Exchange bias and interface electronic structure in Ni/Co3O4(011)

A detailed study of the exchange bias effect and the interfacial electronic structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are observed at low temperatures, and the exchange bias effect persists to temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to ~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy measurements as a function of Ni thickness show that Co reduction and Ni oxidation occur over an extended interfacial region. We conclude that the exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4 systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at the interface.Comment: 8 pages, 6 figures. Accepted for publication in Physical Review B

Toward a Midisuperspace Quantization of LeMaitre-Tolman-Bondi Collapse Models

LeMa\^\i tre-Tolman-Bondi models of spherical dust collapse have been used and continue to be used extensively to study various stellar collapse scenarios. It is by now well-known that these models lead to the formation of black holes and naked singularities from regular initial data. The final outcome of the collapse, particularly in the event of naked singularity formation, depends very heavily on quantum effects during the final stages. These quantum effects cannot generally be treated semi-classically as quantum fluctuations of the gravitational field are expected to dominate before the final state is reached. We present a canonical reduction of LeMa\^\i tre-Tolman-Bondi space-times describing the marginally bound collapse of inhomogeneous dust, in which the physical radius, $R$, the proper time of the collapsing dust, $\tau$, and the mass function, $F$, are the canonical coordinates, $R(r)$, $\tau(r)$ and $F(r)$ on the phase space. Dirac's constraint quantization leads to a simple functional (Wheeler-DeWitt) equation. The equation is solved and the solution can be employed to study some of the effects of quantum gravity during gravitational collapse with different initial conditions.Comment: 9 pages, 1 figure, Latex file. Minor corrections made. A general solution of the constraints is presented. Revised version to appear in Phys. Rev.

Dynamical Mass Constraints on Low-Mass Pre-Main-Sequence Stellar Evolutionary Tracks: An Eclipsing Binary in Orion with a 1.0 Msun Primary and an 0.7 Msun Secondary

We report the discovery of a double-lined, spectroscopic, eclipsing binary in the Orion star-forming region. We analyze the system spectroscopically and photometrically to empirically determine precise, distance-independent masses, radii, effective temperatures, and luminosities for both components. The measured masses for the primary and secondary, accurate to ~1%, are 1.01 Msun and 0.73 Msun, respectively; thus the primary is a definitive pre-main-sequence solar analog, and the secondary is the lowest-mass star yet discovered among pre-main-sequence eclipsing binary systems. We use these fundamental measurements to test the predictions of pre-main-sequence stellar evolutionary tracks. None of the models we examined correctly predict the masses of the two components simultaneously, and we implicate differences between the theoretical and empirical effective temperature scales for this failing. All of the models predict the observed slope of the mass-radius relationship reasonably well, though the observations tend to favor models with low convection efficiencies. Indeed, considering our newly determined mass measurements together with other dynamical mass measurements of pre-main-sequence stars in the literature, as well as measurements of Li abundances in these stars, we show that the data strongly favor evolutionary models with inefficient convection in the stellar interior, even though such models cannot reproduce the properties of the present-day Sun.Comment: Accepted by Ap

Soliton Induced Singularities in 2 d Gravity and their Evaporation

Positive energy singularities induced by Sine-Gordon solitons in 1+1 dimensional dilaton gravity with positive and negative cosmological constant are considered. When the cosmological constant is positive, the singularities combine a white hole, a timelike singularity and a black hole joined smoothly near the soliton center. When the cosmological constant is negative, the solutions describe two timelike singularities joined smoothly near the soliton center. We describe these spacetimes and examine their evaporation in the one loop approximation.Comment: 15 pages (37.7 kb), PHYZZX. Figures available from authors

Quantum Radiation from Black Holes and Naked Singularities in Spherical Dust Collapse

A sufficiently massive collapsing star will end its life as a spacetime singularity. The nature of the Hawking radiation emitted during collapse depends critically on whether the star's boundary conditions are such as would lead to the eventual formation of a black hole or, alternatively, to the formation of a naked singularity. This latter possibility is not excluded by the singularity theorems. We discuss the nature of the Hawking radiation emitted in each case. We justify the use of Bogoliubov transforms in the presence of a Cauchy horizon and show that if spacetime is assumed to terminate at the Cauchy horizon, the resulting spectrum is thermal, but with a temperature different from the Hawking temperature.Comment: PHYZZX macros, 27 pages, 3 figure

IMPACT OF INTERACTION P AND Zn ON BIOFORTIFICATION OF BEAN

INTRODUCTION: A large part of the world population has low levels of micronutrients, especially pregnant women and children in developing countries. Zinc (Zn) is a micronutrient, performing many functions in the organism. Biofortifcation aims to increase the concentration of certain mineral in parts consumed of the cultivated plants. The crops of most interest are those that constitute the basic diet for the majority of the population, including beans. Two main strategies are used in biofortification, selection of cultivars more favorable to biofortification and increase the micronutrient dose. Biofortification of bean with Zn is difficult due to interaction with phosphorus (P). The decrease in zinc absorption caused by phosphorus depends on soil atributes such as pH, cation exchange capacity and direct reaction with Zn and subsequent precipitation. The increase of the dose of Zn can reduce the absorption of iron by plants by competitve inhibition. This study aimed to evaluate the interaction between P and Zn about biofortication in two bean cultivars, evaluating the concentration of Zn and iron in the grain and production

IMPACT OF INTERACTION P AND Zn ON BIOFORTIFICATION OF BEAN

INTRODUCTION: A large part of the world population has low levels of micronutrients, especially pregnant women and children in developing countries. Zinc (Zn) is a micronutrient, performing many functions in the organism. Biofortifcation aims to increase the concentration of certain mineral in parts consumed of the cultivated plants. The crops of most interest are those that constitute the basic diet for the majority of the population, including beans. Two main strategies are used in biofortification, selection of cultivars more favorable to biofortification and increase the micronutrient dose. Biofortification of bean with Zn is difficult due to interaction with phosphorus (P). The decrease in zinc absorption caused by phosphorus depends on soil atributes such as pH, cation exchange capacity and direct reaction with Zn and subsequent precipitation. The increase of the dose of Zn can reduce the absorption of iron by plants by competitve inhibition. This study aimed to evaluate the interaction between P and Zn about biofortication in two bean cultivars, evaluating the concentration of Zn and iron in the grain and production

Convergence to a self-similar solution in general relativistic gravitational collapse

We study the spherical collapse of a perfect fluid with an equation of state $P=k\rho$ by full general relativistic numerical simulations. For 0, it has been known that there exists a general relativistic counterpart of the Larson-Penston self-similar Newtonian solution. The numerical simulations strongly suggest that, in the neighborhood of the center, generic collapse converges to this solution in an approach to a singularity and that self-similar solutions other than this solution, including a ``critical solution'' in the black hole critical behavior, are relevant only when the parameters which parametrize initial data are fine-tuned. This result is supported by a mode analysis on the pertinent self-similar solutions. Since a naked singularity forms in the general relativistic Larson-Penston solution for 0, this will be the most serious known counterexample against cosmic censorship. It also provides strong evidence for the self-similarity hypothesis in general relativistic gravitational collapse. The direct consequence is that critical phenomena will be observed in the collapse of isothermal gas in Newton gravity, and the critical exponent $\gamma$ will be given by $\gamma\approx 0.11$, though the order parameter cannot be the black hole mass.Comment: 22 pages, 15 figures, accepted for publication in Physical Review D, reference added, typos correcte

Variabilidade espacial solo avaliada pela condutividade elétrica aparente e espectroscopia de fluorescência de raio-X.

O conhecimento da variabilidade espacial das propriedades do solo é útil para subsidiar as decisões sobre o manejo tanto do solo como das culturas. O objetivo deste trabalho foi o mapear a variabilidade espacial dos parâmetros do solo da área experimental do LANAPRE. O estudo foi conduzido em área de 3 ha em São Carlos (SP). Para a caracterização dos teores totais de componentes do solo utilizou-se um espectrômetro portátil de fluorescência de raio-X (XRF). A condutividade elétrica aparente do solo (CEa) foi medida com um protótipo de sensor de contato nas profundidades de 0-30 e 0-90cm. A variabilidade espacial das propriedades do solo medidas pelas diferentes técnicas foi modelada utilizando semivariogramas. Os mapas foram obtidos por krigagem com o software Vesper. Os resultados indicaram houve correlação inversa entre o teor de Si e a condutividade elétrica aparente do solo em ambas as profundidades (r=-0,344 e -0,369).SIAGRO 2014

Variabilidade espacial solo avaliada pela condutividade elétrica aparente e espectroscopia de fluorescência de raio-X.

Resumo: O conhecimento da variabilidade espacial das propriedades do solo é útil para subsidiar as decisões sobre o manejo tanto do solo como das culturas. O objetivo deste trabalho foi o mapear a variabilidade espacial dos parâmetros do solo da área experimental do LANAPRE. O estudo foi conduzido em área de 3 ha em São Carlos (SP). Para a caracterização dos teores totais de componentes do solo utilizou-se um espectrômetro portátil de fluorescência de raio-X (XRF). A condutividade elétrica aparente do solo (CEa) foi medida com um protótipo de sensor de contato nas profundidades de 0-30 e 0-90cm. A variabilidade espacial das propriedades do solo medidas pelas diferentes técnicas foi modelada utilizando semivariogramas. Os mapas foram obtidos por krigagem com o software Vesper. Os resultados indicaram houve correlação inversa entre o teor de Si e a condutividade elétrica aparente do solo em ambas as profundidades (r=-0,344 e -0,369).SIAGRO 2014