Phonon modes and raman scattering in SixGe1-x nanocrystals: microscopic modelling

Si1-xGex nanocrystals (NCs) of different composition and size were generated using the Molecular Dynamics (MD) method by minimizing NC’s total energy calculated using Tersoff’s empirical potential and applying rigid boundary conditions. The dynamical matrix of the relaxed NC was constructed and the NC phonon modes were calculated. The localisation of the principal (Si-Si, Si-Ge and Ge-Ge) modes is investigated by analysing their inverse participation ratio. The dependence of the corresponding Raman spectra, obtained by employing the bond polarisability model, upon x and the NC size is presented and compared to previous calculated results and available experimental data.Fundação para a Ciência e a Tecnologia (FCT

Peak Age of Information Distribution for Edge Computing with Wireless Links

Age of Information (AoI) is a critical metric for several Internet of Things (IoT) applications, where sensors keep track of the environment by sending updates that need to be as fresh as possible. The development of edge computing solutions has moved the monitoring process closer to the sensor, reducing the communication delays, but the processing time of the edge node needs to be taken into account. Furthermore, a reliable system design in terms of freshness requires the knowledge of the full distribution of the Peak AoI (PAoI), from which the probability of occurrence of rare, but extremely damaging events can be obtained. In this work, we model the communication and computation delay of such a system as two First Come First Serve (FCFS) queues in tandem, analytically deriving the full distribution of the PAoI for the M/M/1 - M/D/1 and the M/M/1 - M/M/1 tandems, which can represent a wide variety of realistic scenarios.Comment: Preprint version of the paper accepted for publication in the Transactions on Communication

Age of Information in Multi-hop Networks with Priorities

Age of Information is a new metric used in real-time status update tracking applications. It measures at the destination the time elapsed since the generation of the last received packet. In this paper, we consider the co-existence of critical and noncritical status updates in a two-hop system, for which the network assigns different scheduling priorities. Specifically, the high priority is reserved to the packets that traverse the two nodes, as they experience worse latency performance. We obtain the distribution of the age and its natural upper bound termed peak age. We provide tight upper and lower bounds for priority updates and the exact expressions for the non-critical flow of packets with a general service distribution. The results give fundamental insights for the design of age-sensitive multi-hop systems.Comment: Submitted for publication to IEEE Globecom Conferenc

Age of Information in Multi-Hop Connections with Tributary Traffic and no Preemption

Age of Information (AoI) has gained significant attention from the research community because of its applications to Internet of Things (IoT) monitoring and control. In this work, we treat multihop connections over queuing networks with tributary flows and non-preemptive service: packets cannot be discarded because they are utilized for other system objectives, such as data analytics. Without preemption, the key tool for optimizing AoI is then the scheduling policy between the different data flows at each intermediate node. This is the subject of our analysis, along with the impact of packet erasure on the age. We derive upper and lower bounds for the average AoI considering several queuing policies in arbitrary network topologies, and present the results in different scenarios. Network topology, tributary traffic load, and link characteristics such as packet erasure generate complex trade-offs, which affect the optimal operation point and the age performance. The scheduling strategy at each node can also affect performance and fairness among users, particularly at critical bottleneck links, which have a significant impact on the overall performance of the whole network.acceptedVersionPeer reviewe

Enhancing Uplink Performance of NR RedCap in Industrial 5G/B5G Systems

The evolution of cellular fifth-generation (5G) tech-nologies shapes the future of the manufacturing industry by enabling sector automation and digitalization. Smart factories rely primarily on wireless connectivity provided by new radio (NR) systems to meet the stringent requirements of industrial applications. Among these, several industrial wearable and sensor-based services involve devices with relaxed communication capabilities as compared to Rel-15 NR user equipment. Hence, a new category of reduced-capability (RedCap) devices becomes essential in industrial private networks. As RedCap devices may experience degradation of uplink (UL) performance due to simplifications in radio frequency and baseband capabilities, this paper focuses on enhancing NR RedCap operations with existing 5G solutions for UL improvement, namely, dual connectivity, carrier aggregation, and supplementary UL. Specifically, we discuss these options for RedCap wearable devices and evaluate the performance gains of the selected technology using link-level simulations.acceptedVersionPeer reviewe

AI-Aided Integrated Terrestrial and Non-Terrestrial 6G Solutions for Sustainable Maritime Networking

The maritime industry is experiencing a technological revolution that affects shipbuilding, operation of both seagoing and inland vessels, cargo management, and working practices in harbors. This ongoing transformation is driven by the ambition to make the ecosystem more sustainable and cost-efficient. Digitalization and automation help achieve these goals by transforming shipping and cruising into a much more cost- and energy-efficient and decarbonized industry segment. The key enablers in these processes are always-available connectivity and content delivery services, which can not only aid shipping companies in improving their operational efficiency and reducing carbon emissions, but also contribute to enhanced crew welfare and passenger experience. Due to recent advancements in integrating high-capacity and ultra-reliable terrestrial and non-terrestrial networking technologies, ubiquitous maritime connectivity is becoming a reality. To cope with the increased complexity of managing these integrated systems, this article advocates the use of artificial intelligence and machine-learning-based approaches to meet the service requirements and energy efficiency targets in various maritime communications scenarios.acceptedVersionPeer reviewe

Cost- and Delay-Efficient Backhaul Selection for Time-Sensitive Maritime Communications

Extending the existing near-shore terrestrial infrastructure with non-terrestrial network capabilities helps maritime operators alleviate the high costs of communication and meet the requirements imposed by time-sensitive applications. Recognizing that the deployment of terrestrial and non-terrestrial networks necessitates selecting from the available wireless backhaul solutions, which have dissimilar data transmission costs and communication link qualities, it is essential to propose an appropriate backhaul selection policy. Specifically, in this letter, we coin a backhaul selection policy that manages the inherent trade-off between data transmission expenses and timely throughput guarantees for maritime communications. We formulate the backhaul selection problem as a Markov decision process and show that the proposed solution is not only more cost-efficient, but also satisfies the timely throughput requirements in contrast to currently used greedy strategies.publishedVersionPeer reviewe

Impact of disorder on optical phonons confined in CdS nano-crystallites embedded in a SiO2 matrix

Non-resonant Raman spectroscopy studies of a set of CdS films annealed at different temperatures were performed and showed a direct correlation between the width of the Raman peak produced by CdS-like optical phonons and the crystalline quality of the semiconductor phase probed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). In order to decribe the Raman lineshape a model proposed by Trallero-Giner et al (1998 Phys. Rev. B 57 4664) was used, which considers optical phonons confined in small semiconductor spheres with a size distribution. The model is shown to give a good reproduction of the spectra of samples where the semiconductor phase is most crystalline. However, it required too large values of phonon damping to fit the spectra of several other samples, which, according to XRD and TEM data, do contain CdS nano-crystallites. This large broadening of the Raman peak was considered as inhomogeneous, i.e. associated with disorder. Numerical lattice dynamics calculations were performed for 2D binary clusters of arbitrary shape and three kinds of disorder were considered, (i) random variation of the Cd–S bond frequency from one nano-crystallite to another, (ii) cluster shape irregularities and (iii) fluctuations of the nearest-neighbour interaction constant within one cluster. It is shown that ‘ensemble disorder’ (i) can be responsible for a shoulder above the bulk CdS phonon frequency observed for some of our samples. The effect of shape disorder (ii) is similar to that of the size dispersion producing some inhomogeneous broadening of the peak. In addition, it gives rise to an extra low-frequency mode originating from the top of the acoustic band. The force constant’s disorder (iii) is shown to result in a stronger asymmetric broadening of the Raman peak.Fundação para a Ciência e a Tecnologia (FCT

Визначення формальних ознак показників для оцінки ефективності операцій з розподіленими параметрами

Optimization criterion is a reference point for the choice of such technological process parameters to provide the maximum coherence of operational process results with the purpose of its owner. The complexity of this task is mostly connected with the fact that up to the present moment a large number of indicators, designed for operational processes efficiency assessment have already been developed and continue to be developed. It is especially important for operations with the distributed parameters.Therefore, the priority is a preliminary selection of the known indicators with the use of formal signs. It allows reducing significantly the number and the length of the studies at the second and the final testing stages with applying the methods of mathematical modeling.With the use of the cybernetic production operation model, created in the work, the formal signs, which should have the estimated indicators, proposed for efficiency definition of operations with the distributed parameters have been defined.As a result of the performed researches, it has been established that any system operation model can be presented in the form of parametrically comparable input and output functions.As the efficiency of operations with the distributed in time parameters is essentially affected by the distribution function form, the possibility of separate classes’ comparative assessment of such operations has been investigated.It has been established that the second integrated parameter from the input and output function has sensitivity to a change in the distribution function form.The obtained results can be used for the selection of indicators designed to measure operations efficiency by formal signs. Also, the results of the work can be used for cybernetic estimated indicators creation.Исследование относится к области верификации оценочных показателей, в частности к решению задачи предварительного отбора показателей, которые планируется использовать в качестве критериев эффективности или оптимизации. С использованием созданной в работе кибернетической продуктовой модели операции определены формальные признаки, которыми должны обладать оценочные показатели, предназначенные для определения эффективности операций с распределенными параметрамиДослідження відноситься до області верифікації оціночних показників, зокрема до вирішення задачі попереднього відбору показників, які планується використовувати в якості критеріїв ефективності або оптимізації. З використанням створеної в роботі кібернетичної продуктової моделі операції визначені формальні ознаки, якими повинні володіти оціночні показники, призначені для визначення ефективності операцій з розподіленими параметрам