Radial Elastic Moduli Research Articles

A single filament biomechanical study of the enteropathogenic Escherichia coli Type III secretion system reveals a high elastic aspect ratio.

Type III secretion systems (T3SSs) are syringe-like protein complexes used by some of the most harmful bacterial pathogens to infect host cells. While the T3SS filament, a long hollow conduit that bridges between bacteria and host cells, has been characterized structurally, very little is known about its physical properties. These filaments should endure shear and normal stresses imposed by the viscous mucosal flow during infection within the intestinal tract. We used atomic force microscopy (AFM) to probe the longitudinal and radial mechanical response of individual T3SS filaments by pulling on filaments extending directly from bacterial surfaces and later pressing into filaments that were detached from the bacteria. The measured longitudinal elastic moduli were higher by about two orders of magnitude than the radial elastic moduli. These proportions are commensurate with the role of the T3SS filament, which requires horizontal flexibility while maintaining its structural integrity to withstand intense stresses during infection.

Biomechanical changes of the common carotid artery and internal jugular vein in patients with multiple sclerosis.

Investigations of the hemodynamic changes of the venous system in patients with multiple sclerosis (MS) have shown contradictory results. Herein, the biomechanical parameters of the internal jugular vein (IJV) and common carotid artery (CCA) of MS patients were extracted and compared to healthy individuals. B-mode and Doppler sequential ultrasound images of 64 IJVs and CCAs of women including 22 healthy individuals, 22 relapsing-remitting multiple sclerosis (RRMS) patients, and 20 primary-progressive multiple sclerosis (PPMS) patients were recorded and processed. The biomechanical parameters of the IJV and the CCA walls during three cardiac cycles were calculated. The IJV maximum and minimum pressures were higher in the MS patients than in the healthy subjects, by 31% and 19% in RRMS patients and 39% and 24% in PPMS patients. The venous wall thicknesses in RRMS and PPMS patients were 51% and 60% higher than in healthy subjects, respectively. IJV distensibility in RRMS and PPMS patients was 70% and 75% lower, and compliance was 40% and 59% lower than in healthy subjects. The maximum intima-media thicknesses of the CCAs were 38% and 24%, and the minimum intima-media thicknesses were 27% and 23% higher in RRMS and PPMS patients than in healthy individuals, respectively. The shear modulus of CCA walls in RRMS and PPMS patients was 17% and 31%, and the radial elastic moduli were 47% and 9% higher than in healthy individuals. Some physical and biomechanical parameters of the CCA and IJV showed significant differences between MS patients and healthy individuals.

From experimental data, the mechanics relationships describing the behaviour of four different low alloyed steel powders during uniaxial cold compaction

ABSTRACTThis work aims at determining the constitutive model of four commercial water atomised low alloyed steel powders during cold compaction. Single-action experiments were performed, obtaining cylindrical specimens with different H/D ratios. The distribution of axial and radial stresses was investigated, and the relationships describing both the radial stress transmission coefficient and the flow stress as functions of the relative density were determined. The radial stress transmission coefficient also confirmed the hypothesised value of Poisson’s coefficient. The friction coefficient between the powder column and the die wall was determined, also highlighting the influence of the H/D ratio. Measuring the axial and radial strains due to spring-back, the axial and radial elastic moduli were determined, as functions of the relative density. The results obtained for the four materials were compared, also highlighting both differences and similarities.

Acoustic conductance of an anisotropic spherical shell submerged in a liquid 1. Wave model of contact interaction between a solid hollow sphere and a liquid. Degenerate solutions

With the example of a thick-walled spherical shell made of an anisotropic material, the decrease in the vibration intensity across the thickness of shells related to a change in the amplitude of wave propagation is considered. The motion rate of the outer surface of the shell, contacting a liquid medium, as a function of shell thickness and material properties in the circumferential and radial directions is investigated by using a model of radial vibrations caused by a harmonic source located on the inner surface of the shell. The model takes into account the interaction of surface of the shell with the surrounding medium. By using the operational method, with the use of the Laplace transformation, a general solution to the wave problem for radial vibrations is obtained. The amplitude solution is found in an expansion form with the use of the theory of residues. The degenerate solution of the transcendental equation for eigenfrequencies, which, in the general case, is a combination of Bessel functions, is investigated in the cases where the radial and circumferential elastic moduli differ considerably.

Radial elasticity of multi-walled boron nitride nanotubes

We investigated the radial mechanical properties of multi-walled boron nitride nanotubes (MW-BNNTs) using atomic force microscopy. The employed MW-BNNTs were synthesized using pressurized vapor/condenser (PVC) methods and were dispersed in aqueous solution using ultrasonication methods with the aid of ionic surfactants. Our nanomechanical measurements reveal the elastic deformational behaviors of individual BNNTs with two to four tube walls in their transverse directions. Their effective radial elastic moduli were obtained through interpreting their measured radial deformation profiles using Hertzian contact mechanics models. Our results capture the dependences of the effective radial moduli of MW-BNNTs on both the tube outer diameter and the number of tube layers. The effective radial moduli of double-walled BNNTs are found to be several-fold higher than those of single-walled BNNTs within the same diameter range. Our work contributes directly to a complete understanding of the fundamental structural and mechanical properties of BNNTs and the pursuits of their novel structural and electronics applications.

Radial Mechanical Properties of Single‐Walled Boron Nitride Nanotubes

The radial mechanical properties of single-walled boron nitride nanotubes (SW-BNNTs) are investigated by atomic force microscopy. Nanomechanical measurements reveal the radial deformation of individual SW-BNNTs in both elastic and plastic regimes. The measured effective radial elastic moduli of SW-BNNTs are found to follow a decreasing trend with an increase in tube diameter, ranging from 40.78 to 1.85 GPa for tube diameters of 0.58 to 2.38 nm. The results show that SW-BNNTs have relatively lower effective radial elastic moduli than single-walled carbon nanotubes (SWCNTs). The axially strong, but radially supple characteristics suggest that SW-BNNTs may be superior to SWCNTs as reinforcing additives for nanocomposite applications.

Regional stiffening of the mitral valve anterior leaflet in the beating ovine heart

Left atrial muscle extends into the proximal third of the mitral valve (MV) anterior leaflet and transient tensing of this muscle has been proposed as a mechanism aiding valve closure. If such tensing occurs, regional stiffness in the proximal anterior mitral leaflet will be greater during isovolumic contraction (IVC) than isovolumic relaxation (IVR) and this regional stiffness difference will be selectively abolished by β-receptor blockade. We tested this hypothesis in the beating ovine heart. Radiopaque markers were sewn around the MV annulus and on the anterior MV leaflet in 10 sheep hearts. Four-dimensional marker coordinates were obtained from biplane videofluoroscopy before (CRTL) and after administration of esmolol (ESML). Heterogeneous finite element models of each anterior leaflet were developed using marker coordinates over matched pressures during IVC and IVR for CRTL and ESML. Leaflet displacements were simulated using measured left ventricular and atrial pressures and a response function was computed as the difference between simulated and measured displacements. Circumferential and radial elastic moduli for ANNULAR, BELLY and EDGE leaflet regions were iteratively varied until the response function reached a minimum. The stiffness values at this minimum were interpreted as the in vivo regional material properties of the anterior leaflet. For all regions and all CTRL beats IVC stiffness was 40–58% greater than IVR stiffness. ESML reduced ANNULAR IVC stiffness to ANNULAR IVR stiffness values. These results strongly implicate transient tensing of leaflet atrial muscle during IVC as the basis of the ANNULAR IVC–IVR stiffness difference.

Development of an equation to predict radial modulus of elasticity for single-walled carbon nanotubes

Finite element (FE) method is used to model radial deformation of single-walled carbon nanotube (SWCNT) under hydrostatic pressure. Elastic deformation of the nanostructure is simulated via elastic beams. Properties of the beam element are calculated by considering the stiffness of the covalent bonds between the carbon atoms in the hexagonal lattice. By applying the beam elements in a three-dimensional space, elastic properties of the SWCNT in transverse direction are obtained. In this regard, influences of diameter and tube wall thickness on the radial and circumferential elastic moduli of zigzag and armchair SWCNTs are considered. It is observed that there is a good agreement between the FE results and data available in the literatures. The FE data are employed to develop a predictive equation through a statistical non-linear regression model.

Diameter-Dependent Radial and Tangential Elastic Moduli of ZnO Nanowires

We show how contact resonance atomic force microscopy (CR-AFM) can be used to accurately determine the radial elastic moduli of [0001] ZnO nanowires with diameters smaller than 150 nm. Using a realistic tip−nanowire contact geometry, we find the radial indentation modulus from CR-AFM data and the tangential shear modulus from friction-type measurements. Both moduli show a pronounced increase when the wire diameter is reduced below 80 nm. The size dependence of the elastic properties can be explained by a core−shell model that accounts for a bulk-like core and an elastically stiffer surface layer.

Radial moduli of individual single-walled carbon nanotubes with and without electric current flow

Although the radial elastic moduli of single-walled carbon nanotubes (SWCNTs) were studied by simulation or calculation, no experimental results were presented. The authors have studied the radial deformability of different diameters of SWCNTs with and without current flow using nanoindentation with rigid silicon and diamond tips under atomic force microscopy. The radial elastic moduli of SWCNT deduced by the Hertz model were found to be strongly dependent on the diameter, i.e., SWCNTs with smaller diameter have larger moduli. The radial stiffness was also shown to be larger for a SWCNT with current than that without current.

Elastic Properties of Carbon Nanotubes in the Radial Direction

A systematic numerical and theoretical analysis is carried out to study the radial elastic properties of single-walled, double-walled, and multi-walled carbon nanotubes (CNTs). The molecular dynamics simulations are used to study CNTs under radial pressure, and the deformation mechanisms of CNTs are explored by analysing the relationship between radial strain and strain energy. A parallel continuum model based on plane strain theory is verified by molecular dynamics (MD) simulation results in single-walled and double-walled CNTs, and extended into multi-walled CNTs that are computationally expensive for MD simulation. Good agreement is found between MD simulation results and continuum studies. The effective radial elastic moduli of CNTs are presented as a function of tube radii and the number of CNT layers. The results of this paper may be useful when analysing the mechanical integrity of CNT nanocomposites and nanofluidic components.

Rotation Stability of Anisotropic Disks

The critical state caused by the loss of stability of coils in rotating anisotropic disks is investigated by a numerical method. The investigation is performed for different ratios between the circumferential and radial elastic moduli and different relative thicknesses of the disks, Poisson ratios, and the ratios of radial and shear moduli. It is shown that, if a disk is made of materials compliant in the radial direction, the coils can lose their stability and shift according to the first harmonic (with displacement of the center of mass of the disk) or the second and third harmonics of vibrations (without displacement of the center of mass) within the range of its rotational velocities. These vibrations can be real for some materials, e.g., for unidirectional composites with a compliant (polyurethane) binder, and can precede the failure of disks from the action of circumferential stresses.

Analysis of the passive mechanical properties of rat carotid arteries

The passive mechanical properties of rat carotid arteries were studied in vitro. Using a tensile testing machine and a piston pump, intact segments of carotid arteries were subjected to large deformations both in the longitudinal and circumferential directions. Internal pressure, external diameter, length and longitudinal force were measured during the experiment and compared with the in vivo dimensions of the segments prior to excision. The anisotropic mechanical properties of the vessel wall material were analyzed using incremental elastic moduli and incremental Poisson's ratios. The results suggest that there is a characteristic deformation pattern common to all vessels investigated which is highly correlated with the conditions of loading that occur in vivo. That is, under average physiological deformation of the vessel, the longitudinal force is nearly independent of internal pressure. In this range of loading the circumferential incremental elastic modulus is nearly independent of longitudinal strain. However, the longitudinal and radial incremental elastic moduli vary significantly with deformation in this direction. The values of the moduli in all three directions increase with raising internal pressure. The weak coupling between circumferential and longitudinal direction in the wall material of carotid arteries is shown by the small value of the corresponding incremental Poisson's ratios.