A Structural Model of the Venous Wall Considering Elastin Anisotropy

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Rana Rezakhaniha ◽  
Nikos Stergiopulos
Keyword(s):  
Experimental Data ◽  
Smooth Muscle ◽  
Biomechanical Model ◽  
Vascular Wall ◽  
Pressure Force ◽  
Wide Range ◽  
Force Curves ◽  
Longitudinal Stretch ◽  
Venous Wall

The three-dimensional biomechanical behavior of the vascular wall is best described by means of strain energy functions. Significant effort has been devoted lately in the development of structure-based models of the vascular wall, which account for the individual contribution of each major structural component (elastin, collagen, and vascular smooth muscle). However, none of the currently proposed structural models succeeded in simultaneously and accurately describing both the pressure-radius and pressure-longitudinal force curves. We have hypothesized that shortcomings of the current models are, in part, due to unaccounted anisotropic properties of elastin. We extended our previously developed biomechanical model to account for elastin anisotropy. The experimental data were obtained from inflation-extension tests on facial veins of five young white New Zealand rabbits. Tests have been carried out under a fully relaxed state of smooth muscle cells for longitudinal stretch ratios ranging from 100% to 130% of the in vivo length. The experimental data (pressure-radius, pressure-force, and zero-stress-state geometries) provided a complete biaxial mechanical characterization of rabbit facial vein and served as the basis for validating the applicability and accuracy of the new biomechanical model of the venous wall. When only the pressure-radius curves were fitted, both the anisotropic and the isotropic models gave excellent results. However, when both pressure-radius and pressure-force curves are simultaneously fitted, the model with isotropic elastin shows an average weighted residual sum of squares of 8.94 and 23.9 in the outer radius and axial force, respectively, as compared to averages of 6.07 and 4.00, when anisotropic elastin is considered. Both the Alkaike information criterion and Schwartz criterion show that the model with the anisotropic elastin is more successful in predicting the data for a wide range of longitudinal stretch ratios. We conclude that anisotropic description of elastin is required for a full 3D characterization of the biomechanics of the venous wall.

Performance Characterization of a Twin Scroll Volute for Turbocharging Applications

2018 ◽  
Author(s):  
Carlo Cravero ◽  
Mario La Rocca ◽  
Andrea Ottonello
Keyword(s):  
Experimental Data ◽  
Scientific Literature ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Automatic Design ◽  
Cfd Model ◽  
Radial Turbine ◽  
Wide Range ◽  
Partial Admission

The use of twin scroll volutes in radial turbine for turbocharging applications has several advantages over single passage volute related to the engine matching and to the overall compactness. Twin scroll volutes are of increasing interest in power unit development but the open scientific literature on their performance and modelling is still quite limited. In the present work the performance of a twin scroll volute for a turbocharger radial turbine are investigated in some detail in a wide range of operating conditions at both full and partial admission. A CFD model for the volute have been developed and preliminary validated against experimental data available for the radial turbine. Then the numerical model has been used to generate the database of solutions that have been investigated and used to extract the performance. Different parameters and indices are introduced to describe the volute aerodynamic performance in the wide range of operating conditions chosen. The above parameters can be used for volute development or matching with a given rotor or efficiently implemented in automatic design optimization strategies.

scholarly journals Role of smooth muscle activation in the static and dynamic mechanical characterization of human aortas

2022 ◽  
Vol 119 (3) ◽  
pp. e2117232119
Author(s):  
Giulio Franchini ◽  
Ivan D. Breslavsky ◽  
Francesco Giovanniello ◽  
Ali Kassab ◽  
Gerhard A. Holzapfel ◽  
...  
Keyword(s):  
Experimental Data ◽  
Smooth Muscle ◽  
Muscle Activation ◽  
Mechanical Response ◽  
Mechanical Characterization ◽  
Viscoelastic Behavior ◽  
Material Model ◽  
Suitable Material ◽  
Dynamic Mechanical

Experimental data and a suitable material model for human aortas with smooth muscle activation are not available in the literature despite the need for developing advanced grafts; the present study closes this gap. Mechanical characterization of human descending thoracic aortas was performed with and without vascular smooth muscle (VSM) activation. Specimens were taken from 13 heart-beating donors. The aortic segments were cooled in Belzer UW solution during transport and tested within a few hours after explantation. VSM activation was achieved through the use of potassium depolarization and noradrenaline as vasoactive agents. In addition to isometric activation experiments, the quasistatic passive and active stress–strain curves were obtained for circumferential and longitudinal strips of the aortic material. This characterization made it possible to create an original mechanical model of the active aortic material that accurately fits the experimental data. The dynamic mechanical characterization was executed using cyclic strain at different frequencies of physiological interest. An initial prestretch, which corresponded to the physiological conditions, was applied before cyclic loading. Dynamic tests made it possible to identify the differences in the viscoelastic behavior of the passive and active tissue. This work illustrates the importance of VSM activation for the static and dynamic mechanical response of human aortas. Most importantly, this study provides material data and a material model for the development of a future generation of active aortic grafts that mimic natural behavior and help regulate blood pressure.

MELCOR Code Validation on HE-FUS3 Loop

2008 ◽  
Author(s):  
Laurent Sallus ◽  
Walter Van Hove
Keyword(s):  
Experimental Data ◽  
Heat Exchangers ◽  
Hydraulic System ◽  
Transient Analysis ◽  
State Tests ◽  
Wide Range ◽  
Innovative Solutions ◽  
Fluid Design ◽  
Design Pressure

Since the last decade, Tractebel Engineering has been involved in several consecutive projects in the field of High Temperature Gas Reactor (HTGR). The objectives of the present project called RAPHAEL (www.raphael-project.org) is to provide R&D results in order to consolidate available data on generic V/HTR technologies and to develop innovative solutions to further contribute to the improvement of HTR performances. One of the objectives of the RAPHAEL Sub-project Safety is to qualify tools for performing safety analyses and supporting the safety approach and demonstration. One of the work packages concerns the validation of the existing thermal-hydraulic system codes capabilities needed to perform transient analysis in V/HTR. This validation is carried out by benchmarking against experimental data and by comparing simulation results given by several codes. The current paper presents the work performed at Tractebel Engineering on the simulation of the HE-FUS3 experimental loop — ENEA facility, Brasimone (Italy) — with the MELCOR v.1.8.6 code. The HE-FUS3 loop contains a wide range of components characteristic of a V/HTR like compressor, pipes, diffusers, valves, heaters and heat exchangers. Even if the loop characteristics/configuration is not prototypical of a V/HTR design, the loop is useful to assess the objectives identified by the Project, i.e. helium operating fluid, design pressure and temperature set respectively at 10.5 MPa and 530 °C. The experimental data of the HE-FUS3 loop made available for the benchmark are a set of steady state tests for the thermal-hydraulic characterization of the loop and two transient tests — Loss Of Flow Accidents (LOFA). Moreover, to assess the characteristics of the compressor, data have also been provided from a compressor test campaign. From the code-to-experiment comparison the ability of MELCOR v.1.8.6 to reproduce the experimental results is judged.

scholarly journals Venular endothelium-derived NO can affect paired arteriole: a computational model

2006 ◽  
Vol 290 (2) ◽  
pp. H716-H723 ◽  
Author(s):  
Mahendra Kavdia ◽  
Aleksander S. Popel
Keyword(s):  
Smooth Muscle ◽  
Computational Model ◽  
Reaction Rate ◽  
Soluble Guanylate Cyclase ◽  
Experimental Studies ◽  
Vascular Wall ◽  
No Production ◽  
Wide Range ◽  
Venular Endothelium

Venular endothelial cells can release nitric oxide (NO) in response to intraluminal flow both in isolated venules and in vivo. Experimental studies suggest that venular endothelium-released NO causes dilation of the adjacent paired arteriole. In the vascular wall, NO stimulates its target hemoprotein, soluble guanylate cyclase (sGC), which relaxes smooth muscle cells. In this study, a computational model of NO transport for an arteriole and venule pair was developed to determine the importance of the venular endothelium-released NO and its transport to the adjacent arteriole in the tissue. The model predicts that the tissue NO levels are affected within a wide range of parameters, including NO-red blood cell reaction rate and NO production rate in the arteriole and venule. The results predict that changes in the venular NO production affected not only venular endothelial and smooth muscle NO concentration but also endothelial and smooth muscle NO concentration in the adjacent arteriole. This suggests that the anatomy of microvascular tissue can permit the transport of NO from arteriolar to venular side, and vice versa, and may provide a mechanism for dilation of proximal arterioles by venules. These results will have significant implications for our understanding of tissue NO levels in both physiological and pathophysiological conditions.

Determining Functional Finger Capabilities of Healthy Adults: Comparing Experimental Data to a Biomechanical Model

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Samuel T. Leitkam ◽  
Tamara Reid Bush ◽  
Laura Bix
Keyword(s):  
Experimental Data ◽  
Theoretical Model ◽  
Biomechanical Model ◽  
Experimental Models ◽  
Human Hand ◽  
Functional Abilities ◽  
Data Set ◽  
Functional Measures ◽  
Wide Range ◽  
Capture Techniques

The human hand has a wide range of possible functional abilities that can change with age, disease, and injury, and can vary from individual to individual and subsequently can affect a person's quality of life. The objective of this work was to develop a theoretical model of the space that is reachable by the hand, weighted to represent three types of functionality, and to compare this model to an experimental data set obtained from a healthy hand population. A theoretical model, termed the Weighted Fingertip Space, was developed using 50th percentile published hand data and ranges of finger motion. The functional abilities calculated in the model were the abilities to position the fingertip pad, orient the fingertip pad, and apply directional forces through the fingertip pad at all the reachable points in space with respect to the palm. Following the development of this theoretical model, experimental data sets from nine individuals with healthy hands were obtained through motion capture techniques. The experimental data were then compared to the theoretical model. Comparisons between a 50th percentile theoretical model and a subject with a similar sized hand showed good agreement in weighting parameters and overall size and shape of the model spaces. The experimental data set from the entire sample, which ranged from the 2nd to 95th percentile hand sizes, showed resultant models that, on average, reached smaller volumes of space, but yielded higher values of the functional measures within those volumes. Additionally, in comparison to the theoretical model, the variability of the experimental models showed that small changes in hand dimensions and ranges of motion of the finger joints had a large influence in the functional measures of the model. Combined, these results suggest that the modeling technique can calculate functional ability of the hand, but should be used on an individualized basis for evaluating changes in function (e.g., rehabilitation). Further, scaling to hand size has the potential to yield “average” models for larger population samples.

Characterization of in vitro gutlike organ formed from mouse embryonic stem cells

2004 ◽  
Vol 286 (6) ◽  
pp. C1344-C1352 ◽  
Author(s):  
Tadao Ishikawa ◽  
Shinsuke Nakayama ◽  
Tadashi Nakagawa ◽  
Kazuhide Horiguchi ◽  
Hiromi Misawa ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Embryoid Body ◽  
Es Cells ◽  
Embryonic Stem ◽  
Muscle Cells ◽  
Morphological Properties ◽  
Pacemaker Activity ◽  
Wide Range

Using an embryoid body (EB) culture system, we have made a functional organlike cluster: the “gut” from embryonic stem (ES) cells (ES gut). There are many types of ES clusters, because ES cells have a pluripotent ability to develop into a wide range of cell types. Before inducing specific differentiation by exogenously added factors, we characterized comprehensive physiological and morphological properties of ES guts. Each ES gut has a hemispherical (or cystic) structure and exhibits spontaneous contractions [mean frequency: 13.5 ± 8.8 cycles per min (cpm)]. A dense distribution of interstitial cells of Cajal (ICC) was identified by c-Kit immunoreactivity, and specific subcellular structures of ICC and smooth muscle cells were identified with electron microscopy. ICC frequently formed close contacts with the neighboring smooth muscle cells and occasionally formed gap junctions with other ICC. Widely propagating intracellular Ca2+ concentration oscillations were generated in the ES gut from the aggregates of c-Kit immunopositive cells. Plateau potentials, possibly pacemaker potentials in ICC, and electrical slow waves were recorded for the first time. These events were nifedipine insensitive, as in the mouse gut. Our present results indicate that the rhythmic pacemaker activity generated in ICC efficiently spreads to smooth muscle cells and drives spontaneous rhythmic contractions of the ES gut. The present characterization of physiological and morphological properties of ES gut paves the way for making appropriate models to investigate the origin of rhythmicity in the gut.

Model Characterization of Pulmonary Arterial Hypertension: Analysis of Lung Pathology with Respect to Human Disease

2020 ◽  
Author(s):  
◽  
Eptisam lambu
Keyword(s):  
Pulmonary Arterial Hypertension ◽  
Arterial Hypertension ◽  
Human Disease ◽  
Vascular Remodeling ◽  
Vascular Wall ◽  
Lung Pathology ◽  
Pulmonary Arterial ◽  
Lung Pathogenesis ◽  
Arterial Endothelial Cells

Pulmonary arterial hypertension (PAH) is a rare multifactorial disease characterized by abnormal high blood pressure in the pulmonary artery, or increased pulmonary vascular resistance (PVR), caused by obstruction in the small arteries of the lung. Increased PVR is also thought to be caused by abnormal vascular remodeling, due to thickening of the pulmonary vascular wall resulting from significant hypertrophy of pulmonary arterial smooth-muscle cells (PASMCs) and increased proliferation/impaired apoptosis of pulmonary arterial endothelial cells (PAECs). Herein, we investigated the mechanisms and explored molecular pathways mediating the lung pathogenesis in two PAH rat models: Monocrotaline (MCT) and Sugen5416/Hypoxia (SuHx). We analyzed these disease models to determine where the vasculature shows the most severe PAH pathology and which model best recapitulates the human disease. We investigated the role vascular remodeling, hypoxia, cell proliferation, apoptosis, DNA damage and inflammation play in the pathogenesis of PAH. Neither model recapitulated all features of the human disease, however each model presented with some of the pathology seen in PAH patients.

LIQUIDUS THERMO-BAROMETER FOR THE MODELING OF MAGNETITE — MELT EQUILIBRIUM

2018 ◽  
pp. 71-80
Author(s):  
N. S. Aryaeva ◽  
E. V. Koptev-Dvornikov ◽  
D. A. Bychkov
Keyword(s):  
Experimental Data ◽  
Liquidus Temperature ◽  
Vertical Structure ◽  
Maximum Error ◽  
Silicate Melt ◽  
System Of Equations ◽  
Wide Range ◽  
Basaltic Melts ◽  
Multidimensional Statistics

A system of equations of thermobarometer for magnetite-silicate melt equilibrium was obtained by method of multidimensional statistics of 93 experimental data of a magnetite solubility in basaltic melts. Equations reproduce experimental data in a wide range of basalt compositions, temperatures and pressures with small errors. Verification of thermobarometers showed the maximum error in liquidus temperature reproducing does not exceed ±7 °C. The level of cumulative magnetite appearance in the vertical structure of Tsypringa, Kivakka, Burakovsky intrusions predicted with errors from ±10 to ±50 m.

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