State aggregation in dynamic programming — An application to scheduling of independent jobs on parallel processors

Exact dynamic programming formulations of capacity loading problems will, in general, involve a prohibitively large state space. This paper offers a methodology for aggregation of the state space when dealing with such problems. Instead of future costs with respect to a known state, we are considering the costs in the worst (or best) case with respect to the given aggregate information. We apply the technique to scheduling of independent jobs on parallel processors.     

Sigma aromaticity of the bimetallic Au5Zn+ cluster

Experimental and theoretical evidence for a "sigma aromatic" bimetallic cluster is presented. A mass spectrometric analysis of AuNZn+ (N = 2-44) photofragments shows Au5Zn+ to be very abundant, proving its high stability. Calculations predict that Au5Zn+ has a planar geometry and six valence s electrons occupying delocalized sigma-bonded molecular orbitals in a manner similar to that of aromatic organic compounds, except for their nodal properties in the molecular plane. The delocalized sigma electrons provide diamagnetic ring currents, suggesting Au5Zn+ is aromatic.     

Poly(<Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam) microgels. Polymeric stabilization with poly(vinyl alcohol)

Poly(vinyl alcohol), PVA, with different molecular weights, M_w, and degrees of hydrolysis has been used to study the steric stabilization of microgels based on poly(N-vinylcaprolactam). The stabilizer influences the particle size and stability, but has no influence on the thermal properties. The thermal behavior of microgels depends on the heating rate: slow heating leads to the formation of aggregates and fast heating to an intramolecular collapse. The aggregates showed an unusual angular dependence of the diffusion coefficient, which can be explained by the presence of probably an additional rotational diffusion.     

Influence of the Linker Chemistry on the Photoinduced Charge-Transfer Dynamics of Hetero-dinuclear Photocatalysts

To optimize light-driven catalytic processes, light-mediated multi-electron transfer dynamics in molecular dyads need to be studied and correlated with structural changes focusing on the catalytically active metastable intermediates. Here, spectro-electrochemistry has been employed to investigate the structure-dependent photoelectron transfer kinetics in catalytically active intermediates of two Ru−Rh catalysts for light-driven NAD⁺ reduction. The excited-state reactivity of short-lived intermediates was studied along different photoreaction pathways by resonance Raman and time-resolved transient absorption spectro-electrochemistry with sub-picosecond time resolution under operando conditions. The results demonstrate, for the first time, how the bridging ligand serves as a (multi-)electron storage structure, mediates the strength of the electronic coupling of catalytic and photocenter and impacts the targeted electron transfer as well as parasitic electron-transfer kinetics.     

In situ Grignard Metalation Method,Part II: Scope of the One-Pot Synthesis of Organocalcium Compounds

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot strategy to synthesize alkaline-earth metal amides in multi-gram scale with high yields via addition of bromoethane to an ethereal suspension of a primary or secondary amine and magnesium (Part I) or calcium (Part II). This method is highly advantageous because no activation of calcium is required prior to the reaction. Contrary to the magnesium-based iGMM, there are some limitations, the most conspicuous one is the large influence of steric factors. The preparation of Ca(hmds)₂ succeeds smoothly within a few hours with excellent yields opening the opportunity to prepare large amounts of this reagent. Side reactions and transfer of the iGMM to substituted anilines and N-heterocycles as well as other H-acidic substrates such as cyclopentadienes are studied. Bulky amidines cannot be converted directly to calcium amidinates via the iGMM but stoichiometric calciation with Ca(hmds)₂ enables their preparation.     

Experimental study of the synthesis of fused silica by direct combustion hydrolysis

Oxy-fuel flames for direct combustion hydrolysis of fused silica (DQ) are characterized, using non- intrusive optical measurement techniques only. Flow, temperature, concentrations, development of silica nano-particles in the flame, and surface temperature of the glass in the flame are measured. The setup used for characterization of particle distribution via Rayleigh scattering as well as mandatory improvements of the Raman/Rayleigh technique for temperature and concentration measurements in oxy-fuel flames have been developed in the framework of this study and are presented. The measurement techniques herein demonstrated are not only capable of describing these special extremely hot flames, but are broadly applicable in oxy-fuel flames as well as in chemical vapor deposition (CVD) processes. The presented data evidently shows that if the special character of oxy-fuel flames is taken into account, some of the results drawn from earlier investigations into CVD, concerning particle growth, flame stability, and particle deposition efficiency, are transferable into DQ. From the extensive data given, connections between different information are detected and help to reduce required measurements for further investigation and point to simple techniques that might be used for online process monitoring, at least during research and development of similar flames. Received: 18 December 2000 / Accepted: 14 June 2001     

Stability of the T ∞FT < T ∞α relation between Vogel temperatures of flow and glass transition against determination variants

Dynamic shear measurements in the frequency range from 10^–4 to 500 rad/s at the flow and main transition of a polydisperse poly(vinyl acetate) and a monodisperse polystyrene sample are presented. For both samples the Vogel temperature of the flow transition T _FT is smaller than the Vogel temperature of the main transition T , independent of the criteria used for data evaluation. The difference between the two Vogel temperatures corresponds to results for samples with other molecular weight and polydispersity from the literature. The T _FT <T relation is discussed in terms of short () and long (FT) dynamic glass transitions in entangled polymers. The relation is explained by preaveraging of the energy landscape for the long flow transition by the short glass transition.     

Strong Ligand Stabilization Based on π-Extension in a Series of Ruthenium Terpyridine Water Oxidation Catalysts

The substitution behavior of the monodentate Cl ligand of a series of ruthenium(II) terpyridine complexes (terpyridine (tpy)=2,2′:6′,2′′-terpyridine) has been investigated. ¹H NMR kinetic experiments of the dissociation of the chloro ligand in D₂O for the complexes [Ru(tpy)(bpy)Cl]Cl ( 1 , bpy=2,2’-bipyridine) and [Ru(tpy)(dppz)Cl]Cl ( 2 , dppz=dipyrido[3,2-a:2′,3′-c]phenazine) as well as the binuclear complex [Ru(bpy)₂(tpphz)Ru(tpy)Cl]Cl₃ ( 3 b , tpphz=tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine) were conducted, showing increased stability of the chloride ligand for compounds 2 and 3 due to the extended π-system. Compounds 1 – 5 ( 4 =[Ru(tbbpy)₂(tpphz)Ru(tpy)Cl](PF₆)₃, 5 =[Ru(bpy)₂(tpphz)Ru(tpy)(C₃H₈OS)/(H₂O)](PF₆)₃, tbbpy=4,4′-di-tert-butyl-2,2′-bipyridine) are tested for their ability to run water oxidation catalysis (WOC) using cerium(IV) as sacrificial oxidant. The WOC experiments suggest that the stability of monodentate (chloride) ligand strongly correlates to catalytic performance, which follows the trend 1 > 2 > 5 ≥ 3 > 4 . This is also substantiated by quantum chemical calculations, which indicate a stronger binding for the chloride ligand based on the extended π-systems in compounds 2 and 3 . Additionally, a theoretical model of the mechanism of the oxygen evolution of compounds 1 and 2 is presented; this suggests no differences in the elementary steps of the catalytic cycle within the bpy to the dppz complex, thus suggesting that differences in the catalytic performance are indeed based on ligand stability. Due to the presence of a photosensitizer and a catalytic unit, binuclear complexes 3 and 4 were tested for photocatalytic water oxidation. The bridging ligand architecture, however, inhibits the effective electron-transfer cascade that would allow photocatalysis to run efficiently. The findings of this study can elucidate critical factors in catalyst design.