Optimal Recovery of the Derivative of Bounded Analytic Functions

Given (–1, 0), n N, we discuss the optimal recoveryof (), for analytic and bounded in < 1, from the knowledge of the values of at n points z1,.zm[0,l),where these points are chosen to produce the least possibleintrinsic error. The optimal algorithms are explicitly determined.     

Computer program for neutron activation analysis with the SLOWPOKE reactor

A FORTRAN computer program for automatic neutron activation analysis is presented. The program locates and identifies peaks in a gamma-ray spectrum, calculates peak areas and the concentrations of the elements of interest in the sample. This program was specifically designed for the SLOWPOKE reactor, it uses a semi-absolute method and does not need standards or flux monitors. The program was written so as to minimize the computation time, and a typical 4096-channel spectrum is processed in five seconds by an IBM 360/75 computer.     

Synthesis of cis-[Ru(CO)2(S2X)2] [X = CNMe2, COEt, PPh2, P(OEt)2] and Molecular Structure of [Ru(CO){η2-S2P(OEt)2}{μ,η1,η2-S2P(OEt)2}]2

Two routes to 1,1-dithiolate complexes cis-[Ru(CO)₂(S₂X)₂] [X = NMe₂, OEt, PPh₂, P(OEt)₂] are presented. From the reaction of NH₄S₂P(OEt)₂ with the ruthenium(II) complex generated upon reduction of RuCl₃.3H₂O by CO in 2-methoxyethanol, along with the expected mononuclear product, cis-[Ru(CO)₂{η²-S₂P(OEt)₂}₂], binuclear [Ru(CO){η²-S₂P(OEt)₂} {μ,η¹,η²-S₂P(OEt)₂}]₂ was also produced. The latter has been crystallographically characterized and shows a trans-arrangement of carbonyls and cis-arrangement of terminal and bridging dithiolate ligands.     

Quality control of automotive engine oils with mass-sensitive chemical sensors--QCMs and molecularly imprinted polymers

Molecularly imprinted polyurethanes were used as sensor materials for monitoring the degradation of automotive engine oils. Imprinting with characteristic oils permits the analysis of these complex mixtures without accurately knowing their composition. Mass-sensitive quartz crystal microbalances (QCMs) coated with such layers exhibit mass effects in addition to frequency shifts caused by viscosity, which can be compensated by an uncoated quartz or a non-imprint layer. Incorporation of degradation products into the imprinted coatings is a bulk phenomenon, which is proven by variation of the sensor layer height. Therefore, the resulting sensor effects are determined by the degradation products in the oil.     

Ultrafast all-optical demultiplexer based on monolithic Mach–Zehnder interferometer with integrated semiconductor optical amplifiers

A monolithically integrated and fully packaged Mach–Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is demonstrated as polarisation-independent high-speed demultiplexer for up to 160 Gbit/s optical time division multiplexed (OTDM) data streams.     

A theoretical study of the 21Ag ← 11Ag two-photon transition and its vibronic band in trans-stilbene

The two-photon spectrum of the 2¹A_g ← 1¹A_g transition in trans-stilbene has been calculated at the complete active space self-consistent field (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and final states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active π orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest π orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck-Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force fields of both the initial and final states, at the CASSCF level of theory. The results are in agreement with experiment.     

The ammonia dimer equilibrium dissociation energy: convergence to the basis set limit at the correlated level

The low-energy region of the intermolecular potential energy hypersurface (PES) of the ammonia dimer was studied at the level of second-order Moller-Plesset perturbation theory (MP2) using a very large basis set. Individual minima were located on the PES employing the counterpoise (CP) correction to account for the basis set superposition error (BSSE). Apart from these canonical MP2 calculations local MP2 (LMP2) calculations were performed. For the latter the BSSE at the correlated level is inherently absent by virtue of the local truncation of the virtual space. Results from canonical and local MP2 calculations are compared and the reliability of the LMP2 method for intermolecular complexes and clusters is discussed. The canonical MP2 calculations predicted five minimum structures, the four most stable ones lying energetically very close. For these four structures single point MP2 energy calculations with a further extended basis set (1024 functions for the ammonia dimer) were performed. The equilibrium dissociation energies so obtained are close to the one-particle basis set limit, as illustrated by a remaining BSSE of less than 0.2 kJ mol^?1. The geometry optimizations at the LMP2 level, using the three most stable canonical MP2 structures as initial geometries, all collapsed to a single minimum corresponding to an asymmetric structural arrangement. A canonical MP2 single point calculation, at that geometry, revealed that the LMP2 minimum structure is virtually as stable as the lowest minima on the canonical MP2 PES. Based on these calculations the global minimum of the ammonia dimer was assigned to a part of the PES represented by an asymmetric structure with an equilibrium dissociation energy of 13.5±0.3 kJ mol^?1     

Particle‐Stabilized Water Droplets that Sprout Millimeter‐Scale Tubes

Millimeter‐scale tubes are observed to sprout from water droplets injected into a bath of toluene containing ethanol and silica colloids. This phenomenon requires that first a membrane is formed by the colloids which self‐assemble at the droplet interface, and second, that the ethanol preferentially partitions into the aqueous phase leading to an internal over‐pressure. Tube growth, eruption, and shuffling droplets are subsequently observed, depending on the concentration of ethanol and colloids selected. This work opens many possibilities in the field of biomimetic droplets for fundamental studies of artificial growth at the microscale and for emulsion‐related applications.     

Molecular imprinting in chemical sensing – Detection of aromatic and halogenated hydrocarbons as well as polar solvent vapors

The technique of molecular imprinting – a novel tool of sensor material synthesis – can be successfully combined with mass-sensitive transducers. Imprinted polymers are prepared in presence of inert analytes acting as molecular templates. The remaining imprint allows the molecular recognition of an analyte due to host-guest-interactions. The sensor properties of devices coated with imprint polymers can be tuned to the analyte by variation of the polymerization solvent and the amount of cross-linker added. A further sensitivity enhancement can be achieved by rising the resonant frequencies of QMBs and SAW resonators, since the signal to noise-ratio increases in an approximately linear manner with the oscillation frequency.     

The morphology of fibrillar polyethylene crystals

A comparison has been made of the morphology of fibrillar polyethylene crystals prepared by shear-induced crystallization and heterogeneous Ziegler-Natta catalysis under similar solvent and temperature conditions. Both specimens had a shish-kebab superstructure consisting of lamellar overgrowths on a filamentary backbone. For polyethylenes stirrer-crystallized at small supercoolings, the overgrown lamallae were removed by nitric acid oxidation followed by selective dissolution, leaving naked filamentary ribbons. Thermal analysis of these specimens suggested a dual molecular conformation of both folded and extended chains. The fact that these fibrils did not deform easily under uniaxial stress conforms with a core of extended chains. Thermal and oxidative behavior of polyethylenes prepared at lower crystallization temperatures suggested a greater content of chain folds in the central thread as the degree of supercooling increased. The Ziegler-Natta fibrils were degraded into lamellar fragments on oxidation and their thermal behavior suggested a predominantly folded-chain conformation. Uniaxial deformation occurred on stretching the Ziegler-Natta specimens in harmony with a core of folded chains. Molecular models have been proposed to account for the observed phenomena.