Intrinsic Deformation Research Articles

Assessing left ventricular systolic function: from ejection fraction to strain analysis.

The measurement of left ventricular ejection fraction (LVEF) is a ubiquitous component of imaging studies used to evaluate patients with cardiac conditions and acts as an arbiter for many management decisions. This follows early trials investigating heart failure therapies which used a binary LVEF cut-off to select patients with the worst prognosis, who may gain the most benefit. Forty years on, the cardiac disease landscape has changed. Left ventricular ejection fraction is now a poor indicator of prognosis for many heart failure patients; specifically, for the half of patients with heart failure and truly preserved ejection fraction (HF-PEF). It is also recognized that LVEF may remain normal amongst patients with valvular heart disease who have significant myocardial dysfunction. This emphasizes the importance of the interaction between LVEF and left ventricular geometry. Guidelines based on LVEF may therefore miss a proportion of patients who would benefit from early intervention to prevent further myocardial decompensation and future adverse outcomes. The assessment of myocardial strain, or intrinsic deformation, holds promise to improve these issues. The measurement of global longitudinal strain (GLS) has consistently been shown to improve the risk stratification of patients with heart failure and identify patients with valvular heart disease who have myocardial decompensation despite preserved LVEF and an increased risk of adverse outcomes. To complete the integration of GLS into routine clinical practice, further studies are required to confirm that such approaches improve therapy selection and accordingly, the outcome for patients.

Autonomous Surface Reconciliation of a Liquid-Metal Conductor Micropatterned on a Deformable Hydrogel.

Spreading liquid droplets on solid surfaces is a core topic in physical chemistry with significant technological implications. Liquid metals, which are eutectic alloys of constituent metal atoms with low melting temperatures, are practically useful, but difficult to spread on solid surfaces because of their high surface tension. This makes it difficult to use liquid metals as deformable on-board microcircuitry electrodes, despite their intrinsic deformability. In this study, it is discovered that eutectic gallium-indium (EGaIn) can be spread onto the surface of chemically cross-linked hydrogels consisting of aliphatic alkyl chains with numerous hydroxyl groups (OH), thus facilitating the development of directly micropatterned EGaIn electrodes. More importantly, EGaIn patterned on a hydrogel autonomously reconciliates its surface to form a firm hydrogel interface upon mechanical deformation of the hydrogel. This autonomous surface reconciliation of EGaIn on hydrogels allows researchers to reap the benefits of chemically modified hydrogels, such as reversible stretching, self-healing, and water-swelling capability, thereby facilitating the fabrication of superstretchable, self-healable, and water-swellable liquid-metal electrodes with very high conductance tolerance upon deformation. Such electrodes are suitable for a variety of deformable microelectronic applications.

Electronic theoretical study on the influence of shear deformation on the electronic structure and optical properties of Li absorbed silicene

Based on the density functional theory, the influence of shear deformation on the electronic structure and optical properties of Li absorbed silicene system is studied by using the first-principles calculations. In the current research scope, it was found that after silicene adsorbs Li atoms, the silicene around the Li atoms has different degrees of distortion, and the band gap of the silicene increases. The calculation of binding energy shows that the shear deformation has little effect on the structural stability of Li absorbed silicene system. After intrinsic silicene shear deformation, the band gap increases with the increase of shear deformation.The band gap of Li absorbed silicene system decreases with the increase of shear deformation. The shear deformation causes the maximum absorption peak and the maximum reflection peak of the adsorption system to red shift.

3D printed tubular lattice metamaterials with engineered mechanical performance

We numerically and experimentally report 3D tubular lattice metamaterials with sinusoidal ligaments, which enable the deformation pattern to switch from bending to stretching. A non-linear J-shape stress-strain response and auxetic behavior over a large deformation range are observed due to the intrinsic deformation mechanism. Numerical analyses further demonstrate that the proposed tubular lattice metamaterials exhibit a high degree of tunability for Poisson's ratio and mechanical responses. In particular, the design flexibility can be harnessed to create heterogeneous tubular structures that can morph into target shapes. The findings presented here provide insights to develop 3D architected metamaterials with various potential applications, such as tissue engineering, biomedical devices, and stretchable electronics.

Exploiting the intrinsic deformation of a prosthetic foot to estimate the center of pressure and ground reaction force

The properties of the foot deployed in a bipedal robot that targets the rendering of a human-like dynamic gait are crucial. Firstly, it has to implement a set of mechanical mechanisms/properties that improve the efficiency of the locomotion. Secondly, it has to integrate a sensory system that captures the interaction with the ground with suitable precision. Both systems—the mechanical and the sensory system—have to be integrated as tightly as possible to keep the overall dimensions and weight low. Being the most distal element of the leg, especially the latter is crucial for favorable leg dynamics. Regarding the structural properties, a modern prosthetic foot poses a good solution and has hence been adopted in various bipeds. Their elaborated structures—mostly made from carbon fiber composites—are designed to imitate the mechanisms of the anthropomorphic counterpart. The following presents a concept to estimate the ground interaction based on the intrinsic deformation of a commercially available prosthesis. To measure the deformation, strain gauges are applied to its main structural elements. Using this information, the center of pressure and the normal force acting on it are estimated. The performance of two approaches—linear regression and neural networks—is presented and compared. Finally, the accuracy of the strain-based estimation is evaluated in two experiments and compared to a conventional force/torque sensor (FTS)-based system and a pressure insole. While the presented work is initially motivated by robotics research, it might as well be transferred to the design of a modern actively actuated prosthesis.

Coupling of shape and pairing vibrations in a collective Hamiltonian based on nuclear energy density functionals

The quadrupole collective Hamiltonian, based on relativistic energy density functionals, is extended to include a pairing collective coordinate. In addition to quadrupole shape vibrations and rotations, the model describes pairing vibrations and the coupling between shape and pairing degrees of freedom. The parameters of the collective Hamiltonian are determined by constrained self-consistent relativistic mean-field plus Bardeen-Cooper-Schrieffer (RMF+BCS) calculations in the space of intrinsic shape and pairing deformations. The effect of coupling between shape and pairing degrees of freedom is analyzed in a study of low-energy spectra and transition rates of four axially symmetric $N=92$ rare-earth isotones. When compared to results obtained with the standard quadrupole collective Hamiltonian, the inclusion of dynamical pairing increases the moment of inertia, lowers the energies of excited $0^+$ states and reduces the E0-transition strengths, in better agreement with data.

Modified Timoshenko beam model for bending behaviors of layered materials and structures

Layered materials and structures (LMS), such as van der Waals two-dimensional (2D) layered materials and nacre-like layered structures, often exhibit highly anisotropic mechanical properties, i.e., strong in in-plane directions but weak in out-of-plane direction. Despite the strong anisotropy in their mechanical properties, Timoshenko beam model (TBM) is usually used to describe the bending deformation of LMS. We note, however, that there are two fundamental issues in using TBM to describe LMS: First, the stiffness of LMS approaches zero when the interlayer shear modulus G approaches zero; and second, the first derivative of deflection becomes discontinuous at the point of concentrated force. Clearly, both are not true for LMS. In this work, by introducing the bending energy of monolayer into the potential energy of TBM, we develop a modified Timoshenko beam model (MTBM), which is able to not only address these two issues, but also correctly predict the bending stiffness of LMS without any fitting parameters. Our analysis shows that the bending behaviors of LMS are determined by a dimensionless parameter λL, where L is the length of the beam and λ=kGA∕D0+kGA∕(nDbend), where, kGA and D0 are, respectively, the shear and bending rigidity of the beam cross-section, Dbend is the bending rigidity of monolayer, and n is the number of layer. When λL→0, the MTBM degenerates to the multi-beam model with bending stiffness of nDbend; while it degenerates to the TBM whenλL→∞. Furthermore, if kGA is much larger than D0, both MTBM and TBM degenerate to the classical Euler–Bernoulli beam model. We further perform molecular dynamics simulations, finite element simulations and experiments to validate the MTBM. Based on the MTBM, a couple of interesting applications of LMS are also demonstrated. Hence, the MTBM presented here captures the necessary intrinsic deformation modes of LMS and provides an accurate tool for the prediction and optimization of the mechanical properties of LMS.

Limits on assigning a shape to a nucleus

The interpretation of nuclear observables in the laboratory frame in terms of the intrinsic deformation parameters beta and gamma is a classical theme in nuclear structure. Here we use the quadrupole invariants (Kumar), calculated within the framework of the configuration-interaction shell model, to clarify the meaning and limitations of nuclear shapes. We introduce a novel method that enables us to calculate accurately higher-order invariants and, therefore, the fluctuations in both beta and gamma. We find that the shape parameter beta often has a non-negligible degree of softness, and that the angle gamma is usually characterized by large fluctuations, rendering its effective value not meaningful. Contrary to common belief, we conclude that doubly magic nuclei are not spherical because the notion of a well-defined shape does not apply to them.

3d-visualization of magnesium strengthening mechanisms for a description of experimentally obtained data of alloying effect in Mg-Ga system

Based on laws of theory of materials strengthening were discribed the experimentally obtained alloying effect in Mg-Ga system and shown using program for 3d atomic structures. As known from our experiments a homogeneous “wavy” microstructure of the diffusion zone forms as result of mass-transfer of molten gallium into the volume of magnesium alloys. SEM chemical composition shows Mg 65% wt. and Ga 35% wt. and X-ray spectra diffraction data - Mg5Ga2 intermetallic phase formation. Such intermetallic diffusion zone provides the significant strengthening effect of microstructure which was determined experimentally by the indentation method. The 3-d visualization shows the reaction and changing of an original crystal structure of magnesium atomic lattice upon diffusion doping with foreign atoms of gallium and then is shown the coalescence of Mg5Ga2 intermetallic crystal with crystals surfaces of Mg-matrix. So, investigated Mg-alloy strengthening at alloying with Ga explained by two main factors. At first is the formation of intermetallic phases with the ordering and consolidation of the crystal structure of the matrix by the ligature atoms, which is the key factor of the strengthening mechanism fixed experimentally. Second, when hexagonal and orthorhombic atomic structures growth according to their spatial type, a significant disorientation of structural fragments occurs, an increase in the density of the amorphous transition layer, a twinning of the structure in the interphase boundaries, which leads to the formation of intrinsic mutual deformation and a high level of internal stresses.

Reversible deformation in nanocrystalline TWIP steel during cyclic loading by partial slip reversal and detwinning

Mechanical responses of nanostructured twinning induced plasticity (TWIP) steels have attracted attention owing to their ultra high strength and ductility. A set of molecular dynamics simulations were carried out to characterize and track the atomic structure of Fe–22Mn (wt. %) nanocrystalline TWIP steel during reverse loading (tension-compression). The results show that intrinsic stacking faults and deformation twins which were formed during forward tensile loading up to total strain of 5.8% were eliminated upon subsequent reverse compression loading up to strain of 0.0 %. The current study provides the first simulation evidence of detwinning in nanocrystalline TWIP steel during the reverse loading. The atomic structure and dislocation analysis show that the observed detwinning is due to the dependence of shear stress acting on the trailing and leading partial dislocations on the loading direction. The results show that the Schmid factor of the trailing partial dislocations in compression loading are larger than leading partial dislocations one. The reversible deformation by detwinning could allow for reversible plastic deformation, storage of energy and mechanical damping in micro or nano devices.

Experimental study on molecular fluctuations of biomolecules by force spectroscopy

Atomic force microscopy (AFM) measurements of biomolecules, such as proteins, are often affected by molecular fluctuations. Not only due to the intrinsic thermal fluctuation, deformation and displacement of a part or the whole molecule are induced by the AFM tip, especially when the molecules are weakly fixed to a substrate. Here we have studied the effect of the molecular fluctuations on the topography of the streptavidin (SA) protein molecules bound to a DNA origami in two different configurations by force spectroscopy experiments. While the experimental and theoretical height histograms of a tightly-fixed SA molecule were in good agreement, the experimental height histogram of a weakly-fixed SA molecule was distorted. We discussed the origins of the discrepancy of the histogram for the latter and suggested that it was due to the tip-induced deformation or the displacement of the molecule. The methodology presented here is useful for assessment of the appropriate fixation conditions for high-resolution topographic and functional imaging experiments of a single molecule by AFM.

Dual shape recovery of red blood cells flowing out of a microfluidic constriction.

Micropipette aspiration, optical tweezers, rheometry, or ecktacytometry have been used to study the shape recovery of healthy human Red Blood Cells (RBCs) and measure associated relaxation times of the order of 100-300 ms. These measurements are in good agreement with the Kelvin-Voigt model, which describes the cell as a visco-elastic material, predicting that its relaxation time only depends on cell intrinsic properties. However, such mechanical solicitation techniques are far from being relevant regarding RBC solicitation in vivo. In this paper, we report for the first time the existence of two different behaviors of the RBC shape recovery while flowing out of a microfluidic constricted channel. The calculation of the viscous stress corresponding to the frontier between the two recovery modes confirms that the RBC resistance to shear is the elastic property dominating the transition between the two recovery behaviors. We also quantified associated recovery times and report values as low as 4 ms-which is almost two decades smaller than the typical RBC relaxation time-at high viscosity and flow velocity of the carrier fluid. Although we cannot talk about relaxation time because the cell is never at rest, we believe that the measured shape recovery time arises from the coupling of the cell intrinsic deformability and the hydrodynamic stress. Depending on the flow conditions, the cell mechanics becomes dominant and drives the shape recovery process, allowing the measurement of recovery times of the same order of magnitude than relaxation times previously published. Finally, we demonstrated that the measurement of the shape recovery time can be used to distinguish Plasmodium falciparum (causing malaria) infected RBCs from healthy RBCs.

Deformability and solvent penetration in soft nanoparticles at liquid-liquid interfaces

HypothesisThe internal topology of soft nanoparticles – regular (ideal) vs disordered (realistic) networks – and its intrinsic deformability (degree of cross-linking) influences solvent permeability (uptake, invasive and mixing capacities) under interfacial confinement. MethodologyBy means of large-scale molecular dynamics simulations we study nanogels at liquid-liquid (A-B) interfaces covering the whole range of cross-linking degrees and interfacial strengths. The nanogel permeability is analyzed with a grid representation that accounts for the surface fluctuations and adds to the density profiles the exact number of liquid particles inside the nanogel. Unlike in previous investigations, excluded volume interactions are considered for all the particles (monomers and liquids). FindingsNanogel’s permeability is intrinsically related to the particle deformability. Ideal networks show higher values of the total liquid uptake and the invasive capacity (A-particles in B-side and vice versa) than realistic networks, though differences vanish in the limit of rigid interfaces. Uptake and invasion are optimized at a cross-linking degree that depends on the interfacial strength, tending to ~15-20% for moderate and stiff interfaces. As the interfacial strength increases, the miscibility inside the nanogel is enhanced by a factor of up to 5 with respect to the bare interface, with the disordered networks providing a better mixing than their ideal counterparts.

Enhanced nuclear Schiff moment in stable and metastable nuclei

Nuclei with static intrinsic octupole deformation or a soft octupole vibrational mode lead to strongly enhanced collective nuclear Schiff? moments. Interaction between electrons and these Schiff moments produce enhanced time reversal (T) and parity (P) violating electric dipole moments (EDM) in atoms and molecules. Corresponding experiments may be used to test CP-violation theories predicting T,P-violating nuclear forces and to search for axions. Nuclear octupole deformations are predicted in many short lived isotopes. This paper investigates octupole deformations in stable and very long lifetime nuclei such as 153Eu, 235U, 237Np and 227Ac, which can ease atomic experiments substantially. The estimates of the enhanced Schiff? moments, atomic electric dipole momentsand T, P-odd interaction constants in molecules containing these nuclei are presented.

Revealing the Strain Effect on Radiation Response of Amorphous–Crystalline Cu-Zr Laminate

Nanocrystalline materials containing amorphous intergranular films (AIFs) exhibit excellent mechanical properties, radiation resistance, and thermal stability and may serve as promising candidate materials for use in advanced nuclear energy systems. The aim of this work is to reveal the effect of mechanical stress on the radiation damage behavior of AIF systems. Based on a bicrystal Cu system with Zr-doped AIFs, molecular dynamics is used to simulate the radiation process and examine the AIF sink efficiency, defect propensity, defect size distribution, and Zr mixing under uniaxial and hydrostatic strain conditions. The results show that the sink efficiency of the glue-like AIFs is not compromised under applied strains. The anisotropy resulting from the intrinsic microstructure and elastic deformation leads to a distinct radiation response, where extension (contraction) of the structure perpendicular to the AIFs increases (decreases) the vacancy density. The strain-dependent defect density, along with the cluster size distributions, can be interpreted based on the variations in the defect formation energy and anisotropic defect diffusion. Finally, the Zr mixing induced by collision cascades is found to be insensitive to the mechanical strains. These findings provide meaningful information towards understanding the stress effect on the radiation response of AIF systems.

Interconnection of Intrinsic Deformations and Adhesive Phenomena in Modified Disperse Systems

The studies’ results of the adhesive and the cement-polymer compositions shrinkage phenomena are given. Theoretical approaches are justified when selecting additives to reduce the cement-polymer systems shrinkage deformations. A method for measuring water separation and shrinkage with the DBS device (the soil bucking measuring device), which simulates the modified disperse systems intrinsic deformations processes and of the products based on them, is proposed. The adhesion strength results of at the “stone material-solution” boundary are given. It has been shown that the solutions shrinkage has a significant effect on the adhesive strength.

The wear and microstructural characterization of copper surface coated with TiC reinforced FeAl intermetallic composite by ESD method

Iron aluminides, as a technological material, are a member of multicomponent alloys, that contains other alloying elements besides iron and aluminium. Due to superior anti-corrosion properties at high temperatures, these alloys are used as coating materials in many surface development processes. Copper is widely used in industry because of its commercially desired properties such as high thermal and electric conductivity. However, copper cannot be used for special applications where an excellent strength and/or good wear resistance are required due to a lower tensile strength and poor wear resistance. In this study, 1 wt% TiC reinforced iron aluminide intermetallic composite electrode was initially produced and used to coat the copper surface in order to increase the surface hardness and improve the wear rate by forming a hard structure using ESD coating method. It has been observed that surface hardness increased by about 11 times at the end of experimental studies. Wear rate of the coated material increased compared to the uncoated material while the uncoated sample exhibits adhesive wear, also the coated sample exhibits both adhesive and abrasive wear. The wear rate of the coated material was intially lower due to intrinsic low deformation capacity of aluminide coating and later increased substantially because of removal of this aluminide layer.

Oxide shell layer influences on size-dependent tensile and compressive mechanical properties of iron nanowires: A ReaxFF molecular dynamics study

The systematic understanding of an overall deformation mechanism of metallic iron (Fe) nanowires (NWs) with the pre-existing oxide shell layer (Fe/FexOy) under various mechanical loading conditions is of critical importance for their various applications. Herein, we perform molecular dynamics simulations using ReaxFF reactive interatomic potential to systematically investigate the effect of the pre-existing oxide shell layer on the underlying intrinsic mechanical deformation mechanism and related mechanical properties of metallic [001]-oriented Fe NWs under both uniaxial tension and compressive loading. Three different diameters of the NWs are investigated to elucidate the size effect. The Fe NWs with the preoxide shell layer possess unique and intriguing mechanical properties and deformation mechanisms. In particular, the oxide shell layer with the combined effect of the diameter and the applied uniaxial loading mode dictates the strength and the overall stress-strain behaviors of the NWs. Interestingly, the oxide-coated NWs clearly exhibit the diameter-dependent elastic deformation intrinsic mechanism and related properties as compared to the pristine counterparts. Specifically, the pre-existing oxide shell layer expedites the onset of tensile plasticity by drastically reducing the tensile yield stress and significantly decreasing the tensile elastic limit. Contrary to the tensile loading, the presence of the oxide shell layer reduces or increases the compressive yield stress of the pristine Fe NW with respect to its diameter. However, the pre-existing oxide shell layer leads to a significantly delayed onset of compressive plasticity, that is, a significant increase in the compressive elastic limit.

Pronounced transition of crack initiation and propagation modes in the hydrogen-related failure of a Ni-based superalloy 718 under internal and external hydrogen conditions

The role of hydrogen in tensile ductility loss and on the fracture behaviours of Ni-based superalloy 718 was investigated via tensile tests under hydrogen-charged conditions (internal hydrogen) or in gaseous hydrogen environments (external hydrogen), in combination with post-mortem analyses of fractured samples using electron microscopy techniques. Whereas intergranular fracture was responsible for material degradation under external hydrogen, the failure modes under internal hydrogen conditions were primarily dominated by cracking along slip planes or twin boundaries. The mechanisms of crack initiation and propagation are extensively discussed in terms of hydrogen distribution, intrinsic deformation character of the material and hydrogen-modified dislocation behavior.

Strengthening and deformation mechanisms in nanolaminated single-walled carbon nanotube-aluminum composites

Single-walled carbon nanotubes (SWCNTs) have excellent intrinsic mechanical properties and would not suffer from inter-layer sliding as their multi-walled counterparts, making them promising reinforcing candidates for advanced metal matrix composites. In this study, we fabricated nanolaminated SWCNT-aluminum (Al) composites where the SWCNTs were uniformly distributed at the lamella boundaries and were tightly bonded with the Al matrix. Macroscopic tensile tests showed a considerable strengthening effect as a result of SWCNT inclusion, while the uniform elongation of the composites remained unchanged as compared to unreinforced Al. Subsequent micro-pillar compression tests at various pillar orientations and strain rates, together with associated post-mortem site-specific microstructural analysis, revealed that this SWCNT-induced strengthening in the composites can be rationalized by a combined effect from the grain refinement in the Al matrix, the load-sharing of the CNTs, and their alteration of the intrinsic deformation mechanism of the Al matrix.