Methylene-bridged polysilsesquioxanes: substitution of a methylene spacer within a silicate matrix

Polysilsesquioxanes with organic bridging groups have been popular as building blocks for organosilicas used for catalyst supports, membranes, high surface area adsorbents, and dielectric films. The organic bridging is an integral part of the network giving rise to the hypothesis that bridged polysilsesquioxanes are more similar to silica in structure than polysilsesquioxanes with pendant organic groups. However, there is only limited evidence to support this organosilica model. To test the hypothesis, we chose to compare the sol–gel polymerizations of the simplest alkylene-bridged polysilsesquioxane monomer, bis(triethoxysilyl)methane (M-0) with two silica precursors: tetraethoxysilane (T-0) and hexaethoxydisiloxane (H-0), a proposed intermediate in T-0’s polymerization. M-0 and H-0 differ only on whether the bridging group between the two silicons is a methylene or oxygen, respectively. In spite of faster hydrolysis and condensation rates with M-0, comparisons of the methylene-bridged and silica monomers’ sol–gel chemistry and physical properties of the resulting xerogels reveal striking similarities that corroborate the organosilica model. In all three cases, hydrolysis and condensation led to mixtures of acyclic and cyclic intermediates. As one might expect from the structural similarities between the M-0 and H-0 monomers, mass spectrometric analyses of their early hydrolysis and condensation revealed nearly identical reaction pathways. Solid state Si-29 NMR analysis of the xerogels revealed very similar degrees of condensation and surface area analyses of the resulting xerogels (M-1, H-1, and T-1) revealed remarkably similar surface area and pore size distributions, especially between M-1 and H-1.     

Sensitivity to change of generic quality of life instruments in patients with rheumatoid arthritis: preliminary findings in the generic health OMERACT study. OMERACT/ILAR Task Force on Generic Quality of Life. Life Outcome Measures in Rheumatology. International League of Associations for Rheumatology

In order to investigate intraspecific differences in Loxosceles intermedia spider venom we compared some biological properties of male and female venoms. Females produced higher amounts of venom than males. Furthermore, female venom presented more potent dermonecrotic and complement-dependent activities than male venom. Interestingly, the F35 toxin, a dermonecrotic and complement-dependent haemolytic factor, was also present in greater amounts in female venom, as demonstrated by ELISA. Therefore, the higher production and increased toxicity of venom in female specimens as compared to males may contribute to the variability observed in the severity of envenoming caused by L. intermedia spiders.     

A 10-Gb/s 1024-Way-Split 100-km Long-Reach Optical-Access Network

Optical-access networks have been developed to remove the access-network bandwidth bottleneck. However, the current solutions do not adequately address the network economics to provide a truly cost-effective solution. Long-reach optical-access networks introduce a cost-effective solution by connecting the customer directly to the core network, bypassing the metro network, and, hence, removing significant cost. This paper charts the design and development of a 1024-way-split 100-km 10-Gb/s symmetrical network, which experimentally proves the feasibility of long-reach optical-access networks for both the upstream and downstream transmission.     

Cigarette smoking during pregnancy.

Maternal smoking during pregnancy is associated with several adverse developmental outcomes in the offspring. These include preterm delivery, spontaneous abortion, growth restriction, increased risk of sudden infant death syndrome (SIDS), as well as long-term behavioral and psychiatric disorders. However, the underlying physiological mechanisms for these ill-effects are not fully understood. The aim of this paper is to review the animal and human data to date, linking in utero smoke exposure to negative neurodevelopmental outcomes. It is known that nicotine from cigarette smoke exerts its effects by affecting placental vasculature, and also by nicotinic acetylcholine receptor binding in fetal membranes. Thus, subsequent consequences involve a cascade of events causing not only dysregulation of the nicotinic and muscarinic, but also catecholaminergic and serotonergic neurotransmitter systems. These observations provide some insight into how smoking can impair neurodevelopment, but the long-term neurotransmitter involvement in dysregulation of emotion and attention awaits further elucidation. It is important that pregnant women are warned of the detrimental effects of smoking, and encouraged to abstain for healthy fetal development.     

A simulator developed for a twin-pod AUV,the Marport SQX-500

A vertically arranged twin-pod autonomous underwater vehicle (AUV) is presently under development in St. John’s Newfoundland. A large separation of the centre of gravity (CG) and the centre of buoyancy (CB) can be achieved by placing heavy batteries and payloads in the lower pod and placing the light controller and communication electronics on the upper pod. With the large vertical separation between CG and CB the twin-pod vehicle becomes highly stable in pitch and roll and thus provides an ideal platform for obtaining photos, video and sonar images of the seabed. This paper presents the vehicle motion simulations that have been done in support of this novel AUV design and development.

     

Calibration and field verification of semipermeable membrane devices for measuring polycyclic aromatic hydrocarbons in water

The use of semipermeable membrane devices (SPMDs) has become common in environmental sampling of nonpolar organic contaminants, yet few data exist for the uptake or sampling rates of polycyclic aromatic hydrocarbons (PAH). Two separate laboratory calibration experiments were conducted to determine the sampling rates of 28 individual PAH and 19 homologues. PAH with a log Kow > 4.5 remained in the linear uptake phase for 30 days, but PAH with a log Kow < 4.5 began to approach steady state within 15 days. Sampling rates, corrected for dissolved organic carbon, ranged from 2.11 to 6.06 L d(-1). Shear flow across the membrane had no statistically significant effect on rates over the range of 0.01-0.50 cm s(-1). Field verification of these sampling rates yielded agreement within about a factor of 2 for most PAH and a factor of 4 for all PAH. The worst agreement was for the most hydrophobic PAH, where partitioning into dissolved and particulate organic carbon pools are more important and less certain. These SPMD sampling rate data will allow quantitative estimations of freely dissolved concentrations of 47 compounds that are commonly used for PAH and petroleum product source identification and allocation.     

A comparison of rubber stress relaxation models for conveyor belt indentation rolling resistance calculations

Rubber stress relaxation models are the main material input data for numerical and analytical conveyor belt indentation rolling resistance calculations. Stress relaxation data for rubbers, such as those used in the construction of conveyor belts, are difficult to measure directly due to their fast relaxation times and, as such, they are usually derived via a dynamic mechanical analysis; unfortunately, relaxation data for the strain levels reached in conveyor belting cannot be produced with typical dynamic mechanical analysis machines. This paper utilizes high strain level data produced on a high capacity dynamic mechanical analysis machine and compares the indentation rolling resistance predictions derived from the measured high strain relaxation moduli with other high strain relaxation moduli extrapolated from low strain level measurements that can be measured on dynamic mechanical analysers with smaller capacities. Jonker’s equation and a two dimensional finite element analysis model are used to compare the different sets of relaxation moduli and these are compared with results from large scale indentation rolling resistance experiments.