Sociocultural Factors Influencing Students' Learning in Science and Mathematics: An Analysis of the Perspectives of African American Students

The voices of African American students reveal sociocultural factors that influence their achievement in science and mathematics classes. Using a sociocultural theoretical framework ( Mercer & Covey, 1980 ), this ethnographic study interpreted the perspectives of five African American students as they discussed their learning experiences in science and mathematics classrooms. This framework acknowledges the vulnerability of the educational system to societal influences that inevitably assert cultural values and norms. The students' discussions provided insight into their beliefs about the varied ways in which sociocultural factors impact their learning in science and mathematics classrooms.     

Metaheuristics applied to mixed and simultaneous extensions of vehicle routing problems with backhauls

Metaheuristics are a class of approximate methods designed to solve hard combinatorial optimization problems arising within various different areas. The importance of metaheuristics results from their ability to continue the search beyond a local optimum so that near-optimal or optimal solutions are efficiently found. In order to solve the backhauling problem associated with mixed and simultaneous delivery and pick-ups, this paper presents a hybrid algorithm which is comprised of the two metaheuristics of tabu search and variable neighbourhood descent. The primary challenge associated with backhauling consists of creating routes in which vehicles are not only required to deliver goods, but also to perform pick-ups at customer locations. The problems associated with these two categories of problems, however, have received little attention in the literature to date. A set of examples taken from the literature with Euclidean cost matrices are presented. Finally, some numerical results are illustrated to show the effectiveness of the proposed approach.     

Transverse momentum distributions of neutral pions from central and peripheral16O+Au collisions at 200A·GeV

The production of neutral pions by the interaction of 200A·GeV p and¹⁶O projectiles with a Au target has been studied in the pseudorapidity range 1.5≦η≦2.1. Transverse momentum spectra have been measured between 0.4 GeV/c and 3.6 GeV/c and their dependence on the centrality of the collision has been investigated. The peripheral-collision spectra display a marked change of slope with a hard component starting at about 1.8 GeV/c, in contrast to central-collision data. The data are discussed in comparison to p+p and α+α data from the ISR.     

Two new promelacacinidin dimers,including a novel flavanone-flavanol dimer characterized by a unique C(3)-C(4) linkage,from the heartwood of <Emphasis Type="Italic">Acacia nigrescens</Emphasis>

Two new promelacacinidin biflavonoids, mesquitol-(4α,5)-epimesquitol-4β-ol and a 3′,4′,7,8-tetrahydroxyflavanone(3,4)-ent-epimesquitol, were isolated among others from the heartwood of Acacia nigrescens. The flavanone derived dimer, characterized by a unique C(3) to C(4) bridge, which links the monomers via two stereogenic and sp³ hybridized C-atoms, is the prototype of a new subgroup of the flavonoid family. Assessment of the absolute configuration of all five stereogenic centers of this novel flavanone-derived biflavonoid was achieved by correlating the chiroptical properties of the benzoyl chromophore to the absolute configuration of C(2) of the flavanone moiety and hence the absolute stereochemistry of the other four chiral centers. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 437–441, September–October, 2007. Dedicated to Prof. E. Malan, who initiated and supervised this research project, for a noteworthy contribution in the flavonoid field, and who has since retired.     

Das Wachstumsnetz,ein graphisches Hilfsmittel für Entwicklungsprognosen

Zusammenfassung Zur Prognose über das Anwachsen von Verbraucheranzahlen (Fernsprechteilnehmer, Verbraucher von Konsumgütern usw.) wird vielfach mit Erfolg ein Wachstumsmodell benutzt, das sich durch die sogenannte logistische Kurve, d. h. eine durch den Tangens hyperbolicus ausdrückbare Funktion darstellen läßt. Im folgenden wird ein Wachstumsnetz angegeben, in dem sich die Kurven dieser Klasse nach ihrer Normierung (Sättigungswert bei 100%) zu Geraden strecken. So erhält man ein (in der Handhabung dem bekannten Wahrscheinlichkeitsnetz vergleichbares) Prognosehilfsmittel, dessen Gebrauch erläutert wird. Insbesondere ist das Wachstumsnetz geeignet, systematische zeitliche Änderungen der Wachstumsgesetzmäßigkeiten erkennen zu lassen und besser fundierte Approximationen zu liefern, als sie bisher mit graphischen oder numerischen Mitteln erreicht wurden.Ein besonderer Vorteil des Wachstumsnetzes liegt darin, daß es ein einfaches Kriterium dafür liefert, ob ein beobachteter Wachstumsprozeß ganz oder zeitweise einer logistischen Kurve folgt und deshalb eine entsprechende Prognose sinnvoll ist.

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Summary For the purpose of predicting the increase in consumer numbers (telephone subscribers, consumers of various goods) a growth model is often successfully used which can be represented by means of the so-called logistic curve, i. e. a curve that can be expressed in terms of a hyperbolic tangens. In the following, a growth paper is specified where curves in this category become straight lines after normalization (saturation value at 100%). A prediction device, comparable in operation to the well-known probability paper, is thereby obtained and its use is explained. The growth paper permits in particular systematic time variations of growth laws to be recognized and more exact approximations to be obtained than was possible up to now by graphical or numerical means.The growth paper offers the particular advantage of providing a simple criterion for deciding whether a certain observed growth process follows the pattern of a logistic curve closely or partially, and hence whether a prediction based on such a curve is reasonable.

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Vorgel. v.:J. Heinhold.     

Tuneable millimeter-wave gyrotrons

In the course of developing a low-power, tuneable millimeter-wave source, two gyrotrons have been constructed. Gyrotron I was a fixed-frequency device operating at 120 GHz while Gyrotron II produced more than 20 lines in the frequency range 130 to 260 GHz. The design of tuneable gyrotrons is discussed with reference to the Gyrotron II results.     

13C NMR spectroscopic data for glutinol and derivatives

The ¹³C NMR chemical shifts of the triterpenes glutinol, glutinone and acetylglutinol were measured and analysed.