Necessary and sufficient conditions for a Hamiltonian graph

A graph is singular if the zero eigenvalue is in the spectrum of its 0-1 adjacency matrix A. If an eigenvector belonging to the zero eigenspace of A has no zero entries, then the singular graph is said to be a core graph. A ( k,t)-regular set is a subset of the vertices inducing a k -regular subgraph such that every vertex not in the subset has t neighbours in it. We consider the case when k=t which relates to the eigenvalue zero under certain conditions. We show that if a regular graph has a ( k,k )-regular set, then it is a core graph. By considering the walk matrix we develop an algorithm to extract ( k,k )-regular sets and formulate a necessary and sufficient condition for a graph to be Hamiltonian

The Bour's Theorem for invariant surfaces in three-manifolds

In this paper, we apply techniques of the equivariant geometry to give a positive answer to the conjecture that a generalized Bour's Theorem holds for surfaces that are invariant under the action of a one-parameter group of isometries of a three-dimensional Riemannian manifold.Comment: 17 page

Leptin Resistance and the Neuro-Adipose Connection

This article was submitted to Cellular Endocrinology, a section of the journal Frontiers in Endocrinology.Obesity is a public health concern affecting both genders at all ages around the world. The worldwide prevalence of obesity is rapidly increasing and has nearly doubled between 1980 and 2016. Consequently, it places a large financial burden on the economy due to the increased morbidity and mortality, as well as the reduced quality of life and development of chronic diseases. Obesity is typically characterized by excessive amounts of the hormone leptin, a cytokine-like molecule produced in white adipose tissue (WAT) that is secreted into the systemic circulation. The circulating levels of leptin are proportional to the amount of fat and function as the afferent signal in a negative feedback loop that seeks to maintain body fat in a very narrow range of variation. Leptin has a central role in body weight homeostasis due to its inhibition of food intake inhibition and stimulation of energy expenditure. The effect of leptin on body weight is attributed to its action in a specific brain region, the hypothalamus. Hence, leptin is released by adipocytes in proportion to the size of fat depots, enters the circulation, and reaches the central nervous system by crossing the blood-brain barrier (BBB) through receptor-mediated endocytosis in which it acts mainly through the arcuate nucleus of the hypothalamus to mediate most of its actions. Specifically, leptin modulates the activity of two types of neurons to inhibit appetite, through production of anorexigenic peptides by the pro-opiomelanocortin (POMC) neurons and suppression of the orexigenic agouti-related protein (AgRP) neurons. Besides acting on the hypothalamus to suppress appetite, leptin also induces lipolysis in WAT and thermogenesis in brown adipose tissue (BAT) and browning of WAT, via the activation of the sympathetic nervous system (SNS). However, in most obese subjects, despite its high serum levels, leptin fails to perform its physiological functions and consequently fails to reduce weight. This effect has been coined as leptin resistance.Fundação para Ciência e Tecnologia grants: (PD/BD/52437/2013, PTDC-BIM-MET-3750-2014); EMBO grant: (IG3077); Prémios Maratona Saúde 2015: (Diabetes); Human Frontiers Science Program grant:(RGY0070/2016).info:eu-repo/semantics/publishedVersio

Chemical changes of heat treated pine and eucalypt wood monitored by FTIR

A hardwood, Eucalyptus globulus Labill., and a softwood Pinus pinaster Aiton., were heat treated at temperatures between 170 and 210ºC in an oven and in an autoclave. The samples were pre-extracted with dichloromethane, ethanol and water and ground prior to Fourier Transform Infrared (FTIR) spectroscopic analysis. The heat treatment caused significant changes in the chemical composition and structure of wood, in lignin and polysaccharides. Hemicelluloses were the first to degrade as proved by the initial decrease of the 1730 cm-1 peak due to the breaking of acetyl groups in xylan. Hardwood lignin changed more than softwood lignin, with a shift of maximum absorption from 1505 cm-1 to approximately 1512 cm-1 due to decrease of methoxyl groups, loss of syringyl units or breaking of aliphatic side-chains. The macromolecular structure becomes more condensed and there is a clear increase of non-conjugated (1740 cm-1) in relation to conjugated groups (1650 cm-1). However, the changes induced by the thermal treatment are difficult to monitor by FTIR spectroscopy due to the different chemical reactions occurring simultaneously.info:eu-repo/semantics/publishedVersio

Modelling the long term effect of changes in fire frequency on the total area burnt

Wildfires are one of the major problems in Mediterranean countries, and much effort is done by the governments to dissuade people from starting fires. Public campaigns often promote the idea that the more ignitions the larger the surface burnt will be. This reasoning is, however, not so straightforward. This paper addresses the question of how fire frequency relates to the total area burnt by using a model of fire regime that includes variables such as the number of ignitions, fire fighting capacity, fuel accumulation rates, existence of prescribed burning and meteorological variability. This question was addressed by performing three experimental simulations: effect of the number of potential ignitions, the combined effect of the number of ignitions and extinction capacity, and the non random spatial pattern of fire ignitions. Results showed that a larger number ignitions did not have a great effect on the total area burnt but had an effect in the occurrence of large fires, independently of the extinction capacity and of the spatial distribution of ignitions. An explanation for these findings is provided and management implications of these results are briefly discussed

The reward value of sucrose in leptin-deficient obese mice

Leptin-deficient patients report higher "liking" ratings for food, and leptin replacement therapy normalizes these ratings even before weight loss is achieved. Since animals cannot report their ratings, we studied the relationship between leptin and food reward in leptin-deficient ob/ob mice using a optogenetic assay that quantifies the reward value of sucrose. In this assay, mice chose between one sipper dispensing the artificial sweetener sucralose coupled to optogenetic activation of dopaminergic (DA) neurons, and another sipper dispensing sucrose. We found that the reward value of sucrose was high under a state of leptin deficiency, as well as at a dose of leptin that does not suppress food intake (12.5 ng/h). Treatment with higher doses of leptin decreased the reward value of sucrose before weight loss was achieved (100 ng/h), as seen in leptin-deficient patients. These results phenocopy in mice the behavior of leptin-deficient patients.JPB Foundation; The Klarman Family Foundation for Eating Disorders; The Rockefeller Foundation; Gulbenkian Foundation; FCT

Effects of fertiliser practices on the growth and quality of two table grape cultivars: 'Cardinal' and 'D. Maria'.

In this study, the different fertilliser practices of four commercial vineyards (Vitis vinifera L. cv. 'Cardinal' and cv. 'D. Maria') in southern Portugal were assessed and compared in 2002. The vineyards were established in similar soils under the same climatic conditions and additional water was supplied by drip irrigation. At harvest, the mineral composition of petioles (P, K, Mg, Ca, Fe, Cu, Zn and Mn) and quality parameters of the grapes (total soluble solids expressed as degree Brix, cluster length and weight, number of grapes, grapes weight and rachis weight) were recorded. For the 'Cardinal' cultivar, the nutritional status of the plant was correlated with growth and yield, and the greatest values for most of the parameters studied were measured at Alvisquer farm. For the 'D. Maria' cultivar, a single correlation was found between nutrient levels and growth. Shoot and cluster lengths, and grape weight were similar at all farms, though cluster weight, number of grapes and total soluble solids were smaller at Pedras than at Alvisquer or Gomeira

Can a restocking event with European (glass) eels cause early changes in local biological communities and its ecological status?

In an attempt to assist the recovery of the panmictic population of the European eel, declining since the late 1980s, the restocking of areas with low or no natural recruitment has been one of the measures adopted to reverse this trend. However, the main focus in several monitoring programmes for these actions, has been in the best interest of its viability and cost/benefit relationships and, for that, the condition of the released stocks has been the main concern. Yet, so far, no studies have assessed the potential ecological impacts that restocking might have on other biological communities. This pioneer pilot study aimed to evaluate the early ecological impact of a restocking event on other biological communities, considering inter-specific competition (other fish species) and feeding impact (macroinvertebrates).The reference condition of the biological communities of an inland tributary of the Mondego river, the River Ceira, was determined in three sites inaccessible to the natural recruitment of eels, followed by a post-stocking assessment. The results showed no significant changes in the fish assemblages in restocked areas, contrary to the macroinvertebrate community. However, the ecological status for the macroinvertebrate community showed no deleterious effects, with the results suggesting exactly the opposite. This may be related to the low density of the restocked eels and factors influencing the local trophic web. This study confirms the suitability of the habitat for restocking with glass eels, during its early stages, without disrupting the local ecological status, using densities close to those of natural recruitment

Pecuária de corte e a conservação do Pantanal.

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