High-performance permanent magnets

 High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE–TM intermetallic alloys which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE=Nd, Pr, Sm) with transition metals (TM=Fe, Co), in particular magnets based on (Nd,Pr)₂Fe₁₄B and Sm₂(Co,Cu,Fe,Zr)₁₇. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of >15 compared with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new) application fields, to the extent that RE–TM pms now account for nearly half of the worldwide market. This review article first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets, their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a powerful tool for the further development of optimized high-performance pms.     

Evaluation of the biodegradability of copolyesters containing aromatic compounds by investigations of model oligomers

Model oligo esters of terephthalic acid with 1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol have been investigated with regard to their biodegradability in different biological environments. Well-characterized oligomers with weight-average molar masses of from 600 to 2600 g/mol exhibit biodegradation in aqueous systems, soil, and compost at 60°C. SEC investigations showed a fast biological degradation of the oligomer fraction consisting of 1 or 2 repeating units, independent of the diol component used for polycondensation, while polyester oligomers with degrees of polymerization higher than 2 were stable against microbial attack at room temperature in a time frame of 2 months. At 60°C in a compost environment chemical hydrolysis also degrades chains longer than two repeating units, resulting in enhanced degradability of the oligomers. Metabolization of the monomers and the dimers as well by the microorganisms could be confirmed by comparing SEC measurements and carbon balances in a Sturm test experiment. Based on these results degradation characteristics of potential oligomer intermediates resulting from a primary chain scission from copolyesters consisting of aromatic and aliphatic dicarbonic acids can be predicted depending on their composition. These results will have an evident influence on the evaluation of the biodegradability of commercially interesting copolyesters and lead to new ways of tailor-made designing of new biodegradable materials as well.     

Phase relations between a circadian rhythm and its zeitgeber within the range of entrainment

The regular day-night changes in tissues, physiologic functions, and behavior of organisms are based on endogenous rhythmic processes which under constant conditions continue with periods slightly deviating from 24h. These ‘arcadian’ rhythms have properties of self-sustained oscillators. Under natural conditions, circadian rhythms are synchronized (entrained) to 24 h by periodic factors in the environment, the so-called ‘Zeitgebers’. In the laboratory, circadian rhythms can also be entrained to periods other than 24 h within certain limits. Data on the phase relationship between the circadian rhythm and an entraining light-dark cycle for vertebrates, insects, plants, and unicellular organisms are reviewed.     

Transport of particulate matter in natural waters — modelling and in situ-measurements

The significant processes controlling the fate of particulates are convection an dispersion on one hand, and sedimentation on the other hand. Due to inteparticulated reactions, larger aggregates can be formed from smaller units thus changing the sedimentation characteristics. These phenomena are summarized in a mathematical model whereby hydrodynamic effects as well as the control mechanisms of the dissolved phase are included. A relationship was derived on the basis of energy considerations leading to the formulation of a critical sedimentation velocity of the suspensa, which determines the transport capacity of the flowing system. The sedimentation term is calculated from the above discussed transport capacity, hydro-dynamic parameters and suspending media properties. Aggregation effects are taken into account as an increase of sedimentation velocities of the particles. The equations are solved in a particular computational routine such that the horizontal distribution of suspended solids in a natural system can be describe as function of the above discussed phenomena. The model was tested with in situ-measurements. It was found that the observed processes are described satisfactorily by this model.     

Managing the urban environment in a developing country: The Ogunpa river channelization scheme in Ibadan City,Nigeria

A disastrous flood in Ibadan City, Nigeria in April 1978 aroused public interest in the Ogunpa river channelization scheme which had earlier been embarked upon by government. A questionnaire survey of 399 residents near the river was designed to examine three issues: (a) the losses sustained and the people's reaction to and perception of the causes of the flood; (b) their perception of the present and future uses of the river; and (c) their perception of the prospects of the channelization scheme.The results show that about 75% of the respondents were affected by the flood; 41% each lost property worth about N2960.00. Yet, many could not hope to move out of the flood zone mainly because of shortage of residential accomodation in the city. The factors given as being responsible for the flood were poor drainage, heavy rains, refuse disposal in the river, shallowness of the river channel and the unplanned layout of streets and buildings. Indeed, the major use of the river has been as a refuse dump, so that it is heavily polluted. Many respondents would like the river to be reclaimed to alleviate some of the socioeconomic problems confronting them. Recreational use of the river was not much considered. Majority of respondents thought the channelization scheme would bring some benefit. But, they are sceptical about its lasting impact unless it is done within the framework of a comprehensive programme of urban land management and protection and the improvement of living conditions in the city.     

Quality control in low-level radionuclide analysis. Results of recent intercomparisons and programmes for 1979/80 of the international atomic energy agency

The results of recent IAEA intercomparison programs are reviewed.     

CAN SCRAP SAVE US FROM DEPLETION?

Old scrap constitutes varied proportions of consumption of different metals. The authors construct a model in which the share of scrap in total supply is explained by three factors, the growth rate in overall demand for the metal; the share of metal contained in scrapped products actually recovered; and the durability of metal containing products. The model is used to study the impact on the share of scrap in total supply from changes in each of the factors. The strongest impact appears to follow from changes in the growth rate of overall demand. Inserting empirical data for copper into their model, the authors suggest, for instance, that in the long run old scrap could satisfy 100 per cent of copper demand, provided that this demand contracted by 1 per cent per year. La ferraille constitue des proportions variées d'utilisation de différents métaux. Les auteurs de cet article ont construit un modèle dans lequel la part de ferraille dans 'approvisionnement total est expliquée par le jeu de trois facteurs: le taux de croissance de la demande globale pour le métal, la part de métal contenue dans des débris de métaux effectivement récupérés et la durabilité des métaux renfermant des produits. Le modèle est utilisé pour étudier les incidences des changements dans chacun des facteurs sur la part de ferraille dans 'offre totale. L'incidence la plus importante semble provenir de modifications dans le taux de croissance de la demande globale. En introduisant des données empiriques pour le cuivre dans leur modèle, les auteurs suggèrent par exemple, qu' à longue échéance, la ferraille pourrait répondre à la demande totale en cuivre pourvu que cette demande se réduise d'un pour cent par année. El uso de chatarra representa una proporción variable del consumo de los diferentes metales. En este artículo los autores presentan un modelo en el que la proción de la chatarra en la oferta de un metal depende de tres factores: la tasa de crecimiento de la demanda global del metal, la proción del metal contenido en la chatarra recuperada, y la durabilidad o vida económica de los productos que contienen el metal en cuestión. El modelo se utiliza para estudiar el impacto sobre la proporción de chatarra en la oferta total causado por las variaciónes de cada uno de estos factores. El mayor impacto parece ocurrir debido al cambio en la tasa de crecimiento de la demands global. Al utilizar el modelo con datos para el cobre, los autores sugieren, por ejemplo, que en el largo plazo la chatarra de cobre podría satisfacer el cien por ciento de la demanda de este metal siempre que dicha demanda se contraigo en uno por ciento por año.     

Recent IAEA intercomparison on the determination of trace elements in simulated air filters

Results of a recent intercomparison on the determination of trace elements in simulated air filter samples are reported. A large scatter of results is obtained for some elements and systematic differences between laboratories are observed. The performance of different methods, in particular neutron activation analysis and atomic absorption spectrophotometry, used by the various laboratories is discussed (air filter analysis; intercomparison; trace elements; control charts).