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The multi-scale mechanical characterization of nanostructured, innovative structural and functional materials, biomaterials, self-reporting and adaptive structures, hierarchically architectured systems, and miniaturized devices are intriguing due to their unusual and scale-dependent behavior. To unravel this, Smedskjaer's group[7] measured the fracture energy of six high Poisson's ratio oxide glasses, but no such relationship was observed between Poisson's ratio and fracture energy. Oxide glasses typically have a Poisson's ratio <0.3; however, the brittle-to-ductile transition that can also be seen in oxide glass is entirely unknown. Instead, they found a relation between Poisson's ratio and Young's modulus of oxide and metallic glasses. [Extracted from the article]

We consider an equal-mass quantum Toda lattice with balanced loss–gain for two and three particles. The two-particle Toda lattice is integrable, and two integrals of motion that are in involution have been found. The bound-state energy and the corresponding eigenfunctions have been obtained numerically for a few low-lying states. The three-particle quantum Toda lattice with balanced loss–gain and velocity-mediated coupling admits mixed phases of integrability and chaos depending on the value of the loss–gain parameter. We have obtained analytic expressions for two integrals of motion that are in involution. Although an analytic expression for the third integral has not been found, the numerical investigation suggests integrability below a critical value of the loss–gain strength and chaos above this critical value. The level spacing distribution changes from the Wigner–Dyson to the Poisson distribution as the loss–gain parameter passes through this critical value and approaches zero. An identical behavior is seen in terms of the gap-ratio distribution of the energy levels. The existence of mixed phases of quantum integrability and chaos in the specified ranges of the loss–gain parameter has also been confirmed independently via the study of level repulsion and complexity in higher order excited states. [ABSTRACT FROM AUTHOR]

In this work, we study the thermal evolution of the optical and electrical features of an InN thin film. By correlating photoluminescence (PL) and Hall effect results, we determine the appropriate values of the correlation parameter to be used in the empirical power law that associates the electron concentration with the linewidth of the PL spectrum, in the scope of the Burstein–Moss effect across a wide range of temperatures. Additionally, by associating Raman and PL results, we observe the thermally induced compressive strain widening of the bandgap of the InN film. Our findings demonstrate the reliability of optical methods in providing contactless measurements of electrical and structural features of semiconductors. [ABSTRACT FROM AUTHOR]

Ionizing radiation has the potential to cause operational disruptions and destroy microelectronic devices. This paper introduces and demonstrates a method of hardening microelectronic devices for sustained use in applications where exposure to ionizing radiation exists. By incorporating quantum structures below active regions of devices, gettering of charges created by ionizing radiation becomes possible. The gettering of electrons and holes forces recombination of carriers, thus eliminating photocurrent surges and trap filling which would otherwise disrupt device operation. Experimental results discussed here show a reduction in photocurrent of over two orders of magnitude when utilizing energy band engineering to create quantum structures for charge gettering. In this work, a nitride-based high electron mobility two-dimensional electron gas demonstrates the method. However, the theory utilized pertains not only to nitride-based devices, but transfers to other materials as well. [ABSTRACT FROM AUTHOR]

A set of samples containing a single ultrathin InAs layer with varying thickness from 0.5 to 1.4ML in a GaAs matrix have been grown by molecular beam epitaxy on GaAs (001) substrates at low temperatures and investigated by low-temperature photoluminescence (PL). A linear change in emission energy with InAs thickness has been experimentally observed. The PL emission line shape from InAs/GaAs heterostructures has been investigated as a function of incident optical intensity. The interplay between uncorrelated electron-hole pairs, free excitons, and localized excitons, as a function of the excitation intensity, is found to play a significant role on the optical properties of the InAs layer and is described in detail. [ABSTRACT FROM AUTHOR]

The grain–grain interface of cement, which is composed of the complex needle-shaped microstructure of calcium silicate hydrate (C-S-H), is crucial in the development of the mechanical properties of cementitious composites. These C-S-H needles grow radially outward from the grain surface. This work proposes a combined experimental and modeling approach to incorporate the finer details of these needle geometries and the distribution of mechanical properties in an interface-based multiscale mechanical model for hydrating tricalcium silicate (C3S). At micrometer and sub-micrometer length scales (<5 μm), electron microscopy images revealed that the geometrical nature of these needles at the grain interface varies with days of hydration. The mechanical properties of C-S-H at the nanoscale were observed to be higher at the inner core and reduced toward the outer product. The model developed can incorporate the details of these needle microstructures and their mechanical properties at the microscale and can predict the bulk properties of hydrated C3S at higher scales. [ABSTRACT FROM AUTHOR]

We report the effects of nitrogen (N) plasma and indium (In) flux on the In adatom adsorption/desorption kinetics on a GaN(0001) surface at the relatively high plasma-assisted molecular beam epitaxy-growth temperature of 680 °C. We experimentally demonstrate that under an active N flux, the ( 3 × 3 ) R 30 ° surface reconstruction containing In and N quickly appears and the dynamically stable In adlayers sitting on this surface exhibit a continuous change from 0 to 2 MLs as a function of In flux. Compared to the bare GaN 1 × 1 surface which is stable during In exposure without an active N flux, we observed a much faster desorption for the bottom In adlayer and the absence of an In flux window corresponding to an In coverage of 1 ML. Moreover, when the In coverage exceeds 2 MLs, the desorption rates become identical for both surfaces. Finally, the importance of In surface coverage before GaN capping was shown by growing a series of InN/GaN multiple quantum well samples. The photoluminescence data show that a consistent quantum well structure is only formed if the surface is covered by excess In droplets before GaN capping. [ABSTRACT FROM AUTHOR]

Asphalt mix design involves a number of tasks culminating in a laboratory estimation of suitable asphalt binder content which is recommended for bulk manufacture of the mix. Generally, the suitable binder content is that which on an average satisfy the specification limits. However, due to inherent material variability, there exists a possibility that all samples (or batches) of a mix designed with a suitable binder content may not always satisfy the specification requirements. The present paper aims to highlight this variability involved in the asphalt mix design process and develop a procedure to estimate the reliability of a particular mix design. This study is based on Indian specifications, where mix design, like in many other countries, is performed in accordance with Marshall method. As an example, experiments have been conducted to determine the reliability of an asphalt concrete mix. Using the same approach, reliability of asphalt mix design for any other mix and mix design procedure can be suitably derived. CE Database subject headings: Asphalts; Concrete; Mixtures; Reliability. DOI: 10.1061/(ASCE)0733-947X(2010)136:1(31)

We consider a Hamiltonian system of coupled Van der Polâ€"Duffing (VdPD) oscillators with balanced loss and gain. The system is analyzed perturbatively by using renormalization group (RG) techniques as well as multiple scale analysis (MSA). Both the methods produce identical results in the leading order of the perturbation. The RG flow equation is exactly solvable and the slow variation of amplitudes and phases in time can be computed analytically. The system is analyzed numerically and shown to admit periodic solutions in regions of parameter-space, confirming the results of the linear stability analysis and perturbation methods. The complex dynamical behavior of the system is studied in detail by using time-series, PoincarĂ©-sections, power-spectra, auto-correlation function and bifurcation diagrams. The Lyapunov exponents are computed numerically. The numerical analysis reveals chaotic behaviour in the system beyond a critical value of the parameter that couples the two VdPD oscillators through linear coupling, thereby providing yet another example of Hamiltonian chaos in a system with balanced loss and gain. Further, we modify the nonlinear terms of the model to make it a non-Hamiltonian system of coupled VdPD oscillators with balanced loss and gain. The non-Hamiltonian system is analyzed perturbatively as well as numerically and shown to posses regular periodic as well as chaotic solutions. It is seen that the P T -symmetry is not an essential requirement for the existence of regular periodic solutions in both the Hamiltonian as well as non-Hamiltonian systems. [ABSTRACT FROM AUTHOR]

Abstract: To accurately model and understand the mechanism of the evolution of microstructure during swelling, it is extremely important to model the mechanical response of smectite clay interlayers. The mechanical [...]