3 research outputs found
Effects of domain walls on hole motion in the two-dimensional t-J model at finite temperature
The t-J model on the square lattice, close to the t-J_z limit, is studied by
quantum Monte Carlo techniques at finite temperature and in the underdoped
regime. A variant of the Hoshen-Koppelman algorithm was implemented to identify
the antiferromagnetic domains on each Trotter slice. The results show that the
model presents at high enough temperature finite antiferromagnetic (AF) domains
which collapse at lower temperatures into a single ordered AF state. While
there are domains, holes would tend to preferentially move along the domain
walls. In this case, there are indications of hole pairing starting at a
relatively high temperature. At lower temperatures, when the whole system
becomes essentially fully AF ordered, at least in finite clusters, holes would
likely tend to move within phase separated regions. The crossover between both
states moves down in temperature as doping increases and/or as the off-diagonal
exchange increases. The possibility of hole motion along AF domain walls at
zero temperature in the fully isotropic t-J is discussed.Comment: final version, to appear in Physical Review
Brazil is getting older: demographic changes and epidemiological challenges Envelhecimento populacional do Brasil: mudanças demográficas e desafios epidemiológicos
Population ageing is currently a phenomenon not only in developed countries but also in third world countries. In this paper the features of a population's ageing and the process of epidemiological transition are discussed along with the worldwide changes in age-structure. Population statistics in Brazil and the characteristics of the elderly population are presented and analysed in the light of recent changes. The Brazilian elderly population is also discussed, particularly the issues relating to the social cost of the aged population, its urban and rural distribution, the elderly by sex, marital status and level of schooling, and emphasis is given to the imbalance of the sexes and the consequences of it for women.<br>O crescimento da população idosa é um fenômeno que ocorre nos paÃses centrais, mas também, de modo crescente, nos paÃses do Terceiro Mundo. Este artigo apresenta os motivos deste crescimento, discute o processo de transição epidemiológica, as mudanças na estrutura etária da população idosa em todo o mundo, e em particular no Brasil. EstatÃsticas da população brasileira e as caracterÃsticas do idoso brasileiro são apresentadas e analisadas em função das mudanças ocorridas recentemente. O artigo aborda vários tópicos relacionados com o idoso brasileiro: o custo financeiro para a sociedade manter uma população idosa, a distribuição urbana e rural, a diferença numérica entre sexos, o estado conjugal, a escolaridade, entre outros. Ênfase é conferida a algumas caracterÃsticas e particularidades da mulher idosa