Contrast Factors and Character of Dislocations in Cubic and Hexagonal Crystals

2004 ◽  
Vol 443-444 ◽  
pp. 95-98 ◽  
Author(s):  
Iuliana C. Dragomir ◽  
András Borbély ◽  
Tamás Ungár
Keyword(s):  
Crystallite Size ◽  
The Internet ◽  
Slip Systems ◽  
Burgers Vector ◽  
Dislocation Densities ◽  
Contrast Factor ◽  
Diffraction Peaks ◽  
The Individual ◽  
Hexagonal Crystals ◽  
Active Slip

Anisotropic strain broadening of diffraction peaks can be parameterised by dislocation contrast factors. A comprehensive software has been developed and made available through the internet to determine the individual and averaged contrast factors which are also compiled for cubic and hexagonal crystals. Using the theoretical and the measured values of contrast factor the microstructure of the specimen can be characterised in terms of active slip systems, Burgers vector populations, dislocation densities and crystallite size- and size distribution.

Twinning on pyramidal planes in hexagonal close packed crystals determined along with other defects by X-ray line profile analysis

2009 ◽  
Vol 42 (4) ◽  
pp. 580-591 ◽  
Author(s):  
Levente Balogh ◽  
Géza Tichy ◽  
Tamás Ungár
Keyword(s):  
Crystallite Size ◽  
Profile Analysis ◽  
Line Profile Analysis ◽  
Slip Systems ◽  
Line Broadening ◽  
X Ray ◽  
Hexagonal Close Packed ◽  
Dislocation Densities ◽  
Different Temperatures ◽  
Active Slip

A systematic procedure is developed to evaluate the frequency of {10.1}〈10.\overline 2〉 and {11.2}〈11.\overline 3〉 compressive twins and {10.2}〈10.\overline 1〉 and {11.1}〈\overline 1\overline 1.6〉 tensile twins together with dislocation densities, active slip systems and crystallite size in hexagonal close packed (hcp) metals. The effect of pyramidal twinning on X-ray line broadening in hcp metals is fundamentally different from the effect of twinning on close packed planes in face centred cubic (fcc) crystals. Therefore, the usual theoretical descriptions developed previously for fcc crystals cannot be used for pyramidal twinning in hcp crystals. The profile functions of sub-reflections for this type of twinning are derived to be the sum of a symmetrical and an antisymmetrical Lorentzian function. Sub-profile properties are parameterized and the parameter files are incorporated into the convolutional multiple whole profile (CMWP) procedure. The extended procedure,eCMWP, is applied to determine pyramidal twin frequencies together with dislocation densities, active slip systems and crystallite size in Mg deformed at different temperatures, in commercial purity Ti deformed at high temperature and in high-purity Ti deformed at room temperature.

On the Selection of Active Slip Systems in Rate Independent Crystal Plasticity

2013 ◽  
Vol 554-557 ◽  
pp. 1147-1156
Author(s):  
Markus Orthaber ◽  
Thomas Antretter ◽  
Hans Peter Gänser
Keyword(s):  
Crystal Plasticity ◽  
Dislocation Dynamics ◽  
Slip Systems ◽  
Rate Dependency ◽  
Low Viscosity ◽  
Rate Dependent ◽  
Cross Hardening ◽  
The Individual ◽  
Active Slip ◽  
Regularized Model

Non-uniqueness of the set of active slip systems is a crucial issue in crystal plasticity. To avoid this problem one may perform viscoplastic regularization. This introduces a certain rate dependency, while many crystals are known to behave rate independently. One would require very low viscosity parameters in the regularized model to resemble the experimental behavior of rate independent crystals, which in turn entails numerical difficulties. Furthermore, no direct approach is known to model deformation banding using viscoplastically regularized models. Hence, to adequately treat rate independent crystal plasticity an alternative method is needed. The proposed method, Maximum Dissipation Crystal Plasticity (MDCP), achieves uniqueness by selecting the set of active slip systems according to its dissipation. In a finite element calculation, a system of coupled quadratic equations is solved at every integration point to define the material behaviour. This approach is formally equal to the method of incremental energy minimization recently proposed by Petryk et al. It can be shown that a viscoplastically regularized model is a limiting case of MDCP, giving similar results when cross hardening becomes negligible. Nevertheless, recent 3D dislocation dynamics calculations by Devrince et al. show that cross hardening in fcc crystals is far more important than self hardening. In such cases MDCP gives results distinctly different from its rate dependent counterpart. Fewer slip systems are selected by MDCP, resulting in more slip on the individual active systems. The proposed method is numerically implemented as an Abaqus user material subroutine within the large deformation framework, such that the simulation of arbitrary load cases is possible.

Contrast factors of dislocations in the hexagonal crystal system

2002 ◽  
Vol 35 (5) ◽  
pp. 556-564 ◽  
Author(s):  
I. C. Dragomir ◽  
T. Ungár
Keyword(s):  
Lattice Distortion ◽  
Dislocation Model ◽  
Size Distributions ◽  
Hexagonal Crystal ◽  
Strain Anisotropy ◽  
Dislocation Densities ◽  
Contrast Factor ◽  
Parameter Values ◽  
Hexagonal Crystals ◽  
Hexagonal Materials

Strain anisotropy can be well accounted for by the dislocation model of lattice distortion. In a texture-free powder or polycrystal, or if all possible Burgers vectors are equally populated, the dislocation contrast factors are a linear function of the fourth-order invariants of thehklindices. Using this relation the dislocation contrast factors have been evaluated numerically and compiled for a number of common hexagonal materials. A procedure is presented to match experimentally determined contrast factor parameters with the numerically obtained parameter values. The procedure can be used as a tool to extract the microstructure from strain anisotropy in terms of Burgers vector populations, dislocation densities, crystallite size and size distributions in hexagonal crystals. Its practical use is illustrated by the application to plastically deformed titanium.

Characterization of active slip systems in Hg0.8Cd0.2Te

1990 ◽  
Vol 48 (4) ◽  
pp. 846-847
Author(s):  
D. B. McKeagney ◽  
T. J. Campbell
Keyword(s):  
Semiconductor Device ◽  
Infrared Detection ◽  
Slip Systems ◽  
Crystal Surfaces ◽  
Dislocation Generation ◽  
Bulk Growth ◽  
Dislocation Densities ◽  
Bond Strengths ◽  
Active Slip

The compound semiconductor Hg0.8Cd0.2Te is commonly used in the production of infrared detection devices. In bulk growth, due to low Hg-Te bond strengths, high dislocation densities are often encountered. These dislocations, which are generated during the crystal growth process, significantly impair the performance of the semiconductor device. To best control this dislocation generation during growth, a knowledge of the active slip systems within the crystal lattice is desirable.Microhardness tests were performed on two distinct crystal surfaces of Bridgman grown Hg0.8Cd0.2Te crystals. Selected area electron channeling was used to determine trie crystallographic orientations of the surfaces that were tested. The slip lands that were introduced during the indentation process were observed using both the scanning electron and optical microscopes. From the data obtained, using elementary crystallographic techniques, the dominant slip systems active in Hg0.8Cd0.2Te were characterized.

A cross-sectional survey among physicians on Internet use for epilepsy-related information (Preprint)

2019 ◽  
Author(s):  
Francesco Brigo ◽  
Simona Lattanzi ◽  
Giorgia Giussani ◽  
Laura Tassi ◽  
Nicola Pietrafusa ◽  
...  
Keyword(s):  
Internet Use ◽  
The Internet ◽  
Online Information ◽  
Cross Sectional Survey ◽  
Cross Sectional ◽  
Related Information ◽  
Internet Users ◽  
Therapeutic Decisions ◽  
The Individual ◽  
The Web

BACKGROUND The Internet has become one of the most important sources of health information, accessed daily by an ever-growing number of both patients and physicians, seeking medical advice and clinical guidance. A deeper insight into the current use of the Web as source of information on epilepsy would help in clarifying the individual attitude towards this medium by Internet users. OBJECTIVE We investigated views towards the Internet in a sample of Italian healthcare specialists involved in epilepsy field, to explore factors which explained the influence of information found on the internet. METHODS This study was a self-administered survey conducted in a group of members of the Italian Chapter of the International League Against Epilepsy (ILAE) in January 2018. RESULTS 184 questionnaires were analyzed. 97.8% of responders reported to seek online information on epilepsy. The Internet was most frequently searched to obtain new information (69.9%) or to confirm a diagnostic or therapeutic decision (37.3%). The influence of consulting the Internet on clinical practice was associated with registration to social network(s) (OR: 2.94; 95%CI: 1.28-6.76; p=0.011), higher frequency of Internet use (OR: 3.66; 95%CI: 1.56-9.21; p=0.006) and higher confidence in reliability of online information (OR: 2.61; 95%CI: 1.09-6.26; p=0.031). No association was found with age, sex, years in epilepsy practice or easiness to find online information. CONCLUSIONS Internet is frequently used among healthcare professionals involved in the epilepsy to obtain information about this disease. The attitude of being influenced by the Internet for diagnostic and/or therapeutic decisions in epilepsy is independent on age and years of experience in epilepsy, and probably reflects an individual approach towards the Web.

Applications of Web-QFD and E-Delphi method in the higher education system

2004 ◽  
Vol 23 (4) ◽  
pp. 245-256
Author(s):  
Shun-Hsing Chen ◽  
Ching-Chow Yang
Keyword(s):  
Education System ◽  
Delphi Method ◽  
Quality Function Deployment ◽  
Decision Makers ◽  
The Internet ◽  
Total Quality ◽  
Web Based ◽  
Team Members ◽  
Higher Education System ◽  
The Individual

Quality function deployment (QFD) is an essential tool in implementing total quality management (TQM). This study applies a Web-QFD approach using group decision-making analysis in the Web environment to reduce the complicated data collection, aggregation and analysis processes. A Web-based questionnaire is designed by using an active service pages (ASP) involving the Internet relay chat (IRC) technique and the Delphi method with Internet (E-Delphi) to determine the importance degree of the customers' requirements. However, the traditional Delphi method is time-consuming mission. This study applies the proposed Web-QFD approach to efficiently gather the individual opinions of each team member, the requirements that are critical for customers, and then enables decision makers to accurately assess the priorities of these requirements. An empirical example of an education system in Taiwan is employed to demonstrate the practicability of the proposed Web-QFD model. This real world example involves team members communicating easily and quickly with other experts in the team through the Internet to accelerate the reaching of a consensus among multiple decision makers regardless of where their location. Customers' requirements can be rapidly prioritized based on the assessment results.

A model for the individual empowerment using intrinsic personalization of crowdsourcing tasks

2021 ◽  
pp. 1-6
Author(s):  
Dennis Paulino
Keyword(s):  
Cognitive Abilities ◽  
People With Disabilities ◽  
The Internet ◽  
Human Capabilities ◽  
Financial Compensation ◽  
Social Barriers ◽  
Task Description ◽  
The Individual ◽  
Phd Thesis

Crowdsourcing is a paradigm of outsourcing work that is done using human capabilities through the Internet. Given the various possibilities of overcoming cultural and social barriers, crowdsourcing provides an opportunity for people with disabilities to have a financial compensation and help them feel realised. In crowdsourcing, people with disabilities face problems related with the lack of task description or usability. This article it is presented the main threads for my PhD thesis which main goal is to prove, that it is possible to map crowdsourcing tasks effectively to each individual, focusing particularly on the cognitive abilities.

Experimental Analysis and Crystallographic Model of Plastic Deformation after a Change of Loading Path in Mild Steel Polycrystals

1999 ◽  
Vol 578 ◽  
Author(s):  
T. Hoc ◽  
C. Rey
Keyword(s):  
Plastic Deformation ◽  
Mild Steel ◽  
Strain Localization ◽  
Loading Path ◽  
Slip Systems ◽  
Finite Element Code ◽  
Dislocation Densities ◽  
Dislocation Interactions ◽  
Sequential Tests ◽  
Microstructural Anisotropy

AbstractStrain localization in mild steel submitted to a sequential loading paths is investigated at macroscopic, mesoscopic and microscopic scales. The experimental results demonstrate that the morphology of the localization and the nominal load-displacement curves depend on the microstructural anisotropy. A crystalline model using a finite element code is proposed. The anisotropy is described by a hardening matrix whose terms correspond to dislocation-dislocation interactions and depend on the evolution of the dislocation densities on the activated slip systems during the sequential tests. The strain localization predicted by this model fits with the experimental observation and allows us to assume that localization is correlated to the saturation on the activated slip systems.

Positive And Negative Aspects Of The Psychological Impact Of The Virtual World

2021 ◽  
Vol 03 (05) ◽  
pp. 25-29
Author(s):  
Rakhimova I.I. ◽  
◽  
Mukhiddinova U.A. ◽  
Bеrdiqulоvа G.N. ◽  
Suleymanova D.I. ◽  
...  
Keyword(s):  
Mobile Phones ◽  
Virtual World ◽  
Human Life ◽  
Psychological Impact ◽  
Economic Life ◽  
The Internet ◽  
National Values ◽  
Use Of The Internet ◽  
The Individual

In today's age of the Internet, computers and mobile phones for people of all ages are available in almost every home. In addition, in today’s world-wide pandemic, the use of the Internet for education and all aspects of cultural, socio-economic life as well as games such as games is growing rapidly. This, in turn, has a psychological effect on the individual, both positively and negatively on our society and national values. In this article, I have tried to highlight the positive and negative aspects of the internet world that affect the individual. In the article we will focus on the role of the virtual world in human life, the need not to depend on it, to use it for useful purposes.

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