Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Micromechanics-Based Elastic Fields of Closed-Cell Porous Media
Get PDFFluid-filled closed-cell porous media could exhibit distinctive features which are influenced by initial fluid pressures inside the cavities. Based on the equivalent far-field method, micromechanics-based solutions for the local elastic fields of porous media saturated with pressurized fluid are formulated in this paper. In the present micromechanics model, three configurations are introduced to characterize the different state the closed-cell porous media. The fluid-filled cavity is assumed to be a compressible elastic solid with a zero shear modulus, and the pressures in closed pores are represented by eigenstrains introduced in fluid domains. With the assumption of spheroidal fluid-filled pores, the local stress and strain fields in solid matrix of porous media are derived by using the Exterior-Point Eshelby tensors, which are dependent of the Poisson’s ratio of solid matrix and the locations of the investigated material points outside the spheroidal fluid domain. The reliability and accuracy of the analytical elastic solutions are verified by a classical example. Moreover, for finite volume fraction of the fluid inclusions, the local elastic fields of the porous media subjected to the initial fluid pressure and external load are obtained. The results show that the present micromechanics model provides an effective approach to characterize the local elastic fields of the materials with closed-cell fluid-filled pores
Investigation on Purine Corrosion Inhibitions via Quantum Chemical Calculation
Get PDFCorrosion inhibition performances of three purine derivatives were investigated systematically by employing DFT and molecular modeling. The relationship between macroscopic inhibition efficiency and quantum chemical properties was discussed from multiple perspectives, based on frontier orbital theory, and Fukui function theories. Comparative experimental and theoretical studies were taken, indicating the inhibition efficiency could be analyzed in the order of guanine <2,6-diaminopurine <2,6-dithiopurine. The sulphur atom (S5) was validated to be the most susceptible site for electrophile via quantitative surface analysis
A Virtual Boundary Element Method for Three-Dimensional Inverse Heat Conduction Problems in Orthotropic Media
Get PDFThis paper aims to apply a virtual boundary element method (VBEM) to solve the inverse problems of three-dimensional heat conduction in orthotropic media. This method avoids the singular integrations in the conventional boundary element method, and can be treated as a potential approach for solving the inverse problems of the heat conduction owing to the boundary-only discretization and semi-analytical algorithm. When the VBEM is applied to the inverse problems, the numerical instability may occur if a virtual boundary is not properly chosen. The method encounters a highly ill-conditioned matrix for the larger distance between the physical boundary and the virtual boundary, and otherwise is hard to avoid the singularity of the source point. Thus, it must adopt an appropriate regularization method to deal with the ill-posed systems of inverse problems. In this study, the VBEM and different regularization techniques are combined to model the inverse problem of three-dimensional heat conduction in orthotropic media. The proper regularization techniques not only make the virtual boundary to be allocated freer, but also solve the ill-conditioned equation of the inverse problem. Numerical examples demonstrate that the proposed method is efficient, accurate and numerically stable for solving the inverse problems of three-dimensional heat conduction in orthotropic media
An Advanced Quantum-Resistant Signature Scheme for Cloud Based on Eisenstein Ring
Get PDFSignature, widely used in cloud environment, describes the work as readily identifying its creator. The existing signature schemes in the literature mostly rely on the Hardness assumption which can be easily solved by quantum algorithm. In this paper, we proposed an advanced quantum-resistant signature scheme for Cloud based on Eisenstein Ring (ETRUS) which ensures our signature scheme proceed in a lattice with higher density. We proved that ETRUS highly improve the performance of traditional lattice signature schemes. Moreover, the Norm of polynomials decreases significantly in ETRUS which can effectively reduce the amount of polynomials convolution calculation. Furthermore, storage complexity of ETRUS is smaller than classical ones. Finally, according to all convolution of ETRUS enjoy lower degree polynomials, our scheme appropriately accelerate 56.37% speed without reducing its security level
Green Upconversion Emission of Yb3+/Er3+ co-doped Gd2Sn2O7 Nanophosphors as Wide-Range Temperature Sensor
Get PDFGd2Sn2O7:Yb3+/Er3+ (abbreviation for GSO: Yb3+/Er3+) nanophosphors codoped with Er3+ (0.1-2 at%) and Yb3+ (0.5-5 at%) were synthesized by a microwave hydrothermal process and annealed at 800 ℃ for 5 h. Powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and upconversion emission spectra were used to characterize the as-synthesized sample. Under the irradiation of 980 nm laser diode, the GSO: Yb3+/Er3+ nanophosphors emitted green emissions centered at 525 and 546 nm (Er3+ :2H11/2→4I15/2 and 4S3/2→4I15/2 transition), red emissions centered at 659 and 677 nm (Er3+:4F9/2→4I15/2 transition). The temperature dependent emission intensity ratio of the thermally coupled levels (2H11/2/4S3/2) of Er3+ in the wide-range of 110-573 K was recorded to study the optical thermometric properties of GSO: Yb3+/Er3+ nanophosphors. The maximum sensitivity of GSO: Yb3+/Er3+ nanophosphors was approximately 36.34x10-4 K-1 at 466 K. This result indicates that GSO: Yb3+/Er3+ nanophosphors are potential candidates for wide-range optical temperature sensors with high sensitivity
Shape Optimization of Orthopedic Fixation Plate Based on Static Stress Analysis
Get PDFShape optimization of orthopedic fixation plate is of great importance in the treatment of complex fracture. Therefore, a method in this paper to automatically optimize the complex shape of anatomical plate according to static analysis. Based on the theory of finite element analysis (FEA), our approach is processed as follows. First, the three-dimensional finite element model of the fracture fixation is constructed. Next, according to the type and feature of fracture, the anatomical plate was parameterized in two levels (the bounding surface and plate model). Then, parameter constraints are set up to meet the needs of surgical fracture treatment. Finally, by using the theories combined with the method of moving asymptote (MMA) and gradient projection (GP), the plate model is modified automatically based on the principle of plate stress and segment offset minimization. Experimental results show that the displacement of femur segments and the stress of fracture site were decreased slightly and can improve the biomechanical environment around the fracture
Information Monitoring Technology for Support Structure of Railway Tunnel During Operation
Get PDFIn the process of railway construction, because of the inconvenience of geological condition, water bursting and mud surging happen frequently, and the later deformation of support structure on the happening geology section would threaten the normal running of railway. The limit difference of deformation control value of the support structure section where geological accidents frequently happen, is small, and artificial half-automatic supervisory technology cannot get the health condition of tunnel in time, resulting many cars speed-down accidents due to deformation of support structure. Through design innovation, we introduce TGMIS in the later period of Yanzishan railway construction to quickly capture the deformation of support structure, the strain of lining concrete, the strain of steel frame, stress of surrounding soil, stress of surrounding water, strain of second lining steel bar and other situ data. Also we set observation prism and measuring robot device in specific position inside tunnel, and robot laser locator laser spot is projected onto reflection target surface, by graphic processing algorithm, the receiver calculates the measured value and standard value of the 3D coordinates of the laser spot. Then the information is transmitted through transmitting device, transducer and USB-485 to computer to predict and evaluate the health condition of the support structure of the tunnel so as to provide safety warning information. Provide timely and reliable data for the operation company to avoid the occurrence of vicious accidents
Simplified Method and Influence Factors of Vibration Characteristics of Isolated Curved Girder Bridge
Get PDFThe isolated curved girder bridge's vibration characteristics play a major part in the seismic responses of structures and anti-seismic properties. A clear analytic relationship between design parameters and the system's vibration characteristics could be established by its simplified dynamic analysis model, making it convenient for providing a reference to the optimization of design and safety analysis. A double-mass six-degree-of-freedom model for curved girder bridges with isolation bearings installed at the top of the bridge piers is built and a simplified analysis method for the vibration characteristics of the system is provided. Combined with the Matlab programming, the influences of radius of curvature, central angle, bridge deck width and damping ratio of the isolation layer and circular frequency of the isolation layer of isolated curved girder bridges on the pseudo-undamped natural circular frequency (called pseudo-frequency for short) and system damping ratio are systematically analyzed, and the sensitivity of vibration characteristics of isolated curved girder bridges is studied. The results show that the vibration characteristics of isolated curved girder bridges can be reflected well with this simplified model and calculation method. The pseudo-frequency of curved girder and system damping ratios increases with the increase of the isolation layer. The third-order vibration characteristic is more sensitive to the parameters of a curved girder, and the first-order vibration characteristic is sensitive to both central angle and radius of curvature to some extent while insensitive to the width of the bridge deck. Furthermore, the second-order vibration characteristic is not sensitive to the parameters of a curved girder
Biobased Aromatic-Aliphatic Polyols from Cardanol by Thermal Thiol-Ene Reaction
Get PDFCardanol is a natural phenol which is obtained from high vacuum distillation of cashew nut shell liquid. It contains a hydrocarbon chain of 15 carbon atoms in the meta position, either with one, two or three non-conjugated double bonds. This article describes thermal thiol-ene reaction to synthesize new cardanol-based polyols for polyurethanes with aromatic-aliphatic structure. Phenolic hydroxyl group was blocked by alkoxylation and 2-mercaptoethanol was added to the double bonds of propoxylated cardanol. The resultant product is a mixture of polyols that may contain one, two, three or four hydroxyl groups, as a function of the number of double bonds reacted with 2-mercaptoethanol. Similar polyols, but with much higher functionality, were also synthesized from condensation of cardanol-based novolacs with formaldehyde. These cardanolbased polyols were further utilized to prepare rigid polyurethane foams (PUs) with excellent physical and mechanical properties, useful for various applications in chemical and food industries
Enzymatic Synthesis and Characterization of Biodegradable Poly(w-pentadecalactone-co-e-caprolactone) Copolymers
No full textAs an alternative biodegradable aliphatic polyester, poly(w-pentadecalactone-co-ε-caprolactone) copolymer was synthesized via enzymatic ring-opening polymerization. A new biocatalyst, Candida antarctica lipase B, immobilized onto rice husk ash was used for catalysis. Reactions were carried out at various temperatures and periods for varied copolymer compositions in order to obtain the highest molecular weight copolymer. The best reaction parameters were found to be 80 °C and 6 hours and molecular weights increased proportionally with the amount of w-pentadecalactone (w-PDL). The molecular structure of copolymer with 75% weight ratio of w-PDL (Mn = 19720 g/mol) was characterized by proton and carbon nuclear magnetic resonance spectroscopies (1H-NMR and 13C-NMR). Thermal properties of the same copolymer and homopolymers were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Improved thermal features were shown by addition of w-PDL to the structure and compared with poly(ε-caprolactone) (PCL). Consequently, poly(w-pentadecalactone-co-ε-caprolactone) copolymers were found to be good alternatives to widely used polyester, PCL, with their rapid polymerization tendency, higher molecular weights, and improved thermal features