Lattice embedding and equilibrium geometry of metal-halogen chains in the two-band extended Hubbard model

Two-band extended Hubbard model studies show that the shift in optical gap of the metal-halogen (MX) chain upon embedding in a crystalline environment depends upon alternation in the site-diagonal electron-lattice interaction parameter (epsilon(M)) and the strength of electron-electron interactions at the metal site (U(M)). The equilibrium geometry studies on isolated chains show that the MX chains tend to distort for alternating epsilon(M) and small U(M) values.

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

Effect of Short Duration of Load increment on the Compressibility of Soils

This study concerns the effect of duration of load increment (up to 24 h) on the consolidation properties of expansive black cotton soil (liquid limit = 81%) and nonexpansive kaolinite (liquid limit = 49%). It indicates that the amount and rate of compression are not noticeably affected by the duration of loading for a standard sample of 25 mm in height and 76.2 mm in diameter with double drainage. Hence, the compression index and coefficient of consolidation can be obtained with reasonable accuracy even if the duration of each load increment is as short as 4 h. The secondary compression coefficient (C-alpha epsilon) for kaolinite can be obtained for any pressure range with 1/2 h of loading, which, however, requires 4 h for black cotton soil. This is because primary consolidation is completed early in the case of kaolinite. The paper proves that the conventional consolidation test can be carried out with much shorter duration of loading (less than 4 h) than the standard specification of 24 h or more even for remolded fine-grained soils.

Scheduling expression trees with reusable registers on delayed-load architectures

In this paper, we look at the problem of scheduling expression trees with reusable registers on delayed load architectures. Reusable registers come into the picture when the compiler has a data-flow analyzer which is able to estimate the extent of use of the registers. Earlier work considered the same problem without allowing for register variables. Subsequently, Venugopal considered non-reusable registers in the tree. We further extend these efforts to consider a much more general form of the tree. We describe an approximate algorithm for the problem. We formally prove that the code schedule produced by this algorithm will, in the worst case, generate one interlock and use just one more register than that used by the optimal schedule. Spilling is minimized. The approximate algorithm is simple and has linear complexity.

Multi-installment load distribution in tree networks with delays

This paper presents a new strategy for load distribution in a single-level tree network equipped with or without front-ends. The load is distributed in more than one installment in an optimal manner to minimize the processing time. This is a deviation and an improvement over earlier studies in which the load distribution is done in only one installment. Recursive equations for the general case, and their closed form solutions for a special case in which the network has identical processors and identical links, are derived. An asymptotic analysis of the network performance with respect to the number of processors and the number of installments is carried out. Discussions of the results in terms of some practical issues like the tradeoff relationship between the number of processors and the number of installments are also presented.

Quantum-confinement effects on the ordering of the lowest-lying excited states in conjugated chains

The symmetrized density-matrix renormalization-group approach is applied within the extended Hubbard-Peierls model (with parameters U/t, V/t, and bond alternation delta) to study the ordering of the lowest one-photon (1(1)B(u)(-)) and two-photon (2(1)A(g)(+)) states in one-dimensional conjugated systems with chain lengths N up to N = 80 sites. Three different types of crossovers are studied, as a function of U/t, delta, and N. The ''U crossover'' emphasizes the larger ionic character of the 2A(g) state compared to the lowest triplet excitation. The ''delta crossover'' shows strong dependence on both N and U/t. the ''N crossover'' illustrates the more localized nature of the 2A(g) excitation relative to the 1B(u) excitation at intermediate correlation strengths.

Regular versus alternating (FeS4)(n) chains: Magnetism in KFeS2 and CsFeS2

We report crystal magnetic susceptibility results of two S = 1/2 one-dimensional Heisenberg antiferromagnets, KFeS2 and CsFeS2. Both compounds consist of (FeS4)(n) chains with an average Fe-Fe distance of 2.7 Angstrom. In KFeS2, all intrachain Fe-Fe distances are identical. Its magnetic susceptibility is typical of a regular antiferromagnetic chain with spin-spin exchange parameter J = -440.7 K. In CsFeS2, however, the Fe-Fe distances alternate between 2.61 and 2.82 Angstrom. This is reflected in its magnetic susceptibility, which could be fitted with J = -640 K, and the degree of alternation, alpha = 0.3. These compounds form a unique pair, and allow for a convenient experimental comparison of the magnetic properties of regular versus alternating Heisenberg chains.

Anomalous Behavior of Linear Hydrocarbon Chains in Water-DMSO Binary Mixture at Low DMSO Concentration

We find that at a mole fraction 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, a linear hydrocarbon chain of intermediate length (n = 30-40) adopts the most stable collapsed conformation. In pure water, the same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the hydrocarbon of chain length 30 (n = 30) is as large as 17%. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behavior to emerge near x(DMSO) = 0.15, due to a chain-like aggregation of the methyl groups of DMSO in water that lowers the relative concentration of the DMSO molecules in the hydration layer. We further find that as the concentration of DMSO is gradually increased, it progressively attains the extended coiled structure as the stable conformation. Although Flory-Huggins theory (for binary mixture solvent) fails to predict the anomaly at x(DMSO) = 0.05, it seems to capture the essence of the anomaly at 0.15.

Studies on age-hardening characteristics of ceramic particle/matrix interfaces in Al-Cu-SiCp composites using ultra low-load-dynamic microhardness measurements

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al-Cu-5SiC(p) composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.

Polymorphism in Opto-Electronic Materials with a Benzothiazole-fluorene Core: A Consequence of High Conformational Flexibility of pi-Conjugated Backbone and Alkyl Side Chains

Fluorene and its derivatives are well-known organic semiconducting materials in the field of opto-electronic devices because of their charge transport properties. Three new organic semiconducting materials, namely, 2,2'-((9,9-butyl-9H-fluorene-2,7-diyl)bis(4,1 phenylene))bisbenzod]thiazole, C4; 2,2'-((octyl-9H-fluorene-2,7-diyl)bis(4,1 phenylene))bisbenzod]thiazole, C8; and 2,2'-((9,9-dodecayl-9H-fluorene-2,7-diyl)bis(4,1 phenylene))bisbenzod]thiazole, C12 with a benzothiazole-fluorene backbone, were synthesized and characterized for their photophysical properties. A phenomenon of concomitant polymorphism has been investigated in the first two derivatives (C4 and C8) and has been analyzed systematically in terms of the packing characteristics involving pi ... pi interactions. The conformational flexibility of the pi-conjugated 2,2'-(fluorene-2,7-diyl)bis(4,1 phenylene)bisbenzod]thiazole backbone coupled with orientational freedom of the terminal alkyl chains were found to be the key factors responsible for these polymorphic modifications. Attempts to grow suitable crystals for single crystal X-ray diffraction of compound C12 were unsuccessful.

Modelling electricity demand with representative load curves

Models for electricity planning require inclusion of demand. Depending on the type of planning, the demand is usually represented as an annual demand for electricity (GWh), a peak demand (MW) or in the form of annual load-duration curves. The demand for electricity varies with the seasons, economic activities, etc. Existing schemes do not capture the dynamics of demand variations that are important for planning. For this purpose, we introduce the concept of representative load curves (RLCs). Advantages of RLCs are demonstrated in a case study for the state of Karnataka in India. Multiple discriminant analysis is used to cluster the 365 daily load curves for 1993-94 into nine RLCs. Further analyses of these RLCs help to identify important factors, namely, seasonal, industrial, agricultural, and residential (water heating and air-cooling) demand variations besides rationing by the utility. (C) 1999 Elsevier Science Ltd. All rights reserved.

Nematogens with more flexible chains than aromatic rings in the core

Mesogens containing four rings in the main core can accommodate one terminal and two nearby lateral chains on each outside aromatic ring. These compounds containing six chains present an enantiotropic nematic range which is influenced by the rigidity of the links. The conformational behaviour of the first methyleneoxy group within the chains was investigated by one and two dimensional C-13 NMR. The sign of the jump in chemical shifts when entering the nematic phase indicates the folding of each lateral branch. Dipolar oscillations during cross-polarization contact provide the values of the bond order parameter. The two First lateral fragments do not behave in the same way, demonstrating the influence of the fragment along which the chain is back: folded.

Profile-Based Load Scheduling in Wireless Energy Harvesting Sensors for Data Rate Maximization

In this paper, power management algorithms for energy harvesting sensors (EHS) that operate purely based on energy harvested from the environment are proposed. To maintain energy neutrality, EHS nodes schedule their utilization of the harvested power so as to save/draw energy into/from an inefficient battery during peak/low energy harvesting periods, respectively. Under this constraint, one of the key system design goals is to transmit as much data as possible given the energy harvesting profile. For implementational simplicity, it is assumed that the EHS transmits at a constant data rate with power control, when the channel is sufficiently good. By converting the data rate maximization problem into a convex optimization problem, the optimal load scheduling (power management) algorithm that maximizes the average data rate subject to energy neutrality is derived. Also, the energy storage requirements on the battery for implementing the proposed algorithm are calculated. Further, robust schemes that account for the insufficiency of battery storage capacity, or errors in the prediction of the harvested power are proposed. The superior performance of the proposed algorithms over conventional scheduling schemes are demonstrated through computations using numerical data from solar energy harvesting databases.

Relay Load Balancing in Queued Cooperative Wireless Networks with Rateless Codes

Relay selection combined with buffering of packets of relays can substantially increase the throughput of a cooperative network that uses rateless codes. However, buffering also increases the end-to-end delays due to the additional queuing delays at the relay nodes. In this paper we propose a novel method that exploits a unique property of rateless codes that enables a receiver to decode a packet from non-contiguous and unordered portions of the received signal. In it, each relay, depending on its queue length, ignores its received coded bits with a given probability. We show that this substantially reduces the end-to-end delays while retaining almost all of the throughput gain achieved by buffering. In effect, the method increases the odds that the packet is first decoded by a relay with a smaller queue. Thus, the queuing load is balanced across the relays and traded off with transmission times. We derive explicit necessary and sufficient conditions for the stability of this system when the various channels undergo fading. Despite encountering analytically intractable G/GI/1 queues in our system, we also gain insights about the method by analyzing a similar system with a simpler model for the relay-to-destination transmission times.