Scenario Cluster Lagrangian Decomposition in two stage stochastic mixed 0-1 optimization

In this paper we introduce four scenario Cluster based Lagrangian Decomposition (CLD) procedures for obtaining strong lower bounds to the (optimal) solution value of two-stage stochastic mixed 0-1 problems. At each iteration of the Lagrangian based procedures, the traditional aim consists of obtaining the solution value of the corresponding Lagrangian dual via solving scenario submodels once the nonanticipativity constraints have been dualized. Instead of considering a splitting variable representation over the set of scenarios, we propose to decompose the model into a set of scenario clusters. We compare the computational performance of the four Lagrange multiplier updating procedures, namely the Subgradient Method, the Volume Algorithm, the Progressive Hedging Algorithm and the Dynamic Constrained Cutting Plane scheme for different numbers of scenario clusters and different dimensions of the original problem. Our computational experience shows that the CLD bound and its computational effort depend on the number of scenario clusters to consider. In any case, our results show that the CLD procedures outperform the traditional LD scheme for single scenarios both in the quality of the bounds and computational effort. All the procedures have been implemented in a C++ experimental code. A broad computational experience is reported on a test of randomly generated instances by using the MIP solvers COIN-OR and CPLEX for the auxiliary mixed 0-1 cluster submodels, this last solver within the open source engine COIN-OR. We also give computational evidence of the model tightening effect that the preprocessing techniques, cut generation and appending and parallel computing tools have in stochastic integer optimization. Finally, we have observed that the plain use of both solvers does not provide the optimal solution of the instances included in the testbed with which we have experimented but for two toy instances in affordable elapsed time. On the other hand the proposed procedures provide strong lower bounds (or the same solution value) in a considerably shorter elapsed time for the quasi-optimal solution obtained by other means for the original stochastic problem.

Reference Points Based on Dynamic Optimisation: A Versatil Algorithm for Mixed Fishery Management with Bio-economic Agestructured Models

Single-species management objectives may not be consistent within mixed fisheries. They may lead species to unsafe situations, promote discarding of over-quota and/or misreporting of catches. We provide an algorithm for characterising bio-economic reference points for a mixed fishery as the steady-state solution of a dynamic optimal management problem. The optimisation problem takes into account: i) that species are fishing simultaneously in unselective fishing operations and ii)intertemporal discounting and fleet costs to relate reference points to discounted economic profits along optimal trajectories. We illustrate how the algorithm can be implemented by applying it to the European Northern Stock of Hake (Merluccius merluccius), where fleets also capture Northern megrim (Lepidorhombus whiffiagonis) and Northern anglerfish (Lophius piscatorius and Lophius budegassa). We find that optimal mixed management leads to a target reference point that is quite similar to the 2/3 of the Fmsy single-species (hake) target. Mixed management is superior to singlespecies management because it leads the fishery to higher discounted profits with higher long-term SSB for all species. We calculate that the losses due to the use of the Fmsy single-species (hake) target in this mixed fishery account for 11.4% of total discounted profits.

Generating cluster submodels from a multistage stochastic mixed integer optimization model using break stage

We present a scheme to generate clusters submodels with stage ordering from a (symmetric or a nonsymmetric one) multistage stochastic mixed integer optimization model using break stage. We consider a stochastic model in compact representation and MPS format with a known scenario tree. The cluster submodels are built by storing first the 0-1 the variables, stage by stage, and then the continuous ones, also stage by stage. A C++ experimental code has been implemented for reordering the stochastic model as well as the cluster decomposition after the relaxation of the non-anticipativiy constraints until the so-called breakstage. The computational experience shows better performance of the stage ordering in terms of elapsed time in a randomly generated testbed of multistage stochastic mixed integer problems.

Herstellung und Zusammensetzung von asiatischen Fischsaucen

Abstract Fish sauce belongs to the most important condiments in Southeast Asian cuisine. It is a clear, amber to reddish liquid with an intensive smell. Fish sauce is used instead of salt for nearly each meal. Asian fish sauce is made from anchovies and other small fish. For the traditional process whole fresh fish are mixed with salt in the ratio 1:1 to 6:1 in wooden, clay or concrete tanks at tropical temperatures for 6 to 18 months. The liquefaction of the fish tissue is due to the action of endogenous enzymes in fish and exogenous enzymes from bacteria. During the fermentation amino acids, peptides and a lot of other substances are built, which are responsible for the characteristic aroma and flavour of these sauces. You can buy pure fish sauce, diluted fish sauce and fish sauce made from other types of animals like mussels, prawns and squids. In single Asian countries there are different national standards for the quality of fish sauces. In order to get a general idea of these products we have bought 16 fish and two oyster sauces from the retail trade in Hamburg and analyzed them with physical, chemical, sensory and microbiological methods. Kurzfassung Fischsauce gehört zu den wichtigsten Würzsaucen in der südostasiatischen Küche. Es ist eine klare, bernsteinfarbene bis rötlichbraune, sehr intensiv riechende Flüssigkeit. Sie wird anstelle von Salz verwendet und daher fast zu jedem Essen gereicht. Zur Herstellung von Fischsaucen werden hauptsächlich Anchovis und ähnliche kleine Fische verwendet. Bei der traditionellen Herstellung werden die ganzen Fische mit Meersalz in einem Holzfass, Tongefäß oder Betontank im Verhältnis 1:1 bis 6:1 gemischt. Während der anschließenden 6 – 18 Monate dauernden Lagerung bei tropischen Temperaturen bauen sich die Gewebeproteine durch fischeigene Enzyme und Mikroorganismen ab. Bei diesem mehrmonatigen Fermentationsprozess entstehen die für den Geschmack wichtigen Aminosäuren, Peptide und Aromastoffe. Es gibt neben reiner Fischsauce, auch verdünnte Fischsauce und Fischsaucen aus anderen Tieren wie Muscheln, Garnelen und Tintenfische. In den einzelnen asiatischen Ländern gibt es unterschiedliche nationale Qualitätsstandards. Um diese Produktgruppe näher kennen zu lernen, haben wir 16 Fisch- und 2 Austernsaucen aus dem Einzelhandel (Hamburg) mit physikalischen, chemischen, sensorischen und mikrobiologischen Verfahren untersucht.

Ion acceleration with mixed solid targets interacting with circularly polarized lasers

The interaction of a circularly polarized laser pulse with a mixed solid target containing two species of ions is studied by particle in cell simulations and analytical model. After the interaction tends to be stable, it is demonstrated that the acceleration is more efficient for the heavier ions than that in plasmas containing a single kind of heavy ion and the acceleration efficiency is higher when its proportion is lower. To obtain monoenergetic heavy-ion beams, a sandwich target with a thin mixed ion layer between two light ion layers and a microstructured target are proposed. The influences of parameters of the laser pulse and target on ion acceleration are discussed in detail. It is found that, when the target is thick enough, a cold target is more appropriate for heavy-ion acceleration than a warm target, and the velocity of the reflected heavy ions is proportional to the laser amplitude.

I. Spectroscopic evidence for slow vibrational relaxation in excited electronic states of diatomics in rare gas solids. II. Static crystal field effects in the electronic spectra of isotopically mixed benzene crystals

Part I

Studies of vibrational relaxation in excited electronic states of simple diatomic molecules trapped in solid rare-gas matrices at low temperatures are reported. The relaxation is investigated by monitoring the emission intensity from vibrational levels of the excited electronic state to vibrational levels of the ground electronic state. The emission was in all cases excited by bombardment of the doped rare-gas solid with X-rays.

The diatomics studied and the band systems seen are: N₂, Vegard-Kaplan and Second Positive systems; O₂, Herzberg system; OH and OD, A ²Σ⁺ - X²II_i system. The latter has been investigated only in solid Ne, where both emission and absorption spectra were recorded; observed fine structure has been partly interpreted in terms of slightly perturbed rotational motion in the solid. For N₂, OH, and OD emission occurred from v' > 0, establishing a vibrational relaxation time in the excited electronic state of the order, of longer than, the electronic radiative lifetime. The relative emission intensity and decay times for different v' progressions in the Vegard-Kaplan system are found to depend on the rare-gas host and the N₂ concentration, but are independent of temperature in the range 1.7°K to 30°K.

Part II

Static crystal field effects on the absorption, fluorescence, and phosphorescence spectra of isotopically mixed benzene crystals were investigated. Evidence is presented which demonstrate that in the crystal the ground, lowest excited singlet, and lowest triplet states of the guest deviate from hexagonal symmetry. The deviation appears largest in the lowest triplet state and may be due to an intrinsic instability of the ³B_1u state. High resolution absorption and phospho- rescence spectra are reported and analyzed in terms of site-splitting of degenerate vibrations and orientational effects. The guest phosphorescence lifetime for various benzene isotopes in C₆D₆ and sym-C₆H₃D₃ hosts is presented and discussed.

Functionalization of Si(111) surfaces and the formation of mixed monolayers for the covalent attachment of molecular catalysts in photoelectrochemical devices

The functionalization of silicon surfaces with molecular catalysts for proton reduction is an important part of the development of a solar-powered, water-splitting device for solar fuel formation. The covalent attachment of these catalysts to silicon without damaging the underlying electronic properties of silicon that make it a good photocathode has proven difficult. We report the formation of mixed monolayer-functionalized surfaces that incor- porate both methyl and vinylferrocenyl or vinylbipyridyl (vbpy) moieties. The silicon was functionalized using reaction conditions analogous to those of hydrosilylation, but instead of a H-terminated Si surface, a chlorine-terminated Si precursor surface was used to produce the linked vinyl-modified functional group. The functionalized surfaces were characterized by time-resolved photoconductivity decay, X-ray photoelectron spectroscopy (XPS), electro- chemical, and photoelectrochemical measurements. The functionalized Si surfaces were well passivated, exhibited high surface coverage and few remaining reactive Si atop sites, had a very low surface recombination velocity, and displayed little initial surface oxidation. The surfaces were stable toward atmospheric and electrochemical oxidation. The surface coverage of ferrocene or bipyridine was controllably varied from 0 up to 30% of a monolayer without loss of the underlying electronic properties of the silicon. Interfacial charge transfer to the attached ferrocene group was relatively rapid, and a photovoltage of 0.4 V was generated upon illumination of functionalized n-type silicon surfaces in CH₃CN. The immobilized bipyridine ligands bound transition metal ions, and thus enabled the assembly of metal complexes on the silicon surface. XPS studies demonstrated that [Cp∗Rh(vbpy)Cl]Cl, [Cp∗Ir(vbpy)Cl]Cl, and Ru(acac)₂vbpy were assembled on the surface. For the surface prepared with iridium, x-ray absorption spectroscopy at the Ir L_III edge showed an edge energy and post-edge features virtually identical to a powder sample of [Cp∗Ir(bipy)Cl]Cl (bipy is 2,2 ́-bipyridyl). Electrochemical studies on these surfaces confirmed that the assembled complexes were electrochemically active.