A Brief Review on Syntheses, Structures and Applications of Nanoscrolls

Nanoscrolls are papyrus-like nanostructures which present unique properties due to their open ended morphology. These properties can be exploited in a plethora of technological applications, leading to the design of novel and interesting devices. During the past decade, significant advances in the synthesis and characterization of these structures have been made, but many challenges still remain. In this mini review we provide an overview on their history, experimental synthesis methods, basic properties and application perspectives

One-dimensional Silicon and Germanium Nanostructures With No Carbon Analogues

In this work we report new silicon and germanium tubular nanostructures with no corresponding stable carbon analogues. The electronic and mechanical properties of these new tubes were investigated through ab initio methods. Our results show that the structures have lower energy than their corresponding nanoribbon structures and are stable up to high temperatures (500 and 1000 K, for silicon and germanium tubes, respectively). Both tubes are semiconducting with small indirect band gaps, which can be significantly altered by both compressive and tensile strains. Large bandgap variations of almost 50% were observed for strain rates as small as 3%, suggesting possible applications in sensor devices. They also present high Young's modulus values (0.25 and 0.15 TPa, respectively). TEM images were simulated to help the identification of these new structures

Inorganic Graphenylene: A Porous Two-Dimensional Material With Tunable Band Gap

By means of ab initio calculations we investigate the possibility of existence of a boron nitride (BN) porous two-dimensional nanosheet which is geometrically similar to the carbon allotrope known as biphenylene carbon. The proposed structure, which we called Inorganic Graphenylene (IGP), is formed spontaneously after selective dehydrogenation of the porous Boron Nitride (BN) structure proposed by Ding et al. We study the structural and electronic properties of both porous BN and IGP and it is shown that, by selective substitution of B and N atoms with carbon atoms in these structures, the band gap can be significantly reduced, changing their behavior from insulators to semiconductors, thus opening the possibility of band gap engineering for this class of two-dimensional materials

La relación entre la imagen corporal y medidas antropométricas en adolescentes durante el período menstrual y no menstrual: un estudıo transversal.

Introduction: In recent studies, it has been suggested that anxiety about body image increases during menstruation in adolescents and may affect nutritional status. This study aimed to evaluate the relationship between adolescents' body images, body perceptions and anthropometric measurements during menstrual and non-menstrual time periods. Methods: This cross-sectional study was carried out in a private high school between September-November 2021. Participants were adolescent girls aged 14-18. The questionnaire included information about menstruation, anthropometric measurements, and the Body Cathexis Scale (BCS) and Stunkard Figure Rating Scale. Results: The mean age (total=291) was 15.9(1.13) years, body mass index (BMI) was 21.13(3.33) kg/m2, waist circumference was 70.48(8.87) cm and the BCS was 97.39(24.59). The majority of students have normal BMI. However, according to waist circumference 28.5% of the them were obese (≥ 90th percentile). Difference between actual BMIs and body image in the menstrual period was significant (p<0.001), the agreement with each other was slight (K=0.172). There was a significant difference (p<0.001) between actual BMIs and body image in the non-menstrual period and the agreement with each other was moderate (K=0.474). During non-menstrual periods, 79.7% of students with normal BMI perceived their body images as normal, and 70.5% of overweight students perceived as overweight. Conclusions: Since the menstruation is a period in which body image is perceived differently than it is, special consideration of adolescent girls in terms for eating disorders should be encouraged.Introducción: En estudios recientes, se ha sugerido que la ansiedad por la imagen corporal aumenta durante la menstruación en las adolescentes y puede afectar el estado nutricional. Este estudio tuvo como objetivo evaluar la relación entre las imágenes corporales, las percepciones corporales y las medidas antropométricas de adolescentes durante los períodos menstruales y no menstruales. Metodología: Este estudio transversal se realizó en un colegio privado entre septiembre-noviembre de 2021. Las participantes eran chicas adolescentes de 14 a 18 años. El cuestionario incluía información sobre la menstruación, las medidas antropométricas y la Escala de catexis corporal (BCS) y la Escala de calificación de la figura de Stunkard. Resultados: La edad media (total=291) fue de 15,9(1,13) años, el índice de masa corporal (IMC) de 21,13(3,33) kg/m2, el perímetro de cintura de 70,48(8,87) cm y el BCS de 97,39(24,59). La mayoría de los estudiantes tienen un IMC normal. Sin embargo, según el perímetro de cintura el 28,5% de ellas eran obesas (≥ percentil 90). La diferencia entre los IMC reales y la imagen corporal en el período menstrual fue significativa (p<0.001), la concordancia entre ellas fue leve (K=0,172). Hubo una diferencia significativa (p<0.001) entre los IMC reales y la imagen corporal en el período no menstrual y la concordancia entre ellas fue moderada (K=0,474).Durante los períodos no menstruales, el 79,7% de las estudiantes con IMC normal percibían su imagen corporal como normal y el 70,5% de las estudiantes con sobrepeso percibían sobrepeso. Conclusiones: Dado que la menstruación es un período en el que la imagen corporal se percibe diferente de lo que es, se debe fomentar la consideración especial de las adolescentes en términos de trastornos alimentarios

Mechanical Properties and Fracture Dynamics of Silicene Membranes

As graphene became one of the most important materials today, there is a renewed interest on others similar structures. One example is silicene, the silicon analogue of graphene. It share some the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair

Curved Graphene Nanoribbons: Structure and Dynamics of Carbon Nanobelts

Carbon nanoribbons (CNRs) are graphene (planar) structures with large aspect ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into spiral-like structures, i. e., carbon nanoscrolls (CNSs) with large aspect ratio. In this work we investigated the energetics and dynamical aspects of CNBs formed from rolling up CNRs. We have carried out molecular dynamics simulations using reactive empirical bond-order potentials. Our results show that similarly to CNSs, CNBs formation is dominated by two major energy contribution, the increase in the elastic energy due to the bending of the initial planar configuration (decreasing structural stability) and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers (increasing structural stability). Beyond a critical diameter value these scrolled structures can be even more stable (in terms of energy) than their equivalent planar configurations. In contrast to CNSs that require energy assisted processes (sonication, chemical reactions, etc.) to be formed, CNBs can be spontaneously formed from low temperature driven processes. Long CNBs (length of $\sim$ 30.0 nm) tend to exhibit self-folded racket-like conformations with formation dynamics very similar to the one observed for long carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled structures. Possible synthetic routes to fabricate CNBs from graphene membranes are also addressed