NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System

Resistively detected nuclear magnetic resonance (NMR) is observed inside the ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase diagram of a two subband electron system. The NMR signal persists up to 400 mK and is absent in other states with the same quantized Hall conductance. The nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards the ring center. These observations are consistent with the assertion of the ring-like region being a ferromagnetic state that is accompanied by collective spin excitations.Comment: 4 pages, 4 figure

An optimized analytical method for the simultaneous detection of iodoform, iodoacetic acid, and other trihalomethanes and haloacetic acids in drinking water

An optimized method is presented using liquid-liquid extraction and derivatization for the extraction of iodoacetic acid (IAA) and other haloacetic acids (HAA9) and direct extraction of iodoform (IF) and other trihalomethanes (THM4) from drinking water, followed by detection by gas chromatography with electron capture detection (GC-ECD). A Doehlert experimental design was performed to determine the optimum conditions for the five most significant factors in the derivatization step: namely, the volume and concentration of acidic methanol (optimized values  = 15%, 1 mL), the volume and concentration of Na2SO4 solution (129 g/L, 8.5 mL), and the volume of saturated NaHCO3 solution (1 mL). Also, derivatization time and temperature were optimized by a two-variable Doehlert design, resulting in the following optimized parameters: an extraction time of 11 minutes for IF and THM4 and 14 minutes for IAA and HAA9; mass of anhydrous Na2SO4 of 4 g for IF and THM4 and 16 g for IAA and HAA9; derivatization time of 160 min and temperature at 40°C. Under optimal conditions, the optimized procedure achieves excellent linearity (R2 ranges 0.9990–0.9998), low detection limits (0.0008–0.2 µg/L), low quantification limits (0.008–0.4 µg/L), and good recovery (86.6%–106.3%). Intra- and inter-day precision were less than 8.9% and 8.8%, respectively. The method was validated by applying it to the analysis of raw, flocculated, settled, and finished waters collected from a water treatment plant in China

Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions

By use of first-principles electronic structure calculations, we predict that the magnetoresistance of the bcc Co(100)/MgO(100)/bcc Co(100) and FeCo(100)/MgO(100)/FeCo(100) tunneling junctions can be several times larger than the very large magnetoresistance predicted for the Fe(100)/MgO(100)/Fe(100) system. The origin of this large magnetoresistance can be understood using simple physical arguments by considering the electrons at the Fermi energy travelling perpendicular to the interfaces. For the minority spins there is no state with $\Delta_1$ symmetry whereas for the majority spins there is only a $\Delta_1$ state. The $\Delta_1$ state decays much more slowly than the other states within the MgO barrier. In the absence of scattering which breaks the conservation of momentum parallel to the interfaces, the electrons travelling perpendicular to the interfaces undergo total reflection if the moments of the electrodes are anti-parallel. These arguments apply equally well to systems with other well ordered tunnel barriers and for which the most slowly decaying complex energy band in the barrier has $\Delta_1$ symmetry. Examples include systems with (100) layers constructed from Fe, bcc Co, or bcc FeCo electrodes and Ge, GaAs, or ZnSe barriers.Comment: 8 figure files in eps forma

Effects of genetically modified herbicide-tolerant (GMHT) rice on biodiversity of weed in paddy fields

To detect potential changes in properties of weed communities in fields of GMHT rice Bar68-1, trials were carried out from 2007-2008 at Changsha, China with conventional indica rice D68 served as control. The average richness of weed community measured by species accumulation curve tended to be identical in the fields of Bar68-1 and D68 as the number of sampling points increased. There were no significant differences (p > 0.05) in diversity indices which included numbers of species(S), Shannon-Wiener (H’), Pielou evenness (J’), Simpson diversity (D) and evenness (E) indices. Species composition for these two weed communities was roughly comparable. The top four weed species, sorted by individual abundance, were Monochoria vaginalis (Burm. f.) Presl ex Kunth, Lindernia procumbens(Krock.) Philcox, Cyperus diformis L. and Juncellus serotinus (Rottb.) .B. Clarke in the fields of Bar68-1 and D68. ABC curves showed that the weed communities were “unpolluted”. The data above confirm the hypothesis that the difference between the effect of GMHT rice Bar68-1 on biodiversity of weed in paddy fields and that of non-GM rice D68 was not significant