Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3

The complete irreducible co-representations of the paramagnetic space group provide a simple and direct path to explore the symmetry restrictions of magnetically driven ferroelectricity. The method consists of a straightforward generalization of the method commonly used in the case of displacive modulated systems and allows us to determine, in a simple manner, the full magnetic symmetry of a given phase originated from a given magnetic order parameter. The potential ferroic and magneto-electric properties of that phase can then be established and the exact Landau free energy expansions can be derived from general symmetry considerations. In this work, this method is applied to the case of the orthorhombic rare-earth manganites RMnO3. This example will allow us to stress some specific points, such as the differences between commensurate or incommensurate magnetic phases regarding the ferroic and magnetoelectric properties, the possible stabilization of ferroelectricity by a single irreducible order parameter or the possible onset of a polarization oriented parallel to the magnetic modulation. The specific example of TbMnO3 will be considered in more detail, in order to characterize the role played by the magneto-electric effect in the mechanism for the polarization rotation induced by an external magnetic field.Comment: Conference: Aperiodic`0

Parallel structurally-symmetric sparse matrix-vector products on multi-core processors

We consider the problem of developing an efficient multi-threaded implementation of the matrix-vector multiplication algorithm for sparse matrices with structural symmetry. Matrices are stored using the compressed sparse row-column format (CSRC), designed for profiting from the symmetric non-zero pattern observed in global finite element matrices. Unlike classical compressed storage formats, performing the sparse matrix-vector product using the CSRC requires thread-safe access to the destination vector. To avoid race conditions, we have implemented two partitioning strategies. In the first one, each thread allocates an array for storing its contributions, which are later combined in an accumulation step. We analyze how to perform this accumulation in four different ways. The second strategy employs a coloring algorithm for grouping rows that can be concurrently processed by threads. Our results indicate that, although incurring an increase in the working set size, the former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo

Trabalhando com grupos na estratégia saúde da família

A proposta de priorização do atendimento grupal no contexto da atenção básica ancora-se no pressuposto do resgate da “noção de grupo como rede efetiva de suporte, em seu sentido mais amplo”. Trata-se de uma oportunidade de implementar as redes comunitárias como rede significativa de promoção de saúde, nas quais as pessoas são protagonistas do cuidado de si mesmas e do outro. Isso vai de encontro à crença produtivista, presente entre profissionais e gestores do contexto básico, que aponta para a estratégia grupal como possibilidade de atender um maior número de pessoas. Tal lógica responde a uma postura profissional ancorada na falsa ideia de produtividade, em que se está atento ao número de atendimento e de pessoas, e não à qualidade do melhor acolhimento das necessidades de saúde dos usuários.1.0Ministério da Saúde/OPAS/OM

Temperature effect on (2+1) experimental Kardar-Parisi-Zhang growth

We report on the effect of substrate temperature (T) on both local structure and long-wavelength fluctuations of polycrystalline CdTe thin films deposited on Si(001). A strong T-dependent mound evolution is observed and explained in terms of the energy barrier to inter-grain diffusion at grain boundaries, as corroborated by Monte Carlo simulations. This leads to transitions from uncorrelated growth to a crossover from random-to-correlated growth and transient anomalous scaling as T increases. Due to these finite-time effects, we were not able to determine the universality class of the system through the critical exponents. Nevertheless, we demonstrate that this can be circumvented by analyzing height, roughness and maximal height distributions, which allow us to prove that CdTe grows asymptotically according to the Kardar-Parisi-Zhang (KPZ) equation in a broad range of T. More important, one finds positive (negative) velocity excess in the growth at low (high) T, indicating that it is possible to control the KPZ non-linearity by adjusting the temperature.Comment: 6 pages, 5 figure

Irreversible magnetization under rotating fields and lock-in effect on ErBa_2Cu_3O_7 single crystal with columnar defects

We have measured the irreversible magnetization M_i of an ErBa_2Cu_3O_7 single crystal with columnar defects (CD), using a technique based on sample rotation under a fixed magnetic field H. This method is valid for samples whose magnetization vector remains perpendicular to the sample surface over a wide angle range - which is the case for platelets and thin films - and presents several advantages over measurements of M_L(H) loops at fixed angles. The resulting M_i(\Theta) curves for several temperatures show a peak in the CD direction at high fields. At lower fields, a very well defined plateau indicative of the vortex lock-in to the CD develops. The H dependence of the lock-in angle \phi_L follows the H^{-1} theoretical prediction, while the temperature dependence is in agreement with entropic smearing effects corresponding to short range vortex-defects interactions.Comment: 7 pages, 6 figures, to be published in Phys. Rev.

Disorder effects at low temperatures in La_{0.7-x}Y_{x}Ca_{0.3}MnO_{3} manganites

With the aim of probing the effect of magnetic disorder in the low-temperature excitations of manganites, specific-heat measurements were performed in zero field, and in magnetic fields up to 9 T in polycrystalline samples of La_{0.7-x}Y_{x}Ca_{0.3}MnO_{3}, with Y concentrations x=0, 0.10, and 0.15. Yttrium doping yielded the appearance of a cluster-glass state, giving rise to unusual low-temperature behavior of the specific-heat. The main feature observed in the results is a strong enhancement of the specific-heat linear term, which is interpreted as a direct consequence of magnetic disorder. The analysis was further corroborated by resistivity measurements in the same compounds.Comment: 9 pages, 2 figure

The Caregiver Support Ratio in Europe: Estimating the Future of Potentially (Un)Available Caregivers

The caregiver support ratio (CSR) is defined as the number of potential caregivers aged 45–64 years, the most common caregiving age range, for each person aged 80+, the subgroup of older adults most at risk of needing long-term services and support. This study uses data from the CENSUS HUB database and from the UN database to calculate the current (last year available: 2011) and projected (2020, 2030, 2040 and 2050) CSR for a group of European countries. Mediterranean countries, France, Belgium, and Sweden presented the lowest CSR (5:1) in 2011. The countries with the highest CSR were Slovakia (9:1) and Ireland, Poland, Cyprus, and Malta (8:1). The estimated CSR is expected to progressively decline from 6:1 (2011) to 2:1 (2050) for all countries. Although differences in the CSR exist between countries, the number of people aged 45–64 who are available to care for each person aged 80+ will decrease uniformly in the coming decades. Cross-national challenges for gerontological social policies and healthcare provision are expected due to the increasing demand for long-term care among the oldest population.This work was partially supported by National Funds through Fundação para a Ciência e a Tecnologia (FCT) within the CINTESIS R&D Unit (reference UIDB/4255/2020). Some information from this study was presented at the 2019 Annual Meeting of the Gerontological Society of America

Gravitational form factors and decoupling in 2D

We calculate and analyse non-local gravitational form factors induced by quantum matter fields in curved two-dimensional space. The calculations are performed for scalars, spinors and massive vectors by means of the covariant heat kernel method up to the second order in the curvature and confirmed using Feynman diagrams. The analysis of the ultraviolet (UV) limit reveals a generalized “running” form of the Polyakov action for a nonminimal scalar field and the usual Polyakov action in the conformally invariant cases. In the infrared (IR) we establish the gravitational decoupling theorem, which can be seen directly from the form factors or from the physical beta function for fields of any spin

On the magnetically driven ferroelectric phase in GdMnO3

At room temperature, GdMnO3 is a paraelectric and paramagnetic with a distorted perovskite structure of orthorhombic symmetry (space group Pnma). On cooling, it undergoes a phase transition sequence to a magnetic incommensurate phase (k=delta a*; Tc1=42K) and a A-type antiferromagnetic phase (Tc2=27K). At low temperatures (T<12K), a magnetic field applied along the a-axis destabilizes the antiferromagnetic phase and induces a first order transition to a magnetic commensurate modulated phase (delta=1/4) that is also ferroelectric (P//c). This work analyses this field induced phase transition from the point of view of the symmetry and Landau theory.Comment: 13 pages, communication to the 11th European Meeting on Ferroelectricity, Bled (Slovenia)2007; submitted to Ferroelectric