Effective crystal field for trivalent first transition row ions

In the present work the semiempirical effective crystal field (ECF) method previously designed for electronic structure calculations of transition metal complexes and utilizing non‐Hartree–Fock trial wave function and parameterized for complexes of doubly charged Cr²⁺, V²⁺, Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺ cations is extended to complexes of triply charged cations of 3d‐elements. With the parameters adjusted the ECF method is applied to calculations of ground states and low‐energy spectra of the d‐shells of fluoro‐, chloro‐, aqua‐, amino‐, and cyano‐complexes of the triply charged cations. Obtained total spin and symmetry of the ground states match the experimentally observed ones. Satisfactory agreement between the calculated and experimental d‐shell electronic transition energies is achieved as well. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

PbO2阳极在硫酸溶液中的析氧失活行为

采用热分解鄄电镀法制备了以Sb 掺杂SnO₂(Sb-SnO₂)为底层的Ti 基PbO₂阳极(Ti/PbO₂). 采用加速电解寿命测试、电化学阻抗谱、XRD、SEM-EDX 等技术, 研究了Ti/PbO₂阳极在硫酸溶液中的电解失效行为和机制.结果表明,在新制备的PbO₂镀层中, 由于氧空位的存在, PbO₂镀层的内应力表现为拉应力, 随着电解的进行, 阳极表面生成的活性氧原子在向基底扩散的过程中, 将Pb³⁺态氧化为Pb⁴⁺态, 逐渐占据镀层内作为自由电子施主的氧空位, 这不仅导致镀层的导电性能下降, 同时使镀层的应力逐渐由拉应力转变为压应力, 镀层性质逐渐劣化. 这一过程基本结束时,活性氧原子才大量扩散至Ti基底导致基底的钝化, 在Ti 基底和镀层界面出现显著的界面应力, 在界面应力和镀层内压应力的共同作用下, 阳极出现鼓泡、脱落, 迅速进入失活阶段.     

STUDY ON 1-HEXENE POLYMERIZATION BASED ON ZIEGLER-NATTA CATALYSTS WITH DOPED SUPPORT

A series of Ti/Mg supported catalysts are prepared by using ball-milled mixtures of MgCl2-ethanol adducts and NaCl as supports, and 1-hexene polymerizations catalyzed by the novel catalysts are studied. It is found that the molecular weight distribution of poly(1-hexene) becomes apparently narrower when catalysts with doped supports are used, indicating that changing the structure of the support is an effective way to regulate the active center distribution of heterogeneous Ziegler-Natta catalyst.     

RESEARCH ANNOUNCEMENTS ON “DPK: DEEP NEURAL NETWORK APPROXIMATION OF THE FIRST PIOLA-KIRCHHOFF STRESS”

1 Introduction and Main Results Consider the first Piola-Kirchhoff stress P defined as[1]P(F)=?W(F)/?F,(1.1)where F and W refer to the deformation tensor and strain energy density.Due to the principle of material frame-indifference and the material symmetry,two important constraints should be satisfied by these relations[1].     

Residual stress/strain analysis in thin films by X-ray diffraction

Residual stresses are found in the majority of multilayer thin film structures used in modem technology. The measurement and modeling of such stress fields and the elucidation of their effects on structural reliability and device operation have been a “growth area” in the literature, with contributions from authors in various scientific and engineering disciplines.

In this article the measurement of the residual stresses in thin film structures with X-ray diffraction techniques is reviewed and the interpretation of such data and their relationship to mechanical reliability concerns are discussed.     

Two-point Padé approximants for formal Stieltjes series

We prove that certain two-point Padé approximants occupying the diagonal of the Padé table form monotone sequences of lower and upper bounds uniformly converging to a Stieltjes function. The results can be applied to the theory of inhomogeneous media for the calculation of the bounds on the effective transport coefficients of heterogeneous materials.     

Effective electromagnetic and chiral parameters of chiral composite material

The effective parameters of chiral composite are studied using a simple model, that is, randomly oriented non-interacting wire helices embedded in a nonchiral host medium. It is found that both the effective permittivity and permeability are independent on the handedness of the chiral objects while the effective chirality admittance is dependent. It is also found that when the ratio of the radius of the chiral helix to its pitch is about 0.23, maximum chirality admittance is achieved. The effective parameters of equichiral sample are also discussed.     

Effects of steric and hydrophobic forces on the rheological properties of ZrO2 suspensions

 The effect of pH on the flow behavior of ZrO₂ suspensions containing polyacrylic and octanoic acids was evaluated. In the flocculated pH regime, the flow behavior is highly shearthinning and can be described by a power-law model. The shear-thinning behavior increases with increasing degree of flocculation. Maximum shearthinning was observed at the zero zeta potential condition. Hydrophobic interaction arising from adsorbed octanoic acid was found to enhance the shear-thinning behavior. No such enhancement was observed for adsorbed polyacrylic acid. It was also illustrated that the viscosity–pH behavior is a mirror image of the yield stress–pH behavior. A quantitative particle-pair interactions model incorporating steric and hydrophobic interactions was proposed to explain the effects of polyacrylic and octanoic acids on the maximum yield stress. Received: 23 May 1997 Accepted: 4 June 1997     

Development of an HPLC method with electrochemical detection of femtomoles of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine in the presence of uric acid

A selective method based on high performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed to enable simultaneous detection of 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), products of DNA oxidative damage, in the presence of uric acid (UA), a strong interferent in their electrochemical detection. The method developed consists of HPLC isocratic elution with amperometric detection on a glassy carbon electrode, enabling a detection limit for 8-oxoGua and 8-oxodGuo lower than 1 nM in standard mixtures. Detection of low concentrations up to 25 nM of 8-oxoGua and 8-oxodGuo in the presence of UA in a 10⁴-fold higher concentration was achieved after one-step solid phase extraction (SPE). The method was tested with urine samples and it was possible to detect and quantify the presence of 8-oxoGua, and to confirm that UA was eliminated after uricase degradation and SPE. The LOD found in urine samples was about 80 nM, a value higher than in standard mixtures, due to the increase of background current in the urine matrix. The results presented here contribute to the development of a methodological approach to simultaneous determination of 8-oxoGua and 8-oxodGuo in urine samples.     

Effect of molecular orientation distribution and crystallinity on the measurement of the crystal lattice modulus of nylon 6 by x-ray diffraction

The crystal lattice modulus of nylon 6 (-type) was measured by x-ray diffraction using nylon 6 films drawn up to five times. The measured crystal lattice modulus was 173–175 GPa for all specimens whose crystallinity and the Young's modulus were beyond 46% and 3.75 GPa, respectively. These results indicate that a state of homogenous stress can be achieved. In contrast, the values were scattered for the speciments whose crystallinity and Young's modulus are less than the above values. To study the origin, a numerical calculation of the crystal lattice modulus, as measured by x-ray diffraction, was carried out by considering effects on the orientation factors of molecular chains and crystallinity. In this calculation, a previously introduced model was employed, in which oriented crystalline layers are surrounded by oriented amorphous phases so that the strains of the two phases at the boundary are identical. The theoretical results calculated by the introduced model indicated that the crystal lattice modulus by x-ray diffraction is almost equal to the intrinsic crystal modulus if the morphology of the test specimen can be represented as a series model. In contrast, if a parallel model is more appropriate, the difference between the measured modulus and the intrinsic value can be pronounced. Such morphological dependence was found to be less pronounced with increasing high degree of molecular orientation and crystallinity.