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.
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.
This study presents the design and thermodynamic evaluation of an integrated oxy-fuel combustion combined cycle power plant with carbon capture, enhanced by the recovery of cold energy from liquefied natural gas (LNG) regasification. The novelty of this work is the development of a plant-wide NGCC-ASU-CCS flowsheet that cascades LNG cold energy through multi-stream heat exchangers to reduce the auxiliary demand of both the cryogenic air separation unit and the CO2 compression/capture train, while maintaining realistic NGCC operating constraints. Process simulations conducted in Aspen HYSYS indicate that using LNG cold energy significantly reduces the energy consumption of both the cryogenic air separation unit and the carbon capture system, leading to improvements in the overall plant energy and exergy efficiencies of 6.3% and 8.5%, respectively. Sensitivity analyses emphasize the importance of optimizing feed-air temperature, flue gas recycle ratio, and steam cycle parameters to balance combustion stability, turbine protection, and system efficiency. The results highlight LNG cold energy integration as a promising approach to achieving net-zero carbon emissions in natural gas power generation while improving both efficiency and power output performances.
This work examines how varying hydrogen addition levels-namely 0% (D100), 10% (D90H10), 20% (D80H20), and 30% (D70H30)-to a premixed diesel-air charge influence combustion behavior and emission formation when tested in a rapid compression machine (RCM). All tests were carried out under conditions of a 423.5 K chamber temperature and a unity equivalence ratio, with the fuel blend being prepared in a premixing chamber prior to its delivery into the combustion chamber. The results indicate that increasing the hydrogen fraction leads to higher in-cylinder pressure and temperature, accompanied by a pronounced shortening of ignition delay. Compared with D100, the D70H30 case shows a 94.85% reduction in ignition delay (1145.88 ms), while the in-cylinder pressure and temperature rise markedly by 108.51% (31.4 bar) and 69.33% (964.93 K), respectively. Regarding emissions, CO levels increased markedly, rising from 0.84 vol% for D100 to 4.35 vol% for D70H30, which corresponds to more than a fivefold increase. In contrast, CO2 shows a pronounced decline as hydrogen content increases, dropping by nearly three times from 9.46 vol% to 3.25 vol%. Meanwhile, unburned hydrocarbons (UHC) emissions also intensify with hydrogen enrichment, with D70H30 exhibiting an increase of 826 ppm, equivalent to a 74.41% rise compared with D100. With increasing hydrogen content, the combustion process accelerates markedly, as evidenced by the reduction in combustion duration from 190 ms for D100 to 77.5 ms for D70H30, representing a shortening of 112.5 ms or 59.21%. Based on the above results, it can be concluded that hydrogen addition has a significant influence on both combustion characteristics and exhaust emissions. These findings deepen the understanding of hydrogen-assisted combustion and establish a useful reference dataset for combustion kinetics and emission analysis in diesel-hydrogen systems, while also supporting the validation of existing kinetic models under RCM conditions. Moreover, the results highlight hydrogen as a practical near-term decarbonization option without requiring major engine design modifications and simultaneously improving ignition behavior. Collectively, this work lays a basis for dual-fuel engine development and for determining appropriate hydrogen blending levels in future applications.
