Using scenario trees and progressive hedging for stochastic inventory routing problems

The Stochastic Inventory Routing Problem is a challenging problem, combining inventory management and vehicle routing, as well as including stochastic customer demands. The problem can be described by a discounted, infinite horizon Markov Decision Problem, but it has been showed that this can be effectively approximated by solving a finite scenario tree based problem at each epoch. In this paper the use of the Progressive Hedging Algorithm for solving these scenario tree based problems is examined. The Progressive Hedging Algorithm can be suitable for large-scale problems, by giving an effective decomposition, but is not trivially implemented for non-convex problems. Attempting to improve the solution process, the standard algorithm is extended with locking mechanisms, dynamic multiple penalty parameters, and heuristic intermediate solutions. Extensive computational results are reported, giving further insights into the use of scenario trees as approximations of Markov Decision Problem formulations of the Stochastic Inventory Routing Problem.     

Rydberg states with quantum Monte Carlo

Calculations on Rydberg states are performed using quantum Monte Carlo methods. Excitation energies and singlet-triplet splittings are calculated for two model systems, the carbon atom (3P and 1P) and carbon monoxide ((1Sigma and 3Sigma). Kohn-Sham wave functions constructed from open-shell localized Hartree-Fock orbitals are used as trial and guide functions. The fixed-node diffusion quantum Monte Carlo (FN-DMC) method depends strongly on the wave function's nodal hypersurface. Nodal artefacts are investigated for the ground state of the carbon atom. Their effect on the FN-DMC results can be analyzed quantitatively. FN-DMC leads to accurate excitation energies but to less accurate singlet-triplet splittings. Variational Monte Carlo calculations are able to reproduce the experimental results for both the excitation energies and the singlet-triplet splittings.     

Molecular structures of tris(dipivaloylmethanato) complexes of the lanthanide metals, Ln(dpm)3, studied by gas electron diffraction and density functional theory calculations: a comparison of the Ln-O Bond distances and enthalpies in Ln(dpm)3 complexes and the cubic sesquioxides, Ln2O3

The molecular structures of tris(dipivaloylmethanato)neodymium(III), Nd(dpm)3, and tris(dipivaloylmethanato)ytterbium(III), Yb(dpm)3, have been determined by gas electron diffraction (GED) and structure optimizations through density functional theory (DFT) calculations. Both molecules were found to have D3 molecular symmetry. The most important structure parameters (r(a) structure) are as follows (GED/DFT): Nd-O = 2.322(5)/2.383 A, Yb-O = 2.208(5)/2.243 A, O-Nb-O = 72.1(3)/71.3 degrees , and O-Yb-O = 75.3(2)/75.8 degrees . The twist angles of the LnO6 coordination polyhedron, defined as zero for prismatic and 30 degrees for antiprismatic coordination, were theta = 19.1(3)/14.2 degrees for Nd and 20.4(2)/19.2 degrees for Yb. Structure optimizations of La(dpm)3, Gd(dpm)3 Er(dpm)3, and Lu(dpm)3 by DFT also yielded equilibrium structures of D3 symmetry with bond distances of La-O = 2.438 A, Gd-O = 2.322 A, Er-O = 2.267 A, and Lu-O = 2.232 A. The Ln-O bond distances in 12 Ln(dpm)3 complexes studied by GED decrease in a nearly linear manner with the increasing atomic number (Z) of the metal atom, as do the Ln-O bond distances in the cubic modifications of 14 sesquioxides, Ln2O3. The bond distances in the dpm complexes are, however, about 2% shorter. The mean Ln-O bond rupture enthalpies of the cubic sesquioxides calculated from thermodynamic data in the literature vary in an irregular manner with the atomic number; the La-O, Gd-O, Tb-O, and Lu-O bonds are nearly equally strong, and the remaining bonds are significantly weaker. The Ln-O bond rupture enthalpies previously reported for 11 Ln(dpm)3 complexes are on the average 13 kJ mol(-1) or about 5% smaller than in the sesquioxides, but they vary in a similar manner along the series: it is suggested that the pattern reflects variations in the absolute enthalpies of the gaseous Ln atoms.     

DNS Analysis of Wall Heat Transfer and Combustion Regimes in a Turbulent Non-premixed Wall-jet Flame

Understanding the heat-release effects on the wall heat transfer in turbulent reacting flows, i.e. heat transfer with or without significant density variation, is essential for a wide variety of industrial flows, especially combustion problems. The present study focuses on the wall heat transfer and the near-wall reaction characteristics. The heat-release effects on the wall heat transfer and skin-friction coefficients are investigated using three-dimensional direct numerical simulations of a turbulent reacting wall-jet flow with and without heat release. Reductions in the skin-friction coefficient are observed in the exothermic case, compared to the isothermal one, and the underlying mechanism is explained. The absolute wall heat flux also increases, while the corresponding Nusselt number decreases with increasing heat release. Furthermore, the wall effects on the near-wall average burning rate are assessed. It is found that the isothermal cold wall results in an appreciable decrease of the burning rate in the exothermic cases. We observed indications that the wall increases the chances for the development of the premixed mode and its occurrence is very fast in the wall-normal direction.     

An Isoreticular Family of Microporous Metal-Organic Frameworks Based on Zinc and 2-Substituted Imidazolate-4-amide-5-imidate: Syntheses, Structures and Properties

We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-1-4, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.0-1.7??), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and (1) H?MAS and (13) C?CP-MAS?NMR spectroscopy. All IFPs showed high thermal stability (345-400?°C); IFP-1 and IFP-4 were stable in boiling water for 7?d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO(2) was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH(4) (at 298?K), CO(2) (at 298?K) and H(2) (at 77?K) at high pressure were also investigated. In situ IR spectroscopy showed that CO(2) is physisorbed on IFP-1-4 under dry conditions and that both CO(2) and H(2) O are physisorbed on IFP-1 under moist conditions.     

Intramolecular CH Bond Activation through a Flexible Ester Linkage

Replacing the director: A bipyridinyl ligand with an aliphatic side chain determines the regioselectivity of copper-catalyzed C?H oxidation by intramolecular effects. Because the aliphatic chain is attached through an ester linkage, the catalytic cycle can in principle be closed by transesterification. Ion-mobility mass spectrometry and isotopic labeling provide mechanistic insight not available from direct mass spectrometry experiments.     

Controlled synthesis of cell-laden microgels by radical-free gelation in droplet microfluidics

Micrometer-sized hydrogel particles that contain living cells can be fabricated with exquisite control through the use of droplet-based microfluidics and bioinert polymers such as polyethyleneglycol (PEG) and hyperbranched polyglycerol (hPG). However, in existing techniques, the microgel gelation is often achieved through harmful reactions with free radicals. This is detrimental for the viability of the encapsulated cells. To overcome this limitation, we present a technique that combines droplet microfluidic templating with bio-orthogonal thiol-ene click reactions to fabricate monodisperse, cell-laden microgel particles. The gelation of these microgels is achieved via the nucleophilic Michael addition of dithiolated PEG macro-cross-linkers to acrylated hPG building blocks and does not require any initiator. We systematically vary the microgel properties through the use of PEG linkers with different molecular weights along with different concentrations of macromonomers to investigate the influence of these parameters on the viability and proliferation of encapsulated yeast cells. We also demonstrate the encapsulation of mammalian cells including fibroblasts and lymphoblasts.     

Preparation of Bifunctional Mesoporous Silica Nanoparticles by Orthogonal Click Reactions and Their Application in Cooperative Catalysis

The synthesis of bifunctional mesoporous silica nanoparticles is described. Two chemically orthogonal functionalities are incorporated into mesoporous silica by co‐condensation of tetraethoxysilane with two orthogonally functionalized triethoxyalkylsilanes. Post‐functionalization is achieved by orthogonal surface chemistry. A thiol–ene reaction, Cu‐catalyzed 1,3‐dipolar alkyne/azide cycloaddition, and a radical nitroxide exchange reaction are used as orthogonal processes to install two functionalities at the surface that differ in reactivity. Preparation of mesoporous silica nanoparticles bearing acidic and basic sites by this approach is discussed. Particles are analyzed by solid state NMR spectroscopy, elemental analysis, infrared‐spectroscopy, and scanning electron microscopy. As a first application, these particles are successfully used as cooperative catalysts in the Henry reaction.     

A parallel multi-neighborhood cooperative tabu search for capacitated vehicle routing problems

This paper presents a parallel tabu search algorithm that utilizes several different neighborhood structures for solving the capacitated vehicle routing problem. Single neighborhood or neighborhood combinations are encapsulated in tabu search threads and they cooperate through a solution pool for the purpose of exploiting their joint power. The computational experiments on 32 large scale benchmark instances show that the proposed method is highly effective and competitive, providing new best solutions to four instances while the average deviation of all best solutions found from the collective best results reported in the literature is about 0.22%. We are also able to associate the beneficial use of special neighborhoods with some test instance characteristics and uncover some sources of the collective power of multi-neighborhood cooperation.