Non-Cp type titanium precatalysts for ethylene/norbornene copolymerization

Ethylene/norbornene monomers were homo- as well as copolymerized using titanium-based non-Cp precatalysts [2-(2,6-dialkylphenylamino)-1-phenylethoxy TiCl₂] in the presence of methylaluminoxane. The precatalysts polymerized ethylene with moderate activities that increased with increase in temperature reaching a maximum yield of polyethylene at 70 °C. However, these catalysts showed relatively low activity towards norbornene homopolymerization. Precatalysts 1ATiCl₂ and 3ATiCl₂ were used for ethylene/norbornene copolymerization. The microstructural analysis of these copolymers suggests that these are alternating copolymers with meso (major) and racemic (minor) sequences. Higher norbornene incorporation in the copolymer was obtained with precatalyst 3ATiCl₂, which is a more “open” catalyst system. The reactivity ratios for ethylene/norbornene copolymerization suggest that these precatalysts show lesser tendency towards norbornene homopropagation in the copolymerization reactions.     

Associations between persistent organic pollutants and vitamin status in Brünnich's guillemot and common eider hatchlings

The aim of the study was to examine associations between persistent organic pollutants and vitamin A (retinol), retinyl palmitate and vitamin E status (alpha-tocopherol) in two species occupying different trophic positions in the Arctic food web. Levels of polychlorinated biphenyls (PCBs), some selected organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) were analyzed in yolk sac of newly hatched chicks of Brünnich's guillemot (Uria lomvia) and common eider (Somateria mollissima) from Kongsfjorden, Svalbard (Norwegian Arctic) (79 degrees N). Morphological variables were measured, and levels of retinol, retinyl palmitate and alpha-tocopherol were analyzed in plasma and liver. Brünnich's guillemot had significantly higher levels of POPs than common eider, as expected from its higher trophic position. Morphological traits seemed to be negatively related to POPs in Brünnich's guillemots, but not in common eiders. In Brünnich's guillemot, negative relationships were found between some OCPs (hexachlorobenzene, oxychlordane, p,p'-DDE) and liver alpha-tocopherol levels. The negative relationships between these OCPs and liver alpha-tocopherol levels in Brünnich's guillemot hatchlings became less evident when the confounding effect of liver mass was corrected for. In common eider positive relationships were found between summed PCB (SigmaPCBs) and some OCPs (beta-hexachlorocyclohexane, oxychlordane) and liver alpha-tocopherol levels. Differences in relationships between POPs and vitamin status in the two species may be related to differences in POP exposure levels linked to their trophic position in the Arctic marine food web, or to intrinsic physiological differences between the species.     

Studies on steam condensation and particle diffusiophoresis in a heat exhanger tube

In this paper, studies on steam condensation and aerosol behaviour in a heat exchanger are presented. The heat exchanger is a model of one single tube of a Passive Containment Condenser (PCC) that is used in the European Simplified Boiling Water Reactor (ESBWR). A hot carrier gas containing nitrogen and steam with Ag and CsOH particles flows through the heat exchanger. The walls of the heat exchanger are cooled with a water jacket, thus causing steam condensation and diffusiophoretic particle deposition. The amount of condensed steam is measured, as well as the temperatures, particle mass concentrations and size distributions before and after the heat exchanger. The experiments are done with different proportions of steam and nitrogen in the carrier gas. Heat and mass transfer in the system are modelled with well known engineering correlations, producing results that agree nicely with the experimental results. The diffusiophoretic particle deposition velocity is shown to be proportional to the steam condensation rate, as expected.     

A disconfirmation bias in the evaluation of arguments.

Two experiments provided evidence for a disconfirmation bias in argument evaluation such that arguments incompatible with prior beliefs are scrutinized longer, subjected to more extensive refutational analyses, and consequently are judged to be weaker than arguments compatible with prior beliefs. The idea that people are unable to evaluate evidence independently of prior beliefs has been documented elsewhere, including in the classic study by C. G. Lord, L. Ross, and M. R. Lepper (see record 1981-05421-001) . The present findings contribute to this literature by specifying the processes by which prior beliefs affect the evaluation of evidence. The authors compare the disconfirmation model to several other models of how prior beliefs influence current judgments and present data that provide support for the disconfirmation model. Results indicate that whether a person's prior belief is accompanied by emotional conviction affects the magnitude and form of the disconfirmation bias. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of vapor intrusion using controlled building pressure

The use of measured volatile organic chemical (VOC) concentrations in indoor air to evaluate vapor intrusion is complicated by (i) indoor sources of the same VOCs and (ii) temporal variability in vapor intrusion. This study evaluated the efficacy of utilizing induced negative and positive building pressure conditions during a vapor intrusion investigation program to provide an improved understanding of the potential for vapor intrusion. Pressure control was achieved in five of six buildings where the investigation program was tested. For these five buildings, the induced pressure differences were sufficient to control the flow of soil gas through the building foundation. A comparison of VOC concentrations in indoor air measured during the negative and positive pressure test conditions was sufficient to determine whether vapor intrusion was the primary source of VOCs in indoor air at these buildings. The study results indicate that sampling under controlled building pressure can help minimize ambiguity caused by both indoor sources of VOCs and temporal variability in vapor intrusion.     

Single electron spintronics

Single electron electronics is now well developed, and allows the manipulation of electrons one-by-one as they tunnel on and off a nanoscale conducting island. In the past decade or so, there have been concerted efforts in several laboratories to construct single electron devices incorporating ferromagnetic components in order to introduce spin functionality. The use of ferromagnetic electrodes with a non-magnetic island can lead to spin accumulation on the island. On the other hand, making the dot also ferromagnetic introduces new physics such as tunnelling magnetoresistance enhancement in the cotunnelling regime and manifestations of the Kondo effect. Such nanoscale islands are also found to have long spin lifetimes. Conventional spintronics makes use of the average spin-polarization of a large ensemble of electrons: this new approach offers the prospect of accessing the quantum properties of the electron, and is a candidate approach to the construction of solid-state spin-based qubits.     

CO dissociation and CO+O reactions on a nanosized iron cluster

Catalysis over metal nanoparticles is essential for the growth of carbon nanotubes and all the properties of the resulting nanotube, such as diameter and chirality, are affected by the metal particle. Thus, it is very important to understand the carbon chemistry taking place on nanometer size metal particles. Here we present the first ab initio computational study of chemical reactions on a nanosized iron cluster. The clusters have reaction sites, such as edges and vertexes between the facets, Which have not been studied before. First principles electronic structure calculations, fully incorporating the effects of spin polarization and non-collinear magnetic moments, have been used to investigate CO disproportionation on an isolated Fe₅₅ cluster. After CO dissociation, O atoms remain on the surface while C atoms move into the cluster, presumably as the initial step toward carbide formation. Here we show that the lowest CO dissociation barrier found on the cluster (0.77 eV) is lower than on most previously studied Fe surfaces. This dissociation occurs on a vertex between the facets. Several possible paths for CO₂ formation were identified. The calculated lowest reaction barrier is 1.08 eV, which is comparable to the barrier of 0.65 eV obtained by experiment.      

Toward improved catalytic low-temperature NOx removal in diesel-powered vehicles

The potential of different catalytic after treatment techniques to meet future diesel emission standards, which are strongly shifted toward urban driving conditions including cold start, are critically discussed in this Account and evaluated for their suitability for commercial applications. The dominating techniques in this field are NO(x) storage, urea-selective catalytic reduction (SCR), and HC-SCR. Each of these techniques have significant disadvantages such as sulfur sensitiveness and regeneration requirements of NO(x)-storage materials, infrastructure issues and formation of ammonium nitrate (at low temperatures) for urea-SCR, and low-temperature activity of HC-SCR catalysts. Ways to overcome these disadvantages in commercial applications may involve optimized regeneration strategies, reactor modifications, flow reversal, closed-loop NO(x) feedback systems, nonthermal plasma, and/or hydrogen-assisted catalyses, etc.