Simultaneous determination of tetracyclines and their degradation products in environmental waters by liquid chromatography–electrospray tandem mass spectrometry

A sensitive method was developed for the trace determination of six tetracyclines and ten of their degradation products in influent, effluent, and river waters using liquid chromatography–electrospray tandem mass spectrometry detection, combined with Oasis hydrophilic–lipophilic balance (HLB) cartridge extraction and Oasis mixed-mode strong anion exchange (MAX) cartridge cleanup. Tetracyclines and their products were separated by liquid chromatography in 9.5 min, and the instrument detection limits were generally between 0.03 and 0.1 μg/L except for minocycline (0.5 μg/L). The chromatograms were improved through the MAX cleanup and no apparent matrix effect was found. The recoveries of all the target compounds except for 4-epianhydrochlortetracycline and anhydrochlortetracycline (34–52%) were 75–120% for influent, 61–103% for effluent, and 64–113% for river waters. The method detection limits (MDLs) of the analytes varied in the range of 0.8–17.5 ng/L in all studied matrices. The method was applied for the determination of tetracyclines and their products in a sewage treatment plant (STP) and surface waters in Beijing, China. Oxytetracycline (3.8–72.5 ng/L), tetracycline (1.9–16.5 ng/L), and five products including 4-epitetracycline, 4-epioxytetracycline, isochlortetracycline, anhydrotetracycline, and 4-epianhydrochlortetracycline (5.7–25.3 ng/L) were detected in wastewater, while only oxytetracycline and tetracycline (2.2 and 2.1 ng/L) were detected in surface water samples.     

Hermite Subdivision Schemes and Taylor Polynomials

We propose a general study of the convergence of a Hermite subdivision scheme ℋ of degree d>0 in dimension 1. This is done by linking Hermite subdivision schemes and Taylor polynomials and by associating a so-called Taylor subdivision (vector) scheme . The main point of investigation is a spectral condition. If the subdivision scheme of the finite differences of is contractive, then is C ⁰ and ℋ is C ^d . We apply this result to two families of Hermite subdivision schemes. The first one is interpolatory; the second one is a kind of corner cutting. Both of them use the Tchakalov-Obreshkov interpolation polynomial.      

激光诱导击穿光谱对焊缝熔合区的元素成分分布分析

激光诱导击穿光谱(LIBS)是近十几年来快速发展的一种新的表面分析工具,由于具有分析速度快、灵敏度高等优点,故在材料科学领域引起广泛的关注。文中采用LIBS、扫描电子显微镜／能谱仪(SEM/EDS)和电子探针显微分析(EPMA)三种分析方法,对两类不同焊缝的熔合线区域进行线扫描分析,研究了Ni,Mn,C,Si等元素在熔合线区域含量的变化情况。结果表明,对于含量较高且焊缝和母材成分差别较大的Ni和Mn元素,三种方法获得了一致的分析结果,两试样焊缝内的Ni和Mn含量均高于母材,在熔合线区域明显体现出浓度梯度分布。三种方法根据Ni和Mn的浓度分布测得的熔合线区宽度值比较接近。对于含量较低且焊缝和母材成分差别较小的C和Si元素,采用SEM/EDS和EPMA时,焊缝与母材之间的成分差异没有分析出来;而采用LIBS时,两区域的成分差异则可以清晰的展现出来,在熔合区域能够清楚观察到浓度梯度分布曲线。LIBS的分析灵敏度明显高于SEM/EDS和EPMA,在分析低含量元素时更具优势。     

Adiabatic shear banding and scaling laws in chip formation with application to cutting of Ti–6Al–4V

The phenomenon of adiabatic shear banding is analyzed theoretically in the context of metal cutting. The mechanisms of material weakening that are accounted for are (i) thermal softening and (ii) material failure related to a critical value of the accumulated plastic strain. Orthogonal cutting is viewed as a unique configuration where adiabatic shear bands can be experimentally produced under well controlled loading conditions by individually tuning the cutting speed, the feed (uncut chip thickness) and the tool geometry. The role of cutting conditions on adiabatic shear banding and chip serration is investigated by combining finite element calculations and analytical modeling. This leads to the characterization and classification of different regimes of shear banding and the determination of scaling laws which involve dimensionless parameters representative of thermal and inertia effects. The analysis gives new insights into the physical aspects of plastic flow instability in chip formation. The originality with respect to classical works on adiabatic shear banding stems from the various facets of cutting conditions that influence shear banding and from the specific role exercised by convective flow on the evolution of shear bands. Shear bands are generated at the tool tip and propagate towards the chip free surface. They grow within the chip formation region while being convected away by chip flow. It is shown that important changes in the mechanism of shear banding take place when the characteristic time of shear band propagation becomes equal to a characteristic convection time. Application to Ti–6Al–4V titanium are considered and theoretical predictions are compared to available experimental data in a wide range of cutting speeds and feeds. The fundamental knowledge developed in this work is thought to be useful not only for the understanding of metal cutting processes but also, by analogy, to similar problems where convective flow is also interfering with adiabatic shear banding as in impact mechanics and perforation processes. In that perspective, cutting speeds higher than those usually encountered in machining operations have been also explored.     

Investigation of elemental shape for 3D DEM modeling of interaction between soil and a narrow cutting tool

Discrete Element Method (DEM) has been applied in recent studies of soil cutting tool interactions in terramechanics. Actual soil behavior is well known to be inexpressible by simple elemental shapes in DEM, such as circles for 2D or spheres for 3D because of the excessive rotation of elements. To develop a more effective model for approximating real soil behavior by DEM, either the introduction of a rolling resistance moment for simple elemental shape or the combination of simple elements to form a complex model soil particle shape cannot be avoided. This study was conducted to investigate the effects of elemental shape on the cutting resistance of soil by a narrow blade using 3D DEM. Six elemental shapes were prepared by combining unit spheres of equal elemental radius. Moreover, cutting resistance was measured in a soil bin filled with air-dried sand to collect comparative data. The elemental shape, with an axial configuration of three equal spheres overlapped with each radius, showed similar results of soil cutting resistance to those obtained experimentally for the six elemental shapes investigated.     

爆破冲击对早龄期混凝土强度影响的实验研究

以某大型全碎石填方机场工程为背景,针对早龄期混凝土受爆破振动损伤开展了实验研究。通过室内实验模拟场地爆破振动作用于早龄期混凝土试块,测量了不同龄期混凝土受振损伤后的强度。并将实验结果与有限元数值计算和现场爆破场地测试数据相结合,分析了早龄期混凝土损伤后的强度增长规律,建立了场地爆破与混凝土结构浇筑平行施工的安全技术指标。     

岩石爆破开挖诱发振动的等效模拟方法

岩石爆破开挖过程中爆炸荷载的复杂性、岩石介质模型的多变性、本构方程的多样性、以及群孔爆 破模拟计算工作量巨大等诸多因素使得准确模拟爆破诱发的围岩振动存在较大的困难,鉴于此提出一种等 效数值模拟方法。根据爆破过程炮孔周围岩石破坏范围的空间分布特征,确定群孔起爆条件下爆炸荷载作用 的等效弹性边界;通过分析炸药起爆后炮孔空腔动力膨胀、岩体裂纹扩展、炮孔堵塞物运动以及爆生气体的逸 出,计算了等效边界上沿炮孔轴向变化的爆炸荷载。结合瀑布沟水电站1# 尾水隧洞爆破开挖监测,基于动力 有限元法运用该等效技术模拟了围岩的质点振动速度。数值模拟与现场实测数据的对比表明该等效模拟技 术用于岩石爆破开挖围岩响应的计算是合适的。计算结果同时还显示,等效边界邻近岩体力学参数的选取对 计算结果有重要影响。     

超小自聚焦光纤探头的研究进展

梯度折射率（Gradient-index,GRIN）光纤探头是一种全光纤型超小光学镜头,在心血管等狭小空间组织内窥影像检测中具有广阔的应用前景。但其发展一直缺少系统的理论体系。本文讨论探头设计、制作和性能测试等方面的关键问题。基于GRIN光纤探头聚焦性能的特征参数,对解析设计方法与数值仿真设计方法进行比较分析。针对超小GRIN光纤探头的制作难题,研究一种光纤熔接和切割的高精度一体化集成装置,描述GRIN光纤探头的制作方法。此外,分析了超小GRIN光纤探头聚焦性能检测的方法及装置。本文为超小GRIN光纤探头的设计、制作及性能测试提供了一个方法体系。     

晶硅片切割用水基切割液摩擦学性能的研究

重点研究了晶硅片切割用水基切割液中润滑剂的摩擦性能影响因素.选用低分子量的聚乙二醇(PEG)作为润滑剂,研究了不同分子量PEG作为润滑剂的摩擦学性能.在使用PEG300作为水基切割液润滑剂的情况下,相比纯水可减小硅片表面的粗糙度达86.51;;磨损体积可以减少50;,磨损表面磨屑变少.     

一种爆炸二极管机理研究及熄爆通道尺寸对其性能的影响

依据爆炸逻辑元件的工作原理设计了一种爆炸二极管。实验研究了元件内部结构,确定了关键参数为熄爆通道的长度、隔爆序列。隔爆序列内采用激发装置、一次PETN装药、两次PETN装药不同密度分层装药序列。在A、B端连接导爆索,改变熄爆通道尺寸, 确定分层装药参数,进行传爆可靠性、隔爆安全性实验。结果表明:爆轰信号由A端正向输入时,可以顺利通过10~35 mm的熄爆通道并且可靠引爆B端导爆索,满足可靠性功能;爆轰信号由B端反向输入,在熄爆通道长度为15~35 mm时,爆轰信号在通过隔爆序列、熄爆通道时被可靠阻断无法引爆A端导爆索,满足隔爆安全性功能。最终元件选取长度为15~35 mm的熄爆通道, 确定不同密度分层装药参数作为设计标准。应用于爆破网络设计中,使爆轰波信号在网络中单向传播,增加了网络的安全性。