Information theory and communication networks: an unconsummatedunion

Information theory has not yet had a direct impact on networking, although there are similarities in concepts and methodologies that have consistently attracted the attention of researchers from both fields. In this paper, we review several topics that are related to communication networks and that have an information-theoretic flavor, including multiaccess protocols, timing channels, effective bandwidth of bursty data sources, deterministic constraints on datastreams, queuing theory, and switching networks     

Interconversion of Lactose to Lactulose in Alkaline Environment: Comparison of Different Catalysis Concepts

Interconversion of lactulose to lactulose with the aim to determine and optimize the yield of ketose was carried out. Various homogenous and heterogeneous alkaline catalysts were applied (NaOH, MgO, hydrotalcite etc.). The selectivity and activity of the catalysts were compared. The results gave insight to the performance differences among the screened catalysts under the various reaction conditions. From the activity performance point of view, the conversion was limited by the formation of acidic end-products. In general, the selectivity decreased with conversion and the conversion-selectivity pattern was independent of the catalyst.     

Dream of absent-minded transgression: An empirical study of a cognitive withdrawal symptom.

Among 293 smokers abstinent for between 1 and 4 wks, 33% reported having at least 1 dream about smoking. In most dreams, Ss caught themselves smoking and felt strong negative emotions, such as panic and guilt. Dreams about smoking were the result of tobacco withdrawal, as 97% of Ss did not have them while smoking, and their occurrence was significantly related to the duration of abstinence. They were rated as more vivid than the usual dreams and were as common as most major tobacco withdrawal symptoms. In Ss abstinent for 1 yr, 63% recalled having dreams about smoking. They had on average 5 of them, and about a quarter occurred after the 6th mo of abstinence. Having dreams about smoking was prospectively positively related to maintenance of abstinence. An explanation of this finding based on the association of smoking in dreams with aversive emotions is offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective amobarbital test for the determination of language function in patients with epilepsy with frontal and posterior temporal brain lesions

The neutralization of Japanese encephalitis virus (JEV) was studied using JEV-specific neutralizing (NT) monoclonal antibody (MAb) 503 that recognizes the envelope glycoprotein. Analysis using radiolabeled JEV and observations by confocal laser microscopy and electron microscopy indicated that the NT and protection activities of MAb 503 did not result from the prevention of the first step of JEV infection, binding of virus to the cell surface. Treatment with MAb 503 strongly inhibited JEV-induced cell fusion and internalization of JEV into the cells, and resulted in enhanced release of JEV-RNA from the cells. These observations suggested that the NT activity of MAb 503 is involved in the later steps of JEV infection.     

On the capture probability for a large number of stations

The probability of capture under a model (for a land mobile radio direct sequence spread spectrum system) based on the ratio of the largest received power to the sum of interference powers is examined in the limit of a large number of transmitting stations. It is shown in great generality that the limit depends only on the capture ratio threshold and the roll-off exponent of the distribution of power received from a typical station. This exponent is insensitive to many typical channel effects such as Rician or Rayleigh fading and log-normal shadowing. The model is suitable for large systems with noncoherently combined interference     

The relationship between smoking cessation and mouth ulcers.

Patients who stop smoking often complain of aphthous (mouth) ulcers. This symptom is sometimes attributed to the use of smoking cessation medications, but little is known about it. We investigated the incidence, severity, and time course of mouth ulcers in abstaining smokers and the effect of different smoking cessation medications on the symptom. The sample consisted of 1234 smokers who sought treatment at a large smoking cessation clinic, maintained at least 1 week of continuous biochemically validated abstinence, and provided usable data. Participants assessed their mouth ulcers by rating a mouth ulcer item added to the Mood and Physical Symptoms Scale. Subjects made ratings weekly on three occasions while still smoking and over 4 weeks following smoking cessation. After stopping smoking, some 40% of patients developed mouth ulcers, mostly in the first 2 weeks. The problem was generally mild, but 8% reported severe ulceration. The ulcers resolved within 4 weeks in 60% of patients affected. The ulcer ratings in patients using oral nicotine replacement products were higher than in those using patch, nasal spray or bupropion in the first week of abstinence but not afterward. Mouth ulcers were more prevalent in more dependent smokers, and the occurrence of ulcers correlated with other tobacco withdrawal symptoms. Our results confirm that mouth ulcers are a common result of stopping smoking, affecting two in five quitters. Patients should be reassured that the lesions are a result of stopping smoking and not a side-effect of smoking cessation medication.     

Optimal control of two interacting service stations

Optimal controls described by switching curves in the two-dimensional state space are shown to exist for the optimal control of a Markov network with two service stations and linear cost. The controls govern routing and service priorities. Finite horizon and long run average cost problems are considered and value iteration is a key tool. Nonconvex value functions are shown to exist for slightly more general networks. Nonconvex value functions are also shown to arise for a simple single station control problem in which the instantaneous cost is convex but not monotone. Nevertheless, optimality of threshold policies is established for the single station problem. The proof is based on a novel use of stochastic coupling and policy iteration.     

Bounds on evacuation time for deflection routing

Summary Upper bounds are given on the timeT needed to evacuatek packets from a synchronous packet network using deflection routing, whereby all packets that arrive at a node during one time slot leave the node during the next slot. For example,Tn+2(k–1) for a binaryn-cube network when priority is given to packets closer to their destination, and for a single destination networkT is less than or equal to the network diameter plusk–1 times the network deflection index. Deflection routing for one pass through an omega network is also considered. Bruce Hajek received a B.S. in Mathematics and an M.S. in Electrical Engineering from the University of Illinois and a Ph.D. in Electrical Engineering from the University of California at Berkeley. He is a Professor in the Coordinated Science Laboratory and the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign, where he has been since August, 1979. His research interests include communication and computer network algorithms, information theory, random processes, and combinatorial optimization.Supported by the National Science Foundation under contract NSF ECS 83 52030 with matching funds provided by AT&T. Postal address: CSL, 1101 W. Springfield, Urbana IL 61801, USA.     

Scheduling with asynchronous service opportunities withapplications to multiple satellite systems

A single server is assigned to M parallel queues with independent Poisson arrivals. Service times are constant, but the server has the opportunity to initiate service at a given queue only at times forming a Poisson process. Four related scheduling policies are investigated: a simple first-come, first-serve policy for which the stability region is determined: a policy with maximum throughput, but requiring the server to have advance knowledge of service opportunities; a policy of threshold type, which is shown to be optimal among nonlookahead policies with preemption; and an adaptive policy, which when M=2 is shown to provide stability for all arrival rate vectors for which stability is possible under any nonlookahead policy with preemption. The work is motivated by the problem of transmission scheduling for a packet-switched, low-altitude, multiple-satellite system     

Scheduling nonuniform traffic in a packet-switching system withsmall propagation delay

A new model of nonuniform traffic is introduced for a single-hop packet-switching system. This traffic model allows arbitrary traffic streams subject only to a constraint on the number of data packets which can arrive at any, individual source in the system or for any individual destination in the system over time periods of specified length. The nonuniform traffic model is flexible enough to cover integrated data networks carrying diverse classes of data. The system model is rather general, and includes passive optical star wavelength-division networks. Transmission algorithms are introduced for a single-hop packet-switching system with such nonuniform traffic and with propagation delay that is negligible relative to the packet length. The algorithms are based on collision-free scheduling of packets using graph-matching algorithms since the global state of the system is known to all stations at any time