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81.
Martin E. Valdez H. Shibata Alan W. Cramb 《Metallurgical and Materials Transactions B》2006,37(6):959-965
The objective of this study is to determine the conditions under which the inclusions present in liquid steel can act as heterogeneous
nucleants for solidification. In order to study the factors that define the undercooling of a given metal/oxide couple, the
undercooling of a pure iron sessile droplet in contact with Al2O3, ZrO2, and MgO substrates was measured under controlled oxygen partial pressures by observing droplet recalescence. The results
showed that the undercooling of iron, in contact with a particular substrate, did not have a unique value, but was significantly
affected by the oxygen content on the gas phase. For oxygen partial pressures between 10−21 and 10−19, the undercooling of iron on ZrO2 substrates was stable and around 290 °C. In the same range of oxygen partial pressure, the undercooling of iron on MgO substrates
remained below 100 °C due to the low stability of this oxide. At lower oxygen contents, substrate decomposition might be the
cause for the observed drop in the undercooling of iron on ZrO2 substrates to below 100 °C. The undercooling also decreased for increasing oxygen content as verified when the gas was changed
from gettered Ar/Ar-H2 to CO/CO2 mixtures. The variation in undercooling was related to the wetting of the substrate by the liquid metal, where the deep undercooling
observed in the ZrO2 experiments occurred when the highest contact angle between the liquid metal and the substrate was achieved. 相似文献
82.
83.
Ohne Zusammenfassung 相似文献
84.
Xiaoming Zhou Martin Jacobsson Henk Uijterwaal Piet Van Mieghem 《International Journal of Communication Systems》2008,21(6):643-663
Although packet delay and loss are two important parameters of the Internet performance, to the best of our knowledge, the evolution of large‐scale IPv6 delay and loss performance has previously not been studied. In this paper, we analyze more than 600 end‐to‐end IPv6 paths between about 26 testboxes of RIPE Network Coordination Centre over two years, and compare the delay and loss performance over time with their IPv4 counterparts. We present and discuss the measurement methodologies and show that IPv6 paths have a higher delay and loss than their IPv4 counterparts. The main reason for the worse performance stems from IPv6‐in‐IPv4 tunnels rather than from native IPv6 paths and such tunnels are still widely used today. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
85.
With increasing globalization, communication across language and cultural boundaries is becoming an essential requirement
of doing business, delivering education, and providing public services. Due to the considerable cost of human translation
services, only a small fraction of text documents and an even smaller percentage of spoken encounters, such as international
meetings and conferences, are translated, with most resorting to the use of a common language (e.g. English) or not taking
place at all. Technology may provide a potentially revolutionary way out if real-time, domain-independent, simultaneous speech
translation can be realized. In this paper, we present a simultaneous speech translation system based on statistical recognition
and translation technology. We discuss the technology, various system improvements and propose mechanisms for user-friendly
delivery of the result. Over extensive component and end-to-end system evaluations and comparisons with human translation
performance, we conclude that machines can already deliver comprehensible simultaneous translation output. Moreover, while
machine performance is affected by recognition errors (and thus can be improved), human performance is limited by the cognitive
challenge of performing the task in real time. 相似文献
86.
Martin Meyer 《Scientometrics》2007,70(3):779-810
This contribution formulates a number of propositions about the emergence of novel nanoscience and nanotechnology (N&N). Seeking
to complement recent work that aims to define a research agenda and draws on general insights from the innovation literature,
this paper aims to synthesize knowledge from innovation-related studies of the N&N field. More specifically, it is suggested
that N&N is often misconstrued as either a field of technology or an area of (broadly) converging technologies while evidence
to date suggests rather that N&N be considered a set of inter-related and overlapping about not necessarily merging technologies.
The role of instrumentation in connecting the various N&N fields is underlined. Finally, the question is raised whether change
in N&N tends to be incremental rather than discontinuous, being the result of technological path-dependencies and lock-ins
in industry-typical search regimes that are only slowly giving way to more boundary-crossing activities. 相似文献
87.
The deformation characteristics of artificially cemented calcareous soil subjected to undrained cyclic triaxial loading are investigated at different confining pressure and cyclic stress levels. The influence of cementation on the shear stiffness is investigated by comparing the behavior of cemented and uncemented soils with similar initial conditions. It is observed that the deviator stress and the deviatoric strain at yield reduced with increasing number of cycles for cemented sand due to progressive degradation of bond, which results in significant decrease in stiffness. On the other hand, a strain-hardening effect is observed in uncemented sand and this results in increasing yield stress and strain with progressive number of cycles. A linear relationship between degradation index and number of cycles is observed for cemented sand. This relationship has been synthesized in the form of an empirical equation by modifying a previously proposed equation for cohesive soils. This empirical equation was further used to evaluate the fatigue life of soils by adopting a failure criterion. 相似文献
88.
F Wimmer J Lanschützer H Resch A Andretsch H Lempradl H Thöne K Mörwald J Kieweg H P Narzt CFürst 《钢铁》2004,39(Z1):590-592
1前言及历史背景
为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析. 相似文献
89.
S. Klages M. Schöck C. Sürgers H. v. Löhneysen 《Journal of Low Temperature Physics》2004,137(3-4):509-522
The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 ? 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 ? 300 K. With decreasing film thickness, i.e. decreasing sheet conductance Gs, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by Gs ∝ exp[?(T 0 /T) n] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction. PACS numbers: 68.37.-d, 68.55.-a, 73.50.-h, 73.25.+i, 81.15.-z 相似文献
90.
Predictions of the discharge and the associated sediment concentration are very useful ingredients in any water resources reservoir design, planning, maintenance, and operation. Although there are many empirical relationships between the discharge and sediment concentration amounts, they need estimation of model parameters. Generally, parameter estimations are achieved through the regression method (RM), which has several restrictive assumptions. Such models are locally valid and their structures and parameter values are questionable from region to others. This paper proposes a new approach for sediment concentration prediction provided that there are measurements of discharge and sediment concentration. The basis of the methodology is a dynamic transitional model between successive time instances based on two variables, namely, discharge and sediment concentration measurements. The transition matrix elements are estimated from the measurements through a special form of the artificial neural networks as perceptrons. The sediment concentration predictions from discharge measurements are achieved through a perceptron Kalman filtering (PKF) technique. In the meantime, this technique also provides temporal predictions. A certain portion of the measurement sequence is employed for the model parameter estimations through training and the remaining part is used for the model verification. Detailed comparisons between RM and PKF approaches are presented and, finally, it is shown that the latter model works dynamically by simulating the observation scatter diagram in the best possible manner with smaller prediction errors. The application of the methodology is performed for the discharge and sediment concentration measurements obtained from the Mississippi River basin at St. Louis, Missouri. It is found that the PKF methodology has smaller average relative, root-mean-square, and absolute errors than RM. Furthermore, graphical representation, such as the scatter and frequency diagrams, indicated that the PKF approach has superiority over the RM. 相似文献