Synthesis and photophysical properties of poly-(phenylenevinylene) dendrimers with a ruthenium tris-bipyridine core

The photophysical processes have been investigated in first, second and third generation dendrimers with poly-(phenylenevinylene) branches and a ruthenium tris-bipyridine core, RuDn (n = 1–3). These dendrimers show very efficient forward singlet–singlet energy transfer from the branches to the ruthenium core upon UV irradiation, with efficiencies of 0.99 for RuD1 and 0.88 for RuD2 and RuD3 in CH₂Cl₂. The RuDn dendrimers show a bi-exponential emission decay in CH₂Cl₂, when excited with a 460 nm light with short lifetimes, however, the emission decay lifetimes become mono-exponential in 10% Triton X-100 aqueous solution (τ = 840 ns for RuD1, 890 ns for RuD2 and 1120 ns for RuD3).     

Joint replenishment model with substitution

When products are coupled to the same cycle, the joint replenishment model (JRM) is used to determine optimal inventory levels, where the amount to order (for each item) is designed to minimize the joint holding and ordering costs based on a given demand. JRM studies assume that there is no substitution between items. However, this assumption is unrealistic in some settings where substitution cannot be ignored. This paper combines the separate works on substitution and joint replenishment and proposes a solution procedure for solving the joint replenishment model with substitution (JRMS) for two products within the framework of the classical economic order quantity model. We determine the optimal order quantities for each product taking into consideration substitution between them so that demand is partially met and the total cost associated with the delivery, holding, and shortage of the products is minimized. We also provide an extensive scenario analysis and draw insights. In particular, we shed some light on the role of substitution in reducing the fixed cost. We show that JRMS can result in substantial cost savings compared to the ordinary JRM.     

Photophysical properties of new cyclometalated ruthenium complexes and their use in dye sensitized solar cells

A new class of cyclometalated ruthenium complexes, Ru(C^N^N')(N^N'^N')·Cl where N^N'^N' = 4,4',4'-tricarboxy-2,2':6',2'-terpyridine and C^N^N' = substituted 6-phenyl-2,2'-bipyridine, for Dye Sensitized Solar Cells (DSSCs) is proposed. We have investigated the effect of different substituents (R = COOH, thiophen-2-yl, F and OCH(3)) on the ancillary C^N^N' ligand on the photophysical properties and performance of the six different cyclometalated ruthenium complexes in DSSCs. Using an ionic liquid based electrolyte, efficiencies up to η = 3.06% have been attained under 1 sun irradiation. Moreover, the T66 based DSSC exhibited a good stability under 1000 W m(2) light soaking at 60 °C for 24 days, retaining 92.8% of its initial efficiency.     

A branch-and-cut algorithm based on semidefinite programming for the minimum <Emphasis Type="Italic">k</Emphasis>-partition problem

The minimum k-partition (MkP) problem is the problem of partitioning the set of vertices of a graph into k disjoint subsets so as to minimize the total weight of the edges joining vertices in the same partition. The main contribution of this paper is the design and implementation of a branch-and-cut algorithm based on semidefinite programming (SBC) for the MkP problem. The two key ingredients for this algorithm are: the combination of semidefinite programming with polyhedral results; and a novel iterative clustering heuristic (ICH) that finds feasible solutions for the MkP problem. We compare ICH to the hyperplane rounding techniques of Goemans and Williamson and of Frieze and Jerrum, and the computational results support the conclusion that ICH consistently provides better feasible solutions for the MkP problem. ICH is used in our SBC algorithm to provide feasible solutions at each node of the branch-and-bound tree. The SBC algorithm computes globally optimal solutions for dense graphs with up to 60 vertices, for grid graphs with up to 100 vertices, and for different values of k, providing a fast exact approach for k≥3.     

Pulse radiolysis studies of dendritic macromolecules with biphenyl peripheral groups and a ruthenium tris-bipyridine core.

Electron-transfer reactions in Fréchet-type dendrimers with biphenyl peripheral groups and a ruthenium core were investigated by pulse radiolysis techniques. Fast electron-transfer rates found in the two ruthenium dendrimers suggest a very efficient electronic coupling between the peripheral donor groups and the core acceptor.     

Cutting plane approach for the maximum flow interdiction problem

The maximum flow interdiction is a class of leader–follower optimization problems that seek to identify the set of edges in a network whose interruption minimizes the maximum flow across the network. Particularly, maximum flow interdiction is important in assessing the vulnerability of networks to disruptions. In this paper, the problem is formulated as a bi-level mixed-integer program and an iterative cutting plane algorithm is proposed as a solution methodology. The cutting planes are implemented in a branch-and-cut approach that is computationally effective. Extensive computational results are presented on 336 different instances with varying parameters and with networks of sizes up to 50 nodes, 1200 edge, and 800 commodities. The computational results show that the proposed cutting plane approach has significant computational advantage over the direct solution of the monolithic formulation of the maximum flow interdiction problem for the majority of the tested instances.     

Electrostatic layer-by-layer deposition of photoactive dendrimers with triviologen-like cores on their surfaces. Synthesis and electrochemical and photocurrent generation measurements

The stepwise assembly of Fréchet-type dendrimers with naphthalene peripheral groups and positively charged viologen-like cores on quartz and ITO surfaces utilizing the layer-by-layer approach was investigated. We were able to deposit only the (+6) charged dendrimers series on ITO. The number of assembled dendrimers was found to increase as we go to higher-generation dendrimers. This dendrimer generation effect was evident from the UV-vis and electrochemical measurements of the assembled dendrimers. The half-wave potentials (E1/2) of the dendrimers shift to less negative values as the dendrimer generation increases in acetonitrile and to more negative values when assembled on ITO. Anodic photocurrent generation was seen upon light irradiation of the second- and third-generation dendrimers, NB1V3+6 and NB2V3+6, assembled on ITO but not for the zero-generation one, NV3+6. This observation was attributed to a fast charge recombination process in NV3+6 when compared to that of NB1V3+6 and NB2V3+6 dendrimers.     

Analysis of a part design procedure

Summary. In this paper we analyze and illustrate a new "ab initio" part design procedure, in which, given a cost function which reflects performance, materials, and manufacturing considerations, the topology and the geometry of the part are automatically produced. The analysis is based on demonstration of, first, the compactness of the metric space over which the cost function is defined, and, second, lower semi-continuity of the cost function. Examples include beams and elastic supports. Received November 15, 1993     

A Lagrangian decomposition approach for the pump scheduling problem in water networks

Dynamic pricing has become a common form of electricity tariff, where the price of electricity varies in real time based on the realized electricity supply and demand. Hence, optimizing industrial operations to benefit from periods with low electricity prices is vital to maximizing the benefits of dynamic pricing. In the case of water networks, energy consumed by pumping is a substantial cost for water utilities, and optimizing pump schedules to accommodate for the changing price of energy while ensuring a continuous supply of water is essential. In this paper, a Mixed-Integer Non-linear Programming (MINLP) formulation of the optimal pump scheduling problem is presented. Due to the non-linearities, the typical size of water networks, and the discretization of the planning horizon, the problem is not solvable within reasonable time using standard optimization software. We present a Lagrangian decomposition approach that exploits the structure of the problem leading to smaller problems that are solved independently. The Lagrangian decomposition is coupled with a simulation-based, improved limited discrepancy search algorithm that is capable of finding high quality feasible solutions. The proposed approach finds solutions with guaranteed upper and lower bounds. These solutions are compared to those found by a mixed-integer linear programming approach, which uses a piecewise-linearization of the non-linear constraints to find a global optimal solution of the relaxation. Numerical testing is conducted on two real water networks and the results illustrate the significant costs savings due to optimizing pump schedules.     

Enhancement of photocurrent in dye sensitized solar cells incorporating a cyclometalated ruthenium complex with cuprous iodide as an electrolyte additive

A new cyclometalated ruthenium complex, [Ru(6'-phenyl-4'-thiophen-2-yl-[2,2']bipyridinyl-4-carboxylic acid)(4,4',4'-tricarboxy- 2,2':6',2'-terpyridine)]Cl, for Dye Sensitized Solar Cells (DSSCs) is proposed. We have investigated the use of cuprous iodide (CuI) as an electrolyte additive, which in turn has shown photocurrent enhancements of more than 25% in our dye based cells. Using an ionic liquid based electrolyte, an efficiency of η = 5.7% has been accomplished under 1 sun irradiation. The origin of this photocurrent enhancement upon the CuI addition was studied by means of impedance spectroscopy and cyclic voltammetry under dark conditions. The reason behind such a photocurrent enhancement is attributed to an electrocatalytic effect of the CuI on the regeneration of the oxidized dye. Furthermore, the CuI addition did not affect the recombination processes between the injected electrons and the electrolyte nor the electron lifetime in the semiconductor TiO(2) film, which in turn resulted in no changes in the photovoltage.