How do the properties of a glass depend on the cooling rate? A computer simulation study of a Lennard-Jones system

Using molecular dynamics computer simulations we investigate how the glass transition and the properties of the resulting glass depend on the cooling rate with which the sample has been quenched. This is done by studying a two component Lennard-Jones system which is coupled to a heat bath whose temperature is decreased from a high temperature, where the system is a liquid, to zero temperature, where the system is a glass. The temperature $T_b$ of the heat bath is decreased linearly in time, i.e. $T_b=T_0-\gamma t$, where $\gamma$ is the cooling rate. In accordance with simple theoretical arguments and with experimental observations we find that the glass transition, as observed in the specific heat and the thermal expansion coefficient, becomes sharper when $\gamma$ is decreased. A decrease of the cooling rate also leads to a decrease of the glass transition temperature $T_g$ and we show that the dependence of $T_g$ on $\gamma$ can be rationalized by assuming that the temperature dependence of the relaxation times of the system is given by either a Vogel-Fulcher law or a power-law. By investigating the structural properties of the glass, such as the radial distribution functions, the coordination numbers and the angles between three neighbor-sharing particles, we show how the local order of the glass increases with decreasing cooling rate. The enthalpy and the density of the glass decrease and increase, respectively, with decreasing $\gamma$. By investigating the $\gamma$ dependence of clusters of nearest neighbors, we show how these observations can be understood from a microscopic point of view. We also show that the spectrum of the glass, as computed from the dynamical matrix, shows a shift towards higher frequencies when $\gamma$ is decreased. All these effects show that there is a significantComment: 20 pages of RevTex, Figures available upon request from W. Ko

Reversible visible watermarking for H.264/AVC encoded video

Visible watermarked images and videos are generally used to convey ownership information. However, the visible watermark is generally irreversible and thus authenticated users cannot recover the original image or video quality after watermark extraction. This poses a limitation in various scenarios including military, law and medical applications. This paper presents a novel reversible visible watermarking scheme for H.264/AVC encoded video sequences. The proposed approach reversibly embeds the residual information that will then be used by the decoder to recover the original image. The residual information is losslessly compressed using the ZLib Deflector algorithm to minimize the information to be embedded. The compressed information is then encrypted using the 128-bit Advanced Encryption Standard (AES). Simulation results clearly demonstrate the superiority of the proposed scheme to current state of the art where Peak Signal-to-Noise Ration (PSNR) gains of up to 7 dB were achieved.peer-reviewe

Kovacs effects in an aging molecular liquid

We study by means of molecular dynamics simulations the aging behavior of a molecular model of ortho-terphenyl. We find evidence of a a non-monotonic evolution of the volume during an isothermal-isobaric equilibration process, a phenomenon known in polymeric systems as Kovacs effect. We characterize this phenomenology in terms of landscape properties, providing evidence that, far from equilibrium, the system explores region of the potential energy landscape distinct from the one explored in thermal equilibrium. We discuss the relevance of our findings for the present understanding of the thermodynamics of the glass state.Comment: RevTeX 4, 4 pages, 5 eps figure

Temperature in nonequilibrium systems with conserved energy

We study a class of nonequilibrium lattice models which describe local redistributions of a globally conserved energy. A particular subclass can be solved analytically, allowing to define a temperature T_{th} along the same lines as in the equilibrium microcanonical ensemble. The fluctuation-dissipation relation is explicitely found to be linear, but its slope differs from the inverse temperature T_{th}^{-1}. A numerical renormalization group procedure suggests that, at a coarse-grained level, all models behave similarly, leading to a two-parameter description of their macroscopic properties.Comment: 4 pages, 1 figure, final versio

Vision based surveillance system

Due to the numerous amounts of surveillance cameras available, security guards seem to be ubiquitously watching over. However, the number of existing cameras exceeds the number of humans to monitor them and the supervision of all the sensors' output is costly. Thus, video footage from cameras is most often only used as a forensic tool. This suggests the need of an intelligent video surveillance system providing continuous 24-hour monitoring, replacing the traditional ineffective systems. This paper presents an automated vision based surveillance system which is capable to detect and track humans and vehicles from a video footage. Simulation results have shown that the Object Classification module manages to achieve an accuracy of 97.31% and 97.14% for the person and vehicle classification respectively. Furthermore, the system manages to successfully track the objects 97% of the time under no occlusion and 94.14% in presence of occlusion.peer-reviewe

Non-linear swing-up and stabilizing control of an inverted pendulum system

This paper presents the design and implementation of a complete control system for the swing-up and stabilizing control of an inverted pendulum. In particular, this work outlines the effectiveness of a particular swing-up method, based on feedback linearization and energy considerations. The power of modern state-space techniques for the analysis and control of Multiple Input Multiple Output (MIMO) systems is also investigated and a state-feedback controller is employed for stabilizing the pendulum. Cascade control is then utilized to reduce the complexity of the complete controller by splitting it into two separate control loops operating at well distinct bandwidths.Electrotechnical Association of Slovenia,et al.,IEEE Region 8,IEEE Slovenia Section,Ministry of Education, Science and Sport of the Republic of Slovenia,University of Ljubljana.peer-reviewe

A no-reference video quality metric using a natural video statistical model

The demand for high quality multimedia content is increasing rapidly, which has resulted in service providers employing Quality of Service (QoS) strategies to monitor the quality of delivered content. However, the QoS parameters commonly used do not correlate well with the actual quality perceived by the end-users. Numerous objective video quality assessment (VQA) metrics have been proposed to address this problem. However, most of these metrics rely on the availability of additional information from the original undistorted video to perform adequately, which will increase the bandwidth required. This paper presents a No-Reference (NR) VQA algorithm, which extracts a Natural Video Statistical Model using both spatial and temporal features to model the quality experienced by the end-users without needing additional information from the transmitter. These features are based on the observation that the statistics of natural scenes are regular on pristine content but are significantly altered in the presence of distortion. The proposed method achieves a Spearman Rank Order Correlation Coefficient (SROCC) of 0.8161 with subjective data, which is statistically identical and sometimes superior to existing state-of-the-art full and reduced reference VQA metrics.peer-reviewe

Robust wireless video multicast using distributed antennas-based IEEE 802.11n infrastructure

Wireless Video Multicast is prone to suffer from frequent packet losses, resulting from the fact that the IEEE 802.11 standard does not use any mechanisms such as Acknowledgements and retransmissions, to combat the errors that are common in the dynamic wireless medium. However this paper shows that the infrastructure can be adapted to reduce the wireless errors, by using spatial diversity and spatial expansion to combat the wireless medium's random nature. This is obtained by adding a number of antennas placed equidistantly at the edge of the coverage area, using the same total transmit power that would be used with one transmit antenna. Moreover, this paper shows that since the IEEE 802.11n, the standard which facilitates the use of multiple antennas, states that the maximum number of antennas at any transceiver is four, two Access Points can be used to transmit the same data packet in orthogonal time slots to transmit good quality H.264 video resulting in all nodes experiencing an average Peak Signal to Noise Ratio greater than 36dB for MCS-5 and MCS-6 for a coverage area having radius of 60m. Since only two time slots are used, these results are obtained with a ½ code rate which is an improvement to the code rate used in current cooperative schemes.peer-reviewe

Enhancing the error detection capabilities of DCT based codecs using compressed domain dissimilarity metrics

Video compression standards are implemented in wireless data transmission technologies to provide multimedia services efficiently. These compression standards generally utilize the Discrete Cosine Transform (DCT) in conjunction with variable length codes (VLC) in order to achieve the required high compression ratios. While providing the necessary high data rates, this technique has the disadvantage of making the system more susceptible to transmission errors. The standard decoders do not manage to detect a large number of corrupted macroblocks, 40.54% not detected for H.263+, contributing to a significant reduction in the end-to-end video quality as perceived by the end-user. This paper presents three dissimilarity metrics which contain both color and texture information and that can be extracted directly from the compressed DCT coefficients. These metrics can be used to enhance the error-detection capabilities of standard DCT based codecs. Simulation results show that the proposed algorithm increases the error detection rate by 54.06% with a gain in peak signal-to-noise ratio (PSNR) of 3.21 dB. This improvement in performance is superior to other solutions found in literature.peer-reviewe

Enhancing the error detection capabilities of the standard video decoder using pixel domain dissimilarity metrics

The video compression standards commonly adopted in wireless multimedia services utilize variable length codes (VLC) in order to attain high compression ratios. While providing the high data rates required, this technique makes the system more susceptible to transmission errors. Thus the end-to-end quality of the video stream transmitted over an error-prone channel depends on the detection, and concealment of the corrupted macroblocks. The error detection capability of standard decoders is quite limited, for example, in the case of the H.263+ codec around 40.54% of the corrupted macroblocks are undetected, placing a bound on the perceived quality of the reconstructed video sequence. This paper presents a novel solution using eight pixel domain dissimilarity metrics computed in the CIE LUV color space which can be used at decode time to improve the error detection rate of the standard decoder. The spatial dissimilarity metric has been found to perform the best with an average increase in error detection rate of 60.38% when compared to the standard decoder (about 20% more than other published results) with 0% of false detection and a gain in peak signal-to-noise ratio (PSNR) of 3.94 dB.peer-reviewe