Strongly localized states and giant optical absorption induced by multiple flat-bands in AA-stacked multilayer armchair graphenenanoribbons

We propose an AA-stacked multilayer graphene nanoribbon with two symmetrical armchair edges as a multiple flat-band (FB) material. Using the tight-binding Hamiltonian and Green’s function method, we find that the FBs are complete and merged into many dispersive bands. The FBs cause multiple strongly localized states (SLSs) at the sites of the odd lines in every sublayer and a giant optical absorption (GOA) at energy point 2t, where t is the electronic intralayer hopping energy between two nearest-neighbor sites. By driving an electric field perpendicular to the ribbon plane, the bandgaps of the FBs are tunable. Accordingly, the positions of the SLSs in the energy regime can be shifted. However, the position of the GOA is robust against such field, but its strength exhibits a collapse behavior with a fixed quantization step. On the contrary, by driving an electric field parallel to the ribbon plane, the completeness of FBs is destroyed. Resultantly, the SLSs and GOA are suppressed and even quenched. Therefore, such ribbons may be excellent candidates for the design of the controllable information-transmission and optical-electric nanodevices.

Synchronization of Transmission Systems with ANS-DM Codecs

Adaptive Delta Modulation with Non-uniform Sampling (ANS-DM) is one of the waveform coding techniques, where a sampling instant and a quantization step size are adapted to the signal. The ANS-DM modulator produces an output binary stream, that carries information about the signal and includes necessary data of coder parameters (sampling instant and quantization step). In the demodulator, these values are recovered for proper signal reconstruction. The paper reports the problem of synchronizing clocks (transmitting and receiving) in the (ANS-DM) delta codecs systems. The original synchronization method, valuable in systems dedicated to the transmission of the bits with variable time duration was projected and experimentally verified. Performed measurements and observations have shown the elimination of the synchronization loss phenomenon.

ІНФОРМАЦІЙНЕ ЗАБЕЗПЕЧЕННЯ КОНТРОЛЮ ПОТОЧНОГО СТАНУ ІНФОКОМУНІКАЦІЙНОЇ МЕРЕЖІ В УМОВАХ ВПЛИВУ ЗОВНІШНІХ ЗАВАД

The processes of information support of situational management of infocommunication networks in the conditions of influence of external disturbances are considered in the work. The expediency of using the mathematical apparatus of information theory for the analysis of processes of control of parameters of infocommunication networks is substantiated. It is shown that periodic multiple sequential control of the parameters of the infocommunication network provides determination of the state of the network under the influence of external interference and the probability of its transition to a new state in the near future. The entropy of the controlled process changes with changing quantization step and multiple successive measurements. It is noted that in the case of periodic multiple consecutive control, the object is constantly in transition in terms of information. The entropy value of an object can be considered determined only for some short periods of time between measurements or when information about the object is not received. An important condition for improving the quality of control is to reduce and completely eliminate delays in the information process.

Hydrological response of a peri-urban catchment exploiting conventional and unconventional rainfall observations: the case study of Lambro catchment

Commercial Microwave Links (CMLs) can be used as opportunistic and unconventional rainfall sensors by converting the received signal level into path-averaged rainfall intensity. Since in meteorology and hydrology the reliable reconstruction of the rainfall spatial distribution is still a challenging issue, there is a wide-spread interest in integrating the precipitation estimates gathered by the ubiquitous CMLs with the conventional rainfall sensors, i.e. rain gauges (RGs) and weather radars. Here we investigate the potential of a dense CML network, for the estimation of river discharges via a semi-distributed hydrological model. The analysis is conducted on Lambro, a peri-urban catchment located in northern Italy and covered by 50 links. A two-level comparison is made between CML- and RG-based outcomes, relying on 12 storm/flood events. First, rainfall data are spatially interpolated and assessed in a set of significant points of the catchment area. Rainfall depth values obtained from CMLs are definitively comparable with direct RG measurements, except for the spells of persistent light rain, due to limited sensitivity of CMLs caused by the coarse quantization step of raw power data. Moreover, it is showed that, when changing the type of rainfall input, a new calibration of model parameters is required. In fact, after the re-calibration of model parameters, CML-driven outputs performances are comparable with RG-driven ones, confirming that the exploitation of a CML network may lead to benefit in hydrological modelling.

Determining the Minimum Scan Step of an Electronically Scanned Antenna

Introduction. Electronically scanned antennas (ESA) appeared about a century ago. Although the methods of their design and production have been sufficiently studied, some individual parameters are yet to be revealed. One of such parameters is the minimum step of movement, along with a related parameter – the accuracy of beam alignment in a given direction. From the electrodynamic problem of radiation, it is obvious that the step is associated with the number of radiators and the accuracy of phase adjustment in analogue phase shifters, or with the quantization step in the case of using phase shifters with a discrete step.Aim. To discover a connection between the design parameters of ESA and the step of beam steering; to investigate the dependence between the step and the parameters of the phase shifter and types of beam forming phased array circuits; to create a mathematical apparatus for calculating the minimum step of beam movement for the sum and difference radiation patterns.Materials and methods. Analytical relations were determined for calculating the step depending on the geometric dimensions and location of the radiators. A software application was developed for calculating radiation patterns. A software and hardware complex was designed for beam control of an experimental C-band ESA.Results. A method was developed for calculating the minimum step of ESA scanning. Mathematical relations for calculating the minimum step and accuracy of the ESA beam setting were obtained. A comparison of the experimental and theoretical data on the minimum step of movement of the sum and difference beams of a C-band ESA with the ratio D/λ=10 in the X coordinate and D/λ=5 in the Y coordinate showed good agreement.Conclusion. The created mathematical apparatus makes it possible to calculate the minimum step of electron beam scanning with sufficient accuracy. The experimentally measured steps of the beam movement for an array of 144 elements confirmed the obtained analytical relationships. In an ESA with a small number of elements (N < 10), the minimum step of movement can be variable. The theoretically achievable minimum step of beam movement is determined by the phase shift of the least significant bit of the phase shifter and the electrical length of the antenna aperture.

On a Method for Constructing a Linear Nonstationary Discrete System with Full-Dimensional Controlby Changing the Quantization Step

The method that allows one to reduce a stationary system with control of incomplete dimension to a non-stationary periodic system with control of full dimension is considered in this article. The paper proves the equivalence of these systems, and also that the optimal in terms of speed for a non-stationary system is also optimal for the original stationary system. A satellite attitude control system is considered as an example.

Embedding information into JPEG images with distortion masking in frequency domain

Steganography allows to ensure the confidentiality of information by organizing covert data transmission channels. However, the effectiveness of steganographic information protection directly depends on the invisibility of a secret message, both for the human eye and for steganalysis methods. The paper proposes an approach that allows solving the problem of vulnerability of the popular QIM embedding method to statistical steganalysis. For this, it is proposed to use a variable quantization step, which is adaptively selected for each block of the JPEG cover image. The experimental results demonstrate an increase in the security level of steganographic embedding due to the application of the proposed approach.

A Fast Method of Visually Lossless Compression of Dental Images

A noniterative approach to the problem of visually lossless compression of dental images is proposed for an image coder based on the discrete cosine transform (DCT) and partition scheme optimization. This approach considers the following peculiarities of the problem. It is necessary to carry out lossy compression of dental images to achieve large compression ratios (CRs). Since dental images are viewed and analyzed by specialists, it is important to preserve useful diagnostic information preventing appearance of any visible artifacts due to lossy compression. At last, dental images may contain noise having complex statistical and spectral properties. In this paper, we have analyzed and utilized dependences of three quality metrics (Peak signal-to-noise ratio, PSNR; eak Signal-to-Noise Ratio using Human Visual System and Masking (PSNR-HVS-M); and feature similarity, FSIM) on the quantization step (QS), which controls a compression ratio for the so-called advanced DCT coder (ADCTC). The threshold values of distortion visibility for these metrics have been considered. Finally, the recent results on detectable changes in noise intensity have been incorporated in the QS setting. A visual comparison of original and compressed images allows to conclude that the introduced distortions are practically undetectable for the proposed approach; meanwhile, the provided CR lies within the interval.

Robust and Blind Audio Watermarking Algorithm in Dual Domain for Overcoming Synchronization Attacks

How to effectively resist synchronization attacks is the most challenging topic in the research of robust watermarking algorithms. A robust and blind audio watermarking algorithm for overcoming synchronization attacks is proposed in dual domain by considering time domain and transform domain. Based on analysing the characteristics of synchronization attacks, an implicit synchronization mechanism (ISM) is developed in the time domain, which can effectively track the appropriate region for embedding and extracting watermarks. The data in this region will be subjected to discrete cosine transform (DCT) and singular value decomposition (SVD) in turn to obtain the eigenvalue that can be utilized to carry watermarks. In order to extract the watermark blindly, the eigenvalue will be quantized. Genetic algorithm (GA) is utilized to optimize the quantization step to balance both transparency and robustness. The experimental results confirm that the proposed algorithm not only withstands various conventional signal processing operations but also resists malicious synchronization attacks, such as time scale modification (TSM), pitch-shifting modification (PSM), jittering, and random cropping. Especially, it can overcome TSM with strength from −30% to +30%, which is much higher than the standard of the International Federation of the Phonographic Industry (IFPI) and far superior to the other algorithms in related papers.