First commissioning results with the Grenoble test electron cyclotron resonance ion source at iThemba LABS

iThemba Laboratory for Accelerator Based Science (iThemba LABS) is a multi-disciplinary accelerator facility. One of its main activities is the operation of a separated-sector cyclotron with a K-value of 200, which provides beams of various ion species. These beams are used for fundamental nuclear physics research in the intermediate energy region, radioisotope production, and medical physics applications. Due to the requirements of nuclear physics for new ion species and higher energies, the decision was made to install a copy of the so-called Grenoble test source (GTS) at iThemba LABS. In this paper, we will report on the experimental setup and the first results obtained with the GTS2 at iThemba LABS.     

Adsorbed phosphate additives for interrogating the nature of interparticles forces in kaolin clay slurries via rheological yield stress

Unimin’s kaolin clay slurry displayed a maximum yield stress that is not located at the point of zero charge or at low zeta potential. Adsorbed phosphate additives at sufficient concentration caused this yield stress to reduce to zero. The clear implication of these two results is that the particle interactions contributing to the maximum yield stress must be due to unlike charged or positive–negative charge attraction. The adsorbed negatively charged phosphate additives neutralised the positively charge sites of the clay particles causing the suspension to be completely dispersed and the yield stress to disappear. The monophosphate additive is less effective in dispersing the slurries. Based on charge concentration of additives, the pyrophosphate, triphosphate and polyphosphate appeared to be equally as effective in dispersing the clay slurries. The yield stress-DLVO force model that predicts a linear relationship between yield stress and square of zeta potential with a negative slope, is obeyed by the kaolin slurries with adsorbed phosphate additives. However, with the slurry without phosphate additive it displayed three linear relationships with negative and positive slopes. The negative slope relationships were located in the low and high zeta potential regions while the positive slope relationship was found in between these regions.     

消费电子产品寿命终期的生态效益研究(一)

要改善消费电子产品寿命终期阶段的生态效益,对其作全面的评估是需要的。荷兰Delft大学倡导的环境权重再循环和生态效益(QWERTY／EE)理论,其目标是想以最小的产品寿命终期处理成本实现最大化的环境重建。本文生态效益概念的提出是基于一系列改进措施的实现,诸如改变切碎和分离装置,实现塑料和玻璃的回收利用,或对某种产品进行单独分类等。对75种之多的消费电子产品的分析清楚地显示：各种产品类别之间具有分组性能(在衡量环境和经济方面有良好的回收性)和明显区别。从这个意义上说,此评估将引发目前最实用的回收技术的进步。而且,环境权重再循环和生态效益概念,使得对当前和今后的寿命终期处理工艺进行选择和归类成为可能,并能进一步确定哪种方法可以带来最佳投资、环境收益比。对以玻璃为主体的产品中玻璃回收的增加导致了环境的明显改善。对含有贵金属的产品,贵金属的单独分类和处理,也具有同样的价值,比如手机。然而以上事实是基于经济可行的前提。其它的结论和成果对玻璃的回收利用来说只是对处于拆解状态下,并且有阴极射线管(CRT)或液晶显示器(LCD)的大型家电设备才具有生态效益。对中小尺寸的家电设备进行塑料回收利用,其额外成本相对于环境改善是很高的。在绝大多数情况下,对以金属为主体的产品只进行切碎和分离并不能导致环境或经济效益的显著改善。一般来说,提高寿命终期产品生态效益的各种方法导致了很复杂的环境、经济结果。因而,应建立寿命终期政策策略评估体系,在某些情况下还应进一步修正,来支持和提高生态效益改善措施。至于具体的结果,虽然不同的环境评估模型按不同的顺序把单个物质排序,但除了塑料回收环节外,改进措施在系统级上的结果显示出一致性。     

Morphodynamic signatures derived from daily surface elevation dynamics can explain the morphodynamic development of tidal flats

Understanding the sensitivity of tidal flats to environmental changes is challenging. Currently, most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats. In this study, we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development. Surface elevation dynamic (SED) indices focus on the magnitude and period of surface elevation changes, while morphodynamic signature (MDS) indices relate sediment dynamics to environmental drivers. The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat. Using these analyses, we were able to (1) detect a reduction in the daily SED and (2) determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents. Overall, the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats, ecosystem functioning, and sensitivity to physical drivers (wind and tides). Finally, we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats.     

Changes in the tocopherol content of almond,pecan and macadamia kernels during storage

The individual tocopherols present in almond, pecan and macadamia nuts were determined by HPLC. Changes in tocopherol content during 16-months' storage at 30°C and 55% relative humidity were related to keeping quality. The large amount of total tocopherols, mainly α-tocopherol, in almonds accounted for their good storage ability. Pecan nuts with less total tocopherols and mainly γ-tocopherol became rancid after 4 months' storage and macadamia nuts, with practically no tocopherols, were rancid after 2 months' storage. Total tocopherol content decreased in all nuts during storage, possibly as a result of its inhibitory function during auto-oxidation.     

Safety characterstics of the MARS nuclear plant

New design criteria in the field of small and medium sized nuclear reactors will be illustrated; particular consideration will be given to the reactor MARS (Multipurpose Advanced Reactor, Inherently Safe) now under development at the Department of Energetics, University of Rome.An analysis of plant behaviour during a Station Black-out accident has been performed using the computer program RELAP 5/Mod. 2.     

Analysis of the inducer-responsive CAR1 upstream activation sequence (UASI) and the factors required for its operation

Induced production of arginase (CAR1) enzyme activity and steady-state CAR1 mRNA in Saccharomyces cerevisiae requires wild-type ARG80/ARGRI and ARG81/ARGRII gene products. We demonstrate here that these gene products, along with that of the MCM1 gene, are required for the inducer-dependent UAS_I-A, UAS_I-B and UAS_I-C elements to function but they are not required for operation of inducer-independent CAR1 UAS_C1 or UAS_C2M. Through the use of single and multiple point mutations, the CAR1 UAS_I-B and UAS_I-C elements were demonstrated to be at least 23 bp in length. Moreover, simultaneous mutation of both ends of an elements gave stronger phenotypes than mutations at either end. The center of the element was more sensitive to mutation than were the ends.     

Laboratory determination of clay-geotextile interaction

Current design regulations preclude the usage of cohesive backfills in reinforced soil structures regardless of whether the reinforcement is metallic or polymer fabric. The main reasons for this are: firstly, cohesive materials can be expansive; and secondly, the maximum bond strength between the reinforcement and the clay is normally not expected to be more than the undrained strength of the clay, giving no advantage. However, low-plasticity (so-called semi-cohesive) soils are not expansive and could be used in reinforced soil structures provided the reinforcement can give an increase in strength. A large number of shearbox and pull-out tests have been carried out to investigate which are the major factors governing the clay-geotextile interaction in both undrained and drained conditions. Woven and non-woven fabrics and meshes were used in the tests. The results have shown that the shearing strength of clay can be increased by properly selected geotextile reinforcement in both undrained (short-term) and drained (long-term) loading. It has been also shown that the pull-out resistance of the geotextile reinforcement is essentially proportional to the normal stress and for high transmissivity geotextiles or for geogrids it is limited by the tensile strength and relaxation of the material. The low transmissivity however is also a factor obstructing the development of high pull-out resistance in undrained conditions. The results indicate that geotextile reinforced cohesive backfill might be a viable alternative in reinforced soil structures if good-quality granular backfill material is not readily available.