RESUMO
Boron nitride nanotube peapods (BNNT-peapod) are composed of linear chains of C60molecules encapsulated inside BNNTs, they were first synthesized in 2003. In this work, we investigated the mechanical response and fracture dynamics of BNNT-peapods under ultrasonic velocity impacts (from 1 km s-1up to 6 km s-1) against a solid target. We carried out fully atomistic reactive molecular dynamics simulations using a reactive force field. We have considered the case of horizontal and vertical shootings. Depending on the velocity values, we observed tube bending, tube fracture, and C60ejection. Furthermore, the nanotube unzips for horizontal impacts at certain speeds, forming bi-layer nanoribbons 'incrusted' with C60molecules. The methodology used here is applicable to other nanostructures. We hope it motivates other theoretical investigations on the behavior of nanostructures at ultrasonic velocity impacts and aid in interpreting future experimental results. It should be stressed that similar experiments and simulations were carried out on carbon nanotubes trying to obtain nanodiamonds. The present study expands these investigations to include BNNT.
RESUMO
Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( n,0 and 0,n ) and/or diameters and at different temperatures (from 300 up to 1200â K). Results showed that the tubes are thermally stable (at least up to 1200â K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( 0,n ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( n,0 ). Moreover, it was obtained that Young's modulus (YMod ) (750-900â GPa) and ultimate strength (σUS ) (120-150â GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the 0,n showed a quasi-linear dependence with the temperature, the n,0 exhibited no clear trends.
RESUMO
The behavior of nanostructures under high strain-rate conditions has been the object of theoretical and experimental investigations in recent years. For instance, it has been shown that carbon and boron nitride nanotubes can be unzipped into nanoribbons at high-velocity impacts. However, the response of many nanostructures to high strain-rate conditions is still unknown. In this work, we have investigated the mechanical behavior of carbon (CNS) and boron nitride nanoscrolls (BNS) colliding against solid targets at high velocities, using fully atomistic reactive (ReaxFF) molecular dynamics (MD) simulations. CNS (BNS) are graphene (boron nitride) membranes rolled up into papyrus-like structures. Their open-ended topology leads to unique properties not found in their close-ended analogs, such as nanotubes. Our results show that collision products are mainly determined by impact velocities and by two orientation angles, which define the position of the scroll (i) axis and (ii) open edge relative to the target. Our MD results showed that for appropriate velocities and orientations, large-scale deformations and nanoscroll fractures could occur. We also observed unscrolling (scrolls going back to quasi-planar membranes), scroll unzipping into nanoribbons, and significant reconstruction due to breaking and/or formation of new chemical bonds. For particular edge orientations and velocities, conversion from open to close-ended topology is also possible, due to the fusion of nanoscroll walls.
RESUMO
Antimicrobial- and antiseptic-impregnated catheters are strategies recommended to prevent central venous catheter (CVC) colonisation. Few data regarding chlorhexidine/silver sulfadiazine-impregnated catheters in intensive care unit (ICU) patients have been reported. We performed a prospective, randomised study comparing the colonisation rates of chlorhexidine/silver sulfadiazine-impregnated CVCs (group 1) against standard CVCs (group 2). In order to assess catheter colonisation rates, a 4cm segment from the tips of aseptically removed catheters was cultured by the roll-plate method. In all, 109 patients were enrolled with successful catheter insertion, 51 of them in group 1 and 58 in group 2. There were no statistically significant differences between the two groups with regards to age, Sequential Organ Failure Assessment (SOFA) score, ICU admission diagnosis, infection risk, catheter insertion sites or catheter length of stay. The colonisation rates were 29.4% (15 catheters) for group 1 and 34.5% (20 catheters) for group 2 (P=0.50). Double-lumen CVCs impregnated with chlorhexidine and silver sulfadiazine were not effective in reducing the incidence of catheter colonisation in ICU patients.
Assuntos
Antibacterianos/farmacologia , Infecções Relacionadas a Cateter/prevenção & controle , Cateterismo , Clorexidina/farmacologia , Equipamentos e Provisões/microbiologia , Sulfadiazina de Prata/farmacologia , Idoso , Idoso de 80 Anos ou mais , Bactérias/isolamento & purificação , Feminino , Fungos/isolamento & purificação , Humanos , Unidades de Terapia Intensiva , Masculino , Pessoa de Meia-Idade , Estudos ProspectivosRESUMO
OBJECTIVE: The objective of this study was to evaluate the effects of raloxifene on the weight and epithelial thickness of the urethra of castrated female rats. METHODS: Forty castrated female rats were randomly separated into two groups: group I (control, n = 20) received only the vehicle, and group II (raloxifene, n = 20) received 750 microg/day of raloxifene for 30 days. On the 31st day, the animals were sacrificed and the urethras were removed for the study. A model for categorical data using the weighted minimum mean square error method and Student's t test were used for the data analysis (p < 0.05). RESULTS: The mean weights of the urethras in groups I and II were 22 +/- 1.6 mg and 24 +/- 1.7 mg, respectively (p = 0.371). There was an increase in the mean epithelial thickness of the distal segments in group II compared to group I (50.7 +/- 1.9 microm vs. 45.3 +/- 1.6 microm, respectively) (p < 0.04). No statistically significant difference was found in the mean epithelial thickness of the proximal urethra between the two groups (p = 0.187). CONCLUSION: Raloxifene administered to castrated female rats for 30 days increased the distal urethral epithelial thickness and did not alter the weight of the urethra.