力矩教学剖析

力矩在物理课教学中占有举足轻重的地位．力矩的概念并不难理解，但应用起来却涉及到很多知识点，且能翻出不少新花样．让我们来看下面的问题：放在地面上的板条箱(如图)，受到R=120N力的作用．试求该力对点A的力矩：(1)根据力臂计算；(2)根据该力在作用点B处的分力计算；(3)根据该力在作用线上其它某一适当点处的分力计算．     

Laser lineshape effects on cavity-enhanced absorption spectroscopy signals

The quantitative effects of laser lineshape on signals from cavity-enhanced absorption spectroscopy (CEAS) and integrated cavity output spectroscopy (ICOS) experiments are examined. The governing equations for CEAS signals including the laser lineshape are derived. Approximations under which the laser lineshape may be neglected or replaced with an effective lineshape are presented. It is shown that the laser lineshape effects may be parameterized with two dimensionless variables: the laser linewidth normalized by the absorption linewidth, and the peak sample absorbance normalized by the mirror loss. In terms of the dimensionless variables, we simulate CEAS and ICOS signals and the absorbances inferred from them. The simulation results provide a useful tool for CEAS and ICOS practitioners to gauge the importance of laser lineshape effects in specific experiments. Simulations are performed for the four combinations of Gaussian and Lorentzian lineshapes for the laser and the absorption. PACS 42.62.Fi; 78.40.-q; 32.70.Jz     

Determination of 17 kinds of banned organochlorine pesticides in water by activated carbon fiber-solid phase microextraction coupled with GC-MS.

Activated carbon fiber (ACF) as extraction fiber for solid-phase microextraction (SPME) and its application for the analysis of banned organochlorine pesticides (OCPs) were investigated. Firstly, ACF was activated by different concentration of zinc chloride, which indicated that ACF activated by 60% zinc chloride had a reasonable specific surface area, pore volume and pore distribution. Secondly, the parameters for the ACF-SPME procedure, the adsorption and desorption conditions, were also optimized when coupled with gas chromatography-mass spectrometry (GC-MS). Thirdly, the ACF-SPME was used to analyze 17 kinds of OCPs in water. The linearity of most pesticides was found to be between 0.2 and 50 microg/l with GC-MS under the selected ion monitoring (SIM) acquisition mode. The limits of detection (LOD) at the sub microg/l were obtained. The work demonstrated here shows that ACF is a promising alternative for the SPME procedure.     

A comparative study on photo-induced electron transfer from fluorescein to anthraquinone and injection into colloidal TiO2

A dyad-anthraquinone-methyl ester of fluorescein-and its model compound-butyl ester-were synthesized. The effects of photo-induced electron transfer from fluorescein to an organic anthraquinone acceptor and injection into inorganic colloidal TiO(2) were studied respectively. It is found that the photo-induced electron transferring to an organic acceptor is much faster than injecting into inorganic colloidal particles when fluorescein was excited by visible light. While inorganic colloidal TiO(2) was excited by UV, the electron of fluorescein will inject into TiO(2).     

DNA Degradation of Genetically Modified Cottonseed Meal During Feed Processing

The effects of dry heating, wet heating, and extrusion on the degradation of DNA in cottonseed meal (CSM) were studied using polymerase chain reaction (PCR) and real-time PCR approach. Both the sad1 DNA, ranging between 128 and 883 bp in size, and the cry1Ab/c gene, ranging between 183 and 652 bp in size, were detectable in all dry-heated CSM and cottonseed. During wet heating, the sad1 gene (≥883 bp) and the cry1Ab/c (≥952 bp) gene were thoroughly degraded at 105 and 120 °C, respectively. Sizes from 128 to 530 bp for the sad1 gene and sizes from 183 to 652 bp for the cry1Ab/c gene were detected during extrusion at temperatures ranging from 75 to 135 °C. Fragments ≤883 bp for the sad1 gene and ≤952 bp for the cry1Ab/c gene were detected in all of the extruded samples with water content varying between 26 and 34 %. The copy number ratio of cry1Ab/c to sad1 in samples of Bt cottonseed meal decreased rapidly when the temperature increased during the heating process. In conclusion, feed processing markedly degrades the larger DNA fragments of sad1 and cry1Ab/c, with high temperature and water content being the main factors for that degradation.     

Synthesis,structural characterization and catalytic activity of benzimidazole‐functionalized Pd(II) N‐heterocyclic carbene complexes

Two Pd(II)–NHC complexes bearing benzimidazole and pyridine groups have been successfully prepared and fully characterized by NMR and X‐ray diffraction analysis. The structure of palladium complexes are a typical square‐planar with palladium surrounded by two pairs of trans‐arranged benzimidazole and carbene ligands. The Pd–NHC complexes have been proved to be a highly efficient catalyst for the Mizoroki–Heck coupling reaction of aryl halides with various substituted acrylates under mild conditions in excellent yields. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitative analysis and pharmacokinetics study of tigecycline in human serum using a validated sensitive liquid chromatography with tandem mass spectrometry method

Tigecycline, a novel intravenously administered glycylcycline antibiotic, currently plays a key role in the management of complicated multiorganism infections. However, current liquid chromatography with tandem mass spectrometry methods briefly describe parameters and the only reported internal standard was sometimes difficult to obtain. In our study, an updated liquid chromatography with tandem mass spectrometry method for the quantitative analysis of tigecycline in human serum was developed. Sample preparation involved precipitation with 20% trichloroacetic acid. Chromatographic separation of tigecycline and tetracycline (internal standard) was achieved on a Hypersil GOLD C₁₈ column using gradient elution. The selected reaction monitoring transitions were performed at m/z 586.1→513.2 for tigecycline and m/z 445.1→410.2 for tetracycline. The assay was linear over the concentration range of 5–2000 ng/mL. The intra‐ and interday precisions at three concentration levels (10, 100, and 1600 ng/mL) were <15% and their accuracies were within the range of 95.1–106.1%. The mean recovery ranged from 94.3 to 105.6% and the matrix effect from 92.1 to 97.6%. Tigecycline was stable under all tested conditions. This validated method was successfully applied to a pharmacokinetic study in critically ill patients. The data demonstrated that our method allows quantification of tigecycline in serum in a quick and reliable manner for widespread application.     

Determination of Thermal History by Photoluminescence of Core‐Shelled Quantum Dots Going Through Heating Events

A kind of novel thermal history nanosensors are theoretically designed and experimentally demonstrated to permanently record thermal events. The photoluminescence (PL) spectrum of core‐shelled quantum dots (QDs) CdSe/ZnS irreversibly shifts with heating histories (temperature and duration) of thermal events. The induced PL shift of the QDs CdSe/ZnS is employed to permanently record thermal histories. We further model a kind of thermal history nanosensor based on the thermal‐induced phenomena of core‐shelled QDs to permanently record thermal histories at microscale and demonstrate to reconstruct temperature and duration of heating events simultaneously from PL spectra of the QDs. The physical mechanism of the sensors is discussed.     

胆红素在纳米TiO2膜上的吸附行为研究

采用石英晶体微天平现场技术,研究了胆红素在纳米TiO2表面的吸附动力学行为,并考察了溶液pH、硅烷亲脂性试剂及金属离子修饰的纳米TiO2对胆红素吸附的影响。结果表明,胆红素在纳米TiO2表面的吸附平衡常数K为2·0×106L/mol;由于亲水性纳米TiO2表面的羟基和胆红素分子中的羧基发生作用,胆红素吸附量随溶液pH增大而增大;但经过硅烷试剂亲脂性修饰后,吸附量随pH增大而下降;经过金属离子修饰后,改变了TiO2表面电荷导致吸附量增加,且吸附量随金属离子电荷增加而增加,当金属离子所带电荷相同时,吸附量基本相同。     

Treatment of mature landfill leachate by a continuous modular internal micro-electrolysis Fenton reactor

A modular internal micro-electrolysis Fenton reactor (MIME-Fenton) was specifically designed in order to facilitate the performance of internal micro-electrolysis (IME) technology in the treatment of mature landfill leachate. Excellent COD removal efficiency of 90.9 % by the new reactor of mature landfill leachate was observed in bench-scale treatment, which is 193–399, 415–551, and 226–457 % higher than that of conventional treatments of electrolysis, coagulation–sedimentation, and Fenton, respectively. The innovative concept behind the excellent performance is the novel two-step treatment, similar to the anaerobic–aerobic activated sludge method. It is based on a combination effect of reductive IME and oxidative IME with aeration processes and the integration of electro-aggregation and electro-coagulation. Initial pH and air flow rate were optimized, and the effect of auxiliary in situ regeneration of ferrous iron and generation of H₂O₂ was further investigated. The reactor was also particularly efficient in removal of color and HA, and in improvement of the BOD₅/COD ratio. All these results show that the MIME-Fenton reactor, a new approach of IME, is promising for mature landfill leachate treatment because it is efficient and easy to operate.