PES News

This paper presents a new method for the generation of a reference voltage for a dynamic voltage restorer (DVR). These voltages, when injected in series with a distribution feeder by a voltage source inverter, can tightly regulate the voltage at the load terminal against imbalance or harmonics in the source side. It is stipulated that the DVR does not supply any real power in the steady state. The reference voltage generation scheme is validated through digital computer simulation studies.     

Cavitation in Superfluid Helium Possibly Arising from Penning Ionization of Dimers

We have perforated a series of experiments to study cavitation in superfluid helium into which electrons are injected by field-emission from a sharp tip. The injected electrons force open small cavities in the liquid (“electron bubble”). These objects explode at a critical negative pressure P _c, and in previous experiments we have studied the cavitation that resugts from these explosions. In the present experiments we have detected cavitation events that occur before a negative pressure as large as P _c is reached. We suggest that these events may arise from a process in which two neutral helium dimers interact and an electron is injected into the liquid through Penning ionization.     

Direct synthesis of copper faujasite

Copper containing faujasite has been successfully prepared for the first time using a direct synthesis method. Faujasite type zeolite can be prepared in the presence of copper species by tuning the synthesis conditions. Ammonium hydroxide was used to form a copper complex that was later mixed with the reacting gel. Sodium is required to obtain copper faujasite. The complete elimination of sodium ions from the starting gel produces amorphous material. Crystallization took place at 358 K for 11 days. Crystallization temperature of 373 K produces ANA type zeolite as an impurity. Increasing by two times the amount of copper complex added to the reacting gel increases the crystallization time of Cu-FAU from 11 to 20 days (the crystallization rate decreases). The copper containing faujasite obtained was characterized by XRD, FESEM, EDX, EPR, FT-IR, TPR, and BET. According to the XRD pattern only FAU type zeolite was obtained. According to TPR experiments, the reduction temperature for Cu²⁺ ions present in Cu-FAU prepared by direct synthesis was 70 K more than for Cu-FAU prepared by ion-exchange. This difference can be due to the different location of the copper ions in the supercages or in the sodalite cages of the faujasite.     

Purification and some properties of a xylanase from Aspergillus sydowii MG49

Aspergillus sydowii MG49 produces a 30-kDa exosplitting xylobiohydrolase during growth on xylan. A specific chemical modification and substrate protection analysis of purified xylanase provided evidence that tryptophan and carboxy and amino groups are present at the catalytic site of this enzyme. Thermal inactivation of the xylanase occurs because of irreversible polymolecular aggregation, which is slower in the presence of glycerol.     

Screen‐printed biosensor for allergens

Allergen levels in indoor environments, leading to many diseases, eg asthma, rhinitis and conjunctivitis, affect a large and increasing fraction of the population. A quite effective and inexpensive method of a rough but very rapid overall assessment of total allergen level in the environment has been developed. The method involved estimation of protein in allergen extracts by screen‐printed electrodes using two different techniques. The biosensor comprised a rhodinised carbon working electrode, a silver/silver chloride reference electrode and a carbon counter electrode. In the first method the enzyme protease reacted with allergen protein to release amino acid, which produced hydrogen peroxide in the presence of amino acid oxidase. This was detected amperometrically. The second method used potassium bromide as electrolyte and the electrode was subjected to dual potential. Bromine, released due to electrolysis at higher potential, was consumed by the allergen protein at lower potential. In the first method, a unique technique was used to microencapsulate the enzyme protease and immobilise it on the surface of the electrode by in‐situ polymerisation to avoid contact with the amino acid oxidase. A total of seven allergens were tested and the results gave a good correlation with the standard protein measurement method. Environmental specimens from indoors, schools and workplaces can be evaluated for the aeroallergens produced by dust mites, animal hairs, cockroach debris, pollens, etc as a means of determining the exposure risk. Copyright © 2005 Society of Chemical Industry     

Detecting nondeterminacy in parallel programs

Methods and tools for detecting nondeterminacy in programs for shared-memory multiprocessors are discussed. The approach described divides the debugging chore into two phases. The first phase uses tools that automatically detect nondeterminacy to debug synchronization errors, assuming it is decided at the outset to make the parallel program determinate. At the end of this phase, it is known that the program is determinate, that timing differences will not affect results, and the debugging sessions are repeatable. In the second phase, an interactive break-point debugger is used to find arithmetic and logical errors. The proposed tools fall into two groups: those that statically analyze the source program and those that analyze an execution trace of the program     

ENVIRONMENTAL TOBACCO SMOKE REMOVAL CAPABILITY OF ACTIVATED CARBON

Removal of gaseous and vapor constituents of environmental tobacco smoke (ETS) by activated carbons in a packed bed arrangement was studied under dynamic conditions and was compared with that by silica gel and molecular sieve 13X. ETS is a mixture of sidestream smoke and exhaled mainstream smoke, and it consists of various organic and inorganic compounds, trace heavy metals, and particulate matters. Due to the complex nature of ETS-air mixture, its removal from indoors is a challenging task. For experimentation in a laboratory, the ETS was produced from a specially designed smoking apparatus that simulated the puffng of a cigarette by a person. Air containing ETS was passed through a bed containing about 25 grams of activated carbon at room temperature. The flow rate of air-ETS mixture through the bed was 4000 cm3/min. The relative humidity of the air was 50% and contained about 35 to 40 ppm of hydrocarbons as measured as methane-equivalent. The number of particles in the inlet air stream were in the range of 30,000 to 35,000 particles/cm3. About 60% of hydrocarbons present in ETS were removed at these operating conditions for a period of about 70 hours. Based on 15 adsorption and regeneration cycles, it was noted that the carbon bed did not loose its capacity for ETS significantly as indicated by the BET surface area and water adsorption data. At the beginning of an adsorption cycle, the carbon bed captured a significant number of particles. However, the bed rapidly lost its particle capture effciency as the experiment progressed. The number of particles in the outlet air stream was found to be the same as that of the inlet stream within five minutes.     

Characterization of tempered martensite embrittlement using hardness measurement

A series of experiments were carried out on three commercial steels to explore the possibility for characterizing tempered martensite embrittlement (TME) by Rockwell, macro-, and micro-Vickers hardness tests. The results indicate distinct hardness peaks in two steels and an inflection in the other around the TME temperature. A new analytical approach for examining the slope of hardness-tempering temperature plots appears to reveal the TME phenomenon more sensitively. Dilatometric examinations substantiate that the temperature of hardness peak/inflection occurs beyond the second stage of tempering.     

On the notion of control signals in digital designs

The concept of control signals is fundamental to digital design. It evokes the notion of one or more signals that influence computation on other signals in a system, and regulate the behavior of the system. A formal definition of control signals is presented. It is argued that knowledge of the control signals in a complex design such as a microprocessor or a computer is crucial to the comprehension and specification of the design and that knowledge of the control signals of a design leads to a more efficient hardware implementation. The identification of control signals in two microprocessors are presented as examples