Constitutive modeling for anisotropic/asymmetric hardening behavior of magnesium alloy sheets

Magnesium alloy sheets have been extending their field of applications to automotive and electronic industries taking advantage of their excellent light weight property. In addition to well-known lower formability, magnesium alloys have unique mechanical properties which have not been thoroughly studied: high in-plane anisotropy/asymmetry of yield stress and hardening response. The reason of the unusual mechanical behavior of magnesium alloys has been understood by the limited symmetry crystal structure of HCP metals and thus by deformation twinning. In this paper, the phenomenological continuum plasticity models considering the unusual plastic behavior of magnesium alloy sheet were developed for a finite element analysis. A hardening law based on two-surface model was further extended to consider the general stress–strain response of metal sheets including Bauschinger effect, transient behavior and the unusual asymmetry. Three deformation modes observed during the continuous in-plane tension/compression tests were mathematically formulated with simplified relations between the state of deformation and their histories. In terms of the anisotropy and asymmetry of the initial yield stress, the Drucker–Prager’s pressure dependent yield surface was modified to include the anisotropy of magnesium alloy. The numerical formulations and characterization procedures were also presented and finally the correlation of simulation with measurements was performed to validate the proposed theory.     

FEL光学速调管的升级性能分析

通过三维磁场的有限元计算,给出了自由电子激光（FEL）研究用光学速调管升级后的磁参数。国家同步辐射实验室合肥光源（HLS）电子储存环能量可以日常运行在200～800 MeV间,为了与电子储存环能量匹配,并在较高束电子能量下进行实验和得到较多的相干辐射光子,光学速调管从原来的对称结构升级成非对称结构,用于HLS储存环谐波产生FEL实验。给出了升级后非对称光学速调管的几组匹配磁参数,用于在HLS储存环注入能量和可以运行的最高能量下进行谐波FEL实验。初步计算表明,HLS 储存环电子束性能优越,能散很低,FEL实验用最高能散仅为2.05×10-4,相应FEL辐射的能散修正因子在0.96以上,可以忽略不计。     

First Asymmetry Synthesis and Stereochemistry of Glutinone

Rencently, two new sesquiterpenoids, glutinone 1 and lucinone 2, were isolated from the aerial parts of traditional medicine2 Jasonia glutinosa1 by Castillo and co-workers3. However, Castillo only gave the structure of glutinone, but its absolute configuration is still unknown. Here, we wish to report our stereoselective construction of the four possible diastereoisomers (9a, 9b, 9c & 9d) of glutinone. By comparing the spectrum data with that of the natural product, we outlined the stereoc…     

Chemical Effect Analyses of 3dElements by Study of X-Ray Fluorescence Spectra

Spectra of K X-rays emitted from pure 3d transition metals and their oxide and sulfate compounds were measured using a single crystal wavelength dispersive X-ray spectroscopy (WDXRF). The measurements were performed using a ZSX-100e sequential spectrometer equipped with an Rh X-ray tube operated. An accurate analytical representation of each line was obtained by a fit to a Lorentz function. The spectra were analyzed in order to examine the K X-ray peak parameters such as asymmetry index, peak energy and relative intensity ratios. The energy shifts and relative intensities weredetermined tobetter understand the chemical effect.     

Samarium diiodide induced asymmetric synthesis of γ-butyrolactone using chiral auxiliaries derived from isosorbide and isomannide

The asymmetric reductive coupling reaction of various acrylates derived from D-isosorbide and D-isomannide with acetophenone mediated by samarium diiodide to give both enan-tiomers of the optically active γ-butyrolactone was described.The best enantiomeric excess of the products was 60%.     

Bifurcations in excised larynx experiments

Bifurcation analysis was applied to vocal fold vibration in excised larynx experiments. Phonation onset and vocal instabilities were studied in a parameter plane spanned by subglottal pressure and asymmetry of either vocal fold adduction or elongation. Various phonatory regimes were observed, including single vocal fold oscillations. Selected spectra demonstrated correspondence between these regimes and vocal registers noted in the literature. To illustrate the regions spanned by the various phonatory regimes, two-dimensional bifurcation diagrams were generated. Many instabilities or bifurcations were noted in the regions of coexistence, i.e., regions in which the phonatory regimes overlap. Bifurcations were illustrated with spectrograms and fundamental frequency contours. Where possible, results from these studies were related to clinical observations.     

Enantioselective addition of methyllithium to aromatic imines catalyzed by C2 symmetric tertiary diamines

Enantioselective addition of methyllithium to aromatic imines catalyzed by C₂ symmetric tertiary diamines is described. Eleven diamines have been tested, for which dramatic effect of the nitrogen substitution has been observed. Diamines bearing hindered group close to the nitrogen led to racemic product while homologous hindered diamines led to the best results. Enantiomeric excess up to 74% could be achieved. An explanation of the absolute configuration of the product obtained is given considering the mechanism of the reaction.     

Synthesis of Novel Bisoxazoline Ligands for the Enantioselective Diels-Alder Reaction

The Diels-Alder reaction is the most useful method for six-membered ring formation1. As a consequence, a number of effective enantioselective processes have been developed over the years 2-4. Of particular interest, metal bisoxazoline complexes formed fro…     

Moment based approaches to value the risk of contingent claim portfolios

In this paper we describe and apply the estimating function methodology to value the risk of asset derivative portfolios. We first implement the Li’s model based on the first four moments and then we show the limits of this model in forecasting the maximum loss of contingent claims. In addition, we show that four moments are not enough to describe the behavior of the lower percentiles of derivatives. Finally, we propose a model that considers the first six moments and we compare the performances of these models proposing a backtest analysis on several historical and truncated asset derivative portfolios.     

The day-of-the-week effects on the volatility: The role of the asymmetry

In this paper, we propose to evaluate whether asymmetry influences the day-of-the-week effects on volatility. We also investigate empirically the impact of the day-of-the-week effect in major international stock markets using GARCH family models from a forecast framework. Indeed the existence of calendar effects might be interesting only if their incorporation in a model results in better volatility forecasts.