Suggestions that we are on the verge of a second industrial revolution, based on microsystems technology (MST), are apt to leave many of us unmoved. After all, the prospect of tiny machines, less than a hairsbreadth in dimension, that can go to work in optical systems, conventional and RF electronics, a wide range of sensors, robotics, or even our own bodies, has been dangled before us for decades. Yet there are signs that microelectromechanical systems (MEMS) might, at last, be about to take off. Could it be that these barely perceptible (to the human eye) syntheses of microelectronics with micromechanics are finally poised to make a big commercial impact?Market projections are increasingly bullish. For example, a survey by Europe’s Network of Excellence in Multifunctional Microsystems (NEXUS) suggests a world market of $68 billion by 2005, more than double the level of two years ago (Fig. 1
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Fig. 1. This NEXUS graph shows that total world market for microsystems is expected to grow from $30 billion in the year 2000 to $68 billion by the year 2005.). NEXUS had to revise earlier projections because of runaway successes like that of the optical mouse (Agilent Technologies recently shipped its 50 millionth), an anticipated breakthrough later in the period for microoptoelectromechanical systems (MOEMS), enhanced prospects for RF switching systems, and the possible emergence of a market in domestic appliances. Analyst Venture Development Corporation goes further, concluding that the market will grow ‘exponentially’ for the next ten years. The first device to exceed $1 billion in sales is expected to be MEMS-based photonic switches, within about two years. Current breadwinning applications — desktop ink-jet printers, biomedical pressure sensors/systems, and automotive devices — continue to thrive. 相似文献
MEMS @ MIT is a newly created center that is intended to bring together a diverse group of microelectromechanical systems (MEMS) researchers at the Massachusetts Institute of Technology (MIT) Fig. 1
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Fig. 1. MIT’s Killian Court, designed by architect William Welles Bosworth, showing the Great Dome under which runs the famous ‘Infinite Corridor’. and to provide an industrial interface to organizations that seek to interact with the center.The MIT MEMS research program has been in existence for more than 20 years and has seen a steady growth in the number of researchers and faculty. Today, there are more than 20 faculty doing MEMS research at MIT, with approximately 120 students and staff who come from seven different academic departments. The annual contract research volume of this group is well in excess of $12 million. In creating this center, the faculty are recognizing the substantial value that arises from the coordination of activities, as well as the benefits of focused interactions with organizations that seek to commercialize the research. 相似文献
Over the past several years there have been dramatic advances toward the realization of electronic computers integrated on the molecular scale. First, individual molecules were demonstrated that serve as incomprehensibly tiny switches and wires one million times smaller than those on conventional silicon microchips1, 2, 3, 4. This has resulted very recently in the assembly and demonstration of tiny computer logic circuits built from such molecular-scale devices4, 5, 6, 7, 8, 9, 10.A major force responsible for these revolutionary developments has been the molecular electronics or ‘Moletronics’ Program organized by the US Government's Defense Advanced Research Projects Agency (DARPA). Previously, DARPA gave birth to the Internet in the 1970s and 1980s, revolutionizing the way the world communicates. Now, the agency is setting its sights on a new revolution in the nature, structure, and scale of the very materials with which the world both computes and builds. Ultimately, to compute with molecular-scale structures — i.e. nanometer-scale structures — one must learn how to characterize and organize them on similar scales, one by one and in vast arrays. This is creating a whole new science and industry of ‘nanostructured materials’, such as are portrayed in Fig. 1
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Fig. 1. Moletronics nanostructured materials. (a) Electron micrograph of self-assembled ErSi2 nanowires developed at HP. (Reproduced with permission from54.); (b) electron micrograph of cowpea viral particle modified with gold nanoclusters developed at NRL to use as a template for molecular self-assembly; (c) simulation of Rice University's gold-nanoparticle electrical contacts on a surface in a ‘NanoCell’ molecular logic structure51; (d) structural diagram of NDR diode switch molecule20, 28, 35 and a simulation of its molecular orbitals involved in switching. (Reproduced with permision from47. Copyright 2000 American Chemical Society.); (e) gold nanobars synthesized at PSU; (f) electron micrograph of nanowire transistor-based logic circuit4 that was self-assembled and demonstrated at Harvard University.(Reprinted with permission from5. Copyright 2001 American Association for the Advancement of Science.). 相似文献
The transition from 3D to 2D lithium deposition can be achieved with low Li-ion concentrations by forming a multitude of lithium nuclei on the lithium surface prior to the deposition using a nucleation pulse followed by pulsed galvanostatic deposition. Under these conditions, homogeneous lithium metal deposition is favored by the diffusion-controlled mass transfer to the nuclei-enriched surface.
Despite increasing interest in mechanical seals, widespread use of packing (Figure 1
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Figure 1. Packing is made from materials such as Nomex, Kevlar, polytetrafluoroethylene, carbon and graphite and can be cut to the required size.) is still seeing many companies unknowingly incur unnecessary maintenance costs and, in some cases, even causing health and safety concerns. This article examines why mechanical seals provide a more efficient solution to such a problem. 相似文献
It was last year, around this time, that physicists were stunned by the announcement that magnesium diboride, MgB2, a material known since the 1950s, superconducts1 at a critical temperature, Tc, of 39 K. Since this surprising discovery we have witnessed an explosion of research on MgB2 and other related compounds to answer the following questions: is MgB2 unique or are there other similar compounds with higher Tc; what is the mechanism of superconductivity; and what are the potential technical applications of this discovery? This brief report of the progress made in the first year of the MgB2 era gives an insight into the answers to these questions.The serendipitous discovery by Akimitsu’s group1 of the superconductivity of MgB2 at Tc=39 K, almost twice the temperature of other simple intermetallic compounds, has sparked a race to uncover its basic properties and to find other related diborides with even higher Tcs. After the first announcement, the number of preprints appearing on the Los Alamos preprint server (Fig. 1
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Fig. 1. The number of studies about MgB2 appearing in every two weeks in the xxx.lanl.gov e-print archives.) grew almost exponentially, reaching a maximum of about 60 studies in March (two papers a day), then decreasing linearly down to a paper every other day in August, and staying steady at about this rate until now. During the first year of the MgB2 era, more than 300 studies were published, exploring both fundamental and practical issues, such as the mechanism of the superconductivity; synthesis of MgB2 in the form of powder, thin films, wires, and tapes; the effect on Tc of substitution with various elements and on critical current and fields. 相似文献
Differential scanning calorimetry(DSC) analysis, isothermal solidification experiment and Thermo-Calc simulation were employed to investigate solidification characteristics of K417 G Ni-base superalloy. Electron probe microanalysis(EPMA) was employed to analyze the segregation characteristics. Liquidus,solidus and the formation temperatures of main phases were measured. In the process of solidification,the volume fraction of liquid dropped dramatically in the initial stage, while the dropping rate became very low in the final stage due to severe segregation of positive segregation elements into the residual liquid. The solidification began with the formation of primary γ. Then with solidification proceeding, Ti and Mo were enriched in the liquid interdendrite, which resulted in the precipitation of MC carbides in the interdendrite. Al accumulated into liquid at the initial stage, but gathered to solid later due to the precipitation of γ/γ’ eutectic at the intermediate stage of solidification. However, Co tended to segregate toward the solid phase. In the case of K417 G alloy, combining DSC analysis and isothermal solidification experiment is a good way to investigate the solidification characteristics. Thermo-Calc simulation can serve as reference to investigate K417 G alloy. 相似文献
