Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite

We report on unusual magnetic properties observed in the nanofluid room-temperature ferromagnetic graphite (with an average particle size of l=10nm). More precisely, the measured magnetization exhibits a low-temperature anomaly (attributed to manifestation of finite size effects below the quantum temperature) as well as pronounced temperature oscillations above T=50K (attributed to manifestation of the hard-sphere type pair correlations between ferromagnetic particles in the nanofluid)

Quadratic Effective Action for QED in D=2,3 Dimensions

We calculate the effective action for Quantum Electrodynamics (QED) in D=2,3 dimensions at the quadratic approximation in the gauge fields. We analyse the analytic structure of the corresponding nonlocal boson propagators nonperturbatively in k/m. In two dimensions for any nonzero fermion mass, we end up with one massless pole for the gauge boson . We also calculate in D=2 the effective potential between two static charges separated by a distance L and find it to be a linearly increasing function of L in agreement with the bosonized theory (massive Sine-Gordon model). In three dimensions we find nonperturbatively in k/m one massive pole in the effective bosonic action leading to screening. Fitting the numerical results we derive a simple expression for the functional dependence of the boson mass upon the dimensionless parameter e^{2}/m .Comment: 10 pages, 2 figure

Finite size analysis of a two-dimensional Ising model within a nonextensive approach

In this work we present a thorough analysis of the phase transitions that occur in a ferromagnetic 2D Ising model, with only nearest-neighbors interactions, in the framework of the Tsallis nonextensive statistics. We performed Monte Carlo simulations on square lattices with linear sizes L ranging from 32 up to 512. The statistical weight of the Metropolis algorithm was changed according to the nonextensive statistics. Discontinuities in the m(T) curve are observed for $q\leq 0.5$. However, we have verified only one peak on the energy histograms at the critical temperatures, indicating the occurrence of continuous phase transitions. For the $0.5<q\leq 1.0$ regime, we have found continuous phase transitions between the ordered and the disordered phases, and determined the critical exponents via finite-size scaling. We verified that the critical exponents $\alpha$, $\beta$ and $\gamma$ depend on the entropic index $q$ in the range $0.5<q\leq 1.0$ in the form $\alpha (q)=(10 q^{2}-33 q+23)/20$, $\beta (q)=(2 q-1)/8$ and $\gamma (q)=(q^{2}-q+7)/4$. On the other hand, the critical exponent $\nu$ does not depend on $q$. This suggests a violation of the scaling relations $2 \beta +\gamma =d \nu$ and $\alpha +2 \beta +\gamma =2$ and a nonuniversality of the critical exponents along the ferro-paramagnetic frontier.Comment: accepted for publication in Phys. Rev.

Manifestation of finite temperature size effects in nanogranular magnetic graphite

In addition to the double phase transition (with the Curie temperatures T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the magnetization is observed in the bulk magnetic graphite (with an average granular size of L=10nm), which is attributed to manifestation of the size effects below the quantum temperature. The best fits of the high-temperature data (using the mean-field Curie-Weiss and Bloch expressions) produced reasonable estimates for the model parameters, such as defects mediated effective spin exchange energy J=12meV (which defines the intragranular Curie temperature T_C) and proximity mediated interactions between neighboring grains (through potential barriers created by thin layers of non-magnetic graphite) with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and characteristic length, respectively

Efficiency of biological control for fall armyworm resistant to the protein Cry1F.

O entendimento de relações ecológicas e toxicológicas envolvendo culturas geneticamente modificadas (GM) e agentes de controle biológico é de grande importância para discussões relativas à compatibilidade de culturas GM com estratégias de manejo integrado e manejo de resistência de pragas. Este trabalho avaliou o comportamento de busca e a capacidade predatória de Orius insidiosus (Say) (Hemiptera: Anthocoridae) e Doru luteipes (Scudder) (Dermaptera: Forficulidae) sobre ovos e lagartas de Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) resistente ou não à proteína Cry1F expressa em milho Bt. Para determinar o tempo de busca foi utilizado um cronômetro que foi disparado até a captura da primeira presa; a capacidade de predação foi avaliada através da contagem das presas remanescentes 24 h após infestação. Também foram avaliadas as injúrias de S. frugiperda em milho transgênico e milho convencional na presença ou ausência dos predadores. Os predadores não foram capazes de distinguir entre presas (ovos ou lagartas) resistentes e suscetíveis, considerando os comportamentos predatórios avaliados. Não houve diferença no tempo de busca e capacidade predatória sobre ovos e lagartas de S. frugiperda resistente ou suscetível entre os predadores. Na presença dos predadores, as notas de injúria de S. frugiperda resistente nas plantas de milho Bt foram menores. Conclui-se que O. insidiosus e D. luteipes não percebem a presença da proteína Cry1F na presa S. frugiperda, o que pode contribuir para o uso integrado de milho GM e controle biológico em programas de manejo integrado e manejo de resistência de pragas.Ahead of print

Potencial de Pseudomonas sp. psicrotolerantes isoladas da Antártica no biocontrole de Botrytis cinerea.

Resumo: A Antártica, por ser um ambiente extremo, comporta micro-organismos que podem ter características interessantes, como crescimento a baixas temperaturas (psicrotolerância), além da produção de compostos antimicrobianos. Como também a possibilidade de aplicação desses micro-organismos no controle de fitopatogenos que se desenvolveu em baixas temperaturas, como é o caso de Botrytis cinerea, que ataca dezenas de culturas agrícolas em zonas temperadas. O morango, Fragaria vesca, é comumente atacado por este fungo, causando a doença conhecida como podridão cinzenta, principalmente durante a pós-colheita. Desta forma, o objetivo deste trabalho foi prospectar bactérias isoladas da Antártica e avaliar o potencial de inibição deste fitopatogeno. Assim foram testadas 56 bactérias sendo que 42% apresentaram melhor crescimento a 4°C. 4 dessas pertencentes ao gênero Pseudomonas, sendo que a linhagem 44-4 (Pseudomonas Syringae), foi capaz de controlar o desenvolvimento do fungo em morango (4°C). Demonstra-se, portanto, a possibilidade de prospecção de bactérias Psicrofilicas com potencial de reduzir o crescimento de fungos a baixa temperatura. Ensaios estão sendo feitos para elucidação dos compostos químicos responsáveis por este efeito. Abstract: Antarctica, being an extreme environment, includes micro-organisms that may have interesting features, such as growth at low temperatures (psicrotolerância), besides the production of antimicrobial compounds. As well as the possibility of application of these micro-organisms to control plant pathogens that developed at low temperatures, as is the case of Botrytis cinerea, attacking dozens of agricultural crops in temperate zones. The strawberry, Fragaria vesca, is commonly attacked by this fungus causing the disease known as gray mold, especially during post-harvest. Thus, the objective was to prospect for bacteria isolated from Antarctica and evaluate the potential inhibition of this pathogen. So were tested 56 bacteria and 42% showed better growth at 4°C. Four of these belonging to the genus Pseudomonas, and the line 44-4 (Pseudomonas syringae) was able to control the development of the fungus in strawberry (4°C). It is shown so the prospectivity of Psychrophilic bacteria with potential to reduce the fungal growth at low temperature. Tests are being made to elucidation of the chemical compounds responsible for this effect