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Viruses affect all forms of life and their relevance cannot be overstated. The main structural component of a virus is a protein shell known as the capsid which protects and transports the genetic material allowing the virion to infect a cell. It is possible to study the physical properties of the capsid through computational simulations with the use of physico-mathematical models at different approximation levels. In this work, we describe a methodology to generate topologically and geometrically faithful mesh representations of viral capsids through a homogeneous volume discretization using hexahedrons (cubes). The current implementation leverages octree-type binary operations, computer graphics, and high performance computing techniques. This approach reduces the meshing time by orders of magnitude compared to previous strategies. We performed simulations of nanoindentation and shearing of four viral capsids using the octree-type meshes and the Finite Element Method, in order to evaluate their response. Our results show that the capsid material response is consistent in terms of isotropic–anisotropic structural features while it increases numerical accuracy. [ABSTRACT FROM AUTHOR]

• Hierarchically heterogeneous microstructures exist in both SLM- and LMD-processed specimens. • Core-shell FCC precipitates in LMD bear {110} texture at high surface energy and high strain energy. • Hot cracks occurred in both types of specimens due to the incompletely suppressed cu segregation. • A correlation mechanism between microstructure, nano-mechanics, and corrosion behavior was obtained. The present study investigated the microstructure, nanomechanics, and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting (SLM) and laser metal deposition (LMD). The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix (∼90 µm in width) and Cu-rich twinned FCC phase. The columnar grains grew epitaxially along the building direction and exhibited a strong {001} texture. In comparison, a coarse columnar-grained BCC matrix (∼150 µm in width) with a stronger 〈001〉 texture, rod-like B2 precipitates, and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect. Consequently, the LMD-processed specimens showed a lower hardness, wear resistance, and corrosion resistance, but higher creep resistance and reduced Young's modulus than the SLM-processed specimens. Hot cracks occurred in both types of specimens, which could not be completely suppressed due to Cu segregation. [ABSTRACT FROM AUTHOR]

• Modeling mixture unified gradient elasticity beams with load discontinuities. • Variationally consistent interface conditions are derived. • Analysis of the bending of nanobeams with different boundary conditions. • Anticipated nanoscopic features of length-scale parameters are confirmed. Structural schemes of applicative interests in Engineering Science frequently encounter the intricate phenomenon of discontinuity. The present study intends to address the discontinuity in the flexure of elastic nanobeam by adopting an abstract variational scheme. The mixture unified gradient theory of elasticity is invoked to realize the size-effects at the ultra-small scale. The consistent form of the interface conditions, stemming from the established stationary variational principle, is meticulously set forth. The boundary-value problem of equilibrium is properly closed and the analytical solution of the transverse displacement field of the elastic nanobeam is addressed. As an alternative approach, the eigenfunction expansion method is also utilized to scrutinize the efficacy of the presented variational formulation in tackling the flexure of elastic nanobeams with discontinuity. The flexural characteristic of mixture unified gradient beams with diverse kinematic constraints is numerically illustrated and thoroughly discussed. The anticipated nanoscopic features of the characteristic length-scale parameters are confirmed. The demonstrated numerical results can advantageously serve as a benchmark for the analysis and design of pioneering ultra-sensitive nano-sensors. The established variationally consistent size-dependent framework paves the way ahead in nanomechanics and inspires further research contributing to fracture mechanics of ultra-small scale elastic beams. [ABSTRACT FROM AUTHOR]

A recent study conducted at the Chinese Academy of Sciences in Shenzhen, China, has developed a new method for rapidly and non-destructively detecting bacterial viability. The researchers used atomic force microscopy (AFM) imaging, quantitative nano-mechanics, and machine learning algorithms to assess the survival of gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria. The results showed that this methodology had exceptional predictive accuracy, exceeding 95%, for both types of bacteria. This research provides a universal and reliable method for detecting bacterial viability in various sectors, including pharmaceuticals, medicine, and food. [Extracted from the article]

• W microwires with designed microstructure were microfabricated under EBSD guidance. • High-density dislocations were introduced in W with reduced grain boundaries. • Ultrahigh strength and ductility were achieved in engineered W microwires. • The motion of pre-existing high-density dislocations produces high ductility of W. Despite being strong with many outstanding physical properties, tungsten is inherently brittle at room temperature, restricting its structural and functional applications at small scales. Here, a facile strategy has been adopted, to introduce high-density dislocations while reducing grain boundaries, through electron backscatter diffraction (EBSD)-guided microfabrication of cold-drawn bulk tungsten wires. The designed tungsten microwire attains an ultralarge uniform tensile elongation of ~10.6%, while retains a high yield strength of ~2.4 GPa. in situ TEM tensile testing reveals that the large uniform elongation of tungsten microwires originates from the motion of pre-existing high-density dislocations, while the subsequent ductile fracture is attributed to crack-tip plasticity and the inhibition of grain boundary cracking. This work demonstrates the application potential of tungsten microcomponents with superior ductility and workability for micro/nanoscale mechanical, electronic, and energy systems. [Display omitted] [ABSTRACT FROM AUTHOR]

The article reports on the on-chip optical processor, an artificial intelligence (AI) hardware system that is faster at detecting dataset similarities than existing electronic processor-fueled machine learning algorithms, developed by researchers at the University of Oxford in the United Kingdom (UK). The system is said to incorporate classical conditioning and associative learning. It describes how the optical processor works using wavelength-division multiplexing and light as data signal.

This work gives an overview of the theoretical background and of the numerical modelling framework used to describe the mechanical properties and the response of materials on scales ranging from the atomistic, through the microstructure and all the way up to the macroscale. In order to describe the dual nature of the structure of matter, which is continuous when viewed at large length scales and discrete when viewed at the atomic scale, plus the interdependence of these scales, multiscale modelling is required to complement the continuum and the atomistic models. More specifically, what we aim for in this review is to present and discuss the following basic conceptual models, as well as the methodologies that accompany them: (a) discrete models such as ab initio, atomistic / molecular, mesoscopic; (b) continuum mechanics models (CMM) comprising pure CMM, non-local elasticity CMM, higher-order strain gradient and higher-order nonlocal strain gradient elasticity CMM, and surface elasticity CMM; (c) multiscale material models (MMM). Since the field of nanomechanics is currently a rapidly expanding research area, the presented state-of-the art is by no means exhaustive. It simply outlines the research efforts that go behind formulating numerical models for the solution of problems in nanomechanics. Despite the advantages that boundary element methods (BEM) have in solving problems at the physical scale, either as stand-alone or in combination with finite element methods (FEM), their application to multiscale modelling is still limited, despite the promise they seem to hold. [ABSTRACT FROM AUTHOR]

The inverse analysis of indentation curves, aimed at extracting the stress-strain curve of a material, has been under intense development for decades, with progress relying mainly on the use of analytical expressions derived from small data sets. Here, we take a fresh, data-driven perspective to this classic problem, leveraging machine learning techniques to advance indentation technology. Using a neural network (NN), we efficiently assess uniqueness and identify materials that have indistinguishable indentation responses without the need for complex, domain knowledge-based algorithms. We then demonstrate that inclusion of the residual imprint information resolves the non-uniqueness problem. We show that the elasto-plastic properties of a material can be learned directly from indentation pile-up. Notably, an accurate stress-strain curve can be derived using solely the applied indentation load and pile-up information, thereby eliminating the need for depth-sensing. We also present a systematic analysis of the machine learning model, covering important aspects such as prediction performance, sensitivity, feature selection, and permutation importance, providing insight for model development and evaluation. This study introduces and provides the groundwork of a machine-learning-based profilometry-informed indentation inversion (PI3) technique. It showcases the potential of machine learning as a transformative alternative when analytical solutions are difficult or impossible to obtain. [ABSTRACT FROM AUTHOR]

In order to investigate size-dependent creeping plane microfluidic flow, a boundary element method is implemented that involves the calculation of interior quantities and multi-domain problems. The governing equations are formulated using the skew-symmetric character of the couple-stress tensor and its energy conjugate mean-curvature tensor, as established in consistent couple stress theory. This theoretical formulation includes one characteristic material length scale parameter l that represents the size-dependency of the problem. Here, we present the boundary integral representation and numerical implementation for two-dimensional size-dependent steady state creeping incompressible flow, in which velocities, angular velocities, force- and couple-tractions are the primary variables. Beyond the previously known singular fundamental solution kernels for point force and point couple in the velocity and angular velocity integral equations, here we present the integral equations for calculating internal mean curvatures and couple-stresses, along with their corresponding kernels. The formulation is then applied to solve some computational problems both to investigate the size effects on the response resulting from the theory, and to validate the strength of the numerical method. For this purpose, we study the important effect of different boundary conditions on the flow pattern and consider a multi-fluid domain Couette flow problem. [ABSTRACT FROM AUTHOR]

Protein nanomechanics is a rapidly evolving field at the intersection of physics, chemistry and biology focused on the characterisation of the conformational dynamics of proteins under force, of common occurrence in vivo. [ABSTRACT FROM AUTHOR]

Natural samples are characterized by surface roughness which is intrinsically multi-scale as depicted by the well known concept of fractal dimension. Nevertheless, surface asperities are barely taken into account in simulations and modeling where flat surfaces and sharp corners or edges are generally preferred for the sake of simplicity. In this context, we propose here a versatile Python program called Pyrough that aims at building virtual samples characterized by configurable surface roughness for numerical applications such as atomistic and finite-element simulations. The program is open source and relies on the classical roughness theory that integrates the concept of self-affine surface. Several basic shapes including basic blocks, spheres, grains and wires with self-affine surface asperities are implemented and the object-oriented structure of the program simplifies the implementation of more complex objects. Virtual sample design is improved using Pyrough, which enables more realistic simulations to be made. Several application examples including e.g., the design of wavy grain boundaries or nanoindentation testing using a roughened indenter tip are presented. Program Title: Pyrough CPC Library link to program files: https://doi.org/10.17632/x7jdtrbf4s.1 Developer's repository link: https://github.com/jamodeo12/Pyrough Licensing provisions: GNU General Public License 3 Programming language: Python External routines/libraries: Gmsh, Meshio, Wulffpack, ASE, Atomsk, cv2 Nature of problem: 3D virtual samples used for atomistic or finite-element simulations generally rely on simplified geometries and surfaces for the sake of design simplicity. However, the influence of surface roughness play a crucial role in various fields of applications (e.g., mechanics, catalysis, lubrication) and must be taken into account. Solution method: Pyrough allows for the design of 3D virtual objects with rough surfaces by means of the classical roughness theory. The user can easily tune the morphology of surfaces and shape 3D objects. Output samples can be used in finite-element or atomistic simulations according to the user's needs. Additional comments including restrictions and unusual features: The program documentation is available at https://jamodeo12.github.io/Pyrough/ [ABSTRACT FROM AUTHOR]

The mechanical behaviors of crystalline materials, in particular the atomic scale deformation and failure processes, are strongly influenced by the local atomic stress near crystalline defects such as vacancies, dislocations and grain boundaries (GBs). Modern electron microscopy techniques have achieved unprecedented capabilities to image the internal microstructure of crystalline materials with atomic resolution. In comparison, our ability to map the corresponding atomic stress field, especially at grain boundaries with complex atomic structures, remains lagging behind due to the lack of direct experimental methods for stress measurement. Here, we propose a machine learning-based framework to realize atomic structure-stress (Atom-S2) mapping based on in situ transmission electron microscopy images. We demonstrate that, with optimized anti-noise performance and generalization ability, the Atom-S2 framework enables quantitative mapping of atomic stress in symmetrical tilt GBs, twin boundaries (TBs) as well as general GBs with changing curvature in crystalline metals. Moreover, the Atom-S2 can help understand, interpret and predict grain boundary stress evolution and plastic deformation mechanisms based on high-resolution transmission electron microscopy images, which provides a powerful tool to study atomic scale deformation behaviors and holds promises for accelerating materials design through defect engineering. [ABSTRACT FROM AUTHOR]

A new methodology was developed in order to obtain single crystal elastic coefficients from nanoindentation experiments on a cubic polycrystal. The method consists of locating grains that are oriented with a 〈100〉, 〈110〉 or 〈111〉 direction near-parallel to the sample surface normal by means of electron backscattering diffraction. The reduced Young's moduli of the selected grains are then determined by nanoindentation. Finally, the average reduced modulus and Euler angles of each grain are used as input for a least-squares optimisation to calculate the three independent stiffness coefficients, which can then be used to obtain Young's modulus in any crystallographic direction. This technique, which was validated on a single crystal nickel-based superalloy (CMSX-4) with known elastic coefficients, was applied to a polycrystalline nickel-based superalloy (RR1000) with unknown elastic coefficients, resulting in a correct prediction of the general trend of increasing Young's modulus from the 〈100〉 to the 〈110〉 to the 〈111〉 direction. The stiffness coefficients C 11 , C 12 and C 44 were found to be 282, 121 and 108 GPa, respectively. These results, which are representative of the γ/γ' structure as a whole, are in good agreement with literature data on similar superalloys. By constructing a visual representation of the elastic anisotropy based on the crystallographic factor, it is shown that the observed anisotropy is lower compared to other alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Mechanical properties of multiferroic nanostructures are of great importance for their applications, yet their characterization is challenging, especially in a quantitative manner and simultaneously with their piezoelectric properties. In this paper, we show that the widely applied piezoresponse force microscopy, when appropriately carried out and analyzed, can be utilized to quantitatively map the Young's modulus of multiferroic nanofibers with high accuracy and spatial resolution, while their piezoelectricity can be simultaneously determined as usual. The analysis is built on three tightly coupled models, one on contact resonance for the dynamic motion of the cantilever, one for quasi-static contact mechanics between the tip and sample, and the third regarding dynamic tip-sample interaction, with which the mechanical properties of the nanofiber can be deduced from the contact resonance spectrum locally excited by the charged probe, taking advantage of the electromechanical coupling of multiferroic composites. Furthermore, two flexural modes of contact resonances are used in combination with reference material for calibration, so that explicit measurement of some critical model parameters can be avoided. We apply the method to Pb(Zr 0.52 Ti 0.48)O 3 -CoFe 2 O 4 composite nanofibers with different compositions, and demonstrate its excellent agreement with destructive nanoindentation method, globally excited contact resonance approach, as well as micromechanics rule of mixture. The method can be easily applied to a wide variety of multiferroic nanostructures as well. [ABSTRACT FROM AUTHOR]

Abstract The colloidal calcium–silicate–hydrate (C–S–H) gel largely controls the strength of concrete. However, little remains known about how the structural features of the C–S–H gel control its mechanical properties. Here, based on coarse-grained mesoscale simulations, we investigate the effect of grain polydispersity and structural disorder on the nanomechanics of C–S–H. Our simulations offer a good agreement with nanoindentation data over a large range of packing density values. We show that, at constant packing density, stiffness and hardness are not affected by the polydispersity in grain sizes. In contrast, the level of disorder is found to play a critical role. We demonstrate that, in contrast to the case of ordered C–S–H models, the elastic response of disordered C–S–H gels is governed by the existence of stress heterogeneity and nanoyielding within its structure. These results highlight the intrinsically disordered nature of C–S–H and the crucial role of order and disorder in controlling gels' mechanical properties. Graphical abstract The extent of order and disorder in hydrated silicate gels controls mainly shear resistance through stress heterogeneity. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Understanding the mechanical behaviour of nanostructures is of great importance due to their applications in nanodevices such as in nanomechanical resonators, nanoscale mass sensors, electromechanical nanoactuators and nanogenerators. Due to the difficulties of performing accurate experimental measurements at nanoscales and the high computational costs associated with the molecular dynamics simulations, the continuum modelling of nanostructures has attracted a considerable amount of attention. Since size influences have a crucial role in the mechanics of structures at nanoscale levels, classical continuum-based theories have been modified to incorporate these effects. Among various modified continuum-based theories, the nonlocal elasticity and the nonlocal strain gradient elasticity have been employed to estimate the mechanical behaviour of nanostructures. In this review paper, first these two modified elasticity theories are briefly explained. Then, the nonlocal motion equations for different nanostructures including nanorods, nanorings, nanobeams, nanoplates and nanoshells are derived. Several papers which reported on the size-dependent mechanical behaviour of nanostructures using modified continuum models are reviewed. Furthermore, important results reported on the vibration, bending and buckling of nanostructures as well as the results of size-dependent wave propagation analyses are discussed. [ABSTRACT FROM AUTHOR]

Discrete stress relaxations (slip avalanches) in a model metallic glass under uniaxial compression are studied using a metadynamics algorithm for molecular simulation at experimental strain rates. The onset of yielding is observed at the first major stress drop, accompanied, upon analysis, by the formation of a single localized shear band region spanning the entire system. During the elastic response prior to yielding, low concentrations of shear transformation deformation events appear intermittently and spatially uncorrelated. During serrated flow following yielding, small stress drops occur interspersed between large drops. The simulation results point to a threshold value of stress dissipation as a characteristic feature separating major and minor avalanches consistent with mean-field modeling analysis and mechanical testing experiments. We further interpret this behavior to be a consequence of a nonlinear interplay of two prevailing mechanisms of amorphous plasticity, thermally activated atomic diffusion and stress-induced shear transformations, originally proposed by Spaepen and Argon, respectively. Probing the atomistic processes at widely separate strain rates gives insight to different modes of shear band formation: percolation of shear transformations versus crack-like propagation. Additionally a focus on crossover avalanche size has implications for nanomechanical modeling of spatially and temporally heterogeneous dynamics. [ABSTRACT FROM AUTHOR]

Nonlocal strain gradient models are being used more and more extensively in examining the size-dependent effects on the statical and dynamical behaviors of micro/nano-structures. However, for the fake of simplification, the size-dependent effects are often assumed to be neglected in the thickness direction of beams and plates. This simplification is originally aiming at reducing the complexity of the studied beam and plate problems while retaining all the most important mechanical features. Based on the nonlocal strain gradient model without the thickness effect, the size-dependent effect may reveal stiffness-softening or stiffness-hardening effect, which only depends on the values of strain-gradient and stress-gradient parameters but is independent on the geometric feature. In this paper, a nonlocal strain gradient beam model incorporating the thickness effect is developed for the size-dependent buckling analysis of nanobeams, and closed-form solutions are derived for post-buckling configuration and critical buckling force. When incorporating the size-dependent effect of thickness, it is found that the stiffness-softening and stiffness-hardening effects depend not only on the ratio of stress-gradient parameter to strain-gradient parameter, but also on the geometric feature (slenderness ratio). Interestingly, the stiffness-softening effect can be only found for the longitudinal dispersion relation of Silicon, while the stiffness-hardening effect may be observed for the buckling behaviors of nanobeams made of Silicon due to the size-dependent effect of thickness. [ABSTRACT FROM AUTHOR]

Keywords: Bone Research; Health and Medicine; Hip Fracture; Risk and Prevention EN Bone Research Health and Medicine Hip Fracture Risk and Prevention 5524 5524 1 07/03/23 20230707 NES 230707 2023 JUL 7 (NewsRx) -- By a News Reporter-Staff News Editor at Health & Medicine Week -- Investigators publish new report on hip fracture. According to the news editors, the research concluded: "(1) Hip fracture risk is increased by low tissue strain, which can be caused by low collagen or mineral strain. [Extracted from the article]

The article offers update on a study on the reconfiguration of nanomechanical photonic metamaterials by nonthermal optical forces, conducted by a research group at the University of Southeampton's Optoelectronics Research Centre in the United Kingdom (UK). The research indicates the role of coupling optical and mechanical resonances in achieving optical nonlinearity. It suggests the potential application of nano-optomechanical metadevices for the development of photonic switching devices.

A boundary element method is developed to examine two-dimensional size-dependent thermoelastic response in isotropic solids. The formulation is founded on the recently established consistent couple stress theory, in which both the couple-stress tensor and its energy conjugate mean curvature tensor are skew-symmetric. For isotropic materials, there is no thermal mean curvature deformation, and the thermoelastic effect is solely the result of thermal strain deformation. As a result, size-dependency is quantified by one characteristic material length scale parameter l , while the thermal coupling is activated through the classical thermal expansion coefficient α . Interestingly, in this size-dependent multi-physics model, the thermal governing equation is independent of the deformation. However, the mechanical governing equations depend on the temperature field. Here, we develop the boundary integral representation and numerical implementation for this size-dependent thermoelastic boundary element method (BEM) for plane problems, which involves temperatures, displacements, rotations, normal heat fluxes, force-tractions and couple-tractions as primary variables within a boundary-only formulation. Then, we apply this new BEM formulation to several basic computational problems in an effort to validate the robustness of the numerical implementation and to examine size-dependent response. [ABSTRACT FROM AUTHOR]

Keywords: Cancer; Cytoplasm; Drugs and Therapies; Gastric Cancer; Gastroenterology; Genetics; Health and Medicine; Intracellular Space; Nanomechanics; Nanotechnology; Oncology EN Cancer Cytoplasm Drugs and Therapies Gastric Cancer Gastroenterology Genetics Health and Medicine Intracellular Space Nanomechanics Nanotechnology Oncology 817 817 1 05/29/23 20230530 NES 230530 2023 MAY 30 (NewsRx) -- By a News Reporter-Staff News Editor at Cancer Weekly -- New research on gastric cancer is the subject of a new report. Cancer, Cytoplasm, Drugs and Therapies, Gastric Cancer, Gastroenterology, Genetics, Health and Medicine, Intracellular Space, Nanomechanics, Nanotechnology, Oncology. [Extracted from the article]

Uttar Pradesh, India, Asia, Emerging Technologies, Inorganic Chemicals, Minerals, Nanoindentation, Nanotechnology, Nanoindent Keywords: Uttar Pradesh; India; Asia; Emerging Technologies; Inorganic Chemicals; Minerals; Nanoindent; Nanoindentation; Nanotechnology EN Uttar Pradesh India Asia Emerging Technologies Inorganic Chemicals Minerals Nanoindent Nanoindentation Nanotechnology 1748 1748 1 04/10/23 20230414 NES 230414 2023 APR 14 (NewsRx) -- By a News Reporter-Staff News Editor at Genomics & Genetics Weekly -- Investigators discuss new findings in Nanotechnology - Nanoindentation. [Extracted from the article]

The mixture unified gradient theory of elasticity is invoked for the nanoscopic study of the nonlinear flexure mechanics of nanobeams. A mixed variational framework is conceived based on ad hoc functional space of kinetic test fields, wherein a complete set of governing equations, classical and non-standard boundary conditions, and the constitutive relations are integrated into a solitary functional. The size-effect phenomenon associated with the nonlinear flexure of nanobeams are efficiently realized as the stress gradient theory, the strain gradient theory, and the classical elasticity theory are consistently unified within the framework of the mixture unified gradient elasticity. A viable numerical approach is introduced based on the conceived mixed variational framework while the autonomous series solution of the kinematic and kinetic field variables is implemented. As the kinetic field variables are directly determined rather than utilizing post-computations, the established consistent variational theory provides an advantageous means for efficacious approximate approaches. The nonlinear flexural response of the mixture unified gradient beams with kinematics constraints of practical interest in nano-mechanics is detected and thoroughly compared with the linear counterparts in terms of the characteristic parameters. The detected nonlinear flexural characteristics of nano-sized beams can pave the way ahead in the nonlinear mechanics of nano-structures. • Consistent variational framework for the mixture unified gradient elasticity theory. • Unification of stress gradient model, strain gradient theory and classical elasticity. • Rigorous nanoscopic analysis of the nonlinear flexure mechanics of nanobeams. • Introduction of an effective numerical approach based on mixed variational functional. • Applying independent series solutions of the kinematic and kinetic field variables. [ABSTRACT FROM AUTHOR]

Measuring fracture toughness of materials at small scales remains challenging due to limited experimental testing configurations. A recently developed indentation pillar-splitting method has shown promise of improved flexibility in fracture toughness measurements at the microscale, partly due to the occurrence of an unusual fracture instability, i.e., a transition from stable to unstable crack propagation. In spite of growing interest in this method, the underlying mechanism of this phenomenon is yet to be elucidated. Here, we provide a comprehensive description of fracture instability in indentation pillar-splitting by combining in situ experiments with high-fidelity simulations based on cohesive zone and J -integral methods. In addition, a machine-learning-based solution for predicting the critical indentation load of fracture instability is established through Gaussian processes regression for broad use of this method by the community. [ABSTRACT FROM AUTHOR]

Recent advances in electronics have enabled nanomechanical measurements with very low noise, fast time constants and high data acquisition rates. These capabilities open the door for a wide range of ultra-fast nanomechanical testing. Given the inherent dynamic nature of high-speed testing, a thorough understanding of the testing system's dynamics and electronics is extremely important for accurate measurements. In this work, an analytical framework that includes the mechanical and electronic contributions of the instrument and the material constitutive response is presented to provide guidelines for performing high strain rate measurements of hardness by nanoindentation testing. Simple closed-form solutions that provide insights on the choice of test methodology, test parameters and instrument design are presented along with the strain rate range over which accurate measurements can be performed with commercially available nanoindenters. [ABSTRACT FROM AUTHOR]

We study a tripartite quantum system consisting of a coplanar-waveguide (CPW) resonator and a nanomechanical resonator (NAMR) connected by a flux qubit, where the flux qubit has a large detuning from both resonators. By a unitary transformation and a second-order approximation, we obtain a strong and controllable (i.e., magnetic-field-dependent) effective coupling between the NAMR and the CPW resonator. Due to the strong coupling, vacuum Rabi splitting can be observed from the voltage-fluctuation spectrum of the CPW resonator. We further study the properties of single-photon transport as inferred from the reflectance or equivalently the transmittance. We show that the reflectance and the corresponding phase-shift spectra both exhibit doublet of narrow spectral features due to vacuum Rabi splitting. By tuning the external magnetic field, the reflectance and the phase shift can be varied from 0 to 1 and -- π to π, respectively. The results indicate that this hybrid quantum system can act as a quantum router. [ABSTRACT FROM AUTHOR]

Recent studies on nanomechanical devices based on low-dimensional nanomaterials have revealed several different types of thermal fluctuation gradient induced tangential entropic forces (TEFs), including expulsion force, edge force, thermophoretic force, nanodurotaxis force, etc. While all these forces originate from thermal fluctuation gradients, they can take different forms for different problems and have been treated case-by-case in the literature. Here, we develop a unified theoretical framework for TEFs in layered low-dimensional materials. In particular, we derive explicit analytical solutions for TEFs in layered two-dimensional materials and validate them with molecular dynamics simulations for various bilayers composed of graphene, graphyne, hexagonal-boron nitride (h -BN), boron-carbon-nitride (BCN), and double walled nanotubes. We present also approximate solutions to TEFs in hetero- or substrate-supported-bilayers based on a solution-guided machine learning (SGML) technique. The developed concept for TEFs is unique to nanomechanical systems and may serve as one of the founding pillars of nanomechanics. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to investigate the gas flow characteristics in near wall region and the velocity slip phenomenon on the wall in nano-channels based on the molecular dynamics simulation. Design/methodology/approach – An external gravity force was employed to drive the flow. The density and velocity profiles across the channel, and the velocity slip on the wall were studied, considering different gas temperatures and gas-solid interaction strengths. Findings – The simulation results demonstrate that a single layer of gas molecules is adsorbed on wall surface. The density of adsorption layer increases with the decrease of gas temperature and with increase of interaction strength. The near wall region extents several molecular diameters away from the wall. The density profile is flatter at higher temperature and the velocity profile has the traditional parabolic shape. The velocity slip on the wall increases with the increase of temperature and with decrease of interaction strength linearly. The average velocity decreases with the increase of gas-solid interaction strength. Originality/value – This research presents gas flow characteristics in near wall region and the velocity slip phenomenon on the wall in nano-channels. Some interesting results in nano-scale channels are obtained. [ABSTRACT FROM AUTHOR]

Nickel-gamma alumina (Ni-γAl2O3) composite coatings were synthesized by pulsed electrodeposition technique with different concentrations of alumina (0, 10, 20 and 50 g/L) in Watt's bath. Both ultrasonic vibration and magnetic-stirring were utilized to disperse Al2O3 and to achieve its optimum loading. Microstructure shows that agglomerates occur at higher loadings, but 10 g/L Al2O3 addition in bath has shown uniform dispersion of alumina with improved mechanical properties such as hardness, Young's modulus and yield strength by 40%, 46% and 35%, respectively, when compared to that of pure Ni coating. Further, elasto-plastic indentation mechanics has shown that strength at 29% strain is enhanced to 110.5 GPa for 10 g/L Al2O3 electrophoretically deposited Ni-γAl2O3 coating when compared to that of electrodeposited Ni (81.8 GPa). [ABSTRACT FROM AUTHOR]

We have observed nonlinear transduction of the thermomechanical motion of a nanomechanical resonator when detected as laser transmission through a sideband unresolved (stationary) optomechanical cavity. Nonlinear detection mechanisms are of considerable interest as special cases allow for quantum nondemolition measurements of the mechanical resonator's energy. We investigate the origin of the nonlinearity in the optomechanical detection apparatus and derive a theoretical framework for the nonlinear signal transduction, and the optical spring effect, from both nonlinearities in the optical transfer function and second-order optomechanical coupling. By measuring the dependence of the linear and nonlinear signal transduction--as well as the mechanical frequency shift--on laser detuning from optical resonance, we provide estimates of the contributions from the linear and quadratic optomechanical couplings. [ABSTRACT FROM AUTHOR]

The stationary continuous-variable entanglement between an optical cavity and a nanomechanical resonator beam is generated by their common interaction with a quantum dot. To deal with the quantum dot which is modeled as a two-level system, we do not use the low excitation limit approximation to bosonize the spin operators, but we keep them in the quantum Langevin equations. We linearize the quantum Langevin equations reasonably and investigate the stationary continuous-variable entanglement in detail, and finally we show that a high degree of entanglement can be achieved for experimentally feasible parameters. [ABSTRACT FROM AUTHOR]

We study the entangling power of a nanoelectromechanical system (NEMS) simultaneously interacting with two separately trapped ions. To highlight this entangling capability, we consider a special regime where the ion-ion coupling does not generate entanglement in the system and any resulting entanglement will be the result of the NEMS acting as an entangling device. We study the dynamical behavior of the bipartite NEMS-induced ion-ion entanglement as well as the tripartite entanglement of the whole system (ions + NEMS). We found some quite remarkable phenomena in this hybrid system. For instance, the two trapped ions initially uncorrelated and prepared in coherent states can become entangled by interacting with a nanoelectromechanical resonator (also prepared in a coherent state) as soon as the ion-NEMS coupling achieves a certain value, and this can be controlled by external voltage gate on the NEMS device. We also show that, dynamically, the tripartite entanglement presents a more pronounced robustness against the destructive effects of dissipation when compared to the bipartite content. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of single-asperity micro- and nanoscale contacts in which adhesion is present is important for the performance of many small-scale mechanical systems and processes, such as atomic force microscopy (AFM). When analyzing such problems, the bodies in contact are often assumed to have paraboloidal shapes, thus allowing the application of the familiar Johnson–Kendall–Roberts (JKR), Derjaguin–Müller–Toporov (DMT), or Maugis–Dugdale (M–D) adhesive contact models. However, in many situations the asperities do not have paraboloidal shapes and, instead, have geometries that may be better described by a power-law function. An M–D-n analytical model has recently been developed to extend the M–D model to asperities with power-law profiles. We use a combination of M–D-n analytical modeling, finite element (FE) analysis, and experimental measurements to investigate the behavior of nanoscale adhesive contacts with non-paraboloidal geometries. Specifically, we examine the relationship between pull-off force, work of adhesion, and range of adhesion for asperities with power-law-shaped geometries. FE analysis is used to validate the M–D-n model and examine the effect of the shape of the adhesive interaction potential on the pull-off force. In the experiments, the extended M–D model is applied to analyze pull-off force measurements made on nanoscale tips that are engineered via gradual wear to have power-law shapes. The experimental and modeling results demonstrate that the range of the adhesive interaction is a crucial parameter when quantifying the adhesion of non-paraboloidal tips, quite different than the familiar paraboloidal case. The application of the M–D-n model to the experimental results yields an unusually large adhesion range of 4–5nm, a finding we attribute to either the presence of long-range van der Waals forces or deviations from continuum theory due to atomic-scale roughness of the tips. Finally, an adhesion map to aid in analysis of pull-off force measurements of non-paraboloidal tips is presented. The map delineates the cases in which a simplified rigid analysis can be used to analyze experimental data. [Copyright &y& Elsevier]

Abstract: A new frontier of research in the area of computational nanomechanics is to study the behavior of structures at very small length scales. As the dimensions of a structure approach the nanoscale, the classical continuum theories may fail to accurately predict the mechanical behavior of nanostructures. Among these nanostructures, nanobeams are attracting more and more attention due to their great potential engineering applications. One of the most important factors that influence the behavior of such submicron-sized structures is surface stress effect because of their high surface to volume ratio. In this paper, a non-classical solution is proposed to analyze bending and buckling responses of nanobeams including surface stress effects. Explicit formulas are proposed relevant to each type of beam theory to evaluate the surface stress effects on the displacement profile and critical buckling load of the nanobeams. Numerical results are presented to demonstrate the difference between the behaviors of the nanobeam predicted by the classical and non-classical solutions which depends on the magnitudes of the surface elastic constants. [Copyright &y& Elsevier]

Abstract: A theory is developed to explain the spontaneous bending of polar faceted wurtzite nanoribbons, including the widely studied case of zinc oxide (ZnO) nanoarcs and nanorings. A rigorous thermodynamic treatment shows that bending of these nanoribbons can be primarily attributed to the coupling between piezoelectric effects, electric polarization, and the motion of free charge originating from point defects and/or dopants. The present theory explains the following experimental observations: the magnitude and sign of curvature and how this curvature depends on film thickness and dopant concentration. Good agreement between theory and experiment is obtained with no adjustable parameters. We identify three regimes of bending behavior with distinct thickness dependence for bending radius that depend on free carrier density, film thickness, and elastic, piezoelectric and dielectric constants. [Copyright &y& Elsevier]

Abstract: Consideration of surface (interface) energy effects on the elastic field of a solid material has applications in several modern problems in solid mechanics. The Gurtin–Murdoch continuum model [M.E. Gurtin, A.I. Murdoch, Arch. Ration. Mech. Anal. 57 (1975) 291–323; M.E. Gurtin, J. Weissmuller, F. Larché, Philos. Mag. A 78 (1998) 1093–1109] accounting for surface energy effects is applied to analyze the elastic field of an isotropic elastic layer bonded to a rigid base. The surface properties are characterized by the residual surface tension and surface Lame constants. The general solutions of the bulk medium expressed in terms of Fourier integral transforms and Hankel integral transforms are used to formulate the two-dimensional and axisymmetric three-dimensional problems, respectively. The generalized Young–Laplace equation for a surface yields a set of non-classical boundary conditions for the current class of problems. An explicit analytical solution is presented for the elastic field of a layer. The layer solution is specialized to obtain closed-form solutions for semi-infinite domains. Selected numerical results are presented to show the influence of surface elastic constants and layer thickness on stresses and displacements. [Copyright &y& Elsevier]

Nanomechanical behavior of cantilever-DNA chip in label-free biodetection is investigated by the energy method. First, using an equation of state for DNA liquid crystals and an alternative two-variable model for laminated cantilever beams, a relationship between chip energy and some factors, such as nanogeometrical, physical, chemical characteristics of DNA molecules, microscopical geometric dimension, macroscopical mechanical properties of chip, etc., is formulated in consideration of electrostatic energy, hydration energy and configurational fluctuations of DNA layer as well as mechanical energy of chip. Second, theoretical predictions of nanomechanical deflection of DNA chip by the minimum principle of energy are compared with experimental data in Wu's experiments. Third, the influence of stochastic interchain distances and stochastic elastic modulus on chip deflection is investigated. The validity of the simplified two-layer-beam model is also studied. Numerical results show that chip deflection enhances with the increase in length of DNA chains, and the interchain distances should be carefully controlled no less than 4nm during the process of probe molecules self-assembly. [Copyright &y& Elsevier]

• A non-local stress-driven nanobeam model for composite multilayered beams is proposed. • Thermoelastic material behavior is assumed. • Governing equations are solved by Laplace transforms. • Coupling effects enable a lot of possibilities in design of nanomechanical engineering structures. In this paper, the mechanical behavior of multilayered small-scale beams in nonisothermal environment is investigated. Scale phenomena are modeled by means of the mathematically well-posed and experimentally consistent stress-driven integral formulation of elasticity. The present research extends the treatment in Barretta, Čanađija, Luciano, and de Sciarra (2018b) confined to elastically homogeneous nano-scopic structures. It is shown that the non-locality leads to a complex coupling between axial and transverse elastic displacements. Such a size-dependent phenomenon makes the solution of the relevant nonlocal thermoelastostatic problem, governed by a system of two ordinary differential equations with ten standard boundary conditions and non-classical constitutive boundary conditions, significantly more involved with respect to treatments in literature. Thus, a novel solution methodology, based on Laplace transforms, is proposed and illustrated by examining simple structural schemes of current applicative interest in Nanomechanics and Nanotechnology. [ABSTRACT FROM AUTHOR]

Reduction of Brownian thermal noise due to mechanical loss in high-reflectivity mirror coatings is critical for improving the sensitivity of future gravitational wave detectors. In these mirrors, the mechanical loss at room temperature is dominated by the high refractive index component, amorphous tantala (Ta2O5) or tantala doped with titania (Ti∶Ta2O5). Toward the goal of identifying mechanisms that could alter mechanical loss, this work investigates the use of assist ion bombardment in the reactive ion beam sputtering deposition of tantala single layers. Low-energy assist ion bombardment can enhance adatom diffusion. Low-energy assist Ar+ and Xe+ ion bombardment at different conditions was implemented during deposition to identify trends in the mechanical loss with ion mass, ion energy, and ion dose. It is shown that the atomic structure and bonding states of the tantala thin films are not significantly modified by low-energy assist ion bombardment. The coatings mechanical loss remains unaltered by ion bombardment within errors. Based on an analysis of surface diffusivity, it is shown that the dominant deposition of tantala clusters and limited surface diffusion length of oxygen atoms constrain structural changes in the tantala films. A slower deposition rate coupled with a significant increase in the dose of the low-energy assist ions may provide more favorable conditions to improve adatom diffusivity. [ABSTRACT FROM AUTHOR]

The article presents the views of Wei H. Loh, deputy director of the Engineering & Physical Sciences Research Council (EPSRC) Centre for Innovative Manufacturing in Photonics and researcher at the Optoelectronics Research Centre in Great Britain, on new dynamic nanomechanical dual-core optical fibers. Loh says the nanomechanical fiber structure can control the propagation time of light through the fiber by moving the two cores closer together.

Phonon blockade is a purely quantum phenomenon, analogous to Coulomb and photon blockades, in which a single phonon in an anharmonic mechanical resonator can impede the excitation of a second phonon. We propose an experimental method to realize phonon blockade in a driven harmonic nanomechanical resonator coupled to a qubit, where the coupling is proportional to the second-order nonlinear susceptibility χ(2). This is in contrast to the standard realizations of phonon and photon blockade effects in Kerr-type χ(3) nonlinear systems. The nonlinear coupling strength can be adjusted conveniently by changing the coherent drive field. As an example, we apply this model to predict and describe phonon blockade in a nanomechanical resonator coupled to a Cooper-pair box (i.e., a charge qubit) with a linear longitudinal coupling. By obtaining the solutions of the steady state for this composite system, we give the conditions for observing strong antibunching and sub-Poissonian phonon-number statistics in this induced second-order nonlinear system. Besides using the qubit to produce phonon blockade states, the qubit itself can also be employed to detect blockade effects by measuring its states. Numerical simulations indicate that the robustness of the phonon blockade, and the sensitivity of detecting it, will benefit from this strong induced nonlinear coupling. [ABSTRACT FROM AUTHOR]