Distribution of organic and reduced sulfur forms in marsh soils of coastal Louisiana

Soil samples from a Louisiana Barataria Basin brackish marshes were fractionated into acid-volatile sulfides (AVS), HCl-soluble sulfur, elemental sulfur, pyrite sulfur, ester-sulfate sulfur, and carbon-bonded sulfur. Inorganic sulfur composed 13% of total sulfur in brackish marsh soil with HCl-soluble sulfur representing 63–92% of the inorganic sulfur fraction. AVS represented less than 1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounted for 8–33% of the inorganic sulfur pool. Organic sulfur, in the forms of ester-sulfate sulfur and carbon-bonded sulfur, was the most dominant pool representing the majority of total sulfur in brackish marsh. Results were compared to values reported for fresh and salt marshes. Reported inorganic sulfur fractions were greater in adjacent marshes, constituting 24% of total sulfur in salt marsh, and 22% in freshwater marshes. Along a salinity gradient, HCl-soluble sulfur represented 78–86% of the inorganic sulfur fraction in fresh, brackish, and salt marsh. Organic sulfur in the forms of ester-sulfate sulfur and carbon-bonded sulfur was the major constituent (76–87%) of total sulfur in all marshes. Reduced sulfur species, except elemental sulfur, increased seaward along the salinity gradient. Accumulation of reduced sulfur forms through sedimentation processes was significant in marsh energy flow in fresh, brackish and salt marshes.

土壤不同形态氮素在剖面中移动特征的模拟研究

应用室内土柱模拟试验方法 ,在可控水量条件下 ,研究不同水量淋溶情况下 ,土壤不同形态氮素在剖面中的分布和移动特征。研究表明 ,土壤有机氮组分中 ,氨基酸氮和 NH3- N是易于移动的形态 ,非酸解性氮则相对稳定 ;无机氮组分中 NO- 3 - N是易于移动的形态 ,NH+ 4 - N运移性差 ,非交换态 NH+ 4 - N为相对稳定形态 ;水、肥条件是决定 NO- 3 - N淋失的重要因素。研究结果为认识和掌握土壤氮素在剖面中的运移规律 ,为农田水分和氮素养分管理提供了科学依据 ;同时为深入揭示土壤中各种形态氮运移动态机制 ,展示了模拟实验技术的前景

Crystal structure of microwave dielectric ceramics Ba[(Mg1-xCdx)(0.33)Nb-0.67]O-3

A series of complex perovskite solid solutions of Ba[(Mg1-xCdx)(0.33)Nb-0.67]O-3 have been synthesized by the columbite method. Detailed Rietveld refinement of their X-ray diffraction data show that Ba[(Mg1-xCdx)0(.33)Nb(0.67)]O-3 has an order trigonal structure. The ordering degree as determined by the B-site occupancies increases with the partial substitution of Cd for Mg.

Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin Films

The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased.

Spectroscopic Study on Water Diffusion in Poly(ester urethane) Block Copolymer Matrix

The diffusion of water in a phase-separated biodegradable poly(ester urethane) shape-memory polymer with poly(E-caprolactone) (PCL) as the soft segment was investigated using time-resolved FTIR-ATR. On the basis of the band fitting and water ordering in drawn films, the broad water band in the 3800-2800 cm(-1) region was decomposed into four bands located at 3620, 3510, 3400, and 3260 cm(-1), and the first two components at 3620 and 35 10 cm(-1) were assigned to the vibrations of antisymmetric and symmetric stretching of water hydrogen bonded with the C=O group of the soft segment. The other two were associated with water bonded to the urethane hard segments in the forms of N-H:O-H:O=C bridge hydrogen bond and double hydrogen bonds with two C=O groups, respectively. Furthermore, band fitting and two-dimensional correlation analyses revealed that in the diffusion process, water first diffuses into the continuous soft-rich PCL phase and then into the hard-rich urethane domains, forming double hydrogen bonds with two C=O groups prior to the bridge hydrogen bond in the form of N-H:O-H:O=C.

Charge disproportionation in CaCu3Fe4O12

First-principles calculations using the APW+lo method, as implemented in the WIEN2K code, have been used to investigate the structural, electronic, and magnetic properties of the perovskite CaCu3Fe4O12, including the high-temperature Im-3 and low-temperature Pn-3 phase. The high-temperature phase presents a homogeneous valence and an orbital degenerate half-metallic behavior, which is consistent with the previous theoretical result. Instead orbital ordering, charge ordering, or disproportionation on Fe sites occur in the low-temperature phase, leading to the insulating character. More importantly, the charge disproportionation is of 2d(5)L -> d(5)L(2) + d(5) type (where L denotes an oxygen hole or a ligand hole), and the origin for the phenomenon is discussed in detail.

Structure and magnetic properties of new compounds CdYFeWO7

The solid solutions of CdYFeWO7, which are cubic pyrochlores of the type A(2)B(2)O(7), have been prepared and their structures were determined using Ab initio method. Rietveld refinement of the powder XRD data showed that CdYFeWO7 adopted cubic (Fd-3m) structure, while oxides crystallized in a defect-pyrochlore structure where both O (48f) and O'(8b) sites were partially occupied, and the frustrated cations sublattice precluded long range ordering of Fe/W in the pyrochlore structure. Charge distribution analysis also suggested incomplete occupation of different oxygen sites, thus the compound was non-stoichiometric, with the formula CdYFeW0.982O6.94, Magnetic measurements were carried out to find that Fe ions were in the high spin trivalent state. Curie Weiss paramagnetism down to similar to 5 K and the characteristic superposition between FC and ZFC suggested spin liquid rather than spin glass state.

Magnetic and electronic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by first-principles density functional calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3- Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3- Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d(2)) and Cr3+ 3d (d(3)) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 mu(B) for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t(2g) (t(2g)(3)) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.

Development of nanodomain and fractal morphologies in solvent annealed block copolymer thin films

We have systematically studied the thin film morphologies of asymmetric polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer subjected to solvent vapors of varying selectivity for the constituent blocks. Upon a short treatment in neutral or PS-selective vapor, the film exhibited a highly ordered array of hexagonally packed, cylindrical microdomains. In the case of PEO selective vapor annealing, such ordered cylindrical microdomains were not obtained. instead, fractal patterns on the microscale were observed and their growth processes investigated. Furthermore, hierarchical structures could be obtained if the fractal pattern was exposed to neutral or PS selective vapor.

A Monte Carlo simulation of morphology and structure for thin films of symmetric triblock copolymer after quenching and annealing

Self-assembly thin films of symmetric triblock copolymer after annealing and quenching were examined by an effective Monte Carlo simulation method. The defects in the ordered lamellae of the thin films after quenching, which were dependent on the initialization of copolymer melts, are removed in the thin films after annealing. The mean-square gyration radius and end-to-end distance of copolymer chains in the thin films after annealing are smaller than those in the thin films after quenching because of the complete relaxation of polymer during annealing. We also find that the density of A block in the region near to the surface is higher than that in the interior of the thin films. As a result, it is different from the thin films of symmetric A(n)B(n) diblock copolymer, in which surface ordering forms before the interior, that ordering phenomena occurs first in the interior region in the thin films of symmetric A(n)B(m)A(n). triblocl copolymer.

Structure and electrochemical characteristics of RENi3 alloy

The RENi3 (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Y) series compounds have been prepared by arc melting constituent elements under Ar atmosphere. X-ray diffraction (XRD) analysis reveals that the as-prepared alloys have different lattice parameters and cell volumes, depending on different rare earth (RE) element. The electrochemical characteristics, including the electrochemical capacity, P-C isotherms, high rate chargeability (HRC) and high-rate dischargeability (HRD), of these alloys have been studied through the charge-discharge recycle testing at different temperatures, charge currents and discharge currents. The results show that YNi3 has the largest cell volume, smallest density, and moreover, it shows more satisfactory electrochemical characteristics than other alloys, including discharge capacity, HRC, HRD and low temperature dischargeablity.

Crystallization of weakly segregated poly(styrene-b-epsilon-caprolactone) diblock copolymer in thin films

The surface morphology and crystallization behavior of a weakly segregated symmetric diblock copolymer, poly(styrene-b-6-caprolactone) (PS-b-PCL), in thin films were investigated by optical microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). When the samples were annealed in the molten state, surface-induced ordering, that is, relief structures with uniform thickness or droplets in the adsorbed monolayer, were observed depending on the annealing temperature. The polar PCL block preferred to wet the surface of a silicon wafer, while the PS block wet the air interface. This asymmetric wetting behavior led to the adsorbed monolayer with a PCL block layer having a thickness of around 4.0 nm. The crystallization of PCL blocks could overwhelm the microphase-separated structure because of the weak segregation. In situ observation of crystal growth indicated that the nucleation process preferred to occur at the edge of the thick parts of the film, that is, the relief structures or droplets. The crystal growth rate was presented by the time dependence of the distance between the tip of crystal clusters and the edge. At 22 and 17 degreesC, the average crystal growth rates were 55 +/- 10 and 18 +/- 4 nm/min, respectively.

Theoretical studies of nonlinear optical properties of compounds K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd)

K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd) is a special type of frequency doubling compound, whose crystal structure exhibits a scarcity of fluorine ions. This leads to two different coordination polyhedrons in the general position of K(2) atoms: [K(2)O6F(1)(2)F(2)] and [K(21)O6F(1)(2)] in a 2/1 ratio. The chemical bonding structures of all constituent atoms of the compound K4Gd2(CO3)(3)F-4 (KGCOF) are comprehensively studied; moreover, the relationship between the chemical bonding structure and the nonlinear optical (NLO) properties is investigated from the chemical bond viewpoint. The theoretical prediction of the NLO tensor coefficient d(11) of KGCOF is in agreement with experimental observation. Theoretical analyses show that the nonlinearity of this crystal type mainly originates from K-O bonds. In addition, the correlation between the NLO tensor d(11) and the refractive index n(0) of KGCOF is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)07506-X].

Variable selection by orthogonal descriptors and prediction of R-f value of phenol and aniline derivatives

Orthogonal descriptors is a viable method for variable selection, but this method strongly depend on the orthogonalisation ordering of the descriptors. In this paper, we compared the different methods used for order the descriptors. It showed that better results could be achieved with the use of backward elimination ordering. We predicted R-f value of phenol and aniline derivatives by this method, and compared it with classical algorithms such as forward selection, backward elimination, and stepwise procedure. Some interesting hints were obtained.

Double twist in helical polymer "soft" crystals

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed.