S波段低温低噪声放大器技术研究

介绍了低温低噪声放大器使用的HEMT(高迁移率晶体管)器件噪声模型的建立,对HEMT用S参数和噪声参数讲行仿直,获取适合的模型.给出了实例,放大器在低温10K工作,增益≥30dB,噪声温度≤4K.     

Rapid sequential separation of essential oil compounds using continuous heart-cut multi-dimensional gas chromatography-mass spectrometry

A method for separation and identification of peaks in essential oil samples based on rapid repetitive heart-cutting using multidimensional gas chromatography (MDGC)-mass spectrometry (MS) coupled with a cryotrapping interface is described. Lavender essential oil is analyzed by employing repetitive heart-cut intervals of 1.00 and 1.50 min, achieved in a parallel MDGC-MS/GC-FID experiment. The number of peaks that were detected in 1D GC operation above a given response threshold more than tripled when MDGC-MS employing the cryotrapping module method was used. In addition, MDGC-MS enabled detection of peaks that were not individually evident in 1D GC-MS, owing to effective deconvolution in time of previously overlapped peaks in 1D GC. Thus separation using the cryomodulation approach, without recourse to using deconvolution software, was possible. Peaks widths decreased by about 5-7-fold with the described method, peak capacity increased from about 9 per min to 60 per min, and greater sensitivity results. Repeatability of retention times for replicate analyses in the multidimensional mode was better than 0.02% RSD. The present study suggests that the described heart-cutting technique using MDGC-MS can be used for general improvement in separation and identification of volatile compounds.     

低温辐射计紫外探测器光谱响应度测试技术研究北大核心CSCD

通过研制真空多光路切换组件,结合Y型真空比较通道、探测器真空舱,在保证超高真空环境的前提下,实现激光、紫外连续可调单色光以及真空紫外单色光3个光路的快速切换,从而以低温辐射计为基准,以紫外增强硅陷阱探测器为传递标准,实现波长115 nm~400 nm紫外探测器绝对光谱响应度的测量,实验验证绝对光谱响应度测量不确定度在115 nm~230 nm可达到0.8%~1.5%(k=2),在230 nm~400 nm可达到0.5%~1.0%(k=2)。     

A low debris laser plasma soft X-ray source

Low debris laser plasma soft X-ray source is of great importance to micro-lithography and microscopy. In this paper, a 1.06 μm YAG laser with 2 J energy, 10 ns duration is employed to irradiate a CO₂ cryogenic target. Soft X-ray spectra from the CO₂ cryogenic target are obtained. Experimental results of debris measurement from both CO₂ cryogenic and Cu targets demonstrate that the light source based on the CO₂ cryogenic target shows great improvement over conventional metal targets in debris reduction.     

Arsenic speciation in marine product samples: Comparison of extraction-HPLC method and digestion-cryogenic trap method

For the arsenic speciation in marine product samples, two types of pretreatment-analysis combination were compared. One is the combination of solvent extraction and high performance liquid chromatography (HPLC) followed by a highly sensitive arsenic detection, while the other is the combination of alkaline digestion and cryogenic trap (CT) method followed by a highly sensitive arsenic detection. For six certified reference materials (CRMs) of marine animal samples, the concentrations of arsenobetaine (AsB) obtained from the extraction-HPLC method were very consistent with those of trimethylated arsenic species measured by the digestion-CT method. For four seaweed samples, the determination of three arsenosugars (Sugar-1, Sugar-2, and Sugar-3) was favorably carried out by the extraction-HPLC method. Those seaweed samples were also subjected to the digestion-CT method, and the amounts of dimethylated arsenic species measured by the method were approximately equal to the sum of the amounts of dimethylarsinic acid (DMAA) and three arsenosugars (Sugar-1 + Sugar-2 + Sugar-3) obtained from the extraction-HPLC method.     

Standard Reference Materials® (SRMs) for measurement of inorganic environmental contaminants

NIST has developed an extensive collection of environmental SRMs, starting with fuel and biologically related materials in the late 1960s and now encompassing all sectors of environmental research. Advances in analytical methodology, including multi-element isotope-dilution mass spectrometry (IDMS) and expanded instrumental neutron-activation analysis (INAA) capabilities, enable value assignment based on fewer but better-characterized independent analytical techniques. The special advantages of IDMS for determination of S and Hg and for multi-element characterization of small-sample air particulate matter (SRM 2783) by IDMS and INAA are emphasized. Developments in materials production include the issuance of fresh-frozen biological materials and of jet-milled natural-matrix materials with improved homogeneity, including highly homogeneous air particulate matter and sediment SRMs for small-sample analytical techniques.     

常规压缩机混合工质循环气体液化系统研究

小型混合工质低温气体液化系统具有结构简单紧凑、尺寸小型化、投资省、易撬装化、易操作、应用灵活、安全性好等优点,其驱动采用全封闭油润滑压缩机,为常规制冷部件,制造工艺成熟,可市场化采购,成本大大降低。文中介绍搭建的常规压缩机驱动的混合工质低温气体液化实验台,进行了多次实验,并对系统的降温特性、能耗、压缩机性能等进行了测试。实验测试结果表明,常规油润滑压缩机性能稳定、耐用可靠,作为低温气体液化系统的驱动动力是可行的。     

High sensitivity absorption spectroscopy of methane at 80 K in the 1.58 μm transparency window: Temperature dependence and importance of the CH3D contribution

The high resolution absorption spectrum of methane in the 1.58 μm transparency window has been recorded at room temperature and at 79 K by CW-Cavity Ring Down Spectroscopy using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers. The achieved sensitivity (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹) has allowed for a detailed characterization of the 6289-6526 cm⁻¹ region which corresponds to the lowest opacity of the transparency window. A list of 6868 and 4555 transitions with intensities as weak as 1 × 10⁻²⁹ cm/molecule was constructed from the recordings at 297 and 79 K, respectively. By comparison with a spectrum of CH₃D recorded separately by Fourier Transform Spectroscopy, 1282 and 640 transitions of monodeuterated methane, CH₃D, in natural abundance in our sample were identified at 297 and 79 K, respectively.The rotational temperature determined from the intensity distribution of the 3ν₂ band of CH₃D (79.3 K) was found in good agreement with the temperature value previously obtained from the Doppler line broadening. The reduction of the rotational congestion by cooling down to 79 K reveals a spectral region near 6300 cm⁻¹ where CH₃D transitions are dominant.The low energy values of the transitions observed both at 79 K and at room temperature were derived from the variation of their line intensities. These transitions with lower energy determination represent 93.9% and 68.4% of the total absorbance in the region, at 79 K and room temperature, respectively. The quality of the obtained empirical low energy values is demonstrated for CH₄ by the marked propensity of the empirical low J values to be close to integers. The line lists at 79 K and room temperature provided as Supplementary Material allow accounting for the temperature dependence of methane absorption between these two temperatures. The investigated region covering the 5ν₄ band of the ¹²CH₄ isotopologue will be valuable for the theoretical treatment of this band which is the lowest energy band of the icosad.