Approximating the optimal weights for discrete-time generalized processor sharing

Generalized Processor Sharing (GPS) is a simple, flexible and fair scheduling mechanism to achieve delay differentiation between several customer classes. The amount of delay differentiation is regulated by the weights given to the classes. In this paper we assume a discrete-time, two-class GPS queueing system. Our goal is to derive the optimal weights in order to minimize a weighted sum of functions of the mean delays of both classes. As analytical results are scarce we use an approximation method. The approximation is based on power series expansions of the mean queue length of each of the queues for certain weights. Pade approximants are used to extrapolate the approximation to the whole domain of possible weights, resulting in a set of approximations. An algorithm is proposed to filter out the infeasible solutions (with regard to monotonicity and other characteristics of the system) and aggregate the others, resulting in a single approximation. The result proves to be an accurate approximation of the optimal weights w.r.t. the cost function. For a load of 90% we have a maximum misprediction of 1% of the cost, in the case of a weighted sum of squares of the mean delays. The main contribution of this article is that power series approximations can be used effectively for optimization purposes

Cost of intensive routine control and incremental cost of insecticide-treated curtain deployment in a setting with low Aedes aegypti infestation

Introduction: Information regarding the cost of implementing insecticide-treated curtains (ITCs) is scarce. Therefore, we evaluated the ITC implementation cost, in addition to the costs of intensive conventional routine activities of the Aedes control program in the city of Guantanamo, Cuba. Methods: A cost-analysis study was conducted from the perspective of the Aedes control program, nested in an ITC effectiveness trial, during 2009-2010. Data for this study were obtained from bookkeeping records and activity registers of the Provincial Aedes Control Programme Unit and the account records of the ITC trial. Results: The annual cost of the routine Aedes control program activities was US$16.80 per household (p.h). Among 3,015 households, 6,714 ITCs were distributed. The total average cost per ITC distributed was US$3.42, and 74.3% of this cost was attributed to the cost of purchasing the ITCs. The annualized costs p.h. of ITC implementation was US$3.80. The additional annualized cost for deploying ITCs represented 19% and 48.4% of the total cost of the routine Aedes control and adult-stage Aedes control programs, respectively. The trial did not lead to further reductions in the already relatively low Aedes infestation levels. Conclusions: At current curtain prices, ITC deployment can hardly be considered an efficient option in Guantanamo and other comparable environments

JANNAF "Test and Evaluation Guidelines for Liquid Rocket Engines": Status and Application

For many decades, the U.S. rocket propulsion industrial base has performed remarkably in developing complex liquid rocket engines that can propel critical payloads into service for the nation, as well as transport people and hardware for missions that open the frontiers of space exploration for humanity. This has been possible only at considerable expense given the lack of detailed guidance that captures the essence of successful practices and knowledge accumulated over five decades of liquid rocket engine development. In an effort to provide benchmarks and guidance for the next generation of rocket engineers, the Joint Army Navy NASA Air Force (JANNAF) Interagency Propulsion Committee published a liquid rocket engine (LRE) test and evaluation (T&E) guideline document in 2012 focusing on the development challenges and test verification considerations for liquid rocket engine systems. This document has been well received and applied by many current LRE developers as a benchmark and guidance tool, both for government-driven applications as well as for fully commercial ventures. The USAF Space and Missile Systems Center (SMC) has taken an additional near-term step and is directing activity to adapt and augment the content from the JANNAF LRE T&E guideline into a standard for potential application to future USAF requests for proposals for LRE development initiatives and launch vehicles for national security missions. A draft of this standard was already sent out for review and comment, and is intended to be formally approved and released towards the end of 2017. The acceptance and use of the LRE T&E guideline is possible through broad government and industry participation in the JANNAF liquid propulsion committee and associated panels. The sponsoring JANNAF community is expanding upon this initial baseline version and delving into further critical development aspects of liquid rocket propulsion testing at the integrated stage level as well as engine component level, in order to advance the state of the practice. The full participation of the entire U.S. rocket propulsion industrial base is invited and expected at this opportune moment in the continuing advancement of spaceflight technology