Reliability Modeling and Analysis of Communication Networks with Dependent Failures

This paper presents a new model to study the reliability of communication networks in which link failures are statistically dependent. The approach tries to identify and model explicitly the events that cause communication link failures. No conditional probabilities are needed, and so two major difficulties inherent to them, namely, an exponential number of conditional probabilities to deal with and a consistency requirement to satisfy, are avoided. For reliability computations, some existing algorithms for finding network reliability can be used with minor modifications and no significant increase in computational complexity.     

Protocol design for scalable and reliable group rekeying

We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users.     

Mesoscale simulation of block copolymers in aqueous solution: parameterisation, micelle growth kinetics and the effect of temperature and concentration morphology

In this work, we utilise ‘MesoDyn’ [J Chem Phys 99 (1993) 9202; 106 (1997) 4260] density functional simulations to study the effect of temperature and concentration on the micellar morphology of polymeric surfactants. Parameterisation strategies based upon atomistic models and experimental data are discussed. Taking the temperature dependence of interaction energy into account, the change in morphology of Pluronic (PEO-PPO-PEO) block copolymer structure with temperature is well reproduced. As a function of concentration, the diameter of spherical micelles is found to increase in line with previous cryo-TEM observations [Phys Chem Chem Phys 1 (1999) 3331]. Simulations of high concentration PEO-PBO diblock systems show ordering similar to the face-centered cubic structures found experimentally [J Polym Sci B 33 (1995) 1085; Macromolecules 30 (1997) 5721; Polymer 39 (1998) 4891; Phys Chem Chem Phys 1 (1999) 2773].     

(BETS)2[RuX5NO] (X = Cl, Br): An Explanation of Different Conductive Properties Through Structural and Spectroscopic Studies

For the development of new crystal and electronic structures in molecular conductors, dimeric tetrathiafulvalene (TTF) and tetraselenafulvalenes (TSFs)1–3 linked by single or double methyl antimony bridge(s) have been prepared and their neutral crystal structures have been investigated. The donor2 (cis-2) forms a metallic cation radical salt with tetracyanoquinodimethane (TCNQ) containing one-dimensional array interactions.     

An analysis of lighting energy savings and switching frequency for a daylit corridor under various indoor design illuminance levels

Visual comfort and electric lighting energy issues are essential criteria to justify daylighting schemes. The evaluation of energy efficiency due to daylight linked lighting control systems is best demonstrated by case studies. This paper presents field measurements on daylighting for a fully air-conditioned daylit corridor. Artificial lighting load, brightness of the fluorescent luminaires, daylight availability for various switching illuminance levels were systematically recorded and analyzed. The general features and characteristics of the findings including the number of switching operations and electric-lighting energy savings are presented and discussed. Daylighting theories, using cumulative frequency distribution of outdoor illuminance and regression models based on brightness of light output, outdoor illuminance and electric light power to estimate daylight-linked lighting control savings, have been developed and assessed. It has been found that data from both approaches show reasonably good agreements with measured results. The findings from this study provide some operational and energy information, which would be useful and applicable to other interior spaces with similar architectural designs.     

Responses of somatostatin, beta-endorphin and dynorphin A to a glucose load in two groups of women with polycystic ovarian syndrome

Since the late 1980s, the eight-component model of the comprehensive school health program (CSHP), has been adopted widely in the United States and internationally. While it is acknowledged that the eight program elements should be delivered in a coordinated, interactive manner, numerous issues regarding how this integration best can be achieved, including who at the school level should have this responsibility and how the eight components relate conceptually and logistically, have not been addressed adequately. In essence, a CSHP transforms several solo performers into an orchestra. This article proposes the school health coordinator as an essential element in the eight-component model of the CSHP--the maestro, without whom there can be no symphony. The coordinator's principal responsibilities include administration, integration of personnel and programs, evaluation, and direct intervention. Three program elements--staff wellness, healthy environment, and community/family involvement--are subsumed within the coordinator's role, effectively reducing the number of program elements from eight to five. Potential benefits in addition to issues regarding feasibility of the SHC, are discussed and studies examining the effectiveness of the SHC model are recommended.     

Ahch, the mouse homologue of DAX1: cloning, characterization and synteny with GyK, the glycerol kinase locus

We cloned the murine full-length cDNA encoding Ahch, the mouse homologue of DAX1 (DSS-AHC Region on Human X Chromosome, Gene1) which is the gene responsible for human X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HH). Sequence analysis revealed that the murine and human cDNAs have 65% aa identity and 75% aa similarity overall. The cysteine residues in the putative DNA binding domain, which may interact with Zn2+ ions to form zinc fingers, are 100% conserved between the two species, indicating that the novel zinc-finger structures in DAX1 may be functional. In addition, mouse interspecific backcrosses show that the Ahch gene is closely linked to the glycerol kinase locus, GyK, on the mouse X chromosome, indicating that the order of the loci is conserved in this syntenic region between mouse and human.     

Scattering of waves by flaws in anisotropic laminated plates

The strip element method (SEM) is used to investigate wave scattering by rectangular flaws in anisotropic laminated plates. The plates containing flaws are divided by junctions into domains in which the SEM is applied. For each domain, SEM equations are obtained which give a relationship between the traction and displacement vector on the vertical boundaries. A set of equations which gives a relationship between the traction and displacement vector on the junctions is then obtained by assembling the SEM equations for all the domains. This set of equations is solved by using the conditions on the junctions. Scattered wave fields in the frequency domain for isotropic and composite plates with rectangular flaws are computed and discussed in comparison with results for corresponding plates without flaws. A technique for determining the length of a rectangular flaw in a plate is also presented. The results presented in this paper are of importance and could be used in the characterization of flaws in anisotropic laminated plates.