我国医学影像技术近十年发展概述

本文综述了我国近十年医学影像技术的发展概况，主要阐述了一些新的医学成像技术系统和设备在我国的开发研究和应用，如：数字成像，包括计算机放射照相CR，直接数字放射照相DR，数字减影血管造影DSA等；计算机断层放射照相CT，包括多种照相技术，如三维重建、CT仿真内窥镜成像CTVE等；核磁共振成像MRI；图像存档与通讯系统PACS等等。     

Release of internal curing water from lightweight aggregates in cement paste investigated by neutron and X-ray tomography

A sealed sample of cement paste containing a pre-wetted and a dry lightweight aggregate (LWA) particle was investigated in the period between 0.5 and 20.3 h after mixing. Changes in the local water distribution in the sample during hydration were evaluated using the subtraction of 3D images obtained by subsequent neutron tomographies (NT). As both water retention in the LWA and its release to the cement paste are influenced by the pore structure of the aggregate, a high-resolution image of the sample was subsequently captured by X-ray tomography. The internal curing water released from the LWA traveled at least 3 mm from the LWA into the cement paste in the first day. Hardly any gradient in the water content of the cement paste against the distance from the LWA was observed. This suggests that the release of water for internal curing (IC) is relatively fast and the water is distributed fairly homogeneously from the LWA for at least 3 mm within the hydrating cement paste.     

Simulation on kink-band formation during axial compression of a unidirectional carbon fiber-reinforced plastic constructed by X-ray computed tomography images

X-ray computed tomography was used to obtain cross-sectional images of a unidirectional carbon fiber-reinforced plastic, where fiber locations in each cross-sectional image were identified. The three-dimensional model with fiber waviness was developed by connecting the fiber locations along the fiber direction. Numerical simulation for the initiation and formation of a kink-band during axial compression was performed using the three-dimensional finite element model. The load was increased almost linearly until it reached the compressive strength, after which both load and displacement were decreased, showing snap-back behavior. The matrix yielded locally with the increased axial compression, and fibers started to fall due to insufficient support by the yielded matrix. A kink-band was formed with an increase in the yielded area, and thus, the initiation of a kink-band was defined as the local yielding of the matrix. It was also shown that the kink-band was formed at the longitudinal location at which the average of initial local fiber misalignment angles in the cross-section was relatively large.     

Dielectric and magnetic properties of ZnCo-substituted X hexaferrites prepared by citrate sol-gel process

Ba₂Zn_2−xCo_xFe₂₈O₄₆ hexaferrites with x=2.0, 1.6, 1.2, 0.8, 0.4 and 0.0 were prepared by citrate sol-gel process. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The frequency-response complex dielectric constant and complex permeability of Ba₂Zn_2-xCo_xFe₂₈O₄₆ sintered at 1000-1200 °C had been investigated in the range from 100 MHz to 6 GHz. The pronounced natural resonance phenomena were observed in μ″ spectrum for the samples annealed at 1100 and 1200 °C. The natural resonance frequency of Ba₂Zn_2−xCo_xFe₂₈O₄₆ ferrites was intensively affected by the substitution of Zinc ion and annealing temperature.     

Effect of sol concentration on the structural, morphological, optical and photoluminescence properties of zirconia thin films

ZrO₂ thin films were deposited on quartz substrates from 10 wt.%, 20 wt.% and 40 wt.% solutions of Zirconium-n-butoxide in isopropanol by sol-gel dip-coating technique. Higher concentrated sols of 20 wt.% and 40 wt.% exhibited faster gelation, where as 10 wt.% sol remained stable for two months and films synthesized from this sol remained transparent and continuous even for 12 coatings. Ellipsometric study revealed that refractive index of the films increased with increase in sol concentration which is ascribed to the decrease in porosity. X-ray diffraction study showed that a tailoring of grain size from 7.9 to 39.2 nm is possible with increase in sol concentration. Atomic force microscopy studies showed a change in growth mode from vertical to lateral mode with increase in sol concentration. The film surface revealed positive skewness and high kurtosis values which make them favorable for tribological applications. The average optical transmittance in the visible region is highest (greater than 90%) for the film deposited from 10 wt.% sol. The optical band gap decreased from 5.74 to 5.62 eV with increase in the sol concentration. Photoluminescence (PL) spectra of the films exhibit an increase in the emission intensity with increase in sol concentration which substantiates better crystalline quality of the film deposited from 40 wt.% sol and increase in oxygen vacancies. The “Red shift” of the PL spectra with increase in sol concentration originates from the increase in the grain size with sol concentration which makes it suitable for generation of solid state lighting in light emitting diode.     

Determination of interface properties from experiments on the fragmentation process in single-fiber composites

This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as (T_II,max, G_IIc) = (75 MPa, 200 J/m²). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.     

Preparation and properties of transparent conductive indium-tin-oxide/polyimide substrates via a sol-gel process

High temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrates have been prepared from a series of thermally stable, high glass transition temperature (T_g) and colorless copolyimide films. The copolyimides were synthesized from 3,3′-diaminodiphenylsulfone, 9,9′-bis(4-aminophenyl) fluorene and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride monomers. Their T_gs were around 285-365 °C. The conductive ITO was synthesized by a sol-gel method, and then deposited onto the copolyimide films by a spin coating process. After thermal treatment at 300 °C under a nitrogen/hydrogen mixture gas for 24 h, the resistivity of the ITO film was 10⁻³ Ω cm, and its transmittance was 75% at the visible light region. Scanning electron microscopy and X-ray diffraction were used to observe the surface and morphology of the ITO films. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO/plastic substrates can be used in the next generation flexible flat panel displays and solar cell.     

Influence of calcination temperature of kaolin on the structure and properties of final geopolymer

In this paper, the structure of two types of metakaolins from kaolin calcined at 800 and 900 °C, respectively, and the obtained geopolymer were systematically characterized. It was found that calcination temperature had little effect on the environment of silicon atoms but had great effect on that of aluminum ones. ²⁷Al NMR analysis showed that tetrahedral aluminums in the metakaolin from kaolin calcined at 800 and 900 °C were in different environment, of the type AlQ₃(3Si) and AlQ₄(4Si), respectively, leading to different environment of aluminum atoms in the resulted geopolymer. Aluminum atoms in the geopolymer based on metakaolin from kaolin calcined at 800 °C were in the types of tetrahedral and octahedral, and silicon atoms were in the types of tetrahedral Q₄(3Al) together with a small amount of Q₄(0Al). However, geopolymer based on metakaolin from kaolin calcined at 900 °C consisted of Q₄(4Si) unit aluminum and Q₄(3Al) unit silicon. The results revealed that the calcination temperature had a great effect on environment of the aluminum atoms of the metakaolin, thus led to the different structure and properties including mechanical strength and thermal conductivity of the post obtained geopolymer.     

B位Cr替代对BiFeO3介电特性的影响

采用传统的固相反应法制备了BiFe1-xCrO3（x=0，0．01，0．1,0．3，0．5）系列陶瓷样品，运用X射线衍射仪对样品进行结构分析发现，随着Cr含量的增加BiFeO3的微观结构发生了改变；利用HP3458A型万用表在室温下测量样品的电阻率随Cr含量的变化关系发现适当的Cr替代可以在一定程度上提高样品的电阻率；室温下利用HP4294A型阻抗分析仪在100Hz～100kHz的频率范围内测试样品的介电性能随频率的变化关系，结果表明介电常数岛随着Cr替代量的增加先增大然后又减小，而tanδ则随着Cr替代量的增加出现了较为复杂的变化．     

An investigation into the damage development and residual strengths of open-hole specimens in fatigue

An extensive experimental program was carried out to investigate and understand the sequence of damage development throughout the life of open-hole composite laminates loaded in tension–tension fatigue. Quasi-isotropic carbon/epoxy laminates, with stacking sequence [45₂/90₂/−45₂/0₂]_S, [45/90/−45/0]_2S and [45/90/−45/0]_4S were examined. These were selected on the basis that under quasi-static loading the [45₂/90₂/−45₂/0₂]_S configuration exhibited a delamination dominated mode of failure whilst the [45/90/−45/0]_2S and [45/90/−45/0]_4S configurations showed a fibre dominated failure mode, previously described as “pull-out” and “brittle” respectively. Specimens were fatigue loaded to 1 × 10⁶ cycles or catastrophic failure, which ever occurred first. A number of tests were interrupted at various points as the stiffness dropped with increasing cycles, which were inspected using X-ray computed tomography (CT) scanning. A static residual strength program was carried out for run-out specimens of each configuration.     

Influence of hydrogen introduction on structure and properties of ZnO thin films during sputtering and post-annealing

ZnO thin films were prepared in Ar and Ar + H₂ atmospheres by rf magnetron sputtering, and then they were annealed in vacuum and Ar + H₂ atmosphere, respectively. The structure and optical-electrical properties of the films were investigated by X-ray diffraction, transmittance spectra, and resistivity measurement, and their dependences on deposition atmosphere, annealing treatment, and aging were studied. The results showed that adding H₂ in deposition atmosphere improved the crystallinity of the films, decreased lattice constant, increased band gap, decreased the resistivity by the order of 10⁴ Ω cm, but exhibited poor conductive stability with aging. After Ar + H₂ and vacuum annealing, crystallinity of the films deposited in Ar and Ar + H₂ was further improved; their resistivity was decreased by the order of 10⁵ and 10¹ Ω cm, respectively, and exhibited high conductive stability with aging. We suggest that the formed main defect is V_O and H_i when H₂ is introduced during deposition, which decreases the resistivity but cannot improve the conductive stability; hydrogen would remove negatively charged oxygen species near grain boundaries during Ar + H₂ annealing to decrease the resistivity, and grain boundaries are passivated by formation of a number of V_O-H complex (H_O) to improve the conductive stability at the same time. Under vacuum annealing, the hydrogen that is introduced non-intentionally from deposition chamber maybe plays an important role; it exists as H_O in the films to improve the conductive stability of the films.     

Influence of fly ash as a cement addition on the hardened properties of recycled aggregate concrete

The effects of the use of Class F fly ash as a cement addition on the hardened properties of recycled aggregate concrete were determined. In this study, four series of concrete mixtures were prepared with water-to-cement (w/c) ratios of 0.55, 0.50, 0.45 and 0.40. The recycled aggregate was used as 0%, 20%, 50% and 100% replacements of coarse natural aggregate. Furthermore, fly ash was employed as 0% and 25% addition of cement. Although the use of recycled aggregate had a negative effect on the mechanical properties of concrete, it was found that the addition of fly ash was able to mitigate this detrimental effect. Also, the addition of fly ash reduced the drying shrinkage and enhanced the resistance to chloride ion penetration of concrete prepared with recycled aggregate. Moreover, it was found that the drying shrinkage and chloride ion penetration decreased as the compressive strength increased. Compared with the results of our previous study, the present study has quantified the advantages of using fly ash as an additional cementitious material in recycled aggregate concrete over the use of fly use as a replacement of cement.     

On the structural, morphological, optical and electrical properties of sol-gel deposited ZnO:In films

Indium-doped zinc oxide thin films deposition was performed by the sol-gel technique using homogeneous and stable solutions of zinc acetate 2-hydrate and indium chloride in ethanol. Films were spin coated onto glass substrates. After drying and after a heat treatment at 450 °C, highly transparent (80%-90%) films were obtained. The effect on the structural, morphological, optical and electrical thin films properties of the dopant concentration was investigated. The temperature dependencies of the electrical conductivity under vacuum and in open atmosphere were analysed and discussed.     

Effect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12

Crystalline Li₄Ti₅O₁₂ is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li₄Ti₅O₁₂ particles after calcination at 800 °C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li⁺ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.     

Synthesis of alumina powders by the glycine-nitrate combustion process

The combustion synthesis technique using glycine as fuel and aluminum nitrate as an oxidizer is able to produce alumina powders. Thermodynamic modeling of the combustion reaction shows that as the fuel-to-oxidant ratio increases, the amount of gases produced and adiabatic flame temperatures also increases. X-ray diffractions showed the amorphous structure for as-synthesized powder and presence of well-crystallized α-Al₂O₃ after calcination at 1100 °C during soaking time of 1 h. Alumina's largest measured specific surface area was 15 m²/g with BET method and 0.51 glycine-to-nitrate ratio.     

Phase formation process of IrxSi1−x thin films Structure and electrical properties

Experimental data on the phase formation process of amorphous Ir_xSi_1−x thin films with 0.30 ≤ x ≤ 0.41 are presented and discussed in relation to electric transport properties. The structure formation process at temperatures from 300 K up to 1223 K was investigated by means of X-ray diffraction. Distinct phases were observed in the final stage in dependence on the initial composition: Ir₃Si₄, Ir₃Si₅, and IrSi₃. An unknown metastable phase was found in films with a silicon concentration of 61 at.% to 64 at.% after annealing above the crystallization temperature T = 970 K. The crystal structure of this phase was determined by the combined use of X-ray diffraction and electron diffraction. It was found to be monoclinic, basic-face centred with lattice constants a = 1.027 nm, b = 0.796 nm, c = 0.609 nm, and γ = 113.7°. Additionally, microstructure and morphology of the films were investigated by transmission electron microscopy (TEM). The annealing process was studied by means of mechanical stress investigations as well as by electrical resistivity and thermopower measurements. Correlations between the structure, the phase formation and the electrical transport behaviour are discussed on the basis of conduction mechanism.     

致密化工艺对PAN纤维结构和性能的影响研究

在聚丙烯腈基碳纤维原丝纺丝过程中,在干燥致密化之前使用不同的油剂上油,干燥致密化不同的时间,制得PAN纤维。利用SEM、XRD、纤维细度仪、纤维强伸度仪等分别对PAN纤维的表面形貌、晶体结构、纤度、强度、断裂伸长率和体密度进行研究。结果表明油剂可以有效防止纤维变形、粘连、并丝和表面缺陷的产生;随着致密化时间的增加,PAN纤维晶面间距、晶粒尺寸和断裂伸长率变小,结晶度、强度和体密度变大,纤度不变;使用不同的油剂和浓度,最后得到的PAN纤维的性能不同。     

Effect of salt concentration on the electrical and morphological properties of calcium phosphates obtained via microwave-induced combustion synthesis

Calcium phosphates (CaP) have been widely used in biomedical applications. One of the most versatile techniques for obtaining CaP is auto-combustion synthesis. This technique stands out because of its low cost and high efficiency; however, the difficulty of controlling the size and morphology of the product is its principal disadvantage. The aim of this study was to synthesize calcium phosphates through microwave-induced and salt-assisted solution combustion synthesis. The initial ratio of Ca/P was 1.5, employing urea as fuel and potassium chloride as an additive. The morphology and the electrical properties of CaP in relation to the amount of salt added were evaluated using scanning electron microscopy (SEM) and impedance spectroscopy, respectively. It was found that the inclusion of salt during the synthesis affects the morphology of calcium phosphates, creating whisker-like structures, with lengths approximately between 500 nm and 1 µm and widths between 30 nm and 300 nm, which depend on the salt concentration. Calcium pyrophosphate was the major phase of the synthetized product without the addition of salt, and hydroxyapatite (HAP) and chlorapatite (CAP) when salt was included. The dielectric constant exhibited lower values for the samples rich in calcium pyrophosphate and values between 16 and 32 for HAP and CAP at 1 kHz.     

高分子导电聚合物PEDT化学聚合过程及结构性能研究

分析了3,4-乙烯二氧噻吩（EDT）单体聚合过程,系统地研究了聚合条件对PEDT薄膜性能的影响,并对PEDT薄膜电学性能和热稳定性进行分析。结果表明聚合过程的起始温度、聚合时间、导电增强剂的含量、反应过程的溶液体系等因素对导电聚合物PEDT的结构及性能有显著的影响。将所制得的PEDT作为固体电解质用以制造片式钽电解电容器,电容器性能得到了明显的改善,其ESR值低于50mΩ。     

Dynamic modulus simulation of the asphalt concrete using the X-ray computed tomography images

The objective of this study is to predict the dynamic modulus of asphalt mixture using both two-dimensional (2D) and three-dimensional (3D) Distinct Element Method (DEM) generated from the X-ray computed tomography (X-ray CT) images. The 3D internal microstructure of the asphalt mixtures (i.e., spatial distribution of aggregate, sand mastic and air voids) was obtained using the X-ray CT. The X-ray CT images provided exact locations of aggregate, sand mastic and air voids to develop 2D and 3D models. An experimental program was developed with a uniaxial compression test to measure the dynamic modulus of sand mastic and asphalt mixtures at different temperatures and loading frequencies. In the DEM simulation, the mastic dynamic modulus and aggregate elastic modulus were used as input parameters to predict the asphalt mixture dynamic modulus. Three replicates of a 3D DEM and six replicates of a 2D DEM were used in the simulation. The strain response of the asphalt concrete under a compressive load was monitored, and the dynamic modulus was computed. The moduli of the 3D DEM and 2D DEM were then compared with both the experimental measurements results. It was revealed that the 3D discrete element models successfully predicted the asphalt mixture dynamic modulus over a range of temperatures and loading frequencies. It was found that 2D discrete element models under predicted the asphalt mixture dynamic modulus.