Resonant photoacoustic detection of trace gas with DFB diode laser

A resonant photoacoustic detection system based on a low-power distributed feedback diode laser is developed. This sensor has been applied to the detection of acetylene (C₂H₂) using a specifically designed photoacoustic cell operating on its second longitudinal mode. The minimum detectable limit of about 10 parts-per-million volume (SNR=1) is achieved with an average laser power of 3.5 mW at atmospheric pressure, and an integration time constant of 3 ms; thus, the minimum detectable absorption coefficient normalised by power and bandwidth is 4.0×10⁻⁸ W cm⁻¹/√Hz. The optimum operating pressure buffered with N₂ is also investigated. The realisation of our system is described and experimental results are compared with different modulation techniques and other results reported in the literature. A number of issues arising from the conventional use of mechanical chopping of the beam can be effectively suppressed in wavelength modulation PA spectroscopy (WM-PAS) and second harmonic detection.     

Flow stress behavior of porous FVS0812 aluminum alloy during hot-compression

The hot deformation behavior of porous FVS0812 aluminum alloy prepared by spray deposition was studied by means of compression tests on a Gleeble 1500 machine. The samples were hot compressed at temperatures ranging from 573 K to 773 K under various true strain rates of 10⁻⁴–10⁰ s⁻¹. The deformation behaviors are characterized by a significant strain hardening during hot-compression due to the progressive compaction of the pores with increasing compressive strain. A revised formula describing the relationships of the flow stress, strain rate and temperature of the porous alloy at elevated temperatures is proposed by compensation of strain. The theoretical predictions are compared with experimental results, which show good agreement.     

适配体在靶向特异性检测中的最新应用进展

适配体是体外采用SELEX技术筛选得到的一段寡核苷酸序列(DNA或RNA),能折叠成一定的空间结构结合靶物质,实现特异性吸附。其功能类似抗体,但具有抗体无法比拟的优势,如靶物质范围广、特异性强、亲和力高、可体外筛选、易于标记和修饰、稳定性好、没有毒性、易制备等。近年来,适配体已在分析检测、生物化学、食品安全、临床医疗等领域得到广泛应用。本文综述了适配体在金属离子、抗生素、农药残留、真菌毒素、蛋白质、微生物、细胞等成分靶向特异性快速检测方面的应用进展,并分析其存在的局限性和问题,展望其应用前景和发展趋势,以期为适配体应用的拓展和相关研究提供依据和支持。     

巯基/氧化纤维素的制备及氯化体系中Ag(Ⅰ)的选择性吸附

以废纸纤维素为原料,将纤维素氧化开环胺化后再进行巯基化反应,制备得到了一系列巯基修饰的纤维素类吸附剂。研究发现,无论是单一氯化体系还是高铜高镍氯化混合体系,基于氨基硫脲修饰戊二醛交联的氧化纤维素吸附剂对配阴离子AgCl_4~(3-)的吸附效果最好,最大吸附量可达到171.16 mg/g。通过红外、X射线光电子能谱、热力学等技术手段分析探讨了其不同吸附效果的原因及该吸附剂对配阴离子Ag(Ⅰ)的静电引力吸附机理。     

Dispersion and agglomeration mechanism of flaky graphite particles in aqueous solution

The dispersion and agglomeration behavior of flaky graphite particles in an aqueous solution was studied. The small particles of flaky graphite naturally formed a large and compact agglomeration in an aqueous solution at pH 7.0 and 9.0, respectively. The theoretical calculation result based on typical DLVO theory was opposite the phenomenon observed by optical microscope, indicating that the interaction force between the flaky graphite particles exceeded the van der Waals and electrostatic double-layer forces. When the extended DLVO theory was used, the total interaction energy (U_T = U_A + U_R + U_HI) was negative over most of the distance range, indicating that the agglomeration of the small particles was attributed to the attraction. This result indicated that hydrophobic interactions dominated the dispersion and agglomeration behavior of the hydrophobic flaky graphite particles.     

Effect of droplet size of the emulsified kerosene on the floatation of amorphous graphite

The micro-floatation of an amorphous graphite sample was conducted using a Hallimond tube with various droplet sizes of emulsified kerosene as collector. The results showed that the experimental recovery of the sample and the kinetic constants (both k and ?_∞) obtained from the four kinetics models all increased with the decrease of the droplet size. These may be attributed to the fact that the smaller and greater the specific surface area of the droplets, the more easy it is for them to collide with, adhere to, and spread on the sample particles, and then render the particles more hydrophobic. The stronger hydrophobic of particles was better beneficial to the adhesion probability and force between them and the bubbles, which made more amorphous graphite particles floated in the floatation process. In addition, the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was applied to study the interaction between the sample particles and the emulsified kerosene droplets. The results indicated that the hydrophobic attractions played a dominant role in the combined effect of collision and attachment between the sample particles and the droplets.     

A mid-infrared spectrometer based on difference frequency generation

A mid-infrared spectrometer operating in the range from 3.42 to based on difference-frequency mixing of a tunable Ti:Sapphire laser and a diode-pumped monolithic Nd:YAG laser in periodically poled LiNbO₃ (PPLN) crystals was developed. A system line width of about 36 MHz was obtained. An energy conversion efficiency of 0.6 mW/W² was obtained at . The direct absorption spectra of pure methane and pure carbon dioxide samples were measured to test the performance of the spectrometer.     

Ultrabroadband tunable continuous-wave difference-frequency generation in periodically poled lithium niobate waveguides

We report, for what is the first time to our knowledge, widely tunable mid-IR light generation over a range of greater than 1000 nm in the 4 microm region by employing a single quasi-phase-matched periodically poled niobate waveguide at room temperature. The waveguide we used was fabricated by annealed proton exchange based on periodically poled lithium niobate. A peak conversion efficiency of 10%/W and a linewidth as small as 37 MHz were achieved. The developed mid-IR light generator may find wide applications in trace gas detection of multiple atmospheric species and high-resolution spectroscopy.     

Trace analysis of impurities in bulk gases by gas chromatography-pulsed discharge helium ionization detection with "heart-cutting" technique

A method has been developed for the detection of low-nL/L-level impurities in bulk gases such as H(2), O(2), Ar, N(2), He, methane, ethylene and propylene, respectively. The solution presented here is based upon gas chromatography-pulsed discharge helium ionization detection (GC-PDHID) coupled with three two-position valves, one two-way solenoid valve and four packed columns. During the operation, the moisture and heavy compounds are first back-flushed via a pre-column. Then the trace impurities (except CO(2) which is diverted to a separate analytical column for separation and detection) together with the matrix enter onto a main column, followed by the heart-cut of the impurities onto a longer analytical column for complete separation. Finally the detection is performed by PDHID. This method has been applied to different bulk gases and the applicability of detecting impurities in H(2), Ar, and N(2) are herewith demonstrated. As an example, the resulting detection limit of 100 nL/L and a dynamic range of 100-1000 nL/L have been obtained using an Ar sample containing methane.     

A difference frequency generation spectrometer and its detection of atmospheric N2O

The paper reports the realization and characterization of a difference frequency generation spectrometer using periodically poled lithium niobate (PPLN) crystal. The pump and signal laser we used is a Ti:sapphire ring laser and a diode pumped monolithic Nd:YAG laser, respectively. The continuous wave (cw) infrared radiation from 2.8 to 4.8 microm has been generated. The idler radiation can be used to study fundamental absorption bands of molecules and trace gas detection. In this work, we report the detection of nitrous oxide (N(2)O) in atmosphere, the minimum detectable concentration of 10.9 ppbV was achieved using a Herriott cell with the optical path length of 100 m.