The effects of moisture content, xanthan gum (XG) addition and glucose syrup (GS):sucrose ratio on elastic (G′) and viscous (G″) moduli during in situ gelation and on large deformation rheological properties of cured gels were investigated. An increase in both moduli of the samples with XG addition indicates network structure being strengthened. All gel samples exhibited distinct fracture. An increase in GS:sucrose ratio led to a decrease in fracture stress and an increase in fracture strain, implying more flexible polymer network. Decreasing moisture content may lead to phase separation between sugar-rich and polymer-rich phases to form stronger connection within the network structure. Textural characteristics of samples analyzed using a texture map, indicated that increasing GS:sucrose ratio rendered the sample texture more rubbery when the samples contained XG. We also related factors affecting the gelling mechanisms in terms of Tg measured by different techniques including DMA and modulated DSC. 相似文献
The elastic–plastic stress distribution of a solid disk due to nonuniform heat source under external pressure is investigated in this work. The nonuniform heat generation rate
is taken to be a function of the radial position in the form
, where a denotes radius of the solid disk; q0, n and s are constants. The exact solution presented is based on the usual assumptions of plane stress, Tresca's yield condition, its associated flow rule and linear strain hardening material behaviour. According to this analysis, the plastic core in the general case consists of three parts with different forms of the yield condition. The present solution is illustrated by numerical results and is compared with uniform heat generation case. This work provides the basis for a comprehensive investigation of the influence of nonuniform heat generation. 相似文献
The aim of this study was to develop and evaluate statistical models for predicting the uniaxial compressive strength (UCS)
and average Young’s modulus (Eav) for caliches, using some index and physical properties. The caliche samples, from Adana, southern Turkey, were of low strength
and difficult to sample. X-ray diffraction and microscopy were undertaken and the following physical parameters established:
unit weight, apparent porosity, Schmidt rebound number, Shore hardness, P-wave velocity, slake durability, point load, uniaxial
compressive strength and average Young’s modulus. Simple and linear regression variable selection analyses were performed.
The best relationships were obtained for UCS with P-wave velocity and unit weight and for average Young’s modulus with P-wave
velocity, porosity and slake durability. Empirical equations are proposed, although it is emphasised that these may only be
applicable for caliche of a similar geological character.
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Fragility curves are used to represent the probabilities that the structural damages, under various level of seismic excitation, exceed specified damage states by means of earthquake intensity–damage relations. In this study, the fragility curves have been developed for comparative seismic evaluation of several retrofitting measures by incorporation of fluid viscous (VS) dampers applied to a representative high-rise reinforced concrete (R/C) office building located in Istanbul. In the retrofitting strategies considered, similar type of VS dampers was used and designed to provide the structure with three different effective damping ratios of 10%, 15%, and 20%. In the fragility analysis, a set of 240 artificially generated earthquake ground motions compatible with the design spectrum selected to represent the variability in ground motion was employed to study nonlinear dynamic responses of the structures before and after retrofit. Four damage states: slight, moderate, major, and collapse were defined to express the condition of damage. The fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of peak ground acceleration (PGA), spectral acceleration (Sa), spectral displacement (Sd). Comparison of the fragility curves indicated that the VS dampers were very effective in attenuating seismic structural response under various earthquake ground motions. It was also found that a two-fold reduction in the probability of exceeding damage states might be achieved by introducing passive VS damper systems. 相似文献
In a mathematical modeling of the physical behavior of a hygrothermoelastic medium, a moisture field vector and a thermal field vector are introduced, Hamilton's principle is stated, and a three-field variational principle is derived. The differential variational principle is shown, as Euler - Lagrange equations, to generate the divergence equations and the associated natural boundary conditions of a hygrothermoelastic medium. This variational principle is augmented through an involutory transformation in order to incorporate the gradient equations and the constitutive relations of an anisotropic hygrothermoelastic medium; hence, a ten-field variational principle is formulated and some of its special versions recorded. 相似文献
Non-Orthogonal Multiple Access (NOMA) has been proposed as a new radio access technique for cellular networks as an alternative to OMA (Orthogonal Multiple Access) in which the users of a group (pairs or triples of users in a group are considered in this paper) are allowed to use the wireless channel simultaneously. In this paper, for downlink single-input single-output SISO-NOMA, a heuristic power allocation algorithm within a group is first proposed which attempts to ensure that the users of a group benefit from simultaneous transmission equally in terms of achievable throughput. Moreover, a user group scheduling algorithm is proposed for downlink NOMA systems by which a user group is to be dynamically selected for transmission while satisfying long term temporal fairness among the individual contending users. The effectiveness of the proposed power allocation method along with the temporal fair scheduling algorithm for downlink NOMA is validated with simulations and the performance impact of the transmit power and the coverage radius of the base station as well as the number of users are thoroughly studied.
A computational model is developed for efficient solutions of electromagnetic scattering from obstacles having random surface deformations or irregularities (such as roughness or randomly-positioned bump on the surface), by combining the Monte Carlo method with the principles of transformation electromagnetics in the context of finite element method. In conventional implementation of the Monte Carlo technique in such problems, a set of random rough surfaces is defined from a given probability distribution; a mesh is generated anew for each surface realization; and the problem is solved for each surface. Hence, this repeated mesh generation process places a heavy burden on CPU time. In the proposed approach, a single mesh is created assuming smooth surface, and a transformation medium is designed on the smooth surface of the object. Constitutive parameters of the medium are obtained by the coordinate transformation technique combined with the form-invariance property of Maxwell’s equations. At each surface realization, only the material parameters are modified according to the geometry of the deformed surface, thereby avoiding repeated mesh generation process. In this way, a simple, single and uniform mesh is employed; and CPU time is reduced to a great extent. The technique is demonstrated via various finite element simulations for the solution of two-dimensional, Helmholtz-type and transverse magnetic scattering problems. 相似文献
A key property for predicting the effectiveness of stochastic search techniques, including evolutionary algorithms, is the
existence of a positive correlation between the form and the quality of candidate solutions. In this paper we show that when
the ordering of genomic symbols in a genetic algorithm is completely independent of the fitness function and therefore free
to evolve along with the candidate solutions it encodes, the resulting genomes self-organize into self-similar structures
that favor this key stochastic search property. 相似文献