Toughening in graphene ceramic composites.

The majority of work in graphene nanocomposites has focused on polymer matrices. Here we report for the first time the use of graphene to enhance the toughness of bulk silicon nitride ceramics. Ceramics are ideally suited for high-temperature applications but suffer from poor toughness. Our approach uses graphene platelets (GPL) that are homogeneously dispersed with silicon nitride particles and densified, at ∼1650 °C, using spark plasma sintering. The sintering parameters are selected to enable the GPL to survive the harsh processing environment, as confirmed by Raman spectroscopy. We find that the ceramic's fracture toughness increases by up to ∼235% (from ∼2.8 to ∼6.6 MPa·m(1/2)) at ∼1.5% GPL volume fraction. Most interestingly, novel toughening mechanisms were observed that show GPL wrapping and anchoring themselves around individual ceramic grains to resist sheet pullout. The resulting cage-like graphene structures that encapsulate the individual grains were observed to deflect propagating cracks in not just two but three dimensions.

Graphene nanoribbon composites.

It is well established that pristine multiwalled carbon nanotubes offer poor structural reinforcement in epoxy-based composites. There are several reasons for this which include reduced interfacial contact area since the outermost nanotube shields the internal tubes from the matrix, poor wetting and interfacial adhesion with the heavily cross-linked epoxy chains, and intertube slip within the concentric nanotube cylinders leading to a sword-in-sheath type failure. Here we demonstrate that unzipping such multiwalled carbon nanotubes into graphene nanoribbons results in a significant improvement in load transfer effectiveness. For example, at ∼0.3% weight fraction of nanofillers, the Young's modulus of the epoxy composite with graphene nanoribbons shows ∼30% increase compared to its multiwalled carbon nanotube counterpart. Similarly the ultimate tensile strength for graphene nanoribbons at ∼0.3% weight fraction showed ∼22% improvement compared to multiwalled carbon nanotubes at the same weight fraction of nanofillers in the composite. These results demonstrate that unzipping multiwalled carbon nanotubes into graphene nanoribbons can enable their utilization as high-performance additives for mechanical properties enhancement in composites that rival the properties of singlewalled carbon nanotube composites yet at an order of magnitude lower cost.

Three-phase textile nanocomposites: significant improvements in strength, toughness and ductility.

It is well established that in-plane tensile properties of unidirectional microfiber-reinforced composites are not significantly influenced by addition of carbon nanotubes to the matrix. This is because the principal effect of the nanotubes is to enhance the matrix dominated (out-of-plane) properties. Here we report that the above situation changes when nanotubes are incorporated into woven-fabric (textile) composites. We report up to 200% increase in strain-to-break and 180% increase in toughness under in-plane tensile load with approximately 0.05% weight of nanotube additives. We attribute this effect to the geometrical arrangement of the micro-fibers and the critical role of the pure-matrix-block in textile composites.

Enhanced mechanical properties of nanocomposites at low graphene content.

In this study, the mechanical properties of epoxy nanocomposites with graphene platelets, single-walled carbon nanotubes, and multi-walled carbon nanotube additives were compared at a nanofiller weight fraction of 0.1 +/- 0.002%. The mechanical properties measured were the Young's modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material's resistance to fatigue crack propagation. The results indicate that graphene platelets significantly out-perform carbon nanotube additives. The Young's modulus of the graphene nanocomposite was approximately 31% greater than the pristine epoxy as compared to approximately 3% increase for single-walled carbon nanotubes. The tensile strength of the baseline epoxy was enhanced by approximately 40% with graphene platelets compared to approximately 14% improvement for multi-walled carbon nanotubes. The mode I fracture toughness of the nanocomposite with graphene platelets showed approximately 53% increase over the epoxy compared to approximately 20% improvement for multi-walled carbon nanotubes. The fatigue resistance results also showed significantly different trends. While the fatigue suppression response of nanotube/epoxy composites degrades dramatically as the stress intensity factor amplitude is increased, the reverse effect is seen for graphene-based nanocomposites. The superiority of graphene platelets over carbon nanotubes in terms of mechanical properties enhancement may be related to their high specific surface area, enhanced nanofiller-matrix adhesion/interlocking arising from their wrinkled (rough) surface, as well as the two-dimensional (planar) geometry of graphene platelets.

Female sexual responses using signal processing techniques.

INTRODUCTION: An automatic algorithm for processing vaginal photoplethysmograph signals could benefit researchers investigating sexual behaviors by standardizing interlaboratory methods. Female sexual response does not co-vary consistently in the self-report and physiological domains, making the advancement of measurements difficult. Automatic processing algorithms would increase analysis efficiency. Vaginal pulse amplitude (VPA) is a method used to measure female sexual responses. However, VPA are problematic because of the movement artifacts that impinge on the signal. This article suggests a real-time approach for automatic artifact detection of VPA signals. The stochastic changes (artifacts) of VPA are characterized mathematically in this research, and a method is presented to automatically extract the frequency of interest from VPA based on the autocorrelation function and wavelet analysis. Additionally, a calculation is presented for the vaginal blood flow change rate (VBFCR) during female sexual arousal using VPA signals. AIM: The primary aim is to investigate the experimental VPA measures based on theoretical techniques. Particularly, the goal is to introduce an automatic monitoring system for female sexual behaviors, which may be helpful for experts of female sexuality. METHODS: The methods in the research are divided into experimental and theoretical parts. The VPA in twenty women was measured by a common vaginal photoplethysmography system in two conditions. Each subject was tested watching a neutral video followed by an erotic video. For theoretical analysis, an approach was applied based on wavelet transform to process the VPA. MAIN OUTCOME MEASURES: Introduction of an automatic and real-time monitoring system for female sexual behaviors, automatic movement artifact detection, VBFCR, first application of wavelet transform, and correlogram in VPA analysis. RESULTS: The natural and significant frequency information of VPA signals was extracted to automatically detect movement artifacts and to investigate the effects of erotic videos on female sexual responses. CONCLUSIONS: The computerized automatic systems based on advanced math and statistics have several advantages for human sexuality research such as: savings in time and budget; increase in the accuracy of results; and reduction in human errors for data analysis.