Low-Loss Organic Hyperbolic Materials in the Visible Spectral Range: A Joint Experimental and First-Principles Study

Hyperbolic media strengthen numerous attractive applications in optics such as super-resolution imaging, enhanced spontaneous emission, and nanoscale waveguiding. Natural hyperbolic materials exist at visible frequencies; however, implementations of these materials suffer substantial compromises resulting from the high loss in the currently available candidates. Here, the first experimental and theoretical investigation of regioregular poly(3-alkylthiophenes) (rr-P3ATs), a naturally low-loss organic hyperbolic material (OHM) in the visible frequency range, is shown. These hyperbolic properties arise from a highly ordered structure of layered electron-rich conjugated thiophene ring backbones separated by insulating alkyl side chains. The optical and electronic properties of the rr-P3AT can be tuned by controlling the degree of crystallinity and alkyl side chain length. First-principles calculations support the experimental observations, which result from the rr-P3AT's structural and optical anisotropy. Conveniently, rr-P3AT-based OHMs are facile to fabricate, flexible, and biocompatible, which may lead to tremendous new opportunities in a wide range of applications.     

Si nanocolumns as novel nanostructured supports for enzyme immobilization

Silicon nanocolumns have been used as novel supports for the high-density immobilization of enzymes. Silicon nanocolumns with diameters of ca. 50-100 nm and a height of 1 micron were constructed using glancing angle deposition. The surfaces were successively treated with 3-aminopropyltriethoxysilane (APTES) and then with an amine reactive polymer, poly(ethylene-alt-maleic anhydride), to attach soybean peroxidase (SBP) to the support. Optimal coverage of APTES, polymer, and SBP was obtained for incorporation of enzyme onto the sidewalls of the nanocolumns. SBP immobilized on the silicon nanocolumns demonstrated an enhancement in biocatalytic activity of 160% over that of the enzyme immobilized on flat silicon wafers with the same projected area. The enzymatic activity decreased with progressive washes for both supports. This decrease in the activity of enzyme was found to be primarily due to the intrinsic deactivation of immobilized enzyme on the silicon surface. Designing nanocolumns with optimal dimensions, spacing, and surface chemistry may lead to the development of high-density arrays of proteins for applications in biotechnology.     

Effect of hardness on acute toxicity of metal mixtures using Daphnia magna: prediction of acid mine drainage toxicity

In this study, the effect of hardness on the combined outcome of metal mixtures was investigated using Daphnia magna. The toxic unit (TU) was calculated using modified LC(50) values based on the hardness (i.e., LC(50-soft) and LC(50-hard)). From a bioassay test, the degree of sensitivity to hardness on the toxicity changes was in the order: Cd相似文献   

Hydroxyapatite crystallization from a highly concentrated phosphate solution using powdered converter slag as a seed material

A system for recovering phosphorus from membrane-filtrate from a sludge reduction process containing high phosphorus concentrations was developed. In this system, referred to as the completely mixed phosphorus crystallization reactor, powdered converter slag was used as a seed material. In a preliminary experiment, the optimal pH range for metastable crystallization of phosphorus from membrane-filtrate containing about 100mg/L PO(4)-P was found to be 6.6-7.0. The laboratory scale completely mixed phosphorus crystallization reactor, actually operated in pH range of 6.8-7.6 for influent 72.9 mg/L PO(4)-P, achieved an average efficiency of phosphorus removal from the membrane-filtrate of 52.4% during a 30-day experiment. Mixed-liquor suspended solids (MLSS) measurements revealed that, out of 0.24 kg PO(4)-P in the original membrane-filtrate fed into the reactor, 0.12 kg PO(4)-P was recovered on the seed particles after 30 days. X-ray diffraction (XRD) pattern and Fourier transform infrared (FT-IR) spectra of the crystalline material deposited on the seed particles showed peaks consistent with hydroxyapatite. Scanning electron micrograph (SEM) images exhibited that finely distributed crystalline material was formed on the surfaces of seed particles. Energy dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the molar composition ratio of Ca/P of the crystalline material was 1.84. The Ca/P molar ratio>1.67 for crystalline substance might result from the presence of CaCO(3) on the crystalline surfaces. A particle size distribution analysis showed that the average particle size increased from 22 microm for the original converter slag seed particles, to 94 microm after 30 days of phosphorus crystallization. Collectively, the present results suggest that the proposed phosphorus crystallization recovery system is an effective tool for recycling phosphorus from phosphate solution.     

A job shop distributed scheduling based on Lagrangian relaxation to minimise total completion time

This paper considers a distributed job shop scheduling problem where autonomous sub-production systems share common machines with each other. Each sub-production system is responsible for the scheduling of a set of jobs to minimise the total completion time on shared machines. A sub-production system has ultimate responsibility on maintaining private information such as objective function, processing time and routings on shared machines. Also sub-production systems must cooperate each other in order to achieve a global goal while sharing minimum of private information. In this research, we propose a distributed cooperation method in which sub-production systems and shared machines interact with one another to find a compromised solution between a locally optimised solution and a system-wide solution. We tested the proposed method for small, medium and large size of job shop scheduling problems and compared to a global optimal solutions. The proposed method shows promising results in terms of solution qualities and computational times.     

Microstructure characterization of fibrous HAp-(20 vol.% t-ZrO2)/Al2O3-(25 vol.% m-ZrO2) composites by multi-pass extrusion process

Core-shell structured HAp-(t-ZrO₂)/Al₂O₃-(m-ZrO₂) composites were fabricated using a multi extrusion process. The shell of Al₂O₃-(m-ZrO₂) phases was selected due to their excellent biocompatibility and mechanical properties and the core was designed with t-ZrO₂ dispersed in the HAp matrix. The t-ZrO₂ and m-ZrO₂ particles (< 400 nm) were homogeneously dispersed in the HAp and Al₂O₃ phases, respectively. In the HAp-(t-ZrO₂) core region, a heavy strain field contrast was observed due to the mismatch of their thermal expansion coefficients. The values of relative density, bending strength and Vickers hardness of the third pass fibrous HAp-(t-ZrO₂)/Al₂O₃-(m-ZrO₂) composites, which were sintered at 1400 °C, were about 93%, 169 MPa, and 792 Hv, respectively.     

Dependence of the electrical and optical properties of sputter-deposited ZnO:Ga films on the annealing temperature,time, and atmosphere

Effects of annealing process parameters such as annealing temperature, time, and atmosphere on the electrical resistivity and transmittance properties of Ga-doped ZnO (ZnO:Ga) thin films deposited on glass by rf magnetron sputtering were investigated. The electrical resistivity of a ZnO:Ga thin film is effectively decreased with increasing annealing temperature and time in a reducing atmosphere such as N₂ + 5%H₂. This is attributed to passivation of grain boundaries and zinc ions by hydrogen atoms resulting in increases in carrier concentration and mobility. Also the resistivity of 4.9 × 10⁻⁴Ω cm was obtained by annealing at 200°C for 15 h in the same atmosphere, which is not bad for a transparent conductor for solar cell applications. However, annealing at a temperature higher than 400°C is less effective. The lowest resistivity of 2.3 × 10⁻⁴Ω cm was obtained by annealing at 400°C for 1 h in an N₂ + 5%H₂ atmosphere. The optical transmittance of the ZnO:Ga film is improved by annealing regardless of the annealing atmosphere. Annealing in N₂ + 5%H₂ atmosphere widens the optical band gap, while annealing in an O₂ atmosphere makes the band gap narrower, which can be explained as a blue shift phenomenon.     

Q-factor enhancement in a one-dimensional photonic crystal cavity with embedded planar plasmonic metamaterials

We report Q-factor enhancement in a one-dimensional (1D) photonic crystal (PC) cavity by embedding electromagnetic-induced-transparency (EIT) planar plasmonic metamaterials in the cavity. Microwave experiments show tenfold Q-factor enhancements, confirming the numerical simulations. More importantly, the Q-factor enhancement is mainly due to both the longitudinal and lateral confinements contributed by the 1D PC cavity and the planar EIT metamaterials, respectively. The combined PC-EIT structure with a prominent cavity figure of merit may find new applications in nonlinear optics, cavity quantum electrodynamics, and low-threshold lasers.     

A gain-of-function of an amyotrophic lateral sclerosis-associated Cu,Zn-superoxide dismutase mutant: An enhancement of free radical formation due to a decrease in Km for hydrogen peroxide

Cu,Zn-superoxide dismutase (SOD) is known to be a locus of mutation in familial amyotrophic lateral sclerosis (FALS). Transgenic mice that express a mutant Cu,Zn-SOD, Gly-93--> Ala (G93A), have been shown to develop amyotrophic lateral sclerosis (ALS) symptoms. We cloned the FALS mutant, G93A, and wild-type cDNA of human Cu,Zn-SOD, overexpressed them in Sf9 insect cells, purified the proteins, and studied their enzymic activities for catalyzing the dismutation of superoxide anions and the generation of free radicals with H2O2 as substrate. Our results showed that both enzymes contain one copper ion per subunit and have identical dismutation activity. However, the free radical-generating function of the G93A mutant, as measured by the spin trapping method, is enhanced relative to that of the wild-type enzyme, particularly at lower H2O2 concentrations. This is due to a small, but reproducible, decrease in the value of Km for H2O2 for the G93A mutant, while the kcat is identical for both enzymes. Thus, the ALS symptoms observed in G93A transgenic mice are not caused by the reduction of Cu,Zn-SOD activity with the mutant enzyme; rather, it is induced by a gain-of-function, an enhancement of the free radical-generating function. This is consistent with the x-ray crystallographic studies showing the active channel of the FALS mutant is slightly larger than that of the wild-type enzyme; thus, it is more accessible to H2O2. This gain-of-function, in part, may provide an explanation for the association between ALS and Cu,Zn-SOD mutants.