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The collapse potential, mineralogy, microstructure, and particle morphology of a loess from the Loess Plateau, China, were characterized by double oedometer testing, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and image analysis to elucidate the origin of its collapse behavior. Results show that the loess is highly collapsible with a maximum collapse index of 6.7% at a vertical stress of ∼200 kPa. The deposit contains both nonclay (i.e., quartz, albite, muscovite, and calcite) and clay (i.e., two chlorites) minerals. Microstructural, chemical, and image analyses indicate that interparticle calcite and clay cementation and silt particle morphology render the intact soil a metastable structure. Wetting-induced collapse is attributed to both primary and secondary microstructure features. The former is the abundance of weakly cemented, unsaturated, porous pure clay and clay–silt mixture aggregates whose slaking upon wetting initiates the overall structural collapse, while the latter consists of high porosity, unstable particle contacts, and clay coating on silt particles that act synergistically to augment the collapse. A conceptual microstructural model of a four-tiered hierarchy (i.e., primary clay and silt particles, clay aggregates and clay-coated silt particles, clay–silt mixture aggregates, and cemented aggregate matrix) is proposed to represent its structural characteristics and to account for its high collapsibility.

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A novel hybrid solar system has been designed to utilize photovoltaic (PV) cells, thermoelectric (TE) modules, and hot water (HW) through a multilayered building envelope. Water pipelines are cast within a functionally graded material layer to serve as a heat sink, allowing heat to be easily transferred into flowing water through an aluminum-rich surface, while remaining insulated by a polymer rich bottom. The theoretical energy conversion efficiency limit of the system has been investigated for documenting the potential of this hybrid solar panel design. Given the material properties of each layer, the actual energy conversion efficiency depends on the solar irradiation, ambient temperature, and water flow temperature. Compared to the traditional solar panel, this design can achieve better overall efficiencies with higher electrical power output and thermal energy utilization. Based on theoretical conversion efficiency limits, the PV/TE/HW system is superior to PV/HW and traditional PV systems with 30% higher output electrical power. However, the advantages of the PV/TE/HW system are not significant from experimental data due to the low efficiency of the bulk TE material. Thus, QW/QD TE materials are highly recommended to enhance the overall efficiency of the PV/TE/HW design. This design is general and open to new PV and TE materials with emerging nanotechnology for higher efficiencies.

A series of skeletal mechanisms was developed based on a decoupling methodology to describe the oxidation of n-alkanes from n-octane to n-hexadecane. In the decoupling methodology, a fuel oxidation mechanism is divided into two parts: one is an extremely simplified model for species with a carbon atom number larger than two to simulate the ignition characteristics of n-alkane; the other is a detailed mechanism for H2/CO/C1 to predict the concentrations of small molecules, laminar flame speed, and extinction strain rate. The new skeletal mechanism includes only 36 species and 128 reactions for each n-alkane from n-octane to n-hexadecane. The mechanism was extensively validated against the experimental data in a shock tube, jet-stirred reactor, flow reactor, counterflow flame, and premixed laminar flame. Good agreements on ignition delay, the concentrations of major species, laminar flame speed, and extinction strain rate between the predictions and measurements were obtained over wide ranges of temperature, pressure, and equivalence ratio, which demonstrates the capability of the decoupling methodology to build skeletal oxidation mechanisms for n-alkanes. Due to the compact size of the new skeletal mechanism, it can be easily integrated into the computational fluid dynamics (CFD) simulation.