Distributional Chaos in the Baire Space

In this paper we consider the question of distributional chaos on non-compact metric dynamical systems. We focus on a shift space over a countable alphabet, the Baire Space. We prove that on the Baire Space subshifts of finite type exhibit dense distributional chaos and subshifts of bounded type that are perfect and have a dense set of periodic points also have distributional chaos

Free energy conservation in ab initio molecular dynamics simulations and homogeneous melt nucleation

The Z method is a popular atomistic simulation method for determining the melting temperature of solids by using a sequence of molecular dynamics(MD) runs in the microcanonical(NVE) ensemble to target the lowest system energy where the solid always melts. Homogeneous melting at the superheating critical limit($T_h$), is accompanied by a temperature drop to the equilibrium melting temperature($T_m$). Implementation of the Z method interfaced with modern {\it ab initio} electronic structure packages use Hellman-Faynman dynamics to propagate the ions in the NVE ensemble with the Mermin free energy plus the ionic kinetic energy conserved. So the electronic temperature($T_{el}$) is kept fixed along the trajectory which may introduce some spurious ion-electron interactions in MD runs with large temperature changes. We estimate possible systematic errors in evaluating melting temperature with different choices of $T_{el}$. MD runs with the $T_{el}$ = $T_h$ and $T_{el}$ = $T_m$ shows that the difference in melting temperature can be 200-300 K (3-5\% of the melting temperature) for our two test systems. Our results are in good agreement with previous studies with different methods, suggesting the CaSiO$_3$ and SiO$_2$ melts at around 6500 at 100 GPa and 6000 K at 160 GPa. The melting temperature decreases with increasing $T_{el}$ due to the increasing entropic stabilisation of the liquid and the system melts about 3 times faster with $T_{el} = T_h$ than with $T_{el} = T_m$. A careful choice of $T_{el}$ in BOMD is essential for the critical evaluation of the Z method especially at very high temperatures. Inspection of the homogeneous melting process shows that melting occurs via a two-step mechanism: 1) melting of the anion sublattice is accompanied by a small drop in temperature and 2) the formation of small defects which trigger the formation of small liquid clusters and fully melted.Comment: 10 figures, 17 page

A REFORMA PREVIDENCIÁRIA NO GOVERNO LULA

O presente artigo tem por objetivo descrever e analisar a Reforma Previdenciária empreendida pelo Congresso Nacional por iniciativa do Governo Lula, efetivada pelas Emendas Constitucionais nos 41, de 2003, e 47, de 2005. São examinados em detalhes os efeitos das modificações promovidas no sistema previdenciário brasileiro. A Reforma, tal como a que a antecedeu, não considerou a previdência social de forma integrada à seguridade social. Sua forma final acentuou a configuração de um modelo misto, com um limite de benefícios no sistema público, a partir do qual deve-se recorrer ao sistema privado complementar. No sistema público, a Reforma atuou na tendência de unificação de regras entre os regimes geral e próprio dos servidores públicos

Spontaneous separation of two-component Fermi gases in a double-well trap

The two-component Fermi gas in a double-well trap is studied using the density functional theory and the density profile of each component is calculated within the Thomas-Fermi approximation. We show that the two components are spatially separate in the two wells once the repulsive interaction exceeds the Stoner point, signaling the occurrence of the ferromagnetic transition. Therefore, the double-well trap helps to explore itinerant ferromagnetism in atomic Fermi gases, since the spontaneous separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep

Finite-temperature magnetism of Fex_xPd1−x_{1-x} and Cox_xPt1−x_{1-x} alloys

The finite-temperature magnetic properties of Fe$_x$Pd$_{1-x}$ and Co$_x$Pt$_{1-x}$ alloys have been investigated. It is shown that the temperature-dependent magnetic behaviour of alloys, composed of originally magnetic and non-magnetic elements, cannot be described properly unless the coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is included. A scheme for the calculation of the Curie temperature ($T_C$) for this type of systems is presented which is based on the extended Heisenberg Hamiltonian with the appropriate exchange parameters $J_{ij}$ obtained from {\em ab-initio} electronic structure calculations. Within the present study the KKR Green's function method has been used to calculate the $J_{ij}$ parameters. A comparison of the obtained Curie temperatures for Fe$_x$Pd$_{1-x}$ and Co$_x$Pt$_{1-x}$ alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure

C-type related order in the defective fluorites La2Ce2O7 and Nd2Ce2O7 studied by neutron scattering and ab initio MD simulations

This work presents a structural investigation of La2-xNdxCe2O7 (x = 0.0, 0.5, 1.0, 1.5, 2.0) using X-ray powder diffraction and total scattering neutron powder diffraction, analysed using Rietveld and the reverse Monte Carlo method (RMC). Ab initio molecular dynamics (MD) modelling is also performed for further investigations of the local order. The main intensities in the neutron diffraction data for the La2-xNdxCe2O7 series correspond to the fluorite structure. However, additional C-type superlattice peaks are visible for x > 0 and increase in intensity with increasing x. The Nd-containing compositions (x > 0) are best fitted with Rietveld analysis by using a combination of oxygen deficient fluorite and oxygen excess C-type structures. No indications of cation order are found in the RMC or Rietveld analysis, and the absence of cation order is supported by the MD modelling. We argue that the superlattice peaks originate from oxygen vacancy ordering and associated shift in the cation position away from the ideal fluorite site similar to that in the C-type structure, which is seen from the Rietveld refinements and the observed ordering in the MD modelling. The vacancies favour alignments in the , and especially the direction. Moreover, we find that such ordering might also be found to a small extent in La2Ce2O7, explaining the discernible modulated background between the fluorite peaks. The observed overlap of the main Bragg peaks between the fluorite and C-type phase supports the co-existence of vacancy ordered and more disordered domains. This is further supported by the observed similarity of the radial distribution functions as modelled with MD. The increase in long range oxygen vacancy order with increasing Nd-content in La2-xNdxCe2O7 corresponds well with the lower oxide ion conductivity in Nd2Ce2O7 compared to La2Ce2O7 reported earlier

One-hour post-load plasma glucose levels associated with decreased insulin sensitivity and secretion and early makers of cardiometabolic risk.

PURPOSE: Obese adults with normal glucose tolerance (NGT) but with 1-hour post-load plasma glucose (1hPG) ≥ 155 mg/dl are at higher risk of developing type 2 diabetes (T2D) and cardiometabolic complications. Little information is available for the pediatric population, where recently, a lower cutoff, 132.5 mg/dl, has been suggested as being more sensitive to identify subjects at risk of T2D. Our aim was to assess whether obese Caucasian youth with 1hPG ≥ 132.5 mg/dl have worse insulin sensitivity and secretion and a worse cardiometabolic profile compared to obese youth with 1hPG < 132.5 mg/dl. METHODS: Medical records of 244 (43% male; age: 11.1 ± 2.7years) overweight/obese children and adolescents, who had undergone an oral glucose tolerance test (OGTT), were retrieved. Anthropometric and biochemical data were collected from the hard copy archive. Indexes of insulin resistance (HOMA-IR), insulin sensitivity (WBISI), and insulin secretion (Insulinogenic Index, Disposition Index) were calculated. RESULTS: Of the 244 records analyzed, 215 fulfilled criteria for NGT and had complete biochemical data. Among NGT patients, 42 (19.5%) showed 1hPG ≥ 132.5 mg/dL (high-NGT), while the remaining had 1hPG < 132.5 mg/dL (low-NGT). The high-NGT group showed a higher male prevalence (59.5 vs 37%), lower Disposition Index (0.54 [0.39-0.71] vs 0.79 [0.47-1.43]), and WBISI (0.24 [0.18-0.35] vs 0.33 [0.23-0.50]) than the low-NGT group. High-NGT subjects also showed a trend towards lower HDL-cholesterol and higher triglycerides/HDL-cholesterol ratio (2.13 [1.49-3.41] vs 1.66 [1.24-2.49]). CONCLUSIONS: In overweight/obese NGT Caucasian youth a 1hPG ≥ 132.5 mg/dL was able to identify those with impaired insulin sensitivity and secretion and a trend towards a worse cardio-metabolic profile, a group likely at risk for future T2D

Thermodynamic Studies on Non Centrosymmetric Superconductors by AC Calorimetry under High Pressures

We investigated the non centrosymmetric superconductors CePt$_3$Si and UIr by the ac heat capacity measurement under pressures. We determined the pressure phase diagrams of these compounds. In CePt$_3$Si, the N\'{e}el temperature $T_{\rm N}$ = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure $P_{\rm AF}$ $\simeq$ 0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to $P_{\rm AF}$ $\simeq$ 1.5 GPa. The phase diagram of CePt$_3$Si is very unique and has never been reported before for other heavy fermion superconductors. In UIr, the heat capacity shows an anomaly at the Curie temperature $T_{\rm C1}$ = 46 K at ambient pressure, and the heat capacity anomaly shifts to lower temperatures with increasing pressure. The present pressure dependence of $T_{\rm C1}$ was consistent with the previous studies by the resistivity and magnetization measurements. Previous ac magnetic susceptibility and resistivity measurements suggested the existence of three ferromagnetic phases, FM1-3. $C_{\rm ac}$ shows a bending structure at 1.98, 2.21, and 2.40 GPa .The temperatures where these anomalies are observed are close to the phase boundary of the FM3 phase.Comment: This paper was presented at the international workshop ``Novel Pressure-induced Phenomena in Condensed Matter Systems(NP2CMS)" August 26-29 2006, Fukuoka Japa