Length-dependent Behavior Research Articles

Phonon resonance modulation in weak van der Waals heterostructures: Controlling thermal transport in graphene–silicon nanoparticle systems

The drive for efficient thermal management has intensified with the miniaturization of electronic devices. This study explores the modulation of phonon transport within graphene by introducing silicon nanoparticles influenced by van der Waals forces. Our approach involves the application of non-equilibrium molecular dynamics to assess thermal conductivity while varying the interaction strength, leading to a noteworthy reduction in thermal conductivity. Furthermore, we observe a distinct attenuation in length-dependent behavior within the graphene–nanoparticles system. Our exploration combines wave packet simulations with phonon transmission calculations, aligning with a comprehensive analysis of the phonon transport regime to unveil the underlying physical mechanisms at play. Lastly, we conduct transient molecular dynamics simulations to investigate interfacial thermal conductance between the nanoparticles and the graphene, revealing an enhanced thermal boundary conductance. This research not only contributes to our understanding of phonon transport but also opens a new degree of freedom for utilizing van der Waals nanoparticle-induced resonance, offering promising avenues for the modulation of thermal properties in advanced materials and enhancing their performance in various technological applications.

Adaptation of the Calcium-dependent Tension Development in Ventricular Cardiomyocytes

Abstract Today a variety of models describe the physiological behavior of the heart on a cellular level. The intracellular calcium concentration plays an important role, since it is the main driver for the active contraction of the heart. Due to different implementations of the calcium dynamics, simulating cardiac electromechanics can lead to severely different behaviors of the active tension when coupling the same tension model with different electrophysiological models. To handle these variations, we present an optimization tool that adapts the parameters of the most recent, human based tension model. The goal is to generate a physiologically valid tension development when coupled to an electrophysiological cellular model independent of the specifics of that model's calcium transient. In this work, we focus on a ventricular cell model. In order to identify the calcium-sensitive parameters, a sensitivity analysis of the tension model was carried out. In a further step, the cell model was adapted to reproduce the sarcomere length-dependent behavior of troponin C. With a maximum relative deviation of 20.3% per defined characteristic of the tension development, satisfactory results could be obtained for isometric twitch tension. Considering the length-dependent troponin handling, physiological behavior could be reproduced. In conclusion, we propose an algorithm to adapt the tension development model to any calcium transient input to achieve a physiologically valid active contraction on a cellular level. As a proof of concept, the algorithm is successfully applied to one of the most recent human ventricular cell models. This is an important step towards fully coupled electromechanical heart models, which are a valuable tool in personalized health care.

Solvation of quantum dots in 1-alkyl-1-methylpyrrolidinium ionic liquids: toward stably luminescent composites

ABSTRACT CdTe nanoparticles capped with a cationic thiolate ligand were stably dispersed in ionic liquids, 1-alkyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)amides with an alkyl group of n-propyl, butyl and octyl-chain, and in an ionic plastic crystal, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. Dispersion behavior of CdTe nanoparticles in these ionic media was evaluated, in which the solvation of nanoparticles by the ionic components was particularly interested. The ionic media showed alkyl-chain length-dependent solvation behavior, which was suggested by the thermal analysis of nanocomposites. The longer alkyl-chains led to the greater decrease in the thermal melting enthalpy of ionic media with the introduction of nanoparticles. The ionic liquid with an octyl-chain, which is considered to form a thicker solvation layer, afforded better emission durability of CdTe nanoparticles compared to the ionic liquid with a shorter alkyl chain.

Force-Dependent Recruitment from the Myosin Off State Contributes to Length-Dependent Activation

Cardiac muscle develops more force when it is activated at longer lengths. The concentration of Ca2+ required to develop half-maximal force also decreases. These effects are known as length-dependent activation and are thought to play critical roles in the Frank-Starling relationship and cardiovascular homeostasis. The molecular mechanisms underpinning length-dependent activation remain unclear, but recent experiments suggest that they may include recruitment of myosin heads from the off (sometimes called super-relaxed) state. This manuscript presents a mathematical model of muscle contraction that was developed to investigate this hypothesis. Myosin heads in the model transitioned between an off state (that could not interact with actin), an on state (that could bind to actin), and a single attached state. Simulations were fitted to experimental data using multidimensional parameter optimization. Statistical analysis showed that a model in which the rate of the off-to-on transition increased linearly with force reproduced the length-dependent behavior of chemically permeabilized myocardium better than a model with a constant off-to-on transition rate (F-test, p < 0.001). This result suggests that the thick-filament transitions are modulated by force. Additional calculations showed that the model incorporating a mechanosensitive thick filament could also reproduce twitch responses measured in a trabecula stretched to different lengths. A final set of simulations was then used to test the model. These calculations predicted how reducing passive stiffness would impact the length dependence of the calcium sensitivity of contractile force. The prediction (a 60% reduction in ΔpCa50) mimicked the 58% reduction in ΔpCa50 in myocardium from rats that expressed a giant isoform of titin and had low resting tension. Together, these computational results suggest that force-dependent recruitment of myosin heads from the thick-filament off state contributes to length-dependent activation and the Frank-Starling relationship.

A nested pneumatic muscle arrangement for amplified stroke and force behavior

This article presents a compact nested architecture to amplify the displacement and forces of pneumatic artificial muscles for potential use in human assistive devices and other robotic applications. The nested architecture consists of several levels in series, and each level is made up of contracting pneumatic muscles, passive force transfer members, and additively manufactured interconnects. The stroke obtained from the nested pneumatic artificial muscle architecture is not always beneficial and is limited by the length-dependent behavior of pneumatic artificial muscles and other practical manufacturing constraints such as the size of the interconnects. Thus, this article studies the effect of the pneumatic artificial muscle length on its stroke using a modified constrained volume maximization formulation, which predicts the actual shape of the deformed pneumatic artificial muscle, and models additional stiffness due to membrane bending. Using this formulation, a framework is presented to optimally design the number of nested levels and individual actuators in each level to obtain a required stroke. Such a system is designed to actuate the human elbow by an angle of 80°, where almost 40% contraction is obtained using custom-manufactured pneumatic artificial muscles inherently capable of contracting upto 17% of its length. The framework can be used to amplify the stroke and forces of any pneumatic artificial muscle actuator and adapt it to different application requirements.

Chain length dependent alkane/β-cyclodextrin nonamphiphilic supramolecular building blocks.

In this work we report the chain length dependent behavior of the nonamphiphilic supramolecular building blocks based on the host-guest inclusion complexes of alkanes and β-cyclodextrins (β-CD). (1)H NMR, ESI-MS, and SAXS measurements verified that upon increasing the chain length of alkanes, the building blocks for vesicle formation changed from channel type 2alkane@2β-CD via channel type alkane@2β-CD to non-channel type 2alkane@2β-CD. FT-IR and TGA experiments indicated that hydrogen bonding is the extensive driving force for vesicle formation. It revealed that water molecules are involved in vesicle formation in the form of structural water. Upon changing the chain length, the average number of water molecules associated with per building block is about 16-21, depending on the chain length.

Shape-stabilized phase change materials based on poly(ethylene-graft-maleic anhydride)-g-alkyl alcohol comb-like polymers

In this study, a series of shape-stabilized comb-like polymeric phase change materials (CLPPCMs), denoted as EMA-g-CnH2n+1OH (poly(ethylene-graft-maleic anhydride)-g-alkyl alcohol) with n=14, 16, 18, 26, were prepared through an esterification reaction between poly(ethylene-graft-maleic anhydride) (EMA) and n-alkyl alcohols (CnH2n+1OH). The structure, thermal properties and shape-stabilized performance of EMA-g-CnH2n+1OH CLPPCMs were investigated by 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and wide-angle X-ray diffraction (WAXD). EMA-g-CnH2n+1OH CLPPCMs show a good thermal stability and shape-stabilized performance. With the side-chain length increasing, the phase transition temperature and the heat enthalpy change from 36.4 to 67.1°C and from 125.7 to 146.2J/g, respectively, demonstrating a side-chain length-dependent behavior. EMA-g-CnH2n+1OH CLPPCMs prove the excellent thermal reliability and structure stability after 300 heating–cooling cycles. The time of heat storage and release lasts for 205 and 49s, respectively. EMA-g-CnH2n+1OH CLPPCMs show their potential applications under 300°C as the thermal energy storage materials.

Thermal Conductivity of Silicon-Graphene Nanoribbon (SiGNR): An Equilibrium Molecular Dynamics (EMD) Simulation

Silicon-graphene nanoribbon (SiGNR), an allotrope of silicon carbide with sp2 hybridization, gains interest nowadays in the world of two-dimensional materials. In this study, the thermal conductivity of SiGNR is investigated and compared to that of graphene nanoribbon (GNR) and silicene nanoribbon (SiNR). Molecular Dynamics using Tersoff potential through Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) using the Green-Kubo method is employed to predict the thermal conductivity of silicon-graphene materials with armchair chirality. The temperature is varied from 50 K, 77 K, 150 K, 300 K, 500 K, 700 K, 1000 K, 1200 K, and 1500 K with a fixed width of 10 nm and length of 50 nm. The length of the materials is also varied from 10 nm, 20 nm, 30 nm, 40 nm and 50 nm with a fixed temperature of 300 K. Our results show that the thermal conductivity of SiGNR is higher than that of GNR and is approximately 50% larger at room temperature, which may be attributed to the presence of Si atoms inducing larger flexural phonon density of states than in GNR and SiNR. Also, the thermal conductivity of SiGNR follows the same length-dependent behavior of GNR due to its long mean free path. This study presents new insights into the thermal properties of silicon-graphene which will be significant for nanoelectronic applications.

Charge Transport through Carbon Nanomembranes

Molecular junctions incorporating pristine and cross-linked aromatic self-assembled monolayers (SAMs) are fabricated and investigated. A two-terminal setup composed of a eutectic Ga–In (EGaIn) top electrode and the gold substrate on which SAMs are prepared as a bottom electrode was used to characterize the charge transport. SAMs of phenylthiol (PT), biphenylthiol (BPT), p-terphenylthiol (TPT), and p-quaterphenylthiol (QPT) are then irradiated with low-energy electrons and converted into carbon nanomembranes (CNMs). A comparison of charge transport through SAMs and CNMs reveals a decrease of conductance of CNM-based junctions by 1 order of magnitude, as well as a conversion of asymmetric junctions with SAMs into symmetric junctions with CNMs, which could be attributed to the decoupling of CNMs from the Au substrate and the partial loss of aromaticity of CNMs after irradiation. Transition voltage spectroscopy (TVS) was also employed to investigate both types of junctions. We observe the length-dependent behavior of transition voltages in both systems and a reduction of transition voltages of CNM-based junctions in comparison to SAM-based junctions.

Mass and Length Dependent Chaotic Behavior of a Double Pendulum

In this article, chaotic behavior of a double pendulum (DP) is studied numerically by varying its mass and length. The results are analyzed using time series plot, Poincare map and Lyapunov exponent plot. It is observed that the chaotic tendency of the DP increases with mass and length. However, both pendulums of the DP have varying effect on the Lyapunov exponent. The significance of the present study in the optimization and control of the dynamical systems based on the DP is also discussed.

Models of Length Dependent Behavior in Polyglutamine based on Improved Simulation Methods

We present a study of the length-dependent statistical mechanical behavior of monomeric polyglutamine tracts over a broad range of repeat lengths, using implicit solvent as well as novel replica exchange based explicit solvent molecular dynamics techniques that allow for drastic conformational change in peptides of these sizes. First, these methodological changes were validated by comparison with conventional simulations, then equilibrium thermodynamic models were fit to simulation data, showing a crossover from alpha helical structure to either beta sheet rich or disordered structures with increasing monomer length, depending on the choice of solvent model.

Size-Dependent Effects on the Temperature Coefficient of Resistance of Carbon Nanotube Vias

Carbon nanotube (CNT) vias were fabricated at 500 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C with different widths and lengths. The electrical resistance of the CNT vias was measured using four-point probe structures at temperatures between 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C and 190 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. It was found that the temperature coefficient of resistance (TCR) of the CNT vias changes with both length and width. Most of the vias displayed a negative TCR between -300 and -400 ppm/K, against 3900 ppm/K for Cu, but for wider and shorter vias, this value becomes positive. A simple model is introduced, which can explain the length-dependent behavior.

Unstable Fracture Behavior of Rubber Toughened Poly(Styrene-co-Acrylonitrile)

A linear elastic fracture mechanics (LEFM) approach was used to study fracture characteristics of ABS materials. The effects of crack (ligament) length and rubber content on the microscopic deformations taking place at the front of crack tip and in the bulk of the specimens were investigated. The results of fractography studies showed that, in addition to rubber content, the microscopic deformations are influenced by crack length. For some materials this manifests itself as a change in macroscopic response. The ligament length dependent behavior was increased for the samples with higher rubber contents. The results also showed that, although the elastic behavior with unstable crack growth is the dominant micromechanism of deformation, stable crack propagation still occurred in some compositions. All the fracture parameters, including fracture toughness, fracture energy, plastic zone size, and crack tip opening, increased with rubber content. The changes in microscopic and, as a consequence, in the macroscopic deformation behavior of a given specimen with ligament length were attributed to changes in yield stress of the sample and maximum stress on the ligament.

Transition from Tunneling to Hopping in Single Molecular Junctions by Measuring Length and Temperature Dependence

The charge transport characteristics of a family of long conjugated molecular wires have been studied using the scanning tunneling microscope break junction technique. The family consists of four wires ranging from 3.1 to 9.4 nm in length. The two shortest wires show highly length dependent and temperature invariant conductance behavior, whereas the longer two wires show weakly length dependent and temperature variant behavior. This trend is consistent with a model whereby conduction occurs by two different mechanisms in the family of wires: by a coherent tunneling mechanism in the shorter two and by an incoherent charge hopping process in the longer wires. The temperature dependence of the two conduction mechanisms gives rise to a phenomenon whereby at elevated temperatures longer molecules that conduct via charge hopping can yield a higher conductance than shorter wires that conduct via tunneling. The evolution of molecular junctions as the tip retracts has been studied and explained in context of the characteristics of individual transient current decay curves.

High accuracy curve fits for chirality, length and diameter dependent initial modulus of single walled carbon nanotubes

Many previous studies regarding the estimation of mechanical properties of single walled carbon nanotubes (SWCNTs) report that, the modulus of SWCNTs is chirality, length and diameter dependent. Here, this dependence is quantitatively described in terms of high accuracy curve fit equations. These equations allow us to estimate the modulus of long SWCNTs (lengths of about 100–120 nm) if the value at the prescribed low lengths (lengths of about 5–10 nm) is known. This is supposed to save huge computational time and expense. Also, based on the observed length dependent behavior of SWCNT initial modulus, we predict that, SWCNT mechanical properties such as Young's modulus, secant modulus, maximum tensile strength, failure strength, maximum tensile strain and failure strain might also exhibit the length dependent behavior along with chirality and length dependence.

Length dependent behavior of a carbon nanotube interacting at liquid-air interface

We report the irreversible structural failure of individual multiwalled carbon nanotube (MWNT) tips after water submersion. We used 11 individual MWNTs with varying geometries and showed length dependent MWNT failure with scanning electron microscopy. Shorter MWNTs are more likely to survive penetration of the water-air interface. We observed the bending of MWNT probes on the water surface using optical microscopy. Surface tension force acting on MWNTs at the water-air interface was calculated. Compared to shorter MWNTs, the calculations suggest that longer MWNTs exert a smaller bending restoring force with respect to surface tension force, leading to MWNT bending until failure.

New Type of Helix and 27Ribbon Structure Formation in Poly ΔLeu Peptides: Construction of a Single-Handed Template

alpha,beta-Dehydroamino acid residues due to the presence of Calpha = Cbeta double bond influences the main chain and the side chain conformations. These residues have interesting chemical features including the increased resistance to enzymatic degradation. The chain length dependent conformational behavior of poly alpha,beta-dehydroleucine (DeltaLeu) peptides in both the pure forms Z and E and their various combinations like alternate ZE/EZ etc. have been investigated by using quantum mechanical method PCILO (perturbative configuration interaction of localized orbitals). The conformational states in alternate Z and E forms, with Phi, Psi values of -10 degrees , 105 degrees /1 degrees , -88 degrees for Z form and 35 degrees , 22 degrees /-34 degrees , -27 degrees for the E form are found to be the most stable and degenerate than the states in pure Z and E forms and the EZ form etc. The repeated Phi, Psi values give rise to altogether new types of left and right handed helices, and their stability increases with increasing chain length. These structures are stabilized by intramolecular hydrogen bonding, carbonyl-carbonyl interactions and hydrophobic interactions between the side chains of DeltaZLeu and DeltaELeu residues. The 2(7) ribbon structure (seven-membered hydrogen-bonded ring involving two consecutive amino acid residues) is found to be most stable and degenerate in the pentapeptide Ac-DeltaELeu5-NHMe, due to the formation of maximum hydrogen bonds. A right-handed template from achiral DeltaLeu peptides has been achieved by incorporating L-Leu at the C-terminal or D-Leu at the N-terminal.

Relationship between solubility and solubility product: The roles of crystal sizes and crystallographic directions

Grain size- and crystallographic direction-dependence are among the fundamental characteristics of crystal solubility. However, such important material properties are routinely ignored and solubility is often conveniently approximated by a solubility product. In this study, we attempt to outline the relationship between solubility and solubility product using thermodynamic arguments, and to provide observations that demonstrate the occurrence of circumstances where the solubility product cannot properly approximate crystal solubility. Theoretical analysis shows that solubility is always greater than solubility product, but the difference is inversely related to the grain size. Furthermore, the difference can be crystallographic direction specific if the total surface energy change upon the attachment of an individual growth unit is nonequivalent for each symmetrically unrelated crystal faces. In situ AFM experiments conducted on the cleavage face of calcite demonstrate that the 〈 4 ¯ 41 〉 ± steps exhibit direction- and length-dependent behavior. Specifically, the measured critical step lengths are consistent with the predicted inverse relationship to saturation states. Moreover, step retreat at 〈 4 ¯ 41 〉 + and advance at 〈 4 ¯ 41 〉 - are observed simultaneously in a narrow range of saturation at near equilibrium conditions, indicating the existence of direction specific solubility. Whereas these findings justify the rationale for approximating solubility by solubility product in cases where large crystals are concerned, the results imply that the size and direction effect should not be ignored if nanocrystal growth/dissolution is the subject of interest.

Computational Simulation of Characteristic Length Dependent Deformation Behavior of Polycrystalline Metals.

In order to clarify the effect of dislocations that are statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs) on the characteristic length dependent micro-to macroscopic deformation behavior of polycrystalline metals, finite element simulations based on a crystal plasticity theory accounting for SSDs and GNDs have been performed for plane stress polycrystalline metals with different grain sizes. The dislocation lines constructed based on the edge and screw components of GNDs on the slip planes clarify that the grain boundary as well as sub-grain boundary act as the obstacles to dislocation motion and impede easy motion of dislocations. The density of SSDs and GNDs increases as the gain size decreases that yields the increase in the deformation resistance in macroscopic scale. The mean glide path distance and annihilation distance of dislocations strongly affect the micro-to macroscopic deformation behavior of polycrystalline metals. Hall-Petch-like relations between the macroscopic resistance of deformation and grain size are observed.

136 γ'相含有Ni基超合金の寸法依存性変形挙動のモデル化と数値シミュレーション(OS07-2 MD法・GN転位・結晶塑性)(OS07 塑性に関するマルチスケールモデリングとシミュレーション)

136 γ'相含有Ni基超合金の寸法依存性変形挙動のモデル化と数値シミュレーション(OS07-2 MD法・GN転位・結晶塑性)(OS07 塑性に関するマルチスケールモデリングとシミュレーション)