An overview of analytical methodologies for the determination of antibiotics in environmental waters

The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes.     

Surface composition of alloys

The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success.     

SAD phasing by OASIS at different resolutions down to 0.30nm and below

Single-wavelength anomalous diffraction (SAD) phasing is increasingly important in solving de novo protein structures. Direct methods have been proved very efficient in SAD phasing. This paper aims at probing the low-resolution limit of direct-method SAD phasing. Two known proteins TT0570 and Tom70p were used as test samples. Sulfur-SAD data of the protein TT0570 were collected with conventional Cu-K\alpha source at 0.18nm resolution. Its truncated subsets respectively at 0.21, 0.30, 0.35 and 0.40nm resolutions were used in the test. TT0570 Cu-K$\alpha$ sulfur-SAD data have an expected Bijvoet ratio <\vert\Delta F\vert>/\ \sim 0.55%. In the 0.21nm case, a single run of OASIS-DM-ARP/wARP led automatically to a model containing 1178 of the total 1206 residues all docked into the sequence. In 0.30 and 0.35nm cases, SAD phasing by OASIS-DM led to traceable electron density maps. In the 0.40nm case, SAD phasing by OASIS-DM resulted in a degraded electron density map, which may be difficult to trace but still contains useful secondary-structure information. Test on real 0.33nm selenium-SAD data of the protein Tom70p showed that even automatic model building was not successful, the combination of manual tracing and direct-method fragment extension was capable of significantly improving the electron-density map. This provides the possibility of effectively improving the manually built model before structure refinement is performed.     

Challenges of sulfur SAD phasing as a routine method in macromolecular crystallography

The sulfur SAD phasing method allows the determination of protein structures de novo without reference to derivatives such as Se‐methionine. The feasibility for routine automated sulfur SAD phasing using a number of current protein crystallography beamlines at several synchrotrons was examined using crystals of trimeric Achromobacter cycloclastes nitrite reductase (AcNiR), which contains a near average proportion of sulfur‐containing residues and two Cu atoms per subunit. Experiments using X‐ray wavelengths in the range 1.9–2.4 Å show that we are not yet at the level where sulfur SAD is routinely successful for automated structure solution and model building using existing beamlines and current software tools. On the other hand, experiments using the shortest X‐ray wavelengths available on existing beamlines could be routinely exploited to solve and produce unbiased structural models using the similarly weak anomalous scattering signals from the intrinsic metal atoms in proteins. The comparison of long‐wavelength phasing (the Bijvoet ratio for nine S atoms and two Cu atoms is ～1.25% at ～2 Å) and copper phasing (the Bijvoet ratio for two Cu atoms is 0.81% at ～0.75 Å) for AcNiR suggests that lower data multiplicity than is currently required for success should in general be possible for sulfur phasing if appropriate improvements to beamlines and data collection strategies can be implemented.     

A comparison of SAD and two‐wavelength MAD phasing for radiation‐damaged Se‐MET crystals

Although a case has been made that single‐wavelength anomalous dispersion (SAD) is the optimal strategy for data collection in the presence of radiation damage, two‐wavelength MAD experiments at the inflection and a high‐energy remote point of the absorption edge have been shown to be a potentially successful alternative method. In order to further investigate the performance of both data collection strategies, a comparison of SAD and MAD phasing was carried out for increasingly damaged data sets from three different seleno‐methionine protein samples collected under similar experimental conditions. In all but one example the MAD phases appeared to be less affected than SAD phases with increasing exposure to X‐rays, and had a better overall success rate, indicating that this method should be given serious consideration when dealing with radiation‐sensitive crystals. Simultaneous data collection in wedges at all wavelengths seems to be a very important factor in the success of MAD experiments; the decreased absorbed dose resulting from eschewing data collection at the maximum f ′′ wavelength may play a less important role. Specific radiation damage to the selenium atoms is found to be a minor effect compared with the effect on the anomalous dispersion signal, although potentially large enough to be a useful contribution to phasing in both SAD and MAD experiments.     

New developments in the extraction and determination of parabens in cosmetics and environmental samples. A review

Parabens are a family of synthetic esters of p-hydroxibenzoic acid widely used as preservatives in cosmetics and health-care products, among other daily-use commodities. Recently, their potential endocrine disrupting effects have raised concerns about their safety and their potential effects as emerging pollutants, leading to the regulation of the presence of parabens in commercial products by national and trans-national organizations. Also, this has led to an interest in developing sensible and reliable methods for their determination in environmental samples, cosmetics and health-care products.     

基于扩展目标的不变矩跟踪算法

 提出基于边缘区域的不变矩计算方法，在此基础上，针对在运动中形状、尺寸和方位不断变化的扩展目标，提出一种以不变矩作为跟踪特征，粗、精阶段相结合的相关跟踪算法，并根据目标图像的相关性给出一种新的跟踪置信度。实验结果显示算法迅速、有效、匹配精度高，对于复杂背景，较强噪声和运动状态发生变化条件下的扩展目标跟踪稳定可靠。     

纳米氢氧化镍粒子微乳液/反相胶团法制备与表征

微乳液为制备纳米级材料提供了良好的微环境。文章首次分别采用微乳液法与反相胶团法合成了纳米β－Ni（OH）2和纳米a－Ni（OH）2；采用粉末晶体衍射、透射电镜和选区电子衍射对纳米氢氧化镍颗粒进行了表征。粉末晶体衍射与透射电镜分析表明这两种纳米颗粒的基本直径为10nm。选区电子衍射表明，两种纳米颗粒主要由多晶结构组成，同时其 表面还存在有非晶氢氧化镍。非晶相的产生是由于快速成核的氢氧化镍颗粒在表面活性剂的作用下，长大的速度被迅速“冻结”而形成的。     

A wavelet-based forward BSS algorithm for acoustic noise reduction and speech enhancement

In this paper, we address the problem of noise reduction and speech enhancement by adaptive filtering algorithm. Recently, the well known forward blind source separation (FBSS) structure has been largely studied and intensively used to reduce acoustic noise components and to enhance speech signal. The FBSS structure is often combined with adaptive algorithms to accelerate the adaptation of the cross-filters, and to improve noise suppression at the output. In this paper, we propose to use a wavelet transform decomposition in the FBSS structure by using a two-channel forward wavelet symmetric adaptive decorrelating (WFSAD) algorithm. The proposed WFSAD algorithm provides a better compromise between time and frequency resolution and improves robustness of the noise reduction process when compared with the classical two-channel forward symmetric adaptive decorrelating (FSAD) algorithm. Simulation results prove the efficiency of the proposed WFBSS algorithm in comparison with conventional ones in terms of several objective and subjective criteria.     

SAD phasing by OASIS at different resolutions down to 0.30 nm and below

Single-wavelength anomalous diffraction （SAD） phasing is increasingly important in solving de novo protein structures. Direct methods have been proved very efficient in SAD phasing. This paper aims at probing the low-resolution limit of direct-method SAD phasing. Two known proteins TT0570 and Tom70p were used as test samples. Sulfur-SAD data of the protein TT0570 were collected with conventional Cu-Kα source at 0.18 nm resolution. Its truncated subsets respectively at 0.21, 0.30, 0.35 and 0.40 nm resolutions were used in the test. TT0570 Cu-Kα sulfur-SAD data have an expected Bijvoet ratio 〈 ｜△F｜ 〉 / 〈 F 〉 ～ 0.55%. In the 0.21 nm case, a single run of OASIS-DM-ARP/wARP led automatically to a model containing 1178 of the total 1206 residues all docked into the sequence. In 0.30 and 0.35 nm cases, SAD phasing by OASIS-DM led to traceable electron density maps. In the 0.40 nm case, SAD phasing by OASIS-DM resulted in a degraded electron density map, which may be difficult to trace but still contains useful secondary-structure information. Test on real 0.33 nm selenium-SAD data of the protein Tom70p showed that even automatic model building was not successful, the combination of manual tracing and direct-method fragment extension was capable of significantly improving the electron-density map. This provides the possibility of effectively improving the manually built model before structure refinement is performed.