Molecular structure of carbonyl bromide as studied by gas electron diffraction

The molecular structure of COBr₂ has been determined as follows by an analysis of electron diffraction intensity: r_g(CO) = 1.178 ± 0.009 Å, r_g(C-Br) = 1.923 ± 0.005 Å and θ°_α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed.     

Nanostructural aspects, free volume and phase constitution of rapidly solidified Nd-Fe-B

A complement of experimental characterization techniques - positron annihilation spectroscopy (PAS), transmission electron microscopy, synchrotron X-ray diffraction and elevated temperature ac and dc magnetic measurements - were applied to the study of melt-quenched stoichiometric Nd₂Fe₁₄B ribbons modified by various amounts of the alloying additions Ti and C. These alloying additions are known to enhance the glass-forming ability in Nd₂Fe₁₄B melts, allowing for a wider processing window to produce homogeneous nanoscale materials with tailored magnetic properties. The experimental techniques used in this study reveal the complex multi-phase and multi-scale nature of the ribbons, a result that had escaped detection by lower-resolution techniques. The as-quenched ribbons were found to consist of at least three phases: α-Fe nanocrystals, poorly crystalline Nd₂Fe₁₄B and glass. The measured weight fraction of glass does not show a direct correspondence with quenching wheel speed, a result attributed to the complexity of the melt-spinning heat-transfer process. The Curie temperature of the glassy component of the ribbons varies in a non-systematic way with both Ti and C alloying addition content and wheel speed. PAS provides quantitative measurements of the S (or ‘shape’)-parameter which represents the size of a void or open volume in the material volume probed. The experimental results indicate that an excess of free volume in the glass is associated with increased glass stability, a counterintuitive conclusion. However, the results are consistent with the model of Sietsma and Thijsse [Phys. Rev. B 52 (5) (1995) 3248] who propose that thermal relaxation in glass causes the larger free volume regions in the amorphous structure to break up into smaller voids, which necessarily increases the total number of voids, but decreases the volume per void. This void breakup fosters the processes of cooperative diffusion and subsequent devitrification. It is concluded that the free volume concentration in the amorphous component of melt-spun Nd₂Fe₁₄B alloys produced by the highest quenching wheel speeds and Ti/C alloying addition content is thus not sufficient to allow cooperative diffusion to take place, resulting in an increased stability against devitrification.     

Positron annihilation lifetime study of organic-inorganic hybrid materials prepared by irradiation

Silica based hybrid materials, some containing zirconia, prepared by gamma-irradiation, were studied by positron annihilation lifetime (PAL) spectroscopy, in the temperature range of 30-370 K. One long-lived component was observed in group of samples without zirconia. The behavior of this component as a function of temperature resembles that for polymers. This is explained by the elastomer like structure of the samples and the excellent linking between the inorganic and organic networks. The average radius, R, of the free-volume holes was in the range 0.26-0.42 nm depending on the temperature. In the group of samples containing zirconia two long-lived components were observed. A model with three different free-volume holes was suggested to explain the PAL results. Small closed holes (R ∼ 0.26 nm) and large closed holes introduced by Zr (R ∼ 0.5 nm), the sizes of both holes not changing with the temperature, together with intermediate polymer-like free-volume holes - the same behavior as those present in samples not containing zirconia.     

Singular Perturbations of Self-Adjoint Operators

Singular finite rank perturbations of an unbounded self-adjoint operator A ₀ in a Hilbert space ₀ are defined formally as A ₍₎=A ₀+GG ^*, where G is an injective linear mapping from = ^d to the scale space _-k(A₀)k , kN, of generalized elements associated with the self-adjoint operator A ₀, and where is a self-adjoint operator in . The cases k=1 and k=2 have been studied extensively in the literature with applications to problems involving point interactions or zero range potentials. The scalar case with k=2n>1 has been considered recently by various authors from a mathematical point of view. In this paper, singular finite rank perturbations A ₍₎ in the general setting ran G – _k (A ₀), kN, are studied by means of a recent operator model induced by a class of matrix polynomials. As an application, singular perturbations of the Dirac operator are considered.     

Evaluation of Automated ECG Monitoring: Theoretical Model Based upon Point Process Techniques

The development of practical methods of ECG monitoring using dedicated computers has presented problems in the evaluation and comparison of the relative effectiveness of various ECG monitoring systems. A theoretical model based on the application of point process techniques is discussed in this paper.     

Molecular structure of carbonyl fluoride as studied by gas electron diffraction and microwave data

The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are r_z (C=O) = 1.1717 ± 0.0013 Å, r_z (C-F) = 1.3157 ± 0.0005 Å, and ∠_zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α₃, representing the cubic anharmonicity of bond stretching vibrations have been estimated.     

基于LR305的平面荧光太阳能聚光波导研制

光伏发电是目前太阳能最佳的利用方式之一,但发电成本高。利用聚光结构提高光的转换和收集效率,是提高太阳能电池效率、减少电池用量、降低光伏发电系统成本的重要途径。以Lumogen F Red 305 (LR305) 染料作为荧光材料,将其掺杂到PMMA中,通过本体聚合法制作出尺寸为50 mm×50 mm×5 mm的PMMA平面荧光太阳能聚光波导,对其光学特性进行表征,同时将太阳能电池粘贴到聚光波导的输出端面,通过测试平面荧光太阳聚光波导对太阳能电池性能的影响研究了荧光太阳能聚光波导的聚光特性。     

极谱法测定人发中痕量铜的研究

研究了痕量铜与CNS-及TriTonX 30 5非离子表面活性剂形成多元配合物 ,用示波极谱分析法测定痕量铜的新方法 .新方法铜的析出限为 1× 10 -10 g/mL ,工作曲线线性响应浓度范围为 5× 10 -9～ 5× 10 -7g/mL ,回收率为 98%～ 10 3% .直接用于人发、血清等样品中痕量铜的测定 ,其结果与原子吸收分光光度法测定结果对照相吻合     

Weakened Semantics and the Traditional Square of Opposition

In this paper we present a proposal that (i) could validate more relations in the square than those allowed by classical logic (ii) without a modification of canonical notation neither of current symbolization of categorical statements though (iii) with a different but reliable semantics.