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31.
The consideration of orbital angular momentum of an electric field(twisted mode) is applied to the kinetic theory of plasma. The linearized Vlasov–Poisson equation is solved for the anisotropic thermal distributed bi-Maxwellian and Cairns distributions of electrons to obtain the damping rates of twisted waves. The dispersion relation and Landau damping of Langmuir twisted modes are obtained. The presence of twisted modes opens up two more possibilities in Landau damping and dispersion relations. This may generate a mixture with ion sound waves. It seems to play the role of a control parameter of Landau damping.  相似文献   
32.
Cam mechanics is one of the most popular devices for generating irregular motions and is widely used in automatic equipment, such as textile machines, internal combustion engines, and other automatic devices. In order to obtain a positive motion from the follower using a rotating cam, its shape should be correctly designed and manufactured. The development of an adequate CAD/CAM system for a cam profile CNC grinding machine is necessary to manufacture high-precision cams. The purpose of this study is the development of a CAD/CAM system and profile measuring device for a CNC grinding machine to obtain an optimal grinding speed with a constant surface roughness. Three types of disk cams were manufactured using the proposed algorithm and procedures to verify effectiveness of the developed CAD/CAM system.  相似文献   
33.
Ca-doped Na+- β/β′′-alumina was synthesized using a solid-state reaction. The changes in the properties of Na+- β/β′′-alumina resulting from the presence of Ca impurity were studied. Ca (0–5 wt%) was added to the respective samples, which were then sintered. The specimens were characterized using X-ray diffraction, scanning electron microscopy, densimetry and impedance analysis. In the sintered specimens, the β′′-alumina phase fraction decreased as Ca content increased, whereas the relative sintered density increased. The surface morphology of Ca-doped Na+- β/β′′-alumina specimens showed a Ca-rich layer, which was the main cause of increase in the specific resistance.  相似文献   
34.
It is vital, in this competitive global market, that a product be well designed with ease of assembly as well as low product cost and yet meet its functionality objectives. It is therefore essential that a tool be developed to estimate the manufacturing cost of the product during its conceptual design phase. In this paper, the development of cost models for electrical interconnect design is discussed. The cost models can be used by designers in estimating the manufacturing cost of their designs and selecting the design that is economical to produce and functionally, meets the required specifications.  相似文献   
35.
Al2TiO5 was prepared by the sol-gel method from alkoxides and its mechanical and thermal properties measured. The prepared Al2TiO5 powder was very fine and had a narrow particle-size distribution. The addition of mullite and Al2O3 to the prepared Al2TiO5 inhibited the grain growth during sintering, resulting in a decrease of microcracking and an increase of fracture strength. Al2TiO5/mullite composite exhibited a higher fracture strength than Al2TiO5/alumina composite. The thermal expansion coefficient of Al2TiO5 increased with the addition of mullite and alumina, and also increased with temperature up to 1000°C; however, it decreased in the temperature range between 1000 and 1200°C during heating, due to decomposition of Al2TiO5. The addition of mullite inhibited the decomposition of Al2TiO5, but the addition of Al2O3 accelerated it. Al2TiO5 prepared from metal alkoxides was also more stable than that prepared from the commercial alumina and titania powders. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
36.
This paper studied uneven Internet access amongst young people in Singapore. The study finds that young Singaporeans access the Internet mainly through home, school, borrowed, public, and mobile sources, with different implications for each type of Internet access. For those with home or mobile access, Internet use was routinised and often intense, even burdensome and distracting on occasions. For those who relied on borrowed, school, or public access, intermittent use appeared adequate but hampered their ability to hone online skills to the levels of their peers. The study also finds that although systematic incorporation of IT into the national curriculum can encourage parity in basic exposure to online skills, developing greater Internet proficiency is more likely with home Internet access.  相似文献   
37.
The multi-walled carbon nanotube was introduced into the polymer matrix (PANI) to improve the electric conductivity as well as mechanical properties of the original polymer matrix.PANI/multi-walled carbon nanotube (MWCNT) composites were synthesized via ex-situ and in-situ polymerization to improve their electrical property.And the DC conductivities of PANI/MWCNT according to content and diameter of MWCNT were measured by four-point probe.The highest electric conductivity of PANI/MWCNT composite is 20 S/cm when 0.3% (mass fraction) MWCNTs with 10 nm in diameter and 15 μm in length are added in composite.  相似文献   
38.
This paper investigates the transverse vibration of a simply supported nanobeam with an initial axial tension based on the nonlocal stress field theory with a nonlocal size parameter. Considering an axial elongation due to transverse vibration, the internal axial tension is not precisely equal to the external initial tension. A sixth-order nonlinear partial differential equation that governs the transverse vibration for such nonlocal nanobeam is derived. Using a perturbation method, the relation between nat...  相似文献   
39.
40.
Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2O3 cata-lyst has been paid more and more attention. The chemical equilibria involved in the methanol pvxtial oxidation steam reforming reaction network such as methanol partial oxidation, methanol steam reforming, decomposition of methanol and water-gas shift reaction have been examined over the ranges of temperature 473---1073 K under normal pressure. Based on the detailed kinetics of these reactions over a Cu/ZnO/Al2O3 catalyst, and from the basic concept of the effectiveness factor, the intraparticle diffusion limitations were taken into account. The effectiveness factors for each reaction along the bed length were calculated. Then important results were offered for the simulation of this reaction process.  相似文献   
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