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There is proposed a tunable acoustic metamaterials cell composed of a micro-electromagnetic coil as the mass element and a magnetorheological elastomer (MRE) as cladding layer. The cell resonance frequency is changed by changing the magnetic field generated by the micro-electromagnetic coil to control the shear modulus of the MRE cladding layer. The tunable bandgaps, transmission loss, and waveguides of the tunable acoustic metamaterials are investigated using the finite element method. The results show that the bandgap frequency and width, the maximum attenuation frequency and transmission loss increase with the increasing of applied magnetic field strength. Meanwhile, without changing the structure of the acoustic metamaterials, the localization, guidance, demultiplex and multiplex of elastic waves can be realized by changing the cell resonance frequency. These results will greatly contribute to the application of tunable acoustic metamaterials in vibration control, new waveguides, and filter components.

As the fatigue life prediction of wire rope has the defects of large samples and many interference factors, this paper takes the 6×31WS+FC type wire rope as research carrier. Based on small samples, the grey particle filter method has been creatively proposed to realize the wire rope fatigue life prediction under various load conditions. First, combining the reliability life data prediction with the equivalent alternating stress of the dangerous part during the fatigue test, the reliability stress-life curve was determined. Subsequently, the particle filter method has been used to modify the curve to obtain the modified P-S-N curve. Finally, with theory of fatigue damage accumulation, the fatigue life prediction model was established, and compared with the test results. The results show that based on small sample conditions, the proposed method can predict the fatigue life of wire ropes under various loading conditions with high precision, which proves the general applicability.

This paper presents a single-shot, 360-degree, and high-precision three-dimensional shape measurement for human heads based on digital image correlation and plane mirrors, which improves the matching speed of DIC by introducing multiple threads.

Background: The outbreak of the novel coronavirus disease COVID-19 caused panic and psychological stress throughout the World. We investigated the extent of adverse psychological reactions in two medical staff groups in China, and explored the importance of online psychological assistance for them.Methods: A cross-sectional online survey including Hospital Anxiety and Depression Scale (HADS) and Insomnia Severity Index (ISI) was utilized to assess anxiety, depression, and insomnia. Propensity score matching (PSM) was applied to match sex and age between the two groups. Differences in the prevalence of adverse psychological reactions between the two groups were compared by a Chi-square test. A multivariate logistic regression analysis was utilized to search for associated adverse psychological reaction factors of two groups.Results: A total of 2,920 medical staff took part in the survey, including 470 frontline and 2,450 non-frontline medical staff. The risk of the frontline group experiencing anxiety, depression, insomnia-early, insomnia-middle, and insomnia-late were 1.16, 1.28, 1.26, 1.22, 1.28 times those of the non-frontline group after PSM. For frontline medical staff, the spinsterhood state (OR = 1.23, 95% CI: 1.00–1.51; P = 0.05) was a risk factor for anxiety. Bachelor or college degree (OR = 2.23, 95% CI: 1.24–4.02, P = 0.01) and a contact history with COVID-19 patients (OR = 1.62, 95% CI: 1.10–2.40; P = 0.02) were risk factors for insomnia. For non-frontline medical staff, being a woman (OR = 1.49, 95% CI: 1.08–2.06, P = 0.01) was a risk factor for anxiety, whilst being in a middle age group was a protective factor for anxiety (OR = 0.70, 95% CI: 0.50–0.99, P = 0.04) and depression (OR = 0.65, 95% CI: 0.45–0.93, P = 0.02). Being a woman (OR = 1.47, 95% CI: 1.14–1.89, P = 0.003) and working in a COVID-19 unit (OR = 1.31, 95% CI: 1.11–1.54, P = 0.001) were risk factors for insomnia, whilst the spinsterhood state (OR = 0.80, 95% CI: 0.67–0.95; P = 0.01) was a protective factor for insomnia. Online forms of psychological aid were all popular with medical staff.Conclusions: The prevalence of anxiety, depression, and insomnia in frontline medical staff was significantly higher than in the non-frontline group. Appropriate intervention methods should be adopted according to the different influencing factors of the two groups. Online psychological aid was the preferred mechanism for relieving psychological problems.

As the new display technology, Micro-LEDs are of the advantages of low power consumption, high brightness, high resolution and fast response time. However, the strong surface non-radiative recombination significantly reduces their efficiency. Some techniques such as epitaxial growth or wet sulfide have been introduced to inhibit the surface recombination, but these expensive or unstable methods ignore the operability of industrial production. Herein, we use an ion implantation method to modify the high-density surface defects on the sidewall, thereby improve the luminous efficiency effectively by inhibiting carrier surface non-radiative recombination. The photoelectric performances of GaN-based Micro-LEDs after N ion implantation were studied. The characterization results indicated that the photoluminescence intensity of Micro-LEDs was increased by 7 times after passivation, which was attributed to the significant elimination of sidewall damage. In addition, the removal of the surface dangling bonds and oxidized nitrides (Ga–N or Ga-OH bonds) after the passivation process were further proved by Auger electron spectroscopy characterization. As a result of the N ion implantation, the external quantum efficiency of packaged Micro-LEDs chip increased about 33%. Therefore, this manuscript will provide a new direction for improving the photoelectric performance of Micro-LEDs.

In the paper, on the basis of the stress field intensity method, the internal complex wingding structure of 6 × 31SW + FC type wire rope is analyzed and calculated. As a first step, considering the weakening speed of weight function in the stress field intensity method is too fast, a modification is presented to make it more suitable for the calculation of the fatigue life of wire rope. The load spectrum of the critical locations of wire rope is then established, based on the Costello mechanical model and the actual working conditions. Through the stress field intensity method, the time history curve of stress field is then obtained. Subsequently, the fatigue life of wire rope is calculated by using the linear cumulative damage theory of fatigue. The wire rope fatigue test rig is established, and the experimental value of the fatigue life of wire rope is compared with the theoretical calculation value. The results show that the experimental load of 90 t is the demarcation point of high and low cycle fatigue of wire rope, the theoretical values and the test results are close to each other in the fatigue cycle, which proves the effectiveness of the stress field intensity method in predicting the fatigue life of the wire rope.

In order to specify proper tolerances in the product design process, the tolerance optimization model should be established properly and solved accurately. In this paper, several kinds of widely used manufacturing cost functions, including exponential function, reciprocal power function, and polynomial function, are considered simultaneously to calculate the manufacturing cost of different components. Then, the most suitable manufacturing cost function for each component is chosen so that the fitting error is minimized. After the manufacturing cost functions are determined, the tolerance optimization model is established to minimize the total cost including manufacturing cost and quality loss. In the tolerance optimization model, both assembly tolerance constraint and process accuracy constraints are considered. In order to solve the tolerance optimization model accurately, the Lagrange multiplier method is applied and closed-form solutions of optimal tolerances are established. The calculating results demonstrate that the proposed method has high accuracy.

Drug delivery systems are required to be safe, minimally invasive and effectively delivery drug to the target tissues. But delivery drugs to the eye has not yet satisfied this need. Here, we focused on examining the distribution of dexamethasone (DEX) in ocular and plasmic samples following controllable continuous sub-Tenon drug delivery (CCSDD) of dexamethasone disodium phosphate (DEXP) in rabbit, and to compare that with two traditional routes: subconjunctival injection and intravenous injection. The DEX concentration was analyzed by Shimadzu LC–MS 2010 system. In CCSDD group, during observed 24 h, the mean DEX level in collected samples from highest to lowest following in order: sclera, cornea, retina/choroid, iris, plasma, aqueous humor, lens and vitreous body. In ocular solid tissue, the DEX level in posterior segment is higher than in anatomic corresponding anterior segment, but it is opposite in ocular fluid tissue. High levels of DEX were maintained at 12 h in the ocular tissue immediately after the administration. Even at 24 h, the mean DEX concentration was 31.72 ng/ml and 22.40 ng/ml in aqueous and vitreous, respectively. In CCSDD group, the ocular DEX exposure (AUC0-24) is much higher and plasma exposure is much less than IV group, and it is also similar in SC group except iris. The amount of DEX levels are markedly increased in ocular tissues but it yield lower plasma levels indicating reduction of systemic absorption by CCSDD. Thus, CCSDD is an effective method of delivering DEX into anterior and posterior segment of the eye.

Corticosteroids have been used for treatment of posterior segment eye diseases, but the delivery of drug to the posterior segments is still a problem to resolve. In our study, we explore the feasibility of Sub-tenon’s Controllable Continuous Drug Delivery to ocular posterior segment. Controllable continuous sub-tenon drug delivery (CCSDD) system, intravenous injections (IV) and sub-conjunctival injections (SC) were used to deliver dexamethasone disodium phosphate (DEXP) in rabbits, the dexamethasone concentration was measured in the ocular posterior segment tissue by Shimadzu LC-MS 2010 system at different time points in 24 h after first dose injection. Levels of dexamethasone were significantly higher at 12, 24 h in CCSDD than two other approaches, and at 3, 6 h in CCSDD than IV in vitreous body (p

At present, the world economy is developing rapidly and product life cycle become more and more short. But the resources on the earth are limited, leading to the rapid decline of available resources. For these reasons, sustainable development has become an inevitable choice. As a sustainable strategy, remanufacturing has received the attention of many researchers and is widely adopted in the industry. In this paper, selective assembly for remanufacturing engine is researched. In most research about selective assembly, the number of groups is fixed. In this paper, the number of groups and the range of each group are changeable, and the assembly accuracy is improved efficiently.

The micro lighting-emitting diode (Micro-LED) array devices have attracted attention due to increasing demand in augmented reality (AR), virtual reality (VR), LIFI light source, and other micro-display applications. However, with the decrease of micro-LED diameter, the performance of micro-LED is severely limited due to the size effect. In the work, the AlGaInP based red micro-LED with diameter ranging from 2 to 16 μm was prepared to study the size effect of micro-LED array, the array with larger micro-LED diameter show higher external quantum efficiency (EQE), meanwhile, the carrier lifetime decrease with the decreasing of the diameter, which can be explained by more surface states in the micro-LED with smaller diameter. The enhancement of EQE by 2 times has been achieved after surface passivation in (NH4)2Sx solution.

Piezoelectric energy harvesting techniques provide a promising way to transform the vibration energy into electric energy. Since the voltage output peak can drop due to the frequency excitation moving away from the resonance region, the on broadening the bandwidth of operation frequency has drawn great attention. In the paper, a novel two-degree-of-freedom piecewise-linear piezoelectric energy harvester is proposed to achieve wide operation frequency bandwidth by combining the multimodal harvesting technique and nonlinear method. Based on the average method, the analytical solution of the proposed device is achieved. From analytical and experiment results, at an excitation acceleration of 0.3 g, as the excitation frequency is up sweeping, the system achieves frequency bandwidth operation of 7.4 Hz which is about 5.2 times higher to that of conventional two-degree-of-freedom linear harvester, and the power outputs for the first and second resonances can reach up to 429 μW and 411 μW, respectively. Due to the close agreement between the calculated values and experiment results, the analytical solution and the theoretical model could be applied to further MEMS fabrication process and optimized design.

The aim of this study was to investigate the plasma and ocular dexamethasone (DEX) pharmacokinetics characteristics of the sub-tenon microfluidic system (SMS) delivery of dexamethasone sodium phosphate (DEXP) in experimental autoimmune uveitis (EAU) rabbits. The SMS showed sustained DEX release and large amount of drug loading capacity by a miniature pump which connected with a tube that implanted into the sub-Tenon's sac of the EAU rabbit. The DEX concentrations in the plasma and different ocular compartments (cornea, aqueous humor, retina/choroid, sclera and vitreous humor) were quantified by Shimadzu LC–MS 2010 system. The SMS increased total drug delivery of DEX in ocular tissues as compared with traditional combined medication (subconjunctival injection combined with intravenous injection) in EAU rabbit. Moreover, the minimal amount of DEX was found in the blood, indicated that only a small amount of drug could enter into the bloodstream and causing minimal systematic side effect. Overall, the study provided evidence that SMS meet the large amount of drug loading capacity, continuous release drugs and moderate drug level in the EAU ocular tissue and minimal drug level in the blood, which indicated that SMS could be a feasible option for ocular application in clinical trials and maybe can replace or even discard systemic medications for the management of acute ocular inflammation disease.

The fatigue life prediction of wire rope has the characteristics of large sample size required and many uncertain factors. In this paper, the 40 6 × 31SW FC type wire rope is taken as the research object. Under the condition of fatigue life data of small sample size, the fatigue life prediction of wire rope under different load conditions is realized based on gray theory. As a first step, for the problems existing in the current fatigue life prediction of wire rope, this paper constructs an improved GM (1,1) model and predicts the reliability life data of wire rope under small sample size condition. Subsequently, based on this, combined with the equivalent alternating stress of the critical locations of wire rope during the fatigue test, the reliability stress-life curve of the critical locations of wire rope is determined; Finally, the fatigue life prediction model of wire rope is obtained by combining with the cumulative damage theory of fatigue. The fatigue life of wire rope under different loads is predicted and compared with the experimental value. The results show that the proposed method has high accuracy in predicting the small sample fatigue life of wire rope under single and combined loading conditions, which proves the effectiveness of this method.

With the high development of computer technology and communication technology, computer system is facing a growing number of attacks.So, the security of computer system has become study focus in the world. This paper described the security architecture of the computer systems, mainly:ISO7498-2 security architecture and adaptive network security system model.Then, the requirements of the security technology were described by the information security and physical security.Finally, the core technologies of security system were studied in detail: encryption and firewall technology.

With the advent of the ambassador and the rapid development of construction of a high-speed network, digital network resource sharing has penetrated into people's daily work, study and life. Data network storage by which many people share resources, becomes an important way of modern information dissemination and preservation. However, the security of the network storage platform has been a concern to users. Therefore, all kinds of private cloud storage platforms emerge, provide the users with a relatively independent space for personal use. After a long period of use, it is found that the traditional private cloud storage platform can reach a certain amount of security, however, the security is only relative to open public network location. At the same time, there are multiple users under instantaneous access protocol congestion, and big-data feedback delays the problem of high interaction nodes. In view of the traditional architectural characteristics and problems of private cloud causes, the paper, based on the NAS, puts forward private cloud storage platform design and implementation method. The agreement is based on the NAS encryption technology, the optimization of multiple access unit, data compression unit to solve the problems existing in the traditional private cloud. The simulation experiments show that the private cloud storage platform based on the NAS method, the design and implementation of a data storage security access point is high, the peak condition good network smooth general characteristic, high data rate of network transmission interaction, and the advantages of small delay.

A kind of phononic crystal shaft with piezoelectric ceramic circular rings is proposed in this paper. Based on the wave equation, the propagating characteristics of torsional wave are calculated by the transfer matrix method. The torsional wave band structures of infinite piezoelectric phononic crystal shaft (PPC shaft) and transmission curves of finite PPC shaft are analyzed, then simulations are carried out to verify the theoretical results by using ANSYS software. Furthermore, the effects of outer active control on the torsional wave band gaps are considered by changing feedback control gains. The influences of the ratios of length and cross-sectional area on the band gaps are also discussed in detail. Results show that there exist band gaps of torsional vibration in this special PPC shaft and the width together with the position of the band gaps can be adjusted effectively by varying structural parameters and outer active control gains.

Piezoelectric thin rings are periodically introduced and placed on a base plate along the radial direction, forming a one-dimensional thin circular plate of piezoelectric radial phononic crystals (CPPRPC). Based on flexural wave equation of thin circular plate and the transfer matrix method, the behavior of flexural waves propagating in CPPRPC is analyzed theoretically and numerically, especially in the band gaps. The transmission curves of CPPRPC and homogeneous-material plate are calculated for comparison. Afterwards finite element simulations are carried out to verify the theoretical results. Furthermore, the effects of the length ratio, thickness ratio, period number and control gain on the flexural wave band gap are discussed in detail. Our results show that there are band gaps of flexural wave in CPPRPC. Structural parameters and outer active control gain have important influences on the band gaps. In particular, low and broad band gaps can be obtained effectively by varying outer active control gain.

The quasi-zero stiffness (QZS) nonlinear isolators have been paid much attention in recent literatures due to their excellent vibration isolation performance under low frequency excitation compared to traditional linear vibration isolators. However, passive QZS isolators are the most widely studied and they are incapable of dealing with varying conditions such as changing the excitation frequency or load in operating state. To promote the adaptability of QZS isolators, a novel approach to achieve real-time controllable quasi-zero stiffness is proposed in this paper. An electromagnetic negative stiffness unit comprised of two electromagnet with MR elastomer is employed to produce negative stiffness, and the stiffness characteristic of the system can be accurately controlled by adjusting the driving current according the displacement information in real time. Theoretical calculation and finite element analysis is conducted to establish the exact model of electromagnetic force followed by the general design of the system. Then a customized driver is developed for electromagnetic negative stiffness unit, and the dynamic model of the isolator is set up to study the effect of relative parameters on the transmissibility. Finally, a series of experiments are performed to evaluate the real-time controllable QZS characteristic and confirm the vibration isolation effect of the proposed electromagnetic QZS isolator.

For the non-destructive testing of wood moisture content, lack of economical and effective method was still a big challenge for wood industry. Aiming at this problem, a new method was put forward which combined the testing and the mathematics. This method had not any demands to the shape of wood, the distribution of wood moisture content and the positions of wood and electrode plates. At the same time, the corresponding numerical example was given. The numerical results were quite coincident with the experimental results. Compared with previous methods, the new method decreased test working greatly and avoided the waste of medium resource. It made the measurement fast and effective.

In the past, research of magnetorheological (MR) damper mainly focused on how to improve the damping force, response speed and the performance of its control algorithm. With the increasing application of MR dampers in engineering, the adaptability of MR dampers is required to have a greater dynamic range of damping force to achieve better vibration isolation effect in different frequencies. In order to satisfy this demand, an outer multi-pole MR damper is proposed in this paper, which adopts the design of multiple electromagnetic poles integrated in cylinder to obtain greater control range of damping force. A mathematical model of the damping force is established for the proposed MR damper followed by the general structure design of the MR damper, and optimal design is conducted to determine the main structure parameters. 3D analysis of magnetic circuit is conducted utilizing the finite element method, which is used to calculate the magnetic intensity in different areas of the MR damper. Based on the data of magnetic simulation, the mechanical characteristics of the MR damper are numerically simulated. The proposed MR damper is then manufactured and the damping force characteristics are experimentally investigated and compared with other MR dampers in previous studies. The results reveal that the dynamic range of the proposed MR damper is much larger than conventional MR dampers.

For our research, a new hybrid experimental-computational method is presented. We applied a least squares fitting method (LSFM) to reconstruct the wood moisture content (WMC) from the data measured with a planar capacitance sensor. A boundary element method (BEM) was used to compute the relationship between capacitance and the dielectric constant. A functional relationship between MC and the dielectric constant was identified by LSFM. The agreement of this final computation result with the experimental data indicates that this method can be used to estimate the WMC quickly and effectively with engineering analysis. Compared with popular statistical methods, a large number of experiments are avoided, some costs of testing are reduced and the efficiency of testing is enhanced.

A fire fighting cannon is fire-fighting equipment developed for fighting against forest fires; it is considered the tree crown fire and the inaccessible areas which are dangerous for man to get close as extinguishing object. The forest fire fighting cannon is launched by pneumatic method; the timing device within the extinguishing shell will be triggered after launching. After the free-flying and the parachute deceleration phase, the shell will detonate while the temperature in the fire field detected by the temperature sensor arrives at the setting value. The control system of the fire extinguishing cannon was designed firstly, the fly ballistic trajectories were analyzed and calculated, which are involved with the interior ballistic in the process of launching, the exterior ballistics analysis in the state of free-flying with non-parachute and the process of deceleration flight with parachute open. The ballistic calculation provides control with the necessary parameters.

For the propagation of harmonic longitudinal stress wave in phononic crystal rod (PCR), transfer matrix of elastic wave in PCR was derived based on the wave equation and band structure of infinite PCR was calculated. For semi-infinite PCR, theoretical derivation of dynamic stress solutions of arbitrary section and internal interfaces was conducted with Bloch theorem. Inherent relationship between dynamic stress and surface wave modal frequency (SWMF) was analyzed. Afterwards, numerical computation mainly focusing on dynamic stress level of the internal interfaces of PCR was given in detail. Finally, numerical analysis for finite PCR was carried out and verified by finite element simulation. Our results show that SWMF has a significant influence on the dynamic stress, and exactly it is the formal pole of stress solution whose nature is directly determined by the sort order of the two materials constituting the PCR.

This paper presents a model to predict the effect of spherical-tipped additional supports on the surface errors in the peripheral milling of a flexible workpiece. The model takes into account the instantaneous change of cutting forces during the milling process, the change of contact stiffness between the workpiece and spherical-tipped additional supports, and the change of workpiece thickness during the milling process. At each cutter angular step, contact stiffness between the workpiece and spherical tipped additional supports is calculated by an iterative method. According to the contact stiffness at each cutter angular step, the surface errors of the workpiece are calculated. At last, an experiment is executed to verify the model.