Nature of Cl center dot center dot center dot Cl Intermolecular Interactions via Experimental and Theoretical Charge Density Analysis:Correlation of Polar Flattening Effects with Geometry

The experimental charge density distribution in three compounds, 2-chloro-3-quinolinyl methanol, 2-chloro-3-hydroxypyridine, and 2-chloro-3-chloromethyl-8-methylquinoline, has been obtained using high-resolution X-ray diffraction data collected at 100 K based on the aspherical multipole modeling of electron density. These compounds represent type I (cis), type I (trans), and type II geometries, respectively, as defined for short Cl center dot center dot center dot Cl interactions. The experimental results are compared with the theoretical charge densities using theoretical structure factors obtained from a periodic quantum calculation at the B3LYP/6-31G** level. The topological features derived from the Bader's theory of atoms in molecules (AIM) approach unequivocally suggest that both cis and trans type I geometries show decreased repulsion, whereas type II geometry is attractive based on the nature of polar flattening of the electron density around the Cl atom.

Numerical and experimental study of the thermal behaviour of coining and upsetting processes

A numerical simulation technique has been employed to study the thermal behavior of hot-forging type forming processes. Experiments on the coining and upsetting of an aluminum billet were conducted to validate the numerical predictions. Typical forming conditions for both the coining and upsetting processes were then studied in detail. an electrical analogy scheme was used to determine the thermal contact resistance. This scheme can conviniently provide the interface characteristics for typical processing conditions, which normally involve high pressures and temperatures. A single forging cycle was first considered, and then a batch of twenty-five forgings was studied. Each forging cycle includes the billet mounting, ascent, loading, dwelling, unloading, descent, and billet removal stages. The temperature distribution in the first forging to be formed is found to be significantly different from that at the end of the batch. In industry, forging is essentially a batch operation. The influence of forming speed and reduction on thermal characteristics was investigated also. The variations that can occur in the process design by considering differences in temperature characteristics are discussed also.

Studies on helium flow in experimental loops with different impedances operated with fountain effect pumps

An experimental flow loop with He II flow driven by fountain effect pumps (FEPs) is studied with respect to operation at different flow impedances and with thermal loads applied at different positions. The measured values of temperature, flow rate and pressure drop are compared with calculations resulting from a simplified model which assumes ideal performance of the porous plug and of the heat exchangers and which does not take into account Gorter-Mellink (GM) conduction. The main features of the loop are shown to be well described by this model. Refined calculations with a more complex model, including GM conduction of the He II, are only required for predicting the temperature distribution in some discrete regions of the loop.

Algorithms for Routing and Centralized Scheduling in IEEE 802.16 Mesh Networks

IEEE 802.16 standards for Wireless Metropolitan Area Networks (WMANs) include a mesh mode of operation for improving the coverage and throughput of the network. In this paper, we consider the problem of routing and centralized scheduling for such networks. We first fix the routing, which reduces the network to a tree. We then present a finite horizon dynamic programming framework. Using it we obtain various scheduling algorithms depending upon the cost function. Next we consider simpler suboptimal algorithms and compare their performances.

Theoretical and experimental investigation of framed structure-layered soil interaction problems

The plane stress solution for the interaction analysis of a framed structure, with a foundation beam, resting on a layered soil has been studied using both theoretical and photoelastic methods. The theoretical analysis has been done by using a combined analytical and finite element method. In this, the analytical solution has been used for the semi-infinite layered medium and finite element method for the framed structure. The experimental investigation has been carried out using two-dimensional photoelasticity in which modelling of the layered semi-infinite plane and a method to obtain contact pressure distribution have been discussed. The theoretical and experimental results in respect of contact pressure distribution between the foundation beam and layered soil medium, the fibre stresses in the foundation beam and framed structure have been compared. These results have also been compared with theoretical results obtained by idealizing the layered semi-infinite plane as (a) a Winkler model and (b) an equivalent homogeneous semi-infinite medium

Time-domain-finite-wave analysis of the engine exhaust system by means of the stationary-frame method of characteristics. Part II. Computed results and experimental corroboration thereof

Time-domain-finite-wave analysis of engine exhaust systems is usually carried out by means of the method of characteristics. The theory and the computational details of the stationary-frame method have been worked out in the accompanying paper (part I). In this paper (part II), typical computed results are given and discussed. A setup designed for experimental corroboration is described. The results obtained from the simulation are found to be in good agreement with experimental observations.

Experimental Test of the Quantum No-Hiding Theorem

The no-hiding theorem says that if any physical process leads to bleaching of quantum information from the original system, then it must reside in the rest of the Universe with no information being hidden in the correlation between these two subsystems. Here, we report an experimental test of the no-hiding theorem with the technique of nuclear magnetic resonance. We use the quantum state randomization of a qubit as one example of the bleaching process and show that the missing information can be fully recovered up to local unitary transformations in the ancilla qubits.

Selectivity in Garratt-Braverman Cyclization: An Experimental and Computational Study

Bispropargyl sulfones equipped with aromatic rings of dissimilar nature were synthesized. Under basic conditions, these sulfones isomerized to the bisallenic sulfones, creating a competitive scenario between two alternate Garratt-Braverman (GB) cyclization pathways. The observed product distribution ruled out the involvement of any ionic intermediate and supported the diradical mechanism with greater involvement of the electron-rich aromatic ring via the more nucleophilic radical. DFT-based calculations supported the diradical mechanism along with the observed selectivity.

Points-to Analysis as a System of Linear Equations

We propose a novel formulation of the points-to analysis as a system of linear equations. With this, the efficiency of the points-to analysis can be significantly improved by leveraging the advances in solution procedures for solving the systems of linear equations. However, such a formulation is non-trivial and becomes challenging due to various facts, namely, multiple pointer indirections, address-of operators and multiple assignments to the same variable. Further, the problem is exacerbated by the need to keep the transformed equations linear. Despite this, we successfully model all the pointer operations. We propose a novel inclusion-based context-sensitive points-to analysis algorithm based on prime factorization, which can model all the pointer operations. Experimental evaluation on SPEC 2000 benchmarks and two large open source programs reveals that our approach is competitive to the state-of-the-art algorithms. With an average memory requirement of mere 21MB, our context-sensitive points-to analysis algorithm analyzes each benchmark in 55 seconds on an average.

New Approximation Algorithms for Minimum Cycle Bases of Graphs

We consider the problem of computing an approximate minimum cycle basis of an undirected non-negative edge-weighted graph G with m edges and n vertices; the extension to directed graphs is also discussed. In this problem, a {0,1} incidence vector is associated with each cycle and the vector space over F-2 generated by these vectors is the cycle space of G. A set of cycles is called a cycle basis of G if it forms a basis for its cycle space. A cycle basis where the sum of the weights of the cycles is minimum is called a minimum cycle basis of G. Cycle bases of low weight are useful in a number of contexts, e.g. the analysis of electrical networks, structural engineering, chemistry, and surface reconstruction. Although in most such applications any cycle basis can be used, a low weight cycle basis often translates to better performance and/or numerical stability. Despite the fact that the problem can be solved exactly in polynomial time, we design approximation algorithms since the performance of the exact algorithms may be too expensive for some practical applications. We present two new algorithms to compute an approximate minimum cycle basis. For any integer k >= 1, we give (2k - 1)-approximation algorithms with expected running time O(kmn(1+2/k) + mn((1+1/k)(omega-1))) and deterministic running time O(n(3+2/k) ), respectively. Here omega is the best exponent of matrix multiplication. It is presently known that omega < 2.376. Both algorithms are o(m(omega)) for dense graphs. This is the first time that any algorithm which computes sparse cycle bases with a guarantee drops below the Theta(m(omega) ) bound. We also present a 2-approximation algorithm with expected running time O(M-omega root n log n), a linear time 2-approximation algorithm for planar graphs and an O(n(3)) time 2.42-approximation algorithm for the complete Euclidean graph in the plane.

Load balancing algorithms for an extended hypercube

Reduction of the execution time of a job through equitable distribution of work load among the processors in a distributed system is the goal of load balancing. Performance of static and dynamic load balancing algorithms for the extended hypercube, is discussed. Threshold algorithms are very well-known algorithms for dynamic load balancing in distributed systems. An extension of the threshold algorithm, called the multilevel threshold algorithm, has been proposed. The hierarchical interconnection network of the extended hypercube is suitable for implementing the proposed algorithm. The new algorithm has been implemented on a transputer-based system and the performance of the algorithm for an extended hypercube is compared with those for mesh and binary hypercube networks

Absolutely expedient algorithms for learning Nash equilibria

This paper considers a multi-person discrete game with random payoffs. The distribution of the random payoff is unknown to the players and further none of the players know the strategies or the actual moves of other players. A class of absolutely expedient learning algorithms for the game based on a decentralised team of Learning Automata is presented. These algorithms correspond, in some sense, to rational behaviour on the part of the players. All stable stationary points of the algorithm are shown to be Nash equilibria for the game. It is also shown that under some additional constraints on the game, the team will always converge to a Nash equilibrium.

Accelerated gradient based diffuse optical tomographic image reconstruction

Purpose: Fast reconstruction of interior optical parameter distribution using a new approach called Broyden-based model iterative image reconstruction (BMOBIIR) and adjoint Broyden-based MOBIIR (ABMOBIIR) of a tissue and a tissue mimicking phantom from boundary measurement data in diffuse optical tomography (DOT). Methods: DOT is a nonlinear and ill-posed inverse problem. Newton-based MOBIIR algorithm, which is generally used, requires repeated evaluation of the Jacobian which consumes bulk of the computation time for reconstruction. In this study, we propose a Broyden approach-based accelerated scheme for Jacobian computation and it is combined with conjugate gradient scheme (CGS) for fast reconstruction. The method makes explicit use of secant and adjoint information that can be obtained from forward solution of the diffusion equation. This approach reduces the computational time many fold by approximating the system Jacobian successively through low-rank updates. Results: Simulation studies have been carried out with single as well as multiple inhomogeneities. Algorithms are validated using an experimental study carried out on a pork tissue with fat acting as an inhomogeneity. The results obtained through the proposed BMOBIIR and ABMOBIIR approaches are compared with those of Newton-based MOBIIR algorithm. The mean squared error and execution time are used as metrics for comparing the results of reconstruction. Conclusions: We have shown through experimental and simulation studies that Broyden-based MOBIIR and adjoint Broyden-based methods are capable of reconstructing single as well as multiple inhomogeneities in tissue and a tissue-mimicking phantom. Broyden MOBIIR and adjoint Broyden MOBIIR methods are computationally simple and they result in much faster implementations because they avoid direct evaluation of Jacobian. The image reconstructions have been carried out with different initial values using Newton, Broyden, and adjoint Broyden approaches. These algorithms work well when the initial guess is close to the true solution. However, when initial guess is far away from true solution, Newton-based MOBIIR gives better reconstructed images. The proposed methods are found to be stable with noisy measurement data. (C) 2011 American Association of Physicists in Medicine. DOI: 10.1118/1.3531572]

Diastereospecific Coupling of Imines by Low-Valent Titanium: An Experimental and Computational Study

The reaction of phenylsilane (PhSiH3) and titanium(IV) isopropoxide Ti(OiPr)(4)] generates low-valent titanium alkoxides that reduce and reductively couple imines. The C-C coupling reaction is diastereospecific, with exclusive formation of the (+/-)-isomer. The yield is dependent on the concentration of titanium(IV) isopropoxide used. Using imines with varying electronic demand revealed that the coupling is most efficient for unsubstituted imines. The involvement of a trimeric titanium biradical species is invoked to explain the observed concentration dependence and diastereospecificity in the reaction. Multilayer ONIOM (''our own n-layered integrated molecular orbital and molecular mechanics'') calculations were carried out on the plausible intermediates involved by using the Guassian 09 suite of programs. Formation of the trimeric biradical species leading to the formation of the (+/-)-isomer is more favored than formation of the trimeric biradical species, which leads to the meso-isomer. Similar calculations with dimeric intermediates do not predict the (+/-)-selectivity. Mass spectral analysis of the reaction mixture indicates the presence of a trimeric titanium alkoxide species.