Performance Characterization of a Novel Plasma Thruster to Provide a Revolutionary Operationally Responsive Space Capability with Micro- and Nano-Satellites

Few options currently exist to provide propulsion for extremely small satellites due to design constraints on power, volume, and weight. However, future operation will require a capability to conduct orbital maneuvers, momentum dumping, and precision pointing for these low cost satellites. The research presented here represents the first effort to operate and quantify the performance of a new micro plasma thruster design which provides a novel solution to these disparate competing constraints. The thruster in this study represents a deviation from traditional circular Hall thruster design practices, because it eschews a central magnetic circuit, which results in nearly parallel electric and magnetic field lines within the thruster discharge channel. This design decision reduces thruster complexity and thermal susceptibility, but it also reduces the ionization efficiency. The cornerstone of this study involved the direct measurement of thrust in order to quantify the efficiency and specific impulse of this innovative thruster. The investigation also included characterization of the thruster exhaust plume, voltage-current characteristics, and operating limits. Results are enumerated and suggestions for improvement provided

The Effect of Rootstock Cultivar and Bud Load on the Colour of Vitis vinifera L. cv. Muscat noir (Red Muscadel) Grapes

The effects of rootstock cultivar and bud load on colour expression in the grapes of Vi tis vinifera L. cv. Muscat noir were investigated. Different rootstocks had no significant effect on skin colour density of the grapes Grapes from vines with a low bud load (16 buds.vine·') had the highest skin colour density

Preparation of Epidermal Tissues for Light Microscope Studies of Vitis - leaves

A method for preparing epidermal tissues of leaves of Vitis spp. for the study of surface characteristics with the aid of a light microscope is described. Certain morphological characteristics such as trichrome length and frequency, stomata frequency, diameter and index of two cultivars were determined by means of a light microscope which compared very favourably with the results obtained when using a scanning electron microscope

Effect of Growth Arrestment Disease on the Anatomy and Ultrastructure of Vitis vinifera L. var. sultana

The anatomical and ultrastructural changes caused by the so called Growth Arrestment Disease (G.A.D.) in Vitis vinifera L. var. sultana were investigated by means of scanning and transmitted electron microscopy as well as light microscopy. Important morphological symptoms are described. Anatomical abnormalities were found, especially in the leaves and Hower clusters of the affected vines. Heat and moisture stress may induce abnormal physiological changes, and this may give rise to G.A.D.-symptoms

Online counselling services for Youth@risk

Youth today suffer from many socio-economic problems and struggle to operate in the current economic environment. Wellbeing service provision to youth@risk is inadequate to deal with the complexities of societal challenges which are amplified by the fast technology advances in a continuously changing environment. This paper aims to consider the provision of online counselling to enhance current face-to-face services from the provider’s perspective. The case of a volunteer-based online counselling service that has been in operation since 2010 is considered to establish the aspects that influence this type pf service. Related literature was reviewed to determine the issues reported from current studies and a taxonomy of digital services was used to analyse the service objectives of the service provider. Data collected from sessions with the facilitators and observations of a chat session was analysed to establish their experience of online counselling. The findings were interpreted to answer the research question. The contribution of this paper is in response to the many appeals for more empirical research on real cases. It can be concluded that an online counselling service is a viable extension of face-to-face counselling but more research is needed to understand its benefit to the clients and the ability to ensure a sustained service, especially in developing contexts

The Determination of the Homogeneity of a Vitis vinif era L. cv. Cape Riesling Vineyard

The value of Principal Component and Stepwise Discriminant analyses in selecting uniform plants for experimental purposes is discussed. Twenty seven variables were taken into account to establish the homogeniety (uniform plants) of 297 Vitis vinifera L. cv. Cape Riesling vines. A detailed study of the relationship and interrelationship of these variables resulted in 208 vines being selected as a uniform population. This selection provides the researcher with the possibility of using single vines as experimental units. However, it must be pointed out that Principal Component and Stepwise Discriminant analyses can only be used as an aid to normal statistical evaluation of experimental results and not as substitute for statistical experimental design

Strongly bounded groups and infinite powers of finite groups

We define a group as strongly bounded if every isometric action on a metric space has bounded orbits. This latter property is equivalent to the so-called uncountable strong cofinality, recently introduced by G. Bergman. Our main result is that G^I is strongly bounded when G is a finite, perfect group and I is any set. This strengthens a result of Koppelberg and Tits. We also prove that omega_1-existentially closed groups are strongly bounded.Comment: 10 pages, no figure. Versions 1-3 were entitled "Uncountable groups with Property (FH)". To appear in Comm. Algebr

A Comparative Anatomical Study of the Grapevine, Shoot and Cane: II: Periderm and Secondary Phloem

The taxonomic value of ten periderm and secondary phloem features of canes of different grapevine species was investigated. A scatter diagram showed that with few exceptions the American cultivars have a larger periderm with smaller secondary phloem, while the reverse was true for European cultivars. Crosses tend to cluster with one of their parents. It has been found that the largest intercultivar variation occurs at either the middle of the shoot length or the ventral sides of the basal part of the shoots

A Comparative Anatomical Study of the Grapevine Shoot: I Epidermis

Material gathered from three positions on the shoot and cane during veraison and two weeks after harvest were investigated for taxonomic features concerning the epidermis. Stomata and lenticels were present in all the cultivars studied, but trichomes were frequently present only on 99 Richter. Based on epidermal characteristics a dendogram giving the percentage similarity between cultivars, was constructed, and from this was concluded that concerning taxonomic features on Vitis vinifera L. cultivars tend to have a more than 90% similarity irrespective of the position on the shoot