PHASE-TRANSFER SYNTHESIS OF OPTICALLY PURE OXETANES OBTAINED FROM 1,2,2-TRISUBSTITUTED 1,3-PROPANEDIOLS

Treatment of the 3-monomethanesulfonates of 1,2,2-trisubstituted 1,5-propanediols under phase-transfer conditions affords 2-aryl (or alkyl)-3,3-dialkyloxetanes. Twelve oxetanes have been obtained by this method; three of these oxetanes have been obtained enantiomerically pure as both enantiomers starting from the appropriate enantiomerically pure 1,3-diols. In these reactions the chiral center does not undergo inversion and the oxetanes have the same absolute configuration as the starting 1,3-diols.</p

Acid Catalyzed Ring-opening Reactions of Optically Pure 2-Aryl-3,3-dimethyloxetanes

Some ring-opening reactions of optically pure 2-aryl-3,3-dimethyl oxetanes have been examined under strongly protic or Lewis acid conditions. Ring-opening occurred at the benzylic position and partial inversion of configuration was observed in the case of hydrolysis or alcoholysis of the optically pure oxetanes catalyzed by H2SO4. The acid concentration affects the degree of inversion of configuration in water or methanol. On reaction with n-butyllithium or lithium thiolates aided by Lewis acid (BF3.ether) the corresponding β-substituted benzyl alcohols were obtained. Substitution now occurs at the least hindered carbon and the configuration of the asymmetric center remains unaffected

Coupling of RF Antennas to Large Volume Helicon Plasma

Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasma-material interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of $0.5$~m, and exploring its frequency dependence in the range of $13.56-70$~MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important reference for the experimental design of large volume helicon plasma source with high RF power

A review for solar panel fire accident prevention in large-scale PV applications

Due to the wide applications of solar photovoltaic (PV) technology, safe operation and maintenance of the installed solar panels become more critical as there are potential menaces such as hot spot effects and DC arcs, which may cause fire accidents to the solar panels. In order to minimize the risks of fire accidents in large scale applications of solar panels, this review focuses on the latest techniques for reducing hot spot effects and DC arcs. The risk mitigation solutions mainly focus on two aspects: structure reconfiguration and faulty diagnosis algorithm. The first is to reduce the hot spot effect by adjusting the space between two PV modules in a PV array or relocate some PV modules. The second is to detect the DC arc fault before it causes fire. There are three types of arc detection techniques, including physical analysis, neural network analysis, and wavelet detection analysis. Through these detection methods, the faulty PV cells can be found in a timely manner thereby reducing the risk of PV fire. Based on the review, some precautions to prevent solar panel related fire accidents in large-scale solar PV plants that are located adjacent to residential and commercial areas