Keele University

About: Keele University is a education organization based out in Newcastle-under-Lyme, United Kingdom. It is known for research contribution in the topics: Population & Stars. The organization has 11318 authors who have published 26323 publications receiving 894671 citations. The organization is also known as: Keele University.

Sandstone Diagenesis: The Evolution of Sand to Stone

Abstract: ates where geochemical reactions approach completion, gibbsite, kaolin group minerals and smectites form from aluminosilicate precursors. In cooler, temperate climates a greater variety of clay minerals occurs in weathering profiles reflecting metastable, intermediate breakdown products of aluminosilicates. Diagenesis is differentiated from metamorphism by a variety of mineral and thermal-history indices (Fig. 1; Frey, 1987; Slater et al., 1994), but broadly a temperature transition of 180–250°C is thought to separate the two regimes. The classic transition from diagenesis to metamorphism was described eloquently in the Salton Sea geothermal field, south-east California, where sandstones of broadly similar composition are present over a temperature interval of 100°C to 350°C (McDowell & Elders, 1980). Here, clearly diagenetic, non-equilibrium mineral assemblages INTRODUCTION TO DIAGENESIS

Note‐taking: A critical review

Abstract: This paper aims (1) to determine why students take notes, (2) to survey the research findings available in the current literature, (3) to identify inadequacies and omissions in this literature in order to suggest more profitable lines of research for future study, and (4) to suggest guide‐lines for both teachers and students which will exploit more effectively the potential of note‐taking.

Aus der Sicht des Synthetikers: Palladiumkomplexe N-heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

Abstract: Palladiumkatalysierte C-C- und C-N-Kupplungen zahlen zu den vielseitigsten und leistungsfahigsten Syntheseverfahren. Seit 15 Jahren erfreuen sich die N-heterocyclischen Carbene (NHCs) wachsender Beliebtheit als Liganden fur palladiumvermittelte Kreuzkupplungen und ahnliche Methoden. Sie sind in vielerlei Hinsicht den ublichen tertiaren Phosphanen uberlegen. Weil NHCs stark σ-elektronenschiebend sind, konnen sie auch anspruchsvolle Substrate zu oxidativen Insertionen bewegen. Andererseits fuhren ihre Sperrigkeit und ihre besondere Topologie zu einer raschen reduktiven Eliminierung. Schlieslich tragen die starken Pd-NHC-Bindungen zur hohen Stabilitat der aktiven Spezies bei – auch bei niedrigen Ligand/Pd-Verhaltnissen und hohen Temperaturen. Wenn erst stabile, anwenderfreundliche und leistungsstarke NHC-Pd-Prakatalysatoren kommerziell verfugbar sind, liegt das Ziel eines universellen Kreuzkupplungskatalysators in greifbarer Nahe. Dieser Aufsatz beschreibt zunachst die chemischen Grundlagen zu den NHC-Pd-Komplexen, um ihre Besonderheiten kennenzulernen. Anschliesend folgt eine umfassende Diskussion zur Anwendung dieser Katalysatoren in C-C- und C-N-Kreuzkupplungen sowie in der Carbopalladierung.

Family and Collective Remittances to Mexico: A Multi‐dimensional Typology

Abstract: The development potential of remittances has resurfaced as a topic of analysis, based in part on dramatic increases in migration and amounts of money ‘sent home’, and partly in the growing interest and involvement by states and non-state actors in gaining leverage over remittances. The trend is indicative of an emerging remittance-based component of development and poverty reduction planning. This article uses the case of Mexico to make two broad arguments, one related to the importance of extra-economic dimensions of remittances, particularly the social and political meanings of remittances, and the other based on a disaggregation of remittances into family, collective or community-based, and investment remittances. Key dimensions of this typology include the constellation of remitters, receivers, and mediating institutions; the norms and logic(s) that regulate remittances; the uses of remittances (income versus savings); the social and political meanings of remittances; and the implications of such meanings for various interventions. The author concludes that policy and programme interventions need to recognize the specificity of each remittance type. Existing initiatives to bank the un-banked and reduce transfer costs, for example, are effective for family remittances, but attempts to expand the share of remittances allocated to savings, or to turn community donations into profitable ventures, or small investments into large businesses, are much more complex and require a range of other interventions.

The supernova channel of super-AGB stars

Abstract: We study the late evolution of solar metallicity stars in the transition region between white dwarf formation and core collapse. This includes the super-asymptotic giant branch (super-AGB, SAGB) stars, which ignite carbon burning and form an oxygen-neon (ONe) core. SAGB star cores may grow to the Chandrasekhar mass because of continued H- and He-shell burning, ending as core-collapse supernovae. From stellar evolution models we find that the initial mass range for SAGB evolution is -->7.5–9.25 M☉. We perform calculations with three different stellar evolution codes to judge the robustness of our results. The mass range significantly depends on the treatment of semiconvective mixing and convective overshooting. To consider the effect of a large number of thermal pulses, as expected in SAGB stars, we construct synthetic SAGB models that are calibrated through stellar evolution simulations. The synthetic model enables us to compute the evolution of the main properties of SAGB stars from the onset of thermal pulses until the core reaches the Chandrasekhar mass or is uncovered by the stellar wind. Thereby, we differentiate the stellar initial mass ranges that produce ONe WDs from that leading to electron-capture SNe. The latter is found to be -->9.0–9.25 M☉ for our fiducial model, implying that electron-capture SNe would constitute about 4% of all SNe in the local universe. The error in this determination due to uncertainties in the third dredge-up efficiency and AGB mass-loss rate could lead to about a doubling of the number of electron-capture SNe, which provides a firm upper limit to their contribution to all supernovae of ~20%.