Seokhee Lee

Transparency analysis and delay compensation scheme for haptic-based networked virtual environments

Haptic-based NVEs (networked virtual environments) with CS (client/server) communication architectures support better consistency but induce larger end-to-end delays than those with P2P (peer-to-peer) communication architectures. Unfortunately, large delay severely deteriorates the transparency (i.e., reality) of haptic interaction. To improve the haptic interaction quality for haptic-based NVEs with CS communication architectures, in this paper the degradation of haptic interaction quality is analyzed according to network delays. Based on the analysis, the maximum allowable delay bound is predicted and unrealistic force feedback caused by the network delay is compensated. Experimental results confirm that the proposed analysis provides an acceptable quantification method about haptic interaction quality and that the proposed delay-compensation scheme effectively improves haptic interaction quality with respect to network delays.

Influence of Ar buffer gas on the LIBS signal of thin CIGS films

Laser induced breakdown spectroscopy (LIBS) measurement of a thin Cu(In,Ga)Se2 (CIGS) absorber layer was performed under the conditions of open air and argon (Ar) gas jet flow (25 L min−1). A second harmonic Q-switched Nd:YAG laser (λ = 532 nm, τ = 5 ns, top-hat profile) was employed for the ablation of co-evaporated CIGS samples. The use of an Ar gas jet for the LIBS measurement of CIGS thin films leads to two significant differences from the open air measurement results that are important from the precision point of view: (i) the increase of signal intensity and (ii) decrease of relative standard deviation (RSD) of measured intensity or intensity ratios. From calculation of the degree of intensity enhancement, it was shown that the enhancement of signal intensity is primarily due to the increase of plasma temperature and electron density under Ar buffer gas environment. It was also found that in addition to the influence of Ar gas itself the gasdynamic effects of the Ar gas jet contribute significantly to the reduction of RSD.

Quantitative analysis of CuIn1−xGaxSe2 thin films with fluctuation of operational parameters using laser-induced breakdown spectroscopy

To enable a quantitative analysis of CuIn1−xGaxSe2 (CIGS) thin solar cell films using laser-induced breakdown spectroscopy (LIBS), a new method based on the internal standard principle is proposed to identify the spectral line pairs unaffected by the fluctuations of measurement conditions. Due to nonlinear calibration curves resulting from the high concentration of constituent elements of CIGS, the standard deviation of measured line intensity ratios divided by the slope of calibration curves was introduced as a new figure of merit to determine the precision of LIBS analysis along with the linearity of data points in the correlation plots. From the analyses of 39 Cu, 10 In, and 5 Ga emission lines, Cu 324.754 nm–In 325.608 nm, Cu 219.975 nm–Ga 287.424 nm, and In 303.935 nm–Ga 287.424 nm line pairs were identified as the spectral lines of which intensity ratios were least influenced by the fluctuations of spot size, the position of collection optics, and/or laser energy. The selected line pairs, except the Cu 219.975 nm line, had similar upper level energy and consisted of strong resonance lines. It was found that the use of these strong lines has advantages of better reproducibility and precision for the analysis of elements with high concentration for which the calibration curve may become nonlinear due to self-absorption.

A network-adaptive transport scheme for haptic-based collaborative virtual environments

In this paper, we design and implement a transport scheme for haptic interactions in CVEs (collaborative virtual environments). When interacting with haptic interfaces in the CVEs, network delay jitter and packet loss over the Internet may seriously degrade the user experience of haptic interactions. The existing transport schemes tailored for networked haptics claim that their schemes could improve the quality of networked haptic interaction. However, what seems to be lacking is that they do not focus on reducing the transmission rate and end-to-end delay of the haptic events. On the contrary, the proposed transport scheme reduces the transmission rate of haptic events by using network-adaptive aggregated packetization and the priority-based filtering. It also compensates the network delay jitter and loss in order to improve the haptic interaction quality by using haptic event error control and priority-based buffering scheme with low processing delay. According to the experimental results, the proposed transport scheme provides shorter playout delay and less transmission rate than those of the existing networked haptic transports.

Reproducibility of CIGS thin film analysis by laser-induced breakdown spectroscopy

The reproducibility of an elemental analysis of thin CIGS solar cell films by laser-induced breakdown spectroscopy (LIBS) is assessed. A Q-switched Nd:YAG laser (λ = 532 nm, τ = 5 ns, top-hat profile) and an ICCD detector were used for the LIBS measurements. It was shown that the concentration ratios and depth profile of a CIGS sample with unknown composition could be predicted with high precision by using the calibration curves generated with reference CIGS samples. The spot-to-spot relative standard deviation of 1.4% could be achieved for (Ga + In)/Cu at the gate delay of 0.1 μs condition, demonstrating that LIBS can be applied for real time monitoring of the elemental composition of CIGS thin films.

Independence of elemental intensity ratio on plasma property during laser-induced breakdown spectroscopy

The authors report that the elemental composition ratio of Ga to In in a CuIn(1-x)Ga(x)Se(2) compound semiconductor, a thin-film solar cell material, can be measured with little influence of plasma property changes by laser-induced breakdown spectroscopy (λ = 1064 nm, τ = 5 ns). It is shown that the similarity in excitation energy levels of the selected Ga and In emission lines and the fact that these elements belong to the same group of the periodic table are the critical factors ensuring the independence of intensity ratio on plasma conditions.

Depth profiling analysis of CuIn 1-x Ga x Se 2 absorber layer by laser induced breakdown spectroscopy in atmospheric conditions

This work reports the capability of depth profile analysis of thin CuIn1-xGa(x)Se2 (CIGS) absorber layer (1.89 μm) with a sub-hundred nanometer resolution by laser induced breakdown spectroscopy (LIBS). The LIBS analysis was carried out with a commercial CIGS solar cell on flexible substrate by using a pulsed Nd:YAG laser (λ = 532 nm, τ = 5 ns, top-hat profile) and an intensified charge-coupled device spectrometer in atmospheric conditions. The measured LIBS elemental profiles across the CIGS layer agreed closely to those measured by secondary ion mass spectrometry. The resolution of depth profile analysis was about 88 nm. Owing to the short measurement time of LIBS and the capability of in-air measurement, it is expected that LIBS can be applied for in situ analysis of elemental composition and their distribution across the film thickness during development and manufacturing of CIGS solar cells.

A synchronized multiplexing scheme for multi-view HD video over IP system

This paper proposes a prototype realization of multi-view HD video transport system with synchronized multiplexing over IP networks. The proposed synchronized multiplexing considers the synchronization during video acquisition and the multiplexing for the interactive view-selection during transport. For the synchronized acquisition from multiple HDV camcoders through IEEE 1394 interface, we estimate the timeline differences among MPEG-2 compressed video streams by using global time of network between the cameras and a server and correct timelines of video streams by changing the timestamp of the MPEG-2 system stream. Also, we multiplex a selected number of acquired HD views at the MPEG-2 TS (transport stream) level for the interactive view-selection during transport. Thus, with the proposed synchronized multiplexing scheme, we can display synchronized HD view.

Improvement of selenium analysis during laser-induced breakdown spectroscopy measurement of CuIn1−xGaxSe2 solar cell films by self-absorption corrected normalization

The analysis of Se emission lines (196.089 nm and 203.984 nm) of CuIn1−xGaxSe2 (CIGS) thin solar cell films by laser-induced breakdown spectroscopy (LIBS) is reported. With CIGS thin films fabricated by co-evaporation or sputtering methods, LIBS measurement was carried out using a nanosecond laser (λ = 532 nm, τ = 5 ns, top-hat profile) and a CCD spectrometer (gate width = 1.05 ms, gate delay = 0.2 μs) in a flowing Ar gas environment (20 L min−1). From the comparison of calibration curves, it was found that the correlation between the Se/Cu LIBS intensity ratio and the Se/Cu concentration ratio could be improved significantly by applying the self-absorption correction procedure introduced in this study, demonstrating the significance of self-absorption in those Se emission lines. It was shown that normalization alone could reduce the relative standard deviation but was insufficient for accurate LIBS analysis of Se in CIGS thin films.

Performance evaluation of transport protocols for networked haptic collaboration

In this paper, we explain two transport-related experimental results for networked haptic CVEs (collaborative virtual environments). The first set of experiments evaluate the performance changes in terms of QoE (quality of experience) with the haptic-based CVEs under different network settings. The evaluation results are then used to define the minimum networking requirements for CVEs with force-feedback haptic interface. The second experiments verify whether the existing haptics-specialized transport protocols can satisfy the networking QoE requirements for the networked haptic CVEs. The results will be used to suggest in design guidelines for an effective transport protocol for this highly-interactive (i.e., extremely low-delay latency at up to 1 kHz processing cycle) haptic CVEs over the delay-crippled Internet.