钽内标X射线荧光光谱法测定钨精矿中WO_3

提出了以钽为内标波长色散X射线荧光光谱法测定钨精矿中WO3的新方法。以Na2B4O7和Li2B4O7(质量比65:35)的混合物作为熔剂,Ta2O5为内标,同时加入LiNO3为氧化剂,在1200℃下进行熔融制样,最后将本方法应用于实际样品的分析,结果表明,以钽作为内标测定WO3,不仅可以在很大程度上降低实验操作和仪器测量带来的偏差,也可以消除基体效应的影响。方法用于测定白钨精矿和黑钨精矿中WO3,其准确度和精密度优于重量分析法。     

PdO0,±1, PdH0,±1及PdOH分子结构和电子性质的从头计算

利用多种从头计算方法对PdO0,±1, PdH0,±1以及PdOH的结构和电子性质进行了理论研究. 优化了PdO分子两个能量相近的态(3∏和3∑-), 结果表明PdO 的3∏态较3∑-态更为稳定, 在单双激发耦合簇理论(CCSD)水平下3∑-态的总能量比3∏态的高出0.286 eV. 在结构优化的基础上计算了PdO以及PdH的绝热电离能(AIE)和电子亲和能(AEA), 计算结果与实验值符合得很好. PdOH的基态为Cs对称性的角型结构Pd—OH(2A'态), 另外还优化得到两个2A'态的亚稳结构, 分别对应于Pd—OH和O—Pd—H, CCSD水平下两个亚稳态的总能量较基态分别高0.405和2.284 eV, 优化得到了连接这两个2A'态的过渡态, 并计算了相应的反应能垒.     

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states - Part VI: Oxalyl bromide (COBr)2 and summary

The structure of oxalyl bromide (COBr)₂ in the ground and four lowest excited electronic states was theoretically investigated using the CASPT2/cc-pVTZ-DK method. Structural information obtained allowed the reassignment of the and vibronic absorption spectra. Generalization of oxalyl halide structural data for the ground and excited electronic states is presented.     

The microwave spectrum of methyl chlorodifluoroacetate: Methyl internal rotation and chlorine nuclear electric quadrupole coupling

A chirped pulse microwave spectrometer has been used to record microwave spectra of the ³⁵Cl and ³⁷Cl isotopologues of methyl chlorodifluoroacetate, CClF₂C(O)OCH₃, between 8 GHz and 16 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Only one conformer was observed. The rotational spectra were recorded with sufficient resolution to observe (i) splittings due to the internal rotation of the methyl group, and (ii) splittings from the coupling of the chlorine quadrupolar nucleus. A total of 785 transitions have had quantum numbers assigned. Analysis of the spectra observed has produced an experimental barrier to the methyl group internal rotation, V₃, of 370(2) cm⁻¹. It is noted that this barrier is a little lower than that determined for methyl acetate [V₃ = 425 cm⁻¹, J. Sheridan, W. Bossert and A. Bauder, J. Mol. Spectrosc., 80 (1980) 1-11], and this is rationalized through a comparison of molecular structures. Lastly, all components of both the ³⁵Cl and ³⁷Cl chlorine nuclear electric quadrupolar coupling tensor have been determined.     

Gas-phase Raman spectra of hot bands of fundamentals and combinations associated with the torsional vibration of s-trans-1,3-butadiene and its deuterated isotopologues

The gas-phase Raman spectra of 1,3-butadiene and its 2,3-d₂, 1,1,4,4-d₄, and d₆ isotopologues have been recorded with high sensitivity and resolution of 0.7 cm⁻¹. Hot band series of fundamentals and combinations involving the ν₁₃ torsional vibration of the s-trans rotamer have been observed for each of the isotopologues. Modes studied were ν₁₀ (CH wag), ν₁₂ (CH₂ twist), ν₁₀ + ν₁₂, ν₁₅ (CH₂ wag) + ν₁₆ (CH₂ twist), and ν₂₃ (CH₂ rock) + ν₂₄ (CCC deformation). The spacings of the quantum states of the torsional contribution were found to decrease with additional excitation of this mode (ν₁₃) in the upper vibrational states except for the ν₂₃ + ν₂₄ combination state.     

Oxygen relaxation and phase transition in GdBaCo2O5 + δ oxide

Electrical conductivity, internal friction techniques and dilatometer have been used to investigate the oxygen relaxation, phase transition and thermal expansion behavior of GdBaCo₂O_5 + δ. The main electronic charge carriers in GdBaCo₂O_5 + δ are electronic holes, which could be assigned to the formation of Co⁴⁺. The oxygen exchange kinetics intensely depends on oxygen partial pressure and is also closely related to temperature. Both electrical conductivity and internal friction give rise to an abnormal at about 75 °C, which are related to the insulator-metal transition occurring in GdBaCo₂O_5 + δ. One large relaxation internal friction peak, due to the motion of oxygen within Gd-O plane, is also found in the oxide. The average thermal expansion coefficient (TEC) of GdBaCo₂O_5 + δ is about 21.4 × 10⁻⁶ K⁻¹ between 500 °C and 900 °C.     

Arithmetic returns for investment performance measurement

This paper introduces new money-weighted metrics for investment performance analysis, based on arithmetic means of holding period rates weighted by the investment’s market values. This approach generates rates of return which measure a fund’s or portfolio’s performance and a fund manager’s performance. It also enables to show that the Internal Rate of Return (IRR) is a weighted mean of holding period rates associated with interim values which differ from market values, so that value additivity is violated. The manager’s Arithmetic Internal Rate of Return (AIRR) is shown to be the true period equivalent of the cumulative Time Weighted Rate of Return (TWRR), whereas the period TWRR (a geometric return) provides a different ranking. The method is easily generalized for coping with varying benchmark rates. We also cope with the practical problem of estimating interim values whenever they are not available.     

Attitude control of rigid spacecraft with disturbance generated by time varying exosystems

This paper is concerned with the problem of attitude control and disturbance rejection of rigid spacecraft in the presence of parameter uncertainty. It is assumed that the external disturbance is generated by some time varying exosystems. The unit quaternion is used as the kinematic variables since it is free of singularity. An internal model and an adaptive control law are proposed. The parameter uncertainty caused by the unknown inertia matrix is handled by combining the semi-tensor product and adaptive control method. The asymptotical stability of the closed-loop system is given via backstepping and Lyapunov analysis. Finally, an illustrative example is provided to show the effectiveness of the proposed approach.     

Neural network prediction of load from the morphology of trabecular bone

Bone adaptation models are often solved in the forward direction, meaning that the response of bone to a given set of loads is determined by running a bone tissue adaptation model. The model is generally solved using a numerical technique such as the finite element model. Conversely, one may be interested in the loads that have resulted in a given state of bone. This is the inverse of the former problem. Even though the inverse problem has several applications, it has not received as much attention as the forward problem, partly because solving the inverse problem is more difficult. A nonlinear system identification technique is needed for solving the inverse problem. In this study, we use artificial neural networks for prediction of tissue adaptation loads from a given density distribution of trabecular bone. It is shown that the proposed method can successfully identify the loading parameters from the density distribution of the tissue. Two important challenges for all load prediction algorithms are the non-uniqueness of the solution of the inverse problem and the inaccuracies in the measurement of the morphology of the tissue. Both challenges are studied, and it is shown that the load prediction technique proposed in this paper can overcome both.     

Synthesis and biomimetic mineralization of l‐proline substituted polyphosphazenes as bulk and nanofiber

This work presents the synthesis of polyphosphazenes bearing L ‐proline methyl ester (ProOMe) and 4‐hydroxy‐l ‐proline methyl ester (HypOMe), aiming for new bioactive polymers for bone repair. The polymers were characterized by ¹H and ³¹P NMR, FTIR, DSC, and TGA. Electrospun fibers were prepared using poly[bis(l ‐proline methyl ester)phosphazene] (PProP), and their potential for biomimetic mineralization, as well as the bulk material, were tested in simulated body fluid (1×SBF). Samples were analyzed between 24 h and 3 weeks of incubation using SEM/EDS and FTIR. After 24 h, spherical and flower‐like shapes of calcium phosphates (CaP) were crystallized on the bulk samples. The nanofibers presented spherical CaP crystals attached to them after 48 h of incubation. The Ca/P molar ratio of the crystals varied from 1.5 to 1.6. According to this study, PProP presents bioactivity in vitro, and its fibers offer sites for CaP nucleation like the collagen fibers in bone. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1318–1327