Structural Deterioration of Well-Faceted MOFs upon H2S Exposure and Its Effect in the Adsorption Performance

The structural deterioration of archetypical, well-faceted metal–organic frameworks (MOFs) has been evaluated upon exposure to an acidic environment (H₂S). Experimental results show that the structural damage highly depends on the nature of the hybrid network (e.g., softness of the metal ions, hydrophilic properties, among others) and the crystallographic orientation of the exposed facets. Microscopy images show that HKUST-1 with well-defined octahedral (111) facets is completely deteriorated, ZIF-8 with preferentially exposed (110) facets exhibits a large external deterioration with the development of holes or cavities in the mesoporous range, whereas UiO-66-NH₂ with (111) exposed facets, and PCN-250 with (100) facets does not reflect any sign of surface damage. Despite the selectivity in the external deterioration, X-ray diffraction and gas adsorption measurements confirm that indeed all MOFs suffer an important internal deterioration, these effects being more severe for MOFs based on softer cations (e.g., Cu-based HKUST-1 and Fe-based PCN-250). These structural changes have inevitable important effects in the final adsorption performance for CO₂ and CH₄ at low and high pressures.     

X射线辐照后BaFC1中缺陷性质的研究

未掺Eu~(2+)的BaFCl粉末样品在80K下经X射线辐照后,在不同的温度条件下(从80K副273K),用580nm的光波激励样品时观测到310nm和380nm的发光峰.经分析认为,样品经X射线辐照后,在晶体中形成两种卤素离子的F-H’心对.当用F心吸收带的光波激励样品时,两种F—H心对衰变成相应的自陷激子态并复合发光.310nm和380nm分别对应于F-离子和Cl-离子的自陷激子的发光,并且它们的发光强度强烈地依赖于温度的变化。     

Frequency and effects of teachers'' voice problems

This study compared the frequency and effects of voice symptomsin teachers to a group of individuals employed in other occupations. Teachers were more likely to report having a voice problem (15 vs. 6%), having 10 specific voice symptoms, and having 5 symptoms of physical discomfort. They averaged almost 2 symptoms compared with none for nonteachers. Likewise, teachers were more likely to perceive that a voice problem would adversely affect their future career options, had done so in the past, and was limiting their current job performance. Over 20% of teachers but none of the nonteachers had missed any days of work due to a voice problem. These findings suggest that teaching is a high-risk occupation for voice disorders and that this health problem may have significant work-related and economic effects.     

贫金属星的表面丰度与慢中子俘获过程

在不依赖于特定恒星模型的前提下,采用参数化热脉冲模型,对三颗铅星的表面丰度进行了拟合计算.结果表明,无论是否考虑分叉道的影响,结果均能很好地重现观测数据.另外,铅星与非铅星的模型参量对比显示,铅星的平均中子辐照量远大于非铅星,而其挖掘程度明显小于非铅星.这说明尽管参数化热脉冲模型过于简单,但对约束恒星模型仍具有重要意义.     

Synthesis and characterization of negative‐type photosensitive hyperbranched polyimides with excellent organosolubility from an A2 + B3 monomer system

A series of photosensitive hyperbranched polyimides (HB‐PIs) were prepared through facile end‐group modifications of the fully imidized polymer. A triamine, 1,3,5‐tris(4‐aminophenoxy)benzene, and a dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, were condensed with a dropwise addition method in a molar ratio of 1/2 to afford an anhydride‐terminated poly(amic acid) precursor, which was then end‐capped by 4‐aminophenol and chemically imidized to yield a phenol‐terminated HB‐PI. The modifications of the terminal phenol groups of the polyimide by acyl chloride compounds (acryloyl chloride, methylacryloyl chloride, and cinnamoyl chloride) gave the target polymers. The photosensitive HB‐PIs showed good thermal properties and excellent solubility even in low‐boiling‐point solvents at room temperature, such as acetone, 1,1,2‐trichloroethane, tetrahydrofuran, and chloroform. Photosensitive property studies revealed good photolithographic properties with a resolution greater than 3 μm and a sensitivity of 650–680 mJ/cm². © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1735–1744, 2004     

Pulsed magnetic field exposure during pregnancy and implications for NMR foetal imaging: a study with mice

Following the recent progress in NMR imaging of the foetus in utero an investigation has been made of the effect of exposure to strong pulsed magnetic fields on the pregnancy of mice and the post natal development of their litters. 23 pregnant mice received exposures ranging from 3.5-12kT/s with pulse periods in the range 0.33-0.56ms at various times during gestation. A similar number of pregnant mice served as controls. No adverse effect was observed on the pregnancy. There was no significant difference between the litter numbers and growth rates of the exposed litters compared with controls. The implications of these results are discussed with regard to the safety of NMR imaging during pregnancy.     

Organotins: Toxicology and biological effects

Organotins are currently one of the most studied groups of organometallic compounds; their novel and often unique chemical properties have intrigued chemists for over 100 years and, today, many of these compounds find extensive use in agriculture and industry. Over the years, however, a number of the organotins have been demonstrated to be toxic and there is now increasing concern that their widespread use may cause adverse effects within environmental and biological systems. This article reviews and updates the current literature concerning organotin toxicology. It identifies the various target organs and systems, discusses mechanisms and species susceptibility, and directs the reader to additional sources of more specialized information as appropriate.     

Design of photonic band gap structures through a dual-beam multiple exposure technique

We present a dual-beam multiple exposure technique that can generate complex 2-D and 3-D band gap template structures in a photosensitive material. The system parameters related to the planar interference pattern produced by two laser beams and reorientation effect of the sample relative to these planes is presented. Structures such as the 2-D, square and hexagonal arrays of dielectric “rods” and “holes” and the 3-D, cubic, Yablonovite and other profiles are given. We perform band gap calculations on these structures when the dielectric contrast has been increased using a backfill process and discuss techniques for increasing the band gap by sculpting the dielectric profile.     

职业性铅接触与各生物接触参数间的关系评估

在对蓄电池厂１００名铅接触者的健康监护中，各项生物监测按规定的质量控制要求进行，并研究了其间的剂量效应关系，结果发现，空气中铅尘，铅烟低于最高容许多浓度，接触者的血铅，尿铅和ＦＥＰ呈非常显著相关（Ｐ〈０．０１），其中血铅有较好地定量反映接触铅工人体内的铅负荷，并提出了血铅的可接受水平。     

Voltammetric Determination of Urinary 1‐Hydroxypyrene Using Molecularly Imprinted Polymer‐Modified Screen‐Printed Carbon Electrodes

A two step non‐competitive affinity method for the trace determination of 1‐hydroxypyrene (1‐OHP) using a disposable molecularly imprinted polymer (MIP) modified screen‐printed carbon electrode (MIP‐SPCE) has been developed. The MIP was synthesized according to a novel strategy, which is described, and is capable of rebinding the phenolic analyte, 1‐hydroxypyrene (1‐OHP), from high pH aqueous organic media, via ionic interactions. In the first step of our method 1‐OHP was accumulated at the MIP‐SPCE from 35% aqueous methanol containing 0.014 M NaOH and 0.14 M NaCl, at open circuit. In the second step, the resulting SPCE with accumulated 1‐OHP was then transferred to fresh, clean phosphate buffered aqueous methanol, and subjected to cyclic voltammetry (CV) or differential pulse voltammetry (DPV). The latter technique proved to be more sensitive at detecting 1‐OHP, with a limit of detection of 182 nM and a linear range to 125 μM on unmodified electrodes. The possible effects of interference by related phenolic compounds in the MIP‐SPCE of 1‐OHP were investigated. Finally the method was evaluated by carrying out 1‐OHP determinations on spiked human urine samples; the recovery of 1‐OHP was 79.4% and the coefficient of variation was found to be 7.7% (n= 4) using a separate MIP‐SPCE for each determination. Therefore, the performance data suggests that the method is reliable at the concentrations examined in this study. The method was found to be superior to the direct determination of 1‐OHP in human urine by DPV alone, which was greatly affected by interference from uric acid.