AN APPROACH TOWARDS EFFICIENT VIDEO DATA HIDING USING PROHIBITED ZONE

The process of embedding information into a host medium is a data hiding. In general, due to their wide presence and the tolerance of human perceptual systems involved visual and arual media are preferred. The methods vary depending on the nature of such media and the general structure of data hiding process does not depend on the host media type. Due to the design complexities involved video data hiding is still an important research topic. A new video data hiding method that makes use of removal correction capabilities of replicate accumulate codes and advantage of prohibited zone data hiding is proposed in this paper. To determine host signal samples suitable for data hiding selective embedding is utilized in the proposed method. In order to withstand frame drop and insert attacks a temporal synchronization scheme is contained in this method. By typical broadcast material against MPEG- 2, H.264 compression, frame-rate renovation attacks, as well as other renowned video data hiding methods the proposed framework is tested here. For typical system parameters the decoding error values are reported. The imitation results specify that the frame can be effectively utilized in video data hiding applications

Optické a magnetooptické vlastnosti topologických a Diracových materiálů

Kristupas Kazimieras Tikuišis, Oddělení optoelektroniky a magnetooptiky, Fyzikální ústav UK Disertační práce: Optické a magnetooptické vlastnosti topologických a Diracových materiálů Vedoucí práce: RNDr. Martin Veis, Ph.D., Oddělení optoelektroniky a mag- netooptiky Konzultanti: RNDr. Roman Antoš, Ph.D., Oddělení optoelektroniky a mag- netooptiky; Milan Orlita, Ph.D., Národní laboratoř vysokých magnetických polí LNCMI - Grenoble, CNRS (Francie) Abstrakt: Materiály Dirac vykazují neobvyklé vlastnosti, které přitahují zájem jak pro prak- tické aplikace, tak pro základní výzkum v exotické a relativistické fyzice. Tato práce si klade za cíl systematicky studovat základní optické a magnetooptické vlastnosti několika členů těchto materiálů, zejména krystalických topologických izolátorů solí olova a cínu a grafenu. K měření od IR do UV spektrálních oblastí byly použity nedestruktivní experimentální techniky spektroskopické elipsome- trie a FTIR magneto-optické spektroskopie. K popisu nejdůležitějších vlastností pásové struktury systému PbSnSe umístěného v magnetickém poli byl odvozen čtyřpásmový hamiltonovský model. To umožnilo extrahovat pásovou strukturu a topologické parametry zkoumaných vzorků. Jsou prezentovány...Kristupas Kazimieras Tikuišis, Department of Optoelectronics and Magneto- optics, Institute of Physics of Charles University Doctoral thesis: Optical and magneto-optical properties of topological and Dirac materials Supervisor: RNDr. Martin Veis, Ph.D., Department of Optoelectronics and Magneto-optics Advisers: RNDr. Roman Antoš, Ph.D., Department of Optoelectronics and Magneto-optics; Milan Orlita, Ph.D., National Laboratory of High Magnetic Fields LNCMI - Grenoble, CNRS (France) Abstract: Dirac materials exhibit unusual properties that attract interest both for practi- cal applications and fundamental reseach of exotic and relativistic physics. This thesis aims to systematically study basic optical and magneto-optical proper- ties of several members of these materials, namely the lead tin salts crystalline topological insulators and graphene. Non-destructive experimental techniques of spectroscoipic ellipsometry and FTIR magneto-optical spectroscopy were used to perform measurements from IR to UV spectral regions. A four-band Hamilto- nian model was derived to describe the most important band structure features of PbSnSe system placed in a magnetic field. This allowed to extract the band structure and topological parameters of the investigated samples. Extensive mod- eling results based on...Fyzikální ústav UKInstitute of Physics of Charles UniversityMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Efficient Channel Modeling Methods for Mobile Communication Systems

Siirretty Doriast

DCT-Based Image Feature Extraction and Its Application in Image Self-Recovery and Image Watermarking

Feature extraction is a critical element in the design of image self-recovery and watermarking algorithms and its quality can have a big influence on the performance of these processes. The objective of the work presented in this thesis is to develop an effective methodology for feature extraction in the discrete cosine transform (DCT) domain and apply it in the design of adaptive image self-recovery and image watermarking algorithms. The methodology is to use the most significant DCT coefficients that can be at any frequency range to detect and to classify gray level patterns. In this way, gray level variations with a wider range of spatial frequencies can be looked into without increasing computational complexity and the methodology is able to distinguish gray level patterns rather than the orientations of simple edges only as in many existing DCT-based methods. The proposed image self-recovery algorithm uses the developed feature extraction methodology to detect and classify blocks that contain significant gray level variations. According to the profile of each block, the critical frequency components representing the specific gray level pattern of the block are chosen for encoding. The code lengths are made variable depending on the importance of these components in defining the block’s features, which makes the encoding of critical frequency components more precise, while keeping the total length of the reference code short. The proposed image self-recovery algorithm has resulted in remarkably shorter reference codes that are only 1/5 to 3/5 of those produced by existing methods, and consequently a superior visual quality in the embedded images. As the shorter codes contain the critical image information, the proposed algorithm has also achieved above average reconstruction quality for various tampering rates. The proposed image watermarking algorithm is computationally simple and designed for the blind extraction of the watermark. The principle of the algorithm is to embed the watermark in the locations where image data alterations are the least visible. To this end, the properties of the HVS are used to identify the gray level image features of such locations. The characteristics of the frequency components representing these features are identifying by applying the DCT-based feature extraction methodology developed in this thesis. The strength with which the watermark is embedded is made adaptive to the local gray level characteristics. Simulation results have shown that the proposed watermarking algorithm results in significantly higher visual quality in the watermarked images than that of the reported methods with a difference in PSNR of about 2.7 dB, while the embedded watermark is highly robustness against JPEG compression even at low quality factors and to some other common image processes. The good performance of the proposed image self-recovery and watermarking algorithms is an indication of the effectiveness of the developed feature extraction methodology. This methodology can be applied in a wide range of applications and it is suitable for any process where the DCT data is available

Symmetry of the Charge Ordering Phases in Hole-Doped Cuprates Studied by Resonant X-Ray Absorption and Scattering

In the underdoped cuprates, superconductivity coexists with a rich variety of other electronic orders. Understanding the nature of these orders, how they interact with one another, and the mechanisms that produce them is key to understanding the electronic behaviour of this important class of quantum materials. In this dissertation, we report on the results from three novel experiments that used resonant x-ray spectroscopy to explore the symmetry of the charge density wave (CDW) and other phases in La- and Y-based cuprates. For the uninitiated reader, a brief theoretical description of the experimental methods is also provided. Theoretical proposals have suggested that CDW order in the cuprates may adhere to a d-symmetry form factor, where charge on the O sites surrounding Cu in the CuO2 planes modulates out of phase and produces a quadrupolar local environment. This is supported by STM measurements in Bi2Sr2CaCu2O8+x and Ca2-xNaxCuO2Cl2 and resonant x-ray scattering in YBa2Cu3O6+x (YBCO). We conduct our own resonant scattering measurements on La1.875Ba0.125CuO4 and find evidence for a monopolar CDW, confirmed at both the O and Cu absorption edges where the measurement selectively probes the respective in-plane orbitals. Studying the (0 0.31 L) CDW peak at the Cu edge in YBCO, we again find the same result. Furthermore, using an alternative measurement geometry that is more sensitive to the symmetry of the CDW, we are able to contrast our results against a previous study that was limited by experimental accuracy. Finally, we find a surprisingly different symmetry at the (0.31 0 L) peak in YBCO that indicates the presence of orbital order alongside simple charge order. Model calculations for this data propose a CDW with significant in-plane anisotropy, or perhaps with a modulating orbital orientation. Anisotropy in electronic structure that arises from strong correlations-classified as electronic nematicity-has been observed in multiple cuprates, and whether or not this electronic ordering phase should be suspected as a generic feature of the underdoped phase diagram has become a topic of debate. Exploiting a unique structural distortion in the La-based cuprates, we perform anisotropic tensor scattering (ATS) on resonance in samples with a variety of isovalent and heterovalent dopings to investigate the relationship between structure, CDW order, and electronic nematic order. In four of the five samples, we observe a temperature evolution that is distinct from the structural distortion in the spectra that corresponds to orbitals in the CuO2 plane, indicating the presence of an electronic nematic phase. Like CDW order, this phase often onsets at the same temperature as the structural distortion, or else below the base temperature of our spectrometer. However, the CDW is clearly seen to onset at a moderately lower temperature than the other phases in La1.65Eu0.2Sr0.15CuO4, revealing an enhancement in the electronic nematicity at TCDW. We argue that the extent of the tilt in the structural transition, which varies with the unit cell volume, could provide an underlying connection between the properties of the three phases. In an attempt to observe evidence of an electronic nematic state in YBCO, polarized near-edge x-ray absorption spectroscopy is performed at the Cu L and O K edges in three samples that span the material's doping phase diagram: delta = 0.335, delta = 0.5, and delta = 0.999. We argue that electronic nematicity could be observed as a relative change in the temperature evolution of the unoccupied density of states projected along the crystal's a- and b-axes, perhaps as the spontaneous increase of anisotropy below a threshold temperature. We report a modest reduction and broadening of many peaks in the spectra as temperature increases, including at both absorption edges, all dopings, and all polarizations. Alternatively, the peaks associated with the upper Hubbard band and the twin peaks in the c-axis spectra increase. Substantial spectral weight also appears in the region just below the upper Hubbard band. We propose that phonon coupling through a Franck-Condon mechanism could be responsible for the latter effect. The x-ray linear dichroism is calculated between the a- and b-axis spectra, but only subtle changes to the anisotropy are apparent. Ultimately, the presence of an electronic nematic phase cannot be verified, and our results instead provide an upper-limit for the magnitude of any effects from such a phase on the absorption spectra

A Comprehensive Review of Video Steganalysis

Steganography is the art of secret communication and steganalysis is the art of detecting the hidden messages embedded in digital media covers. One of the covers that is gaining interest in the field is video. Presently, the global IP video traffic forms the major part of all consumer Internet traffic. It is also gaining attention in the field of digital forensics and homeland security in which threats of covert communications hold serious consequences. Thus, steganography technicians will prefer video to other types of covers like audio files, still images or texts. Moreover, video steganography will be of more interest because it provides more concealing capacity. Contrariwise, investigation in video steganalysis methods does not seem to follow the momentum even if law enforcement agencies and governments around the world support and encourage investigation in this field. In this paper, we review the most important methods used so far in video steganalysis and sketch the future trends. To the best of our knowledge this is the most comprehensive review of video steganalysis produced so far

Majorana Fermions in Chiral Topological Superconductors

Majorana fermions were first proposed in the context of high energy physics by Ettore Majorana in 1937, just before his mysterious disappearance. Now, over 70 years later, signatures of condensed matter ana-logues of Majorana fermions are finally appearing in low-dimensional superconductor-based heterostructures. In low-dimensional systems, these order parameter, defect-bound Majorana quasiparticles obey non-Abelian quantum statistics and can therefore be used as the building blocks of a topological quantum computer. In this thesis we will analyze the signatures associated with, and the robustness of, Majorana bound states in a variety of one-dimensional superconducting platforms. Our main result is the finding that spatially localized Majorana modes may coexist, without an induced energy splitting, in the presence of additional symmetries. The effects and robustness of Majorana bound states in the presence of timer-reversal, chiral and spatial sym-metries are analyzed in detail. Our results allow us to explain the unexpected robustness of a zero-bias signal in recent experiments purporting to observe Majorana excitations

Selected Papers from the First International Symposium on Future ICT (Future-ICT 2019) in Conjunction with 4th International Symposium on Mobile Internet Security (MobiSec 2019)

The International Symposium on Future ICT (Future-ICT 2019) in conjunction with the 4th International Symposium on Mobile Internet Security (MobiSec 2019) was held on 17–19 October 2019 in Taichung, Taiwan. The symposium provided academic and industry professionals an opportunity to discuss the latest issues and progress in advancing smart applications based on future ICT and its relative security. The symposium aimed to publish high-quality papers strictly related to the various theories and practical applications concerning advanced smart applications, future ICT, and related communications and networks. It was expected that the symposium and its publications would be a trigger for further related research and technology improvements in this field