Micro solar energy harvesting using thin film selective absorber coating and thermoelectric generators

The use of a nanometer-scale solar selective absorber coating to enhance the performance of a thermoelectric generation (TEG) module in solar thermal energy harvesting is presented. The thin film coating is fabricated by electrochemical deposition of a bimetallic layer of tin and nickel on copper substrate. The coating has a dendrite structure with grain size of 100 nm. Testing indicates the ability of these collectors to transform incident radiation into thermal energy. The collectors utilizing the selective coating achieved a final temperature 10 °C higher than the baseline copper device. More importantly, the coating demonstrates the ability to collect and transmit over 90 % of the available heat flux. The harvested thermal energy is applied to drive a TEG module for useful power generation. The device utilized with selective absorber coating shows an output power 4.5 times more than the baseline device. Overall area of the collector plate is 16 cm².     

Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province,northwest China

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan’an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan’an Town with a total volume of about 6.06 × 10⁸ m³ are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper.     

Slope stability analysis of mine waste dumps at a mine site in Southeastern Nigeria

This paper presents results on the stability of slopes of the mine tailing dumps at Enyigba, Southeastern Nigeria. The geotechnical parameters of the slopes were investigated, and stability analysis was carried out with GeoStudio® 2012 developed by Geoslope International Limited. The slope materials were composed of gravel (1.42–30.13%), sand (15.94–33.34%), silt (9.75–26.87%) and clay (32.1–56.25%). The materials have LL, PL and PI ranging from 24 to 49%, 24 to 35% and 9 to 26% respectively, signifying low to medium plastic materials. These results agree with the soil low permeability (10⁻⁴ – 10⁻⁸ cm/s) recorded. The MDD and OMC of the material ranged from 1.86 to 2.22 g/cm³ and 13.45 to 17.05%, while cohesion and internal friction angle were recorded to be 13–34 kN/m² and 8–37° respectively; implying moderately durable materials capable of slip and shear failures. XRD confirmed the presence of swelling mineral (illite) in soil material, hinting at clay plasticity on absorption of moisture, which is one of the factors influencing all forms of mass wasting. The slopes’ computed factor of safety ranged from 0.8 to 1.33, suggesting critical to poor slope stability when exposed to landslide triggering agents. Hence, slope stabilization is required on the mine tailing dumps at Enyigba to prevent major landslide occurrence.

     

Development of bio-cemented constructional materials through microbial induced calcite precipitation

Microbial induced calcite precipitation (MICP) is an environmentally friendly technology to bond sand particle together to form sandstone like materials. In this paper, MICP-treated bio-specimen was developed through MICP. The property of bio-specimen was compared with beams or bricks made through lime modification and cement modification. Ottawa sand was used in MICP-treated bio-specimen preparation. The proportion of lime or cement was in the range of 10–40% by weight of dry sand. The four-point bending tests, brick compression tests and unconfined compression tests were conducted. The test results indicated that flexure strength of MICP-treated bio-specimen was 950 kPa which was similar to flexure strength of 20–25% cement-treated sand beams, but was much higher than flexure strength of 30% lime-treated sand beams. The brick compression strength of MICP-treated bio-specimen achieved 500 kPa, which was similar to brick compression strength of 30% lime-treated sand bricks. The unconfined compression test results showed that the unconfined compression strength (UCS) of MICP-treated bio-specimen (1300 kPa) was higher than UCS of 10% cement-treated specimen (900 kPa), and much higher than UCS of lime-treated sample (around 140 kPa). The relative uniformity of precipitated CaCO₃ distribution was achieved through the sample immersing preparation method. SEM images showed that failure pattern of MICP-treated, cement-treated and lime-treated specimens were bond-particle failure.