Experiments with improved approximate mean value analysis algorithms

Approximate mean value analysis (MVA) is a popular technique for analyzing queueing networks because of the efficiency and accuracy that it affords. In this paper, we present a new software package, called the improved approximate mean value analysis library (IAMVAL), which can be easily integrated into existing commercial and research queueing network analysis packages. The IAMVAL packages include two new approximate MVA algorithms, the queue line (QL) algorithm and the fraction line (FL) algorithm, for analyzing multiple class separable queueing networks. The QL algorithm is always more accurate than, and yet has approximately the same computational efficiency as, the Bard–Schweitzer proportional estimation (PE) algorithm, which is currently the most widely used approximate MVA algorithm. The FL algorithm has the same computational cost and, in noncongested separable queueing networks where queue lengths are quite small, yields more accurate solutions than both the QL and PE algorithms.     

Queueing systems with random service rate

We consider a queue with the arrival process, the service time process and the service rate process as regenerative processes. We provide conditions for its stability, rates of convergence, finiteness of moments and functional limit theorems. This queue can model a queue serving ABR and UBR traffic in an ATM switch; a multiple access channel with TDMA or CDMA protocol and fading; a queue holding best effort or controlled and guaranteed traffic in a router in the integrated service architecture (ISA) of IP-based Internet and a scheduler in the router of a differentiated service architecture. In the process we also provide results for a queue with a leaky bucket controlled bandwidth scheduler. This result is of independent interest. We extend these results to feed-forward networks of queues. We also obtain the results when the arrival rate to the queue can be feedback controlled based on the congestion information in the queue (as in ABR service in the ATM networks or in the real time applications controlled by RTCP protocol in the Internet).     

Traffic overflow in loss systems with selective trunk reservation

We consider two traffic streams competing for service at an n-server queuing system. Jobs from stream 1, the protected stream, are blocked only if all n servers are busy. Jobs from stream 2, the best effort stream, are blocked if n−r, r≥1, servers are busy. Blocked customers are diverted to a secondary group of c−n servers with, possibly, a different service rate. For the case r=1, we calculate the joint probabilities of the number of primary and secondary busy servers. For r>1, we describe a procedure for deriving the joint probabilities. These probabilities allow for the calculation of various performance measures including the overflow probabilities of the primary server and secondary server group. Our model is applicable to traffic control in communication networks that use the selective trunk reservation method.     

An ANTS heuristic for the frequency assignment problem

The problem considered in this paper consists in assigning frequencies to radio links between base stations and mobile transmitters in order to minimize the global interference over a given region. This problem is NP-hard and few results have been reported on techniques for solving it to optimality. We have applied to this problem an ANTS metaheuristic, that is, an approach following the ant colony optimization paradigm. Computational results, obtained on a number of standard problem instances, testify the effectiveness of the proposed approach.     

Integration of heterogeneous CAD databases using STEP and the Internet

In a large-scale design process, designers cooperate in a complex situation where a variety of software tools run on different hardware platforms. This paper presents a data enhancement approach to integrate heterogeneous Computer-Aided Design (CAD) databases through the Internet. The data enhancement means topological changes in a geometric model and additional information in design semantics. The geometric data is enhanced using a non-manifold modeler to produce data sets valuable in downstream applications such as a Finite Element Method (FEM) solver or a detail design system. As a practical example, a shipbuilding product model database has been implemented based on the Standard for the Exchange of Product (STEP) model data methodology and shipbuilding features. The system has been implemented on a network environment that consists of a Web browser, Common Object Request Broker Architecture (CORBA) objects, a relational database management system, a data enhancement module, and various computer-aided applications.     

Chaotic neural networks and chaotic annealing

A simple model of single neuron with chaotic dynamics is proposed. Neural networks coupled by such neurons have the property of temporal retrieval of stored patterns in a chaotic way. The network is also studied from the viewpoint of optimization. A chaotic annealing technique is developed to search for the global minima of the energy with transient chaos.     

浅析电子商务促进区域一体化发展

随着2008年12月提出《珠江三角洲地区改革发展规划纲要》的提出,小珠三角再次成为世界焦点,其中深莞惠区域合作也被世人关注。但是区域合作知易行难,如何解决地方保护主义、同构严重等问题,本文认为,电子商务是一个可行方案并作出证明。     

VACTERL with hydrocephalus. A distinct entity with a variable spectrum of multiple congenital anomalies

In this report we describe the experience and follow-up data in 4 patients presenting the "VACTERL-hydrocephaly association". A review of the literature and the present data show that the inheritance pattern of this association is not clear at the present time and that data on the long-term prognosis are scarse.     

内窥镜鼻窦手术围手术期护理

目的总结内窥镜鼻窦手术的围手术期护理经验。方法对350例行内窥镜鼻窦手术患者资料进行回顾性总结。结果随访1年以上,Ⅰ型治愈率为90.6%,Ⅱ型治愈率为79.5%,Ⅲ型治愈率为63.9%;三型之间治愈率有显著性差异(χ2=16.38,P<0.01)。结论先进、优越、成功的手术,加上优质的围手术期护理,是直接关系到手术的治愈率和控制鼻息肉复发的重要环节。