The Behavior of Arcing Faults in Low-Voltage Switchboards

An arc fault is the discharge of electricity through the air between two conductors creating large quantities of heat and light. It is widely accepted that there are many variables which affect the behavior of an arc in real switchboards, and thus, understanding the phenomena is difficult. This paper is based upon the results of several years of arc testing with circuits from 155 Vdc to three-phase 450 Vac and at power levels from tens of kilowatts to several megawatts. The goals of the testing were to understand the general behavior of arcing faults in low-voltage switchboards-well enough to predict the motion of arcs-and to design electronic monitoring systems that are capable of protecting switchboards against arcs. This paper will focus on the arc behavior, whereas our other papers will discuss its implications upon forensic investigations and upon the arc-fault protective systems.     

Mechanistic investigation into the electrolytic formation of iron from iron(III) oxide in molten sodium hydroxide

Iron(III) oxide tablets were electrolytically reduced to iron in molten sodium hydroxide at 530 °C and recovered to produce iron with 2 wt.% oxygen suitable for re-melting. The cell was operated at 1.7 V and an inert nickel anode was used. The thermodynamics and mechanism of the process was also investigated. By controlling the activity of sodium oxide in the melt, the cell could be operated below the decomposition voltage of the electrolyte with the net sequence of events being the ionization of oxygen, its subsequent transport to the anode and discharge leaving behind iron at the cathode. A reduction time of 1 h was achieved for a 1 g oxide tablet (close to the theoretical reduction time predicted by Faraday’s laws) at a current density of 520 mA cm⁻² with iron phase yields of ∼90 wt.%. The energy consumption was 2.8 kWh kg⁻¹.     

Thermal polymerization of thiol–ene network‐forming systems

The thermal polymerization of a tetrafunctional thiol (PETMP) and divinyl ether (TEGDVE) was monitored by temperature‐ramping differential scanning calorimetry (DSC) and the effects of inhibitor type and concentration, oxygen inhibition and initiator type were studied. The incorporation of inhibitors was required to produce a stable system at room temperature. Butylated hydroxytoluene (BHT) inhibited polymerization at low temperatures, but was inefficient at high temperatures and polymerization rates, and hence BHT is an ideal stabilizer. In contrast, a nitroxide inhibitor (NO‐67) was a very effective inhibitor and no polymerization occurred until all of the nitroxide was depleted. The presence of oxygen retarded the onset of polymerization but did not change the final conversion significantly. Polymerization with initiators having higher half‐life temperatures shifted the DSC peak to higher temperature because the rate of initiator decomposition and thus initiation was slower. Rheological investigations of the cure at different temperatures revealed that the gel time decreased significantly with increasing cure temperature, and the calculated apparent activation energy for PETMP/TEGDVE was 54 kJ mol^?1. Dynamical mechanical thermal analysis of the cured material was undertaken and frequency‐superposed results revealed that the glass transition region of PETMP/TEGDVE/azobisisobutyronitrile was much narrower than that of free‐radically cured dimethacrylate, but was similar to that of an epoxy resin cured with an aromatic diamine. This behaviour could be attributed to PETMP/TEGDVE network homogeneity, or to the less constrained crosslinks in the PETMP/TEGDVE network. Copyright © 2007 Society of Chemical Industry     

Chiroptical filters from aqueous (hydroxypropyl) cellulose liquid crystals

An experimental procedure has been designed for the preparation of aqueous mesophases of (hydroxypropyl)cellulose (HPC) exhibiting a stable low turbidity Sandwich chiroptical filters have been made from these right-handed cholesteric liquid crystals confined between two parallel glass plates. Their optical properties, studied with new circular polarizers prepared from oriented polyethylene films, depend on the mesophase thickness. Thin filters (liquid crystal thickness ≤ 200 μm) reflect selectively up to 36% of normal incident light (i.e., 72% of the right-handed circularly polarized component) in a very narrow wavelength band (bandwidth ≤ 10 nm). An increase of the reflected intensity is observed at higher sample thickness, although it is accompanied by an increasing loss of selectivity of the filter toward circularly polarized light. However, a range of thickness exists where both selectivity and reflectivity are close to their optimum values. The availability, low cost, and UV resistance of (hydroxypropyl)cellulose make HPC–water liquid crystals attractive for optical applications.     

An architecture for a self-improving instructional planner for intelligent tutoring systems

Machine instructional planners use changing and uncertain data to incrementally configure plans and control the execution and dynamic refinement of these plans. Current instructional planners cannot adequately plan, replan, and monitor the delivery of instruction. This is due in part to the fact that current instructional planners are incapable of planning in a global context, developing competing plans in parallel, monitoring their planning behavior, and dynamically adapting their control behavior. In response to these and other deficiencies of instructional planners a generic system architecture based on the blackboard model was implemented. This self-improving instructional planner (SUP) dynamically creates instructional plans, requests execution of these plans, replans, and improves its planning behavior based on a student's responses to tutoring. Global planning was facilitated by explicitly representing decisions about past, current, and future plans on a global data structure called the plan blackboard. Planning in multiple worlds is facilitated by labeling plan decisions by the context in which they were generated. Plan monitoring was implemented as a set of monitoring knowledge sources. The flexible control capability for instructional planner was adapted from the blackboard architecture BB1. The explicit control structure of SUP enabled complex and flexible planning behavior while maintaining a simple planning architecture.     

Separation of a Nonstationary Component from the EEG by a Nonlinear Digital Filter

A new nonlinear digital filter which separates nonstationary waves such as spikes from stationary background waves of the EEG is proposed. This filter is composed of a prediction filter and a simple nonlinear function. Some examples showing the separation of spikes from EEG data of epileptic patients are given.     

The Watershed Architecture of the Mekong River Basin

In this project, I suggest an alternative, speculative future in counterpoint to the recent construction and planned development of large-scale, water-based infrastructural transformations in Southeast Asia. Critical of massive hydropower dam constructions that tend to prioritize certain interests over others, I question the future viability of such actions when weighed in the context of possible negative effects that such dams may have across the entire river basin. Additionally, the current forecast of climate change stressors, especially in regards to freshwater availability, positions the future of the basin as uncertain. The focus of this essay is part of my multiyear project titled “Way Beyond Bigness: The Need for a Watershed Architecture,” which studies the Mekong, Mississippi, and Rhine River Basins in relation to water-based infrastructure and design challenges.