Studies on the photooxidation mechanism of polymers. IV. Effect of ultraviolet light (2537 Å) on solid PVC particles suspended in different liquids

The photolysis of virgin PVC powder suspended in water, methanol, n-hexane, aqueous NH₄OH (30 wt-%), and 0.1 wt-% iodine in methanol and also as dry powder was studied. The mechanism of photolysis of PVC powder has been investigated by using ESR spectroscopy, conductivity titration, gel-permeation chromatography (GPC), and absorption spectroscopy. Photolysis of PVC has been found to occur by a free-radical mechanism. ESR spectroscopy permits a partial identification of several different types of free radicals in PVC such as alkyl, polyenyl, and peroxy radicals. An interpretation is proposed of the mechanism of formation of conjugated polyene structures, and also a new explanation of the crosslinking mechanism, in which transfer of unpaired electrons to double bonds occurs, is suggested. It has also been found that conjugated double bonds can photosensitize free-radical formation as a result of increased ultraviolet absorption due to polyene structures.     

Alkylation of catechol with methanol to guaiacol over sulphate-modified zirconia solid acid catalysts

A series of sulphate-promoted ZrO₂ solid acid catalysts with different contents of SO₄ ²⁻ were calcined at 450°C in air for 4 h and tested for the liquid-phase alkylation of catechol to guaiacol in a fixed-bed down-flow reactor. The 5 wt.% SO₄ ²⁻ on ZrO₂ showed the best conversion (82%) and selectivity for guaiacol (84%) at 200°C and 1 bar pressure. A smooth correlation was observed between the catalytical activity and surface acidity of sulphated zirconia. Based on our results, a surface mechanism is proposed.     

Engineering education and industrial research and development-thepromise and the reality

The author observes that the social fabric of engineering, the support infrastructure of the profession, and the political and economic systems of the world are undergoing shifts that affect what engineering is, how it is accomplished, and what it should do. He asks what these changes mean in terms of the educational system and explores a few of these issues that lie between academia and the industrial environment beyond. He discusses the engineering curriculum as seen from industry, the role of continuing education, research in academia     

Quantum dot capped magnetite nanorings as high performance nanoprobe for multiphoton fluorescence and magnetic resonance imaging

In the present study, quantum dot (QD) capped magnetite nanorings (NRs) with a high luminescence and magnetic vortex core have been successfully developed as a new class of magnetic-fluorescent nanoprobe. Through electrostatic interaction, cationic polyethylenimine (PEI) capped QD have been firmly graft into negatively charged magnetite NRs modified with citric acid on the surface. The obtained biocompatible multicolor QD capped magnetite NRs exhibit a much stronger magnetic resonance (MR) T2* effect where the r2* relaxivity and r2*/r1 ratio are 4 times and 110 times respectively larger than those of a commercial superparamagnetic iron oxide. The multiphoton fluorescence imaging and cell uptake of QD capped magnetite NRs are also demonstrated using MGH bladder cancer cells. In particular, these QD capped magnetite NRs can escape from endosomes and be released into the cytoplasm. The obtained results from these exploratory experiments suggest that the cell-penetrating QD capped magnetite NRs could be an excellent dual-modality nanoprobe for intracellular imaging and therapeutic applications. This work has shown great potential of the magnetic vortex core based multifunctional nanoparticle as a high performance nanoprobe for biomedical applications.     

Improved error performance of a 3/4‐Sezginer space‐time block codes

The Alamouti space‐time block code (STBC) achieves full diversity gain at a rate of 1/2. However, the Alamouti scheme does not provide multiplexing gain. The Silver code offers both diversity and multiplexing gain. It has a minimum normalization determinant of . The Golden code is another STBC that offers both diversity and multiplexing gain. The Golden code is ranked higher than the Silver code because of its lower minimum normalization determinant of , however, the golden code suffers from a high detection complexity in the modulation order of M⁴. The 3/4‐Sezginer code is another STBC, which compromises between the Alamouti scheme and the Golden code in terms of diversity gain and multiplexing gain. The 3/4‐Sezginer code achieves full diversity and half of multiplexing gain. The uncoded space‐time labeling diversity (USTLD) is a recent scheme that improves the error performance when applied to the STBC in multiple‐input multiple‐output (MIMO) systems and will be applied to the 3/4‐Sezginer STBC to improve the error performance in this paper. The theoretical error probability for both the 3/4‐Sezginer STBC and the improved system is formulated using the union bound in this paper. The theoretical error probabilities of both 16‐QAM and 64‐QAM are validated through Monte Carlo simulation. The simulation and theoretical results show that the proposed system with 4 N_R can achieve an SNR gain of 1 dB for 16‐QAM and 1.2 dB 64‐QAM at a bit error rate (BER) of 10^?6.     

彩色负片印片颗粒指数的准确测定

分析了彩色负片印片颗粒指数σper实际测试中不同性能负片的测试特点和影响因素。印片颗粒指数的测试点应根据彩色负片的感光特性确定,为正常扩印时对应正片0．74中灰密度的负片密度点。影响印片颗粒指数值的两个主要因素是彩色相纸的反差修正系数α和彩色负片的覆盖力系数ECP;建立了α和ECP的实验求取方法,并通过对几种负片参量的实际测定,分析和说明了参量变化对印片颗粒指数数值的影响程度和应进行的修正。