Unraveling the effect of hydrogenation on the mechanical properties of coiled carbon nanotubes: a molecular dynamics study.

With the increase in the utilization of nanomaterials in daily life, carbon nanostructures have received the attention of many researchers due to their special physical, chemical, and electrical properties. Chemical functionalization is one of the common methods to improve the thermomechanical properties of carbon nanomaterials used for specific applications. In this research, the effect of functionalization with hydrogen atoms on the mechanical properties of coiled carbon nanotubes with different geometrical dimensions has been examined. In addition, the mechanical properties of CCNTs with random and patterned distributions of hydrogen atoms have been investigated. The random distribution of hydrogen atoms up to 10% causes a sharp decrease in the mechanical properties of CCNTs such as the Young's modulus and spring constant, and increasing the percentage of H-coverage by more than 10% does not cause a significant effect on the mentioned properties. Also, unlike other carbon nanostructures, the stretchability of most CCNTs increases by increasing the percentage of hydrogenation beyond 30 percent. On investigating the effect of temperature on the properties of hydrogenated CCNTs, the temperature increase does not affect the Young's modulus and spring constant, and also there is no explicit relationship between their stretchability and temperature. Exploring the mechanical behavior of hydrogen-functionalized CCNTs via the tensile test and also how their mechanical properties change compared to those of pure CCNTs can help researchers in many applications.

How to characterize interfacial load transfer in spiral carbon-based nanostructure-reinforced nanocomposites: is this a geometry-dependent process?

There is a great deal of attention given to spiral carbon-based nanostructures (SCBNs) because of their unique mechanical, thermal and electrical properties along with fascinating morphology. Dispersing SCBNs inside a polymer matrix leads to extraordinary properties of nanocomposites in diverse fields. However, the role of the interfacial mechanical properties of these nanocomposites remains unknown. Here, using molecular dynamics simulations, the characteristics of interfacial load transfer of SCBN-polyethylene nanocomposites are explored. Considering the geometric characteristics of SCBNs, new insight into the separation behavior of nanoparticles in normal and sliding modes is addressed. Interestingly, the results show that the maximum force and the separation energy of the SCBNs are much larger than those of graphene because of interlocking of the coils and polymer. The heavy influence of changes in the geometric characteristics of SCBNs on the separation behavior is observed. Pullout tests reveal that the influence of parameters such as the length and number of polyethylene chains, temperature, and functionalization of the SCBNs on the interfacial mechanical properties is also significant. This study sheds new light in understanding the crucial effect of the interaction of SCBNs with polymer chains on the interfacial mechanical properties, which can lead to better performance of nanocomposites.

Hydrogenation-controlled mechanical properties in graphene helicoids: exceptional distribution-dependent behavior.

The ever-increasing development of nanotechnology has led to the creation of nanomaterials with spiral geometry such as graphene helicoids (GHs) that are mainly used for mechanical, chemical, and electrical applications. Controlling the properties of these nanomaterials with geometric changes and functionalizations is the most common and accessible task. However, functionalization leads to specific applications. In the present research, using molecular dynamics simulation, mechanical properties of pristine and functionalized GHs have been investigated for various geometries and H-coverages. Also, hydrogenation has been performed for patterned and random distributions. The random H-coverage up to 10 percent results in a decrease in the Young's modulus. Also, by increasing the percentage of H-coverage beyond 10 percent, no conspicuous alteration is observed in the Young's modulus, while the ultimate strain is reduced. By examining the effect of temperature rise on the properties of pristine and functionalized GHs, a sharp decrease in the strain range is observed for both. In addition, it has been shown that the toughness is severely reduced by decreasing the external and internal radii of pristine and functionalized GHs. Investigating the mechanical properties of pristine and hydrogenated GHs leads to better control of the mechanical properties of these nanoparticles and optimal efficiency in nano-scale devices.

Late bacterial endocarditis of an Amplatzer atrial septal device.

A 59-year-old male with an secundum atrial septal defect status post repair with an Amplatzer occluder in 2001 was admitted with sepsis and MRSA bacteremia. Transesophageal Echocardiography (TEE) showed presence of an overlying mobile echogenic structure on the left atrial surface of the device suggestive of a vegetation/infected thrombus. This is only the 3rd case description of late endocarditis involving the Amplatzer ASD closure device in an adult.

A comparison study of the efficacy and side effects of different light sources in hair removal.

Unwanted hairs are a common problem in which different light sources were developed as the treatment of choice. Alexandrite laser, diode laser, and intense pulsed light (IPL) were clinically used for this purpose with long-term scarce comparative results. The objective of the study was to compare the clinical efficacy, complications, and long-term hair reduction of alexandrite laser, diode laser, and IPL. Clinical trials on 232 persons using diode, alexandrite, laser and IPL were conducted. The number of sessions to reach optimal result varied between 3 and 7. Then the side effects were evaluated. Six months after the last session, optimal hair reduction was observed with no significant differences between the light sources, but a hair reduction was found to be higher using the diode laser. Side effects were observed with all light sources but more frequently with diode. Our findings indicate that all three light sources tested have similar effects on hair removal and in Iranian patients, using lower wavelengths minimizes the side effects.