Search Results (332)

A comparative density functional theory (DFT) study was performed to elucidate the mechanistic details of Schiff base formation between 3-pyridinecarboxaldehyde and the three positional isomers of aminobenzoic acid (o-, m-, and p-). Both single proton transfer (SPT) and methanol-assisted double proton transfer (DPT) pathways were systematically investigated in the gas phase and within a polarizable continuum model (PCM) for methanol. All stationary points were optimized at the B3LYP/6-31G and 6-311++G(d,p) levels, and transition states were confirmed by vibrational frequency and intrinsic reaction coordinate (IRC) analyses. The results reveal that the DPT mechanism is consistently associated with significantly lower activation free energies compared to the direct SPT pathway, particularly in methanol, where solvent-mediated proton relay markedly stabilizes the transition states. The positional effect of the amino group influences both the electrostatic potential distribution and the activation barriers, with the para isomer exhibiting enhanced nucleophilicity and improved reaction efficiency. These findings provide detailed mechanistic insight into solvent-assisted proton transfer processes in Schiff base synthesis and highlight the cooperative role of hydrogen-bond networks in reducing energetic barriers. Full article

Static pre-scheduling in inland container depot (ICD)-centered drayage must coordinate tractors, detachable load units, factory loading, and port deadlines before next-day execution. Conventional order-based routing is too rigid for mixed direct haulage, drop-and-pull, relay pickup, street-turn, and buffering operations. This study proposes a task-pooling framework that decomposes logistics orders into atomic tasks and recombines them across tractors in a unified static planning space. A compact route-based MILP is used for reduced-scale calibration, and an enhanced adaptive large neighborhood search (E-ALNS) is developed around ICD-oriented relay recombination and temporal-slack shifting. On a realistic synthetic benchmark with 100 generated order records (90 active executable orders), 60 available tractors, and 330 executable tasks, the proposed method reduces the internal search-ledger value from 42,213.29 to 34,421.22 and the compact ex post blueprint value from 53,802.28 to 47,717.99 relative to the greedy construction baseline. The resulting blueprint preserves an average inter-task slack of 89.86 min and a 5th-percentile slack of 61.73 min. A generic adaptive-neighborhood baseline reaches a slightly lower ex post value of 46,722.48 only with a longer runtime and much lower temporal reserve. The results support a cost–reserve–runtime tradeoff interpretation rather than unconditional cost dominance. Full article

In this paper, we advance the concept of an electronic controller for switching devices actuated by means of direct current (DC) electromagnets. Based on the method of controlling the supply voltage delivery and disconnection moment to the drive coil, it is feasible to control switching-on and switching-off operations of an electromagnetic (EM) circuit-breaker (CB). The developed control method, built upon an ATmega328P microcontroller and operating in the Arduino IDE 2.3.4 environment, minimizes the impact of CB moving part inertia and drive coil (de)energization time. As a result, it enables contacts to be made at the near-to-zero point of the voltage waveform and contacts to break at the near-to-zero point of the current waveform. Consequently, the implementation of the proposed synchronized switching (SS) method allows the minimization of overvoltages and overcurrents during switching operations. Through continuous monitoring of the drive coil supply source parameters, the developed electronic controller allows for minimizing the impact of potential voltage fluctuations on CB switching parameters. Extensive laboratory tests confirmed the effectiveness of the proposed controller and applied method for controlling various types and sizes of EM contactors and relays. Full article

We study the cooperation for the joint unicast and multicast (JUMC) transmission system through a full-duplex (FD) decode-and-forward (DaF) mode relay and propose sub-optimal beamforming schemes for this cooperative JUMC FD relay channel. The beamforming vectors at the access point (AP) and at the full-duplex relay (FDR) are optimized with the metric based on the end-to-end information rate. The cooperation lets the user terminals (UT) outside of the direct coverage of the AP to be served by JUMC from the AP, and hence, the focus of this paper is on the sum rate resulting from the cooperation. As a reference scheme, a zero-forcing-based (ZF) beamforming algorithm is proposed, which suppresses the self-interference (SI) at the FDR perfectly. The SI at the FDR and the minimum operation for the signal-to-interference power ratios (SINR) at involved nodes of the DaF protocol are leveraged in designing and optimizing the second beamforming algorithm, which is the regularized beamforming scheme, since it allows an optimal amount of the SI at the FDR. This algorithm relies on the iterative applications of a quadratically constrained quadratic problem (QCQP) in its central part, while a few one-dimensional searches are running for the optimal SI levels for the individual rates. We consider three different scenarios depending on the existence of an FDR unicast message and the multiple UTs in the coverage of FDR for the application of the proposed algorithms, with some necessary modifications. Corroborating simulation results are presented to show the strengths and weaknesses of the proposed algorithms for the cooperative JUMC system. Full article

Cross-border e-commerce fulfillment depends on coordinated inland container movements across factories, inland container depots (ICDs), and port gateways, yet many container trucking operations still follow synchronous one-truck-one-order execution. This study models the fulfillment network as a platform-enabled socio-technical transportation system in which the ICD acts as a digital–physical coordination node for spatiotemporal decoupling. A drop–buffer–pick task architecture is developed to represent direct execution, relay execution, and delayed dispatch, and a mixed-integer linear programming (MILP) model optimizes task assignment and tractor sequencing under loading-time, port cutoff, inventory, and working-time constraints. In the certified-optimal 10-order instance, gross positive cost decreases from CNY 27,540 to CNY 19,915 (−27.7%); after applying the same post hoc coordination-credit accounting rule, net total fulfillment cost decreases to CNY 18,734 (−32.0%). The 10 orders are served with five tractors under the tested platform configuration, compared with 10 tractors under the restricted benchmark. To address sustainability explicitly, the analysis also reports distance-based emissions and energy-use proxies; the proposed schedule lowers cost and fleet deployment but increases total mileage, showing that economic efficiency and emissions performance do not automatically move together. The evidence is a deterministic baseline for later stochastic, mixed import/export, and collaborative-platform extensions. Full article

With the increasing demand for flexible electric vehicle charging and grid-interactive energy utilization, wireless power transfer (WPT) systems with high efficiency, bidirectional power flow capability, and controllable charging characteristics have attracted growing attention. However, existing WPT systems for electric vehicles still suffer from challenges including low adaptability to multiple operating modes, difficulty in achieving stable constant-current/constant-voltage output, and limited bidirectional power transfer capability under weak-coupling conditions. To address these issues, two relay-based four-coil WPT topologies, namely S-SS-LCC and LCC-SS-LCC, are proposed for electric vehicle charging and bidirectional energy transfer applications. Based on fundamental frequency analysis, frequency-domain models of the two topologies are established to reveal the relationships among resonant characteristics, output behavior, and power transfer direction. The results show that the S-SS-LCC topology can achieve constant-current and constant-voltage output in the forward grid-to-vehicle charging mode, as well as constant-voltage output in the reverse vehicle-to-grid mode. In contrast, the symmetrical LCC-SS-LCC topology can achieve bidirectional constant-current power transfer, making it suitable for vehicle-to-vehicle emergency charging scenarios. Under weak-coupling conditions (k = 0.1), the S-SS-LCC system delivers an output current of approximately 12 A at 85.2 kHz and an output voltage of about 612 V at 87.7 kHz, with a peak efficiency of 91.63%. The LCC-SS-LCC system achieves bidirectional constant-current output at 87.7 kHz with a maximum efficiency of 92.23%. Low-power experimental results further verify the predicted constant-current and constant-voltage characteristics. The proposed topologies provide a promising solution for efficient electric vehicle wireless charging and flexible bidirectional energy interaction in future smart charging systems. Full article

The fault response of inverter-based resources (IBRs) is strongly influenced by their control strategies, which may significantly change the directional information available to line relays during non-ground faults. As a result, conventional directional elements designed according to the fault characteristics of conventional power systems may exhibit poor adaptability in IBR-connected systems. In particular, zero-sequence directional elements cannot be applied to non-ground faults, whereas negative-sequence-based schemes may be adversely affected by the fault-control behavior of IBRs. To address this problem, this paper proposes a directional element for non-ground faults on AC lines in systems with IBRs. First, the positive-sequence measured impedance at the relay locations is analyzed under typical fault conditions, and the dependence of available directional information on the phase characteristic of the IBR fault current is clarified. Then, a control–protection coordinated method is introduced to regulate the fault-current phase of the IBR during faults so that stable and consistent positive-sequence directional features can be established at both line terminals. On this basis, a unified directional criterion is formulated. Finally, PSCAD/EMTDC simulations are carried out to verify the proposed method, and dynamic model experiments are conducted to validate its engineering feasibility. The results show that the proposed element correctly identifies the fault direction under both three-phase and phase-to-phase fault conditions. Additional tests considering measurement noise and opposite-side grid-strength variation further demonstrate the robustness of the proposed criterion. Compared with conventional directional elements, the proposed method improves the adaptability of non-ground fault-direction identification in IBR-connected AC lines. Full article

A two-year field experiment was conducted in Tengchong, Yunnan, to evaluate the effects of tobacco monoculture (TM) and maize relay intercropping with tobacco (TIM) on subsequent tobacco growth and the rhizosphere microenvironment. Results showed that TIM significantly increased plant height by 11.8% and maximum leaf length by 12.4% at the vigorous growth stage without reducing yield. Although leaf chloride content increased and the potassium-to-chloride ratio decreased, both remained within high-quality ranges. Relay-cropped silage maize yielded 4.86 t·hm⁻², adding 1.70 × 10⁴ CNY·hm⁻². TIM reduced nitrogen accumulation in aboveground tobacco and temporarily lowered soil organic matter and available potassium, while increasing acid phosphatase, peroxidase, and urease activities. Soil bacterial α-diversity increased, with enrichment of beneficial genera, including Candidatus Solibacter, Talaromyces, and Penicillium. Metabolomics identified 1043 metabolites, with upregulation of galactinol, N-acetyl-L-tryptophan, and 3-dehydroshikimic acid, enriched in cyanogenic amino acid and cysteine–methionine pathways. PLS-PM and Mantel analyses indicated that relay-cropped maize indirectly regulates nutrient availability via microbial and metabolic pathways. These results show that maize relay intercropping creates a soil “legacy effect,” shifting the system from direct nutrient competition to microbially mediated nutrient buffering. Full article

Conventional nucleophilic radiofluorination requires azeotropic drying to generate reactive [¹⁸F]fluoride, introducing time delays and activity losses. [¹⁸F]Fluoride relay reagents such as [¹⁸F]triflyl fluoride ([¹⁸F]TfF) and [¹⁸F]ethenesulfonyl fluoride ([¹⁸F]E=SF) have recently emerged as efficient alternatives that bypass this step. Here, we introduce [¹⁸F]ethanesulfonyl fluoride ([¹⁸F]E-SF) as a new relay reagent and benchmark its production and radiolabelling performance against [¹⁸F]TfF and [¹⁸F]E=SF. [¹⁸F]E-SF was prepared from commercially available 2,4,6-trichlorophenyl-1-ethanesulfonate (TCP-ethane) using a microlitre-scale radiofluorination approach, enabling direct distillation and SPE trapping of the product. Under optimised conditions, [¹⁸F]E-SF was obtained in 76 ± 23% RCY (n = 6), compared with 27 ± 6% (n = 2) for [¹⁸F]E=SF and up to 97 ± 2% (n = 3) for [¹⁸F]TfF using an optimised literature-based protocol. Subsequent model labelling reactions demonstrated effective aliphatic nucleophilic substitution to [¹⁸F]fluoroethyl tosylate ([¹⁸F]FEtOTs) and aromatic nucleophilic substitution to [¹⁸F]fluorobenzaldehyde with high radiochemical conversion. These results establish [¹⁸F]E-SF as a robust and operationally simple relay reagent with high production yields from a commercially available precursor. It is compatible with SPE trapping and achieves production yields comparable to [¹⁸F]E=SF and [¹⁸F]TfF, respectively, warranting future automated production for supporting the potential use of [¹⁸F]E-SF in streamlined and decentralised ¹⁸F-labelling workflows. Full article

Millimeter-wave (mmWave) unmanned aerial vehicle (UAV) networks are a promising solution for rapidly deployable backhaul systems in urban disaster scenarios, where terrestrial infrastructure may become unavailable. Although mmWave bands provide wide bandwidth for high-capacity transmission, their strong susceptibility to blockage and beam misalignment poses significant challenges in dense urban environments, particularly under UAV positional fluctuations caused by wind. This study investigates the optimization of multi-hop mmWave UAV backhaul networks with the objective of maximizing the bottleneck link capacity. A three-dimensional urban model of the Shinjuku area in Tokyo is employed, and radio propagation is evaluated using a ray-tracing-based approach considering line-of-sight (LoS) constraints and inter-link interference. Particle Swarm Optimization (PSO) is used to determine optimal UAV placements for two- to four-hop configurations. Numerical results demonstrate that multi-hop relaying combined with directional 2 × 2 patch antennas significantly improves the minimum link capacity, enabling the target backhaul capacity of approximately 9 Gbps per link under static conditions. However, capacity degradation is observed when UAV jitter is introduced due to LoS blockage and beam misalignment. To address this issue, a jitter-aware optimization method incorporating an expanded Fresnel-zone constraint is proposed. The proposed method substantially mitigates capacity degradation under realistic positional fluctuations, resulting in more robust backhaul performance. These findings demonstrate that jitter-aware placement design is essential for realizing reliable high-capacity mmWave UAV backhaul networks in dense urban disaster environments. Full article

Optimal coordination of distance and directional overcurrent relays (DR–DOCR) aims to achieve a fast, selective, and reliable protection scheme for transmission and sub-transmission systems. However, it constitutes a complex, nonlinear, and highly constrained optimization problem. In particular, single-setting DOCR characteristics used in conventional DR-DOCR coordination introduce additional challenges in lowering relay operating times while satisfying the coordination time interval (CTI) constraint. To address this issue, this paper proposes a novel DR-DOCR coordination approach that leverages a two-level DOCR characteristic. The objective is to exploit this characteristic, which partitions the relay curve into primary and backup protection regions in a highly flexible manner, thereby enabling easier avoidance of CTI violations. In addition, an enhanced variant of the red-tailed hawk algorithm, called ERTH, has been newly developed to solve this challenging problem. The proposed method is validated on versions of the 8-bus and 33-kV portion of the 30-bus power networks that have been modified to include renewable energy sources. Results demonstrate that the proposed method achieves total relay operating times of 23.681 s and 70.742 s for the 8-bus and 30-bus power systems, respectively. These values correspond to an 80.4% and 81.2% reduction compared to the conventional coordination scheme optimized by the ERTH algorithm, which yields 120.702 s and 376.757 s, respectively. Moreover, the ERTH algorithm exhibits superior performance in attaining near-global optimal solutions compared to the original RTH and other competitive optimization algorithms. In particular, for the 30-bus system under the conventional coordination scheme, the second-best result after ERTH is obtained by the teaching-learning-based optimization algorithm with a total relay operating time of 415.885 s. This indicates a 9.4% improvement achieved by ERTH (376.757 s) and a significantly higher improvement of 83% (70.742 s) achieved by the proposed strategy integrating ERTH with the two-level DOCR-based coordination scheme. Full article

With the deployment and application of the Fifth-Generation (5G) mobile communication technologies and the ongoing research and development of the Sixth-Generation (6G) mobile communication technologies, the space–air–ground–sea integrated network has become the core development vision for future communications. As aerial nodes, Unmanned Aerial Vehicles (UAVs) can be applied in a wide range of scenarios, including emergency rescue, surveying and mapping, environmental monitoring, and communication coverage enhancement. In terms of communication coverage enhancement, the space–air–ground integrated network, with UAVs as a key component, can provide seamless communication coverage for the full-domain three-dimensional space such as remote areas, deserts, and oceans. Benefiting from advantages such as low cost and high flexibility, UAVs have become a critical research focus, and the one-hop Base Station (BS)–relay UAV–slave UAV architecture for communication coverage enhancement has emerged as an important development direction. However, the high mobility and wide coverage characteristics of UAVs also pose significant synchronization challenges. Aiming at the uplink synchronization problem on the sidelink between slave UAVs and the relay UAV, a two-step random-access scheme based on Asynchronous Non-Orthogonal Multiple Access (A-NOMA) is designed to mitigate the Doppler Frequency Offset (DFO), improve access efficiency, reduce resource consumption, and accommodate the asynchrony among different users. This scheme leverages the existing preamble sequences of the Physical Random Access Channel (PRACH) and realizes DFO estimation in combination with the pairing index. On this basis, a Successive Interference Cancellation (SIC) algorithm based on DFO and phase compensation is designed to complete the demodulation of user data. For the downlink synchronization problem on the sidelink between slave UAVs and the relay UAV, the frequency offset estimation performance is improved by redesigning the resource allocation scheme of the Sidelink Synchronization Signal Block (S-SSB). Meanwhile, considering the energy constraint of UAVs, a downsampling-based detection scheme is designed to reduce UAV power consumption, and a full-link algorithm is developed to support the practical implementation of the proposed scheme. Full article

To meet the need for global coverage, space–air–ground integrated networks (SAGINs) are crucial, but the openness of wireless links makes communications vulnerable to eavesdropping. This paper investigates the physical layer security (PLS) of uplink transmissions in a cooperative dual-hop SAGIN. The system comprises a ground source with a directional antenna, an unmanned aerial vehicle (UAV) relay cluster, and a low Earth orbit (LEO) satellite. Utilizing stochastic geometry, we model the spatial randomness of terrestrial eavesdroppers and the multi-layered dual-orbital LEO destination. To combat mixed radio-frequency (RF) and free-space optical (FSO) fading, multiple relay selection and maximum ratio combining (MRC) are integrated into the UAV cluster. We analytically derive the piecewise probability density function for the FSO link distance, obtaining exact closed-form expressions for the end-to-end secrecy outage probability (SOP). Monte Carlo simulations strictly validate the derivations. The results demonstrate that while increasing available relays and antennas enhances PLS via spatial diversity, a security bottleneck restricts the RF-FSO architecture under high-transmit power regimes, generating asymptotic secrecy floors. These findings provide explicit theoretical guidelines for the secure design and parameter optimization of future SAGINs. Full article

T-connected lines are increasingly applied in hybrid DC systems due to their excellent flexibility and scalability. However, their asymmetric boundaries and the unclear physical boundaries at both ends of the LCC-side boundary element pose challenges for relay protection. To address the inability of conventional DC line protection to identify internal and external faults on the LCC side, this paper proposes an identification method based on the attenuation characteristics of electromagnetic wave energy. On this basis, a complete protection scheme for T-connected lines is proposed. The protection is initiated by the rate of voltage change of the T-connected bus; faults inside and outside the T-zone are identified by the direction of the line-mode current on the T-zone outgoing lines; and internal and external faults on the LCC side are identified by the line-mode energy ratio of electromagnetic waves at both ends of the boundary element. Additionally, the fault pole is selected by the electromagnetic wave energy change of the positive and negative poles. A simulation model of a hybrid DC system containing a T-connected line is constructed on PSCAD/EMTDC, and the effectiveness of the method for identifying internal and external faults on the LCC side and the protection scheme are verified. Full article

Multi-hop networks’ performance strongly depends on relay node placement, which affects delay, throughput, and coverage. This work introduces a dual-layer protocol combining Slotted ALOHA for node-to-relay communication and TDMA for relay-to-gateway transmission. Using a Java-based simulator, we evaluate three relay placement strategies—random, square grid, and hexagonal grid—considering metrics such as delay, throughput, packet collisions, and coverage. Results show that the hexagonal grid offers superior performance, reducing collisions, minimizing delay, and expanding coverage. A fallback mechanism for out-of-range nodes and sensitivity analysis of different backoff values are also included. The study quantifies the benefits of structured relay placement for LoRaWAN and wireless sensor networks, while also identifying challenges for realistic deployments. These findings provide guidelines for designing scalable and reliable IoT networks and highlight directions for future work involving irregular placements and dynamic routing. The simulation results are intended to provide comparative, trend-based insights under conservative modeling assumptions, rather than absolute performance predictions. Full article