Mechanical characterization of nanoindented graphene via molecular dynamics simulations

The mechanical behavior of graphene under various indentation depths, velocities, and temperatures is studied using molecular dynamics analysis. The results show that the load, elastic and plastic energies, and relaxation force increased with increasing indentation depth and velocity. Nanoindentation induced pile ups and corrugations of the graphene. Resistance to deformation decreased at higher temperature. Strong adhesion caused topological defects and vacancies during the unloading process.     

Carrier dynamics and intervalley scattering in InN

The carrier cooling and the carrier relaxation of an InN thin film illuminated with two excitation energies of 1.53 and 3.06 eV were studied by an ultrafast time-resolved photoluminescence upconversion apparatus. The hot phonon effect could be accounted for longer effective phonon emission times as compared to the theoretical prediction. The rise time and the LO phonon emission time for 3.06 eV excitation were much smaller than those for 1.53 eV excitation. These differences were attributed to the intervalley scattering between the Γ₁ and Γ₃ valleys in InN when carriers were excited with the energy of 3.06 eV. The intervalley scattering times of 250 fs and 2 ps were estimated for the intervalley scattering from the Γ₁ to Γ₃ valley and the reversed scattering process, respectively.     

Numerical analyses and experiment investigations of an annular micro gas turbine power system using fuels with low heating values

This study investigates the effects of using fuels with low heating values on the performance of an annular micro gas turbine (MGT) experimentally and numerically. The MGT used in this study is MW-54, whose original fuel is liquid (Jet A1). Its fuel supply system is re-designed to use biogas fuel with low heating value (LHV). The purpose is to reduce the size of a biogas distributed power supply system and to enhance its popularization. This study assesses the practicability of using fuels with LHVs by using various mixing ratios of methane (CH₄) and carbon dioxide (CO₂). Prior to experiments, the corresponding simulations, aided by the commercial code CFD-ACE+, were carried out to investigate the cooling effect in a perforated combustion chamber and combustion behavior in an annular MGT when LHV gas was used. The main purposes are to confirm that there are no hot spots occurring in the liners and the exhaust temperatures of combustor are lower than 700°C when MGT is operated under different conditions. In experiments, fuel pressure and mass flow rate, turbine rotational speed, generator power output, and temperature distribution were measured to analyze MGT performance. Experimental results indicate that the presented MGT system operates successfully under each tested condition when the minimum heating value of the simulated fuel is approximately 50% of pure methane. The power output is around 170 W at 85000 r/min as 90% CH₄ with 10% CO₂ is used and 70 W at 60000 r/min as 70% CH₄ with 30% CO₂ is used. When a critical limit of 60% CH₄ is used, the power output is extremely low. Furthermore, the best theoretical Brayton cycle efficiency for such MGT is calculated as 23% according to the experimental data while LHV fuel is used. Finally, the numerical results and experiment results reveal that MGT performance can be improved further and the possible solutions for performance improvement are suggested for the future studies.     

Formation mechanism of microcrystalline spherical graphite particles in solidified nickel

Nickel is a well known catalyst that can readily transform carbon into graphite at high temperature. In our designed arc-discharge experiments, diamond easily dissolved in melted nickel and became small graphitic flakes. After the melted nickel had cooled and solidified, there were many microcrystalline-sized spherical graphite particles found on the nickel grain boundaries, surprisingly. It is interesting that only at the hotter area would the spherical graphite be found. This leads to our proposed forming mechanism: the spherical graphite particles were formed during the solidification of nickel. Because the temperature and solubility are high at the hotter area (zone A), the crystallization and growth of graphite became transport-controlled, instead of surface-controlled, and therefore the most common shape of the particles was spherical. This phenomenon, as far as we know, has not been previously observed.     

Evaluation of bond quality at the interface between steel bar and concrete using the small-dimension break-off test

This paper investigates the feasibility of using the small-dimension break-off test for evaluation of the bond quality at the interface between steel bar and concrete. Experimental studies were performed on bar-type concrete specimens and reinforced concrete beams. Twelve bar-type concrete specimens containing plain and deformed steel bars with different diameters were used to develop the relationship between the break-off moment and the adhesive strength at the steel bar/concrete interface. Subsequently, three reinforced concrete beams containing normal reinforcing bars, epoxy-coated reinforcing bars, and bars smeared with oil to simulate various adhesive conditions at the bar/concrete interface were used to study how the break-off moment and the bond strength were affected by the different adhesive conditions. In addition, two beam specimens containing normal reinforcing bars were vibrated severely on a self-made shaking table shortly after initial setting of concrete to simulate the bond damage in fresh reinforced concrete beams due to unexpected vibration or impact. Experimental results show that the effective break-off moment has a good correlation with the adhesive strength at the interface between steel bar and concrete. The break-off moment increases with an increase in bond strength. It is demonstrated that the small-dimension break-off test is capable of evaluating damage at the steel bar/concrete interface.     

Bilateral Testing of Nano-scale Fault-Tolerant Circuits

As the technology enters the nano dimension, the inherent unreliability of nanoelectronics is making fault-tolerant architectures increasingly necessary in building nano systems. Because fault-tolerant hardwares help to mask the effects caused by increased levels of defects, testing the functionality of the chip together with the embedded fault-tolerance becomes a tremendous challenge. In this paper, a new bilateral testing framework for nano circuits is proposed, where multiple stuck-at faults across different modules in a triple module redundancy (TMR) architecture are considered. In addition, a new test generator is presented for the bilateral testing that takes into account the enormous number of bilateral stuck-at faults possible with new types of guidance in the search, and it can generate a set of vectors that can test the TMR-based nano circuit as a single entity. Experimental results reported for ISCAS’85 and ITC99 circuits demonstrate that the bilateral testing can help to capture many more defects which the single stuck-at fault misses.     

Composite double network hydrogels with thermoresponsive colloidal nanoemulsions

We report the formulation and mechanical characterization of double network (DN) composite hydrogels. The first network consists of covalently crosslinked poly(ethylene glycol diacrylate) (PEGDA), which forms a strong, brittle network that provides elasticity to the gel. The second network, sodium alginate, is ionically crosslinked with Ca²⁺ to allow increased dissipation of mechanical energy. The novelty of this system over existing DN hydrogels is the additional incorporation of a third mesoscale network, composed of thermoresponsive poly(dimethyl siloxane) (PDMS) nanoemulsions, which undergo colloidal gelation through the bridging of the PEGDA hydrophobic end groups into the PDMS droplets. The colloidally gelled microstructures are photopolymerized into a solid hydrogel by crosslinking the precursors with ultraviolet (UV) light. Tensile mechanical experiments performed on the crosslinked DN nanoemulsion hydrogels show that their rupture stress (0.17–0.34 MPa), fracture energy (144–421 J/m²), and Young's modulus (1–2.1 MPa) are comparable to similar systems in the literature. These mechanical measurements suggest that the gels may be suitable for manufacturing processes in which large shear rates and deformations are encountered.     

Antioxidative capacity produced by Bifidobacterium‐ and Lactobacillus acidophilus‐mediated fermentations of konjac glucomannan and glucomannan oligosaccharides

BACKGROUND: Konjac glucomannan (KGM) has been shown to stimulate the growth of bifidobacteria and lactobacilli in the human and rat colon. This study investigated the antioxidative effects produced after 48 h in vitro fermentation of unhydrolysed KGM and two hydrolysed KGM fractions (KH1 and KH2 with degree of polymerisation 10 and 5 respectively) by Bifidobacterium adolescentis, B. bifidum, B. breve, B. longum and Lactobacillus acidophilus respectively. The inhibitory effect on conjugated diene formation, ferric‐chelating capacity, α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical‐scavenging ability and thiobarbituric acid‐reactive substances (TBARS) concentration produced by these fermentations were compared with those of oligofructose (OF) fermentation. RESULTS: The fermentation of KGM by each bacterial strain produced higher ferric‐chelating capacity of the culture supernatant compared with KH2 or OF fermentation. In contrast, the fermentation of KGM by each bacterial strain led to lower inhibition of conjugated diene formation and lower radical‐scavenging ability compared with KH2 fermentation. The fermentation of KH2 produced the lowest amount of TBARS. CONCLUSION: The fermentation of unhydrolysed KGM by colonic lactic acid bacteria in vitro produced antioxidative capacity mainly by preventing the initiation of ferrous ion‐induced peroxidation, whereas the fermentation of konjac oligosaccahrides did so by increasing the radical‐scavenging ability and eliminating lipid peroxide formation. Copyright © 2008 Society of Chemical Industry