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A new molecular mechanism is proposed to explain the shape memory effect of mesogen-jacketed liquid crystalline polymer fiber-poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) fiber-designed in the molecular level. Due to...
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A new molecular mechanism is proposed to explain the shape memory effect of mesogen-jacketed liquid crystalline polymer fiber-poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) fiber-designed in the molecular level. Due to the strong "coupling effect" between flexible backbone and rigid side mesogens, the molecular structure of PBPCS can be regarded as "dual chains" model that is constituted by a flexible backbone chain and a rigid side chain in parallel. The flexible backbone chains are reversible above the transition temperature and act as a switch structure, the physically cross-linked points caused by the pi-pi weak interactions between rigid side mesogens are responsible for memorizing a shape function and act as a fixing structure; therefore, the switch structure (flexible backbone) and the fixing structure (rigid mesogens) are found in each macromolecular chain. Furthermore, the shape memory behavior of PBPCS fibers is discussed by a viscoelastic molecular model consisting of two Maxwell models in parallel, the obtained theoretical values by "dual chains" model was in agreement with experimental results, very well. The viscoelastic molecular model described for shape memory process was correlated to the molecular mechanism explained for shape memory effect. This work provides a new idea and significant approach for design of new shape memory polymers.
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Ship collision accidents occur frequently and developing rapid prediction methods for structural crashworthiness analysis is of crucial importance in the design phase. This paper proposed a new analytical method to rapidly evaluat...
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Ship collision accidents occur frequently and developing rapid prediction methods for structural crashworthiness analysis is of crucial importance in the design phase. This paper proposed a new analytical method to rapidly evaluate side structural responses impacted by a rigid raked bow in right-angle ship collisions with large indentation. Numerical simulations were carried out to help identify and understand the mechanisms of structural deformation of primary structural members. The side structure is divided into different key components and a new analytical model for evaluating the hull shell plating and stiffeners under large indentation subjected to lateral impact was developed. The model considered the shell plating deformation in three different phases, denting, ruptured and tearing phase. Different formulas were derived to cover the analysis from minor deflection to large indentation. Combined with other existing formulas for stiffened decks under in-plane loads, an integrated method was proposed to predict the total resistance and energy dissipation of the side structure. The newly developed method innovatively considered the coupling effects and interactions between various structural members in the collision analysis by dynamically correcting some parameters theoretically. The newly developed method was verified against numerical simulations of full-scale ship collisions through five typical scenarios and good accuracy was achieved. The newly developed method is valuable for use in the preliminary design phase, especially for severe collision scenarios.
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Abstract We have considered the most general from the point of view of coupled processes a linear model of reversible thermomechanical processes, in which gradient thermoelasticity and stationary thermal conductivity are coupled p...
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Abstract We have considered the most general from the point of view of coupled processes a linear model of reversible thermomechanical processes, in which gradient thermoelasticity and stationary thermal conductivity are coupled processes. Mathematical statements for the model including the gradient equilibrium equations of the fourth order, generalized thermal gradient conductivity equation, and the boundary value problems as a whole are considered, the structure of the fundamental solutions is studied, and the general solution is established in analytical form for the one-dimensional problems. We study the influence of both couple effects and scale effects on the deformation process, temperature distribution, and effective mechanical properties of the periodic inhomogeneous structures. Thermal resistance is also taken into account. We show that an analytical solution predicts the possible abnormal effects due to couple and scale effects for diapason of the parameters allowed by the positive definition constraints. Certainly the possible realization of these effects for the inhomogeneous structures is dependent on the real diapason parameters, which must be determined from the experimental data.
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Two methods are generally used for the aeroelastic analysis of bladed-disc assemblies. The first, often referred to as the energy method, assumes that the fluid does not modify invacuum structural dynamic behavior. On the other ha...
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Two methods are generally used for the aeroelastic analysis of bladed-disc assemblies. The first, often referred to as the energy method, assumes that the fluid does not modify invacuum structural dynamic behavior. On the other hand, the second, based on an eigenvalue approach, considers the feedback effect of the fluid on the structure. In this paper, these methods are compared using different test cases, in order to highlight the limitations of the energy method. Within this comparison, the effect of material modifications on the coupled behavior of the assembly is examined.
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A 1-4 and 2-3 residue-correlation model is proposed to predict the beta-turns in proteins. The average rate of correct prediction for the 455 beta-turn tetrapeptides and 4018 non-beta-turn tetrapeptides in the training data base i...
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A 1-4 and 2-3 residue-correlation model is proposed to predict the beta-turns in proteins. The average rate of correct prediction for the 455 beta-turn tetrapeptides and 4018 non-beta-turn tetrapeptides in the training data base is 80.1%, and that for the 223 beta-turn tetrapeptides and 12562 non-beta-turn tetrapeptides in the testing data base is 80.9%. Compared with the rates of correct prediction based on the residue-independent model reported previously, the quality of prediction is significantly improved by the new model, implying that the correlation effect between the Ist and the 4th residues and that between the 2nd and 3rd residues along a tetrapeptide are important for forming a beta-turn in a protein during the process of its folding. (C) 1997 John Wiley & Sons, Inc. [References: 16]
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In this paper, a new method to design a dual band bandpass filter (BPF) is presented. This method is based on a simple principle: different substrates (dielectric constants) will result different resonant frequencies for a resonat...
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In this paper, a new method to design a dual band bandpass filter (BPF) is presented. This method is based on a simple principle: different substrates (dielectric constants) will result different resonant frequencies for a resonator. The basic structure of this method is studied and then a planar band pass resonator is designed to utilize in this structure. Response of the proposed dual layer filter is tuned using resonator shifting and resonator scaling. In addition to improve the filter response, resonator shifting improves the filter size. The final structure is designed, fabricated and measured and simulation results are in good agreement with measured values. The central frequencies of this dual band BPF are f1=3.85 GHz and f2=5.3 GHz and a deep transition zero at 4.57 GHz, guarantees isolation between passbands.
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Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, ...
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Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, which can be regarded as secondary sources radiating light into the waveguide array. As a result, many light beams can be generated in the array by the coupling among the waveguides, and the interference of these light beams after passing the system leads to directional emission. Additionally, the directional emission is greatly affected by the beam distribution on the exit plane of the system. Once the main light beams are formed on the exit plane of the system by modulating the system size, steady beaming effect can be obtained in the horizontal direction.
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Three cases of supertall connected structures are presented and each of them represents a quite style. The first case is a strong-connected structure. The coupling function of towers and connector contributes a lot to the structur...
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Three cases of supertall connected structures are presented and each of them represents a quite style. The first case is a strong-connected structure. The coupling function of towers and connector contributes a lot to the structural stiffness and stability. Its special construction scheme had great impact on the construction quality and the structural safety, and must be accurately considered. For the second case which is a weak-connected structure, the influences of different connecting modes to the structural dynamic characteristic were explained. Then the combined bearings were proposed to achieve the design presume. In the third case which represents the multi-supported structures, the structural distinctive mechanical properties were discussed. For the structural state during construction process is quite different from that in final service condition, two construction procedures were simulated to get an optimal one. Although there are great challenges to designers, the advantages of the supertall connected buildings are obvious. Further work is needed in this area to adapt to the development of future cities.
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High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the stru...
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High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 (CCZFO/BSZTO) composite ceramics prepared by sol-gel method. The XRD results confirm successful formation of the CCZFO/ BSZTO composites without presence of any impurity phase. The mean grain size is about 1.5 mm and it shows double dispersing behavior, the larger grains belong to CCZFO while the smaller ones are ascribed to BSZTO. The maximum dielectric constant and loss appear with the molar ratio is 1:1 due to its more grain boundaries. Two peaks appear in the epsilon similar to T curves, the peak corresponding to the lower temperature corresponds to the Curie temperature of BSZTO, while the other one is resulted by the relaxation polarization. The height of the relaxation peak decreases and the position shifts to higher temperature range with the increase of molar ratio. The maximal remanent polarization is 3.76 mu C/cm(2), obtained at 1 kHz when the molar ratio is 1:1. An enhanced magnetic properties are observed when the molar ratio is 1:1 due to the stronger interface interaction effect between the two phases. Strong direct magnetoelectric coupling coefficient of 1.53 V/(cm.Oe) is obtained at the field of 8000 Oe for the sample 1:4. These results may provide valuable information for improving the multiferroic properties of composite multiferroic materials.
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Thin-film piezoelectric-on-silicon (TPoS) bulk acoustic wave resonator provides an attractive vision of system-on-chip integrated circuits by micro/nano-engineering the timing reference. However, its quality factor (Q) at high fre...
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Thin-film piezoelectric-on-silicon (TPoS) bulk acoustic wave resonator provides an attractive vision of system-on-chip integrated circuits by micro/nano-engineering the timing reference. However, its quality factor (Q) at high frequency is a great challenge due to the mechanical loss. Herein, a novel suspended frame structure on tethers was proposed to significantly enhance the Q and suppress spurious modes of TPoS resonator working in the 30.4 MHz fundamental mode. Compared with the pristine one, the measured Q of fabricated resonator with frame structure showed a maximum 136-fold enhancement. The systematical investigation by both finite-element-analysis (FEA) simulation and experimental comparison revealed that the existing of frame structure effectively decreases the effective coupling coefficient (k(eff)(2)) of resonator and further results in the suppression of spurious modes and the enhancement of Q. As the width of frame structure increases, the k(eff)(2) maintains a consistent value of 0.15% while the anchor loss significantly reduced, which results in the reduction of insertion loss (IL) and the enhancement of Q, (C) 2018 Elsevier B.V. All rights reserved.
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