The relative energies of polypeptide conformers predicted by linear scaling second-order Møller-Plesset perturbation theory

We describe an implementation of the cluster-in-molecule(CIM) resolution of the identity(RI) approximation second-order M?ller–Plesset perturbation theory(CIM-RI-MP2), with the purpose of extending RI-MP2 calculations to very large systems. For typical conformers of several large polypeptides, we calculated their conformational energy differences with the CIM-RI-MP2 and the generalized energy-based fragmentation MP2(GEBF-MP2) methods, and compared these results with the density functional theory(DFT) results obtained with several popular functionals. Our calculations show that the conformational energy differences obtained with CIM-RI-MP2 and GEBF-MP2 are very close to each other. In comparison with the GEBF-MP2 and CIM-RI-MP2 relative energies, we found that the DFT functionals(CAM-B3LYP-D3, LC-?PBE-D3, M05-2X, M06-2X and ?B97XD) can give quite accurate conformational energy differences for structurally similar conformers, but provide less-accurate results for structurally very different conformers.     

Class of tight bounds on the Q‐function with closed‐form upper bound on relative error

In this paper, we propose a novel class of parametric bounds on the Q‐function, which are lower bounds for 1 ≤ a < 3 and x > x_t = (a (a‐1) / (3‐a))^1/2, and upper bound for a = 3. We prove that the lower and upper bounds on the Q‐function can have the same analytical form that is asymptotically equal, which is a unique feature of our class of tight bounds. For the novel class of bounds and for each particular bound from this class, we derive the beneficial closed‐form expression for the upper bound on the relative error. By comparing the bound tightness for moderate and large argument values not only numerically, but also analytically, we demonstrate that our bounds are tighter compared with the previously reported bounds of similar analytical form complexity.     

基于前方交会的5点相对定向

5点相对定向是摄影测量与机器视觉的经典问题,传统的5点相对定向方法采用多项式求解技术,导致了解的多样性。为此,研究了基于前方交会约束的5点相对定向方法,建立包含前方交会约束的同名像点共面条件方程,推导求解5点相对定向问题的最优化目标函数,并采用最小二乘广义逆法求解。非量测相机Nikon D80的8组5点相对定向实验结果表明,该方法仅利用5个同名像点即可获得两张像片的相对位置(相对定向)立体模型,在测量长度为0.92 m的标尺三维(3D)长度时,其误差的标准不确定度为0.28±0.24 mm,与现有的5点算法相比,该方法无需排解即可确保5对同名射线对对相交,并且求解精度高,稳健性好,有实用价值。     

Molecular absorption spectrometry in flames and furnaces: A review

Molecular absorption spectrometry (MAS), originally developed in the 1970s, is a technique to determine non-metals in flames and graphite furnaces by monitoring the absorbance of diatomic molecules. Early studies employed low resolution instruments designed for line source atomic absorption, which provided a limited choice of analytical wavelengths, insufficient spectral resolution, and spectral interferences. However, the development of high-resolution continuum source atomic absorption spectrometry (HR-CS AAS) instrumentation has allowed the analysis of challenging samples for non-metals as well as some difficult elements to determine by AAS, such as aluminum and phosphorus. In this review, theory and analytical considerations for MAS are discussed. The principles and limitations of low resolution MAS are described, along with its applications. HR-CS AAS instrumentation is reviewed, emphasizing performance characteristics most relevant for MAS. Applications of flame and HR-CS GFMAS are reviewed, highlighting the most significant work to date. The paper concludes with an evaluation of the enhanced analytical capabilities provided by HR-CS MAS.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Highly sensitive capillary electrophoresis-mass spectrometry for rapid screening and accurate quantitation of drugs of abuse in urine

The combination of capillary electrophoresis (CE) and mass spectrometry (MS) is particularly well adapted to bioanalysis due to its high separation efficiency, selectivity, and sensitivity; its short analytical time; and its low solvent and sample consumption. For clinical and forensic toxicology, a two-step analysis is usually performed: first, a screening step for compound identification, and second, confirmation and/or accurate quantitation in cases of presumed positive results. In this study, a fast and sensitive CE-MS workflow was developed for the screening and quantitation of drugs of abuse in urine samples. A CE with a time-of-flight MS (CE-TOF/MS) screening method was developed using a simple urine dilution and on-line sample preconcentration with pH-mediated stacking. The sample stacking allowed for a high loading capacity (20.5% of the capillary length), leading to limits of detection as low as 2 ng mL⁻¹ for drugs of abuse. Compound quantitation of positive samples was performed by CE-MS/MS with a triple quadrupole MS equipped with an adapted triple-tube sprayer and an electrospray ionization (ESI) source. The CE-ESI-MS/MS method was validated for two model compounds, cocaine (COC) and methadone (MTD), according to the Guidance of the Food and Drug Administration. The quantitative performance was evaluated for selectivity, response function, the lower limit of quantitation, trueness, precision, and accuracy. COC and MTD detection in urine samples was determined to be accurate over the range of 10–1000 ng mL⁻¹ and 21–1000 ng mL⁻¹, respectively.     

An accurate and reliable analysis of trimethylamine using thermal desorption and gas chromatography–time of flight mass spectrometry

Trimethylamine (TMA) is well-known for manifesting the odor of rotting fish and urine. The analysis of TMA in environmental samples generally suffers from low reproducibility and poor sensitivity. In this study, a technique for the quantitative analysis of gas phase TMA was developed using thermal desorption (TD)-gas chromatography (GC)-time of flight mass spectrometry (TOF-MS). This new approach yielded good linearity (R² = 0.9930), precision (RSE = 1.59%), and high sensitivity with the method detection limit (MDL) of 51 pg, i.e., detection of 0.021 ppb of TMA at 1 L sample (limit of detection (LOD): 5.32 pg (0.002 ppb). This method was tested against gas samples collected from two representative sources of TMA: (1) rotten thornback fish and (2) cat urine-soaked clay. The concentration of TMA in these samples, when analyzed after treatment at varying dilution ratios, averaged 293 ± 29.7 ppm (RSE = 3.82%) and 74.1 ± 5.78 ppb (RSE = 3.19%), respectively. The feasibility of this approach, when tested with TD–GC–Quadruple (Q) MS, showed a good compatibility with moderately reduced sensitivity. The results of this study demonstrated that one can achieve highly reliable and reproducible analysis of TMA from environmental samples when using thermal desorption (for pretreatment) and detection (by the TOF or Q-MS system).     

Reactivity of Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide towards some carbon electrophiles. A comparative study

Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide 2a, 2b have different relative reactivities towards some carbon electrophiles had been discussed.The Z-isomer underwent cyclization to give imidazole derivative 3 and triazine derivative 4, whereas the latter E-isomer does not undergo such cyclization. The reaction of 2a and/or 2b with 1,2-dibenzylidene hydrazine at different reaction conditions afforded the Schiff bases 6, 8 and the triazolidine derivative 9. Reactions of 2a, 2b with formic acid and phthalic anhydride gave the different cyclization products 10–14, respectively. The structures of all the new synthesized compounds were established from their IR, ¹H-NMR and mass spectra as well as elemental analyses.     

一种高集成温湿度测量系统的研制

利用智能温湿度传感器、8位单片机、键盘数字显示模块控制器构成一种高集成温湿度测量系统,该测量系统具有传感器非线性补偿、温度补偿、自校准以及断电保护现场置入等功能,可用于温度、湿度和露点的精确测量。     

晶面选择性生长对球形氢氧化镍形貌及电化学活性的影响

在相同的物理化学条件、不同晶化时间的条件下,采用化学沉淀法制备球形氢氧化镍晶体并应用SEM技术分别考察制得样品的形貌。研究表明：在相同的物理化学条件下,随着晶化时间的增加,样品的微观形貌由不规则状晶体变为完整的球状晶体。结合XRD表征结果分析得出：（001）晶面在晶化时间达到3 h时生长到了一个稳定的状态,并不随着晶化时间的增加而有明显的变化,但（100）与（101）晶面随晶化时间的增加继续生长,当晶化时间达到12 h时氢氧化镍的相对结晶度最大,（100）与（101）衍射峰强度高且峰形尖锐,说明氢氧化镍晶体的结构规整性增强。本文还讨论了氢氧化镍生长结晶过程中晶面选择性生长对晶体形貌及电化学性能的影响。