Variation of the photoluminescence and vacuum ultraviolet excitation characteristics of BaZr(BO3)2:Eu3+ by the incorporation of Al3+, La3+, or Y3+ into the lattice

The photoluminescence (PL) and vacuum ultraviolet (VUV) excitation properties are studied for the BaZr(BO₃)₂:Eu³⁺ phosphor with incorporating the Al³⁺, La³⁺, or Y³⁺ ion into the lattice. The excitation spectrum shows an absorption band in the VUV region with the band-edge at 200 nm and a very weak charge transfer band of Eu³⁺ at about 226 nm. The luminescence spectrum shows a strong emission at 615 nm (⁵D₀ → ⁷F₂ transition) and weak emission at 594 nm (⁵D₀ → ⁷F₁ transition) in BaZr(BO₃)₂:Eu³⁺, with a good red color purity. The PL intensity is increased by incorporating Al³⁺ into the BaZr(BO₃)₂ lattice. The PL intensity has also increased by incorporating La³⁺ into the lattice, however, the red color purity has deteriorated because of the increased centrosymmetric nature of the site. With the incorporation of Y³⁺ into the BaZr(BO₃)₂ lattice, the PL characteristics of the Eu³⁺ activator resembles that in the YBO₃ lattices. The intensity of the red PL for the Eu³⁺ activator is the highest with good color purity for BaZr(BO₃)₂:Eu³⁺ incorporated with both Al³⁺ (10%) and La³⁺ (0.5%).     

Rare earth elements in CO_2-fluid inclusions in mantle Iherzolite

Trace elements including REE (Rare Earth Elements) in fluid inclusions in Iherzolite, olivine, orthopyroxene, and clinopyroxene have been determined by heating-decrepitation and ICP-MS (Element Type Inductively Coupled Plasma-Mass Spectrometry) method. Normalized CO2 fluid/chondrite data show that mantle fluids are rich in REEs, especially LREEs (Light Rare Earth Elements), several times or dozen times higher than mantle rocks and mantle minerals. There are close relationships among the REE data of olivine, orthopyroxene, clinopyroxene and 1herzolite. Compared to the data of chemical dissolution method, it is believed that REE data obtained from heating-decrepitation and ICP-MS technique are contributed by CO2 fluid inclusions. About 60% (mass fraction) of tiny inclusions are observed not to be decrepitated above 1000℃, so REE data obtained are only contributed by decrepitated inclusions. Mantle fluids rich in LREE play an important role in mantle metasomatism, partial melting and mineralization.     

Response of seasonal vegetation development to climatic variations in eastern central Asia

Meteorological records show that central Asia has experienced one of the strongest warming signals in the world over the last 30 years. The objective of this study was to examine the seasonal vegetation response to the recent climatic variation on the Mongolian steppes, the third largest grassland in the world. The onset date of green-up for central Asia was estimated using time-series analysis of advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) biweekly composite data collected between January 1982 and December 1991. Monthly precipitation and mean temperature data (1982-1990) were acquired from 19 meteorological stations throughout the grasslands of the eastern Mongolian steppes in China. Our results showed that while the taiga forest north of the Mongolian steppes (>50°N) experienced an earlier onset of green-up during the study period, a later onset was observed at the eastern and northern edges of the Gobi Desert (40°N-50°N). Responses of different vegetation types to climatic variability appeared to vary with vegetation characteristics and spring soil moisture availability of specific sites. Plant stress caused by drought was the most significant contributor to later vegetation green-up as observed from satellite imagery over the desert steppe. Areas with greater seasonal soil moisture greened up earlier in the growing season. Our results suggested that water budget limitations determine the pattern of vegetation responses to atmospheric warming.     

北极涛动对华北沙尘暴频次的影响

This study has investigated the influence of Arctic Oscillation (AO) on dust storm frequency in North China in spring seasons during 1961-2007. There is a significant linkagebetween dust storm frequency and AO; a negative (positive) AO phase is related to an in-creased (decreased) dust storm frequency in North China. This relationship is closely related to changes in the cold air activity in Mongolia. The cold air activity exerts large impacts on the dust storm frequency; the frequency of cold air activity over Mongolia not only positively cor-relates with the dust storm frequency in North China, but also shows a long-term decreasing trend that is an important reason for the long-term decreasing of dust storm frequency in North China. The AO has large influence on the frequency of cold air activity over Mongolia; a negative (positive) AO phase is highly related to an increased (decreased) frequency of cold air activity over Mongolia, which results in an increased (decreased) dust storm frequency in North China.     

Modeling of Mirex Loadings to the Bottom Sediments of Lake Ontario within the Niagara River Plume

A mathematical model was used to reproduce the observed Mirex concentrations in the bottom sediment within the Niagara River plume in Lake Ontario. Mirex inputs to the sediments were estimated with an optimization technique using historical concentration records; two bottom sediment scenarios were explored, one with no resuspension of sediments, and one with sediment resuspension. Results show that over 34 years a minimum of 8.74 mg of Mirex were deposited over a square metre, but that as much as 12.3–18.7 mg of Mirex might have sedimented before being partially resuspended. This analysis permits an estimation of past Mirex loadings to Lake Ontario, assuming that a constant amount of Mirex in the water column sedimented in the plume. The computed loadings are 28 kg for 1980, compared with a previous estimate of 5–25 kg to a maximum of about 200 kg per year in 1960–1962. Knowledge of the inputs, followed by a good in-lake data base including contaminant concentrations in sediments at different stations, are key factors in the success of models dealing with trace contaminants.     

Catalyst selection for the synthesis of methylpyrazine

An exploratory research programme on catalysts for the cyclisation of a diamine and a glycol to methylpyrazine is described. More than 80 preparations were tested in standard conditions. The best results were obtained with a mixture of ZnO/Zn-chromite, promoted with a few wt % Pd salt, when working at 640–700 K, atmospheric pressure and in presence of excess steam. Under such conditions, up to 60 mol % selectivity was obtained at over 90% conversion. The aged catalyst was easily regenerable, by simple oxidation of the carbonaceous deposits in flowing air.     

Gleichgewichtselektrodepotentiale von MeO2Hx(yH2O)-elektroden—I. Thermodynamik

Non-stoichiometric oxides of the general formula MeO₂H_x (yH₂O) in contact with aqueous electrolytes are discussed with regard to different equilibria between solid and liquid phase. Corresponding relations for the equilibrium electrode potential ε are derived.If the equilibria with respect to H⁺ and Me²⁺ ions and H₂O) are established at the same time, the value of ε is determined if two of the three variables pH, aα_Me²⁺ (activity of the Me²⁺ ions in the electrolyte) and x are given. As one further result of the thermodynamic treatment relations between differential changes of ε and of the composition of the solution are obtained. Discussing the pH dependence of the electrode potential it is shown that (∂ε/∂pH)aα_Me²⁺ increases with increasing value of x.This of particular importance for oxides with large stoichiometric width, eg manganese dioxide.Finally it is shown that the ratio between the activities of hydrogen and metal in the oxide is given by the corresponding ratio of hydrogen ions and metal ions in the solution.     

Thermal model for a hybrid cryostat

To maximize the hold time of a 2 dm³ 4 K helium cryostat, a system has been designed and built which makes use of a closed cycle refrigerator for cooling the radiation shields. The optimization of this so-called hybrid cryostat has been simplified by the use of a thermal model. The properties of a number of models have been obtained from simulation runs. Comparison between simulation results and measurements on the real system has shown good agreement. The real system optimized from model results yields a hold time of 6 days.