Surface Enhanced Raman Scattering Sensing with Nanostructures Fabricated by Soft Nanolithography

The nanospike structures formed with femtosecond laser irradiations have been successfully replicated on the surface of a polyurethane (PU) polymer using a low cost soft nanolithography method. The surface enhanced Raman scattering (SERS) of rhodamine 6G (Rh6G) and dinitrotoluene (DNT) molecules have been measured with silver coated PU nanospike surfaces by a simple portable Raman spectrometer. Compared to a flat silver coated surface, where no Raman Scattering of the molecules can be detected by the simple portable Raman spectrometer, the Raman spectra are enhanced by more than 4 orders of magnitudes. This indicates that the high area/volume ratio and small size of the PU nanospikes can be used for SERS sensing.     

Carbonaceous sorbents for high‐temperature interactive liquid chromatography of polyolefins

The elution behavior of polyethylene (PE) and the three stereoisomers of polypropylene (PP) was studied on porous graphite along with three other carbon‐based sorbents, carbon‐clad zirconia particles, activated carbon, and exfoliated graphite in a systematic way in this work. Decahydronaphthalene, 1,2,3,4‐tetrahydronaphthalene, 1,3,5‐trimethylbenzene, tetrachloroethylene, xylene and p‐xylene were used as mobile phases. While PE is adsorbed to various extents on all the tested carbonaceous sorbents from the majority of the solvents, PP is fully adsorbed only in selected cases. Testing alcohols (C7–C9) as mobile phase with Hypercarb? indicates that all stereoisomers of PP are selectively adsorbed and desorbed when a solvent gradient alcohol→1,2,4‐trichlorobenzene is used at 160°C. The retention of all stereoisomers of PP increases with the polarity of the alcohol. Linear PE is retained on Hypercarb? even from 1,2‐dichloro‐ and 1,2,4‐trichlorobenzene, when a temperature below 120°C is applied, while it is not retained from these solvents at higher temperatures. All stereoisomeric forms of PP are not adsorbed under the same conditions. Some of the tested new sorbent/solvent systems have potential to be applied in routine analysis of industrially synthesised polyolefins.     

One‐Pot Sequential Organocatalysis: Highly Stereoselective Synthesis of Trisubstituted Cyclohexanols

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96 %) synthesis of trisubstituted cyclohexanols was achieved by using a one‐pot sequential organocatalysis that involved a quinidine thiourea‐catalyzed tandem Henry–Michael reaction between nitromethane and 7‐oxo‐hept‐5‐en‐1‐als followed by a tetramethyl guanidine (TMG)‐catalyzed tandem retro‐Henry–Henry reaction on the reaction products of the tandem Henry–Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one‐pot sequential organocatalysis by using the racemic Henry product as the substrate.     

Using Distonic Radical Ions to Probe the Chemistry of Key Combustion Intermediates: The Case of the Benzoxyl Radical Anion

The benzoxyl radical is a key intermediate in the combustion of toluene and other aromatic hydrocarbons, yet relatively little experimental work has been performed on this species. Here, a combination of electrospray ionization (ESI), multistage mass spectrometry experiments, and density functional theory (DFT) calculations are used to examine the formation and fragmentation of a benzoxyl (benzyloxyl) distonic radical anion. Excited 4-carboxylatobenzoxyl radical anions were produced via two methods: (1) collision induced dissociation (CID) of the nitrate ester 4-(nitrooxymethyl)benzoate, ^–O₂CC₆H₄CH₂ONO₂, and (2) reaction of ozone with the 4-carboxylatobenzyl radical anion, ^–O₂CC₆H₄CH₂ ^?. In neither case was the stabilized ^–O₂CC₆H₄CH₂O^? radical anion intermediate detected. Instead, dissociation products at m/z 121 and 149 were observed. These products are attributed to benzaldehyde (O₂ ^-CC₆H₄CHO) and benzene (^–O₂CC₆H₅) products from respective loss of H and HCO radicals in the vibrationally excited benzoxyl intermediate. In no experiments was a product at m/z 120 (i.e., ^–O₂CC₆H₄ ^?) detected, corresponding to absence of the commonly assumed phenyl radical + CH₂=O channel. The results reported suggest that distonic ions are useful surrogates for reactive intermediates formed in combustion chemistry.

Can the Effective Potential of a Linear Quadrupole be Extended to Values of the Mathieu Parameter q Up to 0.90?

The motion of ions in a linear quadrupole is usually described by solutions to the Mathieu equation. A simplifying approximation to this theory that is widely used for low values of the Mathieu parameters a and q describes ion motion in an effective potential. In this work, we have calculated the effective potential for any q from displacements of calculated ion trajectories caused by a dipole DC electric field. It is assumed that the dipole DC electric field at the center of the displaced trajectory is countered by an “effective” electric field. For all q values, the effective electric field is found to increase linearly with the distance from the center of the quadrupole. The trapping forces probed in this way increase continuously with q up to the first stability region boundary at q=0.908. The well depth (D) at any q can be described by $ D=q\frac{V_{rf}}{c} $ , where c=3.955±0.005, very similar to the standard effective potential model with c=4.000.

Cookie-Cutter~集上的~Gibbs~测度

Cookie-Cutter集不仅是动力系统中重要的研究对象,而且是分形中一类重要的集合.而支撑在其上的Gibbs测度对计算分形维数和热力学机制的熵起关键性作用.本文借助于定理2.1构造了支撑在其上的Gibbs测度,并用遍历性证明了该测度的唯一性.     

C NMR of polyolefins with a new high temperature 10 mm cryoprobe

Recently, a high temperature 10 mm cryoprobe was developed. This probe provides a significant sensitivity enhancement for ¹³C NMR of polyolefins at a sample temperature of 120–135 °C, as compared to conventional probes. This greatly increases the speed of NMR studies of comonomer content, sequence distribution, stereo- and regioerrors, saturated chain end, unsaturation, and diffusion of polymers. In this contribution, we first compare the ¹³C NMR sensitivity of this probe with conventional probes. Then, we demonstrate one of the advantages of this probe in its ability to perform 2D Incredible Natural Abundance Double Quantum Transfer Experiment (2D INADEQUATE) in a relatively short period of time. The 2D INADEQUATE has been rarely used for polymer studies because of its inherently very low sensitivity. It becomes even more challenging for studying infrequent polyolefin microstructures, as low probability microstructures represent a small fraction of carbons in the sample. Here, the 2D INADEQUATE experiment was used to assign the ¹³C NMR peaks of 2,1-insertion regioerrors in a poly(propylene-co-1-octene) copolymer.     

Coadsorption of trimethyl phosphine and thiocyanate on colloidal silver: a SERS study combined with theoretical calculations

The adsorption of trimethyl phosphine (TMP) on colloidal silver has been investigated by means of surface‐enhanced Raman scattering spectroscopy (SERS). On the basis of surface selection rules, it is deduced from the SERS results that TMP adsorbs on silver surface via its P atom. The electron donor effect of TMP can be sensitively probed by the coadsorbed SCN⁻. The Raman wavenumber of νCN of the adsorbed SCN⁻ shifts to lower wavenumbers when TMP is coadsorbed with SCN⁻ and the red shift of C≡N stretching wavenumber is found to increase with increasing surface coverage of TMP. This could be explained in terms of the electron donor effect of TMP. Density functional theory (DFT) calculations further confirm the experimental results that the charge transfer is from TMP to silver surface rather than reversely. Natural bond orbital (NBO) analysis indicates that the red shift of C≡N stretching mode is due the increase of electronic populations of π* orbital of C≡N bond induced by coadsorbed TMP, consequently the C≡N bond is weakened, and the νCN shifts to lower wavenumbers. An NBO analysis also indicates that the conjugated effect between S atom and C≡N bond could easily make the charge transfer from silver surface to C≡N bond. Copyright © 2008 John Wiley & Sons, Ltd.     

“强光一号”Al丝阵Z箍缩产生K层辐射实验研究

在“强光一号”加速器开展了Al丝阵Z箍缩产生K层辐射的实验研究,固定Al丝线径20 μm、丝阵直径12 mm,丝根数为8和12的负载获得K层产额分别为0.9 kJ/cm和1.1 kJ/cm,明显高于16和24根丝负载.辐射功率波形和时间分辨的X射线图像显示,低丝数负载存在拖尾质量引起的多次内爆现象.在60%—80%的内爆时间内,丝阵几乎停留在初始位置;主体内爆在随后的25—30 ns内完成,将部分等离子体留在初始位置,形成质量的拖尾分布;内爆后期驱动电流向外围的拖尾质量迁移,引 关键词： Al丝阵 Z箍缩 K层辐射')" href="#">K层辐射 拖尾质量     

基于三维有限元法模拟分析六面顶顶锤的热应力

以有限元法为理论分析手段模拟分析了国产六面顶压机配套顶锤内部的温度场和热应力分布.探寻出了XKY-6×2000 MN型六面顶压机顶锤内部的温度场分布以及热应力取值.模拟结果表明加热顶锤内部温度分布不均匀,不均匀的温度分布产生了热剪切应力,热剪切应力峰值达到0.62 GPa,分布在41.5°小斜面上.加热顶锤内部的剪切应力值较非加热锤内部的剪切应力值高出18.0％.模拟分析结果与金刚石的高压合成实验事实相符,在理论上解释了加热顶锤使用寿命较非加热顶锤使用寿命短的原因,此项工作对于提高大顶锤使用寿命,降低生产 关键词： 热应力 顶锤 有限元法 工业金刚石