We present the results of using a domestically produced component base for the creation of subcarrier wave quantum communication systems. It is shown that such systems demonstrate a quantum bit generation rate of about 10 kbit/s with a channel loss of 1 dB and quantum error coefficient below 3

In media with cubic nonlinearity, broadening of the optical pulses’ spectrum is observed due to their phase modulation and generation of radiation at triple frequencies. When the number of oscillations in the original pulse is small, these spectra may overlap, resulting in unconventional phenomena for traditional nonlinear optics such as mutual amplification or attenuation effects of phase modulation and generation of radiation at triple frequencies, which are nonuniform across the spectrum. The report discusses the theory of these phenomena and presents the results of their experimental observations in the terahertz spectral range.

When the number of oscillations in an optical pulse decreases, the emission spectrum generated at triple frequencies and the spectrum of the fundamental pulse, broadened due to phase self-modulation during propagation in a medium with cubic nonlinearity, begin to overlap. This work demonstrates that the overlap magnitude of the spectrum broadening for a single-period terahertz pulse, caused by the emission of triple frequencies and phase self-modulation of the fundamental pulse, is |s| = 0.85. The complex spectra are phase-shifted by p, which mutually weakens these nonlinear effects. For a single-period pulse, the attenuation coefficient is 7.7. The frequency-dependent inhomogeneity of mutual attenuation of nonlinear effects results in the absence of radiation at the triple frequency relative to the frequency of the maximum spectrum of the single-period wave in the nonlinear medium, while the maximum spectrum of the generated high-frequency radiation shifts to quadrupled frequencies. Thus, for terahertz waves with a small number of oscillations, new possibilities for controlling their parameters during nonlinear processes in optical media open up.

This study examines the bistability characteristics of a “mirrorless” Fabry-Perot interferometer utilizing a medium with a highly nonlinear refractive index and low inertia. Through a combination of analytical simulation and experimental investigation, the research reveals that the use of a nonlinear LiNbO 3 crystal as the medium leads to noticeable optical hysteresis under input intensities of up to $3.5 \times 10^{9} \mathrm{~W} / \mathrm{cm}^{2}$ at a frequency of 0.25 THz.

Designing of the ultrafast terahertz photonics devices requires materials with the biggest nonlinear refractive index coefficient n2 and the lowest settling time of the nonlinear response τ in the terahertz spectral range. In the present study, we show that the ratio n2/τ for media with the vibrational nonlinearity in the terahertz range is determined by the square of the medium thermal expansion coefficient and the fifth power of its dominative stretching vibrational mode frequency. These findings are based on the theory of the media vibrational nature nonlinear polarization response to incident THz radiation. We provide estimated values of the n2/τ ratio for a group of liquids and crystal materials. According to our evaluations, n2/τ value for alpha-pinene in the terahertz spectral range is about 10^6 cm^2/J and is almost the biggest one compared to materials with different nonlinearity types in various spectral ranges.

It is shown that the self-focusing of pulsed terahertz radiation with a spectrum in a region of anomalous group-velocity dispersion of a dielectric medium can be suppressed by such dispersion, in which pulse self-compression is characteristic of positive nonlinearity. The lower the ratio of a wave packet’s length of dispersion to that of diffraction in the medium, the more the self-focusing of a wave with the considered spectrum requires an excess of power over the critical value of self-focusing. Temporal compression of the wave starts before its spatial self-focusing at a length of diffraction shorter than that of dispersion, and vice versa for a longer one.

The dependences of the refractive index of a congruent LiNbO3 crystal cut perpendicular to the x and z axes on the radiation frequency in the range of 0.25–1.25 THz are presented. These dependences are presented for different values of the crystal thickness - 0.52 mm, 1 mm and 2.21 mm. A comparative analysis of the obtained dispersion curves with the results from other works is presented. The comparison was carried out by estimating the dispersion broadening of a THz pulse with time in the process of simulating its propagation in a medium with a given dispersion. It is shown that a 1.5-cycle THz pulse is broadened in media with dispersions found in other works, which does not correspond to experimental data. In accordance with this, it was concluded that the dispersion curves for congruent LiNbO3 from the considered works do not agree with the real values of the refractive index in the THz frequency range.

The continuous growth to the 6G wireless communication technology overcomes storage, stringent computation, privacy and power constraints to make an efficient and intelligent next generation transportation system to alleviate traffic jams and enhance driving experience in vehicular ad-hoc networks (VANETs). In combination with 6G technology, high availability, high reliability and occasionally high throughput are enabled in VANETs. However, the information shared in the VANET system should be secured. In this paper, an efficient batch authentication and key exchange schemes are proposed to provide a high level security by evading communication with the malicious vehicle users. In addition, an anonymous batch authentication scheme is proposed to alleviate the authentication burden on the road side units (RSUs) while performing authentication in the congested areas. Moreover, the integrity of the communicating messages is preserved in this proposed scheme to evade message modification during transmission. Even though many cryptographic schemes were proposed for batch authentication in VANETS, they suffered from lack of privacy-preservation and computational overhead. The discussion of the possible attacks section illustrates that the proposed protocol can survive against potential security attacks. In the performance analysis section, the proposed batch authentication scheme is compared with well-known existing schemes and then it is clearly revealed that the proposed scheme is computationally more efficient than the existing schemes.

Smart connected vehicles are becoming standardized with the incorporation of information and communication technology. Connected vehicles are employed for surveillance and management of road traffic, navigation assistance, etc., by inheriting different analytical and communication techniques. With the Social Internet of Things (SIoT), interogrowthperable and shared computing models are adopted by the connected vehicles to perform application-specific decisions. By considering the need for computation models in smart connected vehicle networks, this article introduces a shared adaptive computing model (SACM) for improving the reliability of vehicle control and traffic management. This computing model considers multiple features of the in-range vehicles in detecting traffic and providing guided solutions for reliable routing in a smart city environment. This computing model is aided by the conditional support vector machine (SVM) for differentiating the complexity of multiflow data processing from the neighboring vehicles. The physical and connectivity-based factors from the smart vehicle using SVM classification learning improve the decision reliability and reduce the computing time and complexity.

Subject of study. The inertia of the oscillatory mechanisms of the nonlinearities of isotropic dielectric media in the field of the terahertz-frequency electromagnetic waves was investigated for resonant and nonresonant interactions between radiation and matter. The purpose of this work was to construct a dynamic model of the nonlinear polarization responses of optical media with oscillatory nature in the field of terahertz pulses and to estimate the time constants characterizing the inertia of such responses during resonant and nonresonant interactions between radiation and media molecular vibrations. Method. The model of anharmonic vibrations of the atoms of each molecule as an oscillator in the general case for an isotropic medium, with both quadratic and cubic nonlinearities, was reduced for a macroscopic optical characteristic-its polarization-to a model as a system of parametrically coupled equations with only cubic nonlinearities. The system parameters were determined from well-known characteristics of a medium, such as its thermal expansion coefficient, stretching molecular vibration frequency, and refractive index. Main results. Expressions were obtained for the inertial time constants of the cubic susceptibilities of optical media with nonlinear vibrations in two- and one-photon resonant interactions with quasi-monochromatic terahertz pulses as well as in nonresonant interactions with broadband terahertz pulsed radiation through the thermal, spectral, and optical characteristics of materials known in the literature. Numerical estimates were obtained for the inertial time constants of the nonlinear susceptibilities of media with particularly high vibrational nonlinearities in the refractive indices, namely, ff-pinene and water, as well as silicon dioxide. For these materials, the inertial time constants of the resonant oscillatory mechanisms of the nonlinearities for radiation in the terahertz spectral rangewere shown to be of the order of hundreds of femtoseconds; for the nonresonant interactions, the time constants decreased to ten femtoseconds or less. Practical significance. The obtained inertial time constant estimations of the polarization responses of materials indicate that their giant nonlinearities in the far infrared spectral range could be used to develop ultrafast photonic devices for pulsed terahertz radiation parameter control. (c) 2022 Optica Publishing Group

Forested areas are extremely vulnerable to disasters leading to environmental destruction.Forest Fire is one among them which requires immediate attention.There are lot of works done by authors where Wireless Sensors and IoT have been used for forest fire monitoring.So, towards monitoring the forest fire and managing the energy efficiently in IoT, Energy Efficient Routing Protocol for Low power lossy networks (E-RPL) was developed.There were challenges about the scalability of the network resulting in a large end-to-end delay and less packet delivery which led to the development of Aggregator-based Energy Efficient RPL with Data Compression (CAA-ERPL).Though CAA-ERPL proved effective in terms of reduced packet delivery, less energy consumption, and increased packet delivery ratio for varying number of nodes, there is still challenge in the selection of aggregator which is based purely on probability percentage of nodes.There has been research work where fuzzy logic been employed for Mobile Ad-hoc Routing, RPL routing and cluster head selection in Wireless Sensor.There has been no work where fuzzy logic is employed for aggregator selection in Energy Efficient RPL.So accordingly, we here have proposed Fuzzy Based Aggregator selection in Energy-efficient RPL for region thereby forming DODAG for communicating to Fog/Edge.We here have developed fuzzy inference rules for selecting the aggregator based on strength which takes residual power, Node degree, and Expected Transmission Count (ETX) as input metrics.The Fuzzy Aggregator Energy Efficient RPL (FA-ERPL) based on fuzzy inference rules were analysed against E-RPL in terms of scalability (First and Half Node die), Energy Consumption, and aggregator node energy deviation.From the analysis, it was found that FA-ERPL performed better than E-RPL.These were simulated using MATLAB and results.

It is known that in the optical range quadratic nonlinear effects in solids appear at relatively low radiation intensities, while the radiation intensity required for a significant manifestation of cubic effects is much higher and can reach the damage threshold values. In this regard, quadratic effects dominate over cubic ones. In this work, it is analytically demonstrated that in the terahertz range the intensities required for the manifestation of cubic effects are much lower than in the optical range. In addition, their contribution to nonlinear effects can exceed the quadratic one by several orders of magnitude.

Respiratory diseases are one of the most common causes of death in the world and this recent COVID-19 pandemic is a key example. Problems such as infections, in general, affect many people and depending on the form of transmission they can spread throughout the world and weaken thousands of people. Two examples are severe acute respiratory syndrome and the recent coronavirus disease. These diseases have mild and severe forms, in which patients gravely affected need ventilatory support. The equipment that serves as a basis for operation of the mechanical ventilator is the air–oxygen blender, responsible for carrying out the air–oxygen mixture in the proper proportions ensuring constant supply. New blender models are described in the literature together with applications of control techniques, such as Proportional, Integrative and Derivative (PID); Fuzzy; and Adaptive. The results obtained from the literature show a significant improvement in patient care when using automatic controls instead of manual adjustment, increasing the safety and accuracy of the treatment. This study presents a deep review of the state of the art in air–oxygen benders, identifies the most relevant characteristics, performs a comparison study considering the most relevant available solutions, and identifies open research directions in the topic.

In this work the dispersion of nonlinear refractive index n2 (vibrational third-order nonlinear response) is estimated for various liquids used in THz photonics – water, ethanol, and isopropanol. To calculate n2 we use the theoretical model that considers known physical, linear and nonlinear optical parameters of liquids. The variation in n2 dispersion in the frequency range with nonresonant electronic contribution for water and ethanol is obtained to be around 15%, which seems to be very important to be considered for THz photonic devices’ design.

Corporate insolvency has significant adverse effects on an economy. With the number of multinationals increasing rapidly, corporate bankruptcy can severely disrupt the global financial environment. However, multinationals do not fail instantaneously; objective strategies combined with a rigorous analysis of both qualitative and quantifiable data can go a long way in identifying an organization's financial risks. Recent advancements in information and communication technologies have made data collection and storage an easy task. The challenge becomes mining the appropriate data about a company's financial risks and implementing it in forecasting a company's insolvency probabilities. In recent years, machine learning has been incorporated into big data analytics owing to its massive success in learning complex models. Machine learning algorithms such as Support Vector Machines (SVM), Random Forests (RF), Artificial Neural Networks, Gaussian Processes, and Adaptive Learning have been used in the analysis of Big Data to predict the financial risks of companies. In this paper, credit scoring is explored with regards to data processed using the collateral as an independent variable. The obtained results indicate that RF algorithm is promising for use in credit risk management. This research shows the advantages of the RF approach over the SVM algorithm are its speed and operational simplicity, and SVM has the benefit of higher classification accuracy than RF. The paper compares the SVM and RF algorithms to forecast the recovered value in a credit task. The execution of the projected intelligent systems uses tests and algorithms for authentication of the projected model.

We demonstrate the dependence of the substructure number in the pulse train and the corresponding frequency comb formed by the interference of two phase-modulated THz pulses on the time delay between pulses for linear and nonlinear chirp cases. The limiting time delay between pulses, at which the correlation of the signal temporal and frequency domains preserving, is shown. The results obtained are important for assessing the capabilities of communication networks based on pulsed THz radiation.

The act of lending is based on trust in the borrower to honour the obligation of paying back the lender. Greater spreads on credit operations may help predict the expected recovery of the credit, based on the sufficiency and liquidity of the guarantee. This study aims to understand how predictive models can provide different estimations of expected recovery based on the same data sets. It classifies credit by the formulation of a rule that describes the values of a categorical variable according to some specified definition. It finds that a simple logistic regression model can easily be extended to a multiple logistic regression model by integrating more than one prediction variable, which indicates increasing difficulty in obtaining multiple observations with an increasing number of independent variables. It compares the efficiency of the logistic regression with that of a linear regression in predicting whether recovery is due in a credit operation, and, thus, identifies the best model for this purpose.

Laser-driven nonlinear phenomena can both reveal the structural features of materials and become the basis for the development of various translated technologies, including highly intense terahertz sources. Here we realize a modified single-color double-pulse excitation scheme for enhancing the terahertz wave generation in flat liquid jets, and we show that the pre-ionization effect is crucial for finding the optimal input conditions. The experimental results, being supported by numerical simulations, reveal the preference for longer pre-pulses to induce the effective ionization process and shorter signals for the strong laser-plasma interaction. In addition to the identified features of the terahertz wave energy enhancement with respect to the duration change for both pulses and their ratio variation, we state the possibility of achieving the optical-to-THz conversion efficiency value up to 0.1% in the case of double-pulse excitation of an α -pinene jet.

Summary Software‐defined networking (SDN) is an agile, modern networking approach that facilitates innovations in the networking paradigm. The abstracted and centralized network operating system facilitates the network management and reduces operational expenditure (OPEX). The open nature and simplicity of the data‐forwarding plane dramatically reduces capital expenditure (CAPEX) by leveraging commodity servers and switches. SDN also lends itself very well to address major cloud computing issues and complement cloud services, especially in terms of network virtualization and networking as a service (NaaS). As a new technology, SDN does involve certain security challenges, which include distributed denial of service (DDoS) threats, build and run time injected malware, insider (tenant) attacks, and security holes resulting from controller misconfigurations. These are severe threats that can cripple an entire network. It is crucial to address the SDN vulnerabilities to ensure its successful deployment in private data center networks, on cloud platforms and beyond. Some security solutions leverage the built‐in features of SDN, such as its controller software component, while other solutions provide external SDN applications running above the controller. This study reviews the security solutions for the vulnerabilities of state‐of‐the‐art SDN controllers and the available countermeasures. Furthermore, an in‐depth analysis of the SDN features that support security is presented, and some unresolved research issues on SDN controllers are identified.