An e.p.r. study of tetradentate Schiff base copper complexes with an N–(CH2)n–N,n = 3–6 backbone

Cu^II complexes of Schiff-base ligands with a general formulation o-HOC₆H₄CH=N–(CH₂) _n –N=CHC₆H₄OH-o, where n = 3–6 have been prepared and their e.p.r. spectra investigated in order to determine the effect of the flexible methylene backbone length on the structure. The room temperature and 77 K e.p.r. spectra of the compounds, n = 3 and 4, are typical of the axially symmetric ground state with g > g . When n = 5, on the other hand, the complex gives an isotropic spectrum at room temperature. For n = 6, g appears to be greater than g . The g _iso value increases gradually from n = 3 to n = 6 indicating deviation from planarity. Simulation of the 77 K spectrum for n = 6 shows the presence of two distinct Cu²⁺ sites of equal probability. The Q-band spectrum of this compound exhibits a narrowed g signal indicative of exchange coupling. The spectrum is a consequence of intermolecular electron exchange giving a pseudo d² _z state.     

Some new results regarding spikes and a heuristic for spike construction

This paper addresses the problem of minimizing the number of columns with superdiagonal nonzeroes (viz., spiked columns) in a square, nonsingular linear system of equations which is to be solved by Gaussian elimination. The exact focus is on a class of min-spike heuristics in which the rows and columns of the coefficient matrix are first permuted to block lower-triangular form. Subsequently, the number of spiked columns in each irreducible block and their heights above the diagonal are minimized heuristically.We show that ifevery column in an irreducible block has exactly two nonzeroes, i.e., is a doubleton, then there is exactly one spiked column. Further, if there is at least one non-doubleton column, there isalways an optimal permutation of rows and columns under whichnone of the doubleton columns are spiked.An analysis of a few benchmark linear programs suggests that singleton and doubleton columns can abound in practice. Hence, it appears that the results of this paper can be practically useful. In the rest of the paper, we develop a polynomial-time min-spike heuristic based on the above results and on a graph-theoretic interpretation of doubleton columns.     

Determination of chlorine in silicate rocks by neutron activation analysis

A simple radiochemical neutron activation analysis scheme has been developed for the determination of chlorine in silicate rocks. The method involves a 15-min thermal neutron irradiation of rock powder followed by a quick separation of ³⁸Cl as AgCl, and Ge(Li) spectrometry. Chemical yield, normally ranging between 95% and 100%, is monitored gravimetrically through the recovery of AgCl. The procedure has been tested on several geochemical standards to assess its accuracy and precision. The values obtained for standard rocks agree with the literature values. At the 100-ppm level, the analytical precision for chlorine is within ±5% (2σ).     

Mössbauer and X-ray investigations of YBa2−x Sn x Cu3O7−δ superconductors

Mössbauer spectra of YBa_2?x Sn _x Cu₃O_7?δ compounds withx=0.2 and 0.3 have revealed two components, both with isomer shifts corresponding to 4⁺ valency for Sn. The temperature dependence of the area of only one component shows an anomaly near the superconducting temperature for both samples, thus suggesting anisotropic behaviour for the lattice rigidity. In the case ofx=0.2 sample X-ray diffraction studies further indicate similar anomaly in the orthorhombic strain. It is concluded that such anomalies are precursors for the superconductivity to occur in these compounds.     

Possible observation of superconductivity at 300K

We report an observation of superconducting transition at 300K in fluorinated Y-Ba-Cu-O system for the first time.     

EPR of Mn2+ in cobalt fluosilicate hexahydrate

The EPR of Mn²⁺ in cobalt fluosilicate hexahydrate has been studied at room temperature. An axial spin-hamiltornian explained the observed spectrum. The presence of a single Mn²⁺ site in an octahedral oxygen environment was confirmed. A phase transition at ?55°C was observed.     

封装Fe(Ⅲ),Ni(Ⅱ)和Cu(Ⅱ)的N,N'-双邻羟苯亚甲基-1,2-苯二胺络合物的Y分子筛催化4-氯-3-甲基苯酚氧化反应

将Fe(Ⅲ),Ni(Ⅲ)和Cu(Ⅱ)与N,N'-双邻羟苯亚甲基-1,2-苯二胺配位的络合物封装在Y分子筛内,作为多相类Fenton的高级氧化过程的催化剂,用于降解4-氯-3-甲基苯酚(PCMC).采用粉末X射线衍射、热重、N2吸附-脱附、红外光谱、元素分析和扫描电镜对所制催化剂的物化性质进行了表征,并考察了H2O2的初始浓度、催化剂用量、温度和pH值等因素对模型有机污染物降解的影响.结果表明,在Fe(Ⅲ),Ni(Ⅲ)和Cu(Ⅱ)催化剂作用下,在较低的酸性pH值、催化剂用量0.1 g、H2O2的初始浓度0.35 mmol/L的条件下,于50℃反应120 min几乎可以完全去除PCMC.同时还考察了所制PCMC降解催化剂的重复使用性能,提出了可能的催化剂失活机理,也研究了PCMC氧化过程中可能的中间产物和动力学.     

Compact standing wave thermoacoustic generator for power conversion applications

In the past decade, a variety of thermoacoustic engines (TAEs) were devised to convert thermal energy to acoustic power. In this paper, we optimized the design of a standing wave thermoacoustic generator that can provide high intensity acoustic pressure and convert it into electrical power output using a low cost alternator. Three prototypes of standing wave thermoacoustic generator (TAG) were designed to optimize the overall efficiency. The first prototype of standing wave TAG could produce an acoustic pressure of 0.9 kPa (153 dB) with an input thermal power of 210 W. Further, the maximum heat to electrical conversion efficiency was 0.045% with an input thermal power of 250 W. However, the performance of this system was not fully optimized. The performance of TAE depends upon various parameters including stack position, stack length and resonator length. Hence, a new second prototype of tunable TAG was developed to tune these critical parameters in order to improve the overall efficiency. A compact third prototype of TAG was successfully built with optimized parameters and has been tested. In the improved design, high intensity acoustic pressure of 2.9 kPa (163.5 dB) was observed for the same 210 W input thermal power. The maximum heat to electrical energy conversion efficiency was 0.084% with an input of 250 W which is 87% higher as compared to the first prototype. The major reason for the lower conversion efficiency is due to the low efficiency of the alternator. In future, high efficiency alternator designs can be employed along with careful impedance matching to obtain higher conversion efficiencies. The results described in this paper demonstrate the potential of developing compact portable acoustic power and electricity generators for decentralized power applications.