C.Q. Chen

Bipolar resistive switching in Cu/AlN/Pt nonvolatile memory device

Highly stable and reproducible bipolar resistive switching effects are reported on Cu/AlN/Pt devices. Memory characteristics including large memory window of 103, long retention time of >106 s and good endurance of >103 were demonstrated. It is concluded that the reset current decreases as compliance current decreases, which provides an approach to suppress power consumption. The dominant conduction mechanisms of low resistance state and high resistance state were verified by Ohmic behavior and trap-controlled space charge limited current, respectively. The memory effect is explained by the model concerning redox reaction mediated formation and rupture of the conducting filament in AlN films.

Vibroacoustic behavior of clamp mounted double-panel partition with enclosure air cavity

A theoretical study on the vibroacoustic performance of a rectangular double-panel partition clamp mounted in an infinite acoustic rigid baffle is presented. With the clamped boundary condition taken into account by the method of modal function, a double Fourier series solution to the dynamic response of the structure is obtained by employing the weighted residual method (i.e., the Galerkin method). The double series solution can be considered as the exact solution of the problem, as the structural and acoustic-structural coupling effects are fully accounted for and the solution converges numerically. The accuracy of the theoretical predictions is checked against existing experimental data, with good agreement achieved. The influence of several key parameters on the sound isolation capability of the double-panel configuration is then systematically studied, including panel dimensions, thickness of air cavity, elevation angle, and azimuth angle of incidence sound. The present method is suitable for double-panel systems of finite or infinite extent and is applicable for both low- and high-frequency ranges. With these merits, the proposed method compares favorably with a number of other approaches, e.g., finite element method, boundary element method, and statistical energy analysis method.

Mechanisms of Bimaterial Attachment At the Interface of Tendon to Bone

The material mismatch at the attachment of tendon to bone is amongst the most severe for any tensile connection in nature. Attaching dissimilar materials is a major challenge in engineering, and has proven to be a challenge in surgical practice as well. Here, we examine the material attachment schemes employed at this connection through the lens of solid mechanics. We identify four strategies to that the body adopts to achieve effective load transfer between tendon and bone: 1) a shallow attachment angle at the insertion of transitional tissue and bone, 2) shaping of gross tissue morphology of the transitional tissue, 3) interdigitation of bone with the transitional tissue, and 4) functional grading of transitional tissue between tendon and bone. We provide solutions to model problems that highlight the first two mechanisms, discuss the third qualitatively in the context of engineering practice, and provide a review of our earlier work on the fourth. We study these strategies both in terms of ways that biomimetic attachment might benefit engineering practice, and of ways that engineering experience might serve to improve surgical healing outcomes.

External Mean Flow Influence on Noise Transmission Through Double-Leaf Aeroelastic Plates

The transmission of external jet noise through the double-leaf skin plate of an aircraft cabin fuselage in the presence of external mean flow is analytically studied. An aeroacoustic-elastic theoretical model is developed and applied to calculate the sound transmission loss versus frequency curves. Four different types of acoustic phenomenon (i.e., the mass-air-mass resonance, the standing-wave attenuation, the standing-wave resonance, and the coincidence resonance) for a flat double-leaf plate as well as the ring frequency resonance for a curved double-leaf plate are identified. Independently of the proposed theoretical model, simple closed-form formulas for the natural frequencies associated with the preceding acoustic phenomena are derived using physical principles. Excellent agreement between the model predictions and the closed-form formulas is achieved. Systematical parametric investigation with the model demonstrate that the presence of the mean flow as well as the sound incidence angles substantially affect the sound transmission behavior of the double-leaf structure. The influences of the panel curvature together with cabin internal pressure on jet noise transmission are also significant and should be taken into account when designing aircraft cabin fuselages.

Modelling the mechanics of partially mineralized collagen fibrils, fibres and tissue

Progressive stiffening of collagen tissue by bioapatite mineral is important physiologically, but the details of this stiffening are uncertain. Unresolved questions about the details of the accommodation of bioapatite within and upon collagens hierarchical structure have posed a central hurdle, but recent microscopy data resolve several major questions. These data suggest how collagen accommodates bioapatite at the lowest relevant hierarchical level (collagen fibrils), and suggest several possibilities for the progressive accommodation of bioapatite at higher hierarchical length scales (fibres and tissue). We developed approximations for the stiffening of collagen across spatial hierarchies based upon these data, and connected models across hierarchies levels to estimate mineralization-dependent tissue-level mechanics. In the five possible sequences of mineralization studied, percolation of the bioapatite phase proved to be an important determinant of the degree of stiffening by bioapatite. The models were applied to study one important instance of partially mineralized tissue, which occurs at the attachment of tendon to bone. All sequences of mineralization considered reproduced experimental observations of a region of tissue between tendon and bone that is more compliant than either tendon or bone, but the size and nature of this region depended strongly upon the sequence of mineralization. These models and observations have implications for engineered tissue scaffolds at the attachment of tendon to bone, bone development and graded biomimetic attachment of dissimilar hierarchical materials in general.

Sound Transmission Through Simply Supported Finite Double-Panel Partitions With Enclosed Air Cavity

The vibro-acoustic performance of a rectangular double-panel partition with enclosed air cavity and simply mounted on an infinite acoustic rigid baffle is investigated analytically. The sound velocity potential method rather than the commonly used cavity modal function method is employed, which possesses good expandability and has significant implications for further vibro-acoustic investigations. The simply supported boundary condition is accounted for by using the method of modal function and the double Fourier series solutions are obtained to characterize the vibro-acoustic behaviors of the structure. The results for sound transmission loss, panel vibration level, and sound pressure level are presented to explore the physical mechanisms of sound energy penetration across the finite double-panel partition. Specifically, focus is placed on the influence of several key system parameters on sound transmission including the thickness of air cavity, structural dimensions, and the elevation angle and azimuth angle of the incidence sound. Further extensions of the sound velocity potential method to typical framed double-panel structures are also proposed.

Reproducible and controllable organic resistive memory based on Al/poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)/Al structure

We report reproducible and controllable bipolar resistive memory devices based on Al/poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)/Al, which show an on/off current ratio as large as 104, reproducibility of more than 103 dc sweeping cycles, and retention time of 104 s. The switching mechanism is confirmed to be the filamentary switching. We show that the compliant current can effectively control the formation of filaments and the performance of the device, including the on-state resistance, the reset current, and the switching-off threshold voltage. In addition, the lowest reset power and the critical compliant current for resistive switching are determined.

Multilevel resistance switching in Cu/TaOx/Pt structures induced by a coupled mechanism

We report on multilevel bipolar resistance switching in Cu/amorphous-TaOx/Pt structures controlled by a coupled mechanism. The devices could be reproducibly programmed into three nonvolatile resistance states, and the on/off ratios between all neighboring states are >20. It is speculated that the switching between the high resistance state and the intermediate resistance state originates from a phase transformation between Ta2O5 and TaO2, while the low resistance state is induced by the formation of Cu filaments. This structure might be promising for developing multilevel logic and memory devices with high reliability. It may also serve as a model system for investigating the coupling effect between different switching mechanisms.

Resistive switching and conductance quantization in Ag/SiO2/indium tin oxide resistive memories

The Ag/SiO2/indium tin oxide (ITO) devices exhibit bipolar resistive switching with a large memory window of ∼102, satisfactory endurance of >500 cycles, good retention property of >2000 s, and fast operation speed of <100 ns, thus being a type of promising resistive memory. Under slow voltage sweep measurements, conductance plateaus with a conductance value of integer or half-integer multiples of single atomic point contact have been observed, which agree well with the physical phenomenon of conductance quantization. More importantly, the Ag/SiO2/ITO devices exhibit more distinct quantized conductance plateaus under pulse measurements, thereby showing the potential for realizing ultra-high storage density.

Effects of degree of formaldehyde acetal treatment and maleic acid crosslinking on solubility and diffusivity of water in PVA membranes

The sorption, desorption and solubility of vapour and liquid water in polyvinyl alcohol (PVA) membranes treated by formaldehyde was studied. The sorption and solubility of water in PVA membranes with different degrees of maleic acid crosslinking was also investigated and compared with that of the formaldehyde-treated membranes. The structural differences that arise as a consequence of these two treatment methods and the corresponding differences in the diffusivity and solubility of water molecules are discussed. In addition, the key step involved in the dehydration of benzene using PVA membranes treated by formaldehyde was analysed. Three common models for pervaporation process are compared.