Blue Straggler Stars: Early Observations that Failed to Solve the Problem

In this chapter, I describe early ideas on blue stragglers, and various observations (some published, some not) that promised but failed to resolve the question of their origin. I review the data and ideas that were circulating from Allan Sandage's original discovery in 1953 of "anomalous blue stars" in the globular cluster M3, up until about 1992, when what seems to have been the only previous meeting devoted to Blue Straggler Stars (BSSs) was held at the Space Telescope Science Institute.Comment: Chapter 2, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

Linear nonadiabatic properties of SX Phoenicis variables

We present a detailed linear, nonadiabatic pulsational scenario for oscillating Blue Stragglers (BSs)/SX Phoenicis (SX Phe) in Galactic Globular Clusters (GGCs) and in Local Group (LG) dwarf galaxies. The sequences of models were constructed by adopting a wide range of input parameters and properly cover the region of the HR diagram in which these objects are expected to be pulsationally unstable. Current calculations together with more metal-rich models already presented by Gilliland et al. suggest that the pulsation properties of SX Phe are partially affected by metal content. Our calculations also suggest that the secular period change seems to be a good observable to identify the pulsation mode of cooler SX Phe variables. The dependence of pulsation properties on the helium envelope content is discussed and we find that the secular period change for He-enhanced models is approximately a factor of two larger than for canonical ones. According to this evidence we suggest that the pulsation properties of SX Phe can be soundly adopted to constrain the evolutionary history of BSs, and in turn to single out the physical mechanisms which trigger their formation.Comment: 25 pages, 9 postscript figures, 1 latex file containing five tables, accepted for publication on Astrophysical Journa

Survey team on : conceptualisations of the role of competencies, knowing and knowledge in mathematics education research

This paper presents the outcomes of the work of the ICME 13 Survey Team on 'Conceptualisation and the role of competencies, knowing and knowledge in mathematics education research'. It surveys a variety of historical and contemporary views and conceptualisations of what it means to master mathematics, focusing on notions such as mathematical competence and competencies, mathematical proficiency, and mathematical practices, amongst others. The paper provides theoretical analyses of these notions-under the generic heading of mathematical competencies-and gives an overview of selected research on and by means of them. Furthermore, an account of the introduction and implementation of competency notions in the curricula in various countries and regions is given, and pertinent issues are reviewed. The paper is concluded with a set of reflections on current trends and challenges concerning mathematical competencie

Mechanisms of ring chromosome formation, ring instability and clinical consequences

<p>Abstract</p> <p>Background</p> <p>The breakpoints and mechanisms of ring chromosome formation were studied and mapped in 14 patients.</p> <p>Methods</p> <p>Several techniques were performed such as genome-wide array, MLPA (Multiplex Ligation-Dependent Probe Amplification) and FISH (Fluorescent <it>in situ </it>Hybridization).</p> <p>Results</p> <p>The ring chromosomes of patients I to XIV were determined to be, respectively: r(3)(p26.1q29), r(4)(p16.3q35.2), r(10)(p15.3q26.2), r(10)(p15.3q26.13), r(13)(p13q31.1), r(13)(p13q34), r(14)(p13q32.33), r(15)(p13q26.2), r(18)(p11.32q22.2), r(18)(p11.32q21.33), r(18)(p11.21q23), r(22)(p13q13.33), r(22)(p13q13.2), and r(22)(p13q13.2). These rings were found to have been formed by different mechanisms, such as: breaks in both chromosome arms followed by end-to-end reunion (patients IV, VIII, IX, XI, XIII and XIV); a break in one chromosome arm followed by fusion with the subtelomeric region of the other (patients I and II); a break in one chromosome arm followed by fusion with the opposite telomeric region (patients III and X); fusion of two subtelomeric regions (patient VII); and telomere-telomere fusion (patient XII). Thus, the r(14) and one r(22) can be considered complete rings, since there was no loss of relevant genetic material. Two patients (V and VI) with r(13) showed duplication along with terminal deletion of 13q, one of them proved to be inverted, a mechanism known as inv-dup-del. Ring instability was detected by ring loss and secondary aberrations in all but three patients, who presented stable ring chromosomes (II, XIII and XIV).</p> <p>Conclusions</p> <p>We concluded that the clinical phenotype of patients with ring chromosomes may be related with different factors, including gene haploinsufficiency, gene duplications and ring instability. Epigenetic factors due to the circular architecture of ring chromosomes must also be considered, since even complete ring chromosomes can result in phenotypic alterations, as observed in our patients with complete r(14) and r(22).</p

ДИАГНОСТИКА ТЕХНОЛОГИЧЕСКИХ ХАРАКТЕРИСТИК МОЩНЫХ ТРАНЗИСТОРОВ С ПОМОЩЬЮ РЕЛАКСАЦИОННОГО ИМПЕДАНС–СПЕКТРОМЕТРА ТЕПЛОВЫХ ПРОЦЕССОВ

The efficient method of determining thermal parameters in high-power field-effect transistors has been developed and tested based on a study of transient processes during self heating by direct current. With the developed relaxation spectrometer of thermal processes differential distribution profiles of thermal resistance of KP723G transistors have been investigated which were selected in accordance with the regimes of setting of their crystals. Thermal resistance spectra have been obtained from the analysis of time−dependent dynamic thermal impedance using a new non−destructive method of differential spectroscopy using higher order derivatives (order 3). We present both continuous (integral) and discrete spectra of the distribution of internal thermal resistance in the transistors and the value of the junction/case thermal resistance. Thermal characteristics of the KP723G transistors and their imported counterparts IRLZ44 and IRLB3036 have been determined. The method of determining the active area of devices has been developed and its decrease during heating has been shown. The proposed methodology is useful in solving technological problems of forming the setting layers of crystals and intermediate layers between a crystal and a heat sink and also for the development of thermal models in SPICE modeling of powerful MOSFETs and diode emitters.На основе исследования переходных процессов при саморазогреве прямым током разработан и апробирован эффективный метод определения тепловых параметров мощных полевых транзисторов. С помощью разработанного релаксационного спектрометра тепловых процессов исследованы дифференциальные профили распределения теплового сопротивления транзисторов КП723Г, подобранных в партии в соответствии с режимами посадки их кристаллов на теплоотводящее основание. Спектры тепловых сопротивлений рассчитаны из анализа временной зависимости динамического теплового импеданса новым неразрушающим методом дифференциальной спектроскопии с использованием производных высших порядков (3-го порядка). Представлены как непрерывные (интегральные), так и дискретные спектры распределения внутреннего теплового сопротивления транзисторов, а также значения теплового сопротивления переход—корпус. Определены тепловые характеристики транзисторов КП723Г и их импортных аналогов IRLZ44 и IRLB3036. Развит метод оценки активной площади приборов и установлено ее уменьшение с нагревом. Показано, что предложенные методики полезны при решении технологических проблем формирования слоев посадки кристаллов и создания промежуточных слоев между кристаллом и теплоотводящим основанием, а также для разработки тепловых моделей при SPICE-моделировании мощных полевых транзисторов и диодных излучателей

Research on Teaching and Learning Mathematics at the Tertiary Level:State-of-the-art and Looking Ahead

This topical survey focuses on research in tertiary mathematics education, a field that has experienced considerable growth over the last 10 years. Drawing on the most recent journal publication as well as the latest advances from recent high quality conference proceedings, our review culls out the following five emergent areas of interest: mathematics teaching at the tertiary level; the role of mathematics in other disciplines; textbooks, assessment and students’ studying practices; transition to the tertiary level; and theoretical-methodological advances. We conclude the survey with a discussion of some potential ways forward for future research in this new and rapidly developing domain of inquiry

Variable Stars in Galactic Globular Clusters

Based on a search of the literature up to May 2001, the number of known variable stars in Galactic globular clusters is approximately 3000. Of these, more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type. In addition to the RR Lyrae population, there are approximately 100 eclipsing binaries, 120 SX Phe variables, 60 Cepheids (including population II Cepheids, anomalous Cepheids and RV Tauri) and 120 SR/red variables. The mean period of the fundamental mode RR Lyrae variables is 0.585, for the overtone variables it is 0.342 (0.349 for the first-overtone pulsators and 0.296 for the second-overtone pulsators) and approximately 30% are overtone pulsators. These numbers indicate that about 65% of RR Lyrae variables in Galactic globular clusters belong to Oosterhoff type I systems. The mean period of the RR Lyrae variables in the Oosterhoff type I clusters seems to be correlated with metal abundance in the sense that the periods are longer in the more metal poor clusters. Such a correlation does not exist for the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue horizontal branches.Comment: 45 pages, 10 figures, to be published in AJ November 200

Measurement of the Quark and Gluon Fragmentation Functions in Z0Z^0 Hadronic Decays

The fragmentation functions and multiplicities in $b\overline{b}$ and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated

Updated precision measurement of the average lifetime of B hadrons

The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.

Investigation of the splitting of quark and gluon jets

The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation TeX . The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution TeX , with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is TeX . Due to non-perturbative effects, the data are below the expectation at small TeX . The transition from the perturbative to the non-perturbative domain appears at smaller TeX for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets