The importance of the plume ejection time for the fragmentation yields observed in the UV ablation of molecular van der Waals films. Ablation of chlorobenzene films at 248 nm

The efficiency of photolysis in the ablation of thick C₆H₅Cl films at 248 nm is probed over 40–300 mJ/cm² by means of time-of-flight quadrupole mass spectrometry. Up to ≈ 150 mJ/cm², the photolysis yield is considerably smaller than that in the gas-phase. We argue that because of plume ejection well after the laser pulse, photolysis occurs exclusively in the film, and as a result, permanent dissociation is limited by the operation of efficient recombination processes characteristic of condensed phases. Fragmentation starts being important only at higher fluences, at which desorption during the laser pulse is indicated to be significant.     

Conformation and coordination of β-diketonates in mixed-ligand copper(II) chelates of 1,2-diamines. Theoretical approach and experimental verification. Crystal structure of [bis(N,N′-dimethyl-1,2-diaminoethane) bis(3-cyano-2,4-pentanedionate)copper(II)]dihydrate

The reaction of the bis(2,4-pentanedionato)copper(II), Cu(acac)₂, and its substituted derivatives (Cu(NC-acac)₂, Cu(O₂N-acac)₂, and Cu(tfac)₂), with 1,2-diaminoethane (en), 1,2-diaminopropane (pn) and certain N-substituted derivatives of 1,2-diaminoethane, enR, is reported. The reaction products were found to depend on the reaction conditions, the extent of N-substitution of the diamine and the nature of the β-diketonate anion, β⁻. The [Cu(enR)β₂] addition compounds are not always sufficiently stable and in most instances the tetragonal species [Cu(enR)₂β₂] prevail as the final product. The 1,2-diamine molecules in [Cu(enR)₂β₂] form chelate rings attaining the gauche conformation while the β-diketonato anions essentially confer electrical neutrality. Density functional theory (DFT) calculations suggest that the active sites of the β-diketonato anion and its conformation depend on their ability to create hydrogen bonds and on the substituents in 3-position. The Fukui indices of chemical reactivity favor the carbonyl oxygens as binding sites of most anions while in the case of the 3-cyano-2,4-pentanedionato anion, NC-acac⁻, bonding through the cyano nitrogen is envisaged with the S(E, Z) conformer having the lowest energy. These findings are in accord with experimental data and further proof is given by single crystal X-ray diffraction analysis of the structure of [Cu(MeenMe)₂(NC-acac)₂] · 2H₂O (MeenMe denoting N,N′-dimethyl-1,2-diaminoethane). In this compound the NC-acac⁻ attains the S(E, Z) conformation and interacts with the square-planar entity [Cu(MeenMe)₂]²⁺ through the cyano nitrogen, while intermolecular hydrogen bonding involving the water molecules leads to supramolecular structure.     

Optimal balking strategies and pricing for the single server Markovian queue with compartmented waiting space

We consider the single server Markovian queue and we assume that arriving customers decide whether to enter the system or balk based on a natural reward-cost structure, which incorporates their desire for service as well as their unwillingness to wait. We suppose that the waiting space of the system is partitioned in compartments of fixed capacity for a customers. Before making his decision, a customer may or may not know the compartment in which he will enter and/or the position within the compartment in which he will enter. Thus, denoting by n the number of customers found by an arriving customer, he may or may not know ? n/a ?+1 and/or (n mod a)+1. We examine customers’ behavior under the various levels of information regarding the system state and we identify equilibrium threshold strategies. We also study the corresponding social and profit maximization problems.     

On the simultaneous optimization of pressure and layout for gas permeation membrane systems

We present a methodology for the simultaneous optimization of pressure and network configurations for gas separation membrane permeators. The methodology targets and refines pressure clusters for efficient operation of membrane networks and follows a three-stage strategy. The first stage produces a pressure target curve (PTC) that allows the identification of Pareto optimal pressure cluster combinations. This is followed by a second stage, where the different optimal pressure ratios are used in an optimal search for process structures to identify the performance of the individual clusters. The third stage processes the information generated in the first two stages in a generalized process superstructure model. Throughout the methodology, a modified process synthesis model for membrane network optimization and design is employed which can be optimized robustly using the simulated annealing algorithm. Three illustrative examples are presented to demonstrate the proposed methodology for simultaneous pressure and layout optimization.     

Structural properties of metal-benzene, Mn(benzene)m, M=Ni, V complexes: an ab initio study

Interactions of Ni and V with benzene (Bz)-molecules are investigated using ab initio methods and tight-binding molecular dynamics (TBMD) simulations. The differences in the behavior for Ni and V is found to be consistent with their similar contrasting bonding behavior found in interactions with graphite, C₆₀ and carbon nanotubes.     

Curvature dependence of the metal catalyst atom interaction with carbon nanotubes walls

Interactions of the transition metal atoms with carbon nanotube walls are investigated using a tight-binding molecular dynamics method that allows for spin unrestricted geometry optimization. Comparison with the results for bonding on graphite indicates major differences in bonding sites, magnetic moments and the direction of charge transfer. The significant values of magnetic moments obtained for the metal atoms on nanotube walls is consistent with the recent experimental findings.     

A wavelet smoothing method to improve conditional sales forecasting

This article proposes a wavelet smoothing method to improve conditional forecasts generated from linear regression sales response models. The method is applied to the forecasted values of the predictors to remove forecast errors and thereby improve the overall forecasting performance of the models. Eight empirical studies are presented in which the purpose was to forecast detergent sales in the Netherlands, and wavelet smoothing was compared with a moving average and a band-pass filter. All methods were found to improve forecasts. Wavelet smoothing provided the best results when applied on highly volatile marketing time series. In contrast, it was less effective when applied on highly aggregated and smooth time series. An advantage of wavelets is that they are flexible enough to allow for data characteristics like abrupt changes, spikes and cyclical changes that are usually associated with price changes and promotions.     

Adsorption of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride on a hanging mercury electrode studied by adsorptive transfer stripping voltammetry

The adsorption of cetyltrimethylammonium bromide (CTAB) and cetyldimethylbenzylammonium chloride (CDBACl) on a hanging mercury electrode is studied using adsorptive transfer stripping voltammetry. The surfactants are adsorbed on mercury and are then transferred in KBr or KCl under various conditions, including temperatures from 1 to 40°C, open or closed circuits with different initial potentials, and repeated scans, etc. The results are compared with previously published results on the adsorption of CTAB or CDBACl on mercury, where condensed films were formed and are quite different than those obtained by adsorptive stripping voltammetry. In this case, an absence of condensed film is observed for CTAB. A condensed film with low capacitance value is formed in the case of CDBACl after transfer at low temperatures, or after repeated scans, resulting in reorientation of the molecules to more compact states. Capacity time curves at the potentials where the film is formed show in a few cases a nucleation and growth mechanism, with induction time and studied by the Avrami formulation, while an observed increase of the capacitance with time is attributed to the formation of hemimicelles. The results also indicate the importance of interactions between the hydrophobic chains.