Hasil untuk "Descriptive and experimental mechanics"

Konstantin Balashev

This review surveys how nanoparticles and biomolecular nanosized structures interact with model membrane systems, and how these interfacial processes govern their performance in drug and gene delivery, antimicrobial strategies, biosensing, and nanotoxicology. The nanostructures covered include polymeric nanoparticles, lipid-based carriers, peptide nanostructures, dendrimers, and multifunctional hybrids. Model membranes span Langmuir monolayers, supported lipid bilayers, vesicles/liposomes across sizes, and emerging hybrid or asymmetric constructs that better approximate native complexity. Mechanistically, interactions follow recurrent routes—surface adsorption, bilayer insertion, pore formation, and lipid extraction/reorganization—regulated by particle size, morphology, charge, ligand architecture, and lipophilicity, in conjunction with membrane composition, phase state, curvature, and asymmetry. A multiscale toolkit links structure, mechanics, and dynamics: Langmuir troughs and Brewster Angle Microscopy map thermodynamics and mesoscale morphology; atomic force microscopy and quartz crystal microbalance with dissipation resolve nanoscale topography and viscoelasticity; fluorescence microscopy/spectroscopy reports on localization and packing; neutron and X-ray reflectometry quantify vertical structure; molecular dynamics provides atomistic pathways and design hypotheses. Historically, the field advanced from early monolayers and bilayers, through the fluid mosaic model, to raft microdomains and modern biomimetic systems, enabling increasingly realistic experiments. Key advances include cross-method integration linking experimental observations with image-based computational models; persistent debates concern the translation from simplified models to living membranes, the role of dynamic coronas, and scale/force-field limits in simulations. Future efforts should prioritize hybrid models incorporating proteins and asymmetric lipidomes, standardized reporting and reference systems, rigorous coupling of experiments with calibrated simulations and machine learning, and alignment with safety-by-design and regulatory expectations, thereby shifting interfacial measurements from descriptive observation to predictive design rules.

Muhammad Zain Ul Abidin, Mashal Mumtaz, Shashwat Shetty et al.

This systematic review synthesizes evidence on biomechanical fracture thresholds of the tibia and fibula under axial and multi-axial loading. A comprehensive search of PubMed, Embase, Scopus, and the Cochrane Library identified six studies, including experimental cadaveric, computational, and material testing investigations, comprising 72 postmortem specimens and validated finite element models. Outcomes assessed included axial force, bending moments, failure load, stress distribution, and fracture patterns. Results indicate that tibial fracture thresholds range from ~7.5 kN in female specimens to 11.3 kN under combined axial and bending loads, with fibula contribution increasing axial tolerance by ~10%. Variance and confidence interval measures were not reported in the included biomechanical studies; therefore, findings are presented descriptively. Multi-axial loading consistently reduced fracture tolerance compared with isolated axial loading, and fracture resistance was influenced by specimen gender, load duration, and biomechanical methodology. Risk of bias ranged from low to moderate across studies. These findings provide clinically relevant benchmarks for injury prediction, preclinical testing, and orthopedic device design, emphasizing the importance of multi-axial assessment in understanding lower-limb fracture mechanics.

Changle Pu, Jiewei Zhan, Da Huang et al.

Anna Alvarez, Anders M. Seawright, Neel A. Tripathi et al.

‘‘Vine robots” are thin-walled, tubular, pneumatic soft robots that lengthen at their tips to navigate constrained and complex environments. Previous studies have already explored the mechanics of vine robot bodies and investigated applications for which the device is well-suited. However, these studies almost exclusively focus on eversion rates in the quasi-static regime, overlooking other potential applications of high-speed vine robots in medical devices, projectile launchers, or for informing biology. To better understand this rapid behavior, we present a dynamic growth model for high-velocity vine robot body extension with a payload mass and verify the model experimentally. To the best of the authors’ knowledge, this is the first instance of vine robots utilized for projectile launching. We find three key results: i) vine robot bodies experience rate-dependent damping that is scale-dependent and monotonically increases with increasing wall thickness; ii) steady-state velocity, or the upper limit of speed in terms of growth velocity, monotonically increases with isometric scaling; and iii) energy efficiency increases with decreasing wall thickness. These findings are used to inform the preliminary design of a large-scale, drug delivery device proof-of-concept, as well as design the fastest–on–record vine, capable of 60 m/s eversion. Our work provides a basic understanding of the dynamic movement of vine robots and opens the door to new areas of application.

Xiaowei Shi, Xingrong Huang, Le Fang

The interaction between the ship hull and the propeller’s rotational motion causes the propeller to operate under non-uniform inflow conditions. In reality, the ship’s effective wake constitutes a complex nonlinear superposition of multiple wave numbers. However, existing studies often neglect these multi-scale interactions. In this work, Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations with a two-scale inflow model are conducted to investigate the fluid–structure interaction of a propeller under multi-scale inflow. The model introduces large-scale and small-scale Fourier modes together with transverse perturbations, allowing systematic variation of inflow characteristics. The results reveal that large-scale modes amplify unsteady thrust fluctuations and enhance vortex fragmentation, while small-scale modes produce similar but weaker effects, mainly influencing the high-frequency components of unsteady thrust. In contrast, transverse perturbations reduce inflow non-uniformity, effectively suppress single blade thrust fluctuations, and preserve the coherent vortex structures of the wake. This study highlights the importance of multi-scale effects in the unsteady hydrodynamic characteristics of marine propellers and provides useful insights for the optimization of propeller design and energy-saving devices.

Mengjie Song, Runmiao Gao, Chaobin Dang et al.

Abstract Frost and ice are ubiquitous in nature and industry, and sometimes cause problems. The solidification of water droplets is in the early stage of frosting and icing and has attracted extensive research interest. However, due to physical occlusion, solidification characteristics inside a droplet are always unclear. In this study, Hele‒Shaw cells were used to produce cross‐sectional slices of water droplets deposited on hydrophilic and hydrophobic surfaces, referred to as two‐dimensional droplets. The solidification characteristics of these droplets were investigated at micrometer spatial and millisecond temporal scales. Results show that the maximum dendrite growth velocity reached 0.45 m/s during the recalescence stage. Using the side‑view freezing front height from a three‑dimensional droplet as a proxy for the true front height introduces errors ranging from ‒35% to +45%. For a ‒30°C substrate, the maximum longitudinal temperature difference within the droplet reached 7.3°C. Additionally, micro‐scale trapped air bubbles with equivalent diameters ranging from 18 to 78 µm switch their growth mode from spheroidal to longitudinal approximately 250 ms into the freezing stage, corresponding to about 17% of the total growing time. These findings provide new insight into frosting and icing physics and may inform enhanced defrosting and de‑icing strategies.

Pouyan Mehryar, Sina Firouzy, Uriel Martinez-Hernandez et al.

<b>Background/Objectives:</b> This study focuses on the motion planning and control of an active ankle–foot orthosis (AFO) that leverages biomechanical insights to mitigate footdrop, a deficit that prevents safe toe clearance during walking. <b>Methods:</b> To adapt the motion of the device to the user’s walking speed, a geometric model was used, together with real-time measurement of the user’s gait cycle. A geometric speed-adaptive model also scales a trapezoidal ankle-velocity profile in real time using the detected gait cycle. The algorithm was tested at three different walking speeds, with a prototype of the AFO worn by a test subject. <b>Results:</b> At walking speeds of 0.44 and 0.61 m/s, reduced tibialis anterior (TA) muscle activity was confirmed by electromyography (EMG) signal measurement during the stance phase of assisted gait. When the AFO was in assistance mode after toe-off (initial and mid-swing phase), it provided an average of 48% of the estimated required power to make up for the deliberate inactivity of the TA muscle. <b>Conclusions:</b> Kinematic analysis of the motion capture data showed that sufficient foot clearance was achieved at all three speeds of the test. No adverse effects or discomfort were reported during the experiment. Future studies should examine the device in populations with footdrop and include a comprehensive evaluation of safety.

San-Dong Guo

Net-zero-magnetization magnets are attracting significant research interest, driven by their potential for ultrahigh density and ultrafast performance. Among these materials, the altermagnets possess alternating spin-splitting band structures and exhibit a range of phenomena previously thought to be exclusive to ferromagnets, including the anomalous Hall and Nernst effects, non-relativistic spin-polarized currents, and the magneto-optical Kerr effect. Bulk altermagnets have been experimentally identified, while two-dimensional (2D) altermagnets remain experimentally unexplored. Here, we take experimentally synthesized 2D ferromagnetic $\mathrm{CrX_3}$ (X=Cl, Br and I) as the parent material and achieve altermagnetism through external field. First, we achieve the transition from ferromagnetism to antiferromagnetism through biaxial strain. Subsequently, we break the space inversion symmetry while preserving the mirror symmetry via an electric field, thereby inducing altermagnetism. Moreover, through the application of Janus engineering to construct $\mathrm{CrX_{1.5}Y_{1.5}}$ (X$\neq$Y=Cl, Br and I), the phase transition from ferromagnetism to antiferromagnetism induced by strain alone is sufficient to trigger the emergence of altermagnetism. All six monolayers possess the symmetry of $i$-wave spin-splitting. The computational results suggest that $\mathrm{CrCl_3}$ can be readily tuned to exhibit altermagnetism through external field in experiment, thanks to its low strain threshold for magnetic phase transition. Our work provides experimentally viable materials and methods for realizing altermagnetism, which can advance the development of 2D altermagnetism.

Georg Elsinger, Herman Oprins, Vladimir Cherman et al.

With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches.

Rim Elfahem, Bastien Bouchet, Boussad Abbes et al.

Whole-body cryotherapy (WBC) is a therapeutic practice involving brief exposure to extreme cold, typically lasting one to four minutes. Given that WBC sessions often occur in groups, there is a hypothesis that cumulative heat dissipation from the group significantly affects the thermo-aerodynamic conditions of the cryotherapy chamber. Computational fluid dynamics (CFD) is employed to investigate thermal exchanges between three subjects (one man, two women) and a cryotherapy chamber at −92 °C during a 3-minute session. The investigation reveals that collective body heat loss significantly influences temperature fields within the cabin, causing global modifications in aerodynamic and thermal conditions. For example, a temperature difference of 6.7 °C was calculated between the average temperature in a cryotherapy chamber with a single subject and that with three subjects. A notable finding is that, under an identical protocol, the thermal response varies among individuals based on their position in the chamber. The aerodynamic and thermal characteristics of the cryotherapy chamber impact the heat released at the body’s surface and the skin-cooling rate needed to achieve recommended analgesic thresholds. This study highlights the complexity of physiological responses in WBC and emphasizes the importance of considering individual positions within the chamber for optimizing therapeutic benefits.

Clive B. Beggs, Rabia Abid, Fariborz Motallebi et al.

COVID-19 is an airborne disease, with the vast majority of infections occurring indoors. In comparison, little transmission occurs outdoors. Here, we investigate the airborne transmission pathways that differentiate the indoors from outdoors and conclude that profound differences exist, which help to explain why SARS-CoV-2 transmission is much more prevalent indoors. Near- and far-field transmission pathways are discussed along with factors that affect infection risk, with aerosol concentration, air entrainment, thermal plumes, and occupancy duration all identified as being influential. In particular, we present the fundamental equations that underpin the Wells–Riley model and show the mathematical relationship between inhaled virus particles and quanta of infection. A simple model is also presented for assessing infection risk in spaces with incomplete air mixing. Transmission risk is assessed in terms of aerosol concentration using simple 1D equations, followed by a description of thermal plume–ceiling interactions. With respect to this, we present new experimental results using Schlieren visualisation and computational fluid dynamics (CFD) based on the Eulerian–Lagrangian approach. Pathways of airborne infection are discussed, with the key differences identified between indoors and outdoors. In particular, the contribution of thermal and exhalation plumes is evaluated, and the presence of a near-field/far-field feedback loop is postulated, which is absent outdoors.

Kishore Thapliyal, Jan Peřina, Ondřej Haderka et al.

Multiple photon addition and subtraction applied to multi-mode thermal and sub-Poissonian fields as well as twin beams is mutually compared using one experimental setup. Twin beams with tight spatial correlations detected by an intensified CCD camera with high spatial resolution are used to prepare the initial fields. Up to three photons are added or subtracted to arrive at the nonclassical and non-Gaussian states. Only the photon-subtracted thermal states remain classical. In general, the experimental photon-added states exhibit greater nonclassicality and non-Gaussianity than the comparable photon-subtracted states. Once photons are added or subtracted in twin beams, both processes result in comparable properties of the obtained states owing to twin-beam photon pairing.

F. Burla, Yuval Mulla, B. Vos et al.

The cells and tissues that make up our body manage contradictory mechanical demands. It is crucial for their survival to be able to withstand large mechanical loads, but it is equally crucial for them to produce forces and actively change shape during biological processes such as tissue growth and repair. The mechanics of cells and tissues is determined by scaffolds of protein polymers known as the cytoskeleton and the extracellular matrix, respectively. Experiments on model systems reconstituted from purified components combined with polymer physics concepts have already uncovered some of the mechanisms that underlie the paradoxical mechanics of living matter. Initial work focused on explaining universal features, such as the nonlinear elasticity of cells and tissues, in terms of polymer network models. However, there is a growing recognition that living matter exhibits many advanced mechanical functionalities that are not captured by these coarse-grained theories. Here, we review recent experimental and theoretical insights that reveal how the porous structure, structural hierarchy, transient crosslinking and mechanochemical activity of biopolymers confer resilience combined with the ability to adapt and self-heal. These physical concepts increase our understanding of cell and tissue biology and provide inspiration for advanced synthetic materials. Biopolymer networks provide mechanical integrity and enable active deformation of cells and tissues. Here, we review recent experimental and theoretical studies of the mechanical behaviour of biopolymer networks with a focus on reductionist approaches. Cells and tissues are supported by biopolymer scaffolds that are mechanically resilient yet dynamic. There is a growing realization that biopolymer networks acquire these unique features from their hierarchical structure combined with internal mechanochemical activity. Biopolymer networks are embedded in water and therefore experience a strong coupling with the solvent, resulting in poroelastic effects. Fibrous networks respond to cyclic mechanical loading with plastic effects, self-healing and fracture. These responses originate from all structural levels — from molecule to fibre to network. Non-equilibrium activity causes biopolymer networks to undergo active stiffening, fluidization or self-driven flow, enabling a cell to deform. Composite biopolymer systems, in which all these mechanisms act together, endow cells and tissues with their adaptive mechanical properties. Cells and tissues are supported by biopolymer scaffolds that are mechanically resilient yet dynamic. There is a growing realization that biopolymer networks acquire these unique features from their hierarchical structure combined with internal mechanochemical activity. Biopolymer networks are embedded in water and therefore experience a strong coupling with the solvent, resulting in poroelastic effects. Fibrous networks respond to cyclic mechanical loading with plastic effects, self-healing and fracture. These responses originate from all structural levels — from molecule to fibre to network. Non-equilibrium activity causes biopolymer networks to undergo active stiffening, fluidization or self-driven flow, enabling a cell to deform. Composite biopolymer systems, in which all these mechanisms act together, endow cells and tissues with their adaptive mechanical properties.

Alexandra Grekova, Svetlana Strelova, Anton Lysikov et al.

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO₂ sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments.

Kiran Siddappaji, Mark Turner

Propellers for electric aviation are used in solo- and multirotor applications. Multifidelity analysis with reduced cycle time is crucial to explore several designs for energy minimization and range maximization. A low-fidelity design tool, py_BEM, is developed for design and analysis of a reverse-engineered solo 2-bladed propeller using blade-element momentum theory with physics enhancements including local Reynolds number effect, boundary-layer rotation, airfoil polar at large AoAs and stall delay. Spanwise properties from py_BEM are converted into 3D blade geometry using T-Blade3. S809 and NACA airfoil polar are utilized, obtained by XFOIL. Lift, drag, performance losses, wake analysis, comparison of 3D steady CFD with low fidelity tool, kinetic energy dissipation, entropy and exergy through irreversibility are analyzed. Spanwise thrust and torque comparison between low and high fidelity reveals the effect of blade rotation on the polar. Vorticity dynamics and boundary-vorticity flux methods describe the onset of flow separation and entropy rise. Various components of drag and loss are accounted. The entropy rise in the boundary layer and downstream propagation and mixing out with freestream are demonstrated qualitatively. Irreversibility is accounted downstream of the rotor using the second-law approach to understand the quality of available energy. The performance metrics are within 5% error for both fidelities.

Yannai A. Gonczarowski, Ori Heffetz, Clayton Thomas

A menu description exposes strategyproofness by presenting a mechanism to player $i$ in two steps. Step (1) uses others' reports to describe $i$'s menu of potential outcomes. Step (2) uses $i$'s report to select $i$'s favorite outcome from her menu. We provide novel menu descriptions of the Deferred Acceptance (DA) and Top Trading Cycles (TTC) matching mechanisms. For TTC, our description additionally yields a proof of the strategyproofness of TTC's traditional description, in a way that we prove is impossible for DA.

Vihtori Mäntylä, Bettina Lehtelä, Fabian Fagerholm

Background: Continuous experimentation (CE) has been proposed as a data-driven approach to software product development. Several challenges with this approach have been described in large organisations, but its application in smaller companies with early-stage products remains largely unexplored. Aims: The goal of this study is to understand what factors could affect the adoption of CE in early-stage software startups. Method: We present a descriptive multiple-case study of five startups in Finland which differ in their utilisation of experimentation. Results: We find that practices often mentioned as prerequisites for CE, such as iterative development and continuous integration and delivery, were used in the case companies. CE was not widely recognised or used as described in the literature. Only one company performed experiments and used experimental data systematically. Conclusions: Our study indicates that small companies may be unlikely to adopt CE unless 1) at least some company employees have prior experience with the practice, 2) the company's limited available resources are not exceeded by its adoption, and 3) the practice solves a problem currently experienced by the company, or the company perceives almost immediate benefit of adopting it. We discuss implications for advancing CE in early-stage startups and outline directions for future research on the approach.

Gaelle Lebrun, Feishi Xu, Claude Le Men et al.

The influence of viscosity and surface tension on oxygen transfer was investigated using planar laser-induced fluorescence with inhibition (PLIF-I). The surface tension and the viscosity were modified using Triton X-100 and polyacrylamide, respectively. Changes in the hydrodynamic parameters of millimetric bubbles were identified, and transfer parameters were calculated. The results revealed a decrease in the mass transferred in the presence of a contaminant. For modified viscosity, the decrease in mass transferred was allowed for by current correlations, but the presence of surfactant led to a sharp decrease in the liquid side mass transfer coefficient, which became even lower when polymer was added. An explanation for the gap between classical correlations and experimental values of k_L is discussed, and a hypothesis of the existence of an accumulation of contaminant in the diffusion layer is proposed. This led to the possibility of a decrease in the diffusion coefficient and oxygen saturation concentration in the liquid film, explaining the discrepancy between models and experience. Adapted values of D_O2 and [O₂] * in this layer were estimated. This original study unravels the complexity of mass transfer from an air bubble in a complex medium.

Thorben Kewitz, Christoph Regula, Maik Fröhlich et al.

Abstract The influence of different nozzle head geometries and, therefore, the variation of the excitation and relaxation volume on the energy flux from an atmospheric pressure plasma jet to a surface have been investigated. Measurements have been performed by passive calorimetric probes under variation of the gas flow through the nozzle. The results show that the geometry of the nozzle head has a significant impact on the resulting energy flux. The relaxation volume affects the dependence of the energy flux on the gas flow. While there is no significant influence of the working gas flow on the energy flux without a relaxation volume, utilizing a relaxation volume leads to a decrease of the energy flux with increasing working gas flow. Within the analyzed parameter range, the energy flux reveals for both nozzle heads a linear dependency on the applied primary voltage.

Erik Higgins, Jonathan Pitt, Eric Paterson

A modified set of governing differential equations for geophysical fluid flows is derived. All of the simulation fields are decomposed into a nominal large-scale background state and a small-scale perturbation from this background, and the new system is closed by the assumption that the perturbation is one-way coupled to the background. The decomposition method, termed the multi-scale localized perturbation method (MSLPM), is then applied to the governing equations of stratified fluid flows, implemented in OpenFOAM, and exercised in order to simulate the interaction of a vertically-varying background shear flow with an axisymmetric perturbation in a turbulent ocean environment. The results demonstrate that the MSLPM can be useful in visualizing the evolution of a perturbation within a complex background while retaining the complex physics that are associated with the original governing equations. The simulation setup may also be simplified under the MSLPM framework. Further applications of the MSLPM, especially to multi-scale simulations that encompass a large range of spatial and temporal scales, may be beneficial for researchers.