Pressure-induced coordination crossover in magnetite; the breakdown of the Verwey–Mott localization hypothesis

Temperature-dependent ⁵⁷Fe Mössbauer spectroscopy to 40 GPa shows that Fe₃O₄ magnetite undergoes a coordination crossover (CC), whereby charge density is shifted from octahedral to tetrahedral sites and the spinel structure thus changes from inverse to normal with increasing pressure and decreasing temperature. A precursor to the CC is a d-charge decoupling within the octahedral sites at the inverse-spinel phase. The CC transition takes place almost exactly at the Verwey transition temperature (T_V=122 K) at ambient pressure. While T_V decreases with pressure the CC-transition temperature increases with pressure, reaching 300 K at 10 GPa. The d electron localization mechanism proposed by Verwey and later by Mott for T<T_V is shown to be unrelated to the actual mechanism of the metal–insulator transition attributed to the Verwey transition. It is proposed that a first-order phase transition taking place at ∼T_V at ambient pressure opens a small gap within the oxygen p-band, resulting in the observed insulating state at T>T_V.     

二茂铁修饰石墨粉-环氧树脂固态电极测定对苯二酚

对苯二酚为一种多酚类化合物,广泛用作显影剂、抑制剂、抗氧化剂和合成染料的原料等,同时也是具有较大毒性的有机污染物。因此,在环境和化工过程中,痕量对苯二酚的检测显得十分重要。痕量对苯二酚常用分光光度法[1]、荧光分析[2]、液相色谱[3]等方法检测。由于对苯二酚在普通电     

在氢氧化铁修饰的硅油碳糊电极上微分脉冲伏安法直接测定污水中的痕量对苯二酚

将石墨粉掺有少量的氢氧化铁粉末作为催化剂,以硅油为黏结剂制成碳糊电极,微分脉冲伏安法直接测定污水中的对苯二酚, 在pH 1.0 HCl支持电解质中,对苯二酚在该碳糊电极上表现为催化行为,微分脉冲的阳极峰电流在0.625-500μmol/L浓度范围内呈较好的线性关系,ip(μA)=0.3402 0.09578C(μmol/L)(r=0.9997,SD=0.374), 检出限为0.3125μmol/L.方法简单快速,直接用于污水中对苯二酚的测定,结果令人满意.     

The nature of the anchimeric assistance by the acetoxy group in solvolysis of (Me3Si)2C(SiMe2)OCOMe) (SiMe2Cl)

Solvolysis of (Me₃Si)₂C(SiMe₂OCOMe)(SiMe₂Cl) in 3/2 v/v MeOH/dioxane at 35°C is ca. 11–14 times as fast as that of (Me₃Si)₂C(SiMe₂OMe)(SiMe₂Cl), which suggests that the anchimeric assistance by the acetoxy group is provided through the carbonyl oxygen.     

Preparation and characterization of highly lipophilic modified potato starch by ultrasound and freeze-thaw treatments

In order to explore the potential application of combined physical treatment in producing highly lipophilic modified starch, the effects of ultrasound combined with freeze-thaw treatment on the microstructure and physicochemical properties of potato starch were investigated. The samples treated by combined treatment had the roughest structure and the oil adsorptive capacity value increased from 59.62% (native starch, NS) to 80.2% (7 cycles of ultrasound-freeze-thaw treatment starch, 7UT-FTS). Compared to NS, the crystalline type and chemical groups of modified starches did not change, but the relative crystallinity, enthalpy change, and paste viscosity decreased to varying degrees, while the gelatinization temperature increased. The digestibility of raw modified starch was higher than that of NS, but this phenomenon disappeared after gelatinization. 7UT-FTS showed better resist-digestibility than NS after encapsulating oil. Hence, this would be an efficient and environmentally friendly way to produce modified starch with safety, highly lipophilic and heat resistance.     

Relaxed stability conditions for continuous‐time Takagi–Sugeno fuzzy systems based on a new upper bound inequality

The important issue of reducing the conservatism of feasible stability criteria for continuous‐time Takagi–Sugeno fuzzy systems is studied in this article. In order to obtain more advanced result than previous ones, a new upper bound inequality is proposed and thus the properties of the normalized fuzzy weighting functions' time derivatives can be better used than the previous ones. In particular, the so‐called “redundant terms” considered in previous literature can be converted to “useful terms” which play a positive role in the underlying analysis process. Moreover, some useless additional variables and their derived inequalities are removed for enhancing the efficiency. Finally, an illustrative example is given to show the effectiveness of the proposed method. © 2016 Wiley Periodicals, Inc. Complexity 21: 289–295, 2016     

Characterization of two chimeric sesterterpene synthases from a fungal symbiont isolated from a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum

Two chimeric sesterterpene synthases (AaTPS1 and AaTPS2) were functionally characterized from Alternaria alternata MB-30 isolated from the leaves of a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum. AaTPS1 generated a 5/8/6/5 tetracyclic sesteraltererol (1) and its absolute stereochemistry was determined by X-ray crystallographic analysis of its derivative 10,11-epoxysesteraltererol (2), which enabled revision of the absolute configuration of C7 of sesterfisherol produced by NfSS and PTTS014 characterized previously and its derivative 10,11-epoxysesterfisherol. AaTPS2 produced a 5/15 bicyclic preterpestacin I (3). Site-directed mutagenesis suggested that F192 in AaTPS1 was likely involved in controlling of the hydroxylation of C12, and eight amino acids were important for the enzyme activity of AaTPS1 and AaTPS2. The engineered Escherichia coli and Saccharomyces cerevisiae strains were constructed for the productions of compounds 1 and 3, and the highest titer of compound 1 reached 62.3 mg/L in shake-flask culture. Both compounds 1 and 2 showed anti-adipogenic activity.     

Stability of switched nonlinear time-delay systems with stable and unstable subsystems

This paper investigates the stability of switched nonlinear time-delay systems with stable and unstable subsystems. Several stability criteria are presented by resorting to novel inequality technique and average dwell time approach, which relax the assumptions that all subsystem matrices are commutative pairwise and Hurwitz stable. Finally, two numerical examples are provided to illustrate the effectiveness of the theoretical results.