Ion energy distribution functions of low energy beams formed by wire extraction electrodes

The two-electrode extractor system made of 0.1 mm diameter tungsten wires separated by 0.7 mm has formed an argon ion beam with 50 V extraction potential. Energy spreads of the extracted beams were typically less than 2 eV when the beam current density was low. The beam intensity rapidly decreased as the distance between the extractor and the beam detector increased, indicating space charge limited transport of the beam. Problems associated with the emittance measurements are also discussed.     

High frequency operation of a hot filament cathode for a magnetized plasma ion source

A tungsten filament cathode has been operated with an ac heating current to excite a plasma in a linear magnetic field. Both the discharge current and the ion saturation current in plasma near the extraction hole of the ion source exhibited fluctuations. The discharge current fluctuated with the amplitude less than 2% of the average, and the frequency two times the frequency of the heating current. Fluctuation amplitude of the ion saturation current was about 10% of the average, while the frequency was the same as that of the heating current. The ac operation has prolonged the lifetime of a hot filament cathode by about 50%.     

Pulsed ion extraction from a hybrid plasma using a shunting arc discharge

A hybrid plasma is generated by combining a burst methane rf (195 kHz) plasma with a carbon shunting arc discharge. The shunting arc discharge triggers the rf methane plasma. As a result, the rf plasma is initiated over a wide range of ambient gas pressure from 0.045 Pa as a base pressure to a methane pressure of 1.26 Pa, at which the rf plasma is not self-ignited. When a target is immersed in the rf- and shunting arc-hybrid plasma, and a negative pulse voltage is applied to the target, carbon ions are extracted from the hybrid plasma. When the carbon shunting arc ionizes the methane gas, an rf plasma is initiated and the ionization of methane is significantly enhanced in the rf plasma. The plasma density in the hybrid plasma increases by a factor of approximately 5-9 compared to that of the shunting arc discharge.     

6-Axis control cutting of overhanging curved grooves by means of non-rotational tool with application of ultrasonic vibrations

This paper presents a new machining method that efficiently cuts overhanging curve grooves on wall surfaces without causing a collision between the tool and the workpiece. It also describes the development of software for 6-axis control grooving and the effect of applied ultrasonic vibrations (USV) in cutting overhanging grooves (OHG). In general, rotational tools are used to produce grooves, thus resulting in long circular arc segments at the cutting end points, as well as placing restrictions on the manufacture of grooves with continuous change in curvature, while ensuring that they do not overshoot the side clearance angle of the cutting edge with the groove. The study aims at machining OHGs presently impossible to machine by conventional methods. From the experimental results, it was found that the new machining method, which is 6-axis control cutting using a non-rotational tool with the application of USV, is capable of cutting an OHG on wall surfaces correctly.     

Effect of Substrate Temperature on Deposition Behavior of Copper Particles on Substrate Surfaces in the Cold Spray Process

The deposition behavior of sprayed individual metallic particles on the substrate surface in the cold spray process was fundamentally investigated. As a preliminary experiment, pure copper (Cu) particles were sprayed on mirror-polished stainless steel and aluminum (Al) alloy substrate surfaces. Process parameters that changed systematically were particle diameter, working gas, gas pressure, gas temperature, and substrate temperature, and the effect of these parameters on the flattening or adhesive behavior of an individual particle was precisely investigated. Deposition ratio on the substrate surface was also evaluated using these parameters. From the results obtained, it was quite noticeable that the higher substrate temperature brought about a higher deposition rate of Cu particles, even under the condition where particles were kept at room temperature. This tendency was promoted more effectively using helium instead of air or nitrogen as a working gas. Both higher velocity and temperature of the particles sprayed are the necessary conditions for the higher deposition ratio in the cold spraying. However, instead of particle heating, substrate heating may bring about the equivalent effect for particle deposition. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Ultrastructure of submandibular salivary glands of mouse: TEM and HRSEM observations

The fine structure of submandibular glands of mouse were analyzed using light microscopy (LM), high resolution scanning electron microscopy (HRSEM), and transmission electron microscopy (TEM) methods. For LM, the specimens were embedded in Spurr resin, stained by toluidin blue solutions. For TEM, the tissues of submandibular salivary glands were fixed with modified Karnovsky solution and postfixed with osmium tetroxide. For HRSEM, the tissues were fixed with 2% osmium tetroxide solution in 1/15M sodium phosphate buffer (pH 7.4). The samples were immersed successively in dymethylsulphoxide and freeze cracked. The maceration was made in diluted osmium tetroxide for 24-48 h. The samples were examined by high resolution scanning electron microscopy. The intracellular components of acinar and ductal cells revealed clearly the Golgi apparatus, rough endoplasmic reticulum, secretory granules, and mitochondria. The end bulbs of Golgi lamellae and flattened cisterns of rough endoplasmic reticulum showed the luminal surface. A few mitochondria were identified intermingling between the rough endoplasmic reticulum and the mitochondriales cristae in three-dimensional HRSEM images. Secretory granules were numerous and presented different sizes. Small granules of ribosomes were attached on cistern surface, measuring 20-25 nm in diameter. Numerous arranged microvilli were found on the luminal surface of secretory canaliculus. The contact surfaces of acinar cells revealed complicated interdigitations by cytoplasmic processes. The mitochondria of duct cells were disposed vertically and surrounded by basal infoldings of plasma membranes. Basement membrane showed a spongy-like structure having an irregular surface with various strands and meshes of fine collagen fibrils.     

Probabilistic distributions of plate buckling strength for normal and bridge high-performance steels

The probabilistic distributions of buckling strengths for compressive plates of normal and bridge high-performance steels were obtained through numerical analyses in order to develop a nominal design strength and a corresponding safety factor. In the numerical analyses, Monte Carlo simulation was used in combination with the response surface method to reduce the effort associated with the finite element analyses. For each value of the slenderness parameter R, a response surface of the normalized local bucking strength was determined based on the results of 114 finite element analyses using different residual stresses and initial defections. The response surface is approximated as a simple algebraic function of the residual stress and the initial deflection. Monte Carlo simulation is then carried out in order to evaluate the probabilistic distribution of the local bucking strength. The mean values obtained in the present study approach those of a mean curve proposed based on experiments. The standard deviation of the present study was approximately half that obtained based on experimental results in the range of 0.6 <R<1.2.     

Experimental and numerical investigations of flow fields behind a small wind turbine with a flanged diffuser

Experimental and numerical investigations were carried out for flow fields of a small wind turbine with a flanged diffuser. The present wind-turbine system gave a power coefficient higher than the Betz limit (=16/27) owing to the effect of the flanged diffuser. To elucidate the flow mechanism, mean velocity profiles behind a wind turbine were measured using a hot-wire technique. By processing the obtained data, characteristic values of the flow fields were estimated and compared with those for a bare wind turbine. In addition, computations corresponding to the experimental conditions were made to assess the predictive performance of the simulation model presently used and also to investigate the flow field in more detail. The present experimental and numerical results gave useful information about the flow mechanism behind a wind turbine with a flanged diffuser. In particular, a considerable difference was seen in the destruction process of the tip vortex between the bare wind turbine and the wind turbine with a flanged diffuser.     

Changes in stable isotopes, lignin-derived phenols, and fossil pigments in sediments of Lake Biwa, Japan: implications for anthropogenic effects over the last 100 years

We measured stable nitrogen (N) and carbon (C) isotope ratios, lignin-derived phenols, and fossil pigments in sediments of known ages to elucidate the historical changes in the ecosystem status of Lake Biwa, Japan, over the last 100 years. Stable N isotope ratios and algal pigments in the sediments increased rapidly from the early 1960s to the 1980s, and then remained relatively constant, indicating that eutrophication occurred in the early 1960s but ceased in the 1980s. Stable C isotope ratios of the sediment increased from the 1960s, but decreased after the 1980s to the present. This decrease in stable C isotope ratios after the 1980s could not be explained by annual changes in either terrestrial input or algal production. However, when the C isotope ratios were corrected for the Suess effect, the shift to more negative isotopic value in atmospheric CO(2) by fossil fuel burning, the isotopic value showed a trend, which is consistent with the other biomarkers and the monitoring data. The trend was also mirrored by the relative abundance of lignin-derived phenols, a unique organic tracer of material that originated from terrestrial plants, which decreased in the early 1960s and recovered to some degree in the 1980s. We detected no notable difference in the composition of lignin phenols, suggesting that the terrestrial plant composition did not change markedly. However, we found that lignin accumulation rate increased around the 1980s. These results suggest that although eutrophication has stabilized since the 1980s, allochthonous organic matter input has changed in Lake Biwa over the past 25 years.     

Group effect on ultimate lateral resistance of piles against uniform ground movement

In earthquake engineering, pile foundations are designed to withstand the lateral loading that results from large displacements due to ground movement caused by strong earthquakes. The distress and failure of superstructures occurs when the lateral load exceeds the ultimate lateral resistance of the piles. The aim of this study is to estimate the ultimate lateral resistance of piles especially in terms of the group effect induced by the pile arrangement. Several experimental and numerical analyses have been conducted on pile groups to investigate the group effect when the groups are subjected to uniform large horizontal ground movement. However, the ultimate lateral resistance of the pile groups in these studies was calculated by applying load to the piles. The present study directly assesses the ultimate lateral resistance of pile groups against ground movement by systematically varying the direction of the ground movement. Although the load bearing ratio of each pile in a pile group, defined as the ratio of the ultimate lateral resistance of each pile in a pile group to that of a single pile, is an important design criterion, it was difficult to assess in past works. This study focuses on the load bearing ratio of each pile against ground movement in various directions. The use of the finite element method (FEM) provides options for simulating the pile-soil system with complex pile arrangements by taking the complicated geometry of the problem into account. The ultimate lateral resistance is examined here for pile groups consisting of a 2?×?2 arrangement of four piles, as well as two piles, three piles, four piles, and an infinite number of piles arranged in a row through case studies in which the pile spacing is changed by applying the two-dimensional rigid plastic finite element method (RPFEM). The RPFEM was extended in this work to calculate not only the total ultimate lateral resistance of pile groups, but also the load bearing ratio of the piles in the group. The obtained results indicate that the load bearing ratio generally increases with an increase in pile spacing and converges to almost unity at a pile spacing ratio of 3.0 with respect to the pile diameter. Moreover, the group effect was further investigated by considering the failure mode of the ground around the piles.