Specific Topology Research Articles

Palladium nanoparticles immobilized on a nano-silica triazine dendritic polymer: a recyclable and sustainable nanoreactor for C-S cross-coupling.

Dendrimers are of great interest due to their special structural topology and chemical versatility. Owing to their properties, dendrimers have found practical applications in catalytic processes as efficient nanoreactors. Therefore, we herein report an environmentally attractive strategy and highly efficient route for the synthesis of a wide variety of diaryl sulfides using palladium nanoparticles immobilized on a nano-silica triazine dendritic polymer (Pdnp-nSTDP) as a nanoreactor. In this manner, different diaryl or aryl heteroaryl sulfides and bis(aryl/heteroarylthio)benzene/anthracene/pyridine derivatives were prepared via C–S cross-coupling reactions of aryl halides with diaryl/diheteroaryl disulfides under thermal conditions and microwave irradiation. The catalyst could be easily recovered and reused several times without any significant loss of its activity.

Exploring the possibilities of Honeypot technology

The role and main tasks of various network traps (Honeypot) in the construction of integrated security systems are defined. Basic classification signs and features of the primary tuning of a few commercial facilities software solutions. It is concluded that the main advantages of Honeypot technology, among other things, are their flexibility and scalability. It is emphasized that at present there are no perfect methods of identification and rapid compromise of network traps. Attention is drawn to the fact that network intelligence tactics and methods of network attacks are constantly progressing. Given this fact, the ongoing audit of HP data and prompt response to identified network incidents is one of the main areas of work for staff on compliance with corporate information security policy requirements. It is noted that the architecture of various traps, in general, is quite well known and therefore potentially vulnerable. Therefore, by providing traps with a more flexible (variable) scenario context and reducing the exposure time, it is possible to maintain their protective potential in the parity enough state. Both of these direction require closer attention (detailed analysis of log-files data and adjustment of behavioral avatar algorithms for the created trap) on the part of staff, and require constant support of them professional competencies. Based on the results of reviewing the capabilities of existing Honeypots and generalizing the typical features of network activity of the most characteristic nodes (in this case the file server), the features of synthesis of the corresponding behavioral profiles (avatars) are considered. It is claim that systematization of avatar rules Honeypot (as a set of behavioral algorithms) and timely correction of existing databases of behavioral profiles is a task that is difficult to formalize. This is caused to the potential variety of network activity options that are specific to each network and the individual settings of existing network nodes. In this sense, excessive unification (narrowing of the possible field of behavioral reactions) of behavioral profiles Honeypot can greatly facilitate the attacker to monitor and subsequently identify the trap created. Therefore, the formation of a basic set of relevant network avatars should be considered as a basis for its further modification under a special task, topology and other features of each individual IT structure (or features of their individual elements). It is emphasized that the introduction of trap technology does not replace other security technologies and tools, but only effectively expands the existing arsenal of countering new security threats (primarily as a tool for operational intelligence and rapid response). Therefore, the way to integrate net-traps with other security solutions is the most balanced way to further improve the overall security of network resources.

An ANN-Based Single Calibration Impedance Measurement System for Skin Impedance Range

Impedance measurement has been widely used as an effective indicator for characterizing samples. Traditional high accuracy impedance analyzers are complicated, expensive, and non-portable. Many kinds of research require low cost, portable, and high precision impedance analyzer devices. AD5933 impedance analyzer integrated circuit has been popularly used for fulfilling these requirements. There are many successful applications of the AD5933 integrated circuit; however, the most significant drawback is nonlinear calibration requirements for high precision measurement in a specified range. The calibration and unknown impedances must be close enough to each other for better measurement accuracy. In the literature, calibration impedance arrays increasing the complexity and processing time are commonly used for high accuracy measurements. In this study, an artificial neural network-based signal post-processing algorithm is proposed to overcome the calibration requirements of the AD5933 integrated circuit, which requires different impedances for different ranges. In the literature, a neural network-based solution has not been applied to this phenomenon. An application specific artificial neural network topology is developed and trained for high precision impedance measurement using a fixed calibration impedance. The proposed measurement system is designed for operating in the range of nominal skin impedance. The average mean square error of measurements is obtained as 0.206%. Although a fixed calibration resistance is used, the proposed signal post-processing approach significantly improved the measurement accuracy of the AD5933 integrated circuit. The high accuracy measurement results prove the effectiveness of the proposed measurement system. The developed system offers portable, simple, and low cost high precision impedance analyzer.

CRetor: An SDN-Based Routing Scheme for Data Centers With Regular Topologies

The blooming of cloud computing leads to the rapid expansion of data center networks (DCN). Conventional link state routing algorithms like OSPF are widely adopted in data center networks, however, those routing algorithms bring great control overheads and long convergence time. Recently, topology-aware routing methods are considered to be efficient especially in data center networks with regular topologies. Lots of topology-aware routing methods (e.g., Fat-Tree and BCube) have been proposed for specific data center network topologies. This paper first proposes a formalized method to describe regular topologies and a regular Topology Description Language (TPDL) based on this method. TPDL is well designed to accurately define regular network topologies in a clear way leveraging their regularities. Based on the Software-Defined Networking (SDN) technology, this paper also proposes a novel topology-aware routing scheme: cRetor (controller-side REgular TOpology Routing scheme). Different from other topology-aware routing methods, cRetor is a TPDL-based general routing method, which means it is expected to work on different kinds of regular topologies. In this scheme, TDPL files are used as a priori knowledge to build an initial topology in the SDN controllers, which eliminates the process of topology discovery via Link Layer Discovery Protocol (LLDP) and hence relieves the bandwidth and processing burdens on controllers. Besides, we also apply the A-star algorithm to SDN controllers to speed up the routing selection, where TPDL's distance formulas act as the heuristic function. The experimental results show that cRetor outperforms LLDP-based SDN, OSPF and DCell in routing calculation performance, convergence speed, routing overheads and fault tolerance.

New Figure-of-Merit Combining Semiconductor and Multi-Level Converter Properties

Figures-of-Merit (FOMs) are widely-used to compare power semiconductor materials and devices and to motivate research and development of new technology nodes. These material- and device-specific FOMs, however, fail to directly translate into quantifiable performance in a specific power electronics application. Here, we combine device performance with specific bridge-leg topologies to propose the extended FOM, or X-FOM, a Figure-of-Merit that quantifies bridge-leg performance in multi-level (ML) topologies and supports the quantitative comparison and optimization of topologies and power devices. To arrive at the proposed X-FOM, we revisit the fundamental scaling laws of the on-state resistance and output capacitance of power semiconductors to first propose a revised device-level semiconductor Figure-of-Merit (D-FOM). The D-FOM is then generalized to a multi-level topology with an arbitrary number of levels, output power, and input voltage, resulting in the X-FOM that quantitatively compares hard-switched semiconductor stage losses and filter stage requirements across different bridge-leg structures and numbers of levels, identifies the maximum achievable efficiency of the semiconductor stage, and determines the loss-optimal combination of semiconductor die area and switching frequency. To validate the new X-FOM and showcase its utility, we perform a case study on candidate bridge-leg structures for a three-phase 10 kW photovoltaic (PV) inverter, with the X-FOM showing that (a) the minimum hard-switching losses are an accurate approximation to predict the theoretically maximum achievable efficiency and relative performance between bridge-legs and (b) the 3-level bridge-leg outperforms the 2-level configuration, despite utilizing a SiC MOSFET with a lower D-FOM than in the 2-level case.

A Distributed Survivable Routing Algorithm for Mega-Constellations With Inclined Orbits

Mega-constellations consisting of hundreds to thousands of low-earth-orbit (LEO) satellites are an attractive solution for providing global ubiquitous network access. Due to good coverage properties for populated areas, inclined orbits are gaining popularity among commercial constellations. A scalable routing algorithm with survivability plays a key role in such systems. In this paper, we propose a distributed survivable routing algorithm for mega-constellations with inclined orbits. First, the special topology characteristic of inclined constellations is identified and formalized. Based on the topology characterization, a basic X-Y routing algorithm is presented to determine multiple primary and secondary paths towards each destination utilizing the regularity of the network topology with minimal computation overhead. Then, a failure recovery mechanism which consists of a restricted flooding mechanism and a pre-detour mechanism is proposed to reduce end-to-end delay and signaling overhead in case of link failures. Besides, a partial-record loop avoidance mechanism is proposed to deal with routing loops with minimal overhead. Finally, a vector-based next hop selection mechanism is proposed to facilitate the selection of next hop while incorporating various criteria. The performance of the proposed routing algorithm is evaluated through simulation on the Starlink constellation. Simulation results show that our proposal achieves scalability by reducing signaling overhead and provides better quality of service in terms of end-to-end delay under link failures.

Network resource optimization configuration in edge computing environment

Edge computing helps break through the resource limitations of the terminal, providing powerful computing power and improving the user experience. Time cost and energy cost are the main considerations for end users to perform edge calculations, so a reasonable edge calculation strategy can ensure that user spending is minimized. This paper first studies the service deployment and edge computing of multi-terminal single-base station scenarios and proposes a resource coordination strategy for multi-base station scenarios. Secondly, the network resource allocation problem is modeled by linear programming. The objective function of the model is to maximize the remaining processing resources of the host with the most processing tasks allocated in the whole network, that is, the load balancing target, and at the same time take into account the routing efficiency; there are three main types of constraints: bandwidth constraint, traffic balancing constraints and processing. The linear optimization tool is used to solve and analyze the optimal configuration results of network resources in a specific network topology. Finally, through the simulation work, it is verified that our scheme is effective for network resource allocation, and the impact of network traffic speed on resource allocation scheme is tested.

Dynamics Modeling of Topologically Simple Parallel Kinematic Manipulators: A Geometric Approach

Abstract Dynamics modeling is indispensable for the design and control of dexterous parallel kinematic manipulators/machines (PKM). Various modeling approaches proposed in the literature build upon the classical formulations for serial manipulators, and thus, inherit those modeling conventions that tend to be restrictive rather than user-friendly. Moreover, the special kinematic topology of PKM is treated either ad hoc or by resolving loop constraints using standard methods from multibody dynamics. Geometric formulations on the other hand, more precisely Lie group formulations, were developed over the last decades that provide a flexible and user-friendly approach to the modeling of robotic systems in general. A dedicated formulation for topologically simple PKM has not yet been proposed, however. Such a formulation is presented in this paper. The frame invariance of the geometric formulation gives rise to a modular modeling approach that further reduces the modeling effort. The equations of motion (EOM) in terms of task space coordinates as well as in actuator coordinates are presented for kinematically nonredundant and redundant topologically simple PKMs. A PKM is topologically simple if its moving platform is connected to the base by simple serial kinematic chains and if there are no other kinematic chains than these. The majority of PKMs are topologically simple, including fully parallel PKM. Applications of the EOM for dynamics simulation and model-based control are briefly discussed. The paper also provides a literature review of approaches to dynamics modeling of PKM.

A Stochastic Approach to Modeling Tidal Creek Evolution: Exploring Environmental Influences on CreekTopologies Through Ensemble Predictions

AbstractA numerical tool integrating hydrodynamics, vegetation growth, stochastic selection, and Monte‐Carlo simulation is developed to predict channel network evolution in a newly inundated back‐barrier wetland. Focusing on the formation and evolution of tidal channels, model simulations suggest a clear tendency towards specific creek topologies with high probability despite creek evolution being subject to random perturbations. These creek topologies are primarily determined by wetland topography while the influence of vegetation is secondary. Ensemble results of Monte‐Carlo simulations identify threshold points leading to bimodal separation of the emergent creek networks characterized by different complexity and efficiency. This, in turn, assists the recognition of necessary human interventions to encourage the formation of complex and far‐reaching creek networks that can promote exchange of materials between estuaries and salt marshes and, hence, maintain salt marsh ecosystem structure and function.

A family of compensation topologies for capacitive power transfer converters for wireless electric vehicle charger

A large scale of electric vehicles can ideally maintain the stability of renewable power supply by acting as storage buffers for alleviating the intermittence in the integration of renewable energy sources for constructing a low-carbon energy system. However, the inconvenient conductive charging becomes a barrier in the popularization of electric vehicles. Wireless power transfer technology is in the spotlight because of the flexibility and convenience in powering electric vehicles. Recently, the Capacitive Power Transfer has received extensive attention due to simple coupler structure, rotatable coupler, and negligible heating of the metal foreign object. In the capacitive-based wireless charging system, the higher-order compensation topology is essential to enhance power transfer capability limited by the small coupling capacitance. However, with the increase of the resonant elements, the form of the resonant network becomes diverse. Currently, the researches focus on the characteristics of specific symmetrical compensation topologies. This paper presents a family of compensation topologies for the Capacitive Power Transfer system to achieve constant-voltage or constant-current output. A design procedure is summarized to construct the resonant networks, so as to design the compensation parameters. Considering the coupling capacitor variations caused by parking position deviation, a parameter tuning method is proposed to realize primary zero-voltage switching by adjusting the parameter of the double-sided inductor-capacitor-inductor-capacitor compensation topology. Experiments show that the prototype achieves constant-current output and zero-voltage switching when the coupling capacitance varies. The system efficiency reaches 93.57% at 1.5 kW input power with the input and output voltage around 250 V.

ПОКРАЩЕННЯ РОЗВАНТАЖУВАЛЬНОЇ ЗДАТНОСТІ ДИСКОВОГОМАГНІТНОГО СЕПАРАТОРА

An improved design of permanent magnet disk separator is proposed, which is designed for cleaning of ferromagnetic inclusions from bulk substances that transported by belt conveyor in order to improve unloading capability of separator. It is shown that use of permanent magnets made of various materials in disk separators leads to improvement of separator's operational characteristics, reduces energy consumption, dimensions and mass, and makes it possible to create a specific magnetic field topology. It is proved that installation of magnets which are differed by their magnetic properties on disk periphery leads to a decrease of radial component of magnetic force and decrease of exit speed of ferromagnetic inclusions from surface of rotating non-magnetic unloading disk. Research focused on distribution of force function in working area of improved design of disk magnetic separator. For this research a numerical finite element method implemented in software environment of COMSOLMultiphysics was applied. Magnetic force function acting on multidomain ferromagnetic particles was investigated. Due to complexity of force field spatial geometry in working area of disk magnetic separator, a three-dimensional computer model of disk magnetic separator was developed, its geometric characteristics and physical properties are described. Comparative analysis of force function distribution in working interval of disk separator is carried out. It has been established that application of improved design of disk magnetic separator can reduce rotation speed of non-magnetic unload disk, at which exit of ferromagnetic inclusions from its surface to unload zone is carried out.

Proposed Topology for Voltage Sag Mitigation with New Control Strategy

voltage sags represent the greatest threat to the sensitive loads of industrial consumers, the microprocessor based-loads, and any electrical sensitive components. In this paper, a special topology is proposed to mitigate deep and long duration sags by using a modified AC to AC boost converter with a new control method. A boost converter is redesigned with a single switch to produces an output voltage that is linearly proportional to the duty cycle of the switch. On the other hand, the proposed control system is based on introducing a mathematical model that relates the missing voltage to the duty cycle of the boost converter switch. The simulation results along with the system analysis are presented to confirm the effectiveness and feasibility of the proposed circuit.

Joint Caching and Routing in Congestible Networks of Arbitrary Topology

In-network caching constitutes a promising approach to reduce traffic loads and alleviate congestion in both wired and wireless networks. In this article, we study the joint caching and routing problem in congestible networks of arbitrary topology (JoCRAT) as a generalization of previous efforts in this particular field. We show that JoCRAT extends many previous problems in the caching literature that are intractable even with specific topologies and/or assumed unlimited bandwidth of communications. To handle this significant but challenging problem, we develop a novel approximation algorithm with guaranteed performance bound based on a randomized rounding technique. Evaluation results demonstrate that our proposed algorithm achieves near-optimal performance over a broad array of synthetic and real networks, while significantly outperforming the state-of-the-art methods.

Top-Down Synthesis of Multiagent Formation Control: An Eigenstructure Assignment Based Approach

We propose a top-down approach for formation control of heterogeneous multi-agent systems, based on the method of eigenstructure assignment. Given the problem of achieving scalable formations on the plane, our approach globally computes a state feedback control that assigns desired closed-loop eigenvalues/eigenvectors. We characterize the relation between the eigenvalues/eigenvectors and the resulting inter-agent communication topology, and design special (sparse) topologies such that the synthesized control may be implemented locally by the individual agents. Moreover, we present a hierarchical synthesis procedure that significantly improves computational efficiency. Finally, we extend the proposed approach to achieve rigid formation and circular motion, and illustrate these results by simulation examples.

Signs of Heritage—An Agent-Based Model of the Dynamics of Heritage Categories

In recent times, heritage has become a key focus of socio-economic concern due to its connections to history, nationalism, and, especially, tourism. It has been highlighted as having major consequences for the sociocultural engagement of local populations. The notion that tourism transforms local heritage through the categorization of local realities has become particularly widespread. However, the specific mechanism through which these transformations occur has remained unformalized in cultural heritage studies. This has resulted in a lack of computational approaches to the issue of heritage categorization, which can connect with other issues of tourism promotion and management. In this article, we conceptualize the cultural dynamics of heritage, such as changes in the categories used to signify heritage, and design and analyze a dedicated computational agent-based model of heritage engagement. Here, we seek to explore the role of communicative strategies, as they relate to social groups, as well as the specific topologies of interaction networks. We attempt to understand what role mediation, such as that produced by online platforms, can play in producing different levels of consensus between tourists. The results suggest that topology plays the greatest role in generating consensus in the evolution of heritage meaning, with different patterns emerging according to the communicative strategies employed. The results have implications for the future direction of the study of heritage and heritage modeling, placing emphasis on the need to analyze tourist communication content, as well as being potentially useful for public policy with regard to heritage management.

Network-constrained thermal unit commitment for hybrid AC/DC transmission grids under wind power uncertainty

The day-ahead energy and reserve management considering transmission restrictions and voltage security limits is a challenging task for large-scale power systems in the presence of volatile renewable energy sources. In this paper, a two-stage robust optimization model is proposed for the joint scheduling of energy and reserve for hybrid AC/DC transmission grids. The optimal schedule, including the commitment, power dispatch, and reserve allocations is computed subject to the feasibility of nonlinear AC and DC network constraints under a specified set of scenarios. Furthermore, the proposed decomposition approach renders the second stage (network security evaluations) into standard optimal power flow problems, which addresses the scalability issues observed with existing methods. A second-order cone relaxation is applied to nonlinear AC and DC network constraints to improve the computational tractability. In simulations, the proposed robust optimization model is illustrated using a recently proposed hybrid AC/DC transmission grid architecture with a specific topology. The results demonstrate the effective utilization of the grid capacity to accommodate more demand and renewable energy sources. This hybrid AC/DC transmission grid architecture induces exactness of the convex relaxation, supporting the validity of the optimal day-ahead schedule. The efficiency and computational performance of the proposed method is compared to the existing literature and the robustness is verified using an out-of-sample analysis.

Optimizing synchronizability in networks of coupled systems

Of collective behaviors in networks of coupled systems, synchronization is of central importance and an extensively studied area. This is due to the fact that it is essential for the proper functioning of a wide variety of natural and engineered systems. Traditionally, uniform coupling strength has been the default choice and the synchronizability measure has been employed for analysis and enhancement of synchronizability. The main drawback of optimizing the synchronizability measure is that it can reach the Pareto frontier but not necessarily a unique point on the Pareto frontier. Additionally, the shortcoming of uniform coupling strength is that it can reach Pareto frontier in specific topologies including edge-transitive graphs. To achieve a unique optimal answer on the Pareto frontier, this paper takes a different approach and addresses the synchronizability in networks of coupled dynamical systems with nonuniform coupling strength and optimizing the synchronizability via maximizing the minimum distance between the nonzero eigenvalues of the Laplacian and the acceptable boundaries for the stability of the system. Furthermore, two solution methods, namely the concave–convex fractional programming and the Semidefinite Programming (SDP) formulations of the problem have been provided. The proposed solution methods have been compared over different topologies and branches of an arbitrary network, where the SDP based approach has shown to be less restricted and more suitable for a wider range of topologies.

Fast Domain Wall Motion Governed by Topology and Œrsted Fields in Cylindrical Magnetic Nanowires.

While the usual approach to tailor the behavior of condensed matter and nanosized systems is the choice of material or finite-size or interfacial effects, topology alone may be the key. In the context of the motion of magnetic domain walls (DWs), known to suffer from dynamic instabilities with low mobilities, we report unprecedented velocities >600 m/s for DWs driven by spin-transfer torques in cylindrical nanowires made of a standard ferromagnetic material. The reason is the robust stabilization of a DW type with a specific topology by the Œrsted field associated with the current. This opens the route to the realization of predicted new physics, such as the strong coupling of DWs with spin waves above >600 m/s.

Early Warning of mmWave Signal Blockage and AoA Transition Using sub-6 GHz Observations

The susceptibility of millimeter-wave (mmWave) signals to physical blockage and abrupt signal strength variations presents a challenge to reliable 5G communication. This work proposes and examines the feasibility of utilizing lower-frequency signals as early-warning indicators of mobile mmWave signal blockage or recovery. A physics-based channel simulation tool incorporating Fresnel diffraction and image sources is employed to demonstrate that sub-6 GHz signals "lead" mmWave signals in reaching a specific signal-strength threshold by several to tens of milliseconds at mobile speeds, suggesting early-warning systems are viable. This predictive approach stems from frequency-dependent properties of diffraction and does not assume a specific topology or mobile and obstacle speeds. Realistic simulations that include transitions from line of sight (LoS) to non-line of sight (NLoS) and reflection scenarios are employed to verify the proposed prediction capabilities. Moreover, prediction of the strongest multipath component and its angle of arrival (AoA) using sub-6 GHz observations is investigated.

Risk of Collision and Detachment in Vehicle Platooning: Time-Delay–Induced Limitations and Tradeoffs

We quantify the value-at-risk of inter-vehicle collision and detachment for a class of platoons, which are governed by second-order dynamics in presence of communication time-delay and exogenous stochastic noise. Closed-form expressions for the risk measures are obtained as functions of Laplacian eigen-spectrum as well as their fine explicit approximations using rational polynomial functions. We quantify several hard limits and fundamental tradeoffs among the risk measures, network connectivity, communication time-delay, and statistics of exogenous stochastic noise. Simultaneous presence of stochastic noise and time delay in a platoon imposes some idiosyncratic limitations on the behavior of collision and detachment risks, for instance, weakening (improving) network connectivity may result in lower (higher) levels of risk. Furthermore, a thorough risk analysis and comparison have been conducted for networks with specific graph topology. We support our theoretical findings via extensive simulations.