We calculate the electronic and optical properties of layered oxychalcogenide (LaO)CuCh (Ch = S, Se, Te) systems by using generalized gradient approximation method based on density-functional theory. As the results, we obtain direct bandgap for Ch = S, Se, and Te of 1.67, 1.44, and 1.20 eV, respectively. We also find that valence band for each Ch element can be divided into three states, i.e., antibonding and bonding states that come from strong hybridization of Cu 3d-t2g and Ch p, and nonbonding states that come from localized Cu 3d-eg states. The local symmetry of Cu ion is distorted tetrahedral due to Jahn–Teller distortion on Cu 3d states, in which dzx and dzy are at the same energy level. Using Drude–Lorentz model, highest dielectric constants and optical dichroism are found in (LaO)CuTe, while p-type conductivity is stronger in (LaO)CuSe system. Energy levels of plasmonic states can also be tuned by changing Ch element. Our results comprehensively present the electronic properties of (LaO)CuCh systems and predict the dielectric functions and plasmonic features, which are essential for novel functional device applications.

No abstract

The role of thermal mass in indoor air-cooling during the day is a common area of study, which is particularly relevant for an era characterized by energy crises. Thermal energy storage (TES) technologies for application in rooms and buildings are not well developed. This study focuses on the use of coconut oil (co_oil) as a temperature control agent for room air conditioning systems in tropical countries such as Indonesia, given its capability to store large amounts of heat at temperatures around its melting point. Heat exchange studies between co_oil and the air environment were performed by considering three factors: Temperature difference between co_oil and the air environment, the heat absorption behavior and the release of co_oil, and the mass of co_oil required to have a significant effect. The co_oil cell sizes were formulated as responses to natural day and night air temperature profiles, while the performance of the co_oil mass for decreasing room air temperature was predicted using a thermal chamber.

The heat island phenomenon in major cities is partly due to the excessive use of concrete and brick, which causes many problems regarding thermal comfort and energy expenditure. The thermal behaviour of the envelope wall material depends on its density, heat capacity, and thermal conductivity, and its effect on the heat island intensity (HII) is reported in this paper. Experiments and simulations were carried out on the four most popular building materials: brick, aerated concrete, wood with glass-wool insulation, and glass fibre-reinforced concrete with glass-wool insulation, with each material having a dimension of 1 m × 1 m. Experiments to analyse the thermal behaviour of the wall materials were performed by exposing each material to heat radiation from 2 × 1000 W halogen lamps for 4 h, followed by 4 h of cooling. The HII simulations were carried out in a simple urban kampong in a tropical area using Energy2D software. Heat flow analyses confirmed the thermal behaviour of the four walls, which can be categorised into two types: heat storage of block wall (BW) type and heat flow inhibition of insulated sandwich wall (ISW) type. The BW type showed 0.32 °C higher indoor air temperature than the ISW type, while the HII simulation showed ISW to be 0.74 °C higher than BW; however, both types increase the intensity and need mitigation treatment. The results of this study are important for the technological approach for dealing with local warming to lower the energy expenditure of poor people in an urban area. Keywords Urban heat island • Thermal behaviour • Block wall type • Insulated sandwich wall • Urban kampong List of symbols ρ Density c Specific heat κ Thermal conductivity avg Average density c avg Average specific heat avg Average thermal conductivity T so Outer surface temperature T si Inner surface temperature T m1 Temperature of the core wall at a depth of 2.5 cm T m2 Temperature of the core wall at a depth of 7.5 cm T m3 Temperature of the core wall at a depth of 12.5 cm P so Heat flow at outer surface P m1 Heat flow at a depth of 2.5 cm P m2 Heat flow at a depth of 7.5 cm P m3 Heat flow at a depth of 12.5 cm P si Heat flow at inner surface T ao Outdoor air temperature T ai Indoor air temperature T ac Outdoor air temperature above the canopy layer

An experimental study has been conducted on the reversible magnetization of a Nd 1.85 Ce 0.15 CuO 4Ϫ␦ single crystal at various magnetic fields applied parallel to the c axis. It was found that the data analyzed following the Hao-Clem model exhibit an excellent fit to the theoretical curve for H c (T) derived from the BCS model over the relatively broad temperature range from 11.25 K to 19 K ͑slightly below the critical temperature of 21 K͒. The result of the analysis yields a constant value of 80 over the temperature range considered. Additional parameters determined in this experiment include H c2 (0)ϭ(9.0Ϯ0.8)ϫ10 5 Oe, ab (0)ϭ(19.14Ϯ1.67) Å with ab (0)ϭ(1493Ϯ131) Å in the dirty limit and H c2 (0)ϭ(6.7Ϯ0.6)ϫ10 5 Oe, ab (0)ϭ(22.22 Ϯ1.94) Å with ab (0)ϭ(1733Ϯ152) Å in the clean limit. It is further established from this experiment that the Hao-Clem model is particularly suited for the study of reversible magnetization of low-T c superconductors with relatively subdued anisotropy such as the sample considered in this study. ͓S0163-1829͑99͒02445-5͔