Changes of fluorescent spectral features after successive rare earth doping of gadolinium oxide powders

We present a complex fluorescence study of a series of gadolinium oxide polycrystalline powders singly, doubly and triply doped with trivalent rare earth ions (Er³⁺, Tb³⁺, and Dy³⁺), to explore a possibility of their use as materials for white light emitting diodes. The excitation and luminescence spectra along with the decay kinetics were measured in the temperature range from 6 to 300 K. The luminescence efficiency was studied within the visible spectral range, i.e. −400 nm to 750 nm under excitation by 355 nm third harmonic Nd:YAG laser pulses. Singly doped Er³⁺ sample gave stronger luminescence signals, but others showed significantly larger decay lifetimes. The successive rare earths doping leads to substantial changes of the spectral positions due to the up-conversion processes. In the singly (Er³⁺) doped sample, following the time resolved spectrum and decay curves, there are two different types of emissions: at 660 nm and at shorter wavelengths (below 640 nm) the red emission's lifetime is ten times longer than at shorter wavelengths. The singly doped sample shows unclear temperature-dependence of luminescence with lifetime at 550 nm (the longest at 100 K, similarly at 6 K and 300 K) and achieved luminous efficacy 73.5 lm/W.     

A Mixture Toxicity Study Employing Binary Combinations Of Dinitrobenzene And Trinitrobenzene Using The Bioluminescent Marine Bacterium Vibrio Harveyi As The Test Organism

A combination mixture study was conducted with two organic compounds, dinitrobenzene and trinitrobenzene, using the marine bioluminescent bacterium Vibrio harveyi . This assay employs the photogenic properties of this organism for determination of toxicity in a direct procedure. Evaluation of toxicity was performed using an additive index methodology, mixture toxicity index and graphic representations. Graphic representations employed were isobole plot and isobologram, both isopleths. The additive index procedure employed both chemicals at their estimated median effective concentration (EC 50 ) for determination of a toxicity value. Isopleths employed combinations of both chemicals, using an equitoxic concentration, at 20% intervals of their EC 50 . An additive index value for this mixture was statistically antagonistic. Mixture toxicity index suggests that these chemical in various combinations are antagonistic. Combinations for both isopleths were similar and exhibited additivity for three mixture values and statistical synergism for one mixture. Statistical analysis of combinations using the z test found some mixtures to be statistically different. This analysis, in part, supports findings for isopleths. These results suggest that different mixtures of the two chemicals may have different interaction outcomes.     

增强现实技术于洪水风险沟通中的应用

气候变迁,特别是洪水问题给地处三角洲的城市带来了与日俱增的风险。作为应对手段,提出一种整合性的洪水风险管理方法,该方法确保了洪水风险沟通在洪水风险管理战略中的重要地位。洪水的可视化作为洪水风险沟通的一种工具,在改变人们对洪水风险的观念方面有着强大的作用。它可以通过互动的方式,使当地的利益相关者了解洪水的剩余风险和未来风险。其中增强现实技术作为一种可视化手段,它的快速发展与应用为风景园林设计、规划与教育等领域提供了崭新的交互方式。首先,探讨增强现实技术(AR)在洪水风险沟通中的应用现状,并重点关注增强现实技术的2个关键应用领域:对现场决策的支持和针对高层次设计的可视化与对景观干预的评估。随后,展示一种基于增强现实技术所开发的应用,该款创新性的应用为洪水风险沟通提供了一种轻量化的可视化手段。     

Structure and magnetic properties of carbon encapsulated Fe nanoparticles obtained by arc plasma and combustion synthesis

Carbon encapsulated Fe nanoparticles were obtained using two methods: arc plasma and combustion synthesis. These powders were characterized by the following methods: SQUID magnetization measurements, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The last two methods showed that Fe nanoparticles, obtained by both techniques belong to metallic and/or carbide phases, and are partially encapsulated by graphitic carbon. The particles had 10-100 nm in diameter, and were covered by carbon 5-15 nm thick layers. The transmission Mössbauer spectra revealed two magnetic and two paramagnetic components. In the plasma samples the largest part of iron was contained in the carbide phase while in the combustion samples the bcc α-Fe encompassed most of iron. The combustion sample has much higher content of carbon, indicating that the Fe particles were not covered by graphite layer totally, and were dissolved in the etching process. The dominant portion of combustion samples was not vaporized, thus the iron phase solidified from the liquid. The plasma-arc samples were synthesized via dual mechanism: growth of nanocrystals from the vapor phase (carbide) and solidification of the liquid micro-droplets in the cold zone (α-Fe and γ-Fe).     

Carbon-encapsulated magnetic nanoparticles as separable and mobile sorbents of heavy metal ions from aqueous solutions

Carbon-encapsulated magnetic nanoparticles (CEMNPs) are studied as mobile sorbents for removal of heavy metal ions (Cu²⁺, Co²⁺, Cd²⁺) from aqueous solutions. The ion uptakes achieve 95% for cadmium and copper. CEMNPs-based sorbents also have excellent adsorption capacities (between 1.23 and 3.21 mg/g), which are considerably higher than the capacities of activated carbons (between 0.37 and 0.39 mg/g).     

Mechanical Properties of Partially Dense Alumina Produced from Powder Compacts

The elastic modulus ( E ), the critical strain energy release rate ( G _c), and the flexural strength (σ) have been determined for two partially dense alumina bodies produced from the same powder but with different initial densities. The mechanical properties were measured for specimens fabricated at four different relative densities. The measured elastic modulus, critical strain energy release rate, and a calculated critical stress intensity factor ( K _c) were observed to be linearly related to (ρ–ρ₀)/(1 –ρ₀), where ρ is the current relative density and ρ₀ is the initial relative density of the powder compact. With the observed linear relations for E, G _c (or K _c), and the assumption that the crack length responsible for failure was present in the initial powder compact and shrunk in proportion to the relative density change, a Griffith equation was constructed to estimate the strength at any relative density. This relation was in good agreement with measurements.