Information guided noise reduction for Monte Carlo integration of oscillatory functions

A simple procedure for decreasing the statistical error associated with Monte Carlo integration of oscillatory functions is presented. The method uses available information about the integral of a similar oscillatory function to correlate the estimates of the positive and negative components of the integral. Numerical tests show that information guided noise reduction (IGNoR) leads to substantial decrease of the statistical error, allowing meaningful results to be obtained with a fraction of the cost required to attain similar precision from the raw Monte Carlo estimate.     

Adsorption at the air-water interface and emulsification properties of grain legume protein derivatives from pea and broad bean

Functional properties of native and modified (through induced autolysis) pea (Pisum sativum L.) and broad bean (Vicia faba L.) protein derivatives are studied. In specific, protein solubility and behavior at the air–water interface through surface pressure measurements are investigated. Furthermore the ability of the protein products to act as emulsifying agents and to stabilize emulsions is studied through oil droplet size distribution measurements and by the protein adsorbed at the oil–water interface. The data reveal that the ability of the proteins to act as surfactants and build up a rigid film around the oil droplets, mainly depends on their suitable molecular configuration and structure. Hydrolysis did not promote the functionality of the legume proteins. Broad bean exhibited better functionality than pea, before and after hydrolysis. Some comparisons were also made with lupin (Lupinus albus L.) protein isolate.     

Atomic resolution scanning tunneling microscopy imaging of Pt electrodes interfaced with β″-Al2O3

Solid electrolytes can be used as active catalyst supports to induce significant and reversible catalytic activity and selectivity enhancement via the effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion which has been recently reported for over fourty catalytic reactions. Atomically resolved Scanning Tunneling Microscopy was used to image the reversible electrochemically controlled dosing (backspillover) of sodium on Pt(111) interfaced to β″-Al₂O₃ at atmospheric pressure, which has been proposed as the cause of the NEMCA effect in the case of Na⁺ conductors. It was found that electrical current application between the Pt(111) monocrystal and a counter electrode also in contact with the β″-Al₂O₃ Na⁺-conducting solid electrolyte causes reversible migration (backspillover and spillover) of sodium which forms a (12×12) hexagonal structure on the Pt(111) surface. In addition to explaining the phenomenon of Electrochemical Promotion in Heterogeneous Catalysis when using Na-β″-Al₂O₃ solid electrolyte these observations provide the first STM confirmation that:

1. spillover-backspillover phenomena can take place over enormous (~mm) atomic distances, and
2. promoters can form ordered structures on catalyst surfaces under ambient conditions relevant to industrial practice.

     

Symmetrized correlation function for liquid para-hydrogen using complex-time pair-product propagators

We present a simple and efficient method for calculating symmetrized time correlation functions of neat quantum fluids. Using the pair-product approximation to each complex-time quantum mechanical propagator, symmetrized correlation functions are written in terms of a double integral for each degree of freedom with a purely positive integrand. At moderate temperatures and densities, where the pair-product approximation to the Boltzmann operator is sufficiently accurate, the method leads to quantitative results for the early time part of the correlation function. The method is tested extensively on liquid para-hydrogen at 25 K and used to obtain accurate quantum mechanical results for the initial 0.2 ps segment of the symmetrized velocity autocorrelation function of this system, as well as the incoherent dynamic structure factor at certain momentum transfer values.     

Inverse gas chromatographic investigation of the effect of hydrogen in carbon monoxide adsorption over silica supported Rh and Pt-Rh alloy catalysts, under hydrogen-rich conditions

Selective CO oxidation (SCO) has attracted scientific and technological interest due to its application to the operation of proton electrolyte membrane fuel cells (PEM-FCs). CO adsorption, being an elementary step of SCO, is studied over silica supported monometallic Rh and Rh0.50 + Pt0.50 alloy catalysts, under various hydrogen atmospheres, namely: 25% H2 + 75% He, 50% H2 + 50% He and 75% H2 + 25% He carrier gas mixture compositions. The investigation of CO adsorption is done by utilizing reversed-flow gas chromatography (RF-GC). As a result rate constants for the adsorption (k1), desorption (k(-1)) and irreversible CO binding (k2) over the studied catalysts as well as the respective activation energies are determined. The variation of the rate constants and the activation energies against the nature of the used catalyst (monometalic or alloy) and the amount of hydrogen in the carrier gas gives useful information for the selectivity as well as the activity of CO oxidation over group VIII noble metals. At low temperatures and under H2-rich conditions compatible with the operation of PEM fuel cells the activity of the monometallic and the alloy catalysts is expected to be similar, however the selectivity of Rh0.50 + Pt0.50 alloy catalyst is expected to be higher, making Pt-Rh alloy catalyst as a better candidate for CO preferential oxidation (PROX). The low energy barrier values found in the present work, most likely are referred to high surface amounts of CO. The desorption barriers determined are in any case much lower than the respective activation energies found for CO desorption in the absence of hydrogen indicating a H2-induced desorption, which can explain the observed in the literature rate enhancement of SCO oxidation.     

Reactions Between 4-Hydroxycoumarins or 4-Hydroxy-1-Methylquinolinone and Dmad in the Presence of Phosphites. Synthesis of (Chromen-3-YL)- and (Quinolin-3-YL)-(Dialkoxyphosphoryl)Succinates

Abstract

Dimethyl (chromen-3-yl)-(dialkoxyphosphoryl)succinates are prepared from the reaction of 4-hydroxycoumarin with DMAD and P(OR)₃. 4-Hydroxy-1-methylquinolinone reacts with DMAD and P(OEt)₃ to give dimethyl (quinoline-3-yl)-(diethoxyphosphoryl)-succinate.

GRAPHICAL ABSTRACT      

Generalizations of Runs and Patterns Distributions for Sequences of Binary Trials

Methodology and Computing in Applied Probability - In the present paper we study the distributions of families of patterns which generalize runs and patterns distributions extensively examined in...     

Combined XAS/SAXS/Electrochemical studies on the conformation of poly(vinylferrocene) under redox conditions

Metal-organic ligand complexes are important to many processes, ranging from the formation of supramolecular assemblies to electrochemical processes. Poly(vinylferrocene), PVF, is an example of a metal-organic polymer that contains localised sites which may be oxidised and reduced. Combined XAS (X-ray Absorption Spectroscopy)/SAXS (Small Angle X-ray Scattering) and electrochemical studies on PVF films in aqueous solution of 0.10 M LiClO₄ and in non-aqueous solution of propylene carbonate/0.25 M TBABF₄ have been carried out. The change in the oxidation Fe²⁺/Fe³⁺state of the PVF film was observed by analysing the near edge region of the XAS spectrum. The local environment around the Fe-centres of the oxidised/reduced films (from the extended region of the XAS spectrum) indicates an increase/reduction of ligand distances during the oxidation and reduction of the film. The SAXS results correlate well with the findings from XAS. The scattering profiles at very low angles are consistent with an expansion/contraction of the overall size of polymer chains upon oxidation/reduction. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.