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[en] EF-hand proteins can be activated by the binding of various heavy metals other than calcium, and such complexes can disturb the calcium-signaling pathway and cause toxicity and disease causing state. So far, no comprehensive study has been done to understand different heavy metals binding to calcium signaling proteins. Energetically, Ca2+ is preferred in three sites, while in one site Ba2+ has better binding energy. The Sr2+-coordination in the EF hand motifs is similar to that of the native Ca2+ bound structure, except for the lack of water coordination. Sr2+-coordination seems to be a pre-formed in nature since all seven coordinating atoms are from the protein itself, which also correlates with entropy contributions in Sr2+ binding. These findings improve our understanding of metal association with calcium binding proteins and of metal induced conformational changes.
[en] In this study, the effect of prestressed strand diameters, providing the beam-to-column connections, was investigated from both experimental and analytical aspects. In the experimental studies, the strength, stiffness and energy dissipation capacities of the precast specimens comprising two prestressed strand samples of 12.70 mm and 15.24 mm diameters, were compared with the reference specimen. The precast specimen with strands of 15.24 mm reached 96% of the maximum strength of the reference specimen; the amount of energy dissipated by this specimen by the end of the experiment reached 48% of the amount of energy dissipated by the reference sample; and the stiffness of the same specimen at a drift of 1.5% reached 77% of the stiffness of the reference specimen at this drift. Parallel results were obtained during the analytical studies from the aspects of strength and behavior, but the initial stiffness of the analytical models was lower than that of the test specimens.
[en] The frequency range over which a mount can isolate a mass from a vibrating base (or vice versa) is often limited by the mount stiffness required to support the weight of the mass. This compromise can be made more favourable by employing non-linear mounts with a softening spring characteristic such that small excursions about the static equilibrium position result in small dynamic spring forces and a correspondingly low natural frequency. This paper concerns the force-displacement characteristic of a so-called quasi-zero-stiffness (QZS) mechanism which is characterised by an appreciable static stiffness but very small (theoretically zero) dynamic stiffness. The mechanism studied comprises a vertical spring acting in parallel with two further springs which, when inclined at an appropriate angle to the vertical, produce a cancelling negative stiffness effect. Analysis of the system shows that a QZS characteristic can be obtained if the systems parameters (angle of inclination and ratio of spring stiffness) are opportunely chosen. By introducing the additional criterion that the displacement of the system be largest without exceeding a desired (low) value of stiffness an optimal set of parameter values is derived. Under sufficiently large displacements the stiffness of the QZS mechanism can eventually exceed that of the simple mass-spring system and criteria for this detrimental scenario to arise are presented
[en] Liquid water confined between hydrophobic objects of sufficient size becomes metastable with respect to its vapor at separations smaller than a critical drying distance. Macroscopic thermodynamic arguments predicting this distance have been restricted to the limit of perfectly rigid confining materials. However, no material is perfectly rigid and it is of interest to account for this fact in the thermodynamic analysis. We present a theory that combines the current macroscopic theory with the thermodynamics of elasticity to derive an expression for the critical drying distance for liquids confined between flexible materials. The resulting expression is the sum of the well-known drying distance for perfectly rigid confining materials and a new term that accounts for flexibility. Thermodynamic arguments show that this new term is necessarily positive, meaning that flexibility increases the critical drying distance. To study the expected magnitude and scaling behavior of the flexible term, we consider the specific case of water and present an example of drying between thin square elastic plates that are simply supported along two opposite edges and free at the remaining two. We find that the flexible term can be the same order of magnitude or greater than the rigid solution for materials of biological interest at ambient conditions. In addition, we find that when the rigid solution scales with the characteristic size of the immersed objects, the flexible term is independent of size and vice versa. Thus, the scaling behavior of the overall drying distance will depend on the relative weights of the rigid and flexible contributions
[en] Drug delivery through hollow microneedle (HMN) arrays has now been recognized as one of the most promising techniques because it minimizes the shortcomings of the traditional drug delivery methods and has many exciting advantages—pain free and tunable release rates, for example. However, this drug delivery method has been hindered greatly from mass clinical application because of the high fabrication cost of HMN arrays. Hence, we developed a simple and cost-effective procedure using silica needles as templates to massively fabricate HMN arrays by using popular materials and industrially applicable processes of micro- imprint, hot embossing, electroplating and polishing. Metal HMN arrays with high quality are prepared with great flexibility with tunable parameters of area, length of needle, size of hollow and array dimension. This efficient and cost-effective fabrication method can also be applied to other applications after minor alterations, such as preparation of optic, acoustic and solar harvesting materials and devices
[en] In order to realistically collect Electroencephalogram (EEG) signals in complicated environments, low impedance and flexibility are considered as two crucial characteristics for EEG electrode. We designed and manufactured a type of dry EEG electrode based on graphene with matrix micro-pyramid structure on the surface. This EEG electrode could not only reduce the contact impedance, but also improve the stability of the electrode. Furthermore, based on these flexible graphene EEG electrodes, we assembled a system that could monitor human EEG signals in real time. When a tested person was answering the phone or driving while tired, the system could give him appropriate warnings, so as to reduce the occurrence of accidents. This brain-computer interface system was wearable and suitable for intelligent detection of EEG signals. (paper)
[en] A model is established to minimize the maximum nodal displacement. The nodal displacement of an adaptive truss can be control by this model. Examples illustrate that the truss nodal displacements can be controlled by this method. This model can be used to reduced the nodal displacements, and the maximum stress in an indeterminate truss can be reduced simultaneously
[en] Antagonistic muscle pairs pulling on a joint are in general able to modulate stiffness through co-activation. Closer analysis of the stiffness, however, shows that, depending on the muscle and joint parameters, domains might occur in joint angle space for which stiffness variation is limited (low stiffness variability) or even impossible (stiffness nodes). As a consequence, stiffness control utilizing pure co-activation might fail. This work presents novel strategies for simultaneous control of torque and stiffness in a hinge joint actuated by two antagonistic muscle pairs. One strategy handles stiffness nodes by shifting them away from the current joint position and thus regaining stiffness controllability. To prevent domains of low stiffness variation, an optimal muscle configuration is sought and finally defined which allows for a maximal stiffness variation across a wide joint angle range. Based on this optimal configuration, four additional control strategies are proposed and tested which deliver stiffnesses and torques comparable to those obtained in the optimal case. The strategies combine torque control and stiffness control by co-activation with novel ideas like activation overflow and an inverse model approach. All strategies are tested in simulation and the results are compared with those of the optimal setup.
[en] The transverse impact characteristics of a rubber pipe expansion joint are studied. A pair of joints assembled end to end with an inserted middle mass is tested on a drop shock testing machine. Based on the test results, an equivalent fixed-fixed beam model with polynomial stiffness and damping is applied to predict the transverse impact response and identify the nonlinear impact parameters. The least square residual between the computed and test results is defined to drive the identification optimization. The response surface methodology in combination with the generalized reduced gradient method is used to search the best matching coefficients. Final results show that the equivalent bending stiffness of the tested rubber expansion joint gradually decreases with the transverse deformation and is greatly influenced by its internal working pressure