The central place system of the Thessaly region of Greece

The settlement system of Thessaly is examined within the framework provided by central place theory. The adoption of a systems approach to the research determines the organization of the work. Firstly, there is an analysis of the sectoral structure of the Greek economy with particular reference to retail trade. The importance of tertiary activity in the economy is indicated and the traditional nature of most Greek retailing is considered. Next, the physical, historical, economic and demographic background of Thessaly is described. The region consists of a fertile plain surrounded on all sides by mountains. The economy is dominated by agriculture and the secondary and tertiary sectors are strongly oriented to it. In the post-war period the population of the area has stagnated because of heavy rural emigration focussed primarily on Athens, The analysis of the settlement system then falls into three parts. The functional regions of Thessaly are identified by subjecting an interaction matrix of bus traffic flows to factor analysis. These describe the general structure of the settlement system and allow the subsequent detailed analysis of the settlement system of West Thessaly to be placed within a wider context. This detailed analysis is based primarily on data collected in the field. It consists of a study of the hierarchical and spatial structure of the system and the aggregate relationships between its components. A well developed hierarchical structure is found, and its historical evolution is examined. Following this, a study of consumer movements in West Thessaly is made which is based on data collected from questionnaires circulated in the region. The behaviour of the settlement system as revealed by this analysis accords closely with the structure of the system. A composite assessment of the settlement system is then made which relates its structure and behaviour to the theoretical framework of the research, and comparisons are made with other studies of settlement systems in-Greece. Finally, the Greek regional problem is examined, one element in which is the nature and role of the provincial settlement system, and the implications of this research for future planning strategies are outlined

The structural characteristics of the central place system of West Thessaly

[Δε διατίθεται περίληψη / no abstract available][Δε διατίθεται περίληψη / no abstract available

Long sperm fertilize more eggs in a bird

Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the zebra finch (Taeniopygia guttata), where sperm size influences sperm swimming velocity, to determine the effect of sperm total length on fertilization success. Sperm competition experiments, in which pairs of males whose sperm differed only in length and swimming speed, revealed that males producing long sperm were more successful in terms of (i) the number of sperm reaching the ova and (ii) fertilizing those ova. Our results reveal that although sperm length is the main factor determining the outcome of sperm competition, complex interactions between male and female reproductive traits may also be important. The mechanisms underlying these interactions are poorly understood, but we suggest that differences in sperm storage and utilization by females may contribute to the outcome of sperm competition

Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird.

The relationship between sperm energetics and sperm function is poorly known, but is central to our understanding of the evolution of sperm traits. The aim of this study was to examine how sperm morphology and ATP content affect sperm swimming velocity in the zebra finch Taeniopygia guttata We exploited the high inter-male variation in this species and created extra experimental power by increasing the number of individuals with very long or short sperm through artificial selection. We found a pronounced quadratic relationship between total sperm length and swimming velocity, with velocity increasing with length up to a point, but declining in the very longest sperm. We also found an unexpected negative association between midpiece length and ATP content: sperm with a short midpiece generally contained the highest concentration of ATP. Low intracellular ATP is therefore unlikely to explain reduced swimming velocity among the very longest sperm (which tend to have a shorter midpiece)

Organic Polymer Hosts for Triplet-Triplet Annihilation Upconversion Systems.

Triplet-triplet annihilation upconversion (TTA-UC) is a process by which a lower energy photon can be upconverted to a higher energy state. The incorporation of TTA-UC materials into solid-state hosts has enabled advances in solar energy and many other applications. The choice of host system is, however, far from trivial and often calls for a careful compromise between characteristics such as high molecular mobility, low oxygen diffusion, and high material stability, factors that often contradict one another. Here, we evaluate these challenges in the context of the state-of-the-art of primarily polymer hosts and the advantages they hold in terms of material selection and tunability of their diffusion or mechanical or thermal properties. We encourage more collaborative research between polymer scientists and photophysicists in order to further optimize the current systems and outline our thoughts for the future direction of the field

A Loading Device for Fracture Testing of Compact Tension Specimens in the Scanning Electron Microscope

A loading device for performing fracture experiments on compact tension specimens in the SEM has been designed. Its key elements are a piezoelectric translator for applying controlled displacements to the loading points on the specimen and a load cell to measure applied loads. The effective transmission of displacement from the piezoelectric driver to the specimen was found to be the major mechanical design problem. The peripheral equipment includes a function generator and a high voltage amplifier that drives the piezoelectric translator as well as a video overlay and standard video equipment to record the image continuously during the course of the experiment. A case study on alumina describes qualitative observations on the toughening mechanism, crack-interface bridging, operating in this material. Quantitative information pertaining to the closure stresses associated with this toughening mode can be obtained by measuring the crack profile

Perceptions of Assessment Among Undergraduate and Postgraduate Students of Four Health Science Disciplines

The use of different types of assessment to improve student learning needs to be balanced with reports that student perception, rather than the objective features of the task, significantly influences how students approach learning. The present study surveyed 492 undergraduate and postgraduate students from four health science disciplines (occupational therapy, physiotherapy, speech pathology, and audiology) at a large Australian university on how helpful different types of assessment had been in assisting their learning. Between 73.4% and 90.4% of the students valued practical exams, individual tasks, written assignments, and written exams requiring application of knowledge. Between 29.1% and 59.7% of the students valued oral presentations, group tasks, portfolios, online assessment, and multiple choice exams. Entry level and type of program were found to influence perceptions. Postgraduate students valued tutorial participation more than undergraduate students (