Low Concentrations of Gold Nanoparticles as Electric Charge Carriers in Piezoelectric Cement-Based Materials.

Piezoelectric cement-based composites could serve to monitor the strain state of structural elements or act as self-powered materials in structural health monitoring (SHM) applications. The incorporation of piezoelectric materials as an active phase within cement matrices has presented a highly attractive avenue until today. However, their application is challenged by the low electrical conductivity of the hydrated cement matrix. Gold nanoparticles (Au NPs) possess substantial potential for elevating the free electrical charge within the matrix, increasing its electrical conductivity between the Au NPs and the cement matrix, thereby enhancing the piezoelectric response of the composite. In this sense, the objective of this study is to investigate the effects of incorporating low concentrations of gold nanoparticles (Au NPs) (442 and 658 ppm) on the electrical and piezoelectric properties of cement-based composites. Additionally, this study considers the effects of such properties when the material is cured under a constant electric field. Electrical impedance spectroscopy was used to evaluate the polarization resistance and piezoresistive properties of the material. Additionally, open-circuit potential measurements were taken alongside the application of mechanical loads to assess the piezoelectric activity of the composites. The findings revealed a notable decrease in the composite's total electrical resistance, reaching a value of 1.5 ± 0.2 kΩ, almost four times lower than the reference specimens. In the realm of piezoelectricity, the piezoelectric voltage parameter g33 exhibited a remarkable advancement, improving by a factor of 57 when compared to reference specimens. This significant enhancement can be attributed to both the concentration of Au NPs and the electrical curing process. In summary, the outcomes of this study underscore the feasibility of creating a highly electrically conductive cement-based matrix, using low concentrations of gold nanoparticles as electric charge carries, and indicate the possible piezoelectric behavior of the studied compposite.

Method for fabricating self-powered cement sensors based on gold nanoparticles.

Nowadays, cement industry researchers are working hard to develop cement sensors based on nanocomposites because they can be used to develop intelligent and sustainable civil structures, self-powered, self-healing, or self-monitoring. In this light, this paper shows a methodology to obtain piezoelectric cement sensors, which produce enough energy not to require an external power source in sensing-strain applications. Mainly, two proposed experimental procedures increased the piezoelectric properties of these cement-based composites: add gold nanoparticles in the proper concentrations and apply a constant electric field during the curing stage. Firstly, the gold nanoparticles were obtained through a pulsed laser ablation system, and their particle size distribution was measured with a particle analyzer Litesizer 500 from Anton Paar, and their morphology was corroborated using a scanning electron microscope. Two concentrations (442 ppm and 658 ppm) of gold nanoparticles were obtained by changing the total ablation time. Next, we fabricated the cement sensors as described by ASTM standards C39-C39M. Hence, the cement was hand mixed with a water-to-cement ratio (w/c) of 0.47 for then poured on cylindrical molds saving the proportions recommended by the ASTM standard; in this stage, the gold nanoparticles were already part of the water ratio. Then, the cement sensors were cured under an external electric field and dried for 24 hours more in an oven to be finally ready for electromechanical characterization. Meanwhile, the electric response in altern current and the piezoelectric behavior were corroborated through electrical impedance spectroscopy and open circuit potential measurements, respectively. The piezoelectric behavior was obtained when a compressive strength was applied to the sensor, and the generated voltage was simultaneously measured. Finally, the electrical and mechanical characterization measurements were processed and analyzed using Python scripts.•The particle size and the families amount of Au NPs are affected by the ablation time.•The correct proportion of Au NPs increases the inherent piezoelectricity of cement paste.•The piezoelectric response can be addressed by coupling electric and mechanical tests.

Interactional quality in middle schools: Latent profiles and their associations with teacher, classroom, and school compositional factors.

High quality teacher-student interactions are critical for the healthy social-emotional, behavioral, and academic development of middle school students. However, few studies have explored patterns of teacher-student interactions in middle school classrooms or the relation between teacher-, classroom-, and school-level factors and patterns of interaction. The current study employed latent profile analyses (LPA) to identify patterns of teacher-student interactional quality in a sample of 334 teachers from 41 schools serving middle school students within the Mid-Atlantic region of the U.S. Three distinct profiles of teacher-student interactional quality were identified that were characteristic of higher, lower, and intermediate quality and were differentially related to teacher, classroom, and school characteristics. Compared to classrooms with lower interactional quality, classrooms with "higher" or "intermediate" profiles were more likely to be taught by early career teachers, to have higher rates of observed student cooperation, and to be in schools in rural fringe areas. Classrooms with lower interactional quality were more likely to have larger student-to-teacher ratios and higher rates of student disruptive behaviors than classrooms with intermediate interactional quality and to be in schools with a higher percentage of out-of-school suspensions than classrooms with higher interactional quality. These findings suggest that interventions at the teacher, classroom, and school levels may promote positive teacher-student interactions, such as consultation to support teachers' effective classroom management, alternatives to out-of-school suspensions, and smaller student-to-teacher ratios.

Annual Research Review: Youth firearm violence disparities in the United States and implications for prevention.

OBJECTIVE: Research has identified the United States (U.S.) as a global outlier in its firearm ownership rates, with a correspondingly higher risk of youth firearm violence compared to other countries. The relative extent of disparities in youth firearm violence within the U.S. has been less clear. Little is known about factors in the social ecology driving these disparities and whether current firearm violence prevention approaches sufficiently address them. METHOD: Applying a health disparities framework, we synthesized epidemiological, sociological, and prevention science literatures, emphasizing structural inequalities in youth sociocultural positionality in life course developmental context. We also highlighted findings from national injury data and other studies regarding the magnitude and impacts of youth firearm violence disparities. RESULTS: The burden of firearm violence varied markedly at intersections of gender, race, place, developmental stage, and homicidal or suicidal intent. Firearm homicide among Black boys and young men (ages 15-24) was at outlier levels - many times greater than the rates of any other demographic group, developmental stage, or violence intent, particularly in urban settings. Recent research has operationalized structural racism and implicated historically racialized spaces as a root cause of this disparity. In contrast, elevated firearm suicide rates were found among Native and White boys and young men in rural settings; firearm-related cultural attitudes and gender socialization were points of consideration to explain these disparities. We highlighted research-based youth firearm violence preventive interventions, and emphasized gaps in efforts focused on structural and sociocultural factors. CONCLUSIONS: More explicit attention to reducing firearm homicide among Black boys and young men and firearm suicide among Native and rural White boys and young men is urgently needed and has potential to substantially lower overall rates of firearm violence in the U.S.