An automatic parallelization framework for multicomputers

Several researchers have looked into various issues related to automatic parallelization of sequential programs for multicomputers. But there is a need for a coherent framework which encompasses all these issues. In this paper we present a such a framework which takes best advantage of the multicomputer architecture. We resort to tiling transformation for iteration space partitioning and propose a scheme of automatic data partitioning and dynamic data distribution. We have tried a simple implementation of our scheme on a transputer based multicomputer [1] and the results are encouraging.

Kinetics of oxidation of boron powder

The kinetics of the oxidation of electrodeposited boron powder and the boron powder produced by the reduction process were studied using thermogravimetry (TG). The oxidation was carried out by heating boron powder in a stream of oxygen. Both isothermal and non-isothermal methods were used to study the kinetics. Model-free isoconversional method was used to derive the kinetics parameters. A two step oxidation reaction (exothermic) was observed. The oxidation reaction could not be completed due to the formation of glassy layer of boric oxide on the surface of boron powder which acts as a barrier for further diffusion of oxygen into the particle. The activation energy obtained using model-free method for electrodeposited boron is 122 +/- 7 kJ mol(-1) whereas a value of 205 +/- 9 kJ mol(-1) was obtained for boron produced by the reduction process (commercially procured boron). Mechanistic interpretation of the oxidation reaction was done using model based method. The activation energy was found to depend on the size distribution of the particles and specific surface area of the powder. (C) 2010 Elsevier B.V. All rights reserved.

Edge Stabilities of Hexagonal Boron Nitride Nanoribbons: A First-Principles Study

We investigate the comparative stability of sp(2) bonded planar hexagonal boron nitride (h-BN) nanoribbon (BNNR) edges, using first principles calculations. We find that the pristine armchair edges have the highest degree of stability. Pristine zigzag edges are metastable, favoring planar reconstructions in the form of 5-7 rings] that minimizes the energy. Our investigation further reveals that the pristine zigzag edges can be stabilized against 5-7 reconstructions by passivating the dangling bonds at the edges by other elements, such as hydrogen (H) atoms. Electronic and magnetic properties of nanoribbons depend on the edge shapes and are strongly affected by edge reconstructions.

Texture Evolution in Boron Modified Ti-6Al-4V Alloy

Owing to their high strength-to-weight ratio, excellent mechanical properties and corrosion resistance, titanium (Ti) and its alloys, especially (alpha+beta) alloys like Ti-6Al-4V is the backbone materials for aerospace, energy, and chemical industries. Trace boron addition (similar to 0.1 wt. %) to the alloy Ti-6Al-4V produces a reduction in as-cast grain size by roughly an order of magnitude resulting in enhanced ductility, higher stiffness, strength and good fracture resistance. Boron addition could also affect the evolution of texture and microstructure in the material. The solidification microstructures of Boron free as well as Boron containing Ti-6Al-4V are found to be almost homogeneous from periphery towards the center of as-cast ingot in terms of both alpha-colony size and distribution. Boron addition substantially reduces alpha-colony size (similar to 50-80 mu m). A gradual change in alpha texture from periphery towards the center has been observed with orientations close to specific texture components suggesting the formation of texture zones. The mechanism of texture evolution can be visualized as a result of variant selection during solidification through (alpha+beta) phase field.

Combining Bayes Classification and Point Group Symmetry under Boolean Framework for Enhanced Protein Quaternary Structure Inference

Our ability to infer the protein quaternary structure automatically from atom and lattice information is inadequate, especially for weak complexes, and heteromeric quaternary structures. Several approaches exist, but they have limited performance. Here, we present a new scheme to infer protein quaternary structure from lattice and protein information, with all-around coverage for strong, weak and very weak affinity homomeric and heteromeric complexes. The scheme combines naive Bayes classifier and point group symmetry under Boolean framework to detect quaternary structures in crystal lattice. It consistently produces >= 90% coverage across diverse benchmarking data sets, including a notably superior 95% coverage for recognition heteromeric complexes, compared with 53% on the same data set by current state-of-the-art method. The detailed study of a limited number of prediction-failed cases offers interesting insights into the intriguing nature of protein contacts in lattice. The findings have implications for accurate inference of quaternary states of proteins, especially weak affinity complexes.

Quantum Dots and Nanoroads of Graphene Embedded in Hexagonal Boron Nitride

The quest for novel two-dimensional materials has led to the discovery of hybrids where graphene and hexagonal boron nitride (h-BN) occur as phase-separated domains. Using first-principles calculations, we study the energetics and electronic and magnetic properties of such hybrids in detail. The formation energy of quantum dot inclusions (consisting of n carbon atoms) varies as 1/root n, owing to the interface. The electronic gap between the occupied and unoccupied energy levels of quantum dots is also inversely proportional to the length scale, 1/root n-a feature of confined Dirac fermions. For zigzag nanoroads, a combination of the intrinsic electric field caused by the polarity of the h-BN matrix and spin polarization at the edges results in half-metallicity; a band gap opens up under the externally applied ``compensating'' electric field. For armchair nanoroads, the electron confinement opens the gap, different among three subfamilies due to different bond length relaxations at the interfaces, and decreasing with the width.

New open-framework phosphate and phosphite compounds of gallium

Five new open-framework compounds of gallium have been synthesized by hydrothermal methods and their structures determined by single crystal X-ray diffraction studies. The compounds, C8N4H26]Ga6F4(PO4)(6)], I, C5N3H11]Ga3F2(PO4)(3)]center dot H2O, II, C6N3H19]Ga-4(C2O4)(PO4)(4)(H2PO4)]center dot 2H(2)O, III, Ga2F3(HPO4)(PO4)]center dot 2H(3)O, IV, and C3N2H5](2)Ga-4(H2O)(3)(HPO3)(7)], V, possess three-dimensional structures. All the compounds are formed by the connectivity between the Ga polyhedra and phosphite/phosphate units. The observation of SBU-6 (I and II) and spiro-5 (IV) secondary building units (SBUs) are noteworthy. The flexibility of the formation of gallium phosphate frameworks has been established by the isolation of two related structures (I and II) from the same SBU units but different organic amines. Some of the present structures have close resemblance to the gallium phosphate phases known earlier. The compounds have been characterized by CHN analysis, powder XRD, IR, and TGA. (C) 2011 Elsevier B. V. All rights reserved.

Reactivation kinetics of boron acceptors in hydrogenated silicon during zero bias anneal

The reactivation kinetics of passivated boron accepters in hydrogenated silicon during zero bias annealing in the temperature range of 65-130 degrees C are reported, For large annealing times and high annealing temperatures, the reactivation process follows second-order kinetics and is rate limited by a thermally activated <(H)over tilde (2)> complex formation process, For short annealing times and low annealing temperatures, the reactivation rate is found to be larger than that due to <(H)over tilde (2)> complex formation alone. We conclude that the faster reactivation is caused by the diffusion of the liberated hydrogen atoms into the bulk as well as <(H)over tilde (2)> complex formation. The effective diffusion coefficient of hydrogen is measured and found to obey the Arrhenius relation with an activation energy (1.41 +/- 0.1) eV. (C) 1997 American Institute of Physics.

Synthetic studies directed towards the potent cytotoxic natural product ottelione A: stereoselective construction of the complete framework

A stereoselective strategy for the rapid acquisition of the complete framework (dideoxyottelione A) of the promising cytotoxic agent ottelione A, with four contiguous stereogenic centres on a hydrindane skeleton and a sensitive 4-methylenecyclohex-2-enone functionality, from the readily available Diels-Alder adduct of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene and norbornadiene, is delineated.

Boron nitride nanotubes and nanowires

Simple methods of preparing boron nitride nanotubes and nanowires have been investigated. The methods involve heating boric acid with activated carbon, multi-walled carbon nanotubes, catalytic iron particles or a mixture of activated carbon and iron particles, in the presence of NH3. While with activated carbon, boron nitride nanowires constitute the primary product, high yields of clean boron nitride nanotubes are obtained with multi-walled carbon nanotubes. Aligned boron nitride nanotubes are produced when aligned multi-walled carbon nanotubes are employed as the starting material suggesting the templating role of the nanotubes. Boron nitride nanotubes with different structures have been obtained by reacting boric acid with NH3 in the presence of a mixture of activated carbon and Fe particles. (C) 2002 Elsevier Science B.V. All rights reserved.

An open-framework cobalt oxalato-squarate containing a ligated amine

A cobalt oxalato-squarate of the formula [Co-2(C4O4)(C2O4)(C3N2H4)(2)], containing a ligated amine has been synthesized hydrothermally and its structure determined by single crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group P2(1)2(1)2 with a = 18.3845(8) Angstrom, b = 5.7884(3) Angstrom, c = 7.2598(4) Angstrom, V = 772.56(7)Angstrom(3) and Z = 4. It has a layered structure where two-dimensional sheets are formed by the connectivity of the squarate and the oxalate units with the cobalt centres, with the ligating amine molecules protruding out from the layers. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

A Convex Optimization Framework for Almost Budget Balanced Allocation of a Divisible Good

We address the problem of allocating a single divisible good to a number of agents. The agents have concave valuation functions parameterized by a scalar type. The agents report only the type. The goal is to find allocatively efficient, strategy proof, nearly budget balanced mechanisms within the Groves class. Near budget balance is attained by returning as much of the received payments as rebates to agents. Two performance criteria are of interest: the maximum ratio of budget surplus to efficient surplus, and the expected budget surplus, within the class of linear rebate functions. The goal is to minimize them. Assuming that the valuation functions are known, we show that both problems reduce to convex optimization problems, where the convex constraint sets are characterized by a continuum of half-plane constraints parameterized by the vector of reported types. We then propose a randomized relaxation of these problems by sampling constraints. The relaxed problem is a linear programming problem (LP). We then identify the number of samples needed for ``near-feasibility'' of the relaxed constraint set. Under some conditions on the valuation function, we show that value of the approximate LP is close to the optimal value. Simulation results show significant improvements of our proposed method over the Vickrey-Clarke-Groves (VCG) mechanism without rebates. In the special case of indivisible goods, the mechanisms in this paper fall back to those proposed by Moulin, by Guo and Conitzer, and by Gujar and Narahari, without any need for randomization. Extension of the proposed mechanisms to situations when the valuation functions are not known to the central planner are also discussed. Note to Practitioners-Our results will be useful in all resource allocation problems that involve gathering of information privately held by strategic users, where the utilities are any concave function of the allocations, and where the resource planner is not interested in maximizing revenue, but in efficient sharing of the resource. Such situations arise quite often in fair sharing of internet resources, fair sharing of funds across departments within the same parent organization, auctioning of public goods, etc. We study methods to achieve near budget balance by first collecting payments according to the celebrated VCG mechanism, and then returning as much of the collected money as rebates. Our focus on linear rebate functions allows for easy implementation. The resulting convex optimization problem is solved via relaxation to a randomized linear programming problem, for which several efficient solvers exist. This relaxation is enabled by constraint sampling. Keeping practitioners in mind, we identify the number of samples that assures a desired level of ``near-feasibility'' with the desired confidence level. Our methodology will occasionally require subsidy from outside the system. We however demonstrate via simulation that, if the mechanism is repeated several times over independent instances, then past surplus can support the subsidy requirements. We also extend our results to situations where the strategic users' utility functions are not known to the allocating entity, a common situation in the context of internet users and other problems.

Understanding the building-up process of three dimensional open-framework metal phosphates: Acid degradation of the 3D structures to lower dimensional structures

Acid degradation of 3D zinc phosphates primarily yields a one-dimensional ladder compound, an observation that is significant considering that the latter forms 3D structures on heating in water.

Development of solidification microstructure in boron-modified alloy Ti-6Al-4V-0.1B

Hypoeutectic boron addition (0.1 wt.%) to Ti-6Al-4V is known to cause significant refinement of the cast microstructure. In the present investigation, it has been observed that trace boron addition to Ti-6Al-4V alloy also ensures excellent microstructural homogeneity throughout the ingot. A subdued thermal gradient, related to the basic grain refinement mechanism by constitutional undercooling, persists during solidification for the boron-containing alloy and maintains equivalent beta grain growth kinetics at different locations in the ingot. The Ti-6Al-4V alloy shows relatively strong texture with preferred components (e.g. ingot axis parallel to[0 0 0 1] or [1 0 (1) over bar 0]) over the entire ingot and gradual transition of texture components along the radius. For Ti-6Al-4V-0.1B alloy, significant weakening characterizes both the high-temperature beta and room-temperature a texture. In addition to solidification factors that are responsible for weak beta texture development, microstructural differences due to boron addition, e.g. the absence of grain boundary alpha phase and presence of TiB particles, strongly affects the mechanism of beta -> alpha phase transformation and consequently weakens the alpha phase texture. Based on the understanding developed for the boron-modified alloy, a novel mechanism has been proposed for the microstructure and texture formation during solidification and phase transformation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.