Thermal decomposition of iron(VI) oxides, K2FeO4 and BaFeO4, in an inert atmosphere

The thermal decomposition of solid samples of iron(VI) oxides, K₂FeO₄·0.088 H₂O (1) and BaFeO₄·0.25H₂O (2) in inert atmosphere has been examined using simultaneous thermogravimetry and differential thermal analysis (TG/DTA), in combination with in situ analysis of the evolved gases by online coupled mass spectrometer (EGA-MS). The final decomposition products were characterized by ⁵⁷Fe Mössbauer spectroscopy. Water molecules were released first, followed by a distinct decomposition step with endothermic DTA peak of 1 and 2 at 273 and 248 °C, respectively, corresponding to the evolution of molecular oxygen as confirmed by EGA-MS. The released amounts of O₂ were determined as 0.42 and 0.52 mol pro formula of 1 and 2, respectively. The decomposition product of K₂FeO₄ at 250 °C was determined as Fe(III) species in the form of KFeO₂. Formation of an amorphous mixture of superoxide, peroxide, and oxide of potassium may be other products of the thermal conversion of iron(VI) oxide 1 to account for less than expected released oxygen. The thermogravimetric and Mössbauer data suggest that barium iron perovskite with the intermediate valence state of iron (between III and IV) was the product of thermal decomposition of iron(VI) oxide 2.     

Cooperative spectrum sensing based on a modified shuffled frog leaping algorithm in 5G network

The explosion of different types of wireless communications is leading to an impending spectrum famine. As a result, spectrum sensing has gained increasing interest from governments, industry and regulators. In this paper, a novel approach for cooperative spectrum sensing is proposed based on a modified shuffled frog leaping algorithm (SFLA). This approach is to fuse the perceived results of multiple nodes, and to improve the detection reliability. Simulations are used to compare the performance of the modified SFLA to the conventional one. The performance of the proposed cooperative spectrum sensing method based on the modified SFLA and that of the cooperative spectrum sensing method using modified deflection coefficient (MDC) are also compared. Results show that the proposed SFLA outperforms the traditional SFLA, and the proposed cooperative spectrum sensing method based on the modified SFLA gives higher miss detection probability than the MDC-based method, which validates the effectiveness of the modified SFLA-based cooperative sensing method.     

A review on the synthesis of heteroannulated quinolones and their biological activities

Molecular Diversity - The quinoline scaffold has become an important construction motif for the development of new drugs. The quinolones and their heteroannulated derivatives have high importance...     

Synthesis of a 2,2'-bipyridyl functionalized oligovinylene-phenylene using Heck and Horner-Wadsworth-Emmons reactions and X-ray crystal structure of E-(4-(4-bromostyryl)phenyl)(methyl)sulfane

The synthesis of a new 2,2'-bipyridyl functionalized oligovinylenephenylene (OVP-5) containing a methyl protected thiol using Heck coupling and the Horner-Wadsworth-Emmons reaction and is described. A key step involving a diisopropylcarbodiimide promoted dehydration of a stable β-hydroxyphosphonate intermediate was identified. The structure of precursor E-(4-(4-bromostyryl)phenyl)(methyl)sulfane was determined using X-ray crystallography.     

Cationic organoaluminum compounds as intramolecular hydroamination catalysts

Cationic dialkylaluminum and m-terphenylalkylaluminum compounds catalyze the intramolecular hydroamination of primary and secondary aminopentenes. The reaction rates are strongly dependent on the substrate and the catalyst substituents. The bulky species [Dipp1AlEt][CHB₁₁H₅I₆] (Dipp1 = 2,6-Dipp₂C₆H₃–, Dipp = 2,6-iPr₂C₆H₃–), 4, was the most active catalyst. Although the neutral species DcpAlEt₂ (Dcp = 2,6-(2,6-Cl₂C₆H₃)₂C₆H₃–), 7, and Dipp1AlEt₂, 8, showed some catalytic activity, they were more than 25 times less reactive than their cationic counterparts [DcpAlEt][CHB₁₁H₅Cl₆], 3, and 4. The cyclization of secondary benzylaminopentenes with [Et₂Al][CHB₁₁H₅I₆], 1, was strongly dependent on the substitution of the C-2 olefinic carbon.     

Synthesis of multiply-bonded dichromium complexes with a variety of formamidinate ligands

A series of dichromium tetraformamidinate complexes with (ArNCHNAr)⁻ where Ar is X₂C₆H₃ or XC₆H₄ and X is the remote substituent 3,5-Cl₂, 3,4-Cl₂, p-Cl, p-CF₃, m-CF₃, p-OCH₃ or m-OCH₃ has been synthesized, and the structures of four of the compounds determined by X-ray crystallography. The Cr–Cr bond distances of the complexes structurally characterized are 1.9072(10) Å [Cr₂((p-ClC₆H₄N)₂CH)₄], 1.9162(10) Å [Cr₂((3,5-Cl₂C₆H₃N)₂CH)₄], 1.9018((8) Å [Cr₂((m-CF₃C₆H₄N)₂CH)₄ ], and 1.9178(11) Å [Cr₂((m-OCH₃C₆H₄N)₂CH)₄]. ¹H NMR spectroscopy and electrochemistry were performed on the series. The diamagnetic anisotropy of the Cr–Cr bond was calculated from X-ray crystallographic and ¹H NMR data and correlates with the Hammett constant of the formamidine ligands.     

Improved parallel QR method for large least squares problems involving Kronecker products

A new algorithm is presented for the efficient solution of large least squares problems in which the coefficient matrix of the linear system is a Kronecker product of two smaller dimension matrices. The solution algorithm is based on QR factorizations of the smaller dimension matrices. Near perfect load balancing is achieved by exploiting a ‘commutativity’ property of the Kronecker product, and communication requirements are minimized by employing a binary exchange algorithm for matrix transposition. The parallel algorithm is presented, and timing results are shown from test runs on an Intel i860 computer.     

含有广义p-Laplace算子的非线性边值问题解的存在性的研究

该文研究了两类含有广义p-Laplace算子的非线性边值问题. 首先, 利用变分不等式解的存在性的结果, 证明了含有广义p-Laplace算子的非线性Dirichlet边值问题解的存在性. 然后, 提出了一类含有广义p-Laplace算子的非线性Neumann边值问题. 通过深入挖掘这两类非线性边值问题间的关系, 借助于极大单调算子值域的一个扰动结果, 证明了含有广义p-Laplace算子的非线性Neumann边值问题解的存在性. 文中采用了一些新的证明技巧,推广和补充了作者以往的一些研究工作.