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To improve the gas driving performance of the piezoelectric gas driver, this paper proposes a piezoelectric gas jet pump that uses the ultrasonic near sound field of the piezoelectric transducer to excite the gas mass points to oscillate and form a gas jet. The working characteristics of the pump are studied theoretically and experimentally. The distribution law of the sound field excited by the transducer in the sixth-order vibration mode is obtained through simulation analysis. Then the prototypes are designed through calculating the Reynolds number and Stokes number of the gas jet excited by ultrasonic near sound field. And the calculation results show that there is a direct relationship between the gas driving ability of the jet pump and the radiated sound pressure of the transducer. On this basis, the experiments are conducted and the results show that the gas driving performance is significantly affected by the position of the jet hole. When the jet hole is arranged in the central area of the piezoelectric transducer, the gas driving performance of the jet pump is the best. When the driving voltage is 80 Vpp and the driving frequency is 20.4 kHz, the gas flow rate reaches 0.39 L/min.

The conductive foamed silicone rubber was prepared by Polymethylvinylsiloxane (PMVS) mixed with acetylene black, fumed silica, and AC foaming agent (azodicarbonamide). Influences of fillers on the microstructure, electrical conductivity and mechanical property were discussed. The results showed that the pore structure was affected by acetylene black. Acetylene black delayed the vulcanization speed of silicone rubbers, leading to bigger pores. Higher content of acetylene black decreased the mechanical properties and the electrical resistivity of rubbers. Fumed silica increased the mechanical properties and limited the aggregation of gas. Higher content of fumed silica led to small and obturator pores generated. Higher content of fumed silica increase the mechanical properties and the electrical resistivity of rubbers. AC foaming agents generated more gas, leading to bigger and irregular pores which affected the mechanical properties negatively, meanwhile AC foaming agents increased the conductivity of rubbers.

Selective cyclooxygenase (COX)-2 inhibitors have been extensively studied for colorectal cancer (CRC) chemoprevention. Celecoxib has been reported to reduce the incidence of colorectal adenomas and CRC but is also associated with an increased risk of cardiovascular events. Here, we report a series of gut-restricted, selective COX-2 inhibitors characterized by high colonic exposure and minimized systemic exposure. By establishing acute ex vivo 18F-FDG uptake attenuation as an efficacy proxy, we identified a subset of analogues that demonstrated statistically significant in vivo dose-dependent inhibition of adenoma progression and survival extension in an APCmin/+ mouse model. However, in vitro-in vivo correlation analysis showed their chemoprotective effects were driven by residual systemic COX-2 inhibition, rationalizing their less than expected efficacies and highlighting the challenges associated with COX-2-mediated CRC disease chemoprevention.

The viscoplastic behavior of solder material is investigated from different scales. Due to the thermal stress in Sn–3.0Ag–0.5Cu alloy at elevated temperatures, the continuous accumulation of unrecoverable deformation becomes the key of interconnections failure in microelectronic packaging. In the current study, the rate and temperature dependence of inelastic deformation and cyclic hardening properties of Sn–3.0Ag–0.5Cu alloy under different loading conditions are studied. A novel phenomenological constitutive model is developed to describe the deformation of lead-free solder interconnections in the microelectronic packaging. The developed model is verified by comparing with the experimental data of bulk solder materials. The results show that the proposed model can accurately describe the viscoplastic properties of bulk solder materials and shows excellent numerical stability. For understanding better the overall deformation behaviors of solder joins, especially the strain–stress relationship, uniaxial compression experiments of spherical joint-scale granules were conducted under different loading rates. The developed model is applied to simulate the compression testing of granules. It shows that the developed model can characterize the viscoplastic compression deformation of Sn–3.0Ag–0.5Cu solder on joint-scale with reasonable accuracy.

Silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The forming SiOx with layered graphene as the 3D network had amorphous carbon layer.

Under asymmetrical stress-controlled cyclic loading accompanied by ratcheting, the evolution of microscopic substructures of stainless steel 304 (SS304), a face-centered cubic metal, was detected using transmission electron microscopy (TEM). This observation demonstrates that dislocation slip is the main mechanism of uniaxial ratcheting in the non-steady stage (stage I). Dislocation proliferate rapidly duo to the high stress level of the cyclic tests, and dislocation density increases continuously with the the number of cycles. The ratcheting rate decreases continuously due to the interaction of moveable dislocations, and the planar dislocation substructures (dislocation pileups and tangles) are the dominant patterns in this stage. In the later stage I, distinct lath $$\alpha $$ -martensite was observed in the material due to the nucleation of martensite and the phase transformation zones increase gradually with the growth of axial ratcheting strain in the stage II of uniaxial ratcheting. The multiply and cross-slip were activated gradually in increasing numbers of grains, and the prevailing dislocation configurations evolve into more complicated and stable ones (dislocation walls and cells). In addition the dislocation configurations after various prescribed tensile strain of the monotonic tension and creep deformation with three different holding times were also observed by TEM. Comparing the evolution of microscopic substructures in various loading modes, the physical mechanism of uniaxial ratcheting of SS304 can be revealed as combination of the evolution of dislocation configurations and martensite transformation in the stage II of uniaxial ratcheting.

The frequent use of location query services in location-based services will come out a large amount of space-time data related to users. Attackers infer information of location or track based on these rich background knowledge. Therefore, aiming at the problem of trajectory privacy, the context adds instant traffic monitoring based on user behavior patterns, trajectory similarity and other background information. According to the idea of k anonymity, proposed a method combined with traffic condition to protect the trajectory privacy. First, the user randomly selects a time point of the real trajectory to rotate to generate dummy trajectory, and then repeat the above process on the real trajectory and dummy trajectory. Up to the generation of k − 1 dummy trajectory, and according to the actual road conditions and trajectory leakage probability, traversing dummy trajectory to adjust. Finally, it is further proved through experiments that the method will be more efficient and protect privacy well.

As the air pollution particulate matter (PM10) is affected by a variety of factors, especially meteorological factors, resulting in a high degree of complexity and volatility of PM10. However, the existing research does not well deal with the multi-factor PM10 forecasting and is limited to the deterministic point forecast of PM10 concentration and does not consider the interval forecast related to uncertainty. To solve these issues, a novel multivariate interval decomposition ensemble approach is proposed for PM10 concentration forecasting, integrating multi-factor selection, data decomposition, intelligent forecasting network and evaluation system. The stability and robustness of this approach have been tested in three cities with different economic characteristics in China, and the results show that our proposed approach is superior other benchmark models in point forecasting and 80% interval forecasting. Our proposed approach is a promising PM10 concentration forecasting approach, which can enable the government to accurately forecast PM10 concentration and make more effective measures to control and manage the adverse effects of air pollution on the current economy and health.

Social network contains the interaction between social members, which constitutes the structure and attribute of social network. The interactive relationship of social network contains a lot of personal privacy information. The direct release of social network data will cause the disclosure of privacy information. Aiming at the dynamic characteristics of social network data release, a new dynamic social network data publishing method based on differential privacy was proposed. This method was consistent with differential privacy. It is named DDPA (Dynamic Differential Privacy Algorithm). DDPA algorithm is an improvement of privacy protection algorithm in static social network data publishing. DDPA adds noise which follows Laplace to network edge weights. DDPA identifies the edge weight information that changes as the number of iterations increases, adding the privacy protection budget. Through experiments on real data sets, the results show that the DDPA algorithm satisfies the user’s privacy requirement in social network. DDPA reduces the execution time brought by iterations and reduces the information loss rate of graph structure.

A silane containing isocynate groups (3-(trimethoxysilyl) propyl cyanic acid ester, NCO) associated with hexamethyldisilazane (HDMS) is used to modify the surface of poly-(p-phenylene terephthalamide) (PPTA) pulps. As concerns surface chemistry, Attenuated Total Reflection Flourier Transformed Infrared Spectroscopy (ATR FT-IR) and X-ray photoelectron spectroscopy (XPS) confirm that NCO associated with HDMS silylated PPTA pulp surface successfully. While the modified PPTA pulps are used as reinforcing fillers for silicone composites, the dispersibility and storage stability of the composites are improved as Mooney testing indicated. The silicone composites filled with modified PPTA pulps present a higher tensile strength and much higher broken elongation (3.30 MPa and 166.54%) than that with unmodified pulps (3.08 MPa and 68.47%), respectively.

A silicone peroxide, tris(tert-butyldioxy)-vinyl-silane (VTPS), was adopted for carbon fibers (CFs) surface modification to improve the mechanical properties of CFs reinforced polydimethylsiloxanes (PDMS) composites. FT-IR and XPS confirmed that the Si-CH=CH2 groups, which could generate covalent bonds between CFs and PDMS, were chemically bonded to CFs surface. And the method gave no obvious damage to CFs as shown by SEM and tensile strength analysis. After VTPS modification, the interfacial shear strength (IFSS) between CFs and PDMS was increased, and then the mechanical properties of CFs/PDMS composites were greatly improved (tensile strength from 0.59 to 0.90 MPa, tear strength from 0.83 to 3.65 kN/m).

The surface of carbonyl iron powder (CIP) was modified in supercritical fluid with silicone polymers containing reactive Si-OCH3 groups. Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and thermo gravimetric analysis were adopted to characterize CIP. The dispersibility of CIP in epoxy resin matrix was evaluated by castor oil absorption factor, dynamic viscosity, Mooney viscosity, and scanning electric micrograph. The electromagnetic reflectivity of the CIP-filled epoxy resin coatings was also checked. It was confirmed that comparing with those treated at atmosphere, the supercritical treated CIP presented higher surface carbon content, higher dispersibility, higher thermal stability, and its original crystalline structure did not change greatly. Even though it experienced a high temperature and a high pressure (250 °C, 7.8 Mpa) during supercritical treatment, it was not oxidized, and its electromagnetic reflectivity did not decrease. Copyright © 2016 John Wiley & Sons, Ltd.

Cloud task scheduling affects the overall operating efficiency of the cloud platform. Thus, how to effectively use resources in the cloud environment and make massive tasks to implement a reasonable and efficient scheduling becomes more crucial. Firstly, the mathematical model of cloud task computing was reconstructed by adding the expected completion time to the task. Secondly, on the basis of the completion time as the fitness function, the task priority was dynamically adjusted by user satisfaction, which was added to reduce the user’s completion time and improve the user’s satisfaction. Thirdly, aiming at the continuous search space, a cloud task scheduling algorithm based on the Symbiotic Organisms Search (CTS-SOS) was proposed. Not only does the CTS-SOS have fewer specific parameters, but also take a little time complexity. Through using the CloudSim toolkit package, the CTS-SOS algorithm was compared with Round Robin algorithm of the CloudSim and ACO algorithm. Experimental results show that CTS-SOS can provide a better optimization and scheduling of resources, reduce the makespan effectively, and improve the efficiency of processing tasks and user’s satisfaction.

In the framework of crystal plasticity, a dislocation-based cyclic polycrystalline visco-plastic constitutive model is proposed to describe the ratchetting of the metals with a face-centered cubic (FCC) crystal structure. A new rate-dependent flow rule considering the thermal activation energy of dislocation slipping is developed, and a dislocation-based Armstrong-Frederick non-linear kinematic hardening rule is introduced to provide a better prediction to the ratchetting. The isotropic hardening associated with the short-ranged interactions of dislocations is represented by the evolution of critical shear stress in each slip system. Comparing the prediction with corresponding experimental results, it is shown that the uniaxial and multiaxial ratchetting of polycrystalline 316L stainless steel are reasonably described by the proposed model. The dependence of the intra-granular ratchetting on the crystallographic orientation of grains can be also reflected by the model.

The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasing applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the constructionmore » of corresponding constitutive model. - Highlights: • A three-staged ratchetting occurs in the stress-controlled cyclic tests of Ti–6Al–4V alloy. • Dislocation patterns change from discrete lines to nets and parallel lines. • Deformation twinning occurs during the uniaxial ratchetting. • Both dislocation slipping and twinning are the causes of ratchetting.« less

With the hypothesis of a small deformation, the novel cyclic visco-plasticity constitutive model (CV-CM) is constructed to study the cyclic deformation responses of polycrystalline metals. In this model, a modified Armstrong–Frederick nonlinear kinematic hardening (NKH) law is adopted to simulate the ratchetting deformation more precisely. The cyclic hardening characteristic of FCC polycrystalline copper is investigated with the use of flow stress evolution of slip system. For the issue of the transition from single crystal to polycrystalline crystals, the explicit [Formula: see text] rule is introduced to compute the polycrystalline response. Finally, through comparison with the experimental data, the proposed model is verified. It is demonstrated that the uniaxial ratchetting response of FCC metal can be precisely captured. The ratchetting response of copper single crystal and its relation with the crystallographic directions can be exactly traced by the present model as well.

The multiaxial ratcheting behaviors of polycrystalline 20 ordinary carbon steel were investigated at room temperature. The macroscopic experimental results showed that the studied multiaxial ratcheting depends greatly on the mean stress, stress amplitude and loading path. The axial ratcheting strain increased with the increase of applied mean stress and stress amplitude. Apparent additional hardening was observed in the non-proportionally multiaxial cyclic loading. The multiaxial ratcheting of 20 carbon steel was lower than the corresponding uniaxial one and varies with different loading paths. Dislocation patterns and their evolutions of the multiaxial ratcheting of different loading paths were then investigated using transmission electron microscopy. The obtained images showed that, with the increasing number of loading cycles, the dislocation patterns evolved from dislocation lines and networks to dislocation tangles, walls and cells. After certain cycles, sub-grains were formed because of the re-arrangement of dislocations in the walls of cells and inside the cells since the cross slip of dislocations can be easily activated for the 20 carbon steel, a kind of body-centered cubic metal. The dislocation evolution of the multiaxial ratcheting is much quicker than that of the uniaxial one. With the reference to the uniaxial one of 20 carbon steel, the macroscopic multiaxial ratcheting behaviors can be qualitatively correlated with the microscopic observation of the dislocation patterns and their evolution.

Dislocation patterns and their evolutions in 316 L stainless steel during the multiaxial ratchetting deformation were observed by transmission electron microscopy (TEM). The microscopic observations indicate that the dislocation evolution presented during the multiaxial ratchetting with four kinds of multiaxial loading paths is similar to that in the uniaxial case [G. Z. Kang et al., Mater Sci Eng A 527 (2010) 5952]. That is, dislocation networks and dislocation tangles are formed quickly by the multiple-slip and cross-slip of dislocation activated by applied multiaxial stress; and then polarized patterns such as dislocation walls and elongated incipient dislocation cells are formed at the last stage of multiaxial ratchetting. The dislocation patterns evolve more quickly from the modes at low dislocation density to the ones at high density during the multiaxial ratchetting than that in the uniaxial case, and some traces of multiple-slip are observed in the multiaxial ones. The dislocation evolution during the multiaxial ratchetting deformation is summarized by comparing the observed dislocation patterns with those presented in the multiaxial strain-controlled and symmetrical stress-controlled cyclic tests. The multiaxial ratchetting of 316 L stainless steel can be microscopically and qualitatively explained by the observed evolution of dislocation patterns.

The uniaxial ratchetting of polycrystalline 20 ordinary carbon steel (denoted as 20CS), a body-centred cubic (BCC) crystal structure metal, was investigated by macroscopic and microscopic observations at room temperature. The microscopic observations were performed by transmission electron microscopy (TEM) to the samples of 20CS obtained at different stages of monotonic tension, strain-controlled cyclic tension–compression and uniaxial ratchetting deformation. Main attention was paid on the dislocation patterns and their evolution during the ratchetting deformation. The results show that the dislocation patterns evolve from some low density modes such as dislocation lines and networks to those with high density, i.e., dislocation tangles, walls and cells. And then, sub-grain structures are formed by the re-arrangement of dislocation after certain number of cycles during the ratchetting deformation. The uniaxial ratchetting of 20CS is qualitatively explained by considering the observed dislocation patterns and their evolution with the increasing number of cycles and comparing with the patterns observed during the monotonic tension and strain-controlled cyclic tension–compression tests.

The uniaxial ratcheting behaviors of several metals with different crystal structures or values of fault energy were observed by the stress-controlled cyclic tests at room temperature. The prescribed metals included 316L stainless steel, pure copper, pure aluminum, and ordinary 20# carbon steel. The effects of applied mean stress, stress amplitude and stress ratio on the uniaxial ratcheting were also investigated. The observations show that different crystal structures or values of fault energy result in more or less different ratcheting behaviors for the prescribed metals. The different ratcheting behaviors are partially caused by the variation of dislocation mobility.

Dislocation patterns and their evolution in 316L stainless steel subjected to uniaxial stress-controlled cyclic loading with occurrence of ratchetting deformation were observed by transmission electron microscopy (TEM). The microscopic observations show that the dislocation patterns change from low density patterns such as dislocation lines and pile-ups to those with higher dislocation density such as dislocation tangles, veins, walls, and cells, when the macroscopic ratchetting strain progressively increases with the number of cycles. Although one or two kinds of dislocation patterns mentioned above are prevailing in most of the grains at certain stage of ratchetting deformation, other patterns can be also observed in some grains at the same time. The features of dislocation evolution presented during the uniaxial ratchetting deformation are summarized by comparing with the dislocation patterns observed during monotonic tension and symmetrical uniaxial strain-controlled cyclic loading. The uniaxial ratchetting of 316L stainless steel can be qualitatively explained by the observed dislocation patterns and their variation with the number of cycles.

The fatigue failure of a super-elastic NiTi alloy was observed by uniaxial stress-controlled cyclic tests. During the cyclic loading a hysteresis loop with a varied but stabilized size after certain cycles was obtained, which is similar to plastic shakedown. The material exhibits unique brittle fracture with a large transformation strain. The fatigue life of the material greatly depends on the applied peak nominal stress, the nominal stress amplitude and the mean nominal stress. A relation between the dissipation energy at the stabilized stage of cyclic loading and the number of cycles at failure was derived from the experimental results. Based on the obtained experimental results, a uniaxial fatigue failure model based on the energy approach was proposed to predict the fatigue life. It was shown that the proposed model provides good predictions to the uniaxial fatigue lives of super-elastic NiTi alloys with different types of cyclic stressing.

The ratcheting behaviors and fatigue failure, as well as their interaction were investigated by uniaxial cyclic stressing tests for 20 carbon steel at room temperature. The ratcheting strain and fatigue life of the material were measured in varied loading levels. The effects of mean stress, stress amplitude and stress ratio on the ratcheting strain and final failure life were discussed. The experimental results show that the ratcheting strain and fatigue life of the material greatly depend on mean stress, stress amplitude and stress ratio in asymmetric stress cycling, and two kinds of failure modes (i.e., ratcheting failure due to large ratcheting strain and fatigue failure caused by the fatigue crack) occur respectively, depending on the applied stress level in the tests.