Seasonal concentrations of cadmium and zinc in native pasture plants: consequences for grazing animals

Aboveground concentrations of Cd and Zn in various grazing plants at three stages of the growing season are reported. The plants were collected at a natural habitat exposed to extensive atmospheric deposition of heavy metals from other parts of Europe. Concentrations of both metals varied considerably among species, also among morphologically similar species growing in the same soil. The two metals correlated in the material as a whole, but the concentration variations were most pronounced for Cd. There were also seasonal variations (generally a concentration reduction during spring). Transfer of metals from twigs to leaves seemed to differ between 'high' and 'low' metal accumulators. The inter-species and seasonal variations in plant metal concentrations complicate assessments of metal exposure to grazing animals through diet. By using diet information from a study conducted in an area similar to the present one, we roughly estimated a daily intake of 1-2 mg Cd for moose (Alces alces) in the autumn. Among the plant species investigated, Populus and Salix species were by far the most important Cd contributors. In areas where high Cd accumulators grow more widely, the daily Cd intake by moose could be as high as 7 mg or more.     

Tissue degradation,amino acid liberation and bacterial decomposition of bulk stored capelin

Bulk stored capelin with high contents of feed in the gut is easily solubilised because of high proteolytic activity. The amino acids most quickly liberated are arginine, serine, histidine, leucine, lysine and tyrosine; glycine, aspartic acid and glutamic acid are liberated at a slower rate. Bacterial activity results in a rapid and considerable decrease in total amounts of tyrosine, lysine, serine, arginine and histidine. The main products formed by bacterial decomposition of lysine, histidine and arginine are cadaverine, histamine and putrescine, respectively. Storage of capelin in the presence of antibiotics increased the amounts of free amino acids and total amino acids. After 10 days' storage at 6°C, about 30% of the total amino acid content in fish treated with antibiotics were fee amino acids.     

A power analysis and data acquisition system for ocean wave energy device testing

In the testing of ocean wave energy devices, the demand for a portable and robust data acquisition and electrical loading system has become apparent. This paper investigates the development of a 30 kW inclusive system combining loading capabilities, real-time power analysis, and data acquisition for the testing of deployed ocean wave energy devices. Hardware results for ocean testing are included.     

A fully-coupled fluid-structure interaction simulation of cerebral aneurysms

This paper presents a computational vascular fluid-structure interaction (FSI) methodology and its application to patient-specific aneurysm models of the middle cerebral artery bifurcation. A fully coupled fluid-structural simulation approach is reviewed, and main aspects of mesh generation in support of patient-specific vascular FSI analyses are presented. Quantities of hemodynamic interest such as wall shear stress and wall tension are studied to examine the relevance of FSI modeling as compared to the rigid arterial wall assumption. We demonstrate the importance of including the flexible wall modeling in vascular blood flow simulations by performing a comparison study that involves four patient-specific models of cerebral aneurysms varying in shape and size.     

Real-time ultrasound simulation using the GPU

Ultrasound simulators can be used for training ultrasound image acquisition and interpretation. In such simulators, synthetic ultrasound images must be generated in real time. Anatomy can be modeled by computed tomography (CT). Shadows can be calculated by combining reflection coefficients and depth dependent, exponential attenuation. To include speckle, a pre-calculated texture map is typically added. Dynamic objects must be simulated separately. We propose to increase the speckle realism and allow for dynamic objects by using a physical model of the underlying scattering process. The model is based on convolution of the point spread function (PSF) of the ultrasound scanner with a scatterer distribution. The challenge is that the typical field-of-view contains millions of scatterers which must be selected by a virtual probe from an even larger body of scatterers. The main idea of this paper is to select and sample scatterers in parallel on the graphic processing unit (GPU). The method was used to image a cyst phantom and a movable needle. Speckle images were produced in real time (more than 10 frames per second) on a standard GPU. The ultrasound images were visually similar to images calculated by a reference method.     

Intratumoral infusion of fluid: estimation of hydraulic conductivity and implications for the delivery of therapeutic agents

We have developed a new technique to measure in vivo tumour tissue fluid transport parameters (hydraulic conductivity and compliance) that influence the systemic and intratumoral delivery of therapeutic agents. An infusion needle approximating a point source was constructed to produce a radially symmetrical fluid source in the centre of human tumours in immunodeficient mice. At constant flow, the pressure gradient generated in the tumour by the infusion of fluid (Evans blue-albumin in saline) was measured as a function of the radial position with micropipettes connected to a servo-null system. To evaluate whether the fluid infused was reabsorbed by blood vessels, infusions were also performed after circulatory arrest. In the colon adenocarcinoma LS174T with a spherically symmetrical distribution of Evans blue-albumin, the median hydraulic conductivity in vivo and after circulatory arrest at a flow rate of 0.1 microl min(-1) was, respectively, 1.7x10(-7) and 2.3x10(-7) cm2 mmHg(-1) s. Compliance estimates were 35 microl mmHg(-1) in vivo, and 100 microl mmHg(-1) after circulatory arrest. In the sarcoma HSTS 26T, hydraulic conductivity and compliance were not calculated because of the asymmetric distribution of the fluid infused. The technique will be helpful in identifying strategies to improve the intratumoral and systemic delivery of gene targeting vectors and other therapeutic agents.     

Trypanosoma brucei gamma-glutamylcysteine synthetase. Characterization of the kinetic mechanism and the role of Cys-319 in cystamine inactivation

The parasitic protozoan Trypanosoma brucei utilizes a conjugate of glutathione and spermidine, termed trypanothione, in place of glutathione to maintain cellular redox balance. The first committed step in the biosynthesis of glutathione and thereby trypanothione, is catalyzed by gamma-glutamylcysteine synthetase (gamma-GCS). We have determined the kinetic mechanism for T. brucei gamma-GCS. The kinetics are best described by a rapid equilibrium random ter-reactant mechanism, in which the model derived Kd values for the binding of L-Glu, L-alpha-aminobutyrate, and ATP to free enzyme are 2.6, 5.1, and 1.4 mM, respectively. However, significant dependences exist between the binding of some of the substrate pairs. The binding of either ATP or L-Glu to the enzyme increases the binding affinity of the other by 18-fold, whereas the binding of L-Glu or L-alpha-aminobutyrate decreases the binding affinity of the other by 6-fold. Similarly to the mammalian enzyme, cystamine is a time-dependent, irreversible inhibitor of T. brucei gamma-GCS. It has been suggested by several studies that cystamine labels an active site Cys residue essential for catalysis. Among the enzymes reported to be inactivated by cystamine, only one Cys residue is invariant (Cys-319 in T. brucei gamma-GCS). Mutation of Cys-319 to Ala in T. brucei gamma-GCS renders the enzyme insensitive to cystamine inactivation without significantly affecting the enzyme's catalytic efficiency, kinetic mechanism, or substrate affinities. These studies suggest that cystamine inactivates the enzyme by blocking substrate access to the active site and not by labeling an essential active site residue.     

Design, construction, and ocean testing of a taut-moored dual-body wave energy converter with a linear generator power take-off

This paper presents an overview of the SeaBeavI project which began in the fall of 2006 and culminated in the ocean testing of a 10 kW direct-drive wave energy conversion system in the fall of 2007. The SeaBeavI project was an interdisciplinary effort bringing together researchers from electrical, mechanical, and ocean engineering. A systems design approach was used to develop the taut-moored dual-body wave energy converter concept with the detailed design focused on production and ease of maintenance.     

Control of a Doubly Fed Induction Wind Generator Under Unbalanced Grid Voltage Conditions

Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three-phase stator voltages cause a number of problems, such as overcurrent, unbalanced currents, reactive power pulsations, and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance, induction wind generators are switched out of the network. This can further weaken the grid. In doubly fed induction generators (DFIGs), control of the rotor currents allows for adjustable speed operation and reactive power control. This paper presents a DFIG control strategy that enhances the standard speed and reactive power control with controllers that can compensate for the problems caused by an unbalanced grid by balancing the stator currents and eliminating torque and reactive power pulsations     

Expression of soluble VEGF receptor 2 and characterization of its binding by surface plasmon resonance

Vascular endothelial growth factor (VEGF) is an endothelial cell specific mitogen that induces angiogenesis in several pathological conditions. To block angiogenesis, soluble VEGF receptor can be used. In this study, we describe a method for high yield expression of soluble VEGF receptor 2 (sFlk-1) in a baculovirus expression system (30 mg purified sFlk-1 per L of insect cell supernatant). We also determined the binding constants for both human and mouse VEGF to the recombinant receptor by surface plasmon resonance. In this cell-free assay, under the given experimental conditions, the on-rate ka was 0.5-2.2 x 10(6) M-1s-1 and the off-rate kd was 2-4 x 10(-4) s-1 (KD = 2-6 x 10(-10) M). To our knowledge this is the first study to report on- and off-rates for the VEGF:sFlk-1 interaction. Heparin was not required for the binding of VEGF to sFlk-1 in this assay. The obtained values will serve as baseline parameters for the design of improved versions of recombinant soluble VEGF receptor.