Pitfalls in the measurement of cerebral blood volume with computed tomography

The use of contrast material and computed tomography (CT) to measure cerebral blood volume (CBV) is valid only if the agent does not egress into cerebral tissue. Since disruption of the blood/brain barrier is common in cerebral disease states, this raises serious doubt as to the validity of this technique. Studies in experimental animals and patients with cerebral lesions demonstrate that contrast material does egress into the extravascular space. In normal brain tissue, contrast enhancement is comparable to the error in CT. Contrast material also causes transient changes in autoregulation, blood pressure, cerebral blood flow, and CBV.     

Computational modeling of muscular thin films for cardiac repair

Motivated by recent success in growing biohybrid material from engineered tissues on synthetic polymer films, we derive a computational simulation tool for muscular thin films in cardiac repair. In this model, the polydimethylsiloxane base layer is simulated in terms of microscopically motivated tetrahedral elements. Their behavior is characterized through a volumetric contribution and a chain contribution that explicitly accounts for the polymeric microstructure of networks of long chain molecules. Neonatal rat ventricular cardiomyocytes cultured on these polymeric films are modeled with actively contracting truss elements located on top of the sheet. The force stretch response of these trusses is motivated by the cardiomyocyte force generated during active contraction as suggested by the filament sliding theory. In contrast to existing phenomenological models, all material parameters of this novel model have a clear biophyisical interpretation. The predictive features of the model will be demonstrated through the simulation of muscular thin films. First, the set of parameters will be fitted for one particular experiment documented in the literature. This parameter set is then used to validate the model for various different experiments. Last, we give an outlook of how the proposed simulation tool could be used to virtually predict the response of multi-layered muscular thin films. These three-dimensional constructs show a tremendous regenerative potential in repair of damaged cardiac tissue. The ability to understand, tune and optimize their structural response is thus of great interest in cardiovascular tissue engineering.     

Effects of feeding combinations of steam-flaked grain sorghum and steam-flaked, high-moisture, or dry-rolled corn on growth performance and carcass characteristics in feedlot cattle

The objective of these two feeding trials was to determine the associative effects of feeding steam-flaked grain sorghum (SFGS) in combination with steam-flaked (SFC), dry-rolled (DRC), or high-moisture (HMC) corn on growth performance and carcass characteristics in feedlot cattle. In Trial 1, 200 yearling heifers were blocked by weight, allotted to 25 pens, and fed one of five finishing diets (77% grain, 15% corn silage, and 8% supplement on a DM basis) for an average of 137 d. The grain combinations were 100:0, 75:25, 50:50, 25:75, and 0:100 SFC:SFGS, respectively. Treatment had no effect on DMI (P > .05), but ADG, gain efficiency, and final live and hot carcass weights decreased linearly (P < .05) as the proportion of SFGS increased in the diet. Carcass backfat, quality grade, and liver abscess score were not affected (P > .05) by treatment. In Trial 2, 306 yearling steers were blocked by weight, allotted to 30 pens, and fed diets that contained 74.5% grain, 10% corn silage, 7.5% soybean meal, 4% tallow, and 4% supplement (DM basis) for an average of 139 d. The grain and grain combinations were 100% DRC, HMC, SFC, or SFGS and a 67%:33% combination of SFGS: DRC or SFGS:HMC. For steers fed diets containing a single source of grain, those fed SFC gained 7% more live weight and had a 7% higher gain efficiency (P < .05) than those fed DRC or HMC. Growth performance of steers fed SFGS was intermediate. Feeding grain combinations (67% SFGS:33% HMC or DRC) resulted in a 5 to 6% positive associative effect (P < .05) for ADG and gain efficiency. Carcass characteristics were not affected (P > .05) by treatment. We concluded that there were significant benefits (positive associative effects) when SFGS was fed in combination with DRC or HMC, but the effects were smaller when SFGS was fed in combination with SFC.     

A finite element method for the computational modelling of cohesive cracks

The present contribution is concerned with the computational modelling of cohesive cracks in quasi‐brittle materials, whereby the discontinuity is not limited to interelement boundaries, but is allowed to propagate freely through the elements. In the elements, which are intersected by the discontinuity, additional displacement degrees of freedom are introduced at the existing nodes. Therefore, two independent copies of the standard basis functions are used. One set is put to zero on one side of the discontinuity, while it takes its usual values on the opposite side, and vice versa for the other set. To model inelastic material behaviour, a discrete damage‐type constitutive model is applied, formulated in terms of displacements and tractions at the surface. Some details on the numerical implementation are given, concerning the failure criterion, the determination of the direction of the discontinuity and the integration scheme. Finally, numerical examples show the performance of the method. Copyright © 2005 John Wiley & Sons, Ltd.     

The reconstruction of a specially structured Jacobi matrix with an application to damage detection in rods

A finite-element discretization of the differential equation for the axial vibration of a rod with varying cross-section leads to a specially structured n × n matrix pencil. The reconstruction of this pencil from its spectrum can be achieved by the reconstruction of a unique Jacobi matrix using half of its spectrum and half of the spectrum of its principal submatrix of order (n − 1). The technique is used in an optimization problem formulated for damage detection in rods defined in terms of changes in the effective cross-sectional area.     

Use of NARX neural networks for Meteosat Second Generation SEVIRI very short-term cloud mask forecasting

In this article, a novel technique based on artificial neural networks (NN) is proposed for cloud coverage short-term forecasting (nowcasting). In particular, the capabilities of multi-layer perceptron NN and time series analysis with nonlinear autoregressive with exogenous input NN are explored and applied to the European meteorological system ‘Meteosat Second Generation’ with its payload Spinning Enhanced Visible and InfraRed Imager. The general neural architecture consists of a first stage addressing the prediction of the radiance images at six bands (0.6, 0.8, 1.6, 3.9, 6.2 and 10.8 μm). In a second stage a cloud masking algorithm, always based on NN, is applied to the predicted images for the cloud coverage nowcasting. The scheme was compared with the most basic forecast algorithm for the prediction: the persistent model. Two test areas characterized by different climatology have been considered for the performance analysis. The results show that about 85% of the changes occurring in the time window were recognized by the proposed technique.     

Broadband modulation of 3-µm light by 10-µm light in p-germanium

High-power CO2laser radiation at 1045 cm^-1is shown to enhance the room temperature transmission of p-Ge in a spectral region extending at least from 3000 to 4000 cm^-1. The interaction arises from radiation-induced changes of the hole populations within the three valence bands. Ultrafast nonradiative relaxation is responsible for the very large interaction bandwidth observed and allows the prediction of a minimum switching time of 1 ps.