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排序方式: 共有1420条查询结果,搜索用时 15 毫秒
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Nanowires with inhomogeneous heterostructures such as polytypes and periodic twin boundaries are interesting due to their potential use as components for optical,electrical,and thermophysical applications.Additionally,the incorporation of metal impurities in semiconductor nanowires could substantially alter their electronic and optical properties.In this highlight article,we review our recent progress and understanding in the deliberate induction of imperfections,in terms of both twin boundaries and additional impurities in germanium nanowires for new/enhanced functionalities.The role of catalysts and catalyst-nanowire interfaces for the growth of engineered nanowires via a three-phase paradigm is explored.Three-phase bottom-up growth is a feasible way to incorporate and engineer imperfections such as crystal defects and impurities in semiconductor nanowires via catalyst and/or interfacial manipulation."Epitaxial defect transfer"process and catalyst-nanowire interfacial engineering are employed to induce twin defects parallel and perpendicular to the nanowire growth axis.By inducing and manipulating twin boundaries in the metal catalysts,twin formation and density are controlled in Ge nanowires.The formation of Ge polytypes is also observed in nanowires for the growth of highly dense lateral twin boundaries.Additionally,metal impurity in the form of Sn is injected and engineered via third-party metal catalysts resulting in above-equilibrium incorporation of Sn adatoms in Ge nanowires.Sn impurities are precipitated into Ge bi-layers during Ge nanowire growth,where the impurity Sn atoms become trapped with the deposition of successive layers,thus giving an extraordinary Sn content (>6 at.%) in Ge nanowires.A larger amount of Sn impingement (>9 at.%) is further encouraged by utilizing the eutectic solubility of Sn in Ge along with impurity trapping. 相似文献
23.
Felix Gensch Sven Gall Christoph Fahrenson Sören Müller Walter Reimers 《Journal of Materials Science》2016,51(8):3888-3896
Extrusions of hollow profiles with weld seams were conducted using the magnesium alloy ME21 applying various extrusion ratios. Subsequent analysis of the profiles’ microstructure was performed comparing weld free with weld seam containing material using (polarized) light optical microscopy (LOM). Additionally, the local texture and microstructure in the weld-free material as well as in the weld seam region has been examined with a scanning electron microscope coupled with electron backscatter diffraction technique (SEM-EBSD). The weld-free material and the weld seam are characterized by recrystallized microstructures, whereas few residual cast grains were identified. The local texture distinctively changes from the weld-free material to the weld seam. The texture of the weld-free material is comparable with the typical ME21 sheet texture. In the weld seam area, a pole density is found, which is distributed towards the transverse direction (TD) combined with a split and broadening of the pole density in the extrusion direction (ED). This texture influences the mechanical anisotropy due to the dependence of the activation of basal 〈a〉-slip and \( \{ 10\bar{1}2\} \;\langle 10\bar{1}1\rangle \)-extension twinning on the loading direction in favorably oriented grains. 相似文献
24.
Sven A. Carlsson Stefan Henningsson Stefan Hrastinski Christina Keller 《Information Systems and E-Business Management》2011,9(1):109-131
Design science research is an essential part of IS research since the field should not only try to understand how the world
is, but also how to change it. We argue that the aim of IS design science research should be to develop practical knowledge
not only for the design of novel information technology (IT), but also for IS governance and management. Whereas at least
some methodological support exists for researchers engaged in IT-centric design science research, limited support is available
for researchers who want to develop design knowledge and theory for IS governance and management. To overcome this shortcoming,
we suggest a socio-technical IS design science research approach. The approach has four main activities: (1) identifying problem
situations and desired outcomes, (2) reviewing extant theories, knowledge and data, (3) proposing/refining design theory and
knowledge, and (4) testing design theory and knowledge. The applicability and usefulness of the proposed approach is shown
by means of a design science research project concerning IS integration management in the context of mergers and acquisitions. 相似文献
25.
Yves Younan Pieter Philippaerts Frank Piessens Wouter Joosen Sven Lachmund Thomas Walter 《Journal in Computer Virology》2011,7(3):173-188
Code injection attacks are one of the most powerful and important classes of attacks on software. In these attacks, the attacker sends malicious input to a software application, where it is stored in memory. The malicious input is chosen in such a way that its representation in memory is also a valid representation of a machine code program that performs actions chosen by the attacker. The attacker then triggers a bug in the application to divert the control flow to this injected machine code. A typical action of the injected code is to launch a command interpreter shell, and hence the malicious input is often called shellcode. Attacks are usually performed against network facing applications, and such applications often perform validations or encodings on input. Hence, a typical hurdle for attackers, is that the shellcode has to pass one or more filtering methods before it is stored in the vulnerable application??s memory space. Clearly, for a code injection attack to succeed, the malicious input must survive such validations and transformations. Alphanumeric input (consisting only of letters and digits) is typically very robust for this purpose: it passes most filters and is untouched by most transformations. This paper studies the power of alphanumeric shellcode on the ARM architecture. It shows that the subset of ARM machine code programs that (when interpreted as data) consist only of alphanumerical characters is a Turing complete subset. This is a non-trivial result, as the number of instructions that consist only of alphanumeric characters is very limited. To craft useful exploit code (and to achieve Turing completeness), several tricks are needed, including the use of self-modifying code. 相似文献
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27.
Feature-Oriented Software Development provides a multitude of formalisms, methods, languages, and tools for building variable, customizable, and extensible software. Along different lines of research, different notions of a feature have been developed. Although these notions have similar goals, no common basis for evaluation, comparison, and integration exists. We present a feature algebra that captures the key ideas of feature orientation and that provides a common ground for current and future research in this field, on which also alternative options can be explored. Furthermore, our algebraic framework is meant to serve as a basis for the development of the technology of automatic feature-based program synthesis and architectural metaprogramming. 相似文献
28.
James E. Corter Sven K. Esche Constantin Chassapis Jing Ma Jeffrey V. Nickerson 《Computers & Education》2011
A large-scale, multi-year, randomized study compared learning activities and outcomes for hands-on, remotely-operated, and simulation-based educational laboratories in an undergraduate engineering course. Students (N = 458) worked in small-group lab teams to perform two experiments involving stress on a cantilever beam. Each team conducted the experiments in one of three lab formats (hands-on, remotely-operated, or simulation-based), collecting data either individually or as a team. Lab format and data-collection mode showed an interaction, such that for the hands-on lab format learning outcomes were higher when the lab team collected data sets working as a group rather than individually collecting data sets to be combined later, while for remotely-operated labs individual data collection was best. The pattern of time spent on various lab-related activities suggests that working with real instead of simulated data may induce higher levels of motivation. The results also suggest that learning with computer-mediated technologies can be improved by careful design and coordination of group and individual activities. 相似文献
29.
Sven Groppe Jinghua Groppe Stefan Böttcher Thomas Wycisk Le Gruenwald 《Knowledge and Information Systems》2009,18(3):331-391
We have to deal with different data formats whenever data formats evolve or data must be integrated from heterogeneous systems.
These data when implemented in XML for data exchange cannot be shared freely among applications without data transformation.
A common approach to solve this problem is to convert the entire XML data from their source format to the applications’ target
formats using the transformations rules specified in XSLT stylesheets. However, in many cases, not all XML data are required
to be transformed except for a smaller part described by a user’s query (application). In this paper, we present an approach
that optimizes the execution time of an XSLT stylesheet for answering a given XPath query by modifying the XSLT stylesheet
in such a way that it would (a) capture only the parts in the XML data that are relevant to the query and (b) process only
those XSLT instructions that are relevant to the query. We prove the correctness of our optimization approach, analyze its
complexity and present experimental results. The experimental results show that our approach performs the best in terms of
execution time, especially when many cost-intensive XSLT instructions can be excluded in the XSLT stylesheet. 相似文献
30.