火焰原子吸收光谱法测定粮食中的铜

碳化酸溶消解试样,用火焰原子吸收光谱法测定三种粮食作物中的铜.回收率:99.5%-107.0%.方法快速、简便、准确度高.     

Intravascular 3.0 T MRI Using an Imaging-Guidewire: a Feasibility Study in Swine

This study was to validate the feasibility of using a magnetic resonance imaging-guidewire (MRIG) for intravascular 3.0 T MR imaging of deep-seated arterial walls of large animals. The functionality of a 0.032-in. MRIG was evaluated and the signal-to-noise ratio (SNR) was calculated. Then, MRI of ten iliofemoral arteries of six pigs was acquired by MRIG and surface coil. The difference in the SNRs of the arterial walls between different coils was compared. Histology examined the potential thermal injuries of the imaged vessels. The MRIG functioned with the 3.0 T MR scanner. The average SNR of the arterial walls was significantly higher with the MRIG than with the surface coils (76.22 ± 34.76 vs. 12.63 ± 4.25, P < 0.01). Histology showed no evidence of thermal injuries at the vessel walls. This study validated the feasibility of generating intravascular 3.0 T MRI of deep-seated arterial walls in large animals, which should facilitate the translation of this technique from 1.5 to 3.0 T MR scanner.     

改性乙醇胺富集烟道气中CO2的FTIR研究

以四(3,5-二叔丁基-4-羟基苯基丙酸)季戊四醇酯(抗氧剂1010)、Na2SO3作为乙醇胺(MEA)的氧化降解的改性剂,考察改性MEA富集模拟烟道气中CO2的效果,利用气相色谱、红外光谱分析抗氧剂1010与Na2SO3的适宜用量、比较两种抗氧剂的抗氧化性能.结果表明,抗氧剂1010和亚硫酸钠的添加量在0.15%时效...     

Photonic bandgap properties of 8-fold symmetric photonic quasicrystals

The bandgap properties of 2D 8-fold symmetric photonic quasicrystals (PQCs) composed of a set of rods are numerically investigated for various fill factors, dielectric constants and propagation angles using the finite difference time domain (FDTD) method. Some interesting properties are found besides the known results: (i) the central frequency of the bandgap shifts to low frequency as r/a increases; (ii) an optimum fill factor to obtain the largest gap width exists, which decreases with increasing dielectric constant; (iii) compared with the behavior for a given fill factor, the variation of bandgap width for the optimum fill factor increases much more significantly with the dielectric constant. Selection guidelines for 8-fold symmetric PQC designs are provided for optimum fill factors and variation of the relative bandgap width at different dielectric constants.     

Anisotropy of sound velocity for a new PbB4O7 crystal as determined by the laser ultrasonic technique

4 O₇ crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer. Received: 27 January 1997/Accepted: 30 July 1997     

Surface reactions of TiCl4 and Al(CH3)3 on GaAs(100) during the first half-cycle of atomic layer deposition

GaAs(100) was exposed to pulses of trimethylaluminum (TMA, Al(CH₃)₃) and titanium tetrachloride (TiCl₄) to mimic the first half-cycle of atomic layer deposition (ALD). Both precursors removed the 9.0 ± 1.6 Å-thick mixed oxide consisting primarily of As₂O₃ with a small Ga₂O component that was left on the surface after aqueous HF treatment and vacuum annealing. In its place, TMA deposited an Al₂O₃ layer, but TiCl₄ exposure left Cl atoms adsorbed to an elemental As layer. This suggests that oxygen was removed by the formation of a volatile oxychloride species. A small TiO₂ coverage of approximately 0.04 monolayer remained on the surface for deposition temperatures of 89 °C to 135 °C, but no TiO₂ was present from 170 °C to 230 °C. The adsorbed Cl layer chemically passivated the surface at these temperatures and blocked TiO₂ deposition even after 50 full ALD cycles of TiCl₄ and water vapor. The Cl and As layers desorbed simultaneously at higher temperature producing peaks in the temperature programmed desorption spectrum in the range 237–297 °C. This allowed TiO₂ deposition at 300 °C in single TiCl₄ pulse experiments. On the native oxide-covered surface where there was a higher proportional Ga oxide composition, TiCl₄ exposure deposited TiO₂.     

Stages in tropoelastin coalescence during synthetic elastin hydrogel formation

Synthetic human tropoelastin was chemically cross-linked to form elastic hydrogel-like structures in vitro. Discrete stages were identified during elastic hydrogel formation by cross-linking tropoelastin with bis(sulfosuccinimidyl) suberate at a range of protein concentrations during this process. In the early stages of this process, particles with the same dimensions as tropoelastin were seen. As hydrogel formation progressed, monomer width fibres were also observed. Overall, four distinct stages were identified: (1) tropoelastin monomers form discrete particles in the order of 200 nm diameter, (2) these particles merge to form larger spheres, (3) spheres coalesce into open linked networks, (4) coalesced spheres consolidate to form a porous structure to give synthetic elastin hydrogels.     

Spectroscopic properties of Yb3+-doped Y3Al5O12 nano-ceramics obtained under different sintering pressures

Yb³⁺:YAG nano-ceramics have been obtained by a low temperature/high pressure sintering process. Structural properties have been studied by X-ray diffraction (XRD). Grain sizes and R.M.S micro-strains have been calculated based on the XRD patterns by Rietveld analysis method. Emission spectra and decay curves have been recorded and analyzed. It has been observed that the decay time decreases with the increase of sintering pressure. Presence of Yb³⁺–Yb³⁺ pairs have been detected by cooperative emission spectroscopy.     

Vibro-acoustic noise control treatments for payload bays of launch vehicles: Discrete to fuzzy solutions

Sound transmitted through an enclosing structure into a cavity has been minimised by optimising the locations, numbers and properties of tuned mass dampers placed on the structure and Helmholtz resonators placed in the cavity. Most of the results presented in the literature show the effect of a few well selected acoustic or vibration absorbers on simple vibro-acoustic systems, whereas the results presented here indicate the trends that occur when a few absorbers are replaced by a large number. The results indicate that for low numbers of absorbers, the result of the optimal configuration is to reduce the response of discrete modes, and for a large number of absorbers the result of the optimal configuration is a tendency for the vibro-acoustic energy to be smeared over a range of frequencies, which is similar to the results seen in fuzzy structures. The enormous computational task was achieved using a distributed computing network and an asynchronous parallel genetic algorithm.