Power Doppler ultrasound evaluation of the shear rate and shearstress dependences of red blood cell aggregation

The use of power Doppler ultrasound at 10 MHz is evaluated as a method to study the shear rate and the shear stress dependences of red blood cell aggregation. This evaluation was based on 6 in vitro experiments conducted in a 1.27-cm diameter tube under steady flow conditions. Porcine whole blood was circulated in the flow model at flow rates ranging between 125 to 1500 ml/min (mean shear rate across the tube ranging between 6 and 74 s^-1). For each flow condition, the variation of the Doppler power across the tube and the velocity profile were measured by moving the Doppler sample volume across the tube diameter. For each radial position, the shear rate within the Doppler sample volume was also determined by considering the radial power pattern of the ultrasound beam. To estimate the shear stress within the Doppler sample volume, the apparent viscosity of blood samples withdrawn from the flow model was measured for each experiment. The variation of the Doppler power as a function of the shear rate within the sample volume showed a rapid reduction of the power between 1 and 5 s^-1, a transition region between 5 and 10 s^-1, and a very slow reduction beyond 10 s^-1. Little variation of the Doppler power was measured for shear stress higher than 2 dyn/cm. The maximum Doppler power for all flow rates was usually found near the center of the tube. Based on the ultrasonic scattering models, which predict that the Doppler power is related to the volume square of the scatterers, the method described in the present study showed a very high sensitivity to the presence of red blood cell aggregation for shear rates below 10 s^-1     

Continuous flow mixing of two miscible liquids of different densities

Positive step demands have been used to study the behavior of miscible liquids with different densities in an imperfectly mixed cylindrical flow tank. A model was elaborated to predict the response of the agitated system. Comparisons between experimental and theoretical results have shown the limits of the proposed model and equations.     

Fonction de transfert d'un réservoir agité en système continu: II Variation des constantes de temps avec et sans différence de densité initiate

The analysis of the dynamic behavior of a continuous stirred tank reactor with a fluorescent tracer has indicated that the short-circuit of a fraction of the liquid feed constitutes the only non-ideality in this case. There is no dead space or piston flow in the reactor when the density difference is zero. The variation of the transfer function time constants was also studied as a first approximation, in a reactor with a density difference between the liquid feed and the reactor contents. This had led to the determination of an ideality criterion which includes the main causes of the non-ideal mixing. The fluorescent tracer technique has permitted the isolation of the effects of physical parameters on the degree of short-circuit from the effects on other causes of non-ideal mixing.     

Characterization of atherosclerotic plaques and mural thrombi with intravascular ultrasound elastography: a potential method evaluated in an aortic rabbit model and a human coronary artery

Plaque rupture is correlated with the plaque morphology, composition, mechanical properties, and with the blood pressure. Whereas the geometry can accurately be assessed with intravascular ultrasound (IVUS) imaging, intravascular elastography (IVE) is capable of extracting information on the plaque local mechanical properties and composition. This paper reports additional IVE validation data regarding reproducibility and potential to characterize atherosclerotic plaques and mural thrombi. In a first investigation, radio frequency (RF) data were acquired from the abdominal aorta of an atherosclerotic rabbit model. In a second investigation, IVUS RF data were recorded from the left coronary artery of a patient referred for angioplasty. In both cases, Galaxy IVUS scanners (Boston Scientific, Freemont, CA), equipped with 40 MHz Atlantis catheters, were used. Elastograms were computed using two methods, the Lagrangian speckle model estimator (LSME) and the scaling factor estimator (SFE). Corroborated with histology, the LSME and the SFE both clearly detected a soft thrombus attached to the vascular wall. Moreover, shear elastograms, only available with the LSME, confirmed the presence of the thrombus. Additionally, IVE was found reproducible with consistent elastograms between cardiac cycles (CCs). Regarding the human dataset, only the LSME was capable of identifying a plaque that presumably sheltered a lipid core. Whereas such an assumption could not be certified with histology, radial shear and tangential strain LSME elastograms enabled the same conclusion. It is worth emphasizing that this paper reports the first ever in vivo tangential strain elastogram with regards to vascular imaging, due to the LSME. It is concluded that the IVE was reproducible exhibiting consistent strain patterns between CCs. The IVE might provide a unique tool to assess coronary wall lesions.     

Tailor made OSB for special application

The purpose of this study was to develop speciality oriented strand board (OSB) with high stiffness for use in products such as engineered wood flooring (EWF). Three-layer oriented strand boards were manufactured from two feedstocks of strands: a mixture of 90% aspen (Populus tremuloides) and 10% of paper birch (Betula papyrifera), and 100% of small diameter ponderosa pine logs (Pinus ponderosa). The OSB panels were manufactured under a factorial design of three resin contents, two density profiles, and three weight ratios for the face and core layers. Tests to determine density, bending modulus of elasticity (MOE), internal bond (IB) and thickness swelling (TS) were performed according to ASTM standard D 1037-06a. The results showed that the higher values of bending MOE for panels made from aspen/birch mixture and ponderosa pine, 8190 and 9050?MPa, respectively, were obtained for the same combination of factors. Such high bending MOE values are very close to Baltic birch (Betula pendula) plywood, a product known for its high stiffness. The effect of resin content on IB is more pronounced for panels made from ponderosa pine than panels made from the aspen/birch mixture. Thickness swelling of panels made from ponderosa pine strands is higher than thickness swelling of panels made from a mixture of aspen and birch strands. The results indicate the potential to tailor an OSB for a specific application such as EWF.     

Physical and mechanical properties of gypsum particleboard reinforced with Portland cement

High thickness swelling, high water absorption and low mechanical properties of gypsum particleboard limit its utilization in building construction. Gypsum particleboard reinforced with Portland cement could result in a product with higher mechanical properties and an acceptable resistance to moisture. Physical and mechanical properties of gypsum-cement particleboards were analyzed for specimens previously conditioned at 20?°C and 60% relative humidity and then soaked in water for 24 hours. The results showed that Portland cement incorporation increased the mechanical resistance of the boards. In the dry state, Portland cement addition generated a modulus of rupture increase ratio of 53% and an internal bond strength increase ratio of 206%. Higher increase ratios were obtained after 24 hours water soaking. An increase ratio of 642% was obtained for the modulus of rupture and 97% for hardness. Furthermore, the addition of Portland cement resulted in a reduction ratio of 21% for water absorption after 2 hours water soaking and 26% after 24 hours water soaking. Moreover, reduction ratios of 43% and 61% in thickness swelling and 33% and 46% in linear variation were observed after 2 and 24 hours water soaking. It can be concluded that Portland cement is a suitable reinforcing material for improving the performance of gypsum particleboard.     

Estimation of polyvinyl alcohol cryogel mechanical properties with four ultrasound elastography methods and comparison with gold standard testings

Tissue-mimicking phantoms are very useful in the field of tissue characterization and essential in elastography for the purpose of validating motion estimators. This study is dedicated to the characterization of polyvinyl alcohol cryogel (PVA-C) for these types of applications. A strict fabrication procedure was defined to optimize the reproducibility of phantoms having a similar elasticity. Following mechanical stretching tests, the phantoms were used to compare the accuracy of four different elastography methods. The four methods were based on a one-dimensional (1-D) scaling factor estimation, on two different implementations of a 2-D Lagrangian speckle model estimator (quasistatic elastography methods), and on a 1-D shear wave transient elastography technique (dynamic method). Young's modulus was investigated as a function of the number of freeze-thaw cycles of PVA-C, and of the concentration of acoustic scatterers. Other mechanical and acoustic parameters-such as the speed of sound, shear wave velocity, mass density, and Poisson's ratio-also were assessed. The Poisson's ratio was estimated with good precision at 0.499 for all samples, and the Young's moduli varied in a range of 20 kPa for one freeze-thaw cycle to 600 kPa for 10 cycles. Nevertheless, above six freeze-thaw cycles, the results were less reliable because of sample geometry artifacts. However, for the samples that underwent less than seven freeze-thaw cycles, the Young's moduli estimated with the four elastography methods showed good matching with the mechanical tensile tests with a regression coefficient varying from 0.97 to 1.07, and correlations R2 varying from 0.93 to 0.99, depending on the method.     

Molecular characterization and role in T cell activation of staphylococcal enterotoxin A binding to the HLA-DR alpha-chain

Superantigens bind to MHC class II-positive cells and stimulate T lymphocytes expressing specific V beta regions of the TCR. Two distinct regions of staphylococcal enterotoxin A superantigen (SEA) have been shown to affect the binding to MHC class II molecules. Results presented here demonstrate for the first time that the SEA-DR interaction can be affected by mutations on the class II alpha-chain. Furthermore, we have precisely mapped the interaction of the SEA N-terminal domain with the alpha1 domain of HLA-DR. Scatchard analysis using DAP cells transfected with mutant class II molecules showed a role for residue DR alpha K39 in the binding of SEA. Also, complementation experiments using mutant SEA molecules revealed an interaction between SEA residue F47 and position alphaQ18 on an outer loop of HLA-DR. These interactions between SEAF47 and the DR alpha-chain are critical, as they allow the recognition by an otherwise nonreactive V beta1+ T cell hybridoma and induction of tyrosine phosphorylation through the TCR.     

Dynamic modelling of protein and oxidative metabolisms simulates the pathogenesis of Parkinson's disease

Research into Parkinson's disease (PD) is difficult and time consuming. It is a complex condition that develops over many decades in the human brain. For such apparently intractable diseases, mathematical models can offer an additional means of investigation. As a contribution to this process, the authors have developed an ordinary differential equation model of the most important cellular processes that have been associated with PD. The model describes the following processes: (i) cellular generation and scavenging of reactive oxygen species; (ii) the possible damage and removal of the protein -synuclein and, (iii) feedback interactions between damaged α-synuclein and reactive oxygen species. Simulation results show that the Parkinsonian condition, with elevated oxidative stress and misfolded α-synuclein accumulation, can be induced in the model by known PD risk factors such as ageing, exposure to toxins and genetic defects. The significant outcome of the paper is the demonstration that it is possible to reproduce in silico the multi-factorial interactions that characterise the pathogenesis of PD. As such, the model provides a systematic explanation of the variability and heterogeneity of PD and provides the basis for computational studies of further facets of this complex multi-factorial condition. [Includes supplementary material].