Experimental study to control the insertion resistance of internal medical instrument using magnetic field oscillation

We present a new method to reduce the insertion resistance for internal medical instruments by means of vibration. A rotating permanent magnet generates an oscillated magnetic field and vibrates the internal medical instruments from outside of the body. We investigated the relation between the frequency of vibration and the insertion resistance with a pin on flat test system in vitro. As a result, vibration is effective to reduce the friction and it is possible to keep a smooth insertion by vibration.     

基于微观损伤模型的强度非均质焊接接头抗延性裂纹扩展阻力特性研究

基于材料微观损伤模型,采用三维有限元数值方法,定量研究了焊接接头中强度匹配、试件几何型式对接头抗延性裂纹扩展阻力特性的影响。首先由标准三点弯曲试件的阻力曲线,得出反映材料微观损伤的特殊单元模型控制参量,再根据该参量对不同接头强度匹配下双边缺口拉伸试件的阻力曲线进行了定量预测,其结果与试验结果相当吻合。表明特殊单元模型能很好地描述材料的抗延性裂纹扩展阻力特性。     

Behaviour of connective tissue in fish surimi on fractionation by sieving

The surimis prepared from the three fish species, red barracuda Sphyraena pinguis, yellow sea bream Dentex tumifrons, and spotted shark Mustelus manazo, were fractionated by sieving through a 30-mesh stainless steel sieve. Chemical analyses revealed significant differences in the collagen content among the residual fraction on the sieve (fraction A), the passed fraction (fraction C), and the original surimi before sieving (fraction B): the fractions A and B showed values 10–20 and 5–10 times higher than those of the fraction C, respectively, for all the species examined. Histological observation indicated the richness of the thick connective tissues derived from myocommata in fractions A and B, while thick connective tissue was hardly observed in fraction C. These results suggested that the present fractionation method may have an effect of reducing the collagen content to about 10–20% of the original value, and that a large part of collagen in fish surimi exists in the relatively thick connective tissue, probably derived from myocommata.     

Fabrication and mechanical properties of monolithic MoSi2 by spark plasma sintering

Fine MoSi₂ powders containing a small amount of Mo₅Si₃ have been prepared by self-propagating high-temperature synthesis (SHS), followed by spark plasma sintering (SPS) for 10 min at 1200-1500°C and 30 MPa. Dense MoSi₂ materials, in which the grain size is ∼7.5 μm, have been fabricated at 1300°C. They exhibit excellent mechanical properties: Vicker’s hardness H_v (10.6 GPa), fracture toughness K_IC (4.5 MPa m^1/2), and bending strength σ_b (560 MPa). The strength of 325 MPa can be retained up to 1000°C.     

局部硬化区周围的应力应变特性对HAZ断裂行为的影响

从力学的观点出发，将高强钢焊接热影响区粗晶区中硬化组织ＭＡ组元视作局部硬化区（ＬＨＺ）。采用二维有限元数值方法分析了ＬＨＺ周围的应力应变分布。结果表明：ＬＨＺ存在时，ＬＨＺ内部应力升高，ＬＨＺ与基体产生变形差。这意味着ＬＨＺ内部或ＬＨＺ与基体界面容易引发裂纹。最后通过对ＴＭＣＰ钢焊接热影响区微观裂纹的实验观察，验证了本文提出的断裂模型。     

Structural and magnetic properties of FePd and CoPd alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001)_B1, (110)_B1, and (111)_B1 orientations at 600 °C by ultra high vacuum rf magnetron sputtering. L1₀-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001)_B1 substrates. FePd epitaxial films consisting of L1₀(110) and L1₀(011) crystals are formed on MgO(110)_B1 substrates. The c-axis of L1₀(110) crystal is parallel to the substrate surface, whereas that of L1₀(011) crystal is 44° canted from perpendicular direction. L1₀-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111)_B1 substrates. L1₀ ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001)_A1, (110)_A1, and (111)_A1 orientations epitaxially grow on MgO substrates of (001)_B1, (110)_B1, and (111)_B1 orientations, respectively. The magnetization properties of L1₀ ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation.     

Fluid flow and heat transfer of opposing mixed convection adjacent to vertical heated plates

Opposing mixed convective flows induced around heated vertical plates were investigated experimentally. The experiments have been carried out with air and test plates of 100 mm and 200 mm long. The flow fields over the heated plates were visualized and the local heat transfer coefficients of the plates were measured for a wide range of Reynolds and Rayleigh numbers; Re_L = 7 × 10²−1.5 × 10⁴, Ra = 9 × 10⁶−8 × 10⁸. The visualization experiments showed that the separation of the boundary layer appears first at the trailing edge of the plate when the non‐dimensional parameter of (Gr/Re) = 0.35, and that the separation point reaches the leading edge when (Gr_L^*/Re_L^2.5) = 1.0. The heat transfer experiments showed that the above flow separation retards the heat transfer significantly from that of pure forced convection. It was also revealed that the flows over the heated plates can be categorized into forced, natural, and combined convection using the above parameter, (Gr/Re), as (Gr/Re) < 0.2, (Gr/Re) > 3 and 0.2 < (Gr/Re) < 3, respectively. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(8): 595–607, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20080     

A new medical microrobot for minimal invasive surgery

A new medical microrobot to drive endoscopes into endocoeles is presented. The structure of the microrobot is very simple; it consists of a right spirally grooved micromotor, a left spirally grooved cylinder and a flexible coupling. When the micromotor rotates, a hydrodynamic mucus film is formed because highly viscous mucus exists in endocoeles. The mucus film can prevent direct contact between the microrobot and the endocoele, and the injury to organic tissues may be avoided. The locomotion speed and the hydrodynamic mucus film thickness formed when the microrobot drives endoscopes into endocoeles have been calculated according to hydrodynamic lubrication theory. The results indicate that the microrobot can be suspended to drive endoscopes quickly into endocoeles. This has been confirmed by experiments.     

Modeling for plasma-enhanced catalytic reduction of nitrogen oxides

In this work, we simulated the whole processes of plasma-enhanced selective catalytic reduction for nitrogen oxides removal with hydrocarbon additive. The simulation model consists of plasma simulation and catalysis simulation. First, single filamentary microdischarge in dielectric barrier discharge was calculated to evaluate the radical production yield as a function of specific input energy. Second, the chemical reaction process in the discharge reactor was simulated to find the gas reforming property by the plasma. This plasma simulation was applied to NO oxidation process in atmospheric pressure N₂/O₂/NO/C₃H₆ mixtures under various discharge conditions. Finally, the catalytic reaction process was modeled using simple mass balance equations in gas-phase and on catalyst surface. The catalytic reaction simulation was tested for the reduction of nitrogen oxides on γ-Al₂O₃ catalyst in N₂/O₂/NO/C₃H₆ and in N₂/O₂/NO₂/C₃H₆.     

Hot Isostatic Pressing of Chromium Nitrides (Cr2N and CrN) Prepared by Self-Propagating High-Temperature Synthesis

Cr₂N, CrN, and their mixtures (with desired fractions) have been prepared via self-propagating high-temperature synthesis (SHS) under a controlled nitrogen pressure, followed by hot isostatic pressing at 1300°C and 196 MPa under an atmosphere of argon gas. The combustion temperature increased as the nitrogen pressure increased. Single-phase Cr₂N was formed at 1040°C under a pressure of 0.18 MPa, and single-phase CrN was formed at 1730°C under a pressure of 2 MPa. The mechanical properties of the dense nitride ceramics (99.2% of the theoretical density) have been examined; the Vickers hardness (11.2 GPa for CrN and 14.5 GPa for Cr₂N) increased linearly as the fraction of Cr₂N increased, whereas the fracture toughness (∼4.7 MPa·m^1/2) and bending strength (∼355 MPa) are constant, regardless of the fraction of Cr₂N/CrN.