旋转回归分析在提高作物产量中的应用

本文根据旋转回归正交试验,深入研究探讨了不同肥量、密度条件下对小麦产量的影响。创建了小麦产量与种植密度、施肥量之间的回归模型。通过检验,肯定了模型的可靠性和应用的有效性。为农业生产起到了很好的指导作用。     

Second-Order Nonlinear Optical Properties of a Polymer Exhibiting Optical Transparency Down to 340 nm

Abstract

The synthesis and characterization of an epoxy-based nonlinear optical (NLO) polymer exhibiting optical transparency down to 340 nm is reported. The synthesized polymers show spectroscopic properties (NMR, IR, UV) in accordance with the proposed structures. A glass transition temperature (T_g) of 92°C and a thermal degradation temperature (T_d) of 322°C were recorded. The poled polymer film exhibits stable second-order nonlinear optical activity (d₃₃ = 4.2 pm/V) over a period of 800 hours as characterized by the temporal response of the second harmonic signal at room temperature.     

H-transfer rates in ion-neutral complexes versus those in intact aliphatic ions

The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd.     

Le problème des diviseurs de zéro pour les groupes de Lie nilpotents

Let G be a non-Abelian, connected, nilpotent Lie group. Then there exist $0\ne \alpha \in C_c(G)$ and $0\ne \xi \in L^2(G)$ such that $\alpha 1\xi =0$, contrary to what happens for the group ${\mathbb{R}}^n$. Moreover, the set of zero divisors is a total subset of $L^2(G)$. This result is first proven for the Heisenberg group $H_n$ where it is based on the existence of non-trivial Schwartz functions f satisfying $f1(X_k+\mathrm{i}{Y}_k)=0$ for $1?k?n$. To cite this article: J. Ludwig et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Ultrasound-assisted synthesis of mesoporous zirconia-hydroxyapatite nanocomposites and their dual surface affinity for Cr3+/Cr2O7(2-) ions

Zirconia-hydroxyapatite nanocomposites were prepared by sol-gel deposition of zirconium oxide from a zirconium alkoxide in the presence of apatite colloidal suspension under ultrasonication. The material porosity evolves from mainly microporous zirconia to mesoporous hydroxyapatite, with decreasing surface area and increasing pore volume. XRD studies indicate that the apatite phase is well-preserved within the composite materials. The homogeneous dispersion of apatite colloids within the zirconia network was supported by TEM observations and nitrogen sorption measurements. (31)P solid-state NMR studies suggest that partial dissolution of apatite may have occurred during the preparation, leading to the adsorption of phosphate species on zirconia particles. This is confirmed by XRD studies of nanocomposites after thermal treatment that demonstrate the preferred formation of tetragonal over monoclinic ZrO(2) in the presence of hydroxyapatite. In order to investigate the surface properties of these novel materials, the adsorption of Pb(2+), Cr(3+), and Cr(2)O(7)(2-) was evaluated. Metal cations were preferentially adsorbed on apatite-rich composites, whereas Cr(2)O(7)(2-) shows a good affinity for the zirconia-rich phases. Zirconia-apatite materials showed the most promising performance in terms of recyclability. These nanocomposites that combine microporosity, mesoporosity and dual sorption properties for these species appear as interesting materials for metal ion remediation and may also find applications as biomaterials.     

Role of carboxylate chelating agents on the chemical, structural and textural properties of hydroxyapatite

Organically-modified hydroxyapatite materials were synthesized through the addition of oxalic, succinic, adipic and citric acids to a calcium hydroxide solution before neutralization by ammonium dihydrogenphosphate. All carboxylic acids have a significant influence on apatite crystallinity and nanoparticle size, as indicated by XRD and TEM. Chemical and thermogravimetric analyses as well as FTIR and {(1)H}-(13)C CP MAS NMR spectroscopies indicate that the additives are present in the final material. (1)H, {(1)H}-(31)P HPDec MAS, CP MAS and 2D {(1)H}-(31)P CP-HETCOR MAS NMR experiments suggest that carboxylic acids are localized on the apatite nanocrystallite surface, resulting in the formation of a disordered outer layer. Nitrogen sorption measurements indicate minor modifications of the specific surface area of the resulting mesoporous materials upon carboxylic acid addition but more significant variations in the average dimensions of the pores as well as in the chemical nature of the pore surface. Although these evolutions are mainly in good agreement with the ligand affinity for calcium ions in solution, an unexpected difference was observed between succinic and adipic acid, that may be attributed to steric constraints resulting from the interfacial nature of the calcium-ligand interactions. These data should provide useful guidelines to identify novel efficient additives to control apatite growth.     

Crystal structure of anhydrous bismuth iodate, Bi(IO3)3

Bismuth iodate was synthesized by precipitation from bismuth nitrate and iodic acid. The powder was dissolved in dilute nitric acid and single crystals were obtained by slow evaporation at 70°C. Bi(IO₃)₃ crystallizes in the monoclinic system, space group P2₁/n (N° 14), a = 8.8882(2) Å, b = 5.9445(2) Å, c = 15.2445(5) Å, = 97.064(1) Å. BiO9 polyhedra are edge-connected forming chains parallel to the b axis; these chains are linked through (IO₃) groups forming layers parallel to (101). The 3D framework is designed by linking these layers through long I–O bonds. DSC analysis shows a remarkable thermal stability.