Understanding the Pointer States

In quantum mechanics, pointer states are eigenstates of the observable of the measurement apparatus that represent the possible positions of the display pointer of the equipment. The origin of this concept lies in attempts to fill the blanks in the Everett's relative-state interpretation, and to make it a fully valid description of physical reality. To achieve this, it was necessary to consider not only the main system interacting with the measurement apparatus (like von Neumann and Everett did) but also the role of the environment in eliminating correlations between different possible measurements when interacting with the measurement apparatus. The interaction of the environment with the main system (and the measurement apparatus) is the core of the decoherence theory, which followed Everett's thesis. In this article, we review the measurement process according to von Neumann, Everett's relative state interpretation, the purpose of decoherence and some of its follow-up until Wojciech Zurek's primordial paper that consolidated the concept of pointer state, previously presented by Heinz Dieter Zeh. Employing a simple physical model consisting of a pair of two-level systems -- one representing the main system, the other the measurement apparatus -- and a thermal bath -- representing the environment -- we show how pointer states emerge, explaining its contributions to the question of measurement in quantum mechanics, as well as its limitations. Finally, we briefly show some of its consequences. This paper is accessible to readers with elementary knowledge about quantum mechanics, on the level of graduate courses.Comment: 29 pages (20 for main text and references, 9 for appendices

Nutrition, metabolic hormones, and sexual development in bulls

A series of experiments was conducted to evaluate the effects of nutrition during calfhood (defined as the period from 10 to 26-30 wk of age) and peripubertal period (defined as the period from 27-31 to 70-74 wk of age) on sexual development and reproductive function in beef bulls. The overall objective of these experiments was to evaluate the effects of nutrition on endogenous metabolic hormones (leptin, insulin, GH, and IGF-I), gonadotropins and testosterone concentrations, sexual development, sperm production, and semen quality in bulls. The results of these experiments demonstrated that nutrition affected GnRH secretion and sexual development in bulls. Increased nutrition during calfhood resulted in a more sustained increase in LH pulse frequency during the early gonadotropin rise and greater testicular development at maturity. On the other hand, low nutrition during calfhood suppressed LH secretion during the early gonadotropin rise and resulted in delayed puberty and reduced testicular development at maturity. When low nutrition was accomplished by restricted feed intake, hypothalamic and pituitary function were compromised and LH secretion was more severely affected. Temporal associations between LH secretion patterns and circulating IGF-I concentrations implied that IGF-I is a possible signal to the central “metabolic sensor” involved in translating body nutritional status to the GnRH pulse generator. Nutrition also affected testicular steroidogenesis (testosterone concentrations), indicating effects on the number or function of Leydig cells, or both. Age-related increases in physiological and GnRH-stimulated circulating testosterone concentrations were hastened in bulls receiving high nutrition and delayed in bulls receiving low nutrition; these effects were probably mediated by both LH secretion and IGF-I concentrations. Circulating leptin and insulin may have only permissive roles on GnRH secretion, but may enhance testicular development. Growth hormone concentrations decreased concomitantly with increasing IGF-I concentrations during sexual development in bulls, suggesting that the testes could contribute considerable amounts of circulating IGF-I. In conclusion, management strategies to optimize reproductive function in bulls should focus on increasing nutrition during calfhood

Impacts of extensive sheep grazing on soil physical and chemical quality in open mountain forests, NE Portugal

Grazing and mechanical clearing are common techniques for vegetation management in open Mediterranean forests. Despite its recognized benefits in the prevention of high-intensity and severity forest fires, it is essential to consider its impacts on the physical and chemical soil properties. In an open mountain forest located in the NE of Portugal, soil samples were analyzed at depths 0–5, 5–10, and 10–20 cm collected at two moments: before mechanical clearing, (Control) and after 18 months of extensive sheep grazing, in areas without grazing, only mechanical clearing (MC) and in areas with both mechanical clearing and grazing (MCG). The results indicate that vegetation cutting has induced a significant decrease in extractable potassium, and an increase in the soil organic matter and total nitrogen. The exchangeable bases and the exchangeable acidity did not undergo expressive changes, as indicated by the pH values and the cation exchangeable capacity. After grazing, extractable phosphorus and potassium, organic matter, total nitrogen, exchangeable bases, and cation exchangeable capacity have increased significantly in the topsoil (0–5 cm), reducing soil acidity. Regarding physical properties, only soil permeability has been negatively affected by grazing. Mediterranean mountain open forests management with the combination of vegetation clearing and extensive sheep grazing proved to be effective in reducing vegetable fuel availability and improving soil quality.The present work was supported by EU SUDOE, grant number SOE2/P5E0804, project entitled “OPEN2PRESERVE (SOE 2/P5/ E0804)—Modelo de gestión sostenible para la preservación de espácios abiertos de montaña de alto valor ambiental.”info:eu-repo/semantics/publishedVersio

Evolution signatures in genome network properties

Genomes maybe organized as networks where protein-protein association plays the role of network links. The resulting networks are far from being random and their topological properties are a consequence of the underlying mechanisms for genome evolution. Considering data on protein-protein association networks from STRING database, we present experimental evidence that degree distribution is not scale free, presenting an increased probability for high degree nodes. We also show that the degree distribution approaches a scale invariant state as the number of genes in the network increases, although real genomes still present finite size effects. Based on the experimental evidence unveiled by these data analyses, we propose a simulation model for genome evolution, where genes in a network are either acquired de novo using a preferential attachment rule, or duplicated, with a duplication probability that linearly grows with gene degree and decreases with its clustering coefficient. The results show that topological distributions are better described than in previous genome evolution models. This model correctly predicts that, in order to produce protein-protein association networks with number of links and number of nodes in the observed range, it is necessary 90% of gene duplication and 10% of de novo gene acquisition. If this scenario is true, it implies a universal mechanism for genome evolution