Radiotekhnika

Optimization of digital signature calculation and verification operations for the FIPS 205 standard. Part 2

2025-11-13T14:07:15+02:00

Currently, hash-based signatures are among the most promising candidates for post-quantum digital signatures. Their advantage is their comprehensible security and robustness and ease of evaluation, as they rely solely on the reliability of cryptographic hash functions.

The previous article discussed and proposed practical improvements to optimize the FIPS 205 algorithm based on the use of parallel computing. This was achieved mainly by optimizing the SHAKE and SHA algorithms. The importance of optimizing hash value computation is related to the fact that hashing is the main operation in FIPS 205. Previous research has shown that common algorithms for key generation, electronic signature creation, and verification consist of sequential steps, each of which applies the result of the previous step, which excludes the possibility of using parallel computing for these algorithms.

This paper discusses optimization methods and results, including those achieved through parallel threads when implementing individual algorithm steps. Optimization through the use of AVX operations is not considered. Basically, the improvement in the performance of individual functions is achieved through more efficient execution of the basic PRF, Tl, H, and F operations, the optimization of which was discussed in the previous article, as well as through the optimization of certain algorithms that are part of other algorithms.

The results obtained show that the implemented improvements allow for acceleration of at least 2 times for all functions and all modes. However, for most functions and modes, the acceleration is more than threefold. The use of parallel computing through the use of multi-core processors significantly increases the performance of functions for WOTS and FORS schemes, as well as the functions that use them. This improvement is very relevant, since the vast majority of modern processors are multi-core.

Implementation of zero trust architecture based on the proposed model to ensure enterprise cyber-security

2025-11-13T17:34:58+02:00

Modern enterprises face increasingly complex cybersecurity challenges, requiring a new approach to protecting digital assets that will ensure secure access to corporate resources anytime, anywhere, as well as their effective function wherever they are located. Traditional approaches, such as perimeter-based security models, no longer guarantee an adequate level of security and are unable to effectively counter modern cyber threats, as enterprise infrastructure is undergoing significant changes related to the expansion of the attack surface, the growth in the number of connected devices, the development of artificial intelligence, the use of cloud technologies, and remote access. Given these changes and challenges, more organizations are turning their attention to a new concept and architecture of protection that can satisfy new requirements for information security and cybersecurity. Such a concept is currently the security paradigm known as “zero trust”, which is based on the principle of “never trust, always verify” and is defined as one of the most effective approaches to countering modern cyber threats. Given the dynamics of cyber threats and the architectural complexity of modern IT enterprises, the successful implementation of zero trust principles requires a systematic approach and involves the integration of modern technologies and security mechanisms. However, despite its obvious advantages, the process of implementing zero trust architecture in corporate information systems is accompanied by significant difficulties from both a technical and organizational point of view. The aim of this paper is to develop a model for implementing zero trust architecture to organize and ensure enterprise cybersecurity. The results presented in this paper are intended to help security specialists use the recommendations provided for the practical implementation of zero trust architecture in their IT enterprises in accordance with the proposed model. Specifically, the paper briefly discusses some recommendations for choosing zero trust architecture deployment models for various types of enterprise activities, and the proposed model for implementing zero trust architecture can help to understand the fundamental changes in the approach to organizing cybersecurity, and effectively implement the zero trust concept, considering the technical and organizational capabilities and requirements of a specific IT enterprise. The proposed zero trust architecture implementation model can serve as a guideline for the effective migration to zero trust architecture in modern digital enterprises, and its use opens significant prospects for the development of more reliable and scalable systems for protecting the information resources of IT enterprises, which is extremely relevant in today's digital cyberspace.

Radio control of radiation from radio electronic devices. Problems and solutions

2025-11-13T18:06:03+02:00

This article analyzes the challenges of radio monitoring in the decameter band, which is crucial for ensuring reliable radio communications. It highlights key issues stemming from the propagation characteristics of decameter waves (surface and sky waves), leading to high spectrum congestion and making it difficult to detect target radio emissions (RE). The drawbacks of existing manual and visual-instrumental monitoring methods are examined, characterized by low speed and an inability to effectively detect short-duration signals.

An approach to automating radio monitoring is proposed, utilizing a priori information about radio emissions, specifically their polarization characteristics, carrier frequency, and source location zone. The effectiveness of «thinning» the stream of analyzed signals is substantiated, allowing for a significant reduction in the number of channels requiring detailed analysis. It is shown that automatic selection of far-zone emissions can reduce the scanning time of the band by tens or hundreds of times. The problem of multi-alternative detection of specified signals under conditions of a priori uncertainty is considered, along with the importance of using onboard computing resources for the flexibility and adaptability of radio monitoring systems. The research results confirm the possibility of significantly improving the speed and quality of decameter band radio monitoring through the implementation of the proposed methods.

Features of constructing nonlinear transformations of block symmetric ciphers

2025-11-13T18:27:02+02:00

The article is devoted to the peculiarities of constructing nonlinear transformations of block symmetric ciphers. The history of the emergence of nonlinear transformations of block symmetric ciphers is briefly reviewed and the evolution of block symmetric ciphers after DES. The paper analyzes the methods of constructing S-blocks (Substitution-boxes), which are the main component that implements nonlinear substitutions and ensures cryptographic stability of the block symmetric cipher. The authors investigate and compare four main types of S-blocks: deterministic (fixed), dynamic (key-dependent), chaotically generated and random ones. The article analyzes in detail the advantages and disadvantages of each approach, as well as the key cryptographic properties ensuring that ensure stable nonlinear transformations, such as high nonlinearity, low differential homogeneity, bijectivity, avalanche effect, balance, high algebraic degree. The influence of post-quantum cryptography conditions is considered, in particular, the opposition to the Grover algorithm. The authors conclude that the choice of the S-block structure is a compromise between security, performance and ease of implementation. In the context of post-quantum symmetric block ciphers, the use of verified, fixed S-blocks combined with a key length sufficient to protect against quantum attacks is preferred. The reasons are the same as in the classical case: the complexity of security analysis, the computational cost of generation, and the problems associated with reproducibility. However, hybrid approaches combining algebraic and heuristic methods can also be used to achieve optimal results.

Zero-knowledge proof protocols: theoretical foundations and applications in modern cryptography

2025-11-13T18:44:41+02:00

The article presents a comprehensive overview of zero-knowledge proof (ZKP) protocols as a fundamental concept of modern cryptography. The historical background of their emergence and the main properties ensuring reliability and confidentiality, i.e., completeness, soundness, and zero-knowledge — are considered. A classification of protocols into interactive and non-interactive ones is provided, with a special focus on modern solutions such as the zk-SNARK and the zk-STARK. The mathematical foundations of ZKPs are described in detail, including discrete logarithm proofs, the use of homomorphic encryption, polynomial commitments, hashing, and elliptic curves. Practical application areas are analyzed, including cryptocurrencies (Zcash, Ethereum), authentication systems, digital identity, and electronic voting. The advantages of using ZKPs are shown, such as enhanced privacy, reduced need for trusted intermediaries, and strengthened security. At the same time, key challenges are outlined, including scalability, implementation complexity, the problem of trusted setup, and potential vulnerability to quantum computing. It is concluded that zero-knowledge proof protocols are a powerful tool for ensuring confidentiality and reliability of digital systems, while further research is aimed at creating more efficient and quantum-resistant solutions.

Development of a typical infrastructure for a quantum random number generator web service

2025-11-13T19:30:11+02:00

Quantum Random Number Generators (QRNGs) provide physically unpredictable entropy essential for cryptography, modeling, and scientific research. Local generation is preferred for the highest level of security, as it eliminates the risks associated with transmitting data over a network. At the same time, public QRNG web services accessible via the API serve as a valuable tool in cases where dedicated hardware is unavailable, enabling rapid integration into software prototypes, statistical testing, large-scale simulations, and educational projects. Combining local and remote sources makes it possible to optimize the balance between security, accessibility, and performance.

This article helps to develop and justify a typical QRNG web service infrastructure, which includes functional components, security requirements, access interfaces (API), methods for quality control of randomness, and recommendations for scalability. The proposed infrastructure is intended to serve as a foundation for creating interoperable, secure, and efficient web services of quantum entropy sources.

A process model for dynamic analysis and prediction of information security risks for personnel

2025-11-13T19:43:19+02:00

The article addresses the problem of dynamic assessment and forecasting of information security risks driven by the growing role of the human factor amid business-process digitalization, hybrid work models, and a changing access context. The purpose of the study is to improve the accuracy and timeliness of risk management for personnel, enhance access controllability through adaptive policies, and advance audit transparency by integrating an RBAC-blockchain into a closed self-learning loop. The object of the study is the process of dynamic information-security risk analysis in corporate systems with personalized consideration of user behavior. The subject of the study comprises the methods and procedures for constructing a multidimensional feature vector, building a user digital twin, designing risk-adaptive access policies, and implementing system self-learning mechanisms. The authors emphasize that static access-control approaches and periodic audits do not match the dynamics of threats and the contextual nature of resource use. The article analyzes the contemporary components of the process model: (f₁) construction of a multidimensional resource-classification matrix; (f₂–f₃) collection, unification, and normalization of behavioral and technical data into the feature vector Q; (f₄) forecasting risky events using a user digital twin with access transactions recorded on an RBAC-blockchain; (f₅–f₆) generation of adaptive countermeasures and delivery of personalized policies and training content; and (f₇–f₈) Fback feedback collection and self-learning with adjustment of weights, models, and access rules. It is shown that combining statistical methods, machine-learning algorithms, and immutable blockchain logging ensures reproducible auditing, reduces the “risk window,” and supports continuous trust validation in line with Zero Trust principles. A scheme for triggering countermeasures is proposed based on the probability matrix R and the resource’s criticality class. Procedures for fine-tuning and transfer learning are described to keep models current without excessive computational costs. Particular attention is paid to personalized dashboards and multichannel delivery of recommendations that shorten user response time. The importance of qualitative Fback metrics (e.g., user satisfaction and content clarity) is emphasized for revealing elements of security culture. Thus, applying the developed process model establishes an “analysis–forecast–action–feedback–self-correction” cycle that improves the accuracy of risk assessment, enhances response timeliness, and advances transparency in access governance. The results can be integrated into SIEM/UEBA environments, access-management systems, and corporate programs for improving personnel cyber literacy.

Ukrainian internet service providers ranking: multi‑criteria model incorporating cybersecurity

2025-11-13T23:33:41+02:00

Internet services have become an integral part of modern life, requiring high standards of quality and security. Choosing an internet provider is a complex task, as it involves many different criteria that often conflict with one another. High demands for speed, stability, and security, along with cost limitations, necessitate an approach that allows for balancing various requirements within a unified system. Despite the growing global attention to cybersecurity, this criterion often remains outside the scope of comprehensive analysis in Ukrainian research. Security is undoubtedly the most important factor when it comes to choosing an internet service provider.

The study presents an analysis of the functioning of internet service providers. It examines organizational principles, identifies key operational characteristics of internet providers, and outlines criteria for evaluating and selecting them. A multi-criteria analysis was conducted using a heuristic procedure, and a mechanism was proposed to ensure the required quality of service for each user when choosing an internet provider.

Evolution of Man-in-the-Middle attacks in 5G telecommunication systems

2025-11-13T23:56:47+02:00

The rapid deployment of fifth-generation (5G) networks has dramatically transformed telecommunications by enabling ultra-low latency, high bandwidth, and dynamic spectrum allocation. However, these innovations have also expanded the attack surface, introducing unprecedented security vulnerabilities. Among them, Man-in-the-Middle (MITM) attacks have evolved into complex, AI-driven, and persistent threats capable of exploiting 5G’s Service-Based Architecture (SBA), virtualized functions, and heterogeneous interoperability with LTE and Wi-Fi. A particularly critical evolution is the rise of Digital Twin attacks, where adversaries replicate devices or network elements with high fidelity, bypassing traditional authentication and maintaining long-term undetectable intrusions. This paper provides a comprehensive analysis of MITM evolution in 5G systems, including vulnerabilities across the OSI model layers, exploitation of NGAP, Diameter, and DSS signaling, and the persistent risks posed by distributed architectures. Special attention is given to quantum-era threats, such as store-now-decrypt-later scenarios and quantum-enhanced MITM attacks undermining 5G-AKA protocols reliant on non-quantum-resistant cryptography. The study emphasizes the need for cryptographic agility, post-quantum authentication, and continuous behavioral validation mechanisms to mitigate persistent and quantum-enhanced MITM exploits. The findings highlight urgent requirements for international standardization and proactive implementation of post-quantum secure protocols in 5G infrastructures.

Features and development prospects of the radio receiving system of the incoherent scatter radars of the Institute of Ionosphere, National Technical University “Kharkiv Polytechnic Institute”

2025-11-14T00:10:22+02:00

The paper presents the current state of a multichannel radio receiving system developed, implemented, and used for many years as part of the incoherent scatter (IS) radars of the Institute of Ionosphere and is constantly being improved. The technical features and structure of this system, which provides high-precision measurements of ionospheric parameters over a wide altitude range, are described. The requirements for sensitivity, stability, and interference immunity considered of the system under conditions of weak IS signal reception are analyzed. The superheterodyne architecture with triple frequency conversion is detailed, along with principles of signal selection and synchronous detection, and the extraction of the quadrature components of the received signal for subsequent computation of IS signal correlation functions. The implementation of Doppler measurements of the velocity of motion of ionospheric plasma and objects in geospace is based on the coherent structure of the radar complex and the coordinated synchronization of the transmitting and receiving paths.

Modes of operation using composite sounding signals are presented, as well as features of receiving and selecting ionospherically scattered elements of these signals for the study of both the lower and upper ionosphere with sufficiently high altitude and temporal resolution. The mode of simultaneous sounding in the vertical and oblique directions has been implemented to enable three-dimensional analysis of the properties and dynamics of the ionospheric plasma.

The subsystem for receiving, digitizing, and processing signals at the intermediate frequency has been integrated into the radar, allowing for improved accuracy in measuring IS signal parameters by eliminating the influence of a number of instrumental factors and employing digital bandpass filters and processing algorithms adapted to signals corresponding to specific heliogeophysical conditions and investigation altitudes.

The hardware implementation of a programmable geospace monitoring radio system based on SDR (Software Defined Radio) technology is proposed, enabling both active and passive observation modes and significantly expanding the functionality of the radiophysical equipment of the observatory of the Institute of Ionosphere for ionospheric research and space environment monitoring.

The presented technical solutions meet the requirements of modern geospace monitoring systems and are useful for ionospheric research and the observation of artificial space objects, particularly in the context of the growing importance of space weather forecasting and space debris issues.

Statistical optimization and analyses of the method of forming radar images in the time and frequency domains

2025-11-14T00:24:08+02:00

The article presents a statistically grounded approach to the formation of scatterometric radar images based on stochastic signal processing. The developed mathematical model takes into account the spatial structure of the reflecting surface, as well as the physical and statistical characteristics of radar signals. The proposed optimal algorithm combines detection, Fourier transformation, decorrelation filtering, and estimation of surface reflectivity coefficients. It is shown that such an approach ensures high resolution and increased noise immunity of the radar system. The statistical optimization is carried out according to the maximum likelihood criterion with minimization of mean square error, using the Cramér–Rao lower bound. The analysis covers both time and frequency domains, with an emphasis on practical implementation of whitening filters and decorrelation procedures in real signal conditions. Simulation examples confirm the theoretical efficiency of the algorithm and justify its application in airborne radar systems using linear frequency modulated signals for high-precision imaging.

Research on drone recognition based on their acoustic emission using fully connected neural networks

2025-11-14T14:30:41+02:00

The relevance of the research on recognizing the self-acoustic emissions of drones using fully connected neural networks and cepstral coefficients has been substantiated. A dataset of acoustic recordings has been created, including self-emissions of various drone models, background sounds, and seven types of sound sources with spectral characteristics similar to drone acoustic emissions. The optimal number of cepstral coefficients has been identified for further recognition by fully connected neural networks in terms of maximizing the probability of correct recognition and minimizing misclassification. The optimal neural network architecture has been determined to ensure the highest probability of correct recognition. The requirements for a microprocessor-based hardware platform for recognizing drone self-acoustic emissions have been calculated.

Peculiarities of detecting small-size unmanned aerial vehicles using the radioacoustic location method

2025-11-14T14:47:03+02:00

The article states that modern technical means for detecting low-observable small-sized unmanned aerial vehicles (sUAVs) in some cases do not provide adequate responsiveness and reliability. One of the promising directions for improving the efficiency of detecting low-observable sUAVs is the use of electromagnetic wave scattering on acoustic disturbances generated by these vehicles in the surrounding air environment. The article examines the characteristics of the acoustic field of sUAVs. Acoustic radiation from sUAVs has a number of specific features that must be considered when developing a radio-acoustic location system. The acoustic emission spectrum of sUAVs contains harmonics of the rotor rotation frequency and blade-passing frequency. Its spatial directivity is complex and, during maneuvering, affects both the intensity and shape of the acoustic signal spectrum. The operating frequency band of the location system should cover the range in which effective resonant scattering of electromagnetic waves is ensured. To reduce the size of highly directional antennas, the radar frequency is selected in such a way that the Bragg conditions are satisfied using higher-order diffraction. When receiving a signal scattered on inhomogeneities caused by the acoustic emission of sUAVs, the signal at the receiver input is the result of the interference of electromagnetic waves reflected from acoustic waves moving in opposite directions. The parameters of the envelope of this signal depend on the speed of sound, the frequency of the acoustic emission, and the ratio of the powers of signals formed in the sections before and after the sUAV within the antenna’s radiation pattern. The method of simulation modeling was used to study the features of higher-order diffraction of electromagnetic waves on the acoustic emission of sUAVs. It was found that the main part of the energy of the scattered signal is formed by acoustic oscillations in the immediate vicinity of the sUAV, whereas the contribution of oscillations at longer distances is negligible due to their attenuation. Maximum values of the reflection coefficient are achieved only when using antennas with a beamwidth of less than 4–6°, which provides spatial selection of the wavefront segments of the acoustic emission that enable coherent summation of the scattered signals. Deviation of the radar antenna from the direction toward the sUAV disrupts the conditions for coherent summation of the scattered signals from the wavefronts of the sUAV’s acoustic field.

Wireless Power Transmission (WPT): Analysis of Standards, Commercial Technologies, and Prospects

2025-11-14T14:54:12+02:00

The article presents the results of a structured analysis of wireless power transmission (WPT) technologies, their purpose, classification by range based on the ITU approaches, and an overview of key commercial standards and solutions. The ITU standards and actual commercial implementations were used as initial data. To describe WPT systems, a classification by three ranges was chosen: short-range (contact), medium-range, and long-range. A systems approach was used as an analysis method, including a comparison of parameters (range, power, efficiency, safety) and practical applicability. The technologies were assessed based on their effectiveness, safety, standardization, and commercial prevalence. The results showed that WPT does not seek to replace cable systems, but solves specific problems where physical connection is impossible, inconvenient, or dangerous. The near field (Qi standard) has received the greatest development and distribution, while far field technologies remain mainly in the area of concepts and specialized applications. Thus, the results confirm that WPT is an actively developing area, where the choice of technology is determined by a specific application, and standardization and research are critical to ensure compatibility, efficiency and safety.

Analysis of the technology for controlling digital data transmission channels with compression in computer systems

2025-11-14T15:05:01+02:00

When transmitting digital data, various types of errors may occur, including in the data address, and accordingly, there is a need to regulate the data transfer rate. In this case, simple synchronization technology is no longer enough, and it is necessary to use a data link control protocol that would provide data flow control, error detection and protection against the latter. For the effective use of high-speed communication lines, signal compression is used, which
allows several transmission sources to use the high bandwidth of the channel.

The paper analyzes the technology for controlling digital data transmission channels with compression in computer systems. Two forms of control are considered: frequency-division multiplexing (FDM) and time-division multiplexing (TDM). It is shown that sufficient data transfer speed and bandwidth, low price and the ability to use when operating from autonomous power sources make xDSL technology relevant, especially as a backup Internet access channel.

Analysis of protocol steganography methods in software-defined networks

2025-11-14T15:17:37+02:00

Networking (SDN), which constitutes a critical part of modern network infrastructure. The SDN specific characteristics are as follows: the centralized control, programmable routing logic, and separation of control and data planes. They
introduce both new threat vectors and opportunities for detecting covert communication channels.

The authors classify the steganographic techniques according to the OSI model layers, namely, from the physical to the application layer, including the session and presentation layers. The study covers both traditional approaches based on header manipulation and timing-based channels, as well as modern methods that exploit specific features of protocols such as OpenFlow, TLS, QUIC, HTTP, and DNS. Special attention is given to the inter-protocol steganography, control plane abuse, and synchronization-based covert channels that enable stealthy coordination of network nodes even in segmented environments.

A comparative analysis is conducted based on key characteristics such as bandwidth, undetectability, operational constraints, and detection vectors. The results are summarized in a comparative table, allowing a reasoned evaluation of risks across OSI layers and the identification of critical areas for steganalysis in SDN. The findings confirm the need for a multi-layered defense approach in SDN infrastructures, incorporating inter-protocol analysis, adaptive anomaly detection systems, and traffic normalization policies. The research provides a scientific foundation for the development of effective countermeasures against hidden communication in next-generation networks.

Data transmission latency mathematical model in an SDN-controlled 5G network

2025-11-14T15:24:31+02:00

Next-generation services are considered and grouped into the following categories: enhanced mobile broadband access, massive connectivity and machine-type data exchange, and ultra-reliable communication with low latency. To support these diverse service delivery scenarios, 5G networks must meet the key requirements of the Quality of Service (QoS) system.

The technologies and main configuration methods of SDN OpenFlow controllers interacting with the data processing center of the 5G network are examined. OpenFlow is the primary protocol of SDN architecture. Controllers use the OpenFlow protocol to communicate with switches (forwarding devices). OpenFlow is vendor-independent, meaning the controller can interact with any switch regardless of its manufacturer.

Quality indicators calculations and probabilistic–temporal analysis of information processing are typically performed at the data processing center of the distributed control system for controlled objects (CO), based on an interaction model between each user and the RAP, with OpenFlow protocol support via the SDN platform for 5G networks.Failures in the operation of SDN controllers are minimized through timely decision-making aimed at ensuring reliability and security indicators for the functioning of controlled consumer (CO)objects within 5G networks.

At the data processing center of the distributed control system for controlled objects based on the OpenFlow SDN platform in 5G networks, the key tasks involve calculating the specified delay metrics using a dedicated mathematical model. A model has been proposed, followed by computation, analysis, and assessment of data transmission latency during the management of 5G network elements on the SDN platform and recommendations are provided for selecting a control system configuration scenario.

Control of contact center model functional parameters to reduce the load on agents

2025-11-14T15:37:06+02:00

The operation of the contact center model has been reviewed, and it has been determined that one of the center’s key objectives is to maintain the minimally required number of agents without call interruptions. For further analysis and the development of a mathematical model for managing a networked contact center, we have identified the key performance indicators (KPIs) for agent efficiency, as well as the core metrics for assessing overall contact center performance. From a technical perspective, a typical contact center is an integrated hardware-software system. Services are executed on servers running specialized software integrated with a CRM system.

The contact center is conceptualized as a dynamic system composed of multiple interacting subsystems. A mathematical model for its operational control integrates statistical data, system feedback loops, and evolving management techniques to enable resource optimization. This model considers: matrix Bi,j - a representation of controllable parameters for each managed object (e.g. operator profiles, call attributes), where each bij is a random variable with known distribution; time delay decomposition total latency Ti , capturing queueing delay, transfer time, and computational processing per cycle. Has been responsed time calculations based on formulas that integrate equipment utilization K, queue depth, and probabilistic response models Bernoulli-type service distributions.

By incorporating has been proposed mathematic model and tical model for calculating the core probabilistic-temporal performance metrics – supplemented by numerical examples – the proposed framework can extend the functionality of the call processing module CPM without complex configurations. It is obtained that load thresholds K > 0.8 activate redistributive mechanisms to balance operator workloads or route calls to backup services. By analyzing traffic intensity, queue dynamics, and call handling performance across service cycles, the model supports adaptive adjustments to operator assignments and system capacity in near real-time. It also contributes to the formation of Key Performance Indicator (KPI) frameworks without requiring complex reconfiguration, enabling flexible enhancements to call routing modules.

Characteristics of the eigenmodes of a photonic crystal waveguide in a kagome lattice

2025-11-14T19:01:21+02:00

A photonic crystal waveguide with a hollow channel has been theoretically investigated. Waveguide cladding consists of an array of dielectric cylinders placed at the nodes of the kagome lattice. The dispersion diagrams of the photonic crystal cladding and the waveguide have been obtained on the basis of numerical calculations by the plane wave expansion method using the MIT Photonic Bands package. Several photonic band gaps of the cladding have been obtained for the considered system parameters. Waveguide eigenmodes with field energy localization in the hollow channel have been realized in each band gap. An additional waveguide eigenmode of the photonic crystal structure has been identified with the frequency locating outside the photonic band gaps. A physical justification for the implementation of an additional mechanism for field energy localization in the hollow waveguide channel, not involving either total internal reflection or the photonic band gap, has been proposed. This mechanism is similar to the mechanism of the so-called inhibited coupling between the modes of the hollow waveguide channel and the cladding modes, theoretically and experimentally investigated in photonic crystal fiber waveguides with a kagome lattice. The spatial distributions calculations results for the electric field of the photonic crystal structure eigenmodes show the effective localization of the field energy in the hollow channel for all the found waveguide modes. The difference in the spatial distribution of the eigenmode field, corresponding to the mechanism of inhibited coupling, is the presence of weak oscillations of the field in the entire space of the waveguide cladding. This indicates the existence of eigenmodes of the cladding, for which the energy exchange with the modes of the hollow channel is weak. The noted field oscillations are absent for the eigenmodes of the waveguide, the frequencies of which are within the photonic band gap of the waveguide cladding.

Silver film and distributed Bragg reflector microcavity: multilayered laser model threshold analysis

2025-11-14T19:20:11+02:00

The paper is devoted to the theoretical investigation of threshold conditions in layered microlaser structures combining a finite-thickness silver film and a dielectric distributed Bragg reflector (DBR). The research is motivated by the growing demand for compact and efficient coherent light sources that can be integrated into modern photonic and optoelectronic systems. Microlasers based on hybrid metal–dielectric cavities attract considerable attention because they offer reduced size, low power consumption, and the potential for precise spectral control. At the same time, their operation is strongly affected by the reflectivity of cavity boundaries, the thickness of the active medium, and the presence of parasitic resonances. In this context, the present work focuses on analyzing how these structural factors determine the lasing threshold and spectral characteristics of operating modes. The study employs the Lasing Eigenvalue Problem approach, which enables a rigorous description of cavity modes at the emission threshold, and the Transfer Matrix Method, which is widely used for multilayer optical systems. The numerical results demonstrate that increasing the silver film thickness can noticeably reduce the lasing threshold, while adjustment of the active layer thickness provides efficient wavelength tuning in the visible and near-infrared ranges. A specific example is given for Nd:YAG-based microlasers, where emission near 1064 nm can be accurately controlled by selecting appropriate cavity parameters.
A significant part of the analysis is dedicated to the role of the DBR. It is shown that the DBR not only forms photonic band gaps that suppress energy leakage, but also gives rise to a series of additional resonances. These parasitic modes originate from sub-cavities within the multilayer reflector and become more numerous as the number of dielectric pairs increases. However, they are characterized by much higher threshold gain values and weak overlap with the active region, which makes them less favorable for practical lasing. The comparison with a purely metallic cavity demonstrates that the inclusion of a sufficiently wide DBR can improve the performance of the primary mode, lowering its threshold while isolating it from parasitic resonances.

The obtained results highlight the potential of combining noble-metal films with DBR structures in the design of advanced microlasers. By carefully adjusting the reflector parameters, it is possible to optimize mode selection, suppress unwanted resonances, and achieve stable, efficient operation. Such approaches are expected to be valuable for the development of integrated photonic devices, optical communication systems, LiDAR sensors, and compact biosensing platforms. The paper provides useful theoretical guidelines for further research and practical implementation of layered microlasers with tunable properties.

Diffraction of light on one and two infinitly narrow slits in a screen

2025-11-14T19:35:44+02:00

The work addresses the solution of the problems of light diffraction at one and two narrow slits in an opaque screen. The diffraction patterns were analyzed. It was established that their appearance depends on the ratio of the characteristic size of the obstacle to the wavelength of the photon. When this ratio is less than unity, we have a smoothly changing illumination with a maximum at the center of symmetry of the system. If it one is greater than unity, then the pattern has the appearance of light and dark stripes. The numerical value of the specified ratio determines the number of maxima. The obtained results allow us to assume that the reason for the well-known paradox in the interpretation of experiments on the diffraction of light at one and two narrow slits is thе next. The experiments at one slit was carried out for the case when the wavelength was greater than the width of the slit, and at two slits - for the case, when the wavelength is much smaller than the distance between slits.

MOSFET transistor modeling including parasitic leakage and drain resistance

2025-11-14T23:24:05+02:00

The aim of the work is to develop and analyze a method for including parasitic source (R_S) and drain (R_D) resistances in the basic SPICE Level 1 MOSFET model. Relevance: even in the simple quadratic MOSFET model (SPICE level 1), ignoring parasitic resistances can lead to significant simulation errors, especially at high currents. This paper provides a literature review of approaches to account for R_S and R_D in compact MOSFET models: from the classic Shichman–Hodges model (SPICE Level 1) to modern works on the extraction of resistances and modeling their impact. Theoretical background describes a modification of the Level 1 model by introducing effective voltages V^eff_GS and V^eff_DS that account for voltage drops across R_S and R_D, and analytical equations for the drain current I_D in linear and saturation regions with these resistances. Methodology includes a numerical iterative algorithm implemented in Python/PySpice which solves the implicit equation I_D(V^eff_GS, V^eff_DS). Results show reduction of current and a shift in saturation point when adding parasitic resistances: for a typical NMOS at V_GS=5 V, introducing R_S=R_D=50 Ω reduces I_D by ≈16% and increases the saturation voltage by ≈ 0.3 V. Output characteristics graphs and tables of relative current deviation are presented. The novelty lies in the proposed simple iterative procedure to include R_S, R_D in the SPICE Level 1 model without resorting to more complex models, and the practical value is the applicability of this approach for educational modeling and quick evaluation of parasitic effects on MOSFET behavior. Conclusions: accounting for R_S, R_D significantly improves the accuracy of Level 1 modeling, bringing results closer to real devices with minimal computational complexity, which is useful for engineering practice and further research.

Design of ultraviolet disinfection with optimization of irradiation dosage by means of measurement and control of uv radiation parameters

2025-11-14T23:34:08+02:00

Modern beekeeping faces complex threats, among which the pesticide poisoning, spread of diseases and parasites, climate change, decrease in the feed base and organizational shortcomings in the apiary management play a key role. Mass losses of bee colonies in Ukraine, reaching 30–50% per year, create a serious environmental and agricultural problem. In this context, the search for safe and effective disinfection methods that can replace chemicals is relevant.

The aim of the study is to assess the effectiveness of ultraviolet (UV-C) radiation in the range of 210–280 nm for combating fungal and viral infections of the surface of hives. The experiments conducted showed that the most effective is radiation with a wavelength of 254 nm, which provides up to 96.8% disinfection of colonies of microorganisms.

The developed experimental installation based on a bactericidal UV-irradiator with autonomous power supply demonstrated high efficiency, cost-effectiveness and environmental safety in comparison with traditional methods (steam, acid and fire treatment). The results confirm the feasibility of using the UV technologies in beekeeping as a promising direction for disease prevention and preservation of bee colonies.

Research into the influence of the electromagnetic field on cell ion channels using modeling and measure-ment systems

2025-11-14T23:47:05+02:00

The relevance of the study is due to the growing interest in the regulation of cellular activity under the influence of electromagnetic fields (EMF), which is a promising direction in biomedical engineering. Ion channels, in particular Na⁺, are crucial for maintaining the membrane potential, generating impulses and controlling cell functions. The article proposes the use of computer-aided design systems (CAD) together with control and measurement methods for modeling the influence of EMF on cell ion channels. Mathematical models of ion transport dynamics are presented, in particular the Navier–Stokes equation for describing fluid oscillations, volume transport models and the modified Kuramoto model for studying the synchronization of cellular pulsations. The simulation conducted in MATLAB/Simulink showed that EMF with a frequency of 50 Hz and an amplitude of 100 nA can cause both depolarization (stimulation) and hyperpolarization (inhibition) of the membrane potential depending on the mode of influence. The results demonstrate the possibility of targeted regulation of the permeability of sodium channels, which is confirmed by the data of other studies. The proposed model allows for a deeper understanding of the mechanisms of electrophysiological regulation of the cell and can become the basis for the creation of new methods of therapeutic influence and the development of bioelectronic devices. The results obtained have high practical significance and open up prospects for further experimental and applied research in biomedical technologies.

Classification of electromyographic signals by their entropic characteristics for differential diagnostics of low back pain using the random forest method

2025-11-14T23:58:34+02:00

The article presents the results of an investigation into the possibilities of using entropic characteristics of electromyographic (EMG) signals for differential diagnostics of pain syndromes in the lumbar spine. Two independent sets of EMG signals recorded in three diagnostic groups were used as initial data: healthy individuals without complaints of back pain, conditionally healthy individuals with complaints of pain (dysfunctional pain), and patients with degenerative diseases of the spine (functional pain). Four entropy indicators were selected to describe the signals – median and mean entropy, as well as median and mean spectral entropy. The random forest algorithm was used as a classification method. Model training was carried out on a data set with a significant class imbalance, and testing was performed using another, independent set. During the study, the number of trees in the ensemble was varied (100, 200, 300 and 500), and the feasibility of taking into account weighting coefficients inversely proportional to the representation of classes in the data was also tested. The quality of the models was assessed based on the classification accuracy, F1-score, area under the ROC curve (AUC), ROC curve and confusion matrix. The results obtained showed that increasing the number of trees above 100 does not provide an increase in the quality of classification, and weighting the training data in most cases does not improve the results compared to unweighted models. The best indicators were achieved when distinguishing the group of patients with dysfunctional pain from the group with functional pain: the F1-score was 0.99, the AUC was 1.00, and the accuracy was 99.09%. Thus, the results confirm the feasibility of using the entropic characteristics of EMG signals in combination with the random forest method to create reliable clinical decision support tools. The greatest diagnostic value is the ability to distinguish the type of pain syndrome (dysfunctional or functional), which can contribute to a more informed choice of treatment tactics in patients with low back pain.