Precise Radial Velocities of Polaris: Detection of Amplitude Growth

We present a first results from a long-term program of a radial velocity study of Cepheid Polaris (F7 Ib) aimed to find amplitude and period of pulsations and nature of secondary periodicities. 264 new precise radial velocity measurements were obtained during 2004-2007 with the fiber-fed echelle spectrograph Bohyunsan Observatory Echelle Spectrograph (BOES) of 1.8m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We find a pulsational radial velocity amplitude and period of Polaris for three seasons of 2005.183, 2006.360, and 2007.349 as 2K = 2.210 +/- 0.048 km/s, 2K = 2.080 +/- 0.042 km/s, and 2K = 2.406 +/- 0.018 km/s respectively, indicating that the pulsational amplitudes of Polaris that had decayed during the last century is now increasing rapidly. The pulsational period was found to be increasing too. This is the first detection of a historical turnaround of pulsational amplitude change in Cepheids. We clearly find the presence of additional radial velocity variations on a time scale of about 119 days and an amplitude of about +/- 138 m/s, that is quasi-periodic rather than strictly periodic. We do not confirm the presence in our data the variation on a time scale 34-45 days found in earlier radial velocity data obtained in 80's and 90's. We assume that both the 119 day quasi-periodic, noncoherent variations found in our data as well as 34-45 day variations found before can be caused by the 119 day rotation periods of Polaris and by surface inhomogeneities such as single or multiple spot configuration varying with the time.Comment: 15 pages, 7 figures, Accepted for publication in The Astronomical Journa

Longitudinal Behavioral Assessment of Neonatal Traumatic Brain Injury

Traumatic brain injury (TBI) in children and infants is a primary cause of cognitive and behavioral problems that can persist through adulthood. In this study, the long-term behavioral effects of neonatal and juvenile TBI (jTBI) were characterized using mice. At an age of post-natal 7 or 10 days, mice underwent moderate or severe closed skull impact or sham surgery. Behavioral testing was conducted at 6 and 8 months post-injury. Tests administered included the open field activity (general activity levels), zero maze (anxiety), forced swim (depression), rotarod (coordination and balance), and water maze (general/spatial learning). jTBI mice showed elevated activity levels, impaired sensorimotor abilities, impaired spatial learning, and less efficient spatial search strategy use compared with sham animals. These differences were consistent and stable up to 8 months post-injury, suggesting that deficits acquired as the result of a TBI can have long-lasting behavioral impacts

Reflections on educational research in South Africa

A definition of educational research is proposed: Educational research is a particular mode of social service, using rigorous scientific endeavours for the continuous improvement of educational practice. The key components of this definition are used to reflect on educational research in South Africa as (1) a particular mode of social service (with discussion of an ethical code for educational research and national educational research priorities), (2) scientific endeavour (with reference to the nature of educational research, dissertations, scientific articles and research programme reports), and (3) role players in the continuous improvement of educational practice (with reference to policy making and operational practice). It is evident that educational research in South Africa has a noteworthy record of national and regional impact. Present threats to its academic stature and praxiological impact can only be overcome by taking appropriate and timely research management action. South African Journal of Education Vol.24(3) 2004: 233-23

Active contraction of the left ventricle with cardiac tissue modelled as a micromorphic medium

The myocardium is composed of interconnected cardiac fibres which are responsible for contraction of the heart chambers. There are several challenges related to computational modelling of cardiac muscle tissue. This is due in part to the anisotropic, non-linear and time-dependent behaviour as well as the complex hierarchical material structure of biological tissues. In general, cardiac tissue is treated as a non-linear elastic and incompressible material. Most computational studies employ the theories of classical continuum mechanics to model the passive response of the myocardium and typically assume the myocardium to be either a transversely isotropic material or an orthotropic material. In this study, instead of a classical continuum formulation, we utilise a micromorphic continuum description for cardiac tissue. The use of a micromorphic model is motivated by the complex microstructure and deformations experienced by cardiac fibres during a heartbeat. The micromorphic theory may be viewed as an extension of the classical continuum theory. Within a micromorphic continuum, continuum particles are endowed with extra degrees of freedom by attaching additional vectors, referred to as directors, to the particles. In this study the directors are chosen such that they represent the deformation experienced by the cardiac fibres. In addition to the passive stresses, the myocardium experiences active stresses as a result of the active tension generated by cardiac fibres. The active tension in the heart is taken to be a function of the sarcomere length, intracellular calcium concentration and the time after the onset of contraction. Experimental studies show that the active behaviour of the myocardium is highly dependent on the tissue arrangement in the heart wall. With a classical continuum description, the sarcomere length is usually defined as a function of the stretch in the initial fibre direction. To allow for a more realistic description of the active behaviour, we define the sarcomere orientation, and consequently also the sarcomere stretch, as a function of the director field. Furthermore, we use the director field to describe the direction in which contraction takes place. The intent of this study is to use a micromorphic continuum formulation and an active-stress model to investigate the behaviour of the left ventricular myocardium during a heartbeat. The simulated results presented here correspond well with typical ventricular mechanics observed in clinical experiments. This work demonstrates the potential of a micromorphic formulation for analysing and better understanding ventricular mechanics

Kernaspekte van ’n model vir skoolsukses in arm gemeenskappe

Key aspects of a model for school success in poor communities Some schools in impoverished communities are effective and successful in the face of the most difficult socio-economic circumstances and challenges. This phenomenon was investigated in a research project which had three phases. The first entailed a literature survey, culminating in a taxonomy of determinants of school success. The second phase consisted of the application of the taxonomy in field work in selected successful schools in impoverished communities. The third phase comprised interpretation of theoretical and empirical data, culminating in a model which depicts partnership as the central factor in all values and mechanisms pertaining to a successful school in an impoverished community. The model’s potential value is indicated, inter alia in guiding schools in impoverished communities towards meaningful self-assessment and change