Numerical approach for the evolution of spin-boson systems and its application to the Buck–Sukumar model

We study the evolution properties of spin-boson systems by a systematic numerical iteration approach, which performs well in the whole coupling regime. This approach evaluates a set of coefficients in the formal expression of the time-dependent Schr?dinger equation by expanding the initial state in Fock space. This set of coefficients is unique for the spin-boson Hamiltonian studied, allowing one to calculate the time evolution from different initial states. To complement our numerical calculations, we apply the method to the Buck–Sukumar model. We find that when the ground-state energy of the model is unbounded and no ground state exists in a certain parameter space, the time evolution of the physical quantities is naturally unstable.     

Rapid resolution liquid chromatography-mass spectrometry and high-performance liquid chromatography-fluorescence detection for metabolism and pharmacokinetic studies of ergosta-4,6,8(14),22-tetraen-3-one

Ergosta-4,6,8(14),22-tetraen-3-one (ergone) from many medicinal plants has been demonstrated to possess a variety of pharmacological activities in vivo and in vitro, including cytotoxic, diuretic and immunosuppressive activity. Metabolism and pharmacokinetic studies on rat were conducted for ergone. Rapid resolution liquid chromatography with atmospheric pressure chemical ionization tandem multi-stage mass spectrometry (RRLC-APCI-MSⁿ) and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) methods were applied for the identification and quantification of ergone and its metabolite from rat plasma, faeces and urine. A metabolite was identified by RRLC-DAD-APCI-MSⁿ: 22,23-epoxy-ergosta-4,6,8(14)-triaen-3-one (epoxyergone). The concentrations of the analyte with its metabolites were determined by HPLC-FLD at excitation wavelength of 370 nm and emission wavelength of 485 nm. The samples were deproteinized with methanol after addition of camptothecin as internal standard (IS). The analysis was performed on a Diamonsil C18 column (150 mm × 4.6 mm × 5 μm) with a mobile phase gradient consisting of methanol and water at a flow rate of 1 mL min⁻¹. The assay was linear over the concentration range of 42-1500, 36-7500 and 42-1500 ng mL⁻¹ for plasma, faecal homogenate and urine respectively. The absolute recoveries were found to be 97.0 ± 1.2%, 98.1 ± 0.7% and 96.6 ± 1.8% for plasma, faecal homogenate and urine respectively. The intra-day and inter-day relative standard deviations (RSD) were less than 10%. The previous HPLC-MS/MS method is not affordable for most laboratories because of the specialty requirement and high equipment cost. However, the HPLC-FLD method is economic and operating simply for quantitative determination of ergone and its metabolite in rat plasma, faeces and urine. In addition, liquid chromatography coupled with ion trap multi-stage mass spectrometry is becoming a useful technique for ergone metabolite identification.     

Iodine-mediated regioselective hydroxyselenenylation of alkenes:Facile access to β-hydroxy selenides

In the presence of molecular iodine, the reaction of alkenes with diselenides proceeds efficiently under mild reaction conditions in MeCN/H₂O, which affording β-hydroxy selenides with high regioselectivity and in good to excellent yields.     

Selaginellin A and B, two novel natural pigments isolated from Selaginella tamariscina

Two new unusual natural pigments were first isolated from the whole herbs of Selaginella tamariscina. The structure of selaginellin A (1) was established as (R,S)-4-[(4'-hydroxy-3-((4-hydroxyphenyl)ethynyl)biphenyl-2-yl)(4-hydroxyphenyl)methylene]-2,5-cyclohexadien-1-one and selaginellin B (2) as (R,S)-4-[(4'-methoxy-4-(methyl)-3-((4-methoxyphenyl)ethynyl)biphenyl-2-yl)(4-methoxyphenyl)methylene]-2,5-cyclohexadien-1-one, along with four known biflavonoids, amentoflavone (3), hinokiflavone (4), heveaflavone (5), and 7'-O-methylamentoflavone (6). Their chemical structures were elucidated by spectral analysis of electrospray ionization mass spectroscopy (ESI-MS), one-dimensional nuclear magnetic resonance spectroscopy (1D-NMR) and two-dimensional-nuclear magnetic resonance spectroscopy (2D-NMR) including (1)H-NMR, (13)C-NMR, distortionless enhancement by polarization transfer (DEPT) and heteronuclear multiple bond coherence (HMBC), and single-crystal X-ray diffraction techniques.     

B与N掺杂对单层石墨纳米带自旋极化输运的影响

通过第一性原理计算研究了具有锯齿状边沿并且具有反铁磁构型的单层石墨纳米带的自旋极化输运.研究发现,在中心散射区同一位置掺入单个B和N原子,尽管对整个体系磁矩的影响完全相同,但对两个自旋分量电流的影响却完全相反.掺B时,自旋向上的电流显著大于自旋向下的电流;而掺N时,自旋向下的电流显著大于自旋向上的电流.这是由于不管掺B还是掺N都将打破自旋简并,使得导带和价带中自旋向上的能级比自旋向下的能级更高.掺B引入空穴,使完全占据的价带变为部分占据,从而自旋向上的能级正好处于费米能级,使得电子透射能力更强、电流更大,而自旋向下的能级则离费米能级较远使电子透射的能力较弱.掺N则引入电子,使得原来全空的导带变为部分占据,从而费米能级穿过导带中自旋向下的能级,使得自旋向下的电子比自旋向上的电子透射能力更强. 关键词： 自旋极化输运 单层石墨纳米带 第一性原理 非平衡格林函数     

氢掺杂单层石墨体系的晶格动力学研究

采用密度泛函理论研究了氢掺杂单层石墨（graphene）体系,并采用密度泛函微扰理论方法计算了体系局域振动模（LVMs）.结果显示,高频位置的LVMs数目与缺陷中氢原子数相等,而不同掺杂类型的LVMs频谱位置各不相同.研究结果及分析表明,LVMs测量是评估质子辐射下石墨样品的替位氢掺杂类型及其含量的有效方法,该方法可推广应用于研究其他掺杂体系. 关键词： 石墨 局域模式 晶格动力学     

部分相干光束经过湍流大气传输研究进展

相较于相干光束,部分相干光束经过湍流大气传输能够有效地抑制湍流引起的光束展宽、光斑漂移及光强闪烁等扰动效应,在自由空间光通信、激光雷达和激光遥感等方面有重要的应用前景.近年来,部分相干光束湍流大气传输研究受到越来越多学者的关注.本文回顾了部分相干光束在湍流大气中传输特性研究的发展历程、理论基础及常用的理论方法,介绍了处理光束经过湍流大气传输的相位屏数值模拟方法,以及如何把该方法运用到处理部分相干光束传输.     

在扫描电子显微镜中原位操纵、加工和测量纳米结构

在电子显微镜中对纳米材料和纳米结构进行原位测量是了解纳米材料的结构与性能关系的最重要手段,并且,在电子显微镜中操纵和加工纳米材料与纳米结构还可研究新结构和新器件.由于扫描电镜有大的样品室、可较容易地引入多个多种测量和操纵探针、并可配备多种探测器从多个角度对同一个样品进行表征,使得扫描电镜中的原位研究在纳米材料和纳米器件...     

Efficient subnanometric gold-catalyzed hydrogen generation via formic acid decomposition under ambient conditions

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.     

Comparison Between the Full Quantum Dynamics and the Quantum—Semiclassical Models to Many—Particle Systems

We consider a simple collinear collision of a “classical“ particle with a harmonic oscillator within quantumsemiclassical model and full quantum dynamics model,in which the latter is solved analytically in squeezed state and exact diagonalization methods and acts as the exact solution of such a system.A comparison of these two models for different mass ratios between the “classical“ particle and the quantum particle is done,which gives a criterion when using the quantum-semiclassical model.