A study of the ion implantation damage and annealing behavior in GaSb

The effects of damages produced by implantation of Te, Er, Hg, and Pb ions into undoped (100) GaSb single crystals and their recovery by Rutherford backscattering (RBS)/channeling were investigated. The implantations with dosages in the range of 10¹³ to 10¹⁵ ions/cm² were carried out at liquid nitrogen temperature, at energies corresponding to a projected range of 447Å in GaSb. Near surface damage equivalent to that of an amorphous layer was observed even at lower doses. The samples were annealed at 600°C for different durations, with the Te implanted sample of the lowest dosage exhibiting the best recovery (Χ_min = 11%) compared to others. This value of Χ^min nearly corresponds to that of the virgin crystal. Examination of the surface morphology as a function of mass, dosage, and annealing duration revealed that it was strongly influenced by the dosage of the implanted ions.     

Genetic search: analysis using fitness moments

Genetic algorithms (GAs) are efficient and robust search methods that are being employed in a plethora of applications with extremely large search spaces. The directed search mechanism employed in GAs performs a simultaneous and balanced exploration of new regions in the search space and exploitation of already-discovered regions. This paper introduces the notion of fitness moments for analyzing the working of GAs. We show that the fitness moments in any generation may be predicted from those of the initial population. Since a knowledge of the fitness moments allows us to estimate the fitness distribution of strings, this approach provides for a method of characterizing the dynamics of GAs. In particular, the average fitness and fitness variance of the population in any generation may be predicted. We introduce the technique of fitness-based disruption of solutions for improving the performance of GAs. Using fitness moments, we demonstrate the advantages of using fitness-based disruption. We also present experimental results comparing the performance of a standard GA and two other GAs (the controlled disruption GA and the adaptive GA) that incorporate the principle of fitness-based disruption. The experimental evidence clearly demonstrates the power of fitness-based disruption     

Performance-driven MCM partitioning through an adaptive geneticalgorithm

We present a novel genetic algorithm-based partitioning scheme for multichip modules (MCM's) which integrates four performance constraints simultaneously: pin count, area, heat dissipation, and timing. We also present a similar partitioning algorithm based on evolutionary programming. Experimental studies demonstrate the superiority of these methods over deterministic Fiduccia-Mattheyes (FM) algorithm and simulated annealing (SA) technique. Our approach performs better than another genetic algorithm-based method recently reported. The adaptive change of crossover and mutation probabilities results in better convergence of the partitioning algorithm     

Ag-doping-induced coordination incompatibility and its effect on superconductivity in YBCO

A series of samples of YBa₂Cu_3-xAg_xO_7-y with 0≤x≤0.12 composition was studied to probe into the Ag substitution effect on oxygen stoichiometry, lattice parameters, and superconducting properties. With the samples prepared at a relatively lower sintering temperature, Ag could be doped in the grains rather than precipitate at grain boundaries. Thus, unlike in the case of YBCO + Ag composites or in doped systems annealed at high temperatures where Ag occupies mostly the grain boundary, the present system showed a drastic change inT _c, oxygen stoichiometry, and lattice parameters with Ag concentration, indicating the substitution of Ag at the Cu(l) sites in the grains. The stable 2-fold oxygen coordination of Ag substituting Cu(l)’s explains the observed variation of oxygen deficiency with Ag. A crystallochemical analysis has been made to reveal the crucial role of Ag-substitution-induced coordination incompatibility and charge state instability on carrier concentration andT _c.     

Comparative study of reactivity and agronomic effectiveness of Indian,US, African and Middle East rock phosphates for growing rice

Comparative reactivity and efficiency of eight Indian, six US, two African and one Middle East sources of rock phosphates for growing rice on laterite, red and alluvial soils under flooded conditions were evaluated in pot and laboratory experiments. When applied to moist aerobic soils, 15 days prior to flooding and transplanting rice, all the Indian sources were as poor as theno phosphate control in the three soil types, in respect of P availability in soil, grain yield response and P uptake by rice. North Carolina rock phosphate used in this study was as good as superphosphate in the laterite and red soils, but was also as poor as control in the black soil.NH₄ -citrate was found to interfere in the colorimetric determination of citrate soluble P by the vanado-molybdate colour method. A modified sulpho-molybdate-Sn Cl₂ blue colour method could successfully be used to determine 2–8µg P in the presence of 0.02 to 0.2 meq NH₄ -citrate, especially in rocks containing small amounts of citrate soluble P. All the Indian, as well as Idaho, Missouri and Tennessee rock phosphates were found to be less reactive as they contained much lower amounts of citrate extractable P in eight successive extracts as compared to North Carolina rock phosphate.The cumulative citrate soluble P of 10 rock phosphates determined experimentally in eight successive extracts was significantly correlated with their reported a₀ (length of a axis of unit apatite crystal), mole ratio of CO₃/PO₄ or weight ratio of F/P₂O₅ of rocks. In the absence of X-ray and computer facilities, these regression equations were used to calculate the a₀, CO₃/PO₄, F/P₂O₅, ACS, empirical formula and the apatite content of the unknown Indian rock samples. The Indian rock phosphates had a lower degree of CO₃ and F substitution for PO₄ in the apatite crystal, giving low ACS values and hence were less reactive. This might explain their lower efficiency for direct application for growing rice, obtained in the present experiment. These Indian rock phosphates had also lower apatite content. The use of the statistical method was limited to francolites alone. Scope for the use of this method for other unknown francolite rock phosphate samples has been discussed.     

Design of a Multibus-compatible colour graphics subsystem

Colour graphics subsystems can be used in a variety of applications such as high-end business graphics, low-end scientific computations, and for realtime display of process control diagrams. The design of such a subsystem is shown. This subsystem can be added to any Multibus-compatible microcomputer system. The use of an NEC 7220 graphics display controller chip has simplified the design to a considerable extent. CGRAM (CORE graphics on Multibus), a comprehensive subset of the CORE graphics standard package, is supported on the subsystem.     

Palliative therapy in advanced ovarian cancer: balancing patient expectations, quality of life and cost

The goals of chemotherapy for recurrent/refractory ovarian cancer are the palliation of disease-related symptoms, and improvement of quality and quantity of life. Previous studies of palliative therapy in advanced ovarian cancer have focused on surrogate measures of patient benefit rather than evaluating palliative end-points such as quality of life and clinical benefit. The impact of palliative chemotherapy on survival, quality of life and cost in advanced ovarian cancer are unknown as there have been no studies comparing palliative treatment with best supportive care. Although there is insufficient information from existing studies to determine whether palliative therapy in advanced ovarian cancer is cost-effective, there is some evidence to suggest that chemotherapy has a role in palliation of symptoms with an apparent improvement in quality of life. We relate the results of two studies. (i) A prospective study evaluating the cost of second/third-line chemotherapy as well as its effectiveness, which found the mean total cost per patient for the study period (one line of chemotherapy) was Canadian $12500. In addition, half of patients seemed to derive some palliative benefit and a quarter of patients had an objective response in their disease. (ii) A retrospective study evaluating all costs from the initiation of palliative chemotherapy until death which demonstrated a cost of Canadian $53000 per patient. Our studies demonstrate that patient expectations of palliative therapy in ovarian cancer are high and patients are willing to put up with significant toxicity for modest benefit. Although palliative therapy may be associated with high costs, even modest prolongation of survival can render such treatment cost-effective. The major cost saving associated with palliative therapy is from the reduced need for hospitalization towards the end of life. Future studies in recurrent/refractory ovarian cancer should focus on palliative end-points and include a comparison with best supportive care.     

Invariant-preserving Petri net reduction and conditions for invariant-existence

The use of invariants is an important tool for analysis of distributed and concurrent systems modeled by Petri nets. For a large practical system, the computation of desired invariants by the existing techniques is a time-consuming task. This paper proposes a theoretical foundation for simplified computation of desired invariants. We provide invariant-preserving Petri net reduction rules followed by the conditions for the existence of invariants in various well-structured nets. If an invariant exists, it can be found directly from the net structure using the formulas derived, or by applying the existing techniques on the reduced net.     

Optimum design of stiffened cylindrical panels with constraint on the frequency in the presence of initial stresses

This paper presents the optimum design of stiffened cylindrical panels with weight as the objective function and constraints on the frequencies in the presence of initial stresses, using unconstrained minimization techniques of non-linear mathematical programming problem. The interaction between the buckling constraints and the frequency constraints in the presence of initial stresses are included in the formulation. Loss of load carrying capacity due to imperfection and due to suddenly applied loads are included in the buckling analyses. Results for cylindrical shell are obtained by setting the panel angle to 360 degrees. The relationship between the weight of the cylinder and the panel (a segment of the cylinder) is examined.     

On automated optimum design of trusses

In the course of formulating the automated design of trusses for a project, some hitherto unexplored ideas have been encountered. These ideas are developed in this article.To explore these ideas systematically, truss design for single and multiple load conditions are considered separately. In the first part the applicability of linear programming is illustrated for single load conditions to safeguard against failures by yielding, buckling, and excessive deformations. Postoptimal behaviour of the structure is also studied.In the second part nonlinear programming is used as the design tool for multiple loading conditions. In this procedure, the members are grouped, a fully utilized design is taken as the starting point, and the condensed matrix displacement method of reanalysis is adopted during optimization iterations.Practical design examples of trussed towers are given to illustrate the capabilities of the computer program developed.