency does not have the resources to perform the Herculean task of monitoring the performance of every drug on the market. Both the Institute of Medicine and the Government Accountability Office have explained the shortcomings in the FDA’s recent performance, and they express doubt that the FDA is in capable of facing an increasingly challenging future. The article then explains how state damages litigation helps uncover and assess risks that are not apparent to the agency during a drug’s approval process, and why this “feedback loop” enables the agency to better do its job. FDA approval of drugs is based on clinical trials that involve, at most, a few thousand patients and last a year or so. These trials cannot detect risks that are relatively rare, affect vulnerable sub-populations, or have long latency periods. For this reason, most serious adverse effects do not become evident until a drug is used in larger population groups for periods in excess of one year. Time and again, failure-to-warn litigation has brought to light information that would not otherwise be available to the FDA, to doctors, to other health care providers, and to consumers. And failure-to-warn litigation often has preceded and clearly influenced FDA decisions to modify labeling, and, at times, to withdraw drugs from the market

The unified transform method for linear initial-boundary value problems: a spectral interpretation

It is known that the unified transform method may be used to solve any well-posed initial-boundary value problem for a linear constant-coefficient evolution equation on the finite interval or the half-line. In contrast, classical methods such as Fourier series and transform techniques may only be used to solve certain problems. The solution representation obtained by such a classical method is known to be an expansion in the eigenfunctions or generalised eigenfunctions of the self-adjoint ordinary differential operator associated with the spatial part of the initial-boundary value problem. In this work, we emphasise that the unified transform method may be viewed as the natural extension of Fourier transform techniques for non-self-adjoint operators. Moreover, we investigate the spectral meaning of the transform pair used in the new method; we discuss the recent definition of a new class of spectral functionals and show how it permits the diagonalisation of certain non-self-adjoint spatial differential operators.Comment: 3 figure

Getting the Haves to Come out Behind: Fixing the Distributive Injustices of American Health Care

Hyman criticizes an article by Havighurst and Richman regarding the distributive injustices of US health care. Hyman also offers a guide for implementing policy reforms based on the analysis by Havighurst and Richman