Thermal and mechanical properties of epoxy composites reinforced by a natural hydrophobic sand

If a low weight percentage of crude fine fillers can improve properties of polymer materials directly without complicated chemical treatment process involved, it will be significant for many industrial applications. Our previous study indicated that a kind of Cancun natural sand could be an effective filler material for polymer composites. In this current work, the epoxy composites reinforced by this kind of natural sand particles were prepared and thermal and mechanical properties of the composites containing up to 5 wt % of the sand particles were characterized. Results showed that the highest flexural strength appears in the epoxy composite containing 1 wt % sand particles. A damage model was used to interpret the flexural properties, which showed an acceptable agreement with the experimental results. The glass transition temperature, high temperature storage modulus, and dimensional stability of the sand/epoxy composites monotonically increased with the addition of the sand particles. The sand particle/epoxy composites also displayed a noticeable enhancement in thermal conductivity. Theoretical analysis showed that in addition to conduction, other heat transport mechanisms played roles in the improved heat transmission through the composites. As a natural porous micron-scale material, Cancun sand has the potential for applications in cost-effective composites with enhanced mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electronic properties of dehydrogenated nanodiamonds: A first-principles study

First-principles calculations using quantum-mechanical density functional theory (DFT) are carried out to study the geometric structure and electronic properties of dehydrogenated nanodiamonds with diameters varying from 0.8 nm to 1.6 nm. The results show that the electronic properties of dehydrogenated nanodiamond are quite different from those of bulk diamond or hydrogenated nanodiamond. Surface atoms play an important role in the electronic structure, especially the states near the Fermi level, for dehydrogenated nanodiamond. In addition, it has been revealed that the size-dependent feature in the electronic properties for dehydrogenated diamonds is also contributed by the surface effect, in addition to the quantum confinement effect.     

Development of composite tissue scaffolds containing naturally sourced mircoporous hydroxyapatite

The aims of this work were to investigate the conversion of a marine alga into hydroxyapatite (HA), and furthermore to design a composite bone tissue engineering scaffold comprising the synthesised HA within a porous bioresorbable polymer. The marine alga, Phymatolithon calcareum, which exhibits a calcium carbonate honeycomb structure, with a natural architecture of interconnecting permeable pores (microporosity 4–11 μm), provided the initial raw material for this study. The objective was to convert the alga into hydroxyapatite while maintaining its porous morphology using a sequential pyrolysis and chemical synthesis processes. Semi-quantitative XRD analysis of the post-hydrothermal material (pyrolised at 700–750 °C), indicated that the calcium phosphate (CaP) ceramic most likely consisted of a calcium carbonate macroporous lattice, with hydroxyapatite crystals on the surface of the macropores. Cell visibility (cytotoxicity) investigations of osteogenic cells were conducted on the CaP ceramic (i.e., the material post-hydrothermal analysis) which was found to be non-cytotoxic and displayed good biocompatibility when seeded with MG63 cells. Furthermore, a hot press scaffold fabrication technique was developed to produce a composite scaffold of CaP (derived from the marine alga) in a polycaprolactone (PCL) matrix. A salt leaching technique was further explored to introduce macroporosity to the structure (50–200 μm). Analysis indicated that the scaffold contained both micro/macroporosity and mechanical strength, considered necessary for bone tissue engineering applications.     

飞行人员骨密度与内分泌调节关系的探讨

对37名骨密度(BD)低下的飞行员(实验组)和BD正常的48名飞行员、100名地面人员(正常对照组)进行了BD和血清TT_3、TT_4、TSH IRMA、CT、PTH、E_2和T放射免疫测定。结果显示,实验组BD均值明显低于对照组(p<0.01),血清TT_3、TT_4、CT、E_2(女性)和T(男性)均值与对照组比较,大多数年龄存在着显著或非常显著差异(p<0.05或p<0.01)。同时对飞行人员BD与几种内分泌激素关系进行了探讨。     

High-speed InGaP/GaAs HBTs with a strained InxGa1-xAs base

A self-aligned InGaP/GaAs heterojunction bipolar transistor with a compositionally graded In_xGa_1-xAs base has been demonstrated with f_T=83 GHz and f_max=197 GHz. To our knowledge, these results are the highest reported for both parameters in InGaP/GaAs HBT's. The graded base, which improves electron transport through the base, results in a DC current gain and a cutoff frequency which are 100% and 20% higher, respectively, than that achieved by an identical device with a nongraded base. The high f_max results from a heavily doped base, self-aligned base contacts, and a self-aligned collector etch. These results demonstrate the applicability of InGaP/GaAs HBT's in high-speed microwave applications     

Characterization of optoacoustic surgical devices

Describes a measurement technique specially developed to characterize optoacoustic sources. The technique provides a convenient baseline for a comparison of different surgical ultrasonic systems utilizing optoacoustic and ultrasonic transducers. In addition, it provides a well-defined tool to optimize the performance of a variety of designs. Attention is focused on the laser-assisted devices in which appropriately delivered light energy is converted into acoustic shock wave. A meaningful comparison of such devices with other therapeutic equipment designed for a direct interaction with tissue requires knowledge of energy needed for a successful surgical treatment. It is demonstrated that knowledge of the key shock wave parameters allows the total acoustic energy associated with the shock wave to be determined. The procedure developed to calculate this energy is discussed and it is shown that the value of this energy can be conveniently used as an indicator of efficacy of an optoacoustic converter in a clinical environment. The influence of the performance of the polyvinylidene fluoride (PVDF) hydrophone probes on the measurement results was also analyzed. It was determined that when appropriately selected, the wide-band PVDF probes are well suited for characterization of the optoacoustic devices in the frequency range 1-100 MHz. The characterization procedure developed is applicable to surgical ultrasonic systems including conventional and laser-assisted phacoemulsifiers     

Cast bulk ZrTiAlCuNi amorphous alloys

Cylindrical bulk amorphous samples with diameters up to 10 mm have been prepared by casting ZrTiAlCuNi alloys in a copper mould. In order to rank glass-forming ability as a function of alloy composition, alloys were also cast into wedge-shaped moulds; to a first approximation, the thickness of the amorphous region obtained can be taken as an indication of glass-forming ability. The compositions which lead to the production of bulk glasses all have reduced glass transition temperatures in excess of 0.65 and the extremely high glass-forming ability of these compositions is discussed. We suggest that both the Al and Ti contents are determining factors for the production of bulk amorphous samples and these are believed to reduce the driving force for, and hence the rate of, crystallisation. These amorphous alloys have been found to display high thermal stability and can be annealed for several minutes in the supercooled liquid region. They are ductile at room temperature and have a high value of yield stress.