トルコ中部の内陸塩性湖沼の珪藻遺骸群衆 : 第四紀後期における古塩分変動の定量的復元への応用

In arid and semi-arid areas, like inner Anatolia, small change in precipitation and evaporation rates can have marked effects on the water environment of inland lakes at closed basins. This study demonstrates the importance of detailed diatom analyses in attempt to identify lake level and lake water quality changes of inland lakes in Turkey. An important first step in using diatoms as salinity indicators is to obtain quantitative data on their ecological characteristics, such as optima and tolerances along salinity gradients. We took 51 samples of living diatoms from 38 lakes and rivers in the central part of Turley, and calculated an abundance-weighted mean salinity (AWM) for each toxin (Kashima, 1996). On the basis of a strong relationship between diatom composition and salinity, we defined the diatom-based transfer functions for salinity reconstruction, and then applied them to Late Quaternary sediments in Turkey. Our drilling surveys were done at Kaman Kalehoyük, Lake Tuz, Konya Basin and in Akgöl Marsh and its surrounding areas. The results show that there was a number of alternations between fresh and saline conditions during the Late Quaternary (Kashima et al., in press)

Mechanistic investigation of Rh(i)-catalysed asymmetric Suzuki–Miyaura coupling with racemic allyl halides

Understanding how catalytic asymmetric reactions with racemic starting materials can operate would enable new enantioselective cross-coupling reactions that give chiral products. Here we propose a catalytic cycle for the highly enantioselective Rh(I)-catalysed Suzuki–Miyaura coupling of boronic acids and racemic allyl halides. Natural abundance 13C kinetic isotope effects provide quantitative information about the transition-state structures of two key elementary steps in the catalytic cycle, transmetallation and oxidative addition. Experiments with configurationally stable, deuterium-labelled substrates revealed that oxidative addition can happen via syn- or anti-pathways, which control diastereoselectivity. Density functional theory calculations attribute the extremely high enantioselectivity to reductive elimination from a common Rh complex formed from both allyl halide enantiomers. Our conclusions are supported by analysis of the reaction kinetics. These insights into the sequence of bond-forming steps and their transition-state structures will contribute to our understanding of asymmetric Rh–allyl chemistry and enable the discovery and application of asymmetric reactions with racemic substrates

Impact of lake level change on deep-water renewal and oxic conditions in deep saline Lake Van, Turkey

Changes in the hydrological regime of the saline closed basin Lake Van, a large, deep lake in eastern Turkey, resulted in a lake level increase by about 2 m between 1988 and 1995, followed by a 1.5 m decrease until 2003 and a relatively constant lake level thereafter. Based on measurements of transient tracers (sulfur hexafluoride, CFC-12, 3H, 3He, 4He, Ne), dissolved oxygen, light transmission, conductivity-temperature-depth profiles, and thermistor data, we investigate the implications associated with lake level fluctuations for deep-water renewal and oxygenation. Our data suggest that deep-water renewal was significantly reduced in Lake Van between 1990 and 2005. This change in mixing conditions resulted in the formation of a more than 100 m thick anoxic deep-water body below 325 m depth. Apparently, the freshwater inflows responsible for the lake level rise between 1988 and 1995 decreased the salinity of the surface water sufficiently that the generation of density plumes during winter cooling was substantially reduced compared to that in the years before the lake level rise. Significant renewal and oxygenation of the deep water did not occur until at least 2005, although by 2003 the lake level was back to almost the same level as in 1988. This study suggests that short-term changes in the hydrological regime, resulting in lake level changes of a couple of meters, can lead to significant and long-lasting changes in deep-water renewal and oxic conditions in deep saline lakes

Bonus and Rebate: Perception of Exclusive GSM Dealers and Their Salesmen in Turkey

The aim of this paper is to study bonus and rebate for exclusive dealers in GSM sector in Turkey, for which operators and handset manufacturers provide special incentives to dealers for exceeding specific sales targets. They develop a theoretical model of dealers and manufacturer behavior based on observations about key aspects of the mobile phone market. The analysis provides important insights about sales bonus. For example, rebate is not preferred by the owners of dealers instead of bonuses. The authors find empirical support when they test the theoretical results