Competition between band filling and steric effect in ordered double perovskites Sr2-xLaxMnMoO6

The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2-xLaxMnMoO6(0 <= x <= 1). The compounds have a monoclinic structure (space group P2(1)/n) and the cell volume expands monotonically with La doping. The T-C and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-xLaxMnMoO6 decreases only at low doping levels (x <= 0.2); while at high doping levels (0.8 <= x <= 1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

Lanthanide complex/polymer composite optical resin with intense narrow band emission, high transparency and good mechanical performance

Novel composite resins possessing good luminescent properties have been synthesized through a free radical copolymerization of styrene, alpha-methylacrylic acid and the binary or ternary complexes of lanthanide ions (Eu3+ and Tb3+). These polymer-based composite resins not only possess good transparency and mechanical performance but also exhibit an intense narrow band emission of lanthanide complexes under UV excitation. We characterized the molecular structure, physical and mechanical performance, and luminescent properties of the composite resins. Spectra investigations indicate that alpha-methyl-acrylic acid act as both solubilizer and ligand. Photoluminescence measurements indicate that the lanthanide complexes show superior emission lines and higher intensities in the resin matrix than in the corresponding pure complex powders, which can be attributed to the restriction of molecular motion of complexes by the polymer chain networks and the exclusion of water molecules from the complex. We also found that the luminescence intensity decreased with increasing content of alpha-methylacrylic acid in the copolymer system. The lifetime of the lanthanide complexes also lengthened when they were incorporated in the polymer matrix. In addition, we found that the relationships between emission intensity and Tb (Eu) content exhibit some extent of concentration quenching.

Predicting the position of the spin-forbidden band for Tb3+ ions in crystal hosts

The energy difference DeltaE between the spin-allowed and spin-forbidden states of Tb3+ in crystals is studied. The environmental factor he representing the character of the host is redefined by using the chemical band of complex crystals. The relationship between h(e) and DeltaE is found to be a linear relation. The results show that the energy difference between the spin-forbidden and spin-allowed states for Tb3+ ions in crystals can be predicted from the environmental factor.

Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4'-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

The interaction of aldolase with the cytoplasmic domain of human erythrocyte band 3 inhibited by lanthanum ions

The effect of lanthanum ions on the activity of the cytoplasmic domain of human erythrocyte band 3 (CDB3), which was measured according to the inhibition to aldolase, was studied. In the presence of low concentration of lanthanum ions, the function of CDB3 to inhibit aldolase activity decreased significantly. It indicated that lanthanum ions in the erythrocyte would change the conformation of CDB3 and influence the control on aldolase activity.

Theoretical representation of shear and pressure influence on the phase separation behavior of PVME/PS mixture

In the framework of lattice fluid model, the Gibbs energy and equation of state are derived by introducing the energy (E-s) stored during flow for polymer blends under shear. From the calculation of the spinodal of poly(vinyl methyl ether) (PVME) and polystyrene (PS) mixtures, we have found the influence of E., an equation of state in pure component is inappreciable, but it is appreciable in the mixture. However, the effect of E, on phase separation behavior is extremely striking. In the calculation of spinodal for the PVME/PS system, a thin, long and banana miscibility gap generated by shear is seen beside the miscibility gap with lower critical solution temperature. Meanwhile, a binodal coalescence of upper and lower miscibility gaps is occurred. The three points of the three-phase equilibrium are forecasted. The shear rate dependence of cloud point temperature at a certain composition is discussed. The calculated results are acceptable compared with the experiment values obtained by Higgins et at. However, the maximum positive shift and the minimum negative shift of cloud point temperature guessed by Higgins are not obtained, Furthermore, the combining effects of pressure and shear on spinodal shift are predicted.

Shear induced mixing/demixing: Blends of homopolymers, of homopolymers plus copolymers, and blends in solution

Shear may shift the phase boundary towards the homogeneous state (shear induced mixing, SIM), or in the opposite direction (shear induced demixing, SID). SIM is the typical behavior of mixtures of components of low molar mass and polymer solutions, SID can be observed with solutions of high molar mass polymers and polymer blends at higher shear rates. The typical sequence with increasing shear rate is SIM, then occurrence of an isolated additional immiscible area (SLD), melting of this island into the main miscibility gap, and finally SIM again. A three phase line originates and ends in two critical end points. Raising pressure increases the shear effects. For copolymer containing systems SID is sometimes observed at very low shear rates, preceding the just mentioned sequence of shear influences.

The influence of muffin-tin approximation on energy band gap

The influence of muffin-tin approximation on energy band gap was studied using LMTO-ASA (Linear Muffin-Tin Orbital-Atomic Sphere Approximation) approach. Since the diverse data are available for LaX(X=N, P, As, Sb), they are presented in our research as an example in order to test the reliability of our results. Four groups of muffin-tin radii were chosen, they were the fitted muffin-tin radii based on the optical properties of the crystals (the first), 1 : 1 for La : X(the second), 1.5 : 1 for La : X(the third), and a group of radii derived by making the charge in the interstitial space to be zero(the fourth). The results show that the fitted muffin-tin radii (the first group) give the best results compared with experimental values, and the predicted energy band gaps are very sensitive to the choice of muffin-tin radius in comparison with the other groups. The second and the third delivered results somewhere in between, while the fourth provided the worst results compared with the other groups. For the same crystal, with the increase of muffin-tin radius of lanthanum, the calculated energy band gaps decreased, going from semi-conductor to semimetal. This again clearly indicated the sensitivity of energy band structure on muffin-tin approximation.

Studies on the energy band structures and chemical bond properties of LaX(X=N, P, As, Sb) crystals

The energy band structures of LaX(X=N, P, As, Sb) crystals have been studied by using LMTO-ASA method. The calculated energy gaps of these crystals are 2. 30 eV for LaN, 2. 05 eV for LaP, 1. 66 eV for LaAs and 1. 34 eV for LaSb. The results are in good agreement with experimental data, At the same time, using these calculated results of energy band structures of these crystals, the chemical bond properties have been analyzed and calculated, The covalency values of these crystals are 26.15% for LaN, 32.54% for LaP, 33.30% for LaAs and 36.49% for LaSb, which agree satisfactorily with the calculated ones by using PV (Phillips-Vechten) theory.

A new wind vector algorithm for C-band SAR

Ocean wind speed and wind direction are estimated simultaneously using the normalized radar cross sections or' corresponding to two neighboring (25-km) blocks, within a given synthetic aperture radar (SAR) image, having slightly different incidence angles. This method is motivated by the methodology used for scatterometer data. The wind direction ambiguity is removed by using the direction closest to that given by a buoy or some other source of information. We demonstrate this method with 11 EN-VISAT Advanced SAR sensor images of the Gulf of Mexico and coastal waters of the North Atlantic. Estimated wind vectors are compared with wind measurements from buoys and scatterometer data. We show that this method can surpass other methods in some cases, even those with insufficient visible wind-induced streaks in the SAR images, to extract wind vectors.

Traveling wave front for the Fisher equation on an infinite band region

Instead of discussing the existence of a one-dimensional traveling wave front solution which connects two constant steady states, the present work deals with the case connecting a constant and a nonhomogeneous steady state on an infinite band region. The corresponding model is the well-known Fisher equation with variational coefficient and Dirichlet boundary condition. (c) 2006 Elsevier Ltd. All rights reserved.

A new method for the estimation of oceanic mixed-layer depth using shipboard X-band radar images

Shipboard X-band radar images acquired on 24 June 2009 are used to study nonlinear internal wave characteristics in the northeastern South China Sea. The studied images show three nonlinear internal waves in a packet. A method based on the Radon Transform technique is introduced to calculate internal wave parameters such as the direction of propagation and internal wave velocity from backscatter images. Assuming that the ocean is a two-layer finite depth system, we can derive the mixed-layer depth by applying the internal wave velocity to the mixed-layer depth formula. Results show reasonably good agreement with in-situ thermistor chain and conductivity-temperature-depth data sets.

Eddy generation and evolution in the North Pacific Subtropical Countercurrent (NPSC) zone

The seasonal generation and evolution of eddies in the region of the North Pacific Subtropical Countercurrent remain poorly understood due to the scarcity of available data. We used TOPEX/POSEIDON altimetry data from 1992 to 2007 to study the eddy field in this zone. We found that velocity shear between this region and the neighboring North Equatorial Current contributes greatly to the eddy generation. Furthermore, the eddy kinetic energy level (EKE) shows an annual cycle, maximum in April/May and minimum in December/January. Analyses of the temporal and spatial distributions of the eddy field revealed clearly that the velocity shear closely related to baroclinic instability processes. The eddy field seems to be more zonal than meridional, and the energy containing length scale shows a surprising lag of 2-3 months in comparison with the 1-D and 2-D EKE level. A similar phenomenon is observed in individual eddies in this zone. The results show that in this eddy field band, the velocity shear may drive the EKE level change so that the eddy field takes another 2-3 months to grow and interact to reach a relatively stable state. This explains the seasonal evolution of identifiable eddies.

Measurements of ocean wave and current field using dual polarized X-band radar

A new ocean wave and sea surface current monitoring system with horizontally-(HH) and vertically-(VV) polarized X-band radar was developed. Two experiments into the use of the radar system were carried out at two sites, respectively, for calibration process in Zhangzi Island of the Yellow Sea, and for validation in the Yellow Sea and South China Sea. Ocean wave parameters and sea surface current velocities were retrieved from the dual polarized radar image sequences based on an inverse method. The results obtained from dual-polarized radar data sets acquired in Zhangzi Island are compared with those from an ocean directional buoy. The results show that ocean wave parameters and sea surface current velocities retrieved from radar image sets are in a good agreement with those observed by the buoy. In particular, it has been found that the vertically-polarized radar is better than the horizontally-polarized radar in retrieving ocean wave parameters, especially in detecting the significant wave height below 1.0 m.

A new empirical model for retrieving sea surface salinity in L band

Sea surface salinity is a key physical parameter in ocean science. It is important in the ocean remote sensing to retrieve sea surface salinity by the microwave probe technology. Based on the in situ measurement data and remote sensing data of the Yellow Sea, we have built a new empirical model in this paper, which can be used to retrieve sea surface salinity of the Yellow Sea by means of the brightness temperature of the sea water at L-band. In this model, the influence of the roughness of the sea surface is considered, and the retrieved result is in good agreement with the in situ measurement data, where the mean absolute error of the retrieved sea surface salinity is about 0.288 psu. This result shows that our model has greater retrieval precision compared with similar models.