Computational study of non-covalent interactions in oxirane…XF complexes (X = H,F, Cl,Br, Li) and their F-/Li-substituted analogues

A computational study found oxirane^…XF (X = H, Cl, Br, F, Li) dimers to be energetically stable, with their interaction energies increasing with the magnitude of the XF dipole moment in the order XF = LiF > BrF ～ HF > ClF > F₂. Their relative stabilities roughly correlate with the amount of charge transferred from the lone pairs on the O atom of oxirane to the antibonding σ* orbital of XF. However, the most strongly bound dimer, oxirane^…LiF, is stabilised by the largest dipole but involves the smallest charge transfer. The variation in the strength of the oxirane^…XF interaction was subsequently investigated by the sequential substitution of the protons on oxirane by either electron-donating Li or electron-withdrawing F atoms.     

Void formation due to gas evolution during the recycling of Acrylonitrile-Butadiene-Styrene copolymer (ABS) from waste electrical and electronic equipment (WEEE)

During processing of recycled ABS and ABS/HIPS blends, voiding defects can occur within the resulting material which can result in deterioration of mechanical properties. The voids were previously thought to be caused by the evolution of volatile substances during processing. This study investigated the recycling of post-consumer ABS from a variety of types of WEEE. The mechanical properties of the processed material were assessed and a combination of visual observation during processing and optical microscopy was used to identify the extent of voiding. It was found that flexural strength and ductility in particular decreased with increased levels of voids. The gases emitted during heating and processing were analysed using Gas Chromatography with Mass Spectroscopy (GCMS) and were found to be breakdown products of the original polymers. These seem to be present in the WEEE, either as polymerization residuals or as products of degradation during the initial service life rather than degradation products from reprocessing. The amounts of volatiles liberated were quantified, which showed that the volatile emissions from post-consumer material were of a similar magnitude to those seen with virgin material. More intensive or longer processing led to a reduction in the emissions and voiding and an improvement in strength, suggesting that there is a finite potential for volatile liberation, and that the problem could be overcome by the use of suitable processing conditions.     

A Cognitive Modeling Tutor Supporting Student Inquiry for Balancing Chemical Equations

Improved interactive tutoring capabilities in educational software for chemistry problem solving is an important need that has been clearly articulated by teachers and students. The purpose of this work is to examine the incorporation of new concepts from the field of artificial intelligence (AI) as a route to meaningful individualized tutoring. The basic shift is to replace specific foreknowledge of problems with a direct representation of chemical and pedagogical principles and then simulate reasoning using these principles to tutor students. To assess the potential of an AI-based approach, we have developed a prototype tutorial program for balancing chemical equations that contains two important advances. First, the system can create a worked-out solution with detailed explanations for any equation entered by the student or teacher. Unlike a conventional tutorial, this is done dynamically, without the equation being stored ahead of time. Second, the program can interactively answer a variety of detailed questions about its work at each step. Studying worked-out examples plays an important role in learning, and this approach to supporting interactive student inquiry is being investigated as a method of cognitive modeling and apprenticeship intended to foster the students own self-explanation and question-asking abilities.     

4-substituted but-2-enylpalladium(II) complexes

The chloro bridges in di-μ-chloro-4-methoxy- and di-μ-chloro-4-acetoxy-2-methyl-but-2-enylchloropalladium are split by Group V donor ligands Ph₃E (where E = P, As and Sb) to give [(η)³-H₂CC(CH₃)CHCH₂X) PdCl · EPh₃], (where X = OCH₃, OCOCH₃). These complexes are readily decomposed by dilute ethanolic hydrogen chloride yielding [Ph₃E · PdCl]₂ and isoprene. The structures of the compounds are discussed in the light of their ¹H NMR spectra.     

The Effects of Warship and Replenishment Ship Attrition on War Arsenal Requirements

A three-phase simulation written in Pascal and using a suite of procedures developed by Lancaster University and the London School of Economics is developed to model a group of ships subject to submarine and air attacks during an extended period of conflict. The simulation collects statistics on weapon usage by the ship group in order to study the impact of attrition, including the effects of preferential targeting, and correlation between the usages of different weapon systems, on war arsenal requirements.     

Critical and three phase behavior in the carbon dioxide/tridecane system

The PT behavior of the carbon dioxide/normal alkane series exhibits a distinct transition in the CO₂/nC₁₃H₂₈ system. This particular diagram is characterized by two liquid—liquid—vapor (l-l-g) loci, a lower liquid-upper liquid (l-l) critical branch extending from high pressures to the upper critical end point (UCEP) and two liquid—vapor (l-g) critical branches which cross near the lower critical end point (LCEP).An experimental PTx diagram in the vicinity of the CO₂ critical point, LCEP and K point reveals the emergene at the LCEP of a l-l region which increases in size with temperture while the upper liquid—vapor (L₂-g) region diminishes, eventually disappearing at the K point. The l-l-g surface illustrates the compositional changes of each phase with temperture.Detailed Px diagrams at three temperatures between the LCEP and K point are presented and each exhibits two critical points, a l-l-g locus and curves of constant phase volume ratio which show discrete changes in both value and slope at the l-l-g locus. Graphical and numerical methods of determining the phase densities and compositions from three phase volumetric behavior are presented.     

Joint European Stable Isotope Users group Meeting. JESIUM 2004

Announcement

Joint European Stable Isotope Users group Meeting. JESIUM 2004     

A measurement of the proton-proton cross section at the CERN ISR

We present a measurement of the total cross section σ_t in proton-proton collisions at the CERN ISR. The method involves determination of the total interaction rate and machine luminosity. A two-arm scintillation hodoscope observes ～ 90% of the total interaction rate, while a streamer chamber is employed for event topologies missed by the main trigger. An increase of about 10% in σ_t is observed in the energy range √s = 23.6 to √s = 62.8 GeV/c in agreement with previous experiments.     

Experimental investigation of high-mach-number 3D hydrodynamic jets at the national ignition facility

The first hydrodynamic experiments were performed on the National Ignition Facility. A supersonic jet was formed via the interaction of a laser driven shock ( approximately 40 Mbar) with 2D and 3D density perturbations. The temporal evolution of the jet's spatial scales and ejected mass were measured with point-projection x-ray radiography. Measurements of the large-scale features and mass are in good agreement with 2D and 3D numerical simulations. These experiments provide quantitative data on the evolution of 3D supersonic jets and provide insight into their 3D behavior.