Modeling the heat diffusion process in the abiotic layers of green roofs

Green roofs have been increasingly installed to alleviate some common environmental problems. The thermal benefit of living vegetation on rooftop has been extensively studied. The individual and joint contribution of the non-living green roof layers, namely soil, rockwool (water storage) and plastic drainage layers, to thermal performance of green roof has seldom been assessed. This study evaluates the insulating and cooling effects of these abiotic materials. A one-dimensional theoretical model was developed to assess the heat diffusion process in the layers. The model was validated with empirical results from three experimental plots. A calibration procedure was successfully applied to determine key model parameters. The model can capture the most critical features of temperature variations and thermal performance of common abiotic green roof materials. The appreciable water-retention capacity of rockwool plays the dual role of supplying water to the soil to enhance evaporative cooling, and increasing the specific heat capacity of the green roof. The plastic drainage sheet with ample air spaces serves as an excellent thermal insulator. The model remains robust despite seasonal and weather variabilities. Our research findings contradict with some researches in the temperate region that the thermal dissipation in green roofs with dense vegetation is lower than thermally insulated bare roofs. The theoretical model could be used to simulate the micro-environmental conditions and predict the thermal performance of different materials to improve green roof design.     

Biophysical properties and thermal performance of an intensive green roof

Green roofs have been increasingly enlisted to alleviate urban environmental problems associated with urban heat island effect and stormwater quantity and quality. Most studies focus on extensive green roofs, with inadequate assessment of the complex intensive type, subtropical region, and thermal insulation effect. This study examines the physical properties, biological processes, and thermal insulation performance of an intensive green roof through four seasons. An experimental woodland installed on a Hong Kong building rooftop was equipped with environmental sensors to monitor microclimatic and soil parameters. The excellent thermal performance of the intensive green roof is verified. Even though our site has a 100 cm thick soil to support tree growth, we found that a thin soil layer of 10 cm is sufficient to reduce heat penetration into building. Seasonal weather variations notably control transpiration and associated cooling effect. The tree canopy reduces solar radiation reaching the soil surface, but the trapped air increases air temperature near the soil surface. The substrate operates an effective heat sink to dampen temperature fluctuations. In winter, the subtropical green roof triggers notable heat loss from the substrate into the ambient air, and draws heat upwards from warmer indoor air to increase energy consumption to warm indoor air. This finding deviates from temperate latitude studies. The results offer hints to optimize the design and thermal performance of intensive green roofs.     

The Versatile 2‐Substituted Imidazoline Nucleus as a Structural Motif of Ligands Directed to the Serotonin 5‐HT1A Receptor

The involvement of the serotonin 5‐HT_1A receptor (5‐HT_1A‐R) in the antidepressant effect of allyphenyline and its analogues indicates that ligands bearing the 2‐substituted imidazoline nucleus as a structural motif interact with 5‐HT_1A‐R. Therefore, we examined the 5‐HT_1A‐R profile of several imidazoline molecules endowed with a common scaffold consisting of an aromatic moiety linked to the 2‐position of an imidazoline nucleus by a biatomic bridge. Our aim was to discover other ligands targeting 5‐HT_1A‐R and to identify the structural features favoring 5‐HT_1A‐R interaction. Structure–activity relationships, supported by modeling studies, suggested that some structural cliché such as a polar function and a methyl group in the bridge, as well as proper steric hindrance in the aromatic area of the above scaffold, favored 5‐HT_1A‐R recognition and activation. We also highlighted the potent antidepressant‐like effect (mouse forced swimming test) of (S)‐(+)‐ 19 [(S)‐(+)‐naphtyline] at very low dose (0.01 mg kg^?1). This effect was clearly mediated by 5‐HT_1A, as it was significantly reduced by pretreatment with the 5‐HT_1A antagonist WAY100635.     

Palladium‐Catalyzed and Hybrid Acids‐Assisted Synthesis of [60]Fulleroazepines in One Pot under Mild Conditions: Annulation of N‐Sulfonyl‐2‐aminobiaryls with [60]Fullerene through Sequential C‐H Bond Activation,C‐C and C‐N Bond Formation

An extraordinarily efficient hybrid acids‐assisted, palladium‐catalyzed and chelating‐group‐assisted C H bond activation of N‐sulfonyl‐2‐aminobiaryls and their annulations with [60]fullerene via sequential C C and C N bond formation at room temperature to afford [60]fulleroazepines is demonstrated. The formation of [60]fulleroazepines is highly regioselective and tolerant to both electron‐withdrawing and electron‐donating groups on the aryl moiety and the reaction gives monofunctionalized fullerenes in good yields (up to 54% isolated yield and 92% based on converted C₆₀).     

Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

ABSTRACT: Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV).PACS: 81.15.Gh.     

Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications

Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals.     

A cross‐cluster and cross‐region analysis of fashion brand extensions

To obtain sustainable growth in revenue and market share, many fashion brands deploy category extensions and line extensions. In this paper, we examine how different fashion brands in Europe, North America, and Asia execute their brand extension strategies over different periods. By classifying different fashion brands into four clusters according to different price points and fashion contents, we conduct a cross‐region and cross‐cluster analysis to examine how different fashion brands execute their brand extension strategies. Our analysis is based on publicly available data associated with 48 fashion brands over a 90‐year period. We discuss our findings along with managerial insights.     

Studies of fluorine‐containing bismaleimide resins part I: Synthesis and characteristics of model compounds

A series of fluorine‐containing bismaleimide (FBMI) monomers are synthesized by a 3‐step reaction for using as the applications of low‐k materials. The synthesized FBMI monomers are characterized by the ¹H, ¹³C, ¹⁹F nuclear magnetic resonance (NMR) spectroscopy and element analysis. These FBMI monomers react with free radical initiator or self‐cure to prepare FBMI‐polymers. All the self‐curing FBMI resins have the glass transition temperatures (T_g) in the range of 128–141°C and show the 5% weight loss temperatures (T_5%) of 235–293°C in nitrogen atmosphere. The higher heat resistance of self‐curing FBMI resin relative to FBMI‐homopolymer is due to its higher crosslinking density. The FBMI resins exhibit improved dielectric properties as compared with commercial bismaleimide (BMI) resins with the dielectric constants (D_k) lower than 2.49, which is related to the low polarizability of the C? F bond and the large free volume of CF₃ groups in the polymers. Besides, the flame retardancy of all these FBMI resins could be enhanced via the introduction of Br‐atom. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Active shunt current shaping scheme for multiple paralleled DC–DC converters

A new shunt current shaping scheme for multiple paralleled dc–dc converters is proposed in this paper. The current command for the shunt current shaper is indirectly obtained by forcing the source current to follow the demanded sinusoidal signal. The amplitude of the demanded sinusoidal source current that is in‐phase with the source voltage can be determined from the sensed load currents of the post‐stage dc–dc converters. Neither high‐order filters nor time‐consuming computations are required. The shunt current shaper supplies all the harmonics and the out‐of‐phase fundamental of the distorted input current and the power source only supplies the in‐phase fundamental component. Experimental results on a prototype system verify the feasibility of the presented scheme. The implemented shunt current shaper demonstrates an efficiency of 92% and a nearly unity power factor at the utility side. Copyright © 2011 John Wiley & Sons, Ltd.