Size-dependent magnetization fluctuations in NiO nanoparticles

The finite size and surface roughness effects on the magnetization of NiO nanoparticles is investigated. A large magnetic moment arises for an antiferromagnetic nanoparticle due to these effects. The magnetic moment without the surface roughness has a non-monotonic and oscillatory dependence on $R$, the size of the particles, with the amplitude of the fluctuations varying linearly with $R$. The geometry of the particle also matters a lot in the calculation of the net magnetic moment. An oblate spheroid shape particle shows an increase in net magnetic moment by increasing oblateness of the particle. However, the magnetic moment values thus calculated are very small compared to the experimental values for various sizes, indicating that the bulk antiferromagnetic structure may not hold near the surface. We incorporate the surface roughness in two different ways; an ordered surface with surface spins inside a surface roughness shell aligned due to an internal field, and a disordered surface with randomly oriented spins inside surface roughness shell. Taking a variational approach we find that the core interaction strength is modified for nontrivial values of $\Delta$ which is a signature of multi-sublattice ordering for nanoparticles. The surface roughness scale $\Delta$ is also showing size dependent fluctuations, with an envelope decay $\Delta\sim R^{-1/5}$. The net magnetic moment values calculated using spheroidal shape and ordered surface are close to the experimental values for different sizes.Comment: 19 pages, 8 figures, Accepted for publication in Int. J. Mod. Phys.

Massive Gravity in de Sitter Space via Gravitational Higgs Mechanism

In this paper we discuss massive gravity in de Sitter space via gravitational Higgs mechanism, which provides a nonlinear definition thereof. The Higgs scalars are described by a nonlinear sigma model, which includes higher derivative terms required to obtain the Fierz-Pauli mass term. Using the aforesaid non-perturbative definition, we address appearance of an enhanced local symmetry and a null norm state in the linearized massive gravity in de Sitter space at the special value of the graviton mass to the Hubble parameter ratio. By studying full non-perturbative equations of motion, we argue that there is no enhanced symmetry in the full nonlinear theory. We then argue that in the full nonlinear theory no null norm state is expected to arise at the aforesaid special value. This suggests that no ghost might be present for lower graviton mass values and the full nonlinear theory might be unitary for all values of the graviton mass and the Hubble parameter with no van Dam-Veltman-Zakharov discontinuity. We argue that this is indeed the case by studying full nonlinear Hamiltonian for the relevant conformal and helicity-0 longitudinal modes. In particular, we argue that no negative norm state is present in the full nonlinear theory.Comment: 22 pages, comments and references added. Phys.Rev.D versio

Economic paradigms and the role of the State in Latin America

Includes bibliographyThis paper looks at the two successive development paradigms that prevailed in Latin America during the second half of the twentieth century, examining in particular the role assigned to the State in each. It will discuss how, in the ECLAC paradigm, a far-reaching role for the State as guide, sponsor and direct participant in productive development became less viable as the State was captured by private interests that no institution was solid enough to contain. Later, after the advent of the Washington consensus, the State became too severely weakened to carry out proper regulation of privatized activities or to sustain its long-term vision or its concern about income concentration. The paper touches upon the social demand for a new type of State and examines the requirements and objectives that will have to be met if the State is to facilitate the effective operation of markets and act to reduce social inequalities, among other things

Agricultural Development in Latin America and the Role of Research and Technological Change: An Overview

Text of the Sir John Crawford Memorial Lecture delivered during International Centers Week, October 1992, by President Enrique V. Iglesias of the Inter American Development Bank (IDB). Iglesias spoke of the role of agriculture in Latin American economic development, the performance of Latin American agricultural exports, and the contribution of agricultural research and technological change. He described IDB strategy for promoting agricultural development in the region and its approach to research within that strategy

Development and equity: the challenge of the 1980s

Includes bibliographyPresenta algunos rasgos principales de la coyuntura internacional y del escenario económico regional a comienzos de la década de los ochenta. Analiza las relaciones centro-periferia y el proceso de industrialización en el marco de la realidad actual. Esboza los problemas estratégicos de la nueva década relativos al comercio internacional, el financiamiento internacional, la transición energética y la seguridad en el abastecimiento de alimentos

A preliminary overview of the Latin American economy during 1983

Includes bibliographyPresenta un balance de la economia en America Latina durante 1983, a partir del examen de la produccion, el empleo, la inflacion y el sector externo. Analiza las politicas de ajuste aplicadas en la region orientadas a restablecer el equilibrio del sector externo y las consecuencias economicas y sociales de dichas politicas

Reflections on the Latin American economy in 1982

Includes bibliographyAnaliza los rasgos principales de la crisis economica que afecta a la region y sus causas a partir de algunos fenomenos como el crecimiento economico, la desocupacion, la inflacion, los desequilibrios del sector externo, y el endeudamiento externo. Esboza el camino que debiera seguir America Latina para enfrentar esta crisis