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Search Results: 1 - 10 of 20946 matches for " Yen-Fu Ou "
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Q-STAR:A Perceptual Video Quality Model Considering Impact of Spatial, Temporal, and Amplitude Resolutions
Yen-Fu Ou,Yuanyi Xue,Yao Wang
Computer Science , 2012,
Abstract: In this paper, we investigate the impact of spatial, temporal and amplitude resolution (STAR) on the perceptual quality of a compressed video. Subjective quality tests were carried out on a mobile device. Seven source sequences are included in the tests and for each source sequence we have 27 test configurations generated by JSVM encoder (3 QP levels, 3 spatial resolutions, and 3 temporal resolutions), resulting a total of 189 processed video sequences (PVSs). Videos coded at different spatial resolutions are displayed at the full screen size of the mobile platform. Subjective data reveal that the impact of spatial resolution (SR), temporal resolution (TR) and quantization stepsize (QS) can each be captured by a function with a single content-dependent parameter. The joint impact of SR, TR and QS can be accurately modeled by the product of these three functions with only three parameters. We further find that the quality decay rates with SR and QS, respectively are independent of TR, and likewise, the decay rate with TR is independent of SR and QS, respectively. However, there is a significant interaction between the effects of SR and QS. The overall quality model is further validated on five other datasets with very high accuracy. The complete model correlates well with the subjective ratings with a Pearson Correlation Coefficient (PCC) of 0.991.
Perceptual Quality of Video with Periodic Frame Rate and Quantization Variation-Subjective Studies and Analytical Modeling
Yen-Fu Ou,Wenzhi Lin,Huiqi Zeng,Yao Wang
Computer Science , 2014,
Abstract: In networked video applications, the frame rate (FR) and quantization stepsize (QS) of a compressed video are often adapted in response to the changes of the available bandwidth. It is important to understand how do the variation of FR and QS and their variation pattern affect the video quality. In this paper, we investigate the impact of temporal variation of FR and QS on the perceptual video quality. Among all possible variation patterns, we focus on videos in which two FR's (or QS's) alternate over a fixed interval. We explore the human responses to such variation by conducting subjective evaluation of test videos with different variation magnitudes and frequencies. We further analyze statistical significance of the impact of variation magnitude, variation frequency, video content, and their interactions. By analyzing the subjective ratings, we propose two models for predicting the quality of video with alternating FR and QS, respectively, The proposed models have simple mathematical forms with a few content-dependent parameters. The models fit the measured data very well using parameters determined by least square fitting with the measured data. We further propose some guidelines for adaptation of FR and QS based on trends observed from subjective test results.
QCD Viscosity to Entropy Density Ratio in the Hadronic Phase
Chen, Jiunn-Wei;Li, Yen-Han;Liu, Yen-Fu;Nakano, Eiji
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.114011
Abstract: Shear viscosity (eta) of QCD in the hadronic phase is computed by the coupled Boltzmann equations of pions and nucleons in low temperatures and low baryon number densities. The eta to entropy density ratio eta/s maps out the nuclear gas-liquid phase transition by forming a valley tracing the phase transition line in the temperature-chemical potential plane. When the phase transition turns into a crossover, the eta/s valley gradually disappears. We suspect the general feature for a first-order phase transition is that eta/s has a discontinuity in the bottom of the eta/s valley. The discontinuity coincides with the phase transition line and ends at the critical point. Beyond the critical point, a smooth eta/s valley is seen. However, the valley could disappear further away from the critical point. The eta/s measurements might provide an alternative to identify the critical points.
QCD Viscosity to Entropy Density Ratio in the Hadronic Phase
Jiunn-Wei Chen,Yen-Han Li,Yen-Fu Liu,Eiji Nakano
Physics , 2007, DOI: 10.1103/PhysRevD.76.114011
Abstract: Shear viscosity (eta) of QCD in the hadronic phase is computed by the coupled Boltzmann equations of pions and nucleons in low temperatures and low baryon number densities. The eta to entropy density ratio eta/s maps out the nuclear gas-liquid phase transition by forming a valley tracing the phase transition line in the temperature-chemical potential plane. When the phase transition turns into a crossover, the eta/s valley gradually disappears. We suspect the general feature for a first-order phase transition is that eta/s has a discontinuity in the bottom of the eta/s valley. The discontinuity coincides with the phase transition line and ends at the critical point. Beyond the critical point, a smooth eta/s valley is seen. However, the valley could disappear further away from the critical point. The eta/s measurements might provide an alternative to identify the critical points.
The Effects of Dietary Intervention on HIV Dyslipidaemia: A Systematic Review and Meta-Analysis
Clare Stradling, Yen-Fu Chen, Tracy Russell, Martin Connock, G. Neil Thomas, Shahrad Taheri
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0038121
Abstract: Background Efficacy of dietary intervention for treatment and prevention of HIV-related lipid disturbances has not been well established. Methods We conducted a systematic search of electronic databases supplemented with manual searches and conference abstracts, without language restriction. All randomised controlled trials (RCTs) with blood lipid outcomes, involving dietary intervention or supplementation for the treatment or prevention of adult HIV dyslipidaemia, versus no or other intervention were included. Two authors using predefined data fields, including study quality indicators, extracted data independently. Results Eighteen studies (n = 873) met our inclusion criteria. Seven RCTs for omega-3 supplementation (n = 372), and four RCTs for dietary intervention (n = 201) were meta-analysed using random-effects models. Mild statistical heterogeneity was observed. Dietary intervention reduced triglyceride levels by ?0·46 mmol/l (95%CI: ?0·85 to ?0·07 mmol/l) compared to control. Omega-3 supplementation reduced triglyceride levels by ?1.12 mmol/l, (95%CI: ?1·57 to ?0·67 mmol/l) and total cholesterol, ?0·36 mmol/l (95%CI: ?0·67 to ?0·05 mmol/l) compared to placebo/control. Conclusions Both omega-3 supplementation and dietary intervention reduced triglyceride level, with the latter possibly to a smaller extent. While dietary interventions are beneficial, more stringent dietary approaches may be necessary to fully address lipid disturbances in HIV patients. Trial Registration PROSPERO 2011:CRD42011001329.
Shear and Bulk Viscosities of a Weakly Coupled Quark Gluon Plasma with Finite Chemical Potential and Temperature---Leading-Log Results
Jiunn-Wei Chen,Yen-Fu Liu,Yu-Kun Song,Qun Wang
Physics , 2012, DOI: 10.1103/PhysRevD.87.036002
Abstract: We calculate the shear (eta) and bulk (zeta) viscosities of a weakly coupled quark gluon plasma at the leading-log order with finite temperature T and quark chemical potential mu. We find that the shear viscosity to entropy density ratio eta/s increases monotonically with mu and eventually scales as (mu/T)^2 at large mu. In contrary, zeta/s is insensitive to mu. Both eta/s and zeta/s are monotonically decreasing functions of the quark flavor number N_f when N_f \geq 2. This property is also observed in pion gas systems. Our perturbative calculation suggests that QCD becomes the most perfect (i.e. with the smallest eta/s) at mu=0 and N_f = 16 (the maximum N_f with asymptotic freedom). It would be interesting to test whether the currently smallest eta/s computed close to the phase transition with mu=0 and N_f = 0 can be further reduced by increasing N_f.
Negative Off-Diagonal Conductivities in a Weakly Coupled Quark Gluon Plasma
Jiunn-Wei Chen,Yen-Fu Liu,Shi Pu,Yu-Kun Song,Qun Wang
Physics , 2013, DOI: 10.1103/PhysRevD.88.085039
Abstract: We calculate the conductivity matrix of a weakly coupled quark-gluon plasma at the leading-log order. By setting all quark chemical potentials to be identical, the diagonal conductivities become degenerate and positive, while the off-diagonal ones become degenerate but negative (or zero when the chemical potential vanishes). This means a potential gradient of a certain fermion flavor can drive backward currents of other flavors. A simple explanation is provided for this seemingly counter intuitive phenomenon. It is speculated that this phenomenon is generic and most easily measured in cold atom experiments.
Pathway-based Screening Strategy for Multitarget Inhibitors of Diverse Proteins in Metabolic Pathways
Kai-Cheng Hsu ,Wen-Chi Cheng ,Yen-Fu Chen,Wen-Ching Wang ,Jinn-Moon Yang
PLOS Computational Biology , 2013, DOI: 10.1371/journal.pcbi.1003127
Abstract: Many virtual screening methods have been developed for identifying single-target inhibitors based on the strategy of “one–disease, one–target, one–drug”. The hit rates of these methods are often low because they cannot capture the features that play key roles in the biological functions of the target protein. Furthermore, single-target inhibitors are often susceptible to drug resistance and are ineffective for complex diseases such as cancers. Therefore, a new strategy is required for enriching the hit rate and identifying multitarget inhibitors. To address these issues, we propose the pathway-based screening strategy (called PathSiMMap) to derive binding mechanisms for increasing the hit rate and discovering multitarget inhibitors using site-moiety maps. This strategy simultaneously screens multiple target proteins in the same pathway; these proteins bind intermediates with common substructures. These proteins possess similar conserved binding environments (pathway anchors) when the product of one protein is the substrate of the next protein in the pathway despite their low sequence identity and structure similarity. We successfully discovered two multitarget inhibitors with IC50 of <10 μM for shikimate dehydrogenase and shikimate kinase in the shikimate pathway of Helicobacter pylori. Furthermore, we found two selective inhibitors (IC50 of <10 μM) for shikimate dehydrogenase using the specific anchors derived by our method. Our experimental results reveal that this strategy can enhance the hit rates and the pathway anchors are highly conserved and important for biological functions. We believe that our strategy provides a great value for elucidating protein binding mechanisms and discovering multitarget inhibitors.
Thickness Scaling Effect on Interfacial Barrier and Electrical Contact to Two-Dimensional MoS2 Layers
Song-Lin Li,K. Komatsu,Shu Nakaharai,Yen-Fu Lin,M. Yamamoto,X. F. Duan,K. Tsukagoshi
Physics , 2014, DOI: 10.1021/nn506138y
Abstract: Understanding the interfacial electrical properties between metallic electrodes and low dimensional semiconductors is essential for both fundamental science and practical applications. Here we report the observation of thickness reduction induced crossover of electrical contact at Au/MoS2 interfaces. For MoS2 thicker than 5 layers, the contact resistivity slightly decreases with reducing MoS2 thickness. By contrast, the contact resistivity sharply increases with reducing MoS2 thickness below 5 layers, mainly governed by the quantum confinement effect. It is found that the interfacial potential barrier can be finely tailored from 0.3 to 0.6 eV by merely varying MoS2 thickness. A full evolution diagram of energy level alignment is also drawn to elucidate the thickness scaling effect. The finding of tailoring interfacial properties with channel thickness represents a useful approach controlling the metal/semiconductor interfaces which may result in conceptually innovative functionalities.
Core Site-Moiety Maps Reveal Inhibitors and Binding Mechanisms of Orthologous Proteins by Screening Compound Libraries
Kai-Cheng Hsu, Wen-Chi Cheng, Yen-Fu Chen, Hung-Jung Wang, Ling-Ting Li, Wen-Ching Wang, Jinn-Moon Yang
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032142
Abstract: Members of protein families often share conserved structural subsites for interaction with chemically similar moieties despite low sequence identity. We propose a core site-moiety map of multiple proteins (called CoreSiMMap) to discover inhibitors and mechanisms by profiling subsite-moiety interactions of immense screening compounds. The consensus anchor, the subsite-moiety interactions with statistical significance, of a CoreSiMMap can be regarded as a “hot spot” that represents the conserved binding environments involved in biological functions. Here, we derive the CoreSiMMap with six consensus anchors and identify six inhibitors (IC50<8.0 μM) of shikimate kinases (SKs) of Mycobacterium tuberculosis and Helicobacter pylori from the NCI database (236,962 compounds). Studies of site-directed mutagenesis and analogues reveal that these conserved interacting residues and moieties contribute to pocket-moiety interaction spots and biological functions. These results reveal that our multi-target screening strategy and the CoreSiMMap can increase the accuracy of screening in the identification of novel inhibitors and subsite-moiety environments for elucidating the binding mechanisms of targets.
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