反相液相色谱用球形共聚物柱填料

采用新颖聚合工艺制备用于反相高效液相色谱柱填料的乙基苯乙烯-二乙烯苯球形共聚物,不需使用备有高速搅拌的混匀器和特殊的筛析设备,聚合物粒径的95％在3～7μm之间,测算了渗透性、柱效和峰不对称性等柱参数,并通过分离实例说明该填料对胺类、酚类和芳烃类具有优良分离性能。     

乙基苯乙烯与二乙烯苯球形共聚物吸附树脂作反相薄层色谱固定相

本文合成了乙基苯乙烯与二乙烯苯球形共聚物PED－9吸附树脂，粒径3～7μm，用作薄层色谱固定相，对板效进行了研究，并通过分离实例说明它对硝基苯酚及芳胺具有优良的分离性能。     

Evaluation of the Coulomb energy in relativistic self-consistent-field theory

 Computational schemes are presented with which to evaluate the electrostatic Coulomb energy in relativistic molecular electronic structure calculations using a basis of four-component Dirac spinor amplitudes. We demonstrate that algorithms may be constructed and implemented which differ only in minor details from those in common use in nonrelativistic quantum chemistry, and that the four-component formalism is neither as complicated nor as expensive as has been suggested recently in the literature. Spherically symmetrical atomic basis sets are presented which indicate that accurate representations of the Coulomb energy may be obtained using modest expansions of the electronic density in a scalar auxiliary basis set of spherical harmonic Gaussian-type functions. Received: 15 April 2002 / Accepted: 15 May 2002 / Published online: 29 July 2002     

Computation of Rotation Matrices Making Lined‐Up to the Local Cartesian Coordinates

Rotation matrices were expressed in terms of Gaunt coefficients and complex spherical harmonics. The rotation matrices were calculated using two different ways. In the first, Gaunt coefficients and normalized complex spherical harmonics were directly calculated using binomial coefficients; in the second, Gaunt coefficients and complex spherical harmonics were recursively calculated. The methods were compared with respect to accuracy and computation time (CPU) for low and very high quantum numbers.     

Preparation and characterization of spherical V2O3 nanopowder

V₂O₃ nanopowder with spherical particles was prepared by reducing pyrolysis of the precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, in H₂ atmosphere. The thermolysis process of the precursor in a H₂ flow was investigated by thermogravimetric analysis and differential thermal analysis. The results indicate that pure V₂O₃ forms at 620°C and crystallizes at 730°C. The effects of various reductive pyrolysis conditions on compositions of V₂O₃ products were studied. Scanning electron micrographs show that the particles of the V₂O₃ powder obtained at 650°C for 1 h are spherical about 30 nm in size with more homogeneous distribution. Experiments show that nanopowder has larger adsorption capacity to gases and is more easily reoxidized by air at room temperature than micropowder. Differential scanning calorimetry experiment indicates that the temperature of phase transition of nano-V₂O₃ powder is −119.5°C on cooling or −99.2°C on heating. The transition heats are −12.55 J g⁻¹ on cooling and 11.42 J g⁻¹ on heating, respectively.     

A comparison of measured room acoustics metrics using a spherical microphone array and conventional methods

The traditional microphone configuration used to measure room impulse responses (IRs) according to ISO 3382:2009 is an omnidirectional and figure-8 microphone pair. IRs measurements were taken in a 2500-seat auditorium to determine how the results from a spherical microphone array (an mh acoustics Eigenmike-em32) compare to those from the traditional microphone setup (a Brüel & Kjær Type-4192 omnidirectional microphone and a Sennheiser MKH30 figure-8 microphone). Measurements were obtained at six receiver locations, with three repetitions each in order to first evaluate repeatability. The metrics considered in this study were: reverberation time (T30), early decay time (EDT), clarity index (C80), strength (G), lateral energy fraction (J_LF) and late lateral energy level (L_J). Before calculating these quantities, the IRs were filtered to equalize the frequency response of the microphones and sound source. For the spherical array measurements, the omnidirectional (monopole) and figure-8 (dipole) patterns were extracted using beamforming. In terms of repeatability, the average standard deviation of the three measurements at each receiver location averaged across all metrics, receivers, and octave bands was found to be 0.01 just noticeable differences (JNDs). The analysis comparing the measurements from the two microphone configurations yielded differences which were less than 1 JND for the majority of metrics, with a few exceptions of EDT and C80 slightly above 1 JND. Based on this case study, these results indicate that spherical microphone arrays can be used to obtain valid room IR measurements, which will allow for the development of new metrics utilizing the higher spatial resolution made possible with spherical arrays.     

Length scale effects in epoxy: The dependence of elastic moduli measurements on spherical indenter tip radius

Significant increases in the measured elastic moduli with decreasing indentation depth have been previously found in various polymers by indentation tests with a Berkovich tip at micro-to nanometer length scales. These increases in the determined elastic moduli were related to second order displacement gradients which increase with decreasing depth when a conical tip is applied. When a spherical tip is applied, such depth dependence should not be present as the second order displacement gradients remain essentially unchanged with indentation depth. However, these gradients should be proportional to the radius of the spherical tip. To examine the notion of second order displacement gradient dependence in measurements of elastic moduli, indentation experiments are conducted on epoxy with spherical tips of different nominal radii. Accounting for tip imperfections, an increase in the determined elastic moduli is found with decreasing tip radius, which corroborates the notion of second order displacement gradient dependence.     

Spherical hollow mesoporous silica supported phosphotungstic acid as a promising catalyst for α-arylstyrenes synthesis via Friedel-Crafts alkenylation

This work presents a scalable approach for preparing spherical hollow mesoporous silica with high surface area/pore volume, serving as outstanding support for supported phosphotungstic acid catalyst with much superior catalytic performance to the one on previously reported spherical mesoporous silica toward diverse transformations, ascribed to the strengthened mass transfer and the enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and mesoporous morphology.     

Approximate analytic expressions for the diffusiophoretic velocity of a spherical colloidal particle

The general expression is derived for the diffusiophoretic velocity of a spherical colloidal particle of radius a in a concentration gradient of symmetrical electrolyte. On the basis of this expression, simple approximate analytic expressions for the diffusiophoretic velocity correct up to the order of 1/κa is derived, where κ is the Debye-Hückel parameter. It is found that the approximate expression correct to order unity can be applied for κa ≥ 50 with negligible errors, while the approximate expression correct to order 1/κa can be applied for κa ≥ 20 with negligible errors.     

新型复合共沉淀法制备高能量/高功率型锂离子二次电池用5V正极材料LiNi_(0.5)Mn_(1.5)O_4及其电化学性能

在传统的固相法的基础上开发了新型复合共沉淀法制备LiNi0.5Mn1.5O4材料.新型复合共沉淀法采用(NH4)2CO3和(NH4)2C2O4共同作为沉淀剂,通过控制共沉淀反应条件,得到了具有均匀球形形貌的沉淀物颗粒.再通过与饱和氢氧化锂溶液的水热反应及高温反应,最终制备出具有球形次级形貌和纯相尖晶石结构的LiNi0.5Mn1.5O4材料.电化学测试表明,制备的LiNi0.5Mn1.5O4具有优异的电化学性能,其初始容量达到了141.4mAh·g-1.在0.3C、1C和3C倍率下经过200次循环后的容量分别为136.0 mAh·g-1(96.3%)、128.6 mAh·g-1(94.4%)和113.9 mAh·g-1(91.1%).通过高温反应及特殊的冷却处理,LiNi0.5Mn1.5O4在4.0 V低压区平台的容量损失得到了有效抑制.更重要的是,通过控制合成过程中的关键步骤,可实现半定量化控制材料结构中的原子有序排布程度,进而得到具有高能量密度和高功率密度的两种LiNi0.5Mn1.5O4材料,其能量密度和功率密度分别达到了648.6 mWh·g-1和7000 mW·g-1以上.