Experimental observation of two-dimensional fluctuation magnetization in the vicinity of T_c for low values of the magnetic field in deoxygenated YBa_2Cu_3O_{7-x}

We measured isofield magnetization curves as a function of temperature in two single crystal of deoxygenated YBaCuO with T_c = 52 and 41.5 K. Isofield MvsT were obtained for fields running from 0.05 to 4 kOe. The reversible region of the magnetization curves was analyzed in terms of a scaling proposed by Prange, but searching for the best exponent $\upsilon$. The scaling analysis carried out for each data sample set with $\upsilon$=0.669, which corresponds to the 3D-xy exponent, did not produced a collapsing of curves when applied to MvsT curves data obtained for the lowest fields. The resulting analysis for the Y123 crystal with T_c = 41.5 K, shows that lower field curves collapse over the entire reversible region following the Prange's scaling with $\upsilon$=1, suggesting a two-dimensional behavior. It is shown that the same data obeying the Prange's scaling with $\upsilon$=1 for crystal with T_c = 41.5 K, as well low field data for crystal with $T_c$ = 52 K, obey the known two-dimensional scaling law obtained in the lowest-Landau-level approximation.Comment: 4 pages, 3 figure

Gold's hedging and safe haven properties for European stock and bond markets

Most portfolio managers and risk managers strive to pick assets that lead to efficient financial risk mitigation; among them, gold stands out. This paper provides new insights into the role of gold as both a hedge and a safe haven towards European stock and sovereign bond markets. We base the analysis on evidence spanning the Euro's inception to the COVID-19 pandemic spread across Europe. To capture gold's hedge ability, we use the ADCC-GARCH and DCC-GARCH models, while for testing gold's safe haven property we use OLS regressions for different quantiles. Our results show that gold is a hedge for stocks, particularly after the Lehman Brothers collapse. Gold also shows strong safe haven properties for the most extreme negative returns (1% and 2.5% quantiles), and during specific events, such as the Lehman Brothers collapse, the Greek bailout and the Brexit Referendum. Still, for the COVID-19 pandemic outbreak, the results do not confirm this property. Conversely, for bonds, both hedge and safe haven effects are not strongly evident, with gold characterised, at best, as a weak hedge and safe haven. These findings have portfolio allocation implications for investors in European markets, namely fund and risk managers, by pointing out gold hedging and safe haven attributes.info:eu-repo/semantics/publishedVersio

Pressure induced effects on the Fermi surface of superconducting 2H-NbSe2_2

The pressure dependence of the critical temperature $T_c$ and upper critical field $H_{c2}(T)$ has been measured up to 19 GPa in the layered superconducting material 2H-NbSe$_2$. Relating the behavior of $H_{c2}(T)$ to Fermi surface parameters, we find that the electron phonon coupling of the 2D Nb 4d derived bands shows a peak at 5 GPa when the charge density wave (CDW) order is suppressed. On the other hand, $T_c(P)$ shows a bell shaped curve with a maximum at 10.5 GPa, well above the pressure for the suppression of the CDW order. Changes in the band structure produce this shift in the maximum of $T_c(P)$, demonstrating that 2H-NbSe$_2$ shows important differences with respect to other compounds where $T_c$ has a maximum in the temperature-density phase diagram shaped by the suppression of another, non-superconducting, ground state.Comment: 5 pages, 4 figures. Small changes in discussion. Typos correcte

Caracterização do sistema produtivo da mangabeira no município de Itaporanga D'Ajuda, Sergipe.

bitstream/CPATC-2010/21506/1/bp-48.pd

Chaos around a H\'enon-Heiles-inspired exact perturbation of a black hole

A solution of the Einstein's equations that represents the superposition of a Schwarszchild black hole with both quadrupolar and octopolar terms describing a halo is exhibited. We show that this solution, in the Newtonian limit, is an analog to the well known H\'enon-Heiles potential. The integrability of orbits of test particles moving around a black hole representing the galactic center is studied and bounded zones of chaotic behavior are found.Comment: 7 pages Revte

Entanglement Controlled Single-Electron Transmittivity

We consider a system consisting of single electrons moving along a 1D wire in the presence of two magnetic impurities. Such system shows strong analogies with a Fabry - Perot interferometer in which the impurities play the role of two mirrors with a quantum degree of freedom: the spin. We have analysed the electron transmittivity of the wire in the presence of entanglement between the impurity spins. The main result of our analysis is that, for suitable values of the electron momentum, there are two maximally entangled state of the impurity spins the first of which makes the wire transparent whatever the electron spin state while the other strongly inhibits the electron transmittivity. Such predicted striking effect is experimentally observable with present day technology.Comment: Published version (6 figures

Bioensaio para identificação de girassol resistente ao herbicida Imazapyr.

O trabalho teve como objetivo a elaboração de metodologia para identificar a resistência do girassol ao herbicida imazapyr, por meio de bioensaio baseado em teste de germinação de sementes. Para tal, foram conduzidos dois experimentos em laboratório específico de análise de sementes. No primeiro experimento foi utilizado o cultivar de girassol Helio 360, susceptível ao imazapyr, em seis concentrações do herbicida: 0, 100, 200, 400, 800 e 1600. No segundo experimento foi comparado o mesmo cultivar com uma linhagem de girassol resistente ao herbicida, denominada IMI EARLY, em cinco concentrações de imazapyr: 0, 50, 100, 200 e 400 ppm. Para o cultivar Helio 360 as soluções com o herbicida reduziram a germinação total de sementes e o número de plântulas normais, que não mais apareceram a partir da concentração de 200 ppm. O cultivar IMI EARLY não foi afetado pelo herbicida. O estudo mostrou que é possível identificar a presença do girassol resistente ao herbicida imazapyr, através do teste de germinação de sementes embebidas na solução do herbicida, a partir da concentração de 200 ppm

Aneurisma Intracraniano na Criança

Os aneurismas cerebrais são raros na criança, embora a sua ruptura seja a principal causa de hemorragia subaracnoideia neste grupo etário. Apresenta-se o caso de uma criança de 11 anos de idade, que recorreu ao hospital por cefaleia súbita e intensa, sem história prévia de traumatismos ou infecções. O estudo clínico e imagiológico realizado foi sugestivo de hemorragia subaracnoideia. A angiografia cerebral permitiu o diagnóstico de aneurisma da bifurcação da artéria carótida interna esquerda. Foi submetida a cirurgia, com boa evolução pós-operatória. Pretende-se com este caso alertar para as dificuldades no diagnóstico diferencial de ruptura de aneurisma cerebral na criança e salientar que um diagnóstico correcto e precoce permite melhorar o prognóstico

Spin dynamics of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy

We use exact diagonalization and the modified Lanczos method to study the finite energy and finite momentum spectral weight of the longitudinal and transverse spin excitations of the anisotropic zig-zag ladder. We find that the spin excitations form continua of gapless or gapped spinons in the different regions of the phase diagram. The results obtained are consistent with a picture previously proposed that in the anisotropic case there is a transition from a gapped regime to a gapless regime, for small interchain coupling. In this regime we find a sharp low-energy peak in the structure function for the transverse spin excitations, consistent with a finite stiffness.Comment: 17 figure