Low-frequency bandgaps are generally achieved by using locally resonant metamaterials at much higher wavelengths than the lattice constant. However, it remains a challenge to control wave propagation and vibration in these structures due to the limited number of conventional options available as periodic unit cell arrangements. This work investigates the band structure of flexural waves in a metamaterial sandwich beam with an hourglass lattice core using the transfer matrix method. The double dome-shaped hourglass unit cell is modelled with different non-dimensional geometric ratios. A sandwiched metamaterial beam model is then established using a periodic finite hourglass array, considered under the flexural wave propagation. The complete hourglass sandwiched system is further studied to obtain the bandgaps corresponding to the microstructure of the hourglass which is varied in the frequency domain. Subsequently, parametric analysis is performed using some specific non-dimensional geometric parameters that are found to be sensitive towards tailoring the mechanical properties of such unit cells. This study builds a foundation for modelling lightweight hourglass lattice sandwich beams with complex dome shape structures and presents guidelines for designing sandwich beams to control wave propagation.

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2-D lattice structures have gained considerable attention over the past few decades due to their high strength-to-weight ratio. Enormous studies have been conducted on various shapes of the 2D lattice structures. Different shapes of the 2-D lattices exhibit different Poisson’s ratio values. The Poisson’s ratio ranges from negative to positive values for conventional lattice structures such as honeycomb and auxetic honeycomb lattice structures. However, there exist such lattice structures that exhibit Zero Poisson’s Ratio (ZPR). In this article, we propose a novel hourglass structure (HG) that exhibits Zero Poisson’s Ratio (ZPR HG), studied dispersion behaviour, and compared with negative (Aux HG) and positive (Hcb HG) Poisson’s Ratios. The emergence of the band structure in the HG-ZPR has been studied analytically and compared with the conventional hourglass structures that exhibit positive/negative Poisson’s ratio. The dependency of the band structure on Poisson’s ratio has been investigated. A significant variation in the band structure has been observed as the microstructure of the hourglass structure varies. This study intends to provide the necessary physical insights showing the dependency of the band structure on Poisson’s ratio.

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Device aging is an important concern in nanoscale designs. Due to aging the electrical behavior of transistors embedded in an integrated circuit deviates from original intended one. This leads to performance degradation in the underlying device, and the ultimate device failure. This effect is exacerbated in emerging technologies. To be able to tailor effective aging mitigation schemes and improve the reliability of devices realized in cutting edge technologies, there is a need to accurately study the effect of aging in high performance industrial applications. According, this paper targets a high performance SRAM memory realized in 14nm FinFET technology and depicts how aging degrades the individual components of this memory as well as the interaction between them. Aging mitigation is critical not only from device reliability point of view but also regarding device security perspectives. It is essential to assure the security of the sensitive tasks performed by the security-sensitive circuits and to guarantee the security of information stored within these devices in the presence of aging. Accordingly in this paper, we also focus on aging-related security concerns and present the cases in which aging need to considered to preserve security.@en

Trailing edge serrations have been proven to work as a passive noise reduction device. Nevertheless, they have also previously been found to increase noise in a particular frequency range, argued in earlier research to be due to the misalignment of the serrations with the direction of the flow in the wake. It emerges as a high-frequency noise increase in a broadband region of the spectrum. This study investigates the effect of serration-flow misalignment on the noise emissions using acoustic beamforming, and finds a correlation with observations made on the flow using particle image velocimetry (PIV). The hydrodynamic source of the noise increase is hereby identified, and a Strouhal number relation for the high-frequency noise increase is proposed@en

We study the effect of particle cohesion on the steady state shear strength of a granular material. For cohesive powders, the steady state shear loci (termination loci) from DEM simulations are nonlinear with a peculiar pressure dependence due to the non-linear increase of contact adhesion with pressure in the contact model. Physical experiments are carried out on fine limestone powder in the direct shear box to validate the interesting non-linearity in the material behavior, as detected by the simulations and to provide a basis for calibration of DEM. In order to enhance the reproducibility, the standard test procedure from Jenike shear tester is ameliorated for the direct shear tester. Finally, the difference between the yield (transition from static to flow) and the steady state shear stress (required to maintain shear motion) will be addressed.@en

Recent studies in the assessment of risk in maritime transportation systems have used simulation-based probabilistic techniques. Amongst them are the San Francisco Bay (SFB) Ferry exposure assessment in 2002, the Washington State Ferry (WFS) Risk Assessment in 1998 and the Prince William Sound (PWS) Risk Assessment in 1996. Representing uncertainty in such simulation models is fundamental to quantifying system risk. This paper illustrates the representation of uncertainty in simulation using Bayesian techniques to model input and output uncertainty. These uncertainty representations describe system randomness as well as lack of knowledge about the system. The study of the impact of proposed ferry service expansions in San Francisco Bay is used as a case study to demonstrate the Bayesian simulation technique. Such characterization of uncertainty in simulation-based analysis provides the user with a greater level of information enabling improved decision making.@en