Phase separation and stripe formation in the 2D t-J model: a comparison of numerical results

We make a critical analysis of numerical results for and against phase separation and stripe formation in the t-J model. We argue that the frustrated phase separation mechanism for stripe formation requires phase separation at too high a doping for it to be consistent with existing numerical studies of the t-J model. We compare variational energies for various methods, and conclude that the most accurate calculations for large systems appear to be from the density matrix renormalization group. These calculations imply that the ground state of the doped t-J model is striped, not phase separated.Comment: This version includes a revised, more careful comparison of numerical results between DMRG and Green's function Monte Carlo. In particular, for the original posted version we were accidentally sent obsolete data by Hellberg and Manousakis; their new results, which are what were used in their Physical Review Letter, are more accurate because a better trial wavefunction was use

A century of trends in adult human height

Being taller is associated with enhanced longevity, and higher education and earnings. We reanalysed 1472 population-based studies, with measurement of height on more than 18.6 million participants to estimate mean height for people born between 1896 and 1996 in 200 countries. The largest gain in adult height over the past century has occurred in South Korean women and Iranian men, who became 20.2 cm (95% credible interval 17.5-22.7) and 16.5 cm (13.3-19.7) taller, respectively. In contrast, there was little change in adult height in some sub-Saharan African countries and in South Asia over the century of analysis. The tallest people over these 100 years are men born in the Netherlands in the last quarter of 20th century, whose average heights surpassed 182.5 cm, and the shortest were women born in Guatemala in 1896 (140.3 cm; 135.8-144.8). The height differential between the tallest and shortest populations was 19-20 cm a century ago, and has remained the same for women and increased for men a century later despite substantial changes in the ranking of countries

HortiBot: A System Design of a Robotic Tool Carrier for High-tech Plant Nursing

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 9 (2007): HortiBot: A System Design of a Robotic Tool Carrier for High-tech Plant Nursing. Manuscript ATOE 07 006. Vol. IX. July, 2007