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Suche nach „[J.] [Li]“ hat 24 Publikationen gefunden
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    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    L. Liu, S. Li, D. Liu, Günther Benstetter, O. Man, J. Michalicka, Y. Zhang, Y. Hong, H. Fan, W. Ni, Q. Yang, Y. Wu, Z. Bi

    The effect of O2 impurity on surface morphology of polycrystalline W during low-energy and high-flux He+ irradiation

    Fusion Engineering and Design, vol. 139, pp. 96-103

    2019

    DOI: 10.1016/j.fusengdes.2019.01.003

    Abstract anzeigen

    The interaction between the impurities (such as carbon, nitrogen, oxygen) and the plasma-facing materials (PFMs) can profoundly influence the performance and service of the PFMs. In this paper, we investigated the influence of oxygen (O2) impurity in the helium radio frequency (RF) plasma on the surface morphology of polycrystalline tungsten (W) irradiated at the surface temperature of 1450 ± 50 K and the ion energy of 100 eV. The pressure ratio of O2 to He (R) in RF source varied from 4.0 × 10−6 to 9.0 × 10-2. The total irradiation flux and fluence were ˜1.2 × 1022 ions·m-2·s-1 and ˜1.0 × 1026 ions·m-2, respectively. After He+ irradiation, the specimen surface morphology was observed by scanning electron microscopy. It was found that with increasing R from 4.0 × 10−6 to 9.0 × 10-2 the thickness of nano-fuzz layer at the W surface was thinner and thinner, accompanied by the formation of rod-like structures. The erosion yield increased from 5.2 × 10-4 to 2.3 × 10-2 W/ion when R varied from 4.0 × 10-6 to 9.0 × 10-2. The X-ray diffraction analysis shows that tungsten oxides were formed at the near surface of specimens when R exceeded 1.8 × 10-2. The erosion yield measurements revealed that in addition to surface physical sputtering process, the chemical erosion process could occur due to the interaction between oxygen-containing species and W at the surface. The results indicated that the presence of O2 impurity in He plasma can obviously affect the surface microstructure of W. The study suggested that O2 impurity can effectively reduce the growth of nano-fuzz structures.

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    J. Li, Wang, J., Marcus Barkowsky, P. Callet

    Exploring the effects of subjective methodology on assessing visual discomfort in immersive multimedia

    Electronic Imaging, Human Vision and Electronic Imaging

    2018

    DOI: 10.2352/ISSN.2470-1173.2018.14.HVEI-527

    Abstract anzeigen

    Visual discomfort is an important factor that influences viewing experience in immersive multimedia, for example, 3DTV and VR. With the added value of depth, the novel perceptual experience, visual discomfort is not an easy task for observers to evaluate. In this study, we investigate how the subjective methodology affects the test results in 3DTV condition. Two subjective visual discomfort experiments were conducted. One used the Pair Comparison (PC) method and the other used the Absolute-Category Rating (ACR) method. The results demonstrated that PC method had more powerful discriminability. For a difficult perceptualrelated tasks, such as visual discomfort in our study, PC was more easy to understand and conduct for the observers which led to reliable results. It also showed some very important but usually ignored conclusions on the subjective experiment, i.e., for measuring the perceived visual discomfort, the observer\textquoterights judgment behavior might be affected by the test methodology.

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    J. Li, A. Wang, Wang, J., Marcus Barkowsky, P. Le Callet

    Visual Discomfort Induced by Three-Dimensional Display Technology (in Chinese)

    Laser and Optoelectronics Progress, vol. 52, no. 3

    2015

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Y. Koudota, Marcus Barkowsky, H. Primon, P. Le Callet

    Comparing Upscaling Algorithms From Hd To Ultra Hd By Evaluating Preference Of Experience

    2014 Sixth International Workshop on Quality of Multimedia Experience (QoMEX)

    2014

    Abstract anzeigen

    As the next generation of TV, Ultra High Definition Television (UHDTV) is attracting more and more people's attention as it provides a new viewing experience. Considering content delivery, due to the lack of Ultra HD resources, a direct question for the industry is that whether the state-of-the-art upscaling algorithms can be utilized to upscale the current HD or Full HD resources to UHD, gaining benefit from the higher resolution but without losing the high quality viewing experience. To investigate this, in this study, we upscaled 720p and 1080p sequences to UHD resolution by different upscaling algorithms. Paired Comparison methodology was used in the subjective experiment to evaluate their performances. The results showed that for the case of fast motion content, viewers' preference on different upscaled video sequences is not significantly different. In general conditions, the low complexity upscaling algorithms (e.g., lanczos-3) performed better than the high complexity algorithms (e.g., Robust Super Resolution algorithm). A novel upscaling algorithm adapted to UHD is recommended to be developed based on the mechanisms of human visual system.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Assessing the Quality of Experience of 3DTV and Beyond: Tackling the Multidimensional Sensation

    3D Future Internet Media, New York

    2014

    ISBN: 978-1-4614-8372-4

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    J. Li, Marcus Barkowsky, P. Callet

    Visual discomfort of stereoscopic 3D videos: Influence of 3D motion

    Displays, vol. 35, no. 1, pp. 49-57

    2014

    DOI: 10.1016/j.displa.2014.01.002

    Abstract anzeigen

    Visual discomfort is one of the most frequent complaints of the viewers while watching 3D images and videos. Large disparity and large amount of motion are two main causes of visual discomfort. To quantify this influence, three objectives are set in this paper. The first one is the comparative analysis on the influence of different types of motion, i.e., static stereoscopic image, planar motion and in-depth motion, on visual discomfort. The second one is the investigation on the influence factors for each motion type, for example, the disparity offset, the disparity amplitude and velocity. The third one is to propose an objective model for visual discomfort. Thirty-six synthetic stereoscopic video stimuli with different types of motion are used in this study. In the subjective test, an efficient paired comparison method called Adaptive Square Design (ASD) was used to reduce the number of comparisons for each observer and keep the results reliable. The experimental results showed that motion does not always induce more visual discomfort than static conditions. The in-depth motion generally induces more visual discomfort than the planar motion. The relative disparity between the foreground and the background, and the motion velocity are identified as main factors for visual discomfort. According to the subjective results, an objective model for comparing visual discomfort induced by different types of motion is proposed which shows high correlation with the subjective perception.

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    J. Li, Marcus Barkowsky, P. Le Callet

    Validation of reliable 3DTV subjective assessment methodology ‐ Establishing a Ground Truth Database

    VQEG (Video Quality Expert Group) eLetter, vol. 1, no. 2

    2014

    Abstract anzeigen

    Quality of Experience (QoE) in 3DTV is a multi-dimensional concept which includes image quality, depth quality, and visual comfort. How to measure this multi-dimensional concept is a challenging issue nowadays. In this letter, we introduce a Ground Truth database which is targeted for the standardization of subjective methodologies for QoE in 3DTV.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    M. Urvoy, Marcus Barkowsky, J. Li, P. Le Callet

    Visual Comfort and Fatigue in Stereoscopy

    3D Video: From Capture to Diffusion, London, UK

    2013

    ISBN: 9781848215078

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Subjective Assessment Methodology For Preference Of Experience In 3dtv

    Proceedings of the 11th IEEE IVMSP Workshop : 3D Image/Video Technologies and Applications, Seoul, South Korea

    2013

    Abstract anzeigen

    The measurement of the Quality of Experience (QoE) in 3DTV re- cently became an important research topic as it relates to the devel- opment of the 3D industry. Pair comparison is a reliable method as it is easier for the observers to provide their preference on a pair rather than give an absolute scale value to a stimulus. The QoE measured by pair comparison is thus called \textquoteright. In this paper, we introduce some efficient designs for pair compari- son which can reduce the number of comparisons. The constraints of the presentation order of the stimuli in pair comparison test are listed. Finally, some analysis methods for pair comparison data are provided accompanied with some examples from the studies of the measurement of PoE.

    DigitalAngewandte Informatik

    Zeitschriftenartikel

    J. Li, Marcus Barkowsky, P. Le Callet

    Recent Advances in Standardization on 3D Quality of Experience

    IEEE COMSOCMMTC E-Letter, vol. 8, no. 3

    2013

    Abstract anzeigen

    For the last decades, video quality assessment has mostly tackled 2D video sequences. Technological advances were mostly tackling coding and transmission schemes while the display technology, especially in lab viewing environments, could be considered as transparent. Subjective assessment methodologies needed to be selected mostly with respect to the severity of the degradations. Typical examples are Absolute Category Rating with Hidden Reference (ACR-HR) from ITU-T P.910 for strong degradations experienced in networked multimedia scenarios, and Paired Comparison (PC) or Double Stimulus Continuous Quality Scale (DSCQS) from ITU-R BT.500 for near lossless scenarios such as satellite transmissions.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Boosting Paired Comparison methodology in measuring visual discomfort of 3DTV: Performances of three different designs

    Proceedings of SPIE Vol. 8648: Stereoscopic Displays and Applications XXIV

    2013

    Abstract anzeigen

    The pair comparison method is often recommended in subjective experiments because of the reliability of the obtained results. However, a drawback of this method is that the number of comparisons increases exponentially with the number of stimuli, which limits its usability for a large number of stimuli. Several design methods that aim to reduce the number of comparisons were proposed in the literature. However, their performances in the context of 3DTV should be evaluated carefully due to the fact that the results obtained from a paired comparison experiment in 3DTV may be influenced by two important factors. One is the observation error from observer's attentiveness, in particular inverting the vote. The second factor concerns the dependence on the context in which the evaluation takes place. In this study, three design methods, namely Full Paired Comparison method (FPC), Square Design method (SD) and the Adaptive Square Design method (ASD) were evaluated by subjective visual discomfort experiment in 3DTV. The results from the FPC method were considered as the ground truth. Comparing with the ground truth, the ASD method provided the most accurate results with a given number of trials. It also showed the highest robustness against observation errors and interdependence of comparisons. Due to the efficiency of the ASD method, paired comparison experiments become feasible with a reasonably large number of stimuli for measuring 3DTV visual discomfort.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    Marcus Barkowsky, J. Li, T. Han, S. Youn, J. Ok, C. Lee, I. Vijai Ananth, K. Wang, K. Brunnström, P. Le Callet

    Towards standardized 3DTV QoE assessment: Cross-lab study on display technology and viewing environment parameters

    Proceedings of SPIE Vol. 8648: Stereoscopic Displays and Applications XXIV;

    2013

    Abstract anzeigen

    Subjective assessment of Quality of Experience in stereoscopic 3D requires new guidelines for the environmental setup as existing standards such as ITU-R BT.500 may no longer be appropriate. A first step is to perform cross-lab experiments in different viewing conditions on the same video sequences. Three international labs performed Absolute Category Rating studies on a freely available video database containing degradations that are mainly related to video quality degradations. Different conditions have been used in the labs: Passive polarized displays, active shutter displays, differences in viewing distance, the number of parallel viewers, and the voting device. Implicit variations were introduced due to the three different languages in Sweden, South Korea, and France. Although the obtained Mean Opinion Scores are comparable, slight differences occur in function of the video degradations and the viewing distance. An analysis on the statistical differences obtained between the MOS of the video sequences revealed that obtaining an equivalent number of differences may require more observers in some viewing conditions. It was also seen that the alignment of the meaning of the attributes used in Absolute Category Rating in different languages may be beneficial. Statistical analysis was performed showing influence of the viewing distance on votes and MOS results.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Visual Discomfort is not always proportonal to Eye Blinking Rate: Exploring Some Effects of Planar and In-Depth Motion on 3DTV QoE

    International Workshop on Video Processing and Quality Metrics for Consumer Electronics VPQM 2013 (Jan 2013; Scottsdale, AZ, USA)

    2013

    Abstract anzeigen

    Visual discomfort is an important factor in determiningQoE in 3DTV. It can be measured by physiological signals. Inthis study, the relationship between 3D video characteristics(e.g., motion type, disparity, velocity, etc), visual discom-fort and eye blinking rate were studied. Three motion typeswere considered, which were static scenes, planar motionand in-depth motion. 44 stimuli with different motion types,disparity levels and velocity levels were studied. The eyeblinking signals of 28 observers were obtained by an electro-physiological measurement device. The experimental resultsshowed that stimulus velocity affected eye blinks significantlyand differently for planar motion stimuli and in-depth motionstimuli. The objective eye blinking model for 3D stimuliwas developed in function of the 3D video characteristics.Furthermore, the results showed that eye blinking rate wasproportional to the visual discomfort of the static 3D stimulibut inversely proportional to the visual discomfort of planarmotion stimuli.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Analysis and Improvement of a Paired Comparison Method in the Application of 3DTV Subjective Experiment

    2012 19th IEEE International Conference on Image Processing

    2012

    Abstract anzeigen

    Paired comparison is a frequently used method in psychophysical studies. However, with the increase of the number of the stimuli, the number of comparisons increases exponentially. Square design is one of the balanced sub-set paired comparison methods which could reduce the number of comparisons while producing comparably precise results under some assumptions. However, when there are observation errors from observers' attentiveness, the square design would produce large estimation errors. Thus, an improved square design which is robust to observation errors is proposed. Using a Monte Carlo simulation, the proposed method is evaluated and shows improvement in efficiency. The original design is applied in a visual discomfort subjective test of 3DTV. In addition, both of the two designs are studied by utilizing our previous full comparison data. The test results showed that the proposed improved square design is more robust to observation errors. Another important finding is that the influence of the occurrence of some other stimuli on voting is significant. Whether the proposed method could reduce the prediction errors induced by it is still under study.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Sun, L. Li, Thomas Stirner, J. Bai, D. Wang

    Particle simulation of the nonlinear oscillation of electrons induced by a nanosecond pulse in rf capacitive hydrogen discharges

    Physics of Plasmas, vol. 19, no. 3

    2012

    DOI: 10.1063/1.3695121

    Abstract anzeigen

    A particle-in-cell simulation was employed to investigate the nature and physical cause of the nonlinear oscillation of electrons induced by a nanosecond pulse in rf capacitive hydrogen discharges. It was found that the applied nanosecond pulse converted the plasma quickly from the bi-Maxwellian equilibrium formed in the rf capacitive discharge into another temporal bi-Maxwellian equilibrium. When the applied electric field collapses within a few nanoseconds, the electric field arising from the space charge serves as a restoring force to generate a swift oscillation of the electrons. The energy stored in the plasma is converted gradually into the chemical energy during the electron periodic movement. It is also found that the rise-, plateau-, and fall-times of the applied pulse affect the evolution of the electron energy distribution. The collective electron oscillation has a repetition frequency approximately equal to the electron plasma frequency, independent of pulse rise-, plateau-, and fall-times. This oscillation of electrons induced by a nanosecond pulse can be used to generate highly excited vibrational states of hydrogen molecules, which are a necessary precursor for negative hydrogen ions.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    Visual Discomfort Induced by Relative Disparity and Planar Motion of Stereoscopic Images

    first Sino French Workshop on Information and Communication Technologies, Nantes, France

    2011

    Abstract anzeigen

    Viewers often complain of visual discomfort or visual fatigue after viewing the stereoscopic images. In this paper, we investigated the effects of planar motion at different depth levels on visual discomfort. In the subjective experiments, the Paired Comparison method was used to allow for a precise measurement. The Bradley-Terry model was used to analyze the subjective experimental data. The experimental results indicated that the relative angular disparity between foreground object and background played a more important role in determining the visual discomfort than the vergence-accommodation conflict. Furthermore, viewers might experience more visual discomfort with the increase of planar motion velocity. In a practical application of our study, it may be concluded that for stereoscopic motion images, the depth range for fast motion sequences should be significantly reduced and for slow motion sequences, the depth range may be increased.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, P. Le Callet

    The Influence of Relative Disparity and Planar Motion Velocity on Visual Discomfort of Stereoscopic Videos

    Proceedings of 2011 Third International Workshop on Quality of Multimedia Experience (QoMEX), Mechelen, Belgique

    2011

    Abstract anzeigen

    The vergence-accommodation conflict, excessive screen disparity,binocular distortions and the motion component in stereoscopicvideos are considered as main factors that may induce visualdiscomfort. In our previous study which was based on theexperts-only experiment, we also found that the large relativedisparity between the foreground and background and the fast planarmotion were more likely to induce visual discomfort. In this study,we conducted the same subjective experiment but on non-expertobservers. The subjective experiment results coincided with ourprevious findings. The two objective visual discomfort modelsdeveloped in our previous study have been evaluated and showedhigh correlation with subjective data. Finally, we found that theobservers could be classified into different clusters according to theirvisual discomfort sensitivity to the velocity or the relative disparity.For some observers, the velocity is the predominant factor that mayinduce visual discomfort; some consider that the relative disparity isthe key factor, and some are sensitive to both the velocity and relativedisparity.

    DigitalAngewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    J. Li, Marcus Barkowsky, Wang, J., P. Le Callet

    Study on Visual Discomfort Induced by Stimulus Movement at Fixed Depth on Stereoscopic Displays using Shutter Glasses

    2011 17th International Conference on Digital Signal Processing (DSP)

    2011

    Abstract anzeigen

    Stereoscopic motion images are able to provide observers with realistic and immersive viewing experience. However, observers often experience visual discomfort during the viewing process. In this paper, we investigated the relationship between visual discomfort and the planar motion at different depth levels. The Paired Comparison method was used in the subjective experiments to allow for a precise measurement. The experimental results indicated that the relative angular disparity between foreground object and background played a more important role in determining the visual discomfort than the vergence-accommodation conflict. Furthermore, the results showed that with the increase of planar motion velocity, viewers might experience more visual discomfort. To quantify the effects of relative angular disparity and velocity on visual discomfort, two visual discomfort models were constructed. The preferred model was chosen based on the performance as well as the algorithmic complexity. This model can be used as an index for other related researches.

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    D. Liu, J. Gu, Z. Feng, D. Li, J. Niu, Günther Benstetter

    Comparison of fluorocarbon film deposition by pulsed/continuous wave and downstream radio frequency plasmas

    Vacuum, vol. 85, no. 2, pp. 253-262

    2010

    Abstract anzeigen

    Fluorocarbon (FC) films have been deposited using pulsed and continuous wave (cw) radio frequency (rf) plasmas fed with hexafluoroethane (C2F6), octafluoropropane (C3F8), or octafluorocyclobutane (C4F8). The effects of feed gases used, discharge pressure, rf power, substrate positions and discharge modes (pulsed or cw) on the deposited films are examined. Film properties are determined using X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. The contact angles of FC films are well related to their compositions and structures. Feed gases used, discharge pressure, rf power, substrate positions and discharge modes strongly affect the morphology of the resulting film, as revealed by atomic force microscopy. Optical emission spectrometry measurements were performed to in-situ characterize the gas-phase compositions of the plasmas and radicals’ emission intensities during film deposition. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. The film growth in pulsed or downstream plasmas was controlled by the surface migration of radicals, such as CF2 towards nucleation centers, which result in the deposition of FC films with less cross-linked nature and rougher surfaces. These results demonstrate that it is possible to control film compositions and surface structure by changing deposition parameters.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Sun, S. Li, Thomas Stirner, et al.

    Molecular dynamics simulation of energy exchanges during hydrogen collision with graphite sheets

    Journal of Applied Physics, vol. 107

    2010

    DOI: 10.1063/1.3428447

    Abstract anzeigen

    Experiments show that the energy of particles incident on divertor plates in fusion devices seldom exceeds 100 eV. Trim code and its variants are not suitable to predict the sputtering yield of carbon-based divertor plates for this energy range and, therefore, a dynamic model, taking into account the C–H bond formation and breaking, and the structure of carbon, is needed. In this paper, the molecular dynamics method is employed to investigate collision processes between incident hydrogen atoms and a graphene sheet. The simulation results demonstrate that the collision processes cannot be adequately described by a simple binary approximation. The energy transfer from the projectile to the graphite sheet exhibits a very complicated behavior when the kinetic energy of the incident hydrogen atom is below 30 eV, strongly depending on the impact position. When its kinetic energy is lower than 0.35 eV, the incident hydrogen is always reflected back from the single, perfect graphite sheet; when its kinetic energy is higher than 0.35 eV, then whether the incident particle penetrates the graphite sheet, is reflected back or is adsorbed depends on the impact position. In certain areas of the graphite sheet, either adsorption or reflection of an incident hydrogen atom can occur in two different energy ranges.