完备化Witt代数中自然出现的一些非有限阶化李代数的表示

讨论了完备化Witt代数的三类非有限阶化子代数的不可约非权模的实现,并利用它们的表示得到一些有趣的组合恒等式.     

Anomalous transport effects for the metal and insulator doped La0.833K0.167MnO3 systems

The La_0.833K_0.167MnO₃:Ag₂O and the La_0.833K_0.167MnO₃:SrTiO₃ samples are fabricated by the sol–gel method. The microstructure, magnetic and transportation properties have been systematically studied. X-ray diffraction patterns show that the La_0.833K_0.167MnO₃:Ag₂O (abbreviated as LKMO/Ag) sample is a two-phase composite and consists of a magnetic La_0.833K_0.167MnO₃ (abbreviated as LKMO) perovskite phase and a nonmagnetic Ag metal phase, while the structure of the La_0.833K_0.167MnO₃:SrTiO₃ (abbreviated as LKMO/STO) sample is a homogeneous solid solution phase. Comparing with the pure LKMO sample, the room temperature magnetoresistance (MR) effect for the LKMO/Ag sample is enhanced significantly due to the addition of Ag metal. The MR ratio increases from ∼25% for the pure LKMO sample to 65% for the LKMO/Ag sample under a higher field of 5.5 T at 300 K. For the LKMO/STO sample, however, the room temperature MR effect is weakened dramatically and is almost close to zero due to the addition of SrTiO₃ insulator. In the low temperature regime below the Curie temperature, the MR behaviors are different from that of the room temperature; that is, the MR effect is decreased for the LKMO/Ag sample and increased for the LKMO/STO sample with temperature decrease. In fact, the low-field (μ₀H=0.5 T) MR decreases from 32% to 5% for the LKMO/Ag sample, while increasing from 0.07% to 25% for the LKMO/STO sample with decreasing temperature from 300 to 4 K. The relative change between the intrinsic and the extrinsic MR, and varied roles of the spin-polarized-tunneling and the spin-dependent scattering mechanisms in different temperature regimes are employed to interpret the anomalous transport behaviors.     

Analytical Solution to Subsurface Air Pressure in a Three-Layer Unsaturated Zone with Atmospheric Pressure Changes

In this study, a solution to one-dimensional vertical airflow induced by the time-dependent atmospheric pressure fluctuations is developed in a three-layer unsaturated zone. The discrete atmospheric pressure data are transformed into a continuous boundary condition using the Fourier series analysis. The solution is applied to interpret the field air pressure data in a three-layer unsaturated zone reported in previous studies. The new solution improves the previous solution by reducing the required data measurement and input. The new solution is found to be accurate enough for the purpose of this study by comparing with a numerical solution developed in COMSOL Multiphysics. Given the necessary hydrogeological parameters, the new solution is capable of calculating the air permeability of each layer above a specified depth where the air pressures are known. Sensitivity analysis of the new solution shows that location, thickness, and air permeability of the less permeable layer impose large influence on the propagation of the atmospheric pressure fluctuations. Variations of air-filled porosity in soil layers in/below the less permeable layer may lead to greater amplitude attenuation and phase lag of air pressure than those in soil layers above the less permeable layer.     

Determination of Malathion Using Corona Discharge – Ion Mobility Spectrometry with Solid-Phase Microextraction

A corona discharge (CD) ion mobility spectrometer combined with solid-phase microextraction was constructed. The detection limit and stability of the system for malathion detection were improved using a novel sample introduction port through which the sample desorption was performed in high-temperature drift tube and the sample was introduced directly to the ionization area. The working parameters of the distance between CD needle tip and carrier gas outlet, the drift tube and carrier gas temperature, the carrier gas flow, and the voltage on CD needle were selected. When the extraction time for standard malathion was set to 5?min, the detection limit was 0.96?µg?L^?1 based on thrice the baseline noise, the linear range was 50–500?µg?L^?1, the correlation coefficient was approximately 0.9941, and the relative standard deviation was below 10%. Malathion-spiked lake water samples were analyzed using the developed system and the recovery was 92–102%. This method is suitable for the rapid detection of organophosphorus pesticide residues.     

Preparation and characterization of nickel hydroxide microspheres assembled by nanoribbons

Abstract  

This article describes a facile green strategy for preparing the Ni(OH)₂ microsphere assembled by nanoribbons by the template of the squama inner coat of onion at mild condition. The method is simple and effective. The results of SEM show the products are Ni(OH)₂ microspheres with diameters in the range of 500–2,500 nm. The results of TEM show the microsphere is assembly by nanoribbons, with thickness in the range of 30–50 nm. The products were characterized by powder X-ray diffraction, IR, and thermogravimetric analysis. A possible formation mechanism was also proposed.     

Distinct magnetic properties of one novel type of nanoscale cobalt-iron Prussian blue analogues synthesized in microemulsion

One novel type of nanoscale cobalt-iron Prussian blue analogues (PBA) in the form of mixed nanorods and nanocubes were synthesized using cetyltrimethyl ammonium bromide (CTAB) as the surfactant in microemulsion at low temperature. The generated products were characterized by SQUID, XRD and IR techniques, etc. The effects of potassium contents, cobalt-to-iron ratios, reaction temperatures on the properties of the nanoscale cobalt-iron PBA were systematically explored. The results showed that the novel type of nanomaterials possessed distinct magnetic properties in that their coercivities were intensely dependent on cobalt-to-iron ratios and potassium contents. Furthermore, it was observed that low reaction temperature not only affected the morphologies of the products, but also had influence on their magnetic properties. Additionally, the cobalt-iron Prussian blue analogues were strongly influenced by CTAB around their surface, which led to higher Curie temperatures.     

An experimental study about the effect of arrangement on the fire behaviors of lithium-ion batteries

The gadolinium ferrochromite (GdFe_1?xCr_xO₃) was used as a case study of influence of chromium substitution on the perovskite structure in the entire composition range. By exploiting thermal analysis techniques (dilatometry, differential thermal analysis) the influence of chromium was investigated in the context of thermal stability of the canted antiferromagnetic ordering. It was found that the higher the chromium concentration was, the more the Néel temperature decreased, e.g., substitution of 26 % of iron atoms corresponded to a depression of about 60 K with respect to undoped gadolinium ferrite. For higher chromium concentrations the mixed gadolinium ferrochromite was paramagnetic at room temperature. Additional information on the crystal structure and, qualitatively, on the magnetic ordering as well was derived from the results of X-ray diffraction and Mössbauer spectroscopy measurements. For chromium content higher than 10 % the gadolinium ferrochromite may be regarded as a solid solution. For lower concentrations, however, a possible formation of clusters with different Fe/Cr ratio occurs as suggested by Mössbauer spectra.