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Zero Level (zero + level)
Selected AbstractsSpace,time modeling of rainfall dataENVIRONMETRICS, Issue 6 2004Luis Guillermo Coca Velarde Abstract Climate variables assume non-negative values and are often measured as zero. This is just the case when the rainfall level, in the dry season, is measured in a specified place. Then, the stochastic modeling demands the inclusion of a probability mass point at the zero level, and the resulting model is a mixture of a continuous and a Bernoulli distribution. In this article, spatial conditional autoregressive effects dealing with the idea that neighbors present similar responses is considered and the response level is modeled in two stages. The aim is to consider spatial interpolation and prediction of levels in a Bayesian context. Data on weekly rainfall levels measured in different stations at the central region of Brazil, an area with two well-marked seasons, will be used as an example. A method for comparing models, based on the deviance function, is also implemented. The main conclusion is that the use of space,time models improves the modeling of hydrological and climatological variables, allowing the inclusion of real life considerations such as the influence of other covariates, space dependence and time effects such as seasonality. Copyright © 2004 John Wiley & Sons, Ltd. [source] Extraction of media and plaque boundaries in intravascular ultrasound images by level sets and min/max flowEXPERT SYSTEMS, Issue 2 2010Ali Iskurt Abstract: Estimation of the plaque area in intravascular ultrasound images after extraction of the media and plaque,lumen interfaces is an important application of computer-aided diagnosis in medical imaging. This paper presents a novel system for fully automatic and fast calculation of plaque quantity by capturing the surrounding ring called media. The system utilizes an algorithm that consists of an enhanced technique for noise removal and a method of detecting different iso levels by sinking the image gradually under zero level. Moreover, an important novelty with this technique is the simultaneous extraction of media and lumen,plaque interfaces at satisfactory levels. There are no higher dimensional surfaces and evolution of contours, stopping at high image gradients. Thus, the system runs really fast with curvature velocity only and has no complexity. Experiments also show that this shape-recovering curvature term not only removes the noisy behaviour of ultrasound images but also strengthens very weak boundaries and even completes the missing walls of the media. In addition, the lumen,plaque interface can be detected simultaneously. For validation, a new and very useful algorithm is developed for labelling of intravascular ultrasound images, taken from video sequences of 15 patients, and a comparison-based verification is done between manual contours by experts and the contours extracted by our system. [source] Low level of gene flow from cultivated beets (Beta vulgaris L. ssp. vulgaris) into Danish populations of sea beet (Beta vulgaris L. ssp. maritima (L.) Arcangeli)MOLECULAR ECOLOGY, Issue 5 2005N. S. ANDERSEN Abstract Gene flow from sugar beets to sea beets occurs in the seed propagation areas in southern Europe. Some seed propagation also takes place in Denmark, but here the crop,wild gene flow has not been investigated. Hence, we studied gene flow to sea beet populations from sugar beet lines used in Danish seed propagation areas. A set of 12 Danish, two Swedish, one French, one Italian, one Dutch, and one Irish populations of sea beets, and four lines of sugar beet were analysed. To evaluate the genetic variation and gene flow, eight microsatellite loci were screened. This analysis revealed hybridization with cultivated beet in one of the sea beet populations from the centre of the Danish seed propagation area. Triploid hybrids found in this population were verified with flow cytometry. Possible hybrids or introgressed plants were also found in the French and Italian populations. However, individual assignment test using a Bayesian method provided 100% assignment success of diploid individuals into their correct subspecies of origin, and a Bayesian Markov chain Monte Carlo (MC MC) approach revealed clear distinction of individuals into groups according to their subspecies of origin, with a zero level of genetic admixture among subspecies. This underlines that introgression beyond the first hybridization is not extensive. The overall pattern of genetic distance and structure showed that Danish and Swedish sea beet populations were closely related to each other, and they are both more closely related to the population from Ireland than to the populations from France, the Netherlands, and Italy. [source] Angiogenesis and Interstitial Pressure in a Rat Tumour ModelANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2005H. Hünigen Introduction and Aim:, Angiogenesis, the formation of new blood vessels, is a crucial process in physiological and pathological growth. Pathological angiogenesis is responsible for growth and metastasis of solid tumours, and, when blocked, improves prognosis. As a result of the angiogenic cascade in solid tumours an irregular, leaky capillary network develops. The aim of the present study was to define malignant tumours' vascular characteristics and reveal functional anatomy by quantification of the microvasculature and interstitial pressure (IP) in relation to tumour fluid dynamics as visualized by contrast enhanced magnetic resonance imaging (MRI). Material and Methods:, Dynamic MRI and measurement of the IP was performed in 21 rats implanted with colon carcinomas subcutaneously. Angiogenesis was studied by morphometry of the capillaries, and immunolocalization of the angiogenic factor VEGF and VEGF-Receptor 2. Results and Conclusions:, Histology, immunohistochemistry and MRI confirmed concentric arrangement of 4 tumour zones. The tumour margin included loose connective tissue with abundant mononuclear cells. Many large microvessels were seen in this most intensely vascularized zone. IP measurement in this zone was adjusted to the zero level. Diameter of the peripheral zone of vital cells measured 1.3 mm. Capillaries were smaller and sparse. Dynamic MRI revealed peripheral washout of the contrast agent in this zone. After an initial increase of the signal intensity a hypo-intense rim was formed within a few minutes. The intermediate region was characterized by islands of vital tumour cells containing 3% capillaries (hot spots). The innermost area, the necrotic zone, took 35% of the total tumour area with less than 0.5% vessels. The IP increased from the periphery to the centre. VEGF and VEGF-receptor 2 was found in the vessels of the tumour margin and vital tumour cells of the peripheral zone. From this can be concluded that the peripheral washout phenomenon seems to be correlated with elevated interstitial pressure and increased capillary density and therefore may be a reliable sign of malignancy. [source] | ||||||||||