Study of the effect of BDMA catalyst in the epoxy novolac curing process by isothermal DSC

Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry     

Magnet Safety Assessment for ITER

The ITER magnet system consists of structurally linked sets of toroidal (TF) and poloidal (PF) field coils, central solenoid (CS), and various support structures. The coils are superconducting, force flow Helium cooled with a Kapton-Glass-Epoxy multilayer insulation system. The stored magnetic energy is about 100GJ in the TF system and 20GJ in the PF-CS. Coils and structure are maintained at 4 K by enclosing them in a vacuum cryostat. The cryostat, comprising an outer envelope to the magnets, forms most of the second radioactivity confinement barrier. The inner primary barrier is formed by the vacuum vessel, its ports and their extensions. To keep the machine size within acceptable bounds, it is essential that the magnets are in close proximity to both of the nuclear confinement barriers. The objective of the magnet design is that, although local damage to one of the barriers may occur in very exceptional circumstances, large scale magnet structural or thermal failure leading to simultaneous breaching of both barriers is not credible. Magnet accidents fall into three categories: thermal (which includes arcing arising from insulation failure and local overheating due to discharge failure in the event of a superconductor quench), structural (which includes component mechanical failure arising from material inadequacies, design errors and exceptional force patterns arising from coil shorts or control failures), and fluid (Helium release due to cooling line failure). After a preliminary survey to select initial faults conceivable within the present design, these faults are systematically analyzed to provide an assessment of the damage potential. The results of this damage assessment together with an assessment of the reliability of the monitoring and protective systems, shows that the magnets can operate with the required safety condition.     

An improved system for the control of dissolved oxygen in freshwater aquaria

A system for the removal and control of dissolved oxygen (DO) from freshwater was designed and constructed with aquarium-type fish studies in mind. Degassed water was obtained using a partial vacuum of -14 psi, and DO regulated at an aquarium scale using electronically controlled aeration with timed partial water renewal. The degassing system was capable of producing water with approximately 1.7 mg L(-1) DO within 10 min of operation, and 0.55 mg L(-1) after 2h. The control system was capable of maintaining DO levels of ca 0.8 mg L(-1) over 48 h in the absence of aeration and further capable of precisely controlling DO levels as low as 1.16+/-0.002 mg L(-1) (mean+/-SEM) with aeration over a 48 h period.     

Effect of profound hearing loss on a central auditory nucleus

The present study was designed to investigate the type and extent of degeneration occurring in the human central auditory system subsequent to profound hearing loss. The authors have examined the size of one population of neurons in the ventral cochlear nucleus in seven subjects with profound hearing loss (audiometric responses poorer than 90-100 dB HL). Six normal subjects, ages 35-78, were used as controls. Cell size in the hearing-impaired subjects ranged from normal to reduced by more than 50 percent. Two factors appear to contribute to the variability in cell size reduction. The correlation coefficient (Spearman rs) of cell size with duration of profound deafness was -0.48, indicating a moderate tendency for neurons to become smaller with longer periods of deafness. The correlation coefficient of cell size with number of surviving cochlear ganglion cells was 0.73, indicating a stronger tendency for neurons to be larger with greater eighth nerve innervation of the cochlear nucleus. Two cases of Scheibe degeneration showed the most severe degenerative change in the central auditory system.     

Active surveillance of health and safety in microbiology laboratories

In microbiology laboratories highly infectious material is handled alongside complex and potentially dangerous equipment, and staff are therefore at risk of infections and accidents. Acts of parliament and regulations exist to protect staff in the workplace, including those exposed to biological agents. The current monitoring of health and safety in laboratories seeks to ensure that employers and employees comply with existing regulations, but this form of passive surveillance is of limited value because it does not highlight shortcomings in techniques, equipment, premises, or personnel. We propose a scheme for the surveillance of health and safety in microbiology laboratories that will actively seek information about laboratory incidents and practices, in order to enable appropriate preventive measures to be instituted.     

Postischemic hyperglycemia worsens neurologic outcome after spinal cord ischemia

PURPOSE: The neurologic effect of induced hyperglycemia in the postischemic period was investigated with a rat aortic occlusion model. METHODS: Sprague-Dawley rats weighing 200 to 350 gm were anesthetized, intubated, and ventilated with 1% to 1.5% halothane. Temperature was continuously monitored and maintained at 37 degrees +/- 0.5 degrees C. The chest was opened, the thymus excised, and the aortic arch exposed. Snares were placed around the aorta distal to the left subclavian artery and the right and left subclavian arteries. The three vessels thus isolated were occluded for 8 minutes. With snare release and withdrawal, the rats received an intraperitoneal injection of 5% dextrose in water (2 gm/kg) or an equivalent volume of 0.9% saline solution. In a second group of rats the administration of glucose or saline solution was delayed until 30 minutes after snare release. Blood samples for blood glucose determination were obtained before operation, before occlusion, immediately after occlusion, and 15, 30, 45, 60, and 240 minutes after occlusion. A neurologic deficit score was assigned at 1, 4, 18, and 24 hours after occlusion to quantify hindlimb neurologic deficit based on 15-point scale (0 = normal, 15 = severe deficit). Sham-operated rats received the same operation and injection, but the snares were only manipulated and not made occlusive. RESULTS: The rats that were administered glucose immediately after snare release showed a statistically significant exacerbation of lower extremity neurologic deficit at 24 hours after occlusion (p < or = 0.05, Mann-Whitney U test). The sham-operated rats were normal (0 score) at 24 hours. Significant elevation of blood glucose (321 +/- 33 mg/dl) was seen in the glucose-injected rats at 15 minutes and continued for up to 4 hours after occlusion (p = 0.040 and 0.014, respectively; Student's t test). CONCLUSION: Postischemic hyperglycemia immediately after a standard spinal cord ischemic stress worsens neurologic outcome.     

The importance of glossaries

Standards cannot be set, specifications cannot be written uniformly and unambiguously, and methods cannot be described succinctly, without an agreed terminology. Producing a glossary is a painstaking process and the fundamental principles involved are described. Some difficulties and misunderstandings are identified.