Characterization of a 10.3-μm pulsed DFB quantum cascade laser

We have measured the output parameters of a 10.3-μm pulsed distributed-feedback (DFB) quantum cascade (QC) laser manufactured by Alpes Lasers and intended for high-sensitivity detection of ammonia and ethylene. The laser beam was collimated with an AR-coated aspheric ZnSe lens with focal length of 11.6 mm and clear aperture of 16.5 mm. Near- and far-field distributions of the laser emission were recorded with an infrared imaging camera. The fast-and slow-axis laser beam divergences were measured to be 1.2 and 1.4 mrad (FWHM), respectively. The divergence was found to be increasing with injection current. An air-spaced Fabry–Perot interferometer with free spectral range of 0.05 cm⁻¹ was used to measure the frequency tuning rates of the laser. The laser was tuned by either heat sink temperature, injection current or pulse repetition rate with rates of −8 × 10⁻² cm⁻¹ K⁻¹, −7 × 10⁻² cm⁻¹ A⁻¹ and −9 × 10⁻⁴ cm⁻¹ kHz⁻¹, respectively. The laser frequency decreased linearly with a rate of 10⁻² cm⁻¹ ns⁻¹ (300 MHz ns⁻¹) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses.     

高频燃烧红外吸收光谱法测定铪合金中碳

通过对称样量、助熔剂、最短分析时间和比较器水平、分析功率等条件进行了优化选择,建立了高频燃烧红外碳硫分析仪对铪合金中碳含量的分析方法。确定采用称样量为0.4g,助熔剂选择为Fe+Sn+W=0.5g+0.1g+1.3g,最短分析时间为45s,比较器水平为1,分析功率选择100%的条件对铪合金中碳含量进行测定。方法用于测定铪合金实际样品中碳的相对标准偏差(RSD)为5.0%,加标回收率为99%～102%。方法重复性好,准确度高,在实际操作中切实可行。     

Selectivity and selectivity tuning in capillary gas chromatography

The selection of stationary phases in capillary gas chromatography is discussed. Methyl silicone, phenyl methyl silicone, trifluoropropylmethyl silicone, biscyanopropyl silicone, and high molecular weight (HMW) polyethylene glycol are considered to be the basic phases. Selectivities and polarities between these phases are obtained by selectivity tuning. Selectivity tuning can be performed in three different ways, namely by synthesizing a tuned stationary phase, by mixing the basic phases, or by coupling capillary columns of different selectivities. In coupling capillary columns the variables are column length, β-value, temperature, and/or pressure.     

Synthesis and characterization of some new Schiff base polymers

Seven Schiff base polymers poly 5,5^′-methylenebis(2-hydroxyacetophenone)semicarbazone (PHASC), poly-5,5^′-methylenebis(2-hydroxyacetophenone)thiosemicarbazone (PHATS), poly 6,6^′-methylenebis(2-hydroxynaphthaldehyde)1,2-propylenediimine (PHNPn), poly 6,6^′-methylenebis (2-hydroxynaphthaldehyde)1,3-propylenediimine (PHNPR), poly 6,6^′-methylenebis (2-hydroxy-naphthaldehyde)thiosemicarbazone (PHNTS), poly 6,6^′-methylenebis(2-hydroxy-naphthaldehyde)urea (PHNU) and poly-6,6^′-methylenebis(2-hydroxynaphthaldehyde)semicarbazone (PHNSC) were prepared by polycondensation of 5,5^′-methylenebis(2-hydroxyacetophenone) (MHA) or 6,6^′-methylenebis(2-hydroxynaphthaldehyde) (MHN) with semicarbazide, thiosemicarbazide, 1,2-propylenediamine, 1,3-propylenediamine or urea. The polymers were characterized by elemental micro-analysis, infrared and ultraviolet spectroscopy and viscosity measurements. The reduced viscosity of the polymers measured in dimethylformamide (DMF) was observed in the range 0.32-0.63 dl/g.     

Selectivity optimization in liquid chromatography via stationary phase tuning

In striving for the best possible separation, the selectivity of stationary phases as an optimization parameter is often underestimated although there are many ways to influence this powerful tool. This review serves to provide an insight into the various ways of adapting the selectivity of a separation in liquid chromatography. Approaches via temperature and flow rate tuning are discussed as a basis followed by focusing on the stationary phase as the superior optimization parameter. Highly selective stationary phases hereby provide an advantage for groups of similar analytes. For more complex mixtures, separations can be improved using mixed-mode technologies where different retention mechanisms are combined. Serial coupling, mixed-bed columns, and stationary phase optimized selectivity liquid chromatography provide solutions to various degrees. Finally, the advantages of stationary phase tuning over adaption of mobile phase and/or temperature are presented in terms of optimum application range.     

Advances of sensitive techniques in laser spectroscopy

Different techniques are used for the sensitive detection of overtone transitions of small molecules, such as H₂S, C₂H₂, OCS, O₃ in the visible and near infrared region. The techniques include: phase-modulated or wavelength-modulation absorption spectroscopy with a widely tunable single mode diode laser, opto-acoustic spectroscopy in resonance cells with a color center laser or a Ti:Sapphire laser, and sub-Doppler opto-thermal spectroscopy in cold collimated molecular beams, using a low temperature bolometer as detector. The three techniques are compared with regard to sensitivity and spectral resolution. The mass selective sensitive detection of small metal clusters Li₃ and Na₃ and their high resolution sub-Doppler spectroscopy, using resonant two-photon ionization with cw lasers, is briefly discussed.     

Substituents modification of meso-aryl BODIPYs for tuning photophysical properties

We successfully synthesized eight meso-aryl BODIPYs with 2,6-diethyl- or 1,2,6,7-tetraethyl substituents and characterized their photophysical properties. The steric hindrance resulting from the phenolic group in the meso-aryl moiety and the ethyl groups on the BODIPY core affected the synthesis of dipyrromethanes as an intermediate as well as the UV–Vis absorption and fluorescence emission of the BODIPYs due to the constrained rotation of the aryl ring. The potential use of the meso-hydroxyphenyl BODIPY as a pH sensor was also shown by the pH-dependent fluorescence emissions.     

Synthesis and spectroscopic properties of nickel complexes of benzo-, 1,2-naphtho-, or 2,3-naphthoannulated β-oxatetraazachlorins

The first β-oxatetraazachlorin derivatives have been synthesized starting from phthalonitrile derivatives and 5,5-dimethyl-1,3-oxazolidine-2,4-dione instead of the previously employed tetramethylsuccinonitrile. Absorption and magnetic circular dichroism (MCD) spectral properties are similar to those obtained for the corresponding tetramethyl-substituted TAC derivatives, confirming the presence of the low-symmetry aromatic structures.     

Mechanical property tuning of semicrystalline network polymers by controlling rates of crystallization and crosslinking

Semicrystalline network polymers were obtained by the Diels–Alder (DA) reaction of furyl‐telechelic poly(ε‐caprolactone) and tris(2‐maleimide ethyl)amine. Controlling the rates of crystallization and crosslinking reaction gave materials with various properties. Curing at a temperature much below T_m of poly(ε‐caprolactone), at which crystallization proceeded first followed by DA reaction, gave a hard and stiff material, whereas curing above T_m gave a soft and stretchable one. When crystallization and crosslinking were promoted simultaneously, tough and ductile materials were obtained. Structural analysis of the network polymers showed that the variation in the properties was derived from the difference in the crystallinity, crystallite size, and network structure. Therefore, materials with various mechanical properties, from soft to hard, could be obtained by simple thermal treatment. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A new nonempirical tuning scheme with single self‐consistent field calculation: Comparison with global and IP‐tuned range‐separated functional

System‐dependent nonempirical tuning of range‐separated functional provides a way to minimize the delocalization error of the system. However, existing nonempirical tuning method requires the computation of several ΔSCF calculations to determine the optimal μ value. In this article, we have defined a scheme to evaluate the optimal μ value with single self‐consistent field calculation. Our method is based on the evaluation of the spherically symmetric average Electron localization function (ELF) region. According to this scheme, the radius of the spherically symmetric average ELF region gives is a measure of the distance at which the long‐range part of the range‐separated functional becomes dominant. Numerical results indicate that our method improves the reproduction of HOMO energies and HOMO‐LUMO gap in comparison to global and IP‐tuned range‐separated functional. Moreover, in case of HOMO energies, maximum error of the ELF‐tuned functional is considerably smaller than the global and IP‐tuned functional. Furthermore, our method gives considerably smaller deviation of HOMO energies from ΔSCF IP than global range‐separated functional. © 2017 Wiley Periodicals, Inc.     

星际分子微波波谱研究进展

介绍了星际分子研究的概况,对微波波谱作为研究星际分子的重要方法的特点、特殊方法和技术以及取得的进展进行了综述,特别对近年来的微波波谱星际分子研究进行了分类介绍,提出了目前研究的难点并展望了发展趋势.     

Structural tuning of coordination polymers by 4-connecting metal node and secondary building process

Due to variation in ligand's conformation, metal node's connecting geometry, and secondary building process by anions, bat-like, dumbell-like, diamondoid, or pillar-layer topologies are achieved.     

Electron Energy Spectroscopic Mapping of Surface Plasmon by Parallel Scanning Method

In this work, electron energy spectroscopic mapping of surface plasmon of Ag nanostructures on highly oriented pyrolytic graphite is reported. Benefitting from the angular dispersive feature of the present scanning probe electron energy spectrometer, a multi-channel detection mode is developed. By scanning along one direction, the two-dimensional intensity distribution of Ag surface plasmon excitation due to the collision of electron emitted from the tip can be obtained in parallel. The spectroscopic spatial resolution is determined to be around 80 nm.     

Selective synthesis of monomeric or dimeric titanatranes via fine tuning in triethanolateamine ligand

Monomeric titanatrane i-PrOTi(OCMe₂CH₂)₃N (1) and dimeric titanatranes [i-PrOTi(OCH₂CH₂)_nN(CH₂CMe₂O)_3−n]₂ (n = 1, 2; n = 2, 3) were synthesized by the reaction of Ti(O-i-Pr)₄ with a series of triethanolateamines such as (OCH₂CH₂)_nN(CH₂CMe₂O)_3−n³⁻ (n = 0, Lig¹; n = 1, Lig²; n = 2, Lig³), which vary by the number of CMe₂ groups adjacent to a OH functionality from 3 (Lig¹H₃) to 2 (Lig²H₃) to 1 (Lig³H₃). The resultant titanatranes 1–3 have been characterized by solution ¹H and ¹³C{¹H} NMR and their solid state structures have been determined by X-ray crystallography. Whereas compound 1 is monomeric in the solid state, compounds 2 and 3 are dimeric, due to the reduction of the steric congestion in the vicinity of the Ti.     

层状液晶的小振幅振荡频率扫描研究

利用小振幅振荡频率扫描研究了非离子表面活性剂所形成的层状液晶的粘弹性, 考察了表面活性剂的浓度、温度, 硝酸银的加入和银的生成对其影响. 结果表明: 储能模量(G′)和损耗模量(G″)随表面活性剂浓度增大而增大; 随温度升高出现三种不同的频率扫描曲线; 硝酸银的加入和银的生成对曲线的形状没有影响, 对G′和G″值的影响随过渡区和单相区的不同而不同.     

Voltage-induced pseudo-dielectric heating and its application for color tuning in a thermally sensitive cholesteric liquid crystal

ABSTRACT

We previously proposed an electrical approach enabling the tuning of the center wavelength λ_c of the cholesteric liquid crystal (CLC) bandgap in the full-color visible spectrum based on the electro-thermal effect. The idea involved the design of a negative CLC with a thermally sensitive bandgap feature and the use of a sandwich-type cell with finite electrode conductivity, allowing the control of cell temperature by applied voltage via pseudo-dielectric heating. It has been demonstrated experimentally that the induced pseudo-dielectric heating is predominated by the pseudo-dielectric relaxation originating from the designated cell geometry. On the basis of this technique, key factors determining the tuning efficacy of the temperature and thus λ_c are primarily investigated in this study. Our results suggest that lowering the electrode resistivity and the specific heat conductivity of the cell can promote the maximum tunable temperature range. Expectedly, optimizing the electrode area, cell gap and dielectric permittivity of the CLC favors a decreased relaxation frequency and, in turn, reducing the voltage as well as the frequency required for λ_c tuning.