Towards More Practical Linear Programming-based Techniques for Algorithmic Mechanism Design

R. Lavi and C. Swamy (FOCS 2005, J. ACM 58(6), 25, 2011) introduced a general method for obtaining truthful-in-expectation mechanisms from linear programming based approximation algorithms. Due to the use of the Ellipsoid method, a direct implementation of the method is unlikely to be efficient in practice. We propose to use the much simpler and usually faster multiplicative weights update method instead. The simplification comes at the cost of slightly weaker approximation and truthfulness guarantees.     

An Efficient Numerical Solution of Fractional Optimal Control Problems by using the Ritz Method and Bernstein Operational Matrix

This paper deals with the Ritz spectral method to solve a class of fractional optimal control problems (FOCPs). The developed numerical procedure is based on the function approximation by the Bernstein polynomials along with fractional operational matrix usage. The approximation method is computationally consistent and moreover, has a good flexibility in the sense of satisfying the initial and boundary conditions of the optimal control problems. We construct a new fractional operational matrix applicable in the Ritz method to estimate the fractional and integer order derivatives of the basis. As a result, we achieve an unconstrained optimization problem. Next, by applying the necessary conditions of optimality, a system of algebraic equations is obtained. The resultant problem is solved via Newton's iterative method. Finally, the convergence of the proposed method is investigated and several illustrative examples are added to demonstrate the effectiveness of the new methodology.     

MCM-41-supported NNO type Schiff base complexes: a highly selective heterogeneous nanocatalyst for esterification,Diels–Alder and aldol condensation

Solid catalysts have been synthesized by anchoring transition metal complexes into organically modified MCM-41. First, the surface of Si-MCM-41 was modified with 3-aminopropyl-triethoxysilane (3-APTES), the imine group of which upon condensation with DFP (4-methyl-2,6-diformylphenol) affords a N₂O-type Schiff base moiety in the mesoporous matrix. The Schiff base moieties were used to anchor Ni (II) and Cu (II) ions. The prepared catalyst have been characterized by DRS (Diffuse Reflectance Spectroscopy), FTIR (Fourier transform infrared) spectroscopy, small-angle X-ray diffraction (SAX), FESEM (Field Emission Scanning Electron Microscope), EDX (Energy-dispersive X-ray spectroscopy) and nitrogen sorption studies. The decrease of crystallinity in the multistep synthesis procedure, as evidenced by SAX (Small-angle X-ray) measurements, was observed. The prepared materials proved to be efficient catalysts for organic transformations such as esterification, Diels–Alder and Aldol condensation at ambient conditions. The immobilized complex does not leach or decompose during the catalytic reactions, showing practical advantages over the free metal complex.     

Cross-layer optimization for wireless mesh networks with smart antennas

A cross-layer optimization framework for wireless mesh networks is presented where at each node, various smart antenna techniques such as beam-forming, spatial division multiple access and spatial division multiplexing are employed. These techniques provide interference suppression, capability for simultaneous communication with several nodes and transmission with higher data rates, respectively, through multiple antennas. By integrating different combinations of the multi-antenna techniques in physical layer with various constraints from MAC and network layers, three Mixed Integer Linear Programming (MILP) models are presented to minimize the system activation time. Since these optimization problems are complex combinatorial, the optimal solution is approached by a Column Generation decomposition method. The numerical results for different network scenarios with various node densities, number of antennas, transmission ranges and number of sessions are provided. It is shown that the resulted directive, multiple access and multiplexing gains combined with scheduling, effectively increase both the spectrum spatial reuse and the capacity of the links and therefore, enhance the achievable system throughput. Our cross-layer approach is also extended to consider heterogeneous networks and we present a multi-criteria optimization framework to model the design problem where the objective is to jointly minimize the cost of deployment and the system activation time. Our results reveal the benefits of joint design in terms of reducing the cost of deployment while achieving higher system performance.     

Output control design and separation principle for a class of port‐Hamiltonian systems

Using a structure preserving observer, a dynamic output controller is proposed for a class of port‐Hamiltonian systems. The core of this method is based on the notion of contractive port‐Hamiltonian systems. The proposed method utilizes an extended form of IDA‐PBC (interconnection and damping assignment passivity‐based control), a well‐known controller design method for port‐Hamiltonian systems and paves the way for using IDA‐PBC in output control design of challenging control objectives, such as output tracking for underactuated mechanical systems. In the line of output control design, a useful separation principle for a class of port‐Hamiltonian systems is achieved, which is valuable in the field of nonlinear systems. Some simulations on magnetic levitation and ball on wheel testbeds show the potency and applicability of the proposed method.     

Theoretical studies on dimerization reactions of 4, 7-diphenyl-1,10-phenanthroline (BPhen) and bathocuproine (BCP) in organic semiconductors

The dimerization reactions of 4, 7-diphenyl-1,10-phenanthroline (BPhen) and bathocuproine (BCP) were studied theoretically. In this work, the molecular geometries, BPhen and BCP monomers, positively charged BPhen and BCP intermediates, and BPhen and BCP dimers were calculated in neutral state at different levels of ab initio methods for the dimerization reactions. The molecular geometries of the BPhen and the BCP monomers and their dimers in their cationic and anionic states were optimized using the B3LYP/6-31G(d) method. The π orbitals interactions in the phenyl groups are responsible for the shortening of the C₆-N₁ and C₇-N₁ bond distances in BPhen and BCP dimers. The large difference between the reorganization energy components of BCP dimer for hole transport process is due to larger energy required to reorganize C₅C₄N₂C₆ and C₈C₁N₁C₇ angles. The methyl groups and the phenyl rings act as sterically hindering groups in the BPhen and BCP dimers. In contrast to BPhen dimer where its electron hopping rate is less than BPhen monomer, the magnitude of electron hopping rate of BCP dimer is 12 times higher than BCP monomer.     

Nano-sized manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis: a review

There has been a tremendous surge in research on the synthesis of various metal compounds aimed at simulating the water-oxidizing complex (WOC) of photosystem II (PSII). This is crucial because the water oxidation half reaction is overwhelmingly rate-limiting and needs high over-voltage (approx. 1 V), which results in low conversion efficiencies when working at current densities required for hydrogen production via water splitting. Particular attention has been given to the manganese compounds not only because manganese has been used by nature to oxidize water but also because manganese is cheap and environmentally friendly. The manganese–calcium cluster in PSII has a dimension of about approximately 0.5 nm. Thus, nano-sized manganese compounds might be good structural and functional models for the cluster. As in the nanometre-size of the synthetic models, most of the active sites are at the surface, these compounds could be more efficient catalysts than micrometre (or bigger) particles. In this paper, we focus on nano-sized manganese oxides as functional and structural models of the WOC of PSII for hydrogen production via water splitting and review nano-sized manganese oxides used in water oxidation by some research groups.     

Transient stability enhancement of power systems via optimal nonlinear state feedback control

In this paper, the transient stabilization of power systems will be enhanced using optimal nonlinear feedback control. To this end, a partial differential equation called Hamilton-Jacobi-Belman (HJB), should be solved, which does not have a closed form solution in general. Nevertheless, there are some approximate solutions to solve HJB equations. In this paper, by using a Taylor Series expansion, a sub-optimal nonlinear control law is obtained. As a result, a transient controller for a single-machine infinite-bus power system is designed. Also, the superiority of the designed nonlinear controller in some grounds like increasing the region of asymptotic stability of the system or in other words, increasing the domain of validity is shown. Simulation results reveal the effectiveness of the proposed approach.     

Static data based damage localization of beam-column structures considering axial load

Abstract

A crack localization method for beam-column structures is proposed considering axial load effects. Application of the method on a simply supported beam and a cantilever with simply supported beam-column demonstrated that the locations of single and multiple damage scenarios can be well determined in low axial loads. However, in the vicinity of the critical load, healthy and damaged static data are uncommon. Moreover, with increase in the axial load, the locations of single and multiple damage scenarios cannot be precisely specified. A more sensitive damage indicator is subsequently proposed to demonstrate the effects of axial forces comparable to critical loads.