A Mechanistic Analysis of the Palladium‐Catalyzed Formation of Branched Allylic Amines Reveals the Origin of the Regio‐ and Enantioselectivity through a Unique Inner‐Sphere Pathway

A recently reported palladium‐catalyzed allylic substitution of vinyl‐substituted cyclic carbonates (VCCs) with aryl amines represents a rare example of a regio‐ and enantioselective synthesis of α,α‐disubstituted allylic N‐aryl amines. However, the underlying reasons for this unusual selectivity profile remain elusive. In the present work, density functional theory (DFT) calculations in combination with mechanistic control experiments were performed to elucidate in detail this allylic amination manifold and the origin of the regio‐ and enantioselectivity. The combined data show that after oxidative addition of the VCC to Pd⁰, the nucleophilic attack via an originally proposed outer‐sphere pathway gives, however, the opposite regioisomer compared to the experimental results. Instead, nucleophilic attack of the amine reagent via a unique type of chelation‐assisted, inner‐sphere pathway accounts for the experimentally observed “branched” regioselectivity and high enantio‐control.     

随机相互作用系综内的镉同位素电磁矩线性演化

在随机相互作用系综内,镉同位素11/2-同质异能态的电四极矩与磁偶极矩总是倾向于随中子数的增加呈线性演化,这与近年来的实验观测是一致的。除了对力对磁矩线性演化的决定性影响之外,特定形式的质子-中子相互作用被认为是这种线性演化的主要驱动力:电矩的线性演化要求质子中子之间的四极相互作用;磁矩则要求质子中子之间的短程相互作用,并且这种相互作用应具有与真实核相互作用一致的相对强度与正负性。In random-interaction ensembles, the electric quadrupole moments (Q) and magnetic moments (μ) of the Iπ=11/2- isomers of the Cd isotopes predominantly present linear correlation with neutron numbers, corresponding to the recently emphasized linear Q and μ systematics in realistic nuclear system. Although the seniority scheme enhances such predominance (more essentially for μ), the configuration mixing due to quadrupolelike and δ-force-like proton-neutron interactions is responsible for the linear Q and μ systematics, respectively, at least in random-interaction ensembles. Especially, the linear μ systematics further requires the proton-neutron interaction have similar relative strength and attractive-repulsive property to realistic nuclear interaction.     

2 + 1 Flavors QCD Equation of State in NJL Model with Proper Time Regularization

Totally symmetric A_1g phonons are studied for the equilibrium and coherent states of a Bi₂Te₃ lattice. Equilibrium phonons were investigated in the frequency domain by the method of spontaneous Raman scattering, whereas coherent phonons were studied by the method of active femtosecond spectroscopy in the time domain. In the latter case, femtosecond laser pulses were used both for generating and detecting coherent A_1g phonons having a well-defined phase allowing the selective optical control of the lattice dynamics. A comparison of the results obtained in the frequency and time domains suggests that diagonal and nondiagonal elements of the density matrix of lattice excitations relax with the same characteristic time to the equilibrium and zero values, respectively.     

欠曝光下光学联合变换相关器位移探测技术的稳健性研究

研究了在低曝光量下光学联合变换相关器位移探测技术的稳健性,为提出的颤震探测系统设计与实现提供可行性论证.通过实际视频,探讨曝光量不足对光学联合变换相关器位移探测的影响.并讨论了不同方差的高斯白噪声对探测的影响.实验结果表明,光学联合变换相关器位移探测技术在欠曝3.5档和存在一定噪声范围内仍能保持良好的运动矢量估计性能,从而说明了光学联合变换相关器像移探测在一定的曝光量范围内仍能准确地得到运动矢量估计,是一种运算速度快、实时性好且稳健性较强的探测技术.     

相邻帧间匹配的迎头点目标跟踪算法

针对海空复杂背景下迎头点目标检测与跟踪难题,提出了一种基于相邻帧间匹配的边检测边跟踪算法.算法对相邻红外图像序列帧间点与点的邻域匹配,标记匹配结果兴趣区域像素点,统计标记次数,与输入单帧图像同步显示迎头目标检测结果.算法主要特点在于无需提前假定疑似目标点位置,单个匹配过程与当前相邻两帧外的其它序列帧无关,整个匹配过程不随目标数目多少或运动状态变化而改变.根据仿真和实拍照片实验,证实了理论上区别于传统算法的上述优点,在军事应用中具有较高的参考价值.     

A model study of quark-number susceptibility at finite chemical potential and temperature

In this Letter, we try to give a direct method for calculating the quark-number susceptibility (QNS) at finite chemical potential and temperature. In our approach the QNS is given by a formula which solely involves (the dressed quark propagator at finite chemical potential μ and temperature T). From this the QNS at finite chemical potential and temperature is calculated in the framework of rainbow-ladder approximation of the Dyson–Schwinger approach using the meromorphic quark propagator proposed in [M.S. Bhagwat, M.A. Pichowsky, P.C. Tandy, Phys. Rev. D 67 (2003) 054019]. It is found that the QNS χ(μ,T) has a singularity when μ comes close to a critical value μ₀, and the susceptibility as a function of T becomes discontinuous at some values of T when μ is near μ₀. At high temperature the QNS approaches the ideal quark gas result, while at very small temperature (T<40 MeV) the susceptibility equals zero. For all values of μ we studied, the susceptibility shows a rapid increase near T=120–140 MeV, which could be regarded as the signal of a crossover.     

Generation of tunable and narrow linewidth continuous-wave yellow laser by sum–frequency mixing of diode-pumped solid-state Nd:YAG ring lasers

We report a tunable, narrow linewidth and high beam quality continuous-wave (CW) yellow laser system at 589 nm. The system is an all solid-state design employing single-pass sum–frequency generation in a KTP crystal by mixing the 1064 nm with 1319 nm lines of two side-pumped Nd:YAG enforcing unidirectional ring lasers. With this method, a CW yellow laser at 589.159 nm with an output power of 0.8 W, a linewidth less than 1.5 GHz and a beam quality M² = 1.29 is obtained. The wavelength of the laser also can be precisely tuned from 589.112 to 589.181 nm in step-length of about 0.22 pm.     

Generalized differential transform method to differential-difference equation

In this Letter, we generalize the differential transform method to solve differential-difference equation for the first time. Two simple but typical examples are applied to illustrate the validity and the great potential of the generalized differential transform method in solving differential-difference equation. A Padé technique is also introduced and combined with GDTM in aim of extending the convergence area of presented series solutions. Comparisons are made between the results of the proposed method and exact solutions. Then we apply the differential transform method to the discrete KdV equation and the discrete mKdV equation, and successfully obtain solitary wave solutions. The results reveal that the proposed method is very effective and simple. We should point out that generalized differential transform method is also easy to be applied to other nonlinear differential-difference equation.     

Stimulated Raman scattering of picosecond pulses in a YVO<Subscript>4</Subscript> crystal

Stimulated Raman scattering (SRS) with a picosecond pulse in YVO₄ crystals in a transient state was investigated. The picosecond gain of YVO₄ crystals pumped by a 532-nm laser evaluated by means of the threshold was 16.13 cm/GW.     

Fast DSC applied to the crystallization of polypropylene

In an effort to find the limit of crystallization of polypropylene, a series of quantitative and semiquantitative DSC experiments at rates up to 10,000 deg/min are described. Even at these fast rates polypropylene crystallized on cooling between 350±15 K and 280±6 K. No fully amorphous polypropylene was produced. No initial stage crystallization to the condis state could be proven by quenching after partial crystallization.

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Zusammenfassung Eine Reihe von quantitativen und semiquentitativen DSC-Versuchen mit Aufheizgeschwindigkeiten bis 10000 K/min wurden ausgeführt, um die Grenze der Kristallisation von Polypropylen festzustellen. Sogar bei diesen schnellen Aufheizgeschwindigkeiten kristallisiert Polypropylen beim Abkühlen zwischen 350±15 K und 280±6 K. Kein völlig amorphes Polypropylen wurde erhalten.

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, 10 000 /. 350±15 280±6 . « » . .

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This work was supported in part by a grant of Hercules, Inc. to the ATHAS effort and in part by the Polymers Program of the National Science Foundation (Grant number DMR 8317097). The experimentation was helped by an instrument gift by the Celanese Company.