Specification-driven approach for protocol design of distributed computing systems

An important issue in the design of a distributed computing system (DCS) is the development of a suitable protocol. This paper presents an effort to systematize the protocol design procedure for a DCS. Protocol design and development can be divided into six phases: specification of the DCS, specification of protocol requirements, protocol design, specification and validation of the designed protocol, performance evaluation, and hardware/software implementation. This paper describes techniques for the second and third phases, while the first phase has been considered by the authors in their earlier work. Matrix and set theoretic based approaches are used for specification of a DCS and for specification of the protocol requirements. These two formal specification techniques form the basis of the development of a simple and straightforward procedure for the design of the protocol. The applicability of the above design procedure has been illustrated by considering an example of a computing system encountered on board a spacecraft. A Petri-net based approach has been adopted to model the protocol. The methodology developed in this paper can be used in other DCS applications.

A computer study of the miscibility limits of Sb-Te-Bi

The quaternary system Sb1bTe1bBi1bSe with small amounts of suitable dopants is of interest for the manufacture of thermoelectric modules which exhibit the Peltier and Seebeck effects. This property could be useful in the production of energy from the thermoelectric effect. Other substances are bismuth telluride (Bi2Te3) and Sb1bTe1bBi and compounds such as ZnIn2Se4. In the present paper the application of computer programs such as MIGAP of Kaufman is used to indicate the stability of the ternary limits of Sb1bTe1bBi within the temperature ranges of interest, namely 273 K to 300 K.

Sequential design of decentralized control systems

Our main result is a new sequential method for the design of decentralized control systems. Controller synthesis is conducted on a loop-by-loop basis, and at each step the designer obtains an explicit characterization of the class C of all compensators for the loop being closed that results in closed-loop system poles being in a specified closed region D of the s-plane, instead of merely stabilizing the closed-loop system. Since one of the primary goals of control system design is to satisfy basic performance requirements that are often directly related to closed-loop pole location (bandwidth, percentage overshoot, rise time, settling time), this approach immediately allows the designer to focus on other concerns such as robustness and sensitivity. By considering only compensators from class C and seeking the optimum member of that set with respect to sensitivity or robustness, the designer has a clearly-defined limited optimization problem to solve without concern for loss of performance. A solution to the decentralized tracking problem is also provided. This design approach has the attractive features of expandability, the use of only 'local models' for controller synthesis, and fault tolerance with respect to certain types of failure.

A novel approach to design of cis-acting DNA structural element for regulation of gene expression in vivo

Taking advantage of the degeneracy of the genetic code we have developed a novel approach to introduce, within a gene, DNA sequences capable of adopting unusual structures and to investigate the role of such sequences in regulation of gene expression in vivo. We used a computer program that generates alternative codon sequences for the same amino-acid sequence to convert a stretch of nucleotides into an inverted-repeat sequence with the potential to adopt cruciform structure. This approach was used to replace a 51-base-pair EcoRI-HindIII segment in the N-terminal region of the beta-galactosidase gene in plasmid pUC19 with a 51-bp synthetic oligonucleotide sequence with the potential to adopt a cruciform structure with 18 bp in the stem region. In selecting the 51-bp sequence, care was taken to include those codons that are preferred in E. coli. E. coli DH5-alpha cells harbouring the plasmid containing the redesigned sequence showed drastic reduction in expression of the beta-galactosidase gene compared to cells harbouring the plasmid with the native sequence. This approach demonstrates the possibility of introducing DNA secondary-structure elements to alter regulation of gene expression in vivo.

Design of solid electrolytes for use with dissimilar gas electrodes

The design of a solid electrolyte that permits the use of dissimilar gas electrodes in an electrochemical cell is presented. It consists of a functionally gradient material with spatial variation in composition. The activity of the conducting ion is fixed at each electrode using different gas species. The system chosen for demonstrating the concept consists of a solid solution between K2CO3 and K2SO4. The composition of the solid solution varies from pure K2CO3 in contact with a CO2 + O2 gas mixture at one electrode to pure K2SO4 exposed to a mixture of SO3 + SO2 + O2 at the other. Two types of composition profiles are studied, one with monotonic variation in composition and the other with extrema. The e.m.f. of the cells is studied as a function of temperature and composition of the gas mixture at each electrode. The results indicate that the e.m.f. is determined primarily by the difference in the chemical potential of potassium at the two electrodes. The diffusion potential caused by ionic concentration gradients in the electrolyte appears to be negligible when the corresponding ionic transport numbers are insignificant. Studies on the response characteristics of the cell based on the gradient electrolyte indicate that the nature of the variation in composition of the electrolyte has only a minor effect on the time evolution of e.m.f. The gradient solid electrolytes have potential application in multielement galvanic sensors at high temperatures.

Real-time Computer Simulation of Three Dimensional Elastostatics using the Finite Point Method

Real-time simulation of deformable solids is essential for some applications such as biological organ simulations for surgical simulators. In this work, deformable solids are approximated to be linear elastic, and an easy and straight forward numerical technique, the Finite Point Method (FPM), is used to model three dimensional linear elastostatics. Graphics Processing Unit (GPU) is used to accelerate computations. Results show that the Finite Point Method, together with GPU, can compute three dimensional linear elastostatic responses of solids at rates suitable for real-time graphics, for solids represented by reasonable number of points.

A new approach to the design of electronic exchanges

Electronic Exchanges are double-sided marketplaces that allows multiple buyers to trade with multiple sellers, with aggregation of demand and supply across the bids to maximize the revenue in the market. In this paper, we propose a new design approach for an one-shot exchange that collects bids from buyers and sellers and clears the market at the end of the bidding period. The main principle of the approach is to decouple the allocation from pricing. It is well known that it is impossible for an exchange with voluntary participation to be efficient and budget-balanced. Budget-balance is a mandatory requirement for an exchange to operate in profit. Our approach is to allocate the trade to maximize the reported values of the agents. The pricing is posed as payoff determination problem that distributes the total payoff fairly to all agents with budget-balance imposed as a constraint. We devise an arbitration scheme by axiomatic approach to solve the payoff determination problem using the added-value concept of game theory.

Design of output dv/dt filter for motor drives

Modern PWM inverter output voltage has high dv/dt, which causes problems such as voltage doubling that can lead to insulation failure, ground currents that results in electromagnetic interference concerns. The IGBT switching device used in such inverter are becoming faster, exacerbating these problems. This paper proposes a new procedure for designing the LC clamp filter. The filter increases the rise time of the output voltage of inverter, resulting in smaller dv/dt. In addition suitable selection of resonance frequency gives LCL filter configuration with improved attenuation. By adding this filter at output terminal of inverter which uses long cable, voltage doubling effect is reduced at the motor terminal. The design procedure is carried out in terms of the power converter based per unit scheme. This generalizes the design procedure to a wide range of power level and to study optimum designs. The effectiveness of the design is verified by computer simulation and experimental measurements.

An advanced design of the solid-state cell for accurate thermodynamic measurements on ternary oxides: system Sm–Pd–O

An advanced design of the solid-state cell incorporating a buffer electrode has been developed for high temperature thermodynamic measurements. The function of the buffer electrode, placed between reference and working electrodes, was to absorb the electrochemical flux of the mobile species through the solid electrolyte caused by trace electronic conductivity. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The application of the novel design and its advantages have been demonstrated by measuring the standard Gibbs energies of formation of ternary oxides of the system Sm–Pd–O. Yttria-stabilized zirconia was used as the solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Sm–Pd–O were investigated at 1273 K. The two ternary oxides, Sm4PdO7 and Sm2Pd2O5, compositions of which fall on the Sm2O3–PdO join, were found to coexist with pure metal Pd. The thermodynamic properties of the ternary oxides were measured using three-phase electrodes in the temperature range 950–1425 K. During electrochemical measurements a third ternary oxide, Sm2PdO4, was found to be stable at low temperature. The standard Gibbs energies of formation (Δf(ox)Go) of the compounds from their component binary oxides Sm2O3 and PdO, can be represented by the equations: Sm4PdO7: Δf(ox)Go (J mol−1)=−34,220+0.84T(K) (±280); Sm2PdO4: Δf(ox)Go (J mol−1)=−33,350+2.49T(K) (±230); Sm2Pd2O5: Δf(ox)Go (J mol−1)=−59,955+1.80T(K) (±320). Based on the thermodynamic information, three-dimensional P–T–C and chemical potential diagrams for the system Sm–Pd–O were developed.

Siding wear of materials

We review here our understanding of the sliding wear phenomenon: some generalities have emerged in the last 50 years of research, these can now be taken as established principles and be used for practical design and maintenance. Other issues related for example to nano-wear, the role of microstructure on wear or mechanism of crack nucleation require renewed efforts, for greater predictivity in wear. The review is based on published literature with examples principally drawn from our work on sliding wear of metals and ceramics.

Use of Vertex Index in Structure-Activity Analysis and Design of Molecules

The last few decades have witnessed application of graph theory and topological indices derived from molecular graph in structure-activity analysis. Such applications are based on regression and various multivariate analyses. Most of the topological indices are computed for the whole molecule and used as descriptors for explaining properties/activities of chemical compounds. However, some substructural descriptors in the form of topological distance based vertex indices have been found to be useful in identifying activity related substructures and in predicting pharmacological and toxicological activities of bioactive compounds. Another important aspect of drug discovery e. g. designing novel pharmaceutical candidates could also be done from the distance distribution associated with such vertex indices. In this article, we will review the development and applications of this approach both in activity prediction as well as in designing novel compounds.

Conservative Failure Criteria for Optimal Design of Composite Structures Including Effect of Shear Loading

A minimum weight design of laminated composite structures is carried out for different loading conditions and failure criteria using genetic algorithm. The phenomenological maximum stress (MS) and Tsai-Wu (TW) criteria and the micro-mechanism-based failure mechanism based (FMB) failure criteria are considered. A new failure envelope called the Most Conservative Failure Envelope (MCFE) is proposed by combining the three failure envelopes based on the lowest absolute values of the strengths predicted. The effect of shear loading on the MCFE is investigated. The interaction between the loading conditions, failure criteria, and strength-based optimal design is brought out.