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51.
52.
In ferritic steels a propagating cleavage microcrack changes its propagation direction as it advances from grain to grain.
This is due to differences in the orientation of the cleavage planes of two neighboring grains. In order to reach a cleavage
plane in a new grain, a microcrack must first penetrate the grain boundary. Grain boundaries therefore act as natural barriers
in cleavage fracture. The influence of a grain boundary and the associated misorientation in cleavage planes on crack arrest
is here examined using a 3D finite element model with axisymmetric periodicity, representing two grains whose cleavage planes
are tilted and twisted relative to each other. The temperature dependent mechanical properties of ferrite are modeled using
a temperature dependent viscoplastic response. The development of the crack front as the microcrack penetrates through a grain
boundary is here presented. The influence of the twist misorientation on the critical grain size, defined as the largest grain
size that can arrest a rapidly propagating microcrack, is examined in a temperature range corresponding to the ductile to
brittle transition (DBT) region. It is shown that when both tilt and twist misorientation are present, the influence of tilt
and twist, respectively, on crack growth resistance can be decoupled. 相似文献
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54.
The pad pitch of modern radio frequency integrated circuits is in the order of few tens of micrometers. Connecting a large number of high‐speed I/Os to the outside world with good signal fidelity at low cost is an extremely challenging task. To cope with this requirement, we need reflection‐free transmission lines from an on‐chip pad to on‐board SMA connectors. Such a transmission line is very hard to design due to the difference in on‐chip and on‐board feature size and the requirement for extremely large bandwidth. In this paper, we propose the use of narrow tracks close to chip and wide tracks away from the chip. This narrow‐to‐wide transition in width results in impedance discontinuity. A step change in substrate thickness is utilized to cancel the effect of the width discontinuity, thus achieving a reflection‐free microstrip. To verify the concept, several microstrips were designed on multilayer FR4 PCB without any additional manufacturing steps. The TDR measurements reveal that the impedance variation is less than 3 Ω for a 50 Ω microstrip and S11 better than –9 dB for the frequency range 1 GHz to 6 GHz when the width changes from 165 µm to 940 µm, and substrate thickness changes from 100 µm to 500 µm. 相似文献
55.
For nearly two centuries, researchers have sought novel methods to increase light transmission in optical systems, as well as to eliminate unwanted reflections and glare. Anti-reflection coatings and surfaces have enabled the increasing performance demands of optical components fabricated from glass-based optical materials. With the current trend of technology moving towards optically transparent polymeric media and coatings, the need for anti-reflection technology and environmentally benign processing methods for polymeric materials independent of shape or size has become quite apparent. We describe an economical, aqueous-based process controlled at the molecular level that simultaneously coats all surfaces of almost any material. Systematically designed nanoporous polymer films are used, which are suitable for optical applications operating at both visible and near-infrared wavelengths. These high-efficiency anti-reflection coatings are created from phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition. Furthermore, such films, easily patterned by an inkjet printing technique, possess potential for pH-responsive biomaterial and membrane applications. 相似文献
56.
Palmblad M Ramström M Markides KE Håkansson P Bergquist J 《Analytical chemistry》2002,74(22):5826-5830
Liquid chromatography coupled on- or off-line with mass spectrometry is rapidly advancing as a tool in proteomics capable of dealing with the inherent complexity in biology and complementing conventional approaches based on two-dimensional gel electrophoresis. Proteins can be identified by proteolytic digestion and peptide mass fingerprinting or by searching databases using short-sequence tags generated by tandem mass spectrometry. This paper shows that information on the chromatographic behavior of peptides can assist protein identification by peptide mass fingerprinting in liquid chromatography/mass spectrometry. This additional information is significant and already available at no extra experimental cost. 相似文献
57.
Jonas Koko 《Journal of scientific computing》2006,26(2):195-216
This paper deals with nonoverlapping domain decomposition methods for two coupled Stokes flows, based on the duality theory.
By introducing a fictitious variable in the transmission condition and using saddle-point equations, the problem is restated
as a linearly constrained maximization problem. According to whether constraints are uncoupled Stokes problems or uncoupled
Poisson problems, two Uzawa-type domain decomposition algorithms are proposed. The results of some numerical experiments on
a model problem are given. 相似文献
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