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排序方式: 共有792条查询结果,搜索用时 140 毫秒
51.
52.
Lee HJ Jin ZX Aleshin AN Lee JY Goh MJ Akagi K Kim YS Kim DW Park YW 《Journal of the American Chemical Society》2004,126(51):16722-16723
To study the transport properties of individual helical polyacetylene (PA) fibers, we developed a method to extract a single fiber from tightly entangled ropes of helical PA bulk film. After a few minutes of sonication of a piece of helical PA bulk film in an organic solution containing surfactant, a droplet of solution is deposited on the pre-pattened electrode under argon atmosphere. AFM images show that extracted helical PA fibers are typically 10 mum in length and 100-200 nm in diameter. We found that the helicity of bulk materials is conserved. We present the temperature dependencies of current-voltage characteristics of individual helical PA fibers doped with iodine. 相似文献
53.
Design and performance evaluation of an ultrasonic motor was discussed in [Wen et al., Thin-disc piezoelectric ultrasonic motor. Part I: design and performance evaluation, Ultrasonics]. Higher precision position control of piezoceramic ultrasonic motor depends on mechanical design and servo control of a very precise and adequate metrology. This paper proposes the design of a driving circuit and controller to deal with non-linearities behavior in the model of piezoceramic-driving ultrasonic motor. The performance of the driver and the effectiveness of the proposed controller are demonstrated by command inputs of sinusoidal and step signals. For comparison purpose, the ultrasonic motor is controlled using two methods: i.e., proportional-integral-derivative (PID) and sliding-mode control (SMC). It was proven that SMC would compensate automatically for unmodeled behaviors such as piezoceramic non-linearities and mechanical stick-slip phenomena. Furthermore, SMC scheme has been successfully applied to position tracking to demonstrate the excellent robust performance in noise rejection. 相似文献
54.
55.
Y.-K. Kuo J.-R. Chen M.-L. Chen B.-T. Liou 《Applied physics. B, Lasers and optics》2007,86(4):623-631
The physical and optical properties of compressively strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting
lasers are numerically studied. The simulation results show that the maximum optical gain, transparency carrier densities,
transparency radiative current densities, and differential gain of InGaAsP quantum wells can be efficiently improved by employing
a compressive strain of approximately 1.24% in the InGaAsP quantum wells. The simulation results suggest that the 850-nm InGaAsP/InGaP
vertical-cavity surface-emitting lasers have the best laser performance when the number of quantum wells is one, which is
mainly attributed to the non-uniform hole distribution in multiple quantum wells due to high valence band offset.
PACS 42.55.Px; 78.20.-e; 78.20.Bh; 78.30.Fs 相似文献
56.
In a real production and distribution business environment with one supplier and multiple heterogeneous buyers, the differences
in buyers’ ordering cycles have influence on production arrangements. Consequently, the average inventory level (AIL) at the
supplier’s end is affected by both the production policy and the ordering policy, typically by the scheduling of deliveries.
Consequently, the average inventory holding cost is most deeply affected. In this paper, it is proposed that the scheduling
of deliveries be formulated as a decision problem to determine the time point at which deliveries are made to buyers in order
to minimize the supplier’s average inventory. A formulation of the average inventory level (AIL) in a production cycle at
the supplier’s end using a lot-for-lot policy is developed. Under the lot-for-lot policy, the scheduling of deliveries (SP) is formulated as a nonlinear programming model used to determine the first delivery point for each buyer with an objective
to minimize the sum of the product of the individual demand quantity and the first delivery time for each buyer. Thus, the
SP model determines not only the sequence of the first deliveries to individual buyers, but also the time when the deliveries
are made. An iterative heuristic procedure (IHP) is developed to solve the SP model assuming a given sequence of buyers. Six sequence rules are considered and evaluated via simulation. 相似文献
57.
In this study the usefulness of micro-Computed Tomography (μ-CT) for the in-depth analysis of enamelled metal objects was
tested. Usually investigations of enamelled metal artefacts are restricted to non-destructive surface analysis or analysis
of cross sections after destructive sampling. Radiography, a commonly used technique in the field of cultural heritage studies,
is limited to providing two-dimensional information about a three-dimensional object (Lang and Middleton, Radiography of Cultural
Material, pp. 60–61, Elsevier-Butterworth-Heinemann, Amsterdam-Stoneham-London, 2005). Obtaining virtual slices and information about the internal structure of these objects was made possible by CT analysis.
With this technique the underlying metal work was studied without removing the decorative enamel layer. Moreover visible defects
such as cracks were measured in both width and depth and as of yet invisible defects and weaker areas are visualised. All
these features are of great interest to restorers and conservators as they allow a view inside these objects without so much
as touching them. 相似文献
58.
Guey‐Sheng Liou Po‐Han Lin Hung‐Ju Yen Yang‐Yen Yu Wen‐Chang Chen 《Journal of polymer science. Part A, Polymer chemistry》2010,48(6):1433-1440
In this study, a novel synthetic route was developed to prepare polyimide–nanocrystalline–titania hybrid optical films with a relatively high titania content (up to 50 wt %) and thickness (20–30 μm) from soluble polyimides containing hydroxyl groups. Two series of newly soluble polyimides were synthesized from the hydroxy‐substituted diamines with various commercial tetracarboxylic dianhydrides. The hydroxyl groups on the backbone of the polyimides could provide the organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, SEM, TEM, and XRD results indicated the formation of well‐dispersed nanocrystalline‐titania. The flexible hybrid films could be successfully obtained and revealed relatively good surface planarity, thermal dimensional stability, tunable refractive index, and high optical transparency. A three‐layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range indicated its potential optical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1433–1440, 2010 相似文献
59.
Y.-K. Kuo S.-H. Yen M.-W. Yao M.-C. Tsai M.-L. Chen B.-T. Liou 《Applied physics. B, Lasers and optics》2008,93(2-3):497-506
In this work, the multiple-quantum-well InGaAsN laser structures with indirect-GaAsP and direct-GaAsN barriers are investigated by using LASTIP simulation program. We vary the quantum-well number, from 1 to 5, to find appropriate barrier material for InGaAsN laser structures. The simulation results show that InGaAsN laser structure has higher characteristic temperature regardless of what quantum-well number is if the indirect-GaAsP barrier is utilized. Furthermore, for InGaAsN laser structure, the usage of indirect-GaAsP barrier is beneficial for reducing the threshold current when the quantum-well number is from 1 to 2 and the usage of direct-GaAsN barrier is beneficial for reducing the threshold current when the quantum-well number is from 3 to 5. 相似文献
60.
Strong convergence of an iterative method for nonexpansive mappings with new control conditions 总被引:1,自引:0,他引:1
The purpose of this paper is to study the convergence problem of an iterative method for nonexpansive mappings in Banach spaces under some new control conditions on parameters. 相似文献