A Generalized Diffusion Tensor for Fully Anisotropic Diffusion of Energetic Particles in the Heliospheric Magnetic Field

The spatial diffusion of cosmic rays in turbulent magnetic fields can, in the most general case, be fully anisotropic, i.e. one has to distinguish three diffusion axes in a local, field-aligned frame. We reexamine the transformation for the diffusion tensor from this local to a global frame, in which the Parker transport equation for energetic particles is usually formulated and solved. Particularly, we generalize the transformation formulas to allow for an explicit choice of two principal local perpendicular diffusion axes. This generalization includes the 'traditional' diffusion tensor in the special case of isotropic perpendicular diffusion. For the local frame, we motivate the choice of the Frenet-Serret trihedron which is related to the intrinsic magnetic field geometry. We directly compare the old and the new tensor elements for two heliospheric magnetic field configurations, namely the hybrid Fisk and the Parker field. Subsequently, we examine the significance of the different formulations for the diffusion tensor in a standard 3D model for the modulation of galactic protons. For this we utilize a numerical code to evaluate a system of stochastic differential equations equivalent to the Parker transport equation and present the resulting modulated spectra. The computed differential fluxes based on the new tensor formulation deviate from those obtained with the 'traditional' one (only valid for isotropic perpendicular diffusion) by up to 60% for energies below a few hundred MeV depending on heliocentric distance.Comment: 8 pages, 6 figures, accepted in Ap

Minimal Holocene retreat of large tidewater glaciers in Køge Bugt, southeast Greenland

Abstract Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming

Nickel-Catalyzed Intermolecular Insertion of Aryl Iodides to Nitriles: A Novel Method to Synthesize Arylketones

[[abstract]]A novel procedure for the NiCl2(DME)/dppp/Zn system catalyzed intermolecular insertion of aryl iodides to nitriles was developed, which afforded variously substituted arylketone derivatives in moderate to good yields with tolerance of a wide variety of functional groups.[[abstract]]芳香酮衍生物也常被發現具有生物活性同時也是天然物的重要核心結構，因此其合成路徑一直是有機化學中非常重要的課題。其中最常見的合成方式是利用Friedel-Crafits酰化來作為主要步驟去建構這樣的產物。 利用腈基的插入反應來建構芳香酮衍生物也是一個相當受到重視的反應路徑。早期這一種建構方式主要是由格林納試劑和鋰試劑來達成；然而，這種嚴苛的反應條件，時常限制了他的應用廣度和複雜結構的建立。而利用過度金屬錯合物來催腈基的插入反應則相對較溫和，也為早期必須利用格林納試劑和鋰試劑提供了另一種的替代途徑。許多的文獻指出前期的過度金屬錯合物如鈦，鎢，鋯，鉬和鈧金屬錯合物可以有效地催化腈基的插入反應。而後期過度金屬催化腈基的插入反應雖然也有報導，但是其催化反應僅有利用硼酸化合物與腈基化合物來進行而不見直接利用芳香鹵化物與腈基化合物來進行的反應。例如在2006年，Larock和Lu分別利用鈀金屬錯合物來催化硼酸化合物對腈基化合物來的插入反應。2010年，鄭老師報導了鎳金屬錯合物來催化硼酸化合物對腈基化合物來的插入反應。 分子內的芳基鹵化物對腈基化合物的插入反應也被Larock報導，然而這篇文獻所報導獨反應完全限制於分子內的環化反應。因此本篇文章所要呈現的是第一個利用過渡金屬錯合物來催化芳基鹵化物對腈基化合物分子間插入反應而合成芳香酮的例子。[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US