Frequency Analysis of Gradient Estimators in Volume Rendering

Gradient information is used in volume rendering to classify and color samples along a ray. In this paper, we present an analysis of the theoretically ideal gradient estimator and compare it to some commonly used gradient estimators. A new method is presented to calculate the gradient at arbitrary sample positions, using the derivative of the interpolation filter as the basis for the new gradient filter. As an example, we will discuss the use of the derivative of the cubic spline. Comparisons with several other methods are demonstrated. Computational efficiency can be realized since parts of the interpolation computation can be leveraged in the gradient estimatio

Digestion in an ectothermic herbivore, the green iguana (<i>Iguana iguana</i>):Effect of food composition and body temperature

In laboratory experiments, the effect of food composition and body temperature on digestive efficiency was investigated in the lizard Iguana iguana on Curacao (Netherlands Antilles). In a series of experiments the animals were kept in cages with a temperature gradient and different foods were offered ad lib. Mean selected daytime body temperatures were 35.0-degrees-36.4-degrees-C (mean 24 h T(b): 31.8-degrees-33.7-degrees-C). Mean apparent dry-matter digestibility (DDM) varied from 30.0% to 84.2%, depending on the kind of food. Mean DDM and digestible energy were significantly inversely related to the cell wall components lignin and cutin, and these components could explain most of the variance in DDM (r = 0.88). The amount of digestible protein was significantly correlated with crude protein content in the food. Mean transit time of food through the digestive tract varied from 3.9 (berries) to 8.5 (leaves) d. A second series of experiments, in which body temperatures were varied (T(b)) range: 30.0-degrees-36.1-degrees-C), showed that an increase in body temperature induced a significant curvilinear decrease of the transit time from 10 d down to 3 d. Dry-matter digestibility, however, was not affected by a change in body temperature. Maximal fresh-food intake was inversely related at a significant level to the transit time. It is argued that body temperature affects the potential digestive capacity of the green iguana

Human Brown Fat and Obesity: Methodological Aspects

Much is known about brown adipose tissue (BAT) in rodents. Its function is to generate heat in response to low environmental temperatures and to diet or overfeeding. The knowledge about BAT in humans is still rather limited despite the recent rediscovery of its functionality in adults. This review highlights the information available on the contribution of BAT in increasing human energy expenditure in relation to obesity. Besides that methodological aspects will be discussed that need special attention in order to unravel the heat producing capacity of human BAT, the recruitment of the tissue, and its functionality

Brown adipose tissue and the regulation of nonshivering thermogenesis.

PURPOSE OF REVIEW: The recent rediscovery of functional cold activated brown adipose tissue (BAT) in adult humans fuelled an uprise in studies on this tissue. This review focuses on the contribution of human BAT to nonshivering thermogenesis and on factors other than cold that activate BAT. RECENT FINDINGS: Earlier studies revealed BAT activity using a glucose tracer for positron emission tomography/computed tomography (PET/CT) scanning. Several recent studies, using a mix of tracers and PET/CT dynamic scanning showed that human brown fat is metabolically active and related to the perfusion of the tissue. The actual contribution of BAT to nonshivering thermogenesis still needs to be explored.The last few years, several new factors that activate human BAT have been described. These studies also highlight the plasticity of brown and white adipose tissue. Some of these factors may have pharmacological significance. SUMMARY: New PET/CT studies provide information on oxidative human BAT metabolism in vivo. This new information in combination with the study on factors activating BAT are promising with respect to management of obesity and related disorders

MARANGONI CONVECTION AROUND A VENTILATED AIR BUBBLE UNDER MICROGRAVITY CONDITIONS

Under microgravity conditions in both parabolic and sounding rocket flights, the mass-transfer-induced Marangoni convection around an air bubble was studied. To prevent the bubble from becoming saturated, the bubble was ventilated. It turned out that the flow rate of the air through the bubble determined the flow pattern in the liquid. A mathematical model is presented which can adequately describe the observed phenomena.</p