Behavior Of Curvature Research Articles

The diffuse interface description of fluid lipid membranes captures key features of the hemifusion pathway and lateral stress profile.

Topological transitions of lipid membranes are ubiquitous in key biological processes for cell life, like neurotransmission, fertilization, morphogenesis, and viral infections. Despite this, they are not well understood due to their multiscale nature, which limits the use of molecular models and calls for a mesoscopic approach such as the celebrated Canham-Helfrich one. Unfortunately, such a model cannot handle topological transitions, hiding the crucial involved forces and the appearance of the experimentally observed hemifused intermediates. In this work, we describe the membrane as a diffuse interface preserving the Canham-Helfrich elasticity. We show that pivotal features of the hemifusion pathway are captured by this mesoscopic approach, e.g. a (meta)stable hemifusion state and the fusogenic behavior of negative monolayer spontaneous curvatures. The membrane lateral stress profile is calculated as a function of the elastic rigidities, yielding a coarse-grained version of molecular models findings. Insights into the fusogenic mechanism are reported and discussed.

Lateral buckling of the compressed edge of a beam under finite bending

This paper investigates the critical condition whereby the compressed edge of a beam subjected to large bending exhibits a sudden lateral heeling. This instability phenomenon occurs through a mechanism different from that usually studied in linear theory and known as flexural–torsional buckling. An experimental test device was specifically designed and built to perform pure bending tests on soft materials. Thus, the experimental campaign provides not only the moment-curvature behavior of beams of narrow rectangular cross section, but also information regarding the post-critical lateral buckling behavior. To study the local bifurcation phenomenon, an analytical model is proposed in which a field of small transversal displacements, typical of the linear stability of thin plates, is superimposed on the large vertical displacement field of an inflexed beam in the nonlinear elasticity theory. Furthermore, numerous numerical simulations through nonlinear FE analysis have been performed. Finally, the results provided by the different methods applied were compared and discussed.

Tissue material properties, whole-bone morphology and mechanical behavior in the Fbn1C1041G/+ mouse model of Marfan syndrome

Marfan syndrome (MFS) is a connective tissue disorder caused by pathogenic mutations in FBN1. In bone, the protein fibrillin-1 is found in the extracellular matrix where it provides structural support of elastic fiber formation, stability for basement membrane, and regulates the bioavailability of growth factors. Individuals with MFS exhibit a range of skeletal complications including low bone mineral density and long bone overgrowth. However, it remains unknown if the bone phenotype is caused by alteration of fibrillin-1′s structural function or distortion of its interactions with bone cells. To assess the structural effects of the fibrillin-1 mutation, we characterized bone curvature, microarchitecture, composition, porosity, and mechanical behavior in the Fbn1C1041G/+ mouse model of MFS. Tibiae of 10, 26, and 52-week-old female Fbn1C1041G/+ and littermate control (LC) mice were analyzed. Mechanical behavior was assessed via in vivo strain gauging, finite element analysis, ex vivo three-point bending, and nanoindentation. Tibial bone morphology and curvature were assessed with micro computed tomography (μCT). Bone composition was measured with Fourier transform infrared (FTIR) imaging. Vascular and osteocyte lacunar porosity were assessed by synchrotron computed tomography. Fbn1C1041G/+ mice exhibited long bone overgrowth and osteopenia consistent with the MFS phenotype. Trabecular thickness was lower in Fbn1C1041G/+ mice but cortical bone microarchitecture was similar in Fbn1C1041G/+ and LC mice. Whole bone curvature was straighter below the tibio-fibular junction in the medial–lateral direction and more curved above in LC compared to Fbn1C1041G/+ mice. The bone matrix crystallinity was 4 % lower in Fbn1C1041G/+ mice compared to LC, implying that mineral platelets in LCs have greater crystal size and perfection than Fbn1C1041G/+ mice. Structural and mechanical properties were similar between genotypes. Cortical diaphyseal lacunar porosity was lower in Fbn1C1041G/+ mice compared to LC; this was a result of the average volume of an individual osteocyte lacunae being smaller. These data provide valuable insights into the bone phenotype and its contribution to fracture risk in this commonly used mouse model of MFS.

Nonperturbative thermodynamic extrinsic curvature of the anyon gas

Thermodynamic extrinsic curvature is a new mathematical tool in thermodynamic geometry. By using the thermodynamic extrinsic curvature, one may obtain a more complete geometric representation of the critical phenomena and thermodynamics. We introduce nonperturbative thermodynamic extrinsic curvature of an ideal two-dimensional gas of anyons. Using extrinsic curvature, we find new fixed points in nonperturbative thermodynamics of the anyon gas that particles behave as semions. Here, we investigate the critical behavior of thermodynamic extrinsic curvature of two-dimensional Kagome Ising model near the critical point [Formula: see text] in a constant magnetic field and show that it behaves as [Formula: see text] with [Formula: see text], where [Formula: see text] denotes the critical exponent of the specific heat. Then, we consider the three-dimensional spherical model and show that the scaling behavior is [Formula: see text], where [Formula: see text]. Finally, using a general argument, we show that extrinsic curvature [Formula: see text] has two different scaling behaviors for positive and negative [Formula: see text]. For [Formula: see text], our results indicate that [Formula: see text]. However, for [Formula: see text], we found a different scaling behavior, where [Formula: see text].

Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Comparative study on flexural performance of ultra‐high performance concrete beams reinforced with steel rebar and steel plate

AbstractTo enhance the mechanical and constructional performance of the ultra‐high performance concrete (UHPC) beams, the steel plate placed at the bottom surface of the UHPC beam is utilized to replace the ordinary steel rebars. In this paper, four 3.2 m UHPC T‐shaped beams with different reinforcement patterns of ordinary steel rebars and external steel plate were fabricated and comparatively tested under flexure loading. Their damage patterns, load versus deflection behavior, flexural capacity, load versus strain behavior, moment versus curvature behavior, stiffness, and crack development were investigated. The flexural experiments indicated that the external steel plate, positioned at the bottom surface of the UHPC members, could resolve the difficulty of installing ordinary steel rebars in slender UHPC components and improve its constructional performance. Compared with the inside steel rebar reinforcement, the employment of the steel plate at the bottom surface of the UHPC beam can effectively increase the distance from the neutral axis to the tensile reinforcement at the serviceability and ultimate states, thereby improving its flexural capacity and stiffness. Additionally, the configuration of the external steel plate was beneficial to reduce the tensile stress level of the tensile reinforcement and limit the opening of UHPC crack width, and thus their crack resistance can be effectively enhanced. Moreover, increasing the thickness of the steel plate or rebar ratio can also significantly improve the flexural capacity, stiffness, and cracking resistance of UHPC beams.

Unexpected temperature dependence of 1H paramagnetic shift in MAS NMR of nickelocene

This work revisits the temperature dependence of 1H paramagnetic shift in nickelocene as a potential nuclear magnetic resonance (NMR) thermometer under fast magic angle spinning (MAS) rate. Surprisingly, an abnormal temperature dependence of 1H paramagnetic shift has been observed. In addition to a 1/T dependence term, a 1/T2 dependence term must be included to correctly describe the curvature behavior of the δ1H-T correlation under fast MAS rate.

Equilibrium behavior of branching curvature and comparison of enantiomer morphology in lipid monolayers

Equilibrium behavior of branching curvature and comparison of enantiomer morphology in lipid monolayers

Analysis of Geometric and Material Nonlinearity in the Column Bending Test

The column bending test (CBT) is an experimental method to measure the moment–curvature behavior and failure curvature of high-strain composites (HSCs), designed to apply a relatively constant bending moment through a sample up to very high curvatures. In this paper, we first calculate the errors involved in the simplified geometric analysis used to model the CBT by considering two different effects: variations in the bending moment through the sample and nonlinearities in the material response of the fibers. The first effect, modeled using Euler’s elastica, results in a set of design guidelines for the test geometry (i.e., length of the grips and the specimens) in order to achieve moderate errors in moment and curvature predictions. The nonlinearity in the fiber behavior (tension stiffening and compression softening) does not have a strong effect on the curvature but produces significant variations in the bending stiffness of HSCs as well as the maximum strain observed in the fibers due to the shift in the neutral axis. This indicates that accounting for the nonlinear behavior of fibers is necessary in order to accurately predict the failure properties of HSCs under bending.

4D printing of shape memory polymer with continuous carbon fiber

Shape memory polymer composites (SMPCs) have gained attention for their shape memory effects and wide-ranging applications. Understanding the bending shape recovery characteristics of 3D printed SMPCs is crucial for optimizing their performance. This study focuses on investigating the influence of different fiber orientations of continuous carbon fiber (CCF) in thermally stimulated SMPC. By controlling printing parameters and fiber orientation during the 3D printing process, we fabricate tailor-made rectangular composite test specimens. These specimens are subjected to controlled bending above the glass transition temperature of the polymer, inducing temporary deformation. The subsequent shape recovery process is carefully captured through high-speed video. Precise measurements of the bending curvature over time are obtained using the row-by-row image processing technique and analyzed. The shape recovery rate, shape recovery ratio, and shape fixity ratio of the test specimens were evaluated as a function of three CCF layout arrangements as well as fiber infill density embedded in Shape Memory Polymer (SMP) test specimens. The results revealed that the addition of CCF in the polymer matrix has a significant impact on shape memory behavior. Vertically aligned CCF in the SMP matrix improves the shape recovery ratio (92.97% compared to 78.77% of the pure SMP sample), while horizontal alignment of CCF ensures maximum shape fixity ratio (91.78% compared to 66.22% of the pure SMP sample). The cross-aligned CCF sample provides good recovery as well as fixity values. Further, it was observed that the horizontal alignment of CCF yields the fastest recovery performance. The outcome confirms that optimizing the fiber orientation enhances shape memory performance. Also, 40% of fiber infill density had greater shape fixity and overall recovery performance when compared to 30% and 50%. These findings have implications for tailored and high-performance SMPCs in biomedical devices, aerospace components, and robotics. Understanding temporal curvature behavior enables optimizing the design of materials with precise control over shape recovery. This research contributes to the design and optimization of SMPCs for diverse applications.

Insight into the Microstructure of FRW Universe from a P-V Phase Transition

The P-V phase transition of the FRW (Friedmann-Robertson-Walker) universe with a perfect fluid has recently been investigated, revealing that the four critical exponents near the critical point are consistent with the values predicted by mean field theory. Notably, the coexistence phase of the P-V phase transition in the FRW universe above the critical temperature, which distinguishes it from van der Waals system and most of AdS black holes system. This unique property allows us to investigate the microstructure of the FRW universe as a thermodynamic system. Our analysis of the Ruppeiner geometry for the FRW universe reveals that the behavior of the thermodynamic scalar curvature near criticality is characterized by a dimensionless constant identical to that of the van der Waals fluid. Additionally, we observe that while repulsive interactions dominate for the coexistence samll phase with higher temperature, the scalar curvature for the coexistence large phase is always negative, indicating attractive interactions, providing new insights into the nature of interactions among the perfect fluid matter constituents in the expanding FRW universe.

Black hole geometrothermodynamics and critical phenomena: A look from Tsallis entropy-based perspective

We analyze geometrothermodynamics of charged anti-de Sitter (AdS) black holes with a global monopole in the framework of Tsallis statistics. The latter arises from a non-additive generalization of Boltzmann–Gibbs entropy, which is still recovered as a particular sub-case. We examine the effects of Tsallis entropy on small-large black holes phase-transitions and critical exponents, comparing the results with the liquid–gas change of phase occurring in van der Waals fluids. We also discuss some physical constraints on Tsallis parameter and the impact on sparsity of BH radiation. Thermodynamic curvature behavior and the nature of microscopic interactions are then explored from a geometric perspective within Ruppeiner formalism on the S−P coordinate space. Similar considerations are extended to charged (2+1)-dimensional Banados–Teitelboim–Zanelli (BTZ) black holes by computing the entropy-pressure and entropy-volume corrected curvatures. Our analysis shows that Tsallis prescription has non-trivial implications on black hole geometrothermodynamics, emphasizing the role of non-additive entropy in the correspondence between black holes and van der Waals systems.

Combinatorial Screening of Cationic Lipidoids Reveals How Molecular Conformation Affects Membrane-Targeting Antimicrobial Activity.

The search for next-generation antibacterial compounds that overcome the development of resistance can be facilitated by identifying how to target the cell membrane of bacteria. Understanding the key molecular features that enable interactions with lipids and lead to membrane disruption is therefore crucial. Here, we employ a library of lipid-like compounds (lipidoids) comprising modular structures with tunable hydrophobic and hydrophilic architecture to shed light on how the chemical functionality and molecular shape of synthetic amphiphilic compounds determine their activity against bacterial membranes. Synthesized from combinations of 8 different polyamines as headgroups and 13 acrylates as tails, 104 different lipidoids are tested for activity against a model Gram-positive bacterial strain (Bacillus subtilis). Results from the combinatorial screening assay show that lipidoids with the most potent antimicrobial properties (down to 2 μM) have intermediate tail hydrophobicity (i.e., c log P values between 3 and 4) and lower headgroup charge density (i.e., longer spacers between charged amines). However, the most important factor appeared to be the ability of a lipidoid to self-assemble into an inverse hexagonal liquid crystalline phase, as observed by small-angle X-ray scattering (SAXS) analysis. The lipidoids active at lowest concentrations, which induced the most significant membrane damage during propidium iodide (PI) permeabilization assays, were those that aggregated into highly curved inverse hexagonal liquid crystal phases. These observations suggest that the introduction of strong curvature stress into the membrane is one way to maximize membrane disruption and lipidoid antimicrobial activity. Lipidoids that demonstrated the ability to furnish this phase consisted of either (i) branched or linear headgroups with shorter linear tails or (ii) cyclic headgroups with 4 bulky nonlinear tails. On the contrary, lipidoids previously observed to adopt disc-like conformations that pack into bicontinuous cubic phases were significantly less effective against B. subtilis. The discovery of these structure-property relationships demonstrates that it is not simply a balance of hydrophobic and hydrophilic moieties that govern membrane-active antibacterial activity, but also their intrinsic curvature and collective behavior.

Bilayer Hydrogel Composed of Elastin-Mimetic Polypeptides as a Bio-Actuator with Bidirectional and Reversible Bending Behaviors.

Biologically derived hydrogels have attracted attention as promising polymers for use in biomedical applications because of their high biocompatibility, biodegradability, and low toxicity. Elastin-mimetic polypeptides (EMPs), which contain a repeated amino acid sequence derived from the hydrophobic domain of tropoelastin, exhibit reversible phase transition behavior, and thus, represent an interesting starting point for the development of biologically derived hydrogels. In this study, we succeeded in developing functional EMP-conjugated hydrogels that displayed temperature-responsive swelling/shrinking properties. The EMP-conjugated hydrogels were prepared through the polymerization of acrylated EMP with acrylamide. The EMP hydrogel swelled and shrank in response to temperature changes, and the swelling/shrinking capacity of the EMP hydrogels could be controlled by altering either the amount of EMP or the salt concentration in the buffer. The EMP hydrogels were able to select a uniform component of EMPs with a desired and specific repeat number of the EMP sequence, which could control the swelling/shrinking property of the EMP hydrogel. Moreover, we developed a smart hydrogel actuator based on EMP crosslinked hydrogels and non-crosslinked hydrogels that exhibited bidirectional curvature behavior in response to changes in temperature. These thermally responsive EMP hydrogels have potential use as bio-actuators for a number of biomedical applications.

Moment–curvature behaviour of RC chimney section under monotonic loading–An experimental study

The latest revision of IS: 4998 (2015 edition) incorporates the limit state method of design and proposes a new stress–strain model for concrete and steel for RC chimneys. Many apparent differences can be noticed between the stress–strain relationships of these two materials when the methodologies of IS: 4998–2015 and other well-established design codes are compared.In order to investigate these differences and to find out the methodology which uses most precision in depicting the stress–strain relationship of these materials, four hollow circular test specimens of typical RC chimneys with openings have been specially designed, fabricated and laboratory tested for bending under monotonically increasing lateral loading. As the results of the cross-section at the bottom of the opening near the base of the chimney are found to be the most critical, the behaviour at especially this section has been emphasized.Test results include strength, crack pattern, failure mechanism; further, the results obtained from this experimental study have been compared in the form of ultimate strength, curvature ductility and energy absorption by plotting moment–curvature relationships using design guidelines given in IS: 4998–2015, CICIND 2011 and ACI: 307–08.

A stretchable sandwich panel metamaterial with auxetic rotating-square surface

Sandwich panels find use as energy-absorbing devices and protective structures in various fields. However, due to their mostly rigid surfaces, they might not meet the protection requirements in complex conditions like non-Euclidean geometries of protected objects. To address this issue, a novel sandwich panel structure inspired by the synclastic curvature behavior of auxetic metamaterial was proposed. The surface of the proposed sandwich panel features rotating squares that allow for horizontal stretching, resulting in an improvement in controllability, auxeticity, flexibility, and synclastic curvature compared to traditional sandwich panels. Experimental and numerical methods were used to compare the similarities and differences between the novel and traditional sandwich panels under uniaxial compression. Additionally, different rotation angles and numbers of unit cells were simulated to examine their mechanical properties. The study also explored the auxeticity, stretchability, synclastic curvature, and potential applications of the novel sandwich panel. It was found that appropriate cuts on the sandwich panel can enhance energy absorption. These findings could pave the way for new opportunities in the application and basic research of sandwich panels while providing ideas for enhancing the survivability of panel structures in complex conditions.

Gravity Is Not Attraction; It’s a Push (Space-Time Expansion Theory)

The space-time expansion has a new perspective on the universe phenomena. In this article, the key features of the Space-Time Expansion Theory are summarized and discussed, with three postulates incorporating different insights into the behavior of space-time expansion, gravity, space-time curvature, and time itself. Gravity is not an attraction; it is a push. Inertia, free fall, the principles of the theory of relativity and some other phenomena support the author’s assertions. The expansion of space-time is universal, occurs everywhere, and produces gravity instead of counteracting it. Being immersed in the same space-time acceleration, we only perceive the disturbance caused by the matter, which is the massive objects push. This study aims to offer scientists an alternative investigation. “Gravitation is not attraction; it’s a push.” All in accordance with hydrodynamic gravitation and expanding Universe.

Evolution of Lifshitz metric anisotropies in Einstein–Proca theory under the Ricci–DeTurck flow

By starting from a Perelman entropy functional and considering the Ricci–DeTurck flow equations, we analyze the behavior of Einstein–Hilbert and Einstein–Proca theories with Lifshitz geometry as functions of a flow parameter. In the former case, we found one consistent fixed point that represents flat space-time as the flow parameter tends to infinity. Massive vector fields in the latter theory enrich the system under study and have the same fixed point achieved at the same rate as in the former case. The geometric flow is parametrized by the metric coefficients and represents a change in anisotropy of the geometry toward an isotropic flat space-time as the flow parameter evolves. Indeed, the flow of the Proca fields depends on certain coefficients that vanish when the flow parameter increases, rendering these fields constant. We have been able to write down the evolving Lifshitz metric solution with positive, but otherwise arbitrary, critical exponents relevant to geometries with spatially anisotropic holographic duals. We show that both the scalar curvature and matter contributions to the Ricci–DeTurck flow vanish under the flow at a fixed point consistent with flat space-time geometry. Thus, the behavior of the scalar curvature always increases, homogenizing the geometry along the flow. Moreover, the theory under study keeps positive-definite, but decreasing, the entropy functional along the Ricci–DeTurck flow.

Nanoscale bimetallic strip: Atomistic bending mechanisms of AuPd bimetallic nanowhiskers

The bimetallic strips combining two metals with different thermal expansion coefficients are widely employed for temperature sensing, actuation and control. In the present study, we fabricated nanoscale bimetallic strip by one-sided coating with Pd of ultra-strong single crystalline Au nanowhiskers grown by molecular beam epitaxy. The as-fabricated bimetallic nanowhiskers were slightly bent due to heteroepitaxial stresses in the single crystalline Pd coating. The temperature-induced shape changes of these bimetallic Au-Pd nanowhiskers were studied via in-situ thermal actuation in scanning electron microscope. Annealing of the bimetallic nanowhisker resulted in a change in the amplitude and sign of the curvature. At low temperatures, the bending was limited and reversible, indicating that, like in the classical bimetallic strip, it is caused by thermal stresses due to the mismatch of thermal expansion coefficients of Au and Pd. At higher temperatures, the bending was irreversible and in opposite direction as compared to thermal bending. This type of bending was attributed to the coherency loss at the semi-coherent Au-Pd interface, and to the interdiffusion of Au and Pd and concomitant change of the lattice parameter of the formed Au-Pd alloy. Our results demonstrate that single crystalline metallic nanowhiskers with controlled curvature, chemical composition and thermal behavior can be produced employing interface engineering and chemical interdiffusion.

The Impact of Different Arrangements of Molecular Chains in Terms of Low and High Shear Rate's Viscosities on Heat and Mass Flow of Nonnewtonian Shear thinning Fluids.

Non-newtonian fluids, especially shear thinning fluids, have several applications in the polymer industry, food industry, and even everyday life. The viscosity of shear thinning fluids is decreased by two or three orders of magnitude due to the alignment of the molecules in order when the shear rate is increased, and it cannot be ignored in the case of polymer processing and lubrication problems. So, the effects of viscosities at the low and high shear rates on the heat and mass boundary layer flow of shear thinning fluid over moving belts are investigated in this study. For this purpose the generalized Carreau model of viscosity relate to shear rate is used in the momentum equation. The Carreau model contains the five parameters: low shear rate viscosity, high shear rate viscosity, viscosity curvature, consistency index, and flow behavior index. For the heat flow, the expression of the thermal conductivity model similar to the viscosity equation due to the non-Newtonian nature of the fluid is used in the energy equation. On the mathematical model of the problem, boundary layer approximations are applied and then simplified by applying the similarity transformations to get the solution. The solution of the simplified equations is obtained by numerical technique RK-shooting method. The results are compared with existing results for limited cases and found good agreement. The results in the form of velocity and temperature profiles under the impact of all the viscosity's parameters are obtained and displayed in graphical form. Moreover, the boundary layer parameters such as the thickness of the regions, momentum thickness, and displacement thickness are calculated to understand the structure of the boundary layer flow of fluid. The velocity and temperature of the fluid are decreased and increased respectively by all viscosity's parameters of the model. So, the results of the boundary layer fluid flow under rheological parameters will not only help engineers to design superior chemical equipment but also help improve the economy and efficiency of the overall process.