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Ultraviolet (UV) radiation present in natural sunlight degrades the chemical and mechanical properties of polymeric matrices in composites. Polyurea possess a unique set of chemical and mechanical properties due to its complex microstructure comprising of hard and soft segments (phases). The primary objective of the work presented here is to characterize the chemical and mechanical degradation of pure polyurea and polyurea - polyhedral oligomeric silsesquioxane (POSS) nanocomposites subjected to UV radiation exposure for 45 days. Control specimen in as-received condition (reference specimen) and UV-aged tensile test specimen are tested in the study. Analysis of Fourier transformed infrared (FTIR) spectra for UV-aged polyurea and polyurea-POSS composites reveals that the addition of POSS nanoparticles accelerate the deterioration of polyurea matrix by breaking the hard phase network and altering the mechanism of degradation for the soft phase present in polyurea microstructure. The deterioration of hard and soft segments cause a significant reduction in tensile properties of polyurea-POSS composites. [ABSTRACT FROM AUTHOR]

The double-porosity saturated medium is widespread in the Earth's crust, rocks and man-made materials. In this paper, we developed the indirect boundary integral equation method abbreviated as IBIEM to investigate the elastic waves scattering characteristics in a fluid-saturated double-porosity half-space with an arbitrary shaped cavity inside. First, the Helmholtz decomposition was utilized to derive the 2-D Green's functions for plane waves in a double-porosity half-space under fluid saturation. Then the scattered wavefield is constructed by line sources of compressive and shear waves located at a virtual surface near the cavity surface. After the verification of numerical accuracy, the scattering of plane P 1 wave by an arbitrary shaped cavity in a 2-D fluid-saturated double-porosity half-space is solved and analysed. Numerical results show that: the displacement, hoop stress and pore pressure amplitudes are strongly dependent on incidence frequencies, porosities and boundary drainage conditions, etc. Displacement amplitudes usually reach their maximums under the dry condition, while hoop stress amplitudes obtain their peak values under the impermeable condition. The presence of matrix pore pressure and fracture pore pressure enhances the energy fluctuations of double-porosity media, which produces more complex seismic response. [ABSTRACT FROM AUTHOR]

Frenkel was a brilliant Russian physicist who made fundamental contributions to the theory of liquid, the theory of metal, the drop theory, defects in crystals, and excitons, among many other subjects in physics, astronomy, and the material sciences. In geophysics, he was the first to predict the existence of the 'second-type wave' in liquid saturated porous media. This article is a brief biography and reviews his scientific accomplishments.

In this paper we discuss teaching fluid mechanics to civil and environmental engineering majors at both the undergraduate and graduate levels. Fluid mechanics is a key course in environmental engineering that ties together the physical aspects with chemical and biological aspects. We survey the historical development of the role of fluid mechanics in environmental engineering, discuss current needs and curriculum, and point out areas for potential improvements. CE Database keywords: Fluid mechanics; Engineering education; Curricula.

The sensitivity of drawdown prediction to the uncertainty in estimating the hydraulic properties of multiple leaky aquifer systems is studied by first-order sensitivity analysis. A new set of dimensionless parameters is suggested to reduce the amount of sensitivity coefficient calculations. The procedure is illustrated for three aquifer configurations pumped by one well: one aquifer with impermeable boundaries (Theis case), one aquifer with two aquitards, and two aquifers with one aquitard. The results allow one to assess the relative contribution of uncertainty of each hydraulic property on the accuracy of predicting drawdown and to reduce the number of parameters that influence uncertainty. The methodology and results may be employed when margins of confidence of the predicted drawdown are needed.

Introduction The effective use of computers in engineering relies on the proficiency of computer languages and tools. It is generally laborious to construct advanced applications with languages such as Fortran [...]

ABSTRACT The inversion of subsurface geological structures is a crucial approach for gaining insights into the internal composition of the earth. In this paper, we propose a novel inversion method combining the nonsingular indirect boundary element method (IBEM) with the multistrategy particle swarm optimization (MSPSO) algorithm, tailored for accurately inverting 3D subsurface cavities. Leveraging the semi‐analytical nature of IBEM offers advantages such as dimensionality reduction, automatic fulfillment of radiation conditions at infinity, and high computational accuracy. Furthermore, to augment global optimization and local search capabilities, an MSPSO algorithm is introduced. Employing multiple optimization strategies enhances particle diversity, accelerates algorithm convergence, and mitigates the risk of local optima. Through the consideration of subsurface cavities with varying parameters, this method quickly identifies the approximate location of the cavity within a wide search range. The final results demonstrate that the proposed method can simultaneously and accurately invert the 3D spatial position, size, and orientation of the cavity. [ABSTRACT FROM AUTHOR]

Performance monitoring and real-time data analysis are essential tools to evaluate the integrity of infrastructure. Among other techniques, non-contact deformation measurement techniques such as satellite or drone-based methods are usually low-cost options, not requiring expensive sensors to be installed on target structures. The techniques are particularly economic for large structures such as levees, major slopes or dams. This study introduces lower bound and upper bound deformation concepts for levees. These two bounds are the deformation at which local failure is about to initiate and at which general failure is about to initiate, respectively. This study compared numerically computed lower and upper bounds deformation to field data from a full-scale loading test for a section of the levee at London Canal Avenue, New Orleans, and it showed that the two deformation criteria could be used to monitor and evaluate the integrity of levees. [ABSTRACT FROM AUTHOR]