Accurate quantification of the reflection and transmission properties of underwater acoustic absorbers is crucial for selecting effective materials in marine noise reduction applications. However, while reflection measurements in water are widely adopted, standardized and reliable methods for simultaneously determining transmission coefficients remain scarce, leaving a critical gap in underwater acoustic characterization. This paper introduces a newly developed water-filled impedance tube (WFIT) that enables simultaneous determination of acoustic reflection and transmission coefficients using only three hydrophones, providing an alternative to the conventional four-hydrophone transfer-matrix approach. The proposed system integrates the three-parameter calibration method for robust and repeatable estimation of reflection coefficients with a transfer-function-based approach for transmission coefficient evaluation. The three-hydrophone WFIT features a dual-chamber design, with the specimen positioned between a lower reflection tube and an upper transmission tube, ensuring complete submersion of the sample in water. Experimental validation was conducted using two types of materials: porous and elastic rubber. Measurements were repeated across multiple time intervals and on different days to assess system repeatability. The proposed method enables simultaneous measurement of underwater acoustic reflection, transmission, and absorption coefficients with simpler instrumentation and broader material applicability.
An efficient activation strategy for peracetic acid (PAA)-based advanced oxidation processes (AOPs) is highly desirable for environmental remediation. Herein, we report a novel CoNi alloy embedded in N-doped carbon (NCCoNi) derived from a nitrogen-rich cyano-coordination framework as an efficient heterogeneous catalyst for activating a system composed of tetraacetylethylenediamine (TAED) and sodium percarbonate (SPC), which enables the in-situ generation of PAA. The unique architecture integrates uniformly dispersed CoNi alloy nano-particles with a conductive N-doped carbon (NC) matrix. The NCCoNi catalyst exhibits significantly superior catalytic performance compared to commercial Co3O4 and NiO, NCCo, NCNi, and NC. This enhancement originates from CoNi alloying and the synergistic electronic interaction between CoNi alloy and NC, rather than surface area alone. Mechanistic investigations combining DFT calculations, EPR and electrochemical analyses reveal that the oxidation process proceeds through the combined effect of singlet oxygen (1O2), superoxide oxygen (O2 center dot-), and electron transfer pathway. As a representative azo toxicant, Orange II was employed to evaluate the system performance. Its azo linkage and adjacent aromatic carbons are identified as the primary reactive sites. Importantly, this work demonstrates the potential of CoNi alloy for SPC/TAED activation and provides a representative application of this system for azo dye degradation, offering new insights into alloy-carbon synergy for sustainable AOPs.
Repetitively pulsed vacuum arc thrusters are subjected to periodic energy deposition, and increasing the pulse repetition frequency reduces the available inter-pulse cooling time, potentially resulting in cumulative thermal loading and accelerated component degradation. This study experimentally investigates the frequency-dependent thermal response and its association with long-term discharge deterioration in a triggerless vacuum arc thruster incorporating a graphite/PTFE multilayer insulator. Long-duration tests of approximately 100,000 ignition pulses were conducted at 12.5, 25, and 50 Hz while maintaining nearly constant input energy per pulse at 56.58-57.03 mJ, thereby isolating the cumulative effect of repetition frequency. The electrical discharge characteristics, electrode-temperature evolution, net mass loss, and post-test surface degradation were systematically evaluated using voltage-current diagnostics, thermocouple measurements, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Increasing the ignition frequency substantially intensified thermal accumulation. The measured steady-state anode temperature increased from 341.59 K at 12.5 Hz to 431.75 K at 50 Hz, while the corresponding cathode temperature increased from 334.77 to 368.40 K. At 50 Hz, pronounced thermal accumulation was accompanied by a stepwise increase in breakdown voltage and substantial reductions in transferred charge, average discharge current, and discharge duration. Surface characterization further revealed increasingly severe pitting, interlayer separation, fragmentation, and deformation of the multilayer structure with increasing frequency, together with progressive fluorine depletion and increased relative carbon and copper fractions. These results demonstrate that reduced inter-pulse cooling under high-frequency operation promotes cumulative thermal loading and is strongly associated with accelerated interfacial degradation and deterioration of discharge initiation and sustainment. The findings highlight the importance of thermal-load management and structural integrity in the design and high-repetition-rate operation of pulsed vacuum arc devices.
A viscoelastic model of a material with brick-and-mortar architecture is proposed in this paper. This model can be used to simulate the uniaxial mechanical behavior of natural bone tissue and man-made bone-like materials. Using the unit cell approach and the formulation in the time domain, we derive the closed-form responses of bone and bone-like materials under different loading paths. These closed-form solutions enable us to investigate the influence of microstructures on the effective properties of the bone and bone-like materials, including the instantaneous modulus and viscosity; the asymptotic modulus and viscosity; the relaxation; the creep; the toughness; and the energy dissipation. Our study shows the different effects of the volume fraction and the aspect ratio of the inclusion. It also exhibits the effect of the staggering patterns of matrix and inclusion on the mechanical features of the bone-like material under the stress- and strain-controlled cases. This research supports the design of bone-like materials with specified performance theoretically and it also provides a foundation for future computational design of bone-like materials.
Objective The purpose of this systematic review and meta-analysis was to compare the effects of supervised versus non-supervised exercise interventions, in which both groups performed exercise training, on blood pressure reduction in individuals with hypertension and prehypertension, and to determine which exercise modalities provide the greatest benefits for clinical practice. Methods Three databases (EMBASE, MEDLINE/PubMed, and Cochrane CENTRAL) were searched from inception to July 2025. Adults with hypertension or prehypertension were included. The intervention of interest was supervised exercise training, compared with non-supervised exercise training. Primary outcomes were systolic and diastolic blood pressure. Only randomized controlled trials reporting pre- and post-intervention blood pressure outcomes were included. Mean differences and standard deviations (SDs) for systolic and diastolic blood pressure were extracted. A random-effects meta-analysis was performed, and heterogeneity was assessed using the I² statistic. Subgroup analyses were conducted by training program. Study quality was assessed using the PEDro scale. Results Eleven studies were included in the systematic review, with 10 proceeding to the meta-analysis. The included studies had an average PEDro score of 5.3±1.6, ranging from fair to good methodological quality. Interventions included continuous aerobic training, high-intensity interval training, isometric handgrip, and combined exercise. Meta-analysis showed a significant between-group difference in systolic blood pressure reduction favoring supervised exercise (mean difference = -3.46 mmHg; 95% CI: -5.94, -0.97; p = 0.006), although heterogeneity was substantial (I² = 74%), particularly during continuous aerobic training in the subgroup analysis (p = 0.003, I2 = 64%). In contrast, no significant between-group difference was observed in diastolic blood pressure reduction (mean difference = -0.99 mmHg; 95% CI: -3.38, 1.39; p = 0.41), with high heterogeneity (I² = 89%). Conclusion Supervised exercise interventions may be more effective than non-supervised programs in lowering systolic blood pressure, particularly with continuous aerobic training. However, no significant between-group differences were observed for diastolic blood pressure reduction, and the influence of supervision on diastolic blood pressure outcomes remains uncertain. These findings should be interpreted with caution due to the substantial heterogeneity and methodological limitations among the included studies.
