Preventing HIV transmission in chinese internal migrants: A behavioral approach

This study is a step towards a behavioral intervention to prevent HIV transmission among Chinese internal migrants. To explore important and changeable determinants of condom use and inspect effective and feasible me

Electronic and photocatalytic properties of transition metal decorated molybdenum disulfide

Abstract This thesis is dedicated to realizations and physical understanding of electronic and photocatalytic properties after decorating transition metals to the semiconducting molybdenum disulfide. Synthesized via facile wet chemical methods, the MoS₂-Au, MoS₂-Au-Ni and MoS₂-Ag-Ni composites were formed as binary or ternary compounds. The Au nanoparticles are stably joined to the MoS₂ matrix without deteriorating layered structures of the host. After introducing the Au nanoglue as a common buffer, a metallic contact is reached between Ni and MoS₂, and attributed to new electron migration channel via MoS₂ edge contact. Adapting the Ag as the buffer element can attach the Ni to the basal plane of the MoS₂ beside edge contact. The Ni-Ag-MoS₂ composite effectively splits water under visible light irradiation and produce hydrogen. The excellent photocatalytic activity is attributed to effective charge migration through dangling bonds at the MoS2-Ag-Ni alloy interface and the activation of MoS₂ basal planes

Transition metal adsorbed-doped ZnO monolayer:2D dilute magnetic semiconductor, magnetic mechanism, and beyond 2D

Abstract As an improvement over organic or inorganic layered crystals, the synthetic monolayer ZnO(M) inherits semiconductivity and hostability from its bulk, yet it acts as a promising host for dilute magnetic semiconductors. Here, we report the electronic and magnetic properties of ZnO(M) doped with one 3d transition metal ion and simultaneously adsorbed with another 3d transition metal ion. Two sequences are studied, one where the dopant is fixed to Mn and the adsorbate is varied from Sc to Zn and another where the dopant and adsorbate are reversed. First-principles results show that the stable adsorbed−doped systems possess a lower bandgap energy than that of the host. System magnetic moments can be tuned to |5 − x|μB, where x refers to the magnetic moment of the individual 3d atom. An interplay between superexchange and direct exchange yields a ferromagnetic system dually adsorbed−doped with Mn. In addition to a novel material design route, the magnetic interaction mechanism is found beyond two dimensions, having been identified for its three-dimensional bulk and zero-dimensional cluster counterparts

Leaf-mimicking polymers for hydrophobicity and high transmission haze

Abstract Gifted with unique optical and hydrophobic properties, the plant leaves have been recently considered as micro/nanostructure prototypes for functional surface engineering. Imprinting bio-inspired structures onto surfaces can yield in similar functional properties than in the nature. In this article, we report on a simple and effective method to copy leaf surface structures onto poly-(methyl methacrylate) sheets. The replicated surface structures reduce optical reflectance and enhance optical haze. Besides, the artificial polymer sheets exhibit good hydrophobic properties. Correlation between optical haze and hydrophobicity was studied

Antireflective design of Si-based photovoltaics via biomimicking structures on black butterfly scales

Abstract The naturally evolved sunlight harvesters are not limited to foliage. Animals also harvest sunlight for light-heat conversion. A typical antireflective and light-trapping scheme has been well demonstrated on thin butterfly scales where solar energy is converted to heat besides being diffracted for surface coloration. Biomimicking scale structures offers a unique route to enhance light harvesting efficiencies happening on manmade solar cells. Herein, we performed a computational investigation of using microstructures on black butterflies for solar cell efficiency enhancement. Scale microstructures were obtained from nine species of black butterflies and employed as coating structures in numerical models built on Si-slabs. Introducing butterfly wing structures not only reduces the light reflection and transmittance but also increases the light absorption within Si-slabs. Surface reflection was decreased down to 10%, and the short-circuit current was increased by 66% correspondingly. An antireflection design strategy is given and hoped to benefit light harvesting in Si-based solar cells eventually

Tensile creep characterization and prediction of Zr-based metallic glass at high temperatures

Abstract The high temperature creep behaviors of a Zr-based bulk metallic glass (BMG) are studied by uniaxial tensile creep experiments under applied stresses of 50–180 MPa at temperatures of 660–700 K. The microstructural observations of the BMG samples after creep tests show that crystalline phases can be detected under high temperature or high applied stress. Constitutive models for predicting the high temperature creep behaviors of the studied Zr-based BMG are established based on the Ɵ projection method. The creep activation energy and stress exponent are also calculated to establish the creep model. The parameters of the established models are found to be closely associated with the applied stress and temperature. The results show an excellent agreement between the measured and predicted results, confirming the validity of the established model to accurately estimate the high temperature creep curves for the Zr-based BMG. Moreover, based on the classical diffusion creep theory, a schematic model is proposed to describe the creep behaviors of BMGs from the framework of free volume theory

Nickel nanoparticle-activated MoS₂ for efficient visible light photocatalytic hydrogen evolution

Abstract Direct sunlight-induced water splitting for photocatalytic hydrogen evolution is the dream for an ultimate clean energy source. So far, typical photocatalysts require complicated synthetic processes and barely work without additives or electrolytes. Here, we report the realization of a hydrogen evolution strategy with a novel Ni–Ag–MoS₂ ternary nanocatalyst under visible/sun light. Synthesized through an ultrasound-assisted wet method, the composite exhibits stable catalytic activity for long-term hydrogen production from both pure and natural water. A high efficiency of 73 μmol g⁻¹ W⁻¹ h⁻¹ is achieved with only a visible light source and the (MoS₂)₈₄Ag₁₀Ni₆ catalyst, matching the values of present additive-enriched photocatalysts. Verified by experimental characterizations and first-principles calculations, the enhanced photocatalytic ability is attributed to effective charge migration through the dangling bonds at the Ni–Ag–MoS₂ alloy interface and the activation of the MoS₂ basal planes

Enhanced mechanical properties and corrosion resistance by minor Gd alloying with a hot-extruded Mg alloy

Abstract The microstructure, mechanical properties, and corrosion resistance to simulated body fluid solution behavior of as-extruded Mg-1.8Zn-0.5Zr alloys with different Gd additions are investigated. It is found that dynamic recrystallization occurs in the alloys during extrusion and the grain size gradually decreases with Gd alloying. The mechanical properties and corrosion resistance to simulated body fluid of the investigated alloys enhance firstly and then weaken with the increase in Gd content. The results reveal that the Mg-1.8Zn-0.5Zr with a 1.5 wt.% Gd addition has optimized mechanical properties and corrosion resistance. A three-stage corrosion mechanism, including sequential stages from hydroxidation, phosphatization and hydroxidation, to formation-dissolution dynamic equilibrium, is proposed through electrochemical measurements and corroded surface analyses. This study reveals the extruded Mg-1.8Zn-0.5Zr-1.5Gd alloy can be regarded as a potential candidate for using as biodegradable magnesium implants

Introducing magnetism into 2D nonmagnetic inorganic layered crystals:a brief review from first-principles aspects

Abstract Pioneering explorations of the two-dimensional (2D) inorganic layered crystals (ILCs) in electronics have boosted low-dimensional materials research beyond the prototypical but semi-metallic graphene. Thanks to species variety and compositional richness, ILCs are further activated as hosting matrices to reach intrinsic magnetism due to their semiconductive natures. Herein, we briefly review the latest progresses of manipulation strategies that introduce magnetism into the nonmagnetic 2D and quasi-2D ILCs from the first-principles computational perspectives. The matrices are concerned within naturally occurring species such as MoS², MoSe², WS², BN, and synthetic monolayers such as ZnO and g-C²N. Greater attention is spent on nondestructive routes through magnetic dopant adsorption; defect engineering; and a combination of doping-absorbing methods. Along with structural stability and electric uniqueness from hosts, tailored magnetic properties are successfully introduced to low-dimensional ILCs. Different from the three-dimensional (3D) bulk or zero-dimensional (0D) cluster cases, origins of magnetism in the 2D space move past most conventional physical models. Besides magnetic interactions, geometric symmetry contributes a non-negligible impact on the magnetic properties of ILCs, and surprisingly leads to broken symmetry for magnetism. At the end of the review, we also propose possible combination routes to create 2D ILC magnetic semiconductors, tentative theoretical models based on topology for mechanical interpretations, and next-step first-principles research within the domain

Brazing Ti-48Al-2Nb-2Cr alloys with Cu-based amorphous alloy filler

Abstract In this work, the Ti-48Al-2Nb-2Cr (at. %) alloy was successfully brazed using a Cu-based amorphous filler in 600 s under varied brazing temperatures. The element diffusion, microstructure, and precipitation phase of the joints are analyzed in detail, and the formation schemes are discussed. Reaction products in the joints are found as AlCuTi, Ti2Al, α-Ti, and (Ti,Zr)2(Cu,Ni). The interfacial microstructures varied subjected to the brazing temperature, while the shear strength of the joint firstly increased, and then accordingly decreased. The maximum shear strength of 266 MPa was reached under a brazing temperature of 1213 K and a holding time of 600 s. A formation mechanism was proposed to explain the shear strength variation following the width and amount of brittle compounds in the interfacial reaction layer