液滴机械手的数值仿真与试验研究

为分析液滴机械手的控制机理, 建立液滴机械手的流体动力学仿真模型,仿真分析液滴机械手的控制机理,研究机械手端面形成液滴的形态跟随机械手端面形状的变化关系,讨论影响液滴机械手性能的因素,并通过试验验证仿真模型的正确性和提出方法的可行性．数值仿真和试验结果表明:通过控制各钨丝棒的上下移动量,可以改变液体和各钨丝棒的接触壁面,使机械手端面形成液滴的形态随之改变;基于表面张力吸附在液滴上的微小部件的姿态将随着液滴形态的改变而变化,从而可以实现对于微小部件姿态的控制．适当调整机械手的参数,如钨丝棒的数目、尺寸、各钨丝棒的移动量,以及改变液滴的性质等,可以满足微装配过程中各种操作目标的要求．     

Fabrication of Function‐Graded Proton Exchange Membranes for Direct Methanol Fuel Cells Using Electron Beam‐Grafting

Function‐graded proton exchange membranes (G‐PEMs) based on poly(tetrafluoroethylene‐co‐hexafluoropropylene) were fabricated for direct methanol fuel cells (DMFCs) via electron beam‐grafting using the heterogeneous energy deposition technique. The G‐PEMs had a water uptake gradient in the proton transfer direction, originating from the sulfonic acid group gradient. The distribution of sulfonic acid groups in the various G‐PEMs was evaluated using X‐ray photoelectron spectroscopy. Four types of PEMs (flat‐type, strong‐gradient, meso‐gradient, and weak‐gradient types) were fabricated. By varying the direction of the G‐PEMs, the methanol permeation test and DMFC operation were performed with two orientations of the sulfonic acid group gradient, decreasing from the methanol injection (anode) side (decrease‐type) or the other (cathode) side (increase‐type). The methanol permeability of the strong‐gradient, meso‐gradient, and weak‐gradient G‐PEMs was lower than that of Nafion®117 and the flat‐type PEM. The “increase‐type” orientation of the strong‐gradient G‐PEM resulted in the lowest methanol permeability. The DMFC performance of the G‐PEMs was influenced by the thickness direction, such as “decrease‐type” and “increase‐type.” The performance of the “decrease‐type” assembly was higher than that of the “increase‐type.” The “decrease‐type” assembly with P‐200 k (weak‐gradient G‐PEM) exhibited the highest performance of the fabricated PEMs, comparable to that of Nafion®117.     

How does heme axial ligand deletion affect the structure and the function of cytochrome b562?

We have recently generated a new mutant of cytochrome b₅₆₂ (cytb₅₆₂)in which Met7, one of the axial heme ligands, is replaced byAla (M7A cytb₅₆₂). The M7A cytb₅₆₂ can bind heme and the UV-visibleabsorption spectrum is of a typical high-spin ferric heme. Toinvestigate the effect of the lack of Met7 ligation on the structuralintegrity of cytb₅₆₂, thermal transition analyses of M7A cytb₅₆₂were conducted. From the thermodynamic parameters obtained,it is concluded that the folding of M7A cytb₅₆₂ is comparableto the apoprotein despite the presence of heme. On the otherhand, exogenous ligands such as cyanide and azide ions are readilybound to the heme iron, indicating that the axial coordinationsite is available for substrate binding. The peroxidase activityof this mutant is thus examined to evaluate new enzymatic functionat this site and M7A cytb₅₆₂ was found to catalyze an oxidationreaction of aromatic substrates with hydrogen peroxide. Theseobservations demonstrate that the Met7/His102 bis-ligation tothe heme iron is crucial for the stable folding of cytb₅₆₂,whereas the functional conversion of cytb₅₆₂ is successfullyachieved by the loose folding together with the open coordinationsite.     

Basic characterization of polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) synthesized from propene and 1,5‐hexadiene with modified stopped‐flow method

Block copolymerization of propene and 1,5‐hexadiene was carried out by a modified stopped‐flow polymerization method with an MgCl₂‐supported Ziegler catalyst. The resulting polymer, polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) (PP‐b‐(PMCP‐co‐PP)), in which the crystallizable PP part was linked with the non‐crystallizable PMCP‐co‐PP part, was characterized by optical microscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile testing. The block copolymer having a chemical linkage between PP and PMCP‐co‐PP showed properties different from those of homopolymer, random copolymer and blend polymer. © 2001 Society of Chemical Industry     

Facile orientation of unmodified BN nanosheets in polysiloxane/BN composite films using a high magnetic field

Composite films consisting of highly oriented boron nitride (BN) nanosheets in polysiloxane were fabricated without modifying the BN surface by applying a high magnetic field generated by a superconducting magnet. The hexagonal BN nanosheets were dispersed by sonication in a prepolymer mixture of polysiloxane. The homogeneous suspension was then cast on a polyamide spacer of microscale thickness and a magnetic field was applied before the mixture became crosslinked. The BN nanosheets in the polysiloxane were aligned with high anisotropy either parallel or perpendicular to the composite film plane depending on the magnetic flux direction. The fabricated composite films exhibited enhanced thermal conductivity by controlling the anisotropy of the BN nanosheets in the film. The mechanisms for rotation of BN nanosheets and heat diffusion across the composite film are discussed.     

Diffusion of platinum, vanadium and manganese in Ni3Al phase under high pressure

Diffusion of platinum, vanadium, and manganese in the Ni₃Al phase is investigated under high pressure. Platinum atoms occupy cubic face centred sites (α) in the L1₂ ordering structure. Vanadium atoms occupy cubic corner sites (β). Manganese atoms occupy both sites. Activation volumes ΔV for diffusion of these diffusing atoms to the molar volume of the Ni₃Al phase V₀ are as follows:

Additive effects of tripalmitin and low-density polyethylene on morphologies and tensile properties of polybutene-1/micro fibrous cellulose composite

Effects of tripalmitin (TP) and low-density polyethylene (LDPE) loading on morphologies and tensile properties of polybutene-1 (PB)/micro fibrous cellulose (MFC)/composite were studied. The scanning electron microscope (SEM) observation showed that the 10 % TP loading brought about good dispersity of the MFC in PB matrix. The TP worked as a good compatibilizer for the composite. The Young’s moduli of the PB/TP (10 %)/MFC (10 and 20 %) content were slightly lower than those of the corresponding PB/MFC under 0, 48 and 96 h aging treatments at r. t., and that of the PB/TP (10 %)/MFC (50 %) specifically decreased up to 73 %. The TP loading increased the PB crystal phase transformation rate, and its behavior suggested that there existed TP in the interface between the PB and MFC. The elongation at break values increased up to 281 % of the corresponding PB/MFC ones. The 30 % TP loading little improved the tensile properties of the composite as compared with the 10 % one. The 10 % LDPE loading brought about 5–51 % higher Young’s moduli than those of the corresponding PB/MFC without the aging treatment although the composite rapidly became embrittlement by the higher MFC content and aging. It was found that the LDPE loading highly improved the interface strength, in particular, without the aging treatment.     

An 80-ns 1-Mb flash memory with on-chip erase/erase-verifycontroller

An internal erase and erase-verify control system has been implemented in an electrically erasable, reprogrammable, 80-ns 1-Mb flash memory, which is suitable for in-system reprogram applications. The memory utilizes a one-transistor type cell with a cell area of 10.4 μ². The die area is 32.3 mm². An erase mode is initiated by a 50-ns pulse. An erase and erase-verify sequence is automatically conducted in a chip without any further external control. The internal status can be checked through a status-polling mode. The 80-ns access time results from advanced sense amplifiers as well as low-resistance polysilicide word lines and scaled periphery transistors. To realize high-sensitivity, high-speed sense circuits, a pMOS transistor (whose gate is connected to its drain) is used as a load transistor     

Facile preparation of a polysiloxane-based hybrid composite with highly-oriented boron nitride nanosheets and an unmodified surface

A facile technique was developed to fabricate polysiloxane-based hybrid composite films containing boron nitride (BN) nanosheets using a nanopulse-width electric field. BN nanosheets assumed anisotrophic alignment under the electric field, without requiring surface coating with metallic nano particles despite the wide band gap. BN was dispersed by sonication in a pre-polymer polysiloxane mixture. The homogeneous suspension was cast on a glass spacer and subjected to either a DC electric field or a nanopulse-width electric field before the mixture was cured through polymerization. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that BN nanosheets in the polysiloxane matrix were aligned with high anisotropy to the electric field direction, which was perpendicular to the film plane. The transmittance of the film samples, measured by UV–visible spectrometry, indicated that the composite, prepared using a nanopulse-width electric field manifested a significantly improved transmittance, compared with composites prepared without using the electric field.