Preparation of controlled particulate mixtures with glass beads of different sizes

A method of mixing/preparing binary and ternary mixtures of glass beads was developed using a viscous solution of glycerol in water. After mixing, the mixture was transferred to a prismatic vessel and glycerol was washed out. The different sized beads were differently coloured and digital pictures taken from each face were automatically treated by image analysis to determine the coloured fraction present in each face. Statistical analysis showed that no significant deviation existed in the colour distribution of each of the four faces.Achi-square test showed that a uniform distribution could be accepted for the beads, no segregation of bead size nearby the edges was observed and that no wall effect was present. The two-dimensional picture obtained by image analysis was converted to the corresponding three-dimensional distribution, from which the expected bed porositywas inferred. The porosity previously estimatedwas compared with the experimental porosity determined by gravimetry directly on the bed.Nosignificant deviations were found, thereby proving that the mixing method developed was reliable. Hundreds of experiments were done showing a very high reproducibility. The developed methodwas further used for studies on mixing of binary and ternary mixtures. In certain conditions (mixtures enriched with large size particles and having a significant difference in size) a segregation layering effect took place and the bottom layer presented a composition corresponding to the packing with the smallest porosity possible.Fundação para a Ciência e a Tecnologia (FCT) e FEDER - POCTI/EQU/37500/2001

Total Aortic Arch Replacement: Superior Ventriculo-Arterial Coupling with Decellularized Allografts Compared with Conventional Prostheses.

BACKGROUND: To date, no experimental or clinical study provides detailed analysis of vascular impedance changes after total aortic arch replacement. This study investigated ventriculoarterial coupling and vascular impedance after replacement of the aortic arch with conventional prostheses vs. decellularized allografts. METHODS: After preparing decellularized aortic arch allografts, their mechanical, histological and biochemical properties were evaluated and compared to native aortic arches and conventional prostheses in vitro. In open-chest dogs, total aortic arch replacement was performed with conventional prostheses and compared to decellularized allografts (n = 5/group). Aortic flow and pressure were recorded continuously, left ventricular pressure-volume relations were measured by using a pressure-conductance catheter. From the hemodynamic variables end-systolic elastance (Ees), arterial elastance (Ea) and ventriculoarterial coupling were calculated. Characteristic impedance (Z) was assessed by Fourier analysis. RESULTS: While Ees did not differ between the groups and over time (4.1+/-1.19 vs. 4.58+/-1.39 mmHg/mL and 3.21+/-0.97 vs. 3.96+/-1.16 mmHg/mL), Ea showed a higher increase in the prosthesis group (4.01+/-0.67 vs. 6.18+/-0.20 mmHg/mL, P<0.05) in comparison to decellularized allografts (5.03+/-0.35 vs. 5.99+/-1.09 mmHg/mL). This led to impaired ventriculoarterial coupling in the prosthesis group, while it remained unchanged in the allograft group (62.5+/-50.9 vs. 3.9+/-23.4%). Z showed a strong increasing tendency in the prosthesis group and it was markedly higher after replacement when compared to decellularized allografts (44.6+/-8.3dyn.sec.cm-5 vs. 32.4+/-2.0dyn.sec.cm-5, P<0.05). CONCLUSIONS: Total aortic arch replacement leads to contractility-afterload mismatch by means of increased impedance and invert ventriculoarterial coupling ratio after implantation of conventional prostheses. Implantation of decellularized allografts preserves vascular impedance thereby improving ventriculoarterial mechanoenergetics after aortic arch replacement

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

Numerical comparisons of two long-wave limit models

The Benney-Luke equation (BL) is a model for the evolution of three-dimensional weakly nonlinear, long water waves of small amplitude. In this paper we propose a nearly conservative scheme for the numerical resolution of (BL). Moreover, it is known (Paumond, Differential Integral Equations 16 (2003) 1039–1064; Pego and Quintero, Physica D 132 (1999) 476–496) that (BL) is linked to the Kadomtsev-Petviashvili equation for almost one-dimensional waves propagating in one direction. We study here numerically the link between (KP) and (BL) and we point out the coupling effects emerging by considering two solitary waves propagating in two opposite directions

Large mode-2 internal solitary waves in three-layer flows

In this paper, we investigate mode-2 solitary waves in a three-layer stratified flow model. Localised travelling wave solutions to both the fully nonlinear problem (Euler equations), and the three-layer Miyata–Choi–Camassa equations are found numerically and compared. Mode-2 solitary waves with speeds slower than the linear mode-1 long-wave speed are typically generalised solitary waves with infinite tails consisting of a resonant mode-1 periodic wave train. Herein, we evidence the existence of mode-2 embedded solitary waves, that is, we show that for specific values of the parameters, the amplitude of the oscillations in the tail are zero. For sufficiently thick middle layers, we also find branches of mode-2 solitary waves with speeds that extend beyond the mode-1 linear waves and are no longer embedded. In addition, we show how large amplitude embedded solitary waves are intimately linked to the conjugate states of the problem