An NMR study of hydrogen bonding in some azo dyestuffs

The ¹H, ¹³C, and ¹⁵N NMR data reported for compounds 1–4 show that in DMSO solutions all of them exist in the azo form only and do not participate in the azo–hydrazoimine equilibrium. The NMR data for compounds 1 and 2 show the presence of a weak hydrogen bond for the non-protonated forms, between N10 and the 2-NHCH₃ proton. All compounds have also been studied in TFA solutions in which they are protonated. The site of protonation of 1, 2 and 3 is determined to be at N10 in TFA solutions. These results are supported by some ab initio GIAO-CHF molecular orbital calculations.     

铁系无铬(NBC-1)型高温变换催化剂 Ⅳ.吸附性能及CO变换反应机理的研究

通过程序升温脱附（ＴＰＤ）、程序升温表面反应（ＴＰＳＲ）及脉冲反应（ＰＳＲ）等化学物理技术,综合分析研究了铁系无铬（ＮＢＣ－１）型ＣＯ高温变换催化剂的吸附性能及化学反应特性。研究表明,ＮＢＣ－１型催化剂对Ｈ２Ｏ具有很强的吸附能力,不易吸附ＣＯ及ＣＯ２,该催化剂上水煤气变换反应的机理为氧化－还原（ｒｅｄｏｘ）反应机理     

New design of the CDB-spectrometer at NEPOMUC for T-dependent defect spectroscopy in Mg

Crystal defects in magnesium and magnesium-based alloys like AZ31 are of major interest for the understanding of their macroscopic properties. Coincident Doppler broadening spectroscopy with positrons (CDBS) is a well-established technique to investigate lattice defects and their chemical surrounding in solids. However, Mg and its alloys are demanding materials for positron spectroscopy, since the trapping rate in Mg is low and the trapping sites are shallow. In order to increase the trapping rate, the CDBS-facility at the high intense positron beam NEPOMUC is currently redesigned and improved with a cryostat for sample cooling. Furthermore, the recently installed remoderator provides a beam energy between 20 and 200 eV. On the contrary to the previous beam energy of 1 keV, the beam is therefore no longer non-adiabatically released from the magnetic field at the grounded field termination. Hence it is necessary to construct an insulated field termination where voltages up to 5 kV can be applied.     

Structure and linear spectroscopic properties of near IR polymethine dyes

We performed a detailed experimental investigation and quantum-chemical analysis of a new series of near IR polymethine dyes with 5-butyl-7,8-dihydrobenzo[cd]furo[2,3-f]indolium terminal groups. We also synthesized and studied two neutral dyes, squaraine and tetraone, with the same terminal groups and performed a comparison of the spectroscopic properties of this set of “near IR” dyes (polymethine, squaraine, and tetraone) with an analogous set of “visible” dyes with simpler benzo[e]indolium terminal groups. From these measurements, we find that the dyes with dihydrobenzo[cd]furo[2,3-f]indolium terminal groups are characterized by a remarkably large shift ≈300 nm (≈200 nm for tetraone) of their absorption bands towards the red region. We discuss the difference in electronic structure for these molecules and show that the “near IR” dyes are characterized by an additional weak fluorescence band from the higher lying excited states connected with the terminal groups. Absorption spectra for the longest polymethines are solvent-dependent and are characterized by a broadening of the main band in polar solvents, which is explained by ground state symmetry breaking and reduced charge delocalization within the polymethine chromophore. The results of these experiments combined with the agreement of quantum chemical calculations moves us closer to a predictive capability for structure-property relations in cyanine-like molecules.     

轴向隐失波激励的回音壁模式光纤激光器

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器.在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应.实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽.用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果.低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段.     

一种新的自由空间光通信调制方式——圆偏振位移键控

自由空间光通信(FSO)在开放的大气链路中传输光信号, 不可避免地会受到大气扰动和背景光噪声的影响, 导致系统的可靠性降低。为了抑制大气扰动等对FSO系统造成的不利影响, 提出一种新的光信号调制方式——圆偏振位移键控(CPOLSK)。该调制方式利用圆偏振光的两种旋光状态进行数据的传送, 接收端结合差分方法进行光信号接收。给出了CPOLSK的装置模型, 并对其性能进行了分析。与目前广泛采用的开关键控(OOK)、脉冲位置调制(PPM)方式相比, CPOLSK很好地抑制了背景光噪声的影响, 同时对光电探测器内部噪声也有一定的抑制效果。     

堆积啁啾脉冲在单模光纤中的非线性传输特性

通过数值求解广义非线性薛定谔方程,分析了32路线性啁啾高斯脉冲堆积后的整形脉冲在单模光纤中的传输特性。结果表明经50 m单模光纤传输后脉冲的脉宽和包络形状基本不变; 非线性效应中的自相位调制和脉冲内Raman散射对脉冲频域特性影响较大,使频谱展宽约40 THz,中心角频率下移约10 THz; 而自陡效应,三阶色散对传输特性影响不大。     

Characterization of transition shifts in perpendicular magnetic recording using 3D FEM

Transition shift can create serious timing problems for high density recording environments. However, it is possible to use techniques such as write precompensation to offset the timing error introduced if the magnitude and the behaviour of the transition shift are properly understood. This paper introduces a 3D finite element method (FEM) to analyse the transition shift in perpendicular magnetic recording (PMR) quantitatively, allowing the combinational effects of the transition shifts from non-linear transition shift (NLTS), HTS, and neighbourhood-induced transition shift (NITS) to be examined. The consideration of all contributing factors to the final written transition position is important in determining the precompensation scheme of magnetic data recording, and 3D FEM can facilitate such quantitative analysis.     

基于乘法器的超声多普勒实验仪的研究

介绍了一种基于模拟乘法器的超声多普勒效应实验仪.该设备利用超声发射换能器的激励信号和经过限幅放大处理后的接收换能器的输出信号,作为模拟乘法器的输入;将乘法器的输出经过低通滤波器后得到多普勒频移信号,从而获得接收换能器的运动速度.该设备具有结构清晰、操作方便、物理现象明显等特点,十分适合在大学物理实验教学中应用.     

条形耦合波导对光子晶体耦合缺陷模的影响

光子晶体的耦合缺陷模可以通过透射谱形状来表征,而透射谱形状则与连接缺陷的条形耦合波导相关.不同于直接耦合时信号相移只依赖于缺陷模的共振频率,当存在耦合波导时信号相移也决定于波导的长度和色散关系.随着波导长度的增加,透射谱形状发生从三峰到两峰,再到平项,最后又回到三峰的周期性变化.时间耦合模的分析表明,在缺陷模频率附近理论结果与时域有限差分法的计算结果完全一致,表明在此复杂情况下理论模型依然有效.