Search Results (292)

Spirocyclic architectures, which feature two rings sharing a single atom, are common in natural products and exhibit beneficial biological and material properties. Due to the significance of these architectures, biocatalytic dearomative spirocyclization has recently emerged as a powerful approach for constructing three-dimensional spirocyclic frameworks under mild, sustainable conditions and with exquisite stereocontrol. This review surveys the latest advances in biocatalyzed spirocyclization of all-carbon arenes (phenols and benzenes), aza-aromatics (indoles and pyrroles), and oxa-aromatics (furans). We highlight cytochrome P450s, flavin-dependent monooxygenases, multicopper oxidases, and novel metalloenzyme platforms that effect regio- and stereoselective oxidative coupling, epoxidation/semi-pinacol rearrangement, and radical-mediated cyclization to produce diverse spirocycles. Mechanistic insights gleaned from structural, computational, and isotope-labeling studies are discussed where necessary to help the readers further understand the reported reactions. Collectively, these examples demonstrate the transformative potential of biocatalysis to streamline access to spirocyclic scaffolds that are challenging to prepare through traditional methods, underscoring biocatalysis as a transformative tool for synthesizing pharmaceutically relevant spiroscaffolds while adhering to green chemistry paradigms to ultimately contribute to a cleaner and more sustainable future. Full article

To address the challenges of extracting rolling bearing degradation information and the insufficient performance of conventional convolutional networks, this paper proposes a rolling bearing degradation state identification method based on the improved monopulse feature extraction and a one-dimensional dilated residual convolutional neural network (1D-DRCNN). First, the fault pulse envelope waveform features are extracted through phase scanning and synchronous averaging, and a two-stage grid search strategy is employed to achieve FCC calibration. Subsequently, a 1D-DRCNN model is constructed to identify rolling bearing degradation states under different working conditions. The experimental study collects the vibration signals of nine degradation states, including the different sizes of inner and outer ring local faults as well as normal conditions, to comparatively analyze the proposed method’s rapid calibration capability and feature extraction quality. Furthermore, t-SNE visualization is utilized to analyze the network response to bearing degradation features. Finally, the degradation state identification performance across different network architectures is compared in pattern recognition experiments. The results show that the proposed improved feature extraction method significantly reduces the iterative calibration computational burden while effectively extracting local fault degradation information and overcoming complex working condition influence. The established 1D-DRCNN model integrates the advantages of dilated convolution and residual connections and can deeply mine sensitive features and accurately identify different bearing degradation states. The overall recognition accuracy can reach 97.33%. Full article

Tetracyclic bis-piperidine alkaloids (TcBPAs) are structurally complex natural products primarily isolated from marine sponges of the order Haplosclerida. Distinguished by their intricate architecture, TcBPAs feature two central piperidine units linked by dual macrocyclic rings. These unique structural motifs contribute significantly to their biological activities. For example, TcBPAs exhibit antiproliferative activities at low micromolar concentrations across various cancer cell lines, including leukemia, melanoma, breast, colon, fibrosarcoma, and glioblastoma. Despite this promising therapeutic profile, the structural intricacy of TcBPAs has posed considerable challenges to the development of efficient synthetic methodologies, thereby limiting comprehensive exploration and potential clinical advancement. This review highlights recent progress and persisting challenges in the synthesis, structural analysis, and biological evaluation of TcBPAs, underscoring their therapeutic potential in anticancer drug discovery. Full article

This study aims to investigate the influence of various metal compounds (ZnO, ZnCl₂, Zn(OH)₂, MgO, MgCl₂, and Mg(OH)₂) on the structural and electrochemical properties of chars derived from the pyrolysis of polyvinyl chloride (PVC). Raw PVC samples mixed with different metal compounds were firstly pyrolyzed at 500 °C in a fixed-bed reactor. The produced chars were further pyrolyzed at 800 °C. The objective was to evaluate the impact of these metal compounds on the char structure through comparative analysis. The pyrolytic chars were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. Zinc-based additives notably increased carbon yield to 32–34 wt.%, attributed to ZnCl₂-induced cross-linking. Specifically, ZnO facilitated porous architectures and aromatic structures with six or more rings. Mg-based compounds induce the formation of a highly stacked carbon structure primarily composed of crosslinked cyclic alkenes, rather than large polyaromatic domains. Upon further thermal treatment, these aliphatic-rich stacked structures can be progressively transformed into aromatic frameworks through dehydrogenation reactions at elevated temperatures. A high-surface-area porous carbon material (PVC/ZnO-800, SSA = 609.382 m² g⁻¹) was synthesized, demonstrating a specific capacitance of 306 F g⁻¹ at 1 A g⁻¹ current density. Full article

Traditional cryptographic systems face critical vulnerabilities posed by the rapid advancement of quantum computing, particularly concerning key exchange mechanisms and the quality of entropy sources for random number generation. To address these challenges, this paper proposes a multi-layered, quantum-resistant hybrid cryptographic architecture. First, to ensure robust data confidentiality and secure key establishment, the architecture employs AES-256 (Advanced Encryption Standard-256) for data encryption and utilizes the Kyber Key Encapsulation Mechanism (KEM), which is based on the Learning With Errors (LWE) problem, for secure key exchange. Second, to further bolster overall security by establishing a high-quality cryptographic foundation, we design a TRNG (true random number generator) system based on a multi-level Ring Oscillator (RO) architecture (employing 5, 7, 9, and 11 inverter stages), which provides a reliable and high-quality entropy source. Third, to enable intelligent and adaptive security management, we introduce FA-Kyber (Flow-Adaptive Kyber), a dual-trigger key exchange framework facilitating dynamic key management strategies. Experimental evaluations demonstrate that our implementation exhibits robust performance, achieving an encrypted data transmission throughput of over 550 Mbps with an average end-to-end latency of only 3.14 ms and a key exchange success rate of 99.99% under various network conditions. The system exhibits excellent stability under network congestion, maintaining 86% of baseline throughput under moderate stress, while adaptively increasing the key rotation frequency to enhance security. This comprehensive approach strikes an optimal balance between performance and post-quantum resilience for sensitive communications. Full article

A low-profile dual-polarized shared-aperture phased array antenna is proposed for Ku-band satellite communications in this paper. The stacked octagonal patches loaded with Via-rings are proposed as dual-polarized shared-aperture radiation elements, with the characteristics of wide impedance bandwidth, high gain, and weak coupling. Furthermore, innovative minimized three-port ring couplers are utilized for the differential-fed antenna array, further suppressing the cross-polarization component. Substrate integrated coaxial line (SICL) and microstrip line (MS) feed networks are employed for the excitation of transmitting band (Tx) horizontal polarization and receiving band (Rx) vertical polarization, respectively. The non-uniform subarray architecture is optimized to minimize the sidelobe levels with the reduced number of transmitter and receiver (T/R) radio frequency phase-shifting modules. As proof-of-concept examples, 16 × 24 and 32 × 24 array antennas are demonstrated and fabricated. The measured impedance bandwidths of the proposed phased array antennas are around 21.1%, while the in-band isolations are above 36.7 dB. Gains up to 29 dBi and 32.4 dBi are performed by two prototypes separately. In addition, the T/R phase-shifting modules are utilized to validate the beam-scanning characteristic, which is of value for dynamic satellite communications. Full article

This fundamental understanding of molecular structure–NLO property relationships provides critical design principles for next-generation optical limiting materials, quantum photonic devices, and ultrafast nonlinear optical switches, addressing the growing demand for high-performance organic optoelectronic materials in laser protection and photonic computing applications. In this study, it was observed that selenophene-incorporated fused D-A-D architectures exhibit a remarkable enhancement in two-photon absorption characteristics. By strategically modifying the heteroatomic composition of the Y6-derived fused-ring core, replacing thiophene (BDS) with selenophene (BDSe), the optimized system achieves unprecedented NLO performance. BDSe displays a nonlinear absorption coefficient (β) of 3.32 × 10⁻¹⁰ m/W and an effective two-photon absorption cross-section (σ_TPA) of 2428.2 GM under 532 nm with ns pulse excitation. Comprehensive characterization combining Z-scan measurements, transient absorption spectroscopy, and DFT calculations reveals that the heavy atom effect of selenium induces enhanced spin–orbit coupling, optimized intramolecular charge transfer dynamics and stabilized excited states, collectively contributing to the superior reverse saturable absorption behavior. It is believed that this molecular engineering strategy establishes critical structure–property relationships for the rational design of organic NLO materials. Full article

Terahertz reconfigurable reflectarray antennas (RRAs) hold significant promise for next-generation wireless communication systems by enabling dynamic beam control to mitigate severe path loss at high frequencies. This work presents a Complementary Metal-Oxide-Semiconductor (CMOS)-based RRA for terahertz amplitude control using tunable split-ring resonators. First, a terahertz switch in standard 65 nm CMOS process is designed, tested, and calibrated on the chip to extract the equivalent impedance, enabling precise RRA element design. Next, a reconfigurable element architecture is presented through the co-design of a split-ring radiator, control line, and a single switch. Experimental characterization demonstrates that the fabricated RRA achieves 3 dB amplitude variation at 0.290 THz with <8.5 dB element loss under 0.8 V gate bias. The measured results validate that the proposed single-switch topology effectively balances reconfigurability and loss performance in the terahertz regime. The demonstrated CMOS-compatible RRA provides a scalable solution for real-time beamforming in terahertz communication systems. Full article

Fourier Single-Pixel Imaging exhibits significant advantages over conventional imaging techniques, including high interference resistance, broad spectral adaptability, nonlocal imaging capability, and long-range detection. However, in practical applications, FSPI relies on undersampling reconstruction, which inevitably leads to ringing artifacts that degrade image quality. To enhance reconstruction performance, a Transformer-based FSPI reconstruction network is proposed. The network adopts a U-shaped architecture, composed of multiple Hybrid Self-Attention Transformer Modules and Feature Fusion Modules. The experimental results demonstrate that the proposed network achieves high-quality reconstruction at low sampling rates and outperforms traditional reconstruction methods and convolutional network-based approaches in terms of both visual appearance and image quality metrics. This method holds significant potential for high-speed single-pixel imaging applications, enabling the reconstruction of high-quality images at extremely low sampling rates. Full article

With the large-scale integration of renewable energy sources, power electronic components within power grids have surged. Traditional synchronous generator-based power generation is gradually transitioning to renewable energy generation integrated with grid-following (GFL) and grid-forming (GFM) inverters. Furthermore, power grid topology structures are evolving from traditional radial and ring-type configurations toward meshed-type architectures. The impact of grid topology structures on the stability of hybrid systems combining GFL and GFM inverters urgently requires systematic investigation. This paper establishes state-space models of GFM and GFL inverters under three typical grid topology structures and then compares the small signal stability of hybrid systems. First, mathematical models of inverters and transmission lines are established, and a full-order state-space model of the system is accordingly derived. Second, key stability indicators, including eigenvalues, damping ratio, participation factors, and sensitivity indices, are obtained by analyzing the system state matrix. Finally, simulation models for these grid topology structures are implemented in MATLAB/Simulink R2022b to validate the influences of grid topology structures on the stability related to inverters. The results demonstrate that GFL inverters are highly sensitive to grid topology structures, whereas GFM inverters are more influenced by their synchronization control capabilities. Smaller GFL inverters connection impedances and larger GFM inverters connection impedances can enhance system stability. Full article

The management of power supply and distribution is becoming increasingly challenging because of the significant increase in energy demand brought on by global population growth. Buildings are estimated to be accountable for 40% of the worldwide use of energy, which underlines how important accurate demand estimation is for the design and construction of electrical infrastructure. In this respect, transmission and distribution network planning must be adjusted to ensure a smooth transition to the National Interconnected System (NIS). A technical and analytical scientific approach to a modern neighbourhood in Ecuador called “the Nuevo Samborondón” case study (NSCS) is laid out in this article. Collecting geo-referenced data, evaluating the current electrical infrastructure, and forecasting energy demand constitute the first stages in this research procedure. The sector’s energy behaviour is accurately modelled using advanced programs such as 3D design software for modelling and drawing urban architecture along with a whole building energy simulation program and geographical information systems (GIS). For the purpose of recreating several operational situations and building the distribution infrastructure while giving priority to the current urban planning, an electrical system model is subsequently developed using power system analysis software at both levels of transmission and distribution. Furthermore, seamless digital substations are suggested as a component of the nation’s electrical infrastructure upgrade to provide redundancy and zero downtime. According to our findings, installing a 69 kV ring is a crucial step in electrifying NSCS and aligning electrical network innovations with urban planning. The system’s capacity to adjust and optimize power distribution would be strengthened provided the algorithms were given the freedom to react dynamically to changes or disruptions brought about by distributed generation sources. Full article

Analyzing network connectivity is important for evaluating the robustness, efficiency, and overall performance of various architectural designs. By examining the intricate interactions among nodes and their connections, researchers can determine a network’s resilience to failures, its capacity to support efficient information flow, and its adaptability to dynamic conditions. These insights are critical across multiple domains—such as telecommunications, computer science, biology, and social networks—where optimizing connectivity can significantly enhance functionality and reliability. In the literature, there are many variations of connectivity to measure network resilience and fault tolerance. In this survey, we focus on connectivity, tightly super connectivity, and h-extra connectivity within DVcube networks—a compound architecture combining disk-ring and hypercube-like topologies. Additionally, we identify several open problems to encourage further exploration in future research. Full article

The Ring Oscillator Physical Unclonable Function (RO-PUF) is a hardware security innovation that creates a secure and distinct identifier by utilizing the special physical properties of ring oscillators. Their unique response, low hardware overhead, and difficulty of reproduction are some of the security benefits that make them valuable in safe authentication systems. Numerous developments, such as temperature adjustment methods, aging mitigation, and better architecture and layout, have been created to increase its security, dependability, and efficiency. However, achieving the sacrifice metric makes it challenging to implement with additional complex circuits. This work focuses on stability improvement in terms of the reliability of the RO-PUF in enhanced challenge and response (CRP) by exploiting existing on-chip hard processors. This work establishes only ROs and their counters inside the chip. The built-in microprocessor performs the remaining process using the intermediary process of a Q factor and new frequency mapping. As a result, the reliability improves significantly to 95.8% compared to previous methods. The proper use of resources due to the limitation of on-chip resources has been emphasized by considering that a hard processor exists inside the new FPGA chip. Full article

This article discloses the synthesis of four new positional isomeric zwitterionic ligands exhibiting semi-flexible and flexible characteristics—n-pyridinium-1,2,3-triazole-4-carboxy-5-Acetate (n-PTCA), and n-methylpyridinium-1,2,3-triazole-4-carboxy-5-Acetate (n-MPTCA; where n = 3, 4)—which were derived from an aqueous solution of the corresponding sodium salts in an acidic medium (HCl). These compounds are successfully synthesized and characterized with FT-IR and multinuclear NMR spectroscopy; likewise, proper single crystals are obtained for each compound. All compounds adopt zwitterionic forms in the solid state, which are stabilized via intermolecular proton transfer processes involving HCl and solvent molecules. A single-crystal X-ray analysis revealed how positional isomerism and molecular flexibility influence the supramolecular topology. Specifically, 3-PTCA and 4-PTCA exhibit isomorphic hydrogen bond networks, while 3-MPTCA and 4-MPTCA display distinct packing motifs, attributed to the presence of a methylene spacer between the pyridinium and triazole rings. The Hirshfeld surface analysis quantitatively confirmed the dominance of O···H/H···O and N···H/H···N interactions in the solid-state architecture. These strong hydrogen-bonding networks are indicative of the potential proton-conductive behavior in the crystalline state, positioning these compounds as promising candidates for applications in proton-conducting materials. The structural insights gained underscore the pivotal role of molecular topology in tailoring crystal packing, with implications for the rational design of zwitterionic ligands in functional materials, including MOFs and coordination polymers. The calculated HOMO-LUMO energy gaps reveal a significant electronic variability among the ligands, influenced primarily by the positional isomerism and structural flexibility introduced by the methylene spacer. Full article

This paper extends the concept of the total graph $T_{\mathsf{\Gamma }}\left(R\right)$ associated with a commutative ring to the three-fold Cartesian product $R={\mathbb{Z}}_n\times {\mathbb{Z}}_m\times {\mathbb{Z}}_p$, where $n,m,p>1$. We present complete and self-contained proofs for a wide range of graph-theoretic properties of $T_{\mathsf{\Gamma }}\left(R\right)$, including connectivity, diameter, regularity conditions, clique and independence numbers, and exact criteria for Hamiltonicity and Eulericity. We also derive improved lower bounds for the genus and characterize the automorphism group in both general and symmetric cases. Each result is illustrated through concrete numerical examples for clarity. Beyond theoretical contributions, we discuss potential applications in cryptographic key-exchange systems, fault-tolerant network architectures, and algebraic code design. This work generalizes and deepens prior studies on two-factor total graphs, and establishes a foundational framework for future exploration of higher-dimensional total graphs over finite commutative rings. Full article