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Suche nach „[W.] [Chen]“ hat 9 Publikationen gefunden
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    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    S. Chen, L. Jiang, M. Buckwell, X. Jing, Y. Ji, E. Grustan-Gutierrez, Günther Benstetter, F. Hui, Y. Shi, M. Rommel, A. Paskaleva, W. Ng, A. Mehonic, A. Kenyon, M. Lanza

    On the Limits of Scalpel AFM for the 3D Electrical Characterization of Nanomaterials

    Advanced Functional Materials, vol. 28, no. 52

    2018

    DOI: 10.1002/adfm.201802266

    Abstract anzeigen

    Conductive atomic force microscopy (CAFM) has been widely used for electrical characterization of thin dielectrics by applying a gentle contact force that ensures a good electrical contact without inducing additional high‐pressure related phenomena (e.g., flexoelectricity, local heat, scratching). Recently, the CAFM has been used to obtain 3D electrical images of thin dielectrics by etching their surface. However, the effect of the high contact forces/pressures applied during the etching on the electrical properties of the materials has never been considered. By collecting cross‐sectional transmission electron microscopy images at the etched regions, it is shown here that the etching process can modify the morphology of Al2O3 thin films (producing phase change, generation of defects, and metal penetration). It is also observed that this technique severely modifies the electrical properties of pSi and TiO2 wafers during the etching, and several behaviors ignored in previous studies, including i) observation of high currents in the absence of bias, ii) instabilities of etching rate, and iii) degradation of CAFM tips, are reported. Overall, this work should contribute to understand better the limitations of this technique and disseminate it among those applications in which it can be really useful.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    X.-N. Chen, Rui Li, A. Rineiski, W. Jäger

    Macroscopic pin bundle model and its blockage simulations

    Energy Conversion and Management, vol. 91, pp. 93-100

    2015

    DOI: 10.1016/j.enconman.2014.11.053

    Abstract anzeigen

    In this paper a macroscopic continuum differential model of pin bundle flow is proposed and developed for computational fluid dynamics (CFD) simulations of a reactor core. Thereby the pin bundle flow is regarded as a porous medium flow that is characterized by a certain coolant volume fraction and an associated wet area. The frictional drags experienced by pins and wrappers in the axial and radial directions are converted to pressure drops, i.e. momentum exchange terms, which are therefore anisotropic from the macroscopic point of view. Such a model reduces the number of CFD meshes very much and can be applied for a whole reactor core flow simulation without losing details of subchannel flow. In particular the model is implemented in the SIMMER-III code and applied for the MYRRHA reactor design. A steady state of subchannel flow, which is considerably non-uniform in the radial direction, is investigated and compared with a subchannel code. Satisfactory agreements are achieved. As a practical example the subchannel blockage in the central channels is considered and simulated. The scenario of pin failure and fuel sweep-out is expected, but it can take place already at 50% area blockage in a fuel assembly, if the blockage is located at the entrance of the active zone.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    Rui Li, X.-N. Chen, C. Matzerath Boccaccini, A. Rineiski, W. Maschek

    Study on Severe Accident Scenarios: Pin Failure Possibility of MYRRHA-FASTEF Critical Core

    Energy Procedia, vol. 71, pp. 14-21

    2015

    DOI: 10.1016/j.egypro.2014.11.850

    Abstract anzeigen

    The present work is carried out within the European FP7 project SEARCH, in which the MYRRHA demonstrator reactor is designed to be able to operate both in ADS mode and in critical mode using lead-bismuth eutectic (LBE) as primary coolant. According to the project task definition, the pin failure and fuel dispersion scenarios in severe accidents have to be extensively studied for reactor safety analysis. In this paper, the unprotected severe transients analyses for the MYRRHA-FASTEF critical core were performed using SIMMER-III code. The aim of the current work was to obtain a deeper understanding of core material redistribution processes before and after pin damage, since the Archimedes force could move pellets, chunks and fuel particles upwards out of the core and redistribute them into the upper pool region and peripheral structures. Starting the simulations with the steady state calculation, relevant parameters reflect good agreement with the design operational conditions. For the transients three postulated severe accident scenarios were proposed that may possibly lead to pin failure and furthermore core damage: unprotected loss of flow (ULOF), unprotected transient overpower (UTOP) and unprotected blockage accident (UBA), where in particular the entrance of fuel assembly is blocked as a side window is still open. The three transients, starting from the steady state conditions, have been investigated. The calculation results show for the MYRRHA-FASTEF that under the conditions chosen all simulated transient cases do not lead to a pin failure and fuel redistribution.

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    W. Chen, J. Fournier, Marcus Barkowsky, P. Le Callet

    Methodologies for Assessing 3D QoE: Standards and Explorative Studies

    ZTE Communications, vol. 11, no. 1, pp. 2-10

    2013

    Abstract anzeigen

    Mastering quality of experience (QoE) is key to the widespread adoption of stereoscopic 3DTV (S-3DTV). However, assessing QoE of S-3DTV is not straightforward. Methods for determining observer experience need to be clearly defined and sufficiently robust. In this paper, we present state-of-the-art subjective QoE assessment for S-3DTV. We present conventional stan⁃ dardized ITU recommendations for evaluating picture quality and discuss new ITU activities in the area of S-3DTV assess⁃ ment. We also present and discuss explorative studies from the literature. We then introduce ways of using conventional quality assessment for S-3DTV QoE assessment. In discussing our pro⁃ posal, we mainly focus on QoE indicators and common features of subjective assessment. Multidimensional QoE indicators need to be used in S-3DTV to highlight advantages and reveal problems. In the second part of our proposal, we discuss the re⁃ quirements for adapting ITU-R BT.500, a conventional subjec⁃ tive QoE assessment method, ITU-R BT.500, for assessing QoE of S-3DTV are presented.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    W. Chen, J. Fournier, Marcus Barkowsky, P. Le Callet

    Quality of experience model for 3DTV

    Proceedings of IS&T/SPIE ELECTRONIC IMAGING | Stereoscopic Displays and Applications XXIII , San Francisco, CA, USA, vol. 8288, no. 59

    2012

    DOI: 10.1117/12.907873

    Abstract anzeigen

    Modern stereoscopic 3DTV brings new QoE (quality of experience) to viewers, which not only enhances the 3D sensation due to the added binocular depth, but may also induce new problems such as visual discomfort. Subjective quality assessment is the conventional method to assess the QoE. However, the conventional perceived image quality concept is not enough to reveal the advantages and the drawbacks of stereoscopic images in 3DTV. Higher-level concepts such as visual experience were proposed to represent the overall visual QoE for stereoscopic images. In this paper, both the higher-level concept quality indicator, i.e. visual experience and the basic level concepts quality indicators including image quality, depth quantity, and visual comfort are defined. We aim to explore 3D QoE by constructing the visual experience as a weight sum of image quality, depth quantity and visual comfort. Two experiments in which depth quantity and image quality are varied respectively are designed to validate this model. In the first experiment, the stimuli consist of three natural scenes and for each scene, there are four levels of perceived depth variation in terms of depth of focus: 0, 0.1, 0.2 and 0.3 diopters. In the second experiment, five levels of JPEG 2000 compression ratio, 0, 50, 100, 175 and 250 are used to represent the image quality variation. Subjective quality assessments based on the SAMVIQ method are used in both experiments to evaluate the subject's opinion in basic level quality indicators as well as the higher-level indicator. Statistical analysis of result reveals how the perceived depth and image quality variation affect different perceptual scales as well as the relationship between different quality aspects.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    W. Chen, J. Fournier, Marcus Barkowsky, P. Le Callet

    Exploration of Quality of Experience of Stereoscopic Images: Binocular Depth

    Sixth International Workshop on Video Processing and Quality Metrics for Consumer Electronics - VPQM 2012 (Jan 2012; Scottsdale, AZ, USA)

    2012

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    W. Chen, J. Fournier, Marcus Barkowsky, P. Le Callet

    New stereoscopic video shooting rule based on stereoscopic distortion parameters and comfortable viewing zone

    Proceedings of SPIE Vol. 7863: Stereoscopic Displays and Applications XXII;

    2011

    Abstract anzeigen

    Human binocular depth perception, the most important element brought by 3DTV, is proved to be closely connected to not only the content acquisition (camera focal length, camera baseline and etc.) but also the viewing environment (viewing distance, screen size and etc.). Conventional 3D stereography rule in the literature usually consider the general viewing condition and basic human factors to guide the content acquisition, such as assuming human inter-pupil baseline as the maximum disparity. A lot of new elements or problems of stereoscopic viewing was not considered or precisely defined so that advanced shooting rule is needed to guarantee the overall quality of stereoscopic video. In this paper, we proposed a new stereoscopic video shooting rule considering two most important issues in 3DTV: stereoscopic distortion and comfortable viewing zone. Firstly, a mathematic model mapping the camera space to visualization space is established in order to geometrically estimate the stereoscopic depth distortion. Depth and shape distortion factors are defined and used to describe the stereoscopic distortion. Secondly, comfortable viewing zone (or Depth of focus) is considered to reduce the problem of visual discomfort and visual fatigue. The new shooting rule is to optimize the camera parameters (focal length, camera baseline and etc.) in order to control depth and shape distortion and also guarantee that the perceived scene is located in comfortable viewing zone as possible. However, in some scenarios, the above two conditions cannot be fulfill simultaneously, even sometimes contradict with each other so that priority should be decided. In this paper, experimental stereoscopic synthetic content generation with various sets of camera parameters and various sets of scenes representing different depth range are presented. Justification of the proposed new shooting rule is based on 3D concepts (depth rendering, visual comfort and visual experience) subjective video assessment. The results of this study will provide a new method to propose camera parameters based on management of new criteria (shape distortion and depth of focus) in order to produce optimized stereoscopic images and videos.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    W. Chen, J. Fournier, Marcus Barkowsky, P. Le Callet

    New Requirements of Subjective Video Quality Assessment Methodologies for 3DTV

    Fifth International Workshop on Video Processing and Quality Metrics (VPQM) [Scottsdale, AZ, USA]

    2010

    Abstract anzeigen

    In this paper, the new challenges of 3DTV for subjective assessment are discussed. Conventional 2D methods have severe limitations which will be revealed. Based on the understanding of the new characteristics brought by 3DTV, changes and additions in the requirements for subjective assessment are proposed in order to develop a novel subjective video quality assessment methodology for 3DTV. In particular, depth rendering for 3D display is selected to give a further discussion. The depth rendering abilities are defined as a combination of the physical parameters and the perceptual constrains. We analyze different types of stereoscopic and multiview displays. Several problems regarding depth rendering are discussed in order to highlight the diversity and complexity of assessing 3DTV.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J.H.C. Hogg, J. Nicholls, Thomas Stirner, P. Chen, W. Hagston, B. Lunn, D. Ashenford

    Determination of the band offset of CdTe/Cd1-xMnxTe multiple quantum wells with very low x values

    Physical Review B - condensed matter and materials physics, vol. 52, no. 7, pp. 4732-4735

    1995