A new inertial-type hybrid projection-proximal algorithm for monotone inclusions

This paper investigates an enhanced proximal algorithm with interesting practical features and convergence properties for solving non-smooth convex minimization problems, or approximating zeroes of maximal monotone operators, in Hilbert spaces. The considered algorithm involves a recent inertial-type extrapolation technique, the use of enlargement of operators and also a recently proposed hybrid strategy, which combines inexact computation of the proximal iteration with a projection. Compared to other existing related methods, the resulting algorithm inherits the good convergence properties of the inertial-type extrapolation and the relaxed projection strategy. It also inherits the relative error tolerance of the hybrid proximal-projection method. As a special result, an update of inexact Newton-proximal method is derived and global convergence results are established.     

Enhancing high-order above-threshold dissociation of H2+ beams with few-cycle laser pulses

High-order (three-photon or more) above-threshold dissociation (ATD) of H(2)(+) has generally not been observed using 800 nm light. We demonstrate a strong enhancement of its probability using intense 7 fs laser pulses interacting with beams of H(2)(+), HD(+), and D(2)(+) ions. The mechanism invokes a dynamic control of the dissociation pathway. These measurements are supported by theory that additionally reveals, for the first time, an unexpectedly large contribution to ATD from highly excited electronic states.     

The daguerreotype surface as a SERS substrate: characterization of image deterioration in plates from the 19th century studio of Southworth & Hawes

Dramatic condition changes were noted in a group of daguerreotypes during a 10 month‐long exhibition featuring masterworks of the prominent Boston‐based studio of Southworth & Hawes. The changes took the form of a hazy, extended white surface layer and of white spots that partially obscured the images after between four weeks and 10 months of exhibition. Raman spectroscopy, complemented by in situ scanning electron microscopy–energy dispersive X‐ray spectrometry (SEM–EDS), was used to nondestructively characterize this form of image deterioration in eight representative daguerreotypes from the studio. Raman proved to be a sensitive technique to noninvasively identify the compounds on the plates due to the fact that their Ag surfaces behave as surface‐enhanced Raman scattering (SERS) substrates. A band at ca 242 cm⁻¹ assigned to the Ag Cl stretching mode was observed in the areas where a white surface layer or white spots are present. In some of the areas probed, substituted aromatic compounds were also detected. The presence of Ag Cl bonds on daguerreotype surfaces has profound implications for their exhibition and preservation due to the photosensitivity of silver chloride in the ultraviolet–visible range, which can generate metallic silver that would redeposit on the surfaces. The possible sources of the compounds detected on the surfaces of the plates are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Chalcedony (a crystalline variety of silica): biogenic origin in electric organs from living Psammobatis extenta (family Rajidae)

The electric organs of electric fish have been used extensively for the study of peripheral cholinergic synapses. Aluminum and silicon have been observed in the electrocytes of Psammobatis extenta, a fish belonging to the family Rajidae, using a combination of scanning electron microscopy and X-ray spectrometry. Based on this evidence, the presence of silica minerals has been documented by means of mineralogical techniques. Electric organ cryostat sections and subcellular fractions were observed using a Leica DMLP mineralogical microscope. The shape, size and color, among other properties, were analyzed in plane-polarized light, while birefringence and the extinction angle, which allow for mineral identification, were observed through crossed-polarized illumination. The distribution of chalcedony, an oxide silicon mineral, in the sections and all the fractions of the electric organ was recorded. X-ray diffraction analysis of the electric organ segments showed a similar result, with a low-quartz variety. Chalcedony precipitation occurred at a specific pH (7-8) and oxidation potential (Eh; 0.0 to -0.2). This observation supports the important role played by pH and Eh conditions in silica precipitation in electrocytes, as has been reported in geological environments. It is possible that silica formation and silica degradation in electric organs are also related to the enzymes, silicatein and silicase, that direct the polymerization and depolymerization of amorphous silica in sponges. Carbonic anhydrases (silicase) are involved in physiological pH regulation. Crystallization of chalcedony via spiral growth from a partially polymerized fluid is consistent with processes known to occur in organic systems. This is the first time that a biogenically produced crystalline mineral phase (i.e., chalcedony) has been observed in the electrocytes and cholinergic nerves from living electric fish.     

Reaction of an N‐Heterocyclic Carbene‐Stabilized Silicon(II) Monohydride with Alkynes: [2+2+1] Cycloaddition versus Hydrogen Abstraction

An in depth study of the reactivity of an N‐heterocyclic carbene (NHC)‐stabilized silylene monohydride with alkynes is reported. The reaction of silylene monohydride 1 , tBu₃Si(H)Si←NHC, with diphenylacetylene afforded silole 2 , tBu₃Si(H)Si(C₄Ph₄). The density functional theory (DFT) calculations for the reaction mechanism of the [2+2+1] cycloaddition revealed that the NHC played a major part stabilizing zwitterionic transition states and intermediates to assist the cyclization pathway. A significantly different outcome was observed, when silylene monohydride 1 was treated with phenylacetylene, which gave rise to supersilyl substituted 1‐alkenyl‐1‐alkynylsilane 3 , tBu₃Si(H)Si(CH?CHPh)(C?CPh). Mechanistic investigations using an isotope labelling technique and DFT calculations suggest that this reaction occurs through a similar zwitterionic intermediate and subsequent hydrogen abstraction from a second molecule of phenylacetylene.     

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1).     

Quantification of fenitrothion and its main metabolites in poplar leaves by isotope dilution gas chromatography-mass spectrometry coupled with solid-phase microextraction

A sensitive and specific method for determining fenitrothion and its main metabolites, 3-methyl-4-nitrophenol and fenitrooxon, in poplar leaves using deuterated isotopes as the internal standard is described. The analytes and the labeled isotopes were extracted from leaves by solid-phase microextraction and subsequently analysed by gas chromatography coupled with mass spectrometry. The method had a chromatographic run time of 17.0 min and good linearity over the range 0.01-10 mg kg(-1). The detection limits ranged between 2.5 and 0.6 microg kg(-1). The isotopic dilution technique allowed improving significantly the repetitivity even using different fibers with the same coating (RSD<5.1%). The method was applied successfully to study the persistence of fenitrothion in forestal matrices in a poplar forest after cannon spray application of the insecticide.     

Correlation and prediction of partition coefficient between the gas phase and water, and the solvents dry methyl acetate, dry and wet ethyl acetate, and dry and wet butyl acetate

Experimental partition coefficient data have been compiled from the published literature for the water/methyl acetate, water/ethyl acetate and water/butyl acetate partition systems, log P data, and for the gas/methyl acetate, gas/ethyl acetate and gas/butyl acetate partition systems, log K data. Application of the Abraham solvation parameter model to the sets of partition coefficients leads to equations that correlate the log P data and log K data to 0.18 log units for the three dry alkyl acetate solvents. Slightly larger deviations were noted for solute partition into both wet ethyl acetate and wet butyl acetate. The derived correlations were validated using training set and test set analyses.