Intrinsic switching field distribution of arrays of Ni80Fe20 nanowires probed by in situ\mathit{in\, situ} magnetic force microscopy

The progress of magnetization reversal of weakly packed ferromagnetic Ni80Fe20 nanowire arrays of different diameters (40, 50, 70 and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighbouring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays.Comment: 4 pages, 5 figures. To appear in Journal of Superconductivity and Novel Magnetis

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.Comment: 7 pages, 5 figure

Toxic effect of antibiotics in grapevine (Vitis vinifera 'Albariño') for embryo emergence and transgenic plant regeneration from embryogenic cell suspension

Regeneration of grapevine (Vitis vinifera L.) from embryogenic cultures after gene transfer is traditionally linked to a selection procedure using antibiotic containing media. The neomycin phosphotransferase II (npt-II) and hygromycin phosphotransferase (hpt) genes that confer resistance to the antibiotics kanamycin and hygromycin, respectively, have been the selectable marker genes most frequently used for selection of transgenic grapevines. In this work, the phytotoxic effects on embryo development and plant growth of these two antibiotics were examined in 'Albariño'. Embryogenic cell suspensions were evaluated based on a twostep strategy using untransformed and transformed tissues. The phytotoxic effect was significantly different at 20 mg∙L-1 (and higher) for kanamycin and at 5 mg∙L-1 (and higher) for hygromycin. Minimal killing concentrations of kanamycin and hygromycin for 'Albariño' cell suspensions were 50 and 12.5 mg∙L-1, respectively. Embryogenic cell suspensions were bombarded using the biolistic system with the construct pBI426, harboring the selectable npt-II gene, and incubated on kanamycin containing media to determine the best inhibitory concentration allowing embryo and shoot development of only transgenic events. Only 20 % of PCR-positive transgenic embryos and 20 % of plant regeneration resulted from embryos emerged on 30 mg∙L-1. However, 80 % of PCR-positive transgenic embryos but only 10 % of plant regeneration were obtained from embryos emerged on 40 mg∙L-1. The method described, based in untransformed and transformed plant material, could be used to determine the optimal antibiotic concentration for other V. vinifera cultivars for efficient selection and regeneration of transgenic events.

Some Heteroptera From Virginia and North Carolina

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Adapting cognitive diagnosis computerized adaptive testing item selection rules to traditional item response theory

Currently, there are two predominant approaches in adaptive testing. One, referred to as cognitive diagnosis computerized adaptive testing (CD-CAT), is based on cognitive diagnosis models, and the other, the traditional CAT, is based on item response theory. The present study evaluates the performance of two item selection rules (ISRs) originally developed in the CD-CAT framework, the double Kullback-Leibler information (DKL) and the generalized deterministic inputs, noisy and gate model discrimination index (GDI), in the context of traditional CAT. The accuracy and test security associated with these two ISRs are compared to those of the point Fisher information and weighted KL using a simulation study. The impact of the trait level estimation method is also investigated. The results show that the new ISRs, particularly DKL, could be used to improve the accuracy of CAT. Better accuracy for DKL is achieved at the expense of higher item overlap rate. Differences among the item selection rules become smaller as the test gets longer. The two CD-CAT ISRs select different types of items: items with the highest possible a parameter with DKL, and items with the lowest possible c parameter with GDI. Regarding the trait level estimator, expected a posteriori method is generally better in the first stages of the CAT, and converges with the maximum likelihood method when a medium to large number of items are involved. The use of DKL can be recommended in low-stakes settings where test security is less of a concern