A Heuristic Procedure for Leasing Channels in Telecommunications Networks

Rapid advances in computing and communications technology have made distributed computing an attractive alternative for geographically dispersed organizations. A telecommunication sub-network forms the backbone of these distributed systems. In general, this paper focuses on the assignment of communication channel capacities in the presence of time variant usage patterns. Specifically, we concentrate on long-range capacity planning for organizations that construct networks by leasing communication channels from telecommunication companies. We formulate the capacity assignment problem as a 0-1 integer program that seeks to minimize total leasing cost subject to communication delay restrictions. Unlike previous models that include a single-system wide-average delay constraint, our model allows the flexibility of specifying delay restrictions by communicating node pairs. We propose an efficient heuristic, and a Lagrangian relaxation based procedure to obtain performance guarantees on the solution obtained from the heuristic.     

Collision-induced dissociation in (He, H2(+)(v = 0-2; j = 0-3)) system: a time-dependent quantum mechanical investigation

The collision-induced process He + H(2)(+)(v = 0-2; j = 0-3) → He + H + H(+) has been investigated using a time-dependent quantum mechanical wave packet approach, within the centrifugal sudden approximation. The exchange reaction He + H(2)(+) → HeH(+) + H, which has a lower threshold, dominates over the dissociation process over the entire energy range considered in this study. The reaction cross section for both the exchange and dissociation channels and the branching ratio between the two channels have been computed on the McLaughlin-Thompson-Joseph-Sathyamurthy potential-energy surface and compared with the available experimental and quasiclassical trajectory results.     

Quantum 1/f noise associated with ionized impurity scattering and electron-phonon scattering in condensed matter

Scattering of charged particles is accompanied by the emission of soft photons. Handel's theory of 1/f noise, based on the infrared quasi-divergent coupling of the system to the electromagnetic field, indicates that the current associated with a beam of scattered particles will exhibit 1/f noise. His derivation is valid in a vacuum. Here we extend his results and obtain the fluctuation spectrum for the fluctuations in cross-section and for the scattering rates w _kk′ in k-space, using the Born approximation. Next we consider mobility fluctuations due to these scattering rates, employing the relaxation time solutions of the Boltzmann transport equation, valid in non-degenerate semiconductors. Explicit results are obtained for the mobility-fluctuation noise caused by ionized impurity scattering, acoustic phonon scattering, optical phonon scattering, polar optical phonon scattering, and intervalley scattering. We derive Hooge's law, and the Hooge parameters for the above-mentioned processes are obtained in detail. This is then applied to n-type silicon and n-type gallium arsenide; the overall Hooge parameter, which is a weighted average of the partial α-parameters, is computed as a function of temperature and compared with experiment. For silicon, good agreement is obtained with available data. As a byproduct we also find the mobilities as function of temperature for these materials. Excellent agreement with the well-known experimental data is observed.

We still note that this is the first theoretical derivation of Hooge's law and that the magnitude of the noise is obtained in detail without adjustable parameters. We believe that quantum 1/f noise gives the limiting value of 1/f noise that can be observed.     

Catalytic addition methods for the synthesis of functionalized diazoacetoacetates and application to the construction of highly substituted cyclobutanones

[reaction: see text] Methyl 3-(trialkylsilanyloxy)-2-diazo-3-butenoate undergoes Lewis acid-catalyzed Mukaiyama aldol addition with aromatic and aliphatic aldehydes in the presence of low catalytic amounts of Lewis acids in nearly quantitative yields. Scandium(III) triflate is the preferred catalyst and, notably, addition proceeds without decomposition of the diazo moiety. Diazoacetoacetate products from reactions with aromatic aldehydes undergo rhodium(II)-catalyzed ring closure to cyclobutanones with high diastereocontrol. Examples of complimentary Mannich-type addition reactions with imines are reported.     

Hydroacylation of 2-vinyl benzaldehyde systems: an efficient method for the synthesis of chiral 3-substituted indanones

Asymmetric rhodium-catalyzed hydroacylation has been utilized in the synthesis of 3-substituted indanones with high conversions and enantioselectivity. The hydroacylation reaction of 2-vinyl benzaldehyde had been previously reported to give a low yield of indanone and an unidentified product. We have identified this compound as a dimer of the starting material. Substitution at the alpha-position of the 2-vinyl benzaldehyde substrates blocks the competitive dimerization reaction and allows the reaction to proceed with yields generally greater than 90%. Utilization of BINAP as a chiral ligand results in good chemical yields and enantioselectivity greater than 95% in most cases.     

2-D finite element analysis of rigid pavement considering dynamic vehicle–pavement interaction effects

In the present study, an improved solution algorithm based on Finite Element Method for dynamic analysis of rigid pavements under moving loads is presented incorporating vehicle–pavement interaction which is having significant effect on the response. The concrete pavement is discretized by finite and infinite plate elements. The underlying soil medium is modeled by Pasternak model. An attempt is made to consider the infinite extent of the pavement with introduction of infinite elements at both ends. A detailed study is carried out for the range of velocities for pavements of finite and infinite lengths resting on two parameter soil medium. The effect of soil modulus, shear modulus, pavement thickness and the vehicle–pavement interaction on the response of pavement is presented. Relationships are suggested in non-dimensional form to predict critical velocity and maximum deflection for three prominent peaks in case of analysis without VPI and first critical velocity range of analysis with VPI. Predicted values using these relationships are in good agreement with the actual values. The comparison between the response of finite and infinite pavement lengths revealed that the deflections are decreased and the critical velocity range is narrowed in case of pavements of infinite length.     

Simulation of two photon absorption in silicon wire waveguide for implementation of all optical logic gates

All optical switching action of silicon wire waveguide for the design of the proposed logic gates is simulated. This is one possible building block of the future all optical computer or photonic devices. All optical logic gates NOT, NAND and AND gates using two photon absorption in silicon wire waveguide are presented. Use of ultra short pulse has negligible free carrier absorption effect; hence the operating speed of the gates is very high and has potential application in photonic processing. NAND gate is universal one and thus one can perform any logical operation using this. The device (Si wire WG) requires low energy pulse and is ultrafast one.