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In order to develop a suitable washing mode for knapsack, mechanical agitation (1), water bath vibration (2), ultrasonic (3), micro-nano bubble (4) and complex washing mode of the two were systematically investigated. Results showed that regardless of fabric, the washing efficiency of composite washing mode {mechanical agitation + ultrasonic (1 + 3), mechanical agitation + micro-nano bubble (1 + 4)}, was highest among all washing modes. Moreover, the decrease of stiffness, tensile strength, smoothness and micro-morphology of knapsack by using complex washing mode {mechanical agitation + ultrasonic (1 + 3), mechanical agitation + micro-nano bubble (1 + 4)} significantly lower than that of mechanical agitation. This indicated that mechanical agitation was the key to remove stain, micro-nano bubbles and ultrasound only assisted its removal. But the addition of micro-nano bubbles and ultrasound was helpful to improve the washing efficiency and reduce the performance degradation caused by washing mode of mechanical agitation. Complex washing mode {mechanical agitation + ultrasonic (1 + 3), mechanical agitation + micro-nano bubble (1 + 4)} was optimal washing combination for knapsack, especially the composite mode of mechanical agitation + ultrasonic (1 + 3), due to its ability to remove residual stains in the inner layer and slit. Moreover, the complex washing mode was also more environmental-friendly and sustainable, compared to other washing mode, because of washing time and detergent dosage reducing occurred by its high washing efficiency. The results were not only helpful to guide manufacturers of washing machine to develop a program dedicated to the daily washing and care knapsack, but also provided scientific care guidance and optimization ideas for subsequent research and applications.

Piezoelectric wind energy harvesters consisting a bluff body and a piezoelectric cantilever beam have great potential for powering small-sized wireless devices. To achieve a higher energy output, the beam is designed for large deformation. This results in the nonlinear nature of the energy harvesters. In this paper, a nonlinear model of a piezoelectric wind harvester with different geometrical parameters is developed. A comparison of the energy harvesting performance of these energy harvesters with different geometrical parameters is provided. Results show that the onset speeds of galloping for trapezoidal and exponential piezoelectric energy harvesters are significantly lower than those of rectangular beam. The average power output density of the beam with exponential shape is larger than trapezoidal and rectangular beams. Therefore, designing a beam with exponentially varying shape can obtain the largest power density and therefore can reduce the cost of piezoelectric wind energy harvester.

Thermoelectric (TE) materials have a broad range of application in engineering such as cooling for thermal protection. Due to the brittle nature, TE semiconductors are prone to crack/voids under thermal shock. The investigation of the transient problem in cracked thermoelectric materials is essential for engineering applications. This paper describes a thermal-mechanical coupling method to analyze the transient response of the TE medium of finite size with an arbitrarily located inner crack. Based on the Fourier and Laplace transform, the crack problem is simplified into a system of singularity integral equations which can be solved by simple allocation. Besides, the results of this paper are verified through the finite element method (FEM). Furthermore, the effects of the crack position, crack's thermal and electrical permeability are discussed. Also, the effect of crack on the thermoelectric energy conversion efficiency is studied. Results show that the field concentrations at the crack tip become more significant when the crack is centrally located in the vertical direction. The electrical permeability of the crack has a limited influence on the energy conversion efficiency. However, as thermal permeability of the crack goes up, the efficiency falls significantly.

Thermoelectric (TE) materials as energy functional semiconductors can directly convert heat into electrical power. Due to the brittle nature of semiconductors, voids or inclusions are easy to be produced in the TE materials. This paper studies the three-dimensional ellipsoidal inclusion problem in thermoelectric materials. By introducing two auxiliary functions, we successfully simplify the non-linear coupled governing equations into linear un-coupled equations and the linearization is validated by two practical cases. Based on the Green's function method, the analytical solutions of this problem are derived. We find that the thermoelectric field inside the ellipsoidal inclusion is always uniform when subjected to far-field uniform loads. Furthermore, we derive the effective material properties of the matrix-inclusion system in closed-form. We find that it is possible to enhance the thermoelectric properties as well as the figure of merit by inserting specific inclusions. Moreover, among the different shapes of inclusions, the elliptical cylinder fiber that lies along the loading direction has the most significant improvements to the material properties. This paper is the first that derives the analytical solutions of three-dimensional inclusion problems in TE materials.

This paper analyses a two-dimensional problem in thermoelectric materials with an inclined elliptic inclusion. We have obtained the closed-form solutions of electric current density and temperature considering the inclusion's electrical and thermal permeability. Based on the derived thermoelectric field, the thermal stresses are given in the explicit form and the effect of inclusion on effective thermoelectric properties is investigated. The electrically impermeable and thermally impermeable inclusions will respectively cause maximum electric current concentration and heat concentration. The thermally impermeable and rigid inclusion will cause maximum stress concentration around the inclusion. Furthermore, we find that the effective electric conductivity (effective thermal conductivity) of the matrix-inclusion system is increased when the inclusion have higher electric conductivity (thermal conductivity) than the matrix. It is possible to enhance the effective figure of merit by inserting inclusions with specific electric conductivity and heat conductivity. It predicts a new way for the design of high-performance thermoelectric devices. The results in this paper can be directly used for reliability consideration in design and optimization of thermoelectric devices in engineering.

A novel bended wrinkle structure is proposed for layout design in flexible electronics, which is formed by compressive local buckling of the thin film bonded onto a pre-strained, finite-thickness substrate upon release of the pre-strain. The excellent performance of stretchability of this structure, which could be as high as 309%, is shown according to theoretical analyses and validated by finite element method (FEM). Furthermore, the maximum strain of the proposed design is examined to ensure reliability of application devices. Except for the approach to compressibility based on maximum strain analyses, the bended wrinkle structure is taken as a laminate with geometrical imperfections and buckling analyses are conducted to obtain the critical buckling loads, consequently another evaluation criterion for compressibility is established. It is also revealed that the stretchability can be further enhanced by bonding the two ends of the structure to another pre-strained compliant basal substrate, though the pre-strain for the basal substrate is restricted by the compressibility. In the current work, an alternative to existing planar wavelike layout designs is presented and the results obtained offer important design guidelines for future applications.

Recently, open cellular substrates instead of traditional solid substrates have been used in flexible electronics, catering to the need for high permeability of bio-fluids through the device. The Poisson ratio of the existing open cellular designs, however, remains positive, which is inappropriate for the cellular substrates mounting on some biological auxetic materials, as the resulting mismatch in deformation may cause irritation. In the current work, a type of triangular lattice networks is presented with satisfactory negative Poisson ratio effect over large strains. A finite deformation model is developed for the deformed angles, constitutive relation and maximum strain of the building block, with nonlinear finite element method (FEM) validations. Results demonstrate desired negative Poisson ratios and mechanical properties can be achieved in an isotropic manner by tailoring three geometric parameters (arc angle θ0, length/radius ratio L/R and width/radius ratio w/R). Thereinto, longer arm lengths not only yield lower equivalent modulus and maximum strain, but also enable wider range of isotropic negative Poisson ratios (from -0.35 to 0) and applied strains (from 0% to 80%), providing more flexibility in network designs and new possibilities to emerging biomedical applications.

Dynamic performance of sandwich beam with shear thickening fluid (STF) core subjected to a periodic excitation is investigated. The addition of STF enables the sandwich beam to have a tuning stiffness and damping capacity under dynamic deformation. Here, the constitutive model of STF is described by a complex shear modulus related to the shear rate. The transverse moving beam is modeled based on Newtonian law and derived nonlinear equations are solved by finite difference method. It is found that the resonant frequency of the beam increases with the amplitude of the external excitation by a power law. In addition, the initial damping ratio decreases first and then increases with the increase of the amplitude of the initial excitation for the STF with shear thinning zone. The minimum value of the initial damping ratio should be avoided, which is caused by initial shear thinning. This work can be used to guide the designing of structures with enhanced damping and the preparation of STF materials for application to such structures.

The coronavirus disease (COVID-19) has led to a global pandemic and caused huge healthy and economic losses. Non-pharmaceutical interventions, especially contact tracing and social distance restrictions, play a vital role in the control of COVID-19. Understanding the spatial impact is essential for designing such a control policy. Based on epidemic data of the confirmed cases after the Wuhan lockdown, we calculate the invasive reproduction numbers of COVID-19 in the different regions of China. Statistical analysis indicates a significant positive correlation between the reproduction numbers and the population input sizes from Wuhan, which indicates that the large-scale population movement contributed a lot to the geographic spread of COVID-19 in China. Moreover, there is a significant positive correlation between reproduction numbers and local population densities, which shows that the higher population density intensifies the spread of disease. Considering that in the early stage, there were sequential imported cases that affected the estimation of reproduction numbers, we classify the imported cases and local cases through the information of epidemiological data and calculate the net invasive reproduction number to quantify the local spread of the epidemic. The results are applied to the design of border control policy on the basis of vaccination coverage.

In this paper, considering the proven role of exosomes and the inevitable randomization within-host, we establish a hepatitis B virus (HBV) model with cell-to-cell transmission and CTL immune response from a deterministic framework to a stochastic differential equation (SDE). By introducing the reproduction number $ R_0 $, we prove that $ R_0 $ can be used to govern the stochastic dynamics of the SDE HBV model. Under certain assumptions, if $ R_{0}\leq1 $, the solution of the SDE model always fluctuates around the infection-free equilibrium of the deterministic model, which indicates that the HBV will eventually disappear almost surely; if $ R_{0} > 1 $, under extra conditions, the solution of the SDE model fluctuates around endemic equilibrium of the corresponding deterministic model, which leads to the stochastic persistence of the HBV with probability one. One of the most interesting findings is that the fluctuation amplitude is positively related to the intensity of the white noise, which can provide us some useful control strategies to regulate HBV infection dynamics.

Although COVID-19 has been controlled in China, the risk of invasion of imported cases remains. We aimed to characterize the impact of the number of imported cases and the implementation of first-level emergency response (FLER) policy.A SCQIHR switching model was constructed and verified by the complete phased data of COVID-19 in Chongqing in 2020. Then it was used to investigate the impact of the number of imported cases and the timing of FLER. Lastly, it was evaluated by three actual scenarios in Chongqing in 2021.The proposed model can fit the multidimensional time series well. After the implementation of FLER, the mean effective reproduction number, contact rate and misdetection rate were decreased significantly, but the quarantine rate for close contacts and isolation rate for non-hospitalized infectious cases were increased significantly. The peaks of quarantined close contacts and hospitalized infectious cases increased linearly with the increase of the number of imported cases and the lag of FLER time, which was verified by three actual scenarios in Chongqing in 2021.These findings can provide guidance for local public health policy-making and allocation of medical resources, reduce the impact of COVID-19 on the local population.

Gene sequencing technology has been playing an important role in many aspects, such as life science, disease medicine and health medicine, particularly in the extremely tough process of fighting against 2019-novel coronavirus. Drawing DNA restriction map is a particularly important technology in genetic biology. The simplified partial digestion method (SPDP), a biological method, has been widely used to cut DNA molecules into DNA fragments and obtain the biological information of each fragment. In this work, we propose an algorithm based on 0–1 planning for the location of restriction sites on a DNA molecule, which is able to solve the problem of DNA fragment reconstruction just based on data of fragments’ length. Two specific examples are presented in detail. Furthermore, based on 1000 groups of original DNA sequences randomly generated, we define the coincidence rate and unique coincidence rate between the reconstructed DNA sequence and the original DNA sequence, and then analyze separately the effect of the number of fragments and the maximum length of DNA fragments on the coincidence rate and unique coincidence rate as defined. The effectiveness of the algorithm is proved. Besides, based on the existing optimization solution obtained, we simulate and discuss the influence of the error by computation method. It turns out that the error of position of one restriction site does not affect other restriction sites and errors of most restriction sites may lead to the failure of sequence reconstruction. Matlab 7.1 program is used to solve feasible solutions of the location of restriction sites, derive DNA fragment sequence and carry out the statistical analysis and error analysis. This paper focuses on basic computer algorithm implementation of rearrangement and sequencing rather than biochemical technology. The innovative application of the mathematical idea of 0–1 planning to DNA sequence mapping construction, to a certain extent, greatly simplifies the difficulty and complexity of calculation and accelerates the process of 'jigsaw' of DNA fragments. Supplementary Information The online version contains supplementary material available at 10.1007/s12539-021-00419-6.

BACKGROUND Hepatitis B surface antigen (HBsAg) loss/seroconversion is considered to be an ideal endpoint for antiviral therapy and a final therapeutic target for chronic hepatitis (CHB). This study aimed to evaluate the HBsAg kinetics in CHB patients during peginterferon-alpha (Peg-IFN-alpha) treatment. MATERIAL AND METHODS A retrospective cohort study was performed using a case database, which included 151 patients who received Peg-IFN-alpha treatment and with HBsAg load of no less than 4 time points from May 1, 2018 to January 31, 2019. The HBsAg kinetic pattern was analyzed by Q-type clustering, and a clinical prognostic empirical model was constructed based on the HBsAg kinetic pattern of uncured patients. RESULTS Changes of HBsAg in 13 functionally cured patients were attributed to 3 kinetic patterns by cluster analysis, and there was a significant positive correlation between functionally cure time and baseline HBsAg. For uncured 116 patients with treatment duration longer than or equal to 56 days, 5 HBsAg kinetic patterns were obtained by cluster analysis, and the clinical prognosis empirical model was established. Finally, 13 new functionally cured patients preliminarily confirmed the rationality of the proposed empirical model. CONCLUSIONS According to empirical model, we recommend that the therapeutic regime should be timely adjusted to improve sustained response rate and reduce patients' medical burden for patients with second (Z type) and fifth (Z+W type) kinds of patterns. While for the rest of patterns' patients, it is recommended to continue treatment for a longer period of time to achieve the desired therapeutic goal.

This paper formultes a thermo-mechanical nonlinear bending model of multilayered microplates with size effects. The model simultaneously includes the effects of geometrically nonlinear, isogeometric parameter, and the higher order shear deformation of the plate. Based on the proposed model, the geometrically nonlinear bending behaviors of a flexible organic solar cell (OSC) that have five different layers under the photo-thermal and wind load are investigated. Both the uniform and non-uniform temperature fileds along the thickness direction of the plate are discussed. Results show that the size effects reduce the normalized deflections remarkably. Significantly, as the thickness downs to the characteristic size of the material length scale parameter, the deflection can decrease as much as 75%. Subsequently, as the wind speed increases, the impact of the small-scale effect becomes increasingly significant. A semi-empirical formula for the relationship between the tensile stress and solar irradiation of the layers is derived. The optimal solar irradiation and the efficiency of the OSC are obtained. Keywords: multilayered microplates; isogeometric analysis; size effect; residual thermal stress; geometrically nonlinear

A fracture mechanics analysis is conducted for a delamination problem of a multilayered thermoelectric material (TEM) that consists of an n-type layer and a p-type layer sandwiched by an insulating layer. A time-varying energy release rate is presented when the n-type layer delaminates from the insulating layer. Effects of the temperature difference across the system and the applied electric current on the energy release rate are identified. The influence of the thickness ratio of the insulating layer to the thermoelectric (TE) layer is also examined. Based on the energy release rate criterion, the critical temperature difference for delamination propagation is obtained. Some useful conclusions are given.

Different from piezoelectric effect, the flexoelectric effect is size dependent and becomes more significant at nanoscale. A nonlinear dynamic model of nanoscale flexoelectric shells is developed based on modified couples stress theory. The governing equations for nonlinear vibration of a flexoelectric cylindrical nanoshell are obtained. The natural frequency and generated voltage of the flexoelectric cylindrical nanoshell is achieved. Effects of geometric dimension, character material length, and vibration amplitude on the natural frequency and the generated voltage are discussed in detail. Results demonstrate that modified couple stress theory and large deformation theory are coupled together and interact with each other in the analyses of natural frequency and electromechanical behavior. Simultaneously taking nonlinearity and couple stress theory into account is necessary.

Unimorph piezoelectric energy harvesters are typically a unimorph cantilever beam located on a vibrating host structure. Delamination is one of the major failure modes of such unimorph cantilevers and therefore is studied in this article. The delaminated cantilever unimorph is modeled with one through-width crack using four Euler beams connected at delamination edges. The governing equations, the corresponding boundary conditions, and the kinematic continuity conditions are derived based on the Hamiltonian principle. The solutions of the voltage and power output for the present model are derived. The influence of the position and the length of the delamination, frequency of input base excitation, and load resistance on the voltage and power output are discussed in detail. The results show that delamination in the unimorph of the energy harvester will impressively decrease the voltage and power outputs. Influences of the delamination located at the free end of the cantilever are more obvious. For a given active length of the delaminated cantilever energy harvester, it is useful to increase the overall length of the cantilever to obtain a higher voltage and power outputs.

Magnetically actuated robots are attracting much interest due to the advantages of fast response, remote manipulation and enabling operations in enclosed spaces. Recent advances in fabricating ferromagnetic polymeric matrices embedded with hard magnetic fillers provide routes to multimodal locomotion for soft-bodied robots. One limitation of these matrix-based robot designs is that it requires low volume fraction of hard magnetic fillers to achieve soft and compliant robot body such that moderate magnetic fields are sufficient for actuation. However, low volume fraction of functional magnetic fillers leads to magnetically weak soft robots that are difficult to actuate. Here, we propose a compliant and high-performance robot design operating at magnetic fields down to 1 mT by utilizing a high-quality ferromagnetic film and mechanics-guided three-dimensional (3D) assembly technique. A parylene coating is deposited to keep the assembled arch shape, allowing releasing and actuating the structure as a freestanding robot. The robot would unfold and fold periodically under cyclic magnetic fields, driving the robot in a desired direction. To illustrate the versatile applicability of this approach, robots in two different representative geometries are presented, one in traditional straight configuration and the other in serpentine configuration. Through theoretical analysis and finite element analysis, fundamental results are offered for the proposed robot design, including concise solutions to the unfolding deformation, the effects of coating thickness on spring back, the maximum strain in the hard ferromagnetic film and a comparison of unfolding deformation of both designs. The results clearly show the effect of geometry/material parameters, external magnetic field and prestrain in assembly process, providing essential design guidelines to compliant and fast-moving magnetic robots via the proposed method.

In this article, a non-classical shell model incorporating flexoelectric effect is presented to investigate the buckling behavior of piezoelectric cylindrical nanoshell based on the couple stress theory. This non-classical shell model contains both material length scale parameter and flexoelectric parameter and can capture the size effect and piezoelectricity of nanoscale shells. The closed-form solution of the critical buckling load is achieved by energy variational approach. Results show a significant dependence of the buckling modes of the nanoshell on the flexoelectric constant as well as the material length scale parameter. It is also found that the buckling load of the nanoshell is enhanced with the consideration of the flexoelectric effect and the couple stress theory due to their enhancement on the stiffness of the nanoshell. Although the effect of flexoelectricity is more pronounced in short shells, the influence of the material length scale parameter on the buckling load is remarkable even in long shells. In addition, the effects of flexoelectricity and the material length scale parameter on the critical buckling load are more evident for thicker shells.

This paper studies the vibration behaviours of laminated plates with consideration of the influences of surface and interface energies. Geometric nonlinearity is taken into account in this model to obtain the results of large amplitude vibrations. Approximate closed-form solutions for simply supported plates, clamped plates and clamped circular plates are provided. Numerical results show that the surface/interface effect can affect the dynamic behaviours of laminated plates at nanometer scale. This is especially for nonlinear (large-amplitude) vibration. In addition, the ratio of the thickness to length of the plate, the external load and number of layers also affect the surface/interface effects for large amplitude vibration. This study is helpful for designing and examining the non-linear dynamic behaviour of laminated nanoplates and nanoscale devices.

Serpentine-shaped interconnects are widely employed to achieve high level of stretchability in stretchable electronic devices. In the current work, an analytical model for the mechanical response of planar serpentine interconnects with thermal effect is developed and verified by finite element method (FEM). Specifically, the closed-formed expressions to compliance and stretchability are derived based on curved beam theory and energy method. The numerical results indicate that a considerable error (e.g., >10% relatively) could be induced for many representative configurations using the model with thermal loads absent. The present work provides more accurate predictions for the structural response of serpentine interconnects in practical working conditions, which help in optimal design in future applications.

With the improvement on materials performance gradually reaching its bottleneck, more and more works focus on optimizing the device structures to seek further performance enhancement of thermoelectric (TE) devices. This paper proposed an analytical model to calculate the performance of thermoelectric generators (TEGs) with varied leg cross-sections considering temperature-dependent material properties. The explicit expressions of output power and efficiency are derived and the model is verified by finite element method (FEM). Furthermore, the optimization of leg geometry for higher device performance is performed based on the presented model, the results show that the key to maximum output power is to minimize the leg resistance; and increasing the leg volume may simultaneously raise the output power and efficiency. In addition, we apply the presented model to optimize the leg shape of a commercial TEG module and find that the optimized geometry can simultaneously achieve an enhancement up to 43.1% for output power and 9.67% for efficiency. The presented model thus may be useful in designing high-performance TEGs and shed considerable light on the principles of TEG design.

In this paper, based on quasi steady-state assumption, a phenomenological model of viral infections with intracellular delay is proposed to explore viral infection process. The existence as well as stability of equilibria and bifurcation are studied. The results indicate that the basic reproduction number is a sharp threshold parameter to determine the outcomes of infection when the intracellular delay is omitted. Otherwise, Hopf bifurcation may occur under some conditions. Combining with numerical simulations, we observe that the explicit dynamics of free virus can affect the dynamics behavior, the fluctuation scenario may appears in the case of full logistic proliferation term even if there is no intracellular delay. In addition, there are different patterns of bifurcation under different drug effectiveness and patient’s age interacting with intracellular delay, which indicates that intracellular delay may induce complicated kinetics of virus infection.

In this paper, large amplitude free vibration of electrically actuated nanobeams with consideration of surface energy, temperature change and Casimir force is studied. Results show that neglecting of surface energy and intermolecular Casimir force will result in a lower prediction and a higher prediction of fundamental frequency, respectively. Thermal effect may change the relationship between fundamental frequency and applied voltage. In addition, the effect of geometric nonlinear deformation on the fundamental frequency is more significant for large applied voltage. The influence of surface energy and geometric nonlinear deformation on the fundamental frequency depends on the length and height of the nanobeams.

Efficiently converting vibration energy from surrounding environment to electric energy for powering micro/nano-electromechanical systems (MEMS/NEMS), without using batteries, is an interesting research subject. One of the most important applications of flexoelectricity is in the field of transducers in energy harvesters where flexoelectric effect is significant at micro/nano-scale. In this paper, a theoretical model incorporating flexoelectricity and piezoelectricity for energy harvesting is developed. The model includes geometric nonlinearity deformation and damping effect so that it can more accurately predict the electromechanical behavior of energy harvesters. A special case study for a cantilever beam (which is the most common configuration of vibration energy harvesters) is carried out. Two types of commonly-used cantilevered energy harvesters, a single layer and a unimorph energy harvester, are derived. It is found that, in some cases, voltage output contributed by flexoelectric effect is extremely (e.g., five times) higher than that solely contributed by piezoelectric effect.

The influence of nonlinear elasticity on the bending of nanofilms under transverse load has been studied. The effects of second order elasticity, surface energy and large deformation are incorporated in the present model. The general governing equation for the nonlinear bending of a rectangle shaped nano-film is derived. The general method for solving the general governing equation is illustrated. The results indicated that the existence of nonlinear elastic effects makes it easier for the nano-film to deform, the nonlinear effect is amplified in pace with the increase of the transverse load. Moreover, the effect of nonlinear elasticity on the nonlinear bending of the nanofilms is more significant for the nanofilms with negative surface energy and a large aspect ratio and large length-thickness ratio.

In this paper, we formulate a virus dynamics model with the recruitment of immune responses, saturation effects and an intracellular time delay. With the help of uniform persistence theory and Lyapunov method, we show that the global stability of the model is totally determined by the basic reproductive number $R_0$. Furthermore, we analyze the effects of the recruitment of immune responses on virus infection by numerical simulation. The results show ignoring the recruitment of immune responses will result in overestimation of the basic reproductive number and the severity of viral infection.

Older adults with subjective memory complaints (SMCs) are at increased risk for episodic memory decline. Episodic memory decline is an important predictor of objective memory impairment (one of the earliest symptoms of Alzheimer’s disease) and an often-suggested criterion of successful memory aging. Therefore, it is important to explore the determinant factors that influence episodic memory in older adults with SMCs. Roy adaptation model and preliminary evidence suggest that older adults with SMCs undergo a coping and adaptation process, a process influenced by many health-related risks and protective factors. This study aimed to explore the relationship between coping capacity and episodic memory, and the mediating role of healthy lifestyle between coping capacity and episodic memory in a sample of 309 community-dwelling older adults with SMCs. Results from the structural equation modeling showed that coping capacity directly affects episodic memory (r=0.629, p＜0.001), and there is a partial mediating effect (60.5%) of healthy lifestyle among this sample of older adults with SMCs. This study demonstrates that coping capacity and adaptation positively correlate with episodic memory in older adults with SMCs, and that these correlations are mediated by healthy lifestyle. The results suggest that older adults with poor coping capacity should be assessed and monitored regularly, and clear lifestyle-related interventions initiated by healthcare providers that promote healthy lifestyles may effectively improve coping capacity and episodic memory in this population group. Note: First author: Feilong Wang, Co-first author: Shijie li, Corresponding author: Yanni Yang

Three-dimensional (3D) serpentine mesostructures assembled by mechanics-guided, deterministic 3D assembly have potential applications in energy harvesting, mechanical sensing, and soft robotics. One limitation is that the serpentine structures are required to have sufficient bending stiffness such that they can overcome the adhesion with the underlying substrate to fully buckle into the 3D shape (global buckling). This note introduces the use of cellular substrate in place of conventional homogeneous substrate to reduce the adhesion energy and therefore ease the above limitation. A theoretical model based on energetic analysis suggests that cellular substrates significantly enlarge the design space of global buckling. Numerical examples show that the enlarged design space enables 3D serpentine structures with reduced maximum strains and resonant frequencies, which offers more possibilities for their potential applications.

Thermoelectric (TE) materials are well-known to be able to directly convert heat into electricity. In developing high-performance TE materials, the inclusions are often used to enhance its energy conversion efficiency. In this paper, an effective medium model is developed to evaluate the effective behaviors of anisotropic TE composites containing multiple inclusions. First, the non-linearly coupled TE governing equations are solved by defining two generalized field variables. Then, the effective TE properties are derived based on the fundamental idea of Eshelby’s theory and the self-consistent method, and the explicit solutions for some particular inclusion cases are given. Furthermore, the presented models are validated by finite element simulations and the effects of inclusion properties and inclusion shapes on the performance of the TE composite are discussed. The results show that specific inclusions may greatly boost the TE figure of merit of the composite. Furthermore, we apply the presented model to a commercial thermoelectric cooler(TEC) module, and find that the cooling performance can be enhanced by as much as 22.79% by inserting voids. The presented research thus sheds considerable insight into the performance evaluation of effective behavior of TE composites and may pave a new way of boosting the performance of TE devices.

The all-optical switch is one of the key elements of all-optical high speed information networks and computing systems. Their bending behavior, actuated by optical gradient forces, dramatically influences their switching performance and is therefore the research topic of this paper. The coupled behavior between optical gradient forces and the bending deflection is taken into account in the present model. The effects of the effective refractive index and the stretching induced by bending are included and their influences on the resonance wavelength shift of the signal light are discussed. Results show that the resonance wavelength shift increases almost linearly at first, and then increases suddenly as the circulating power increases. The resonance wavelength shift increases as the central angle of the suspended part increases, while it decreases with the initial gap. The present theoretical model may be helpful when designing all-optical switches.

In this paper we derive the minimal wave speed of bacteria development for a bacterial colony model with the transitions between active bacteria and inactive bacteria. The existence of traveling wave solutions is obtained by introducing an auxiliary system and applying Schauder’s fixed point theorem. The non-existence of traveling wave solutions is established with the aid of a negative one-sided Laplace transform. The upper bounds of colony waves and their energies are provided.

Harvesting mechanical vibration energy in the surrounding medium is an attractive way to provide sources for self-powered micro and nano devices. At nanoscale, the properties of materials exhibit strong scaling with size. In this paper, an analytical model incorporating flexoelectric effect is developed for nanoscale unimorph piezoelectric energy harvesters with arbitrary length and position of piezoelectric layer and proof mass. The governing equation is derived based on the Hamiltonian principle. Approximated closed-form solutions for voltage out, power output and optimal load resistance are obtained. Results show that the influence of flexoelectric effect on voltage output and power output is significant, for small thickness of piezoelectric layer. In some cases, the maximum power output of the model with flexoelectric effect is almost twelve times that of classical model which only includes piezoelectric effect. Attaching the piezoelectric layer on the clamped end of the beam can get the largest power output. To obtain higher power output and conversion efficiency, especially to fit the vibration environment, attached proof mass on the end of cantilever energy harvesters is a useful way.

In this paper, the small scale effect on the pull-in instability and frequency of graphene sheets subjected to electrostatic and van der Waals forces is studied. Eringen's nonlocal elasticity theory is used to account for the small scale effect, and the graphene sheet is modeled as a nonlocal plate. Reduce-order model incorporating nonlocal effect and van der Waals force is derived. Results show that nonlocal elasticity reduces the pull-in voltages and fundamental frequencies. The effect of nonlocal parameter on pull-in voltages and fundamental frequencies is more obvious if the size of nanoplate is smaller. In addition, an empirical formula for pull-in voltage is explored. The form of the empirical formula is relatively simple, therefore is convenient for engineers to indicate an experimental method to determine the nonlocal parameters of the materials and to design nano-switches.

In this paper, fracture behavior of a micro-scale double cantilever beam (DCB) made of superconducting materials is investigated based on the strain gradient theory. Both zero-field cooling (ZFC) and field cooling (FC) magnetization processes are considered. The closed-form solutions of the energy release rates and stress intensity factors are obtained. For ZFC process, superconducting materials are easy to damage during the process of reducing magnetic field rather than increasing magnetic field. For FC process, applied magnetic field will impede superconductors to damage. Moreover, the normalized energy release rate predicted by classical beam theory is larger than that predicted by strain gradient theory. As the characteristic length increases, the normalized energy release rate decreases. The present model may be useful for designing experiments to test the fracture toughness of micro-scale high-temperature superconductors.

Cracking is a critical issue in the preparation and application of thermoelectric materials. Traditional models for thermoelectric fracture predict infinite electric current and heat flux at the crack tip. However, it is impossible since infinite electric current and heat cannot be sustained at the atomic level. To give a physically reasonable fracture prediction of thermoelectric materials, this paper proposes an analytical model of thermoelectric fracture based on the concept of electrical and thermal field saturation along a strip at the crack front, in which we assume the electric current and heat flux cannot exceed a saturation limit. Firstly, based on the complex variable method, we derive the thermoelectric field solutions with electrical and thermal field saturation at the crack tip. Then, the thermally induced stresses and the fracture criterions are given. The results show that the thermoelectric field predicted by the saturation model exhibits no singularity at the crack tip, which may give better agreement with the experimental observations and thus shows better application potential.

Effects of surface energy on the pull-in instability and free vibration of electrostatically actuated micro/nanoscale plates are analyzed based on the modified couple stress theory. A reduced-order model is derived to consider the geometrically nonlinear strain, surface energy, the Casimir force and the material length scale simultaneously. Results show that the pull-in voltage and fundamental frequency of the plate are considerably enhanced by the material length scale, surface energy and geometrically nonlinear deformation. However, these quantities are weakened with the inclusion of Casimir force. The effects of surface energy and the material length scale become more significant if the thickness decreases. In addition, the effects of surface energy and geometrically nonlinear strain on the pull-in voltage are the largest for a square plate.

A general model for nano-cantilever switches with consideration of surface stress, nonlinear curvature, the location and length of the fixed electrode is developed. Some representative cantilever switch architectures are incorporated into this model. The governing equation is derived by using Hamilton principal and solved numerical. Results show that the influence of nonlinear curvature and surface effect on the pull-in instability and free vibration is significant for a switch with a large gap-length ratio and a short fixed electrode (the length of the fixed electrode is smaller than that of the cantilever nanobeam). The length and position of the fixed electrode have a significant effect on the pull-in parameters.

The vibration behavior of a bridged single walled carbon nanotube with a bio-mass adsorbed at various positions subjected to temperature change is investigated. The frequency equation of the sensor is derived analytically based on nonlocal Euler–Bernoulli beam theory. The relationship between the vibration frequency, the temperature change, the nonlocal parameter, the attached bio-mass and its location was obtained. Results without temperature change are compared with available results of analytical and molecular mechanics. It is found that the influence of thermal effect on the frequency and sensitivity of the biosensor is significant if its length-to-diameter ratio is large. On the other hand, the effect of nonlocal parameter on the frequency and sensitivity of the biosensor increases if its length-to-diameter ratio decreases.

The governing equation of a nanotube-based mass sensor is derived with consideration of surface energy, transverse shear deformation, and rotary inertia. Dependencies of the frequency shift and the sensitivity of the sensor on the attached mass are obtained in closed form. The results show that the traditional model, which neglects the surface energy, predicts a higher attached mass and lower sensitivity of the sensor. On the other hand, neglecting the transverse shear deformation and rotary inertia of the sensor will result in a lower prediction of attached mass and a higher prediction of sensitivity of the sensor. It is also found that the surface energy has no effect on the mode shape of the sensor. However, the effect of the location of the attached mass on the mode shape is significant. In particular, if the attached mass is close to the midpoint of the sensor, the frequency shift and sensitivity become very significant.

To study the effect of immune response in viral infections, a new mathematical model is proposed and analyzed. It describes the interactions between susceptible host cells, infected host cells, free virus, lytic and nonlytic immune response. Using the LaSalle's invariance principle, we establish conditions for the global stability of equilibria. Uniform persistence is obtained when there is a unique endemic equilibrium. Mathematical analysis and numerical simulations indicate that the basic reproduction number of the virus and immune response reproductive number are sharp threshold parameters to determine outcomes of infection. Lytic and nonlytic antiviral activities play a significant role in the amount of susceptible host cells and immune cells in the endemic steady state. We also present potential applications of the model in clinical practice by introducing antiviral effects of antiviral drugs.

A modified continuum model of the nanoscale multilayered beams is established by incorporating surface and interface energies. Through the principle of minimum potential energy, the governing equations and boundary conditions are obtained. The closed-form solutions are presented and the overall Young's modulus of the beam is studied. The surface and interface energies are found to have a major influence on the bending behavior and the overall Young's modulus of the beam. The effect of surface and interface energies on the overall Young's modulus depends on the boundary condition of the beam, the values of the surface/interface elasticity constants and the initial surface/interface energy of the system. The results can be used to guide the determinations of the surface/interface elasticity properties and the initial surface/interface energies of the nanoscale multilayered materials through nanoscale beam bending experiments.

To quantitatively study the relationship between nutritional enrichment and the oscillation of water quality, a new nutrient-plankton dynamics model is proposed in the light of a water ecosystem, such as the Three Gorges Reservoir Area. The derived results show that the plankton-free equilibrium is globally asymptotically stable if the concentration of the input nutrient is sufficient small. When nutrient recycling is absent, the zooplankton-free equilibrium is globally asymptotically stable for the middle concentration of the input nutrient, whereas the coexistent equilibrium is globally asymptotically stable for sufficient large concentration of the input nutrient. Furthermore, numerical simulation results confirm that the comprehensive effect of eutrophication by environmental pollution, nutrient recycling and excessive fishing intensity can induce the oscillation of water quality and the collapse of the water ecosystem.