Nanoscopic processes of Current Induced Switching in thin tunnel junctions

In magnetic nanostructures one usually uses a magnetic field to commute between two resistance (R) states. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current, preferably of low intensity. Such Current Induced Switching (CIS) was recently observed in thin magnetic tunnel junctions, and attributed to electromigration of atoms into/out of the insulator. Here we study the Current Induced Switching, electrical resistance, and magnetoresistance of thin MnIr/CoFe/AlO$_x$/CoFe tunnel junctions. The CIS effect at room temperature amounts to 6.9% R-change between the high and low states and is attributed to nanostructural rearrangements of metallic ions in the electrode/barrier interfaces. After switching to the low R-state some electro-migrated ions return to their initial sites through two different energy channels. A low (high) energy barrier of $\sim$0.13 eV ($\sim$0.85 eV) was estimated. Ionic electromigration then occurs through two microscopic processes associated with different types of ions sites/defects. Measurements under an external magnetic field showed an additional intermediate R-state due to the simultaneous conjugation of the MR (magnetic) and CIS (structural) effects.Comment: 6 pages, 4 figure

Three new species and new records of Oligochaeta, Glossoscolecidae, from the Venezuelan Andes

Five species of Oligochaeta, Glossoscolecidae, from Venezuela, Merida State (1,500 to 4,350 m a.s.1.) were studied by dissection and serial microscopical sections. Andiorrhinus (Amazonidrilus) gavi n. sp. is characterized by the space aa wider in XX-XXIII and seven pairs of hearts in VII-XIII. A. (Meridrilus) rimeda, n. sp. is notable for the pair of puberal bands lateral do b in XX-XXIII flanked by two longitudinal cords. Rhinodrilus mucuba, n. sp. has a typical arrangement of the setae and spermathecae. New observations are reported for the previously known Onychochaeta windlei and A. (M.) kuika; the variability of the latter species is recorded. Key words: Oligochaeta, Glossoscolecidae, Venezuela, Andes, Taxonomy.Five species of Oligochaeta, Glossoscolecidae, from Venezuela, Merida State (1,500 to 4,350 m a.s.1.) were studied by dissection and serial microscopical sections. Andiorrhinus (Amazonidrilus) gavi n. sp. is characterized by the space aa wider in XX-XXIII and seven pairs of hearts in VII-XIII. A. (Meridrilus) rimeda, n. sp. is notable for the pair of puberal bands lateral do b in XX-XXIII flanked by two longitudinal cords. Rhinodrilus mucuba, n. sp. has a typical arrangement of the setae and spermathecae. New observations are reported for the previously known Onychochaeta windlei and A. (M.) kuika; the variability of the latter species is recorded. Key words: Oligochaeta, Glossoscolecidae, Venezuela, Andes, Taxonomy.Five species of Oligochaeta, Glossoscolecidae, from Venezuela, Merida State (1,500 to 4,350 m a.s.1.) were studied by dissection and serial microscopical sections. Andiorrhinus (Amazonidrilus) gavi n. sp. is characterized by the space aa wider in XX-XXIII and seven pairs of hearts in VII-XIII. A. (Meridrilus) rimeda, n. sp. is notable for the pair of puberal bands lateral do b in XX-XXIII flanked by two longitudinal cords. Rhinodrilus mucuba, n. sp. has a typical arrangement of the setae and spermathecae. New observations are reported for the previously known Onychochaeta windlei and A. (M.) kuika; the variability of the latter species is recorded. Key words: Oligochaeta, Glossoscolecidae, Venezuela, Andes, Taxonomy

Comparison between the Torquato-Rintoul theory of the interface effect in composite media and elementary results

We show that the interface effect on the properties of composite media recently proposed by Torquato and Rintoul (TR) [Phys. Rev. Lett. 75, 4067 (1995)] is in fact elementary, and follows directly from taking the limit in the dipolar polarizability of a coated sphere: the TR ``critical values'' are simply those that make the dipolar polarizability vanish. Furthermore, the new bounds developed by TR either coincide with the Clausius-Mossotti (CM) relation or provide poor estimates. Finally, we show that the new bounds of TR do not agree particularly well with the original experimental data that they quote.Comment: 13 pages, Revtex, 8 Postscript figure

Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension

Extensive simulations are performed of the diffusion-limited reaction A$+$B$\to 0$ in one dimension, with initially separated reagents. The reaction rate profile, and the probability distributions of the separation and midpoint of the nearest-neighbour pair of A and B particles, are all shown to exhibit dynamic scaling, independently of the presence of fluctuations in the initial state and of an exclusion principle in the model. The data is consistent with all lengthscales behaving as $t^{1/4}$ as $t\to\infty$. Evidence of multiscaling, found by other authors, is discussed in the light of these findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0, 10 pages with 16 Encapsulated Postscript figures (need epsf). University of Geneva preprint UGVA/DPT 1994/10-85

Research note: The influence of micro-oxygenation on the long-term ageing ability of Pinot noir wine

In this study, Pinot noir wines were bottle aged for 12 and 18 months after micro-oxygenation (MOX) applied before or after malolactic fermentation (MLF) at two doses (10.8 and 52.4 mg/L/month). After ageing, a greater decrease in the total SO₂ concentration was found in wines with the higher MOX dosage, demonstrating a long-term impact of higher oxygen exposure on wines’ SO₂ requirement. Meanwhile, a negative impact of MOX on wine colour development occurred over time, resulting in a large loss of colour measures (i.e., 420 nm for brown hues, 520 nm for red colour, SO₂ resistant pigments, and colour intensity), which was greater with the early oxygen exposure. This was linked to a significantly lower content of large polymeric pigments in MOX treatments. Tannin concentration was, in the end, not affected by the MOX treatments. However, regarding tannin composition, considerably higher (-)-epicatechin extension units but much lower (-)-epicatechin terminal units were found with MOX treatments. In addition, a significant reduction of tannin trihydroxylation (%Tri-OH) but a higher galloylation (%Galloyl) and mean degree of tannin polymerisation (mDP) remained in wines with MOX, indicating a long-term negative influence on astringency intensity

A infestação da vegetação arbórea do Passeio Público de Curitiba, Paraná, por erva-de-passarinho: um estudo de caso.

Foi analisada a infestação por erva-de-passarinho na população arbórea do Passeio Público de Curitiba,PR. No local predomina a vegetação arbórea nativa, correspondendo a 68% da composição florística total de 130 espécies de árvores nativas e exóticas. Essa predominância se repete, também, em relação ao número de indivíduos encontrados (60%) na população, que possui um total de 1.865 árvores. Três espécies de erva-de-passarinho ocorrem no local, infestando os troncos, copas e galhos das árvores: Tripodanthus acutifolius, Struthanthus vulgaris e Struthanhus polyrhysus, predominando a primeira espécie. Cerca de 14% da vegetação arbórea do Passeio Público encontra-se infestada por erva-de-passarinho, apresentando algum nível de infestação por uma das três espécies ou por mais de uma espécie na mesma árvore. A maior infestação acontece entre as árvores de espécies exóticas (67%), mesma tendência observada no número de indivíduos atacados (92%). Algumas famílias e, dentro delas algumas espécies, apresentaram-se resistentes ou, pelo menos momentaneamente, imunes à infestação. Esta espécies devem ser mais valorizadas nos plantios urbanos e outras, como o alfeneiro, casuarina e extremosa devem ser menos utilizadas, até que se consiga um método de controle eficaz da proliferação da erva-de-passarinho, já que apresentam susceptibilidade à contaminação.bitstream/CNPF-2009-09/40964/1/BPD26_CD.pd

Nonmagnetic-Defect-Induced Magnetism in Graphene

It is shown that a strong impurity potential induces short-range antiferromagnetic (ferrimagnetic) order around itself in a Hubbard model on a half-filled honeycomb lattice. This implies that short-range magnetic order is induced in monolayer graphene by a nonmagnetic defect such as a vacancy with full hydrogen termination or a chemisorption defect.Comment: 5 pages, 8 figure