A novel cBN–hardened B12(C,Si,B)3–SiC composite was successfully fabricated by reactive spark plasma sintering (SPS), and its unlubricated sliding wear performance was evaluated. Powder mixtures with varying B4C:Si:cBN ratios (vol%) were consolidated under different SPS conditions, and the resulting materials were characterised microstructurally and mechanically to identify suitable processing conditions for obtaining a dense (>98%) fine-grained (<1 μm) cBN–hardened (∼33.4 GPa) B12(C,Si,B)3–SiC composite—namely, 72B4C:18Si:10cBN (vol%) SPSed at 1500 °C, with a heating rate of 200 °C/min, a dwell time of 15 min, and an applied pressure of 75 MPa. This novel composite was then tested tribologically against diamond at a 40 N load under unlubricated sliding conditions, demonstrating a threefold improvement in wear resistance (∼(2.7 ± 0.3)·107 (N·m)/mm3) relative to that of its cBN–free reference counterpart—with very mild abrasion and no evidence of plastic grooving or grain pull-out. This enhanced performance results from the cBN third phase increasing the overall hardness of the composite and promoting the formation of a more protective and lubricating oxide tribolayer. Incorporating cBN into ceramic microstructures could thus be an effective strategy to enhance hardness and tribological performance, provided that sintering conditions are sufficiently mild to prevent its transformation into hBN.
Accurate speed and range estimation is critical in modern radar and sonar systems operating under challenging conditions such as high target velocities, low Signal-to-Noise Ratios (SNRs), and Doppler-induced distortions. Traditional linear frequency-modulated (LFM) signals suffer from range-Doppler coupling and reduced correlation performance when subjected to substantial Doppler shifts. This paper presents a comprehensive analytical and simulation-based study of Dual Hyperbolic Frequency-Modulated (DHFM) signals, which combine upward and downward frequency sweeps to enable simultaneous and decoupled estimation of target speed and range. We derive closed-form expressions for the matched filter response of DHFM waveforms under Doppler scaling and develop explicit formulas for speed and range extraction from the time separation of correlation peaks. Through extensive software simulations of an airborne sonar system, we systematically evaluate the impact of three key parameters: the sweep rate (k), Signal-to-Noise Ratio (SNR), and propagation-induced attenuation. Our results demonstrate that speed estimation errors drop below 0.05 m/s for k > 5000 across target speeds of up to 100 m/s, while range estimation remains below 0.2 m accuracy even at SNR levels as low as-15 dB. Distance attenuation analysis under ISO 9613-1 atmospheric absorption models shows that both estimators remain robust up to 200 m range with moderate k values. The findings establish DHFM signals as a superior alternative to conventional LFM waveforms for applications requiring high-accuracy parameter estimation in Doppler-sensitive environments, with particular relevance to airborne and underwater sonar systems.
Research design constitutes a core component of the scientific process, as it structures the logical coherence among the theoretical framework, methodological decisions, data collection and analysis, and the interpretation of results. However, in Sport Sciences, conceptual ambiguity persists in the use of terms such as methodology, design, method, and instruments, along with a frequent lack of explicit identification of the adopted design in numerous studies. The aim of this article is to clarify the conceptual role of research design within the research process and to propose an original, comprehensive, and flexible classification specifically tailored to the field through a narrative review. To this end, the relationship among methodology, design, method, and techniques/instruments is hierarchically delineated, and an integrative framework of six broad study types is presented: methodological, theoretical, and instrumental designs, and empirical designs (quantitative, qualitative, and mixed methods). The proposal conceives design as a multidimensional and non-exclusive structure, in which different criteria can coexist and be integrated within a single study depending on the objectives, context, and analytical strategy. This approach facilitates the identification, communication, and evaluation of research design, and supports the recommendation of systematically reporting it as a specific subsection within the methods section to strengthen transparency, replicability, and research quality in Sport Sciences.
This manuscript reports the preparation, surface characterization, and modeling of chars and activated carbons obtained from avocado biomass for hydrogen storage. Activated carbons were prepared from avocado biomass via the following stages: (a) pyrolysis of avocado biomass, (b) impregnation of the avocado-based char using an aqueous lithium solution, and (c) thermal activation of lithium-loaded avocado char. The synthesis conditions of char and activated carbon samples were tailored to maximize their hydrogen adsorption properties at 77 K, where the impact of both pyrolysis and activation conditions was assessed. The hydrogen storage mechanism was discussed based on computational chemistry calculations and multilayer adsorption simulation. The modelling focuses on the analysis of the saturation of activated carbon active sites via the adsorption of multiple hydrogen molecules. The results showed that the activated carbon samples displayed adsorption capacities higher than their char counterparts by 71-91% because of the proposed activation protocol. The best activated carbon obtained from avocado residues showed a maximum hydrogen adsorption capacity of 142 cm3/g, and its storage performance can compete with other carbonaceous adsorbents reported in the literature. The hydrogen adsorption mechanism implied the formation of 2-4 layers on activated carbon surface, where physical interactions via oxygenated functionalities played a relevant role in the binding of hydrogen dimers and trimers. The results of this study contribute to the application of low-cost activated carbons from residual biomass as a storage medium in the green hydrogen supply chain.
Breast cancer remains the most common cancer among women and is linked to persistent frailty symptoms such as fatigue, falls, and dizziness, which impact survivors’ quality of life. Regular moderate or vigorous physical activity can reduce these symptoms. The aim of this research was to analyze the association between the frequency of moderate and vigorous physical activity and the presence and number of frailty symptoms in European women aged 50–85 years with a history of breast cancer. This cross-sectional study used data from Wave 9 of the Survey of Health, Ageing and Retirement in Europe (SHARE). A total of 794 women aged 50–85 with a diagnosis of breast cancer were selected. Sociodemographic, biopsychosocial, and lifestyle variables (frequency of moderate and vigorous physical activity) were analyzed. Frailty symptoms included falls, fear of falling, dizziness/fainting, and fatigue. Chi-square tests and Cramér’s V were used to assess associations between physical activity frequency and frailty symptoms. Multivariate binary logistic regression and Poisson regression were used to identify predictors of the presence of frailty and their number of frailty symptoms. A total of 61
