Blends of silicone rubber (SR) and ethylene propylene diene monomer (EPDM) are immiscible due to different polarity and poor interfacial surface tension between their rubber chains. In this study, compatibilizing effect of a nanoclay addition in SR/EPDM blends was investigated. Viscoelasticity and morphology of nanocomposites based on SR and EPDM, containing 10, 20 and 30 wt% of EPDM and 3, 6 and 9 phr of nanoclay (Cloisite 15A), were studied. The curing behavior of the samples showed that the vulcanization rate and cross-link density of the blends increased with increases in SR content. Morphological study was conducted by XRD, SEM and EDX analyses and they indicated that the nanoparticles tended to disperse in the EPDM phase and consequently caused hardness and the elasticity of this phase in nanocomposites increased. Tensile properties of the samples showed a good fitting between that of experiments and the Maxwell model at initial time of testing (1.5 s) for all the blends. Sample parameters including modulus (E), viscosity (h) and relaxation time (t) calculated by the Maxwell model revealed that those samples with higher content of nanoparticles exhibit higher modulus and lower relaxation time. The good match in tensile properties based on Maxwell model and those of the experimental data was attributed to good dispersion of nanoclay in the blends.

The objective of this study is to develop a general finite element formulation associated with an incremental adaptive procedure established for the calculation of contact pressure distributions in viscoelastic structures. A generalized Maxwell model has been used to model the viscoelastic constitutive equations in which bulk and shear relaxation functions are represented by sum of a series of decaying exponential functions of time. Based on the principle of virtual work, an effective finite element formulation, associated with an incremental relaxation procedure, has been developed. The viscoelastic contact behavior has been studied through an improved augmented Lagrangian approach, based on kinematical conditions of contact bodies. The proper convergence caused by the numerical examples with those obtained from analytical results shows the applicability of presented finite element formulation.

In this paper, the investigation is carried out to study the structural responses of two adjacent structures connected with Maxwell dampers under various earthquake excitations. The specific objective of this study is to evaluate the optimum damper parameter and its importance in response reduction of adjacent structures coupled by Maxwell dampers. The optimum damper parameter is investigated for the adjacent coupled structures subjected to four different types of earthquake ground motions. A formulation of the equations of motion for the two adjacent multi-degree-of-freedom (MDOF) structures connected with Maxwell dampers is presented. The numerical study is carried out for two adjacent MDOF structures connected with Maxwell dampers having same damper parameter in all dampers as well as, having different damper parameter in the dampers. The investigation is also carried out for effectiveness of the damper in terms of the structural response reduction, namely, displacement, acceleration and shear forces of adjacent connected structures. In addition, to minimize the cost of the dampers, the optimal location of the dampers, rather than providing the dampers at all floor levels is also investigated. Results show that using Maxwell dampers of appropriate parameter to connect the adjacent structures of different fundamental frequencies can effectively reduce earthquake-induced responses of either structure. Further, lesser dampers at appropriate locations can significantly reduce the earthquake response of connected system, thereby reducing cost of damper significantly.

In practical applications, it is difficult to link dashpot absolutely rigidly between the structure and the mass blocks of the multiple tuned mass dampers (MTMD). In order to cope with this practical issue, Maxwell damper based multiple tuned mass dampers (referred to as the MD-MTMD) have been presented for attenuating the response of structures excited by the ground acceleration. By resorting to the formulated transfer functions of the MD-MTMD structure system, the dynamic magnification factors (DMF) are then defined of the MDMTMD structure system. The criterion for the optimum searching can thus be selected as the minimization of the minimum values of the maximum DMF (min. min. max. DMF).Employing this criterion, the effects of the normalized relaxation time constant (NRTC) are investigated on the optimum parameters and effectiveness of the MD-MTMD. Likewise, the effects of the RTC on the stroke of the MD-MTMD are estimated in terms of maximizing the dynamic magnification factors (DMF) of each MD-TMD in the MD-MTMD. The numerical results have indicated that the MD-MTMD is a feasible solution for the practical issue mentioned above of the traditional MTMD.

In the present study, the onset of Darcy-Brinkman double diffusive convection in a Maxwell fluid-saturated anisotropic porous layer is studied analytically using stability analysis. The linear stability analysis is based on normal technique. The modified Darcy-Brinkmam Maxwell model is used for the momentum equation.The Rayleigh number for stationary, oscillatory and finite amplitude convection is obtained analytically. The effect of the stress relaxation parameter, solute Rayleigh number, Darcy number, Darcy-Prandtl number, Lewis number, mechanical and thermal anisotropy parameters, and normal porosity parameter on the stationary, oscillatory and finite amplitude convection is shown graphically. The nonlinear theory is based on the truncated representation of the Fourier series method and is used to find the heat and mass transfer. The transient behavior of the Nusselt and Sherwood numbers is obtained by solving the finite amplitude equations using the Runge-Kutta method.

Plant development can be defined as a programmed qualitative change in plant form, which leads plant to maturity, and researchers call it as phasic development or phenology. Recognizing the timing of occurring each development stage is necessary for managing system in order to yield increment. The timing of occurring development stages depend on climate, genotype specifications and sowing date then determination of these times in different regions is difficult and it is only possible through the using of crop simulation models which can predict the timing of occurrence each development stage by integrating effective factors. The model was constructed based on linear equation of plant temperature response. In order to model evaluation two experiments were carried out in agricultural and natural resources research center of Khuzistan in 2003-2004 and 2004-2005 cropping years. Wheat development stages were determined based on Kirby and Appleyard’s scale by stereoscopic microscope and required GDD for each development stage as well. The constructed model was calibrated and run for simulation. Comparison of simulated and observed data showed that the model can strongly predict wheat development stages.

In most of transport models the flux of a component through a membrane is connected to its own concentration gradient using a single permeability factor and it is simply assumed that the flux of each species is not affected by the presence of other components. In these models the selectivity is ideally defined as a permeability ratio factor of two penetrating components. However, this is a fact that the analysis of multicomponent transport is complicated by the need to account for the potential coupling of fluxes. In this study, the theoretical description of multicomponent gas transport through glassy polymers was investigated using the mechanistic Maxwell-Stefan formulation. The developed models account for equilibrium and/or kinetic coupling of fluxes. The experimental data available in the literature for the selective transport of CO2/CH4 gaseous mixture through glassy polyimide membrane were used to validate the developed model in this study. The experimental sorption and permeation data for pure CO2 and CH4 were used to establish the multicomponent equilibrium and diffusivity matrix for mixed gas transport. The model predicted values of penetrability and selectivity show a good agreement with the experimental data. The results obtained indicate that the kinetic coupling plays no role in transport across the membrane for the system under study and can be safely ignored. However, the equilibrium coupling is shown has a major contribution to the transport via membrane and should be considered in the transport model using a proper equilibrium sorption isotherm.

Background and Aim: Job enrichment is a method that has been used to increase employee satisfaction and work motivation. The Hackman and Oldham job characteristics model (1976) has served as the foundation for many job enrichment efforts. In particular, a considerable amount of research has been devoted to the study of the job characteristics-job satisfaction relations. Te purpose of this study was to statistically determine the relation between job characteristics and job satisfaction among employees of hospitals affiliated to Tehran University of Medical Sciences (TUMS) in 2007. Materials and Methods: This study was a cross-sectional one, including 6 TUMS-affiliated hospitals-Emam, Shariati, Baharlo, Ziaeian, Madaen and Azadi. The sample size was 400, consisting of 200 administrative employees (50%), 151 nurses (38%) and 49 physicians (12%). The random sampling and stratified proportional sampling methods were used to select the hospitals and interviewees, respectively. Two questionnaires were developed and used to identify job characteristics and job satisfaction: 1) job diagnostics surveys (JDS) and 2) Hertzberg's job satisfaction questionnaire. The reliability of the questionnaires was ascertained by test-retest using the Pearson correlation coefficient (r = 0.88). Linear-by-linear association and ordinal logistics regression analysis were used for analyzing the data gathered.Results:The relations between the Motivational Potential Score (MPS) and job characteristics (except for feedback) with job satisfaction were statistically significant (p<0.05). Task identity was the most effective determinant of job satisfaction. Conclusion: It appears that all the job characteristics (except feedback) are important determinants of job satisfaction of the hospital employees. Although the work environment is in need of restructuring, it is important to note, from a positive perspective, that the job characteristics discussed in this study are readily amenable to change job satisfaction at the organizational level.

One-dimensional transient flows of three layers immiscible fractional Maxwell fluids in a cylindrical domain have been investigated in the presence of a porous medium. In the flow, the domain is considered the concentric regions namely one clear region and other two annular regions are filled with a homogeneous porous medium saturated by a generalized Maxwell fluid. The studied problem is based on a mathematical model focused on the fluids with memory described by a constitutive equation with time-fractional Caputo derivative. Analytical solutions to the problem with initial-boundary conditions and interface fluidfluid conditions are determined by employing the integral transform method (the Laplace transform, the finite Hankel transform and the finite Weber transform). The memory effects and the influence of the porosity coefficient on the fluid motion have been studied. Numerical results and graphical illustrations, obtained with the Mathcad software, have been used to analyze the fluid behavior. The influence of the memory on the fluid motion is significant at the beginning of motion and it is attenuated in time.

Zeolites are microporous crystalline materials with a uniform pore size distribution on a molecular scale and with high thermal and chemical stability. Zeolite membranes NaA, ZSM-5, Mordenite< NaX and NaY grown onto seeded mullite supports. Separation performance of zeolite membranes were studied for water-dimethyl hydrazine mixtures using pervaporation (PV) method. The best flux and separation factor of the membranes were 0.62 kg/m2.h and 52000, respectively, for NaA zeolite membrane. Strong electrostatic interaction between ionic sites and water molecules (due to its polar nature) makes the zeolite NaA membrane very hydrophilic. Zeolite NaA membranes are thus well suited for separating liquid-phase mixtures by pervaporation method. In this study, experiments were conducted with various UDMH-water mixtures (1-20 wt. %) at 25oC. Total flux for UDMH-water mixtures was found to vary from 0.331 to 0.241 kg/m2.h with increasing UDMH concentration from 1 to 20 wt.%. Ionic sites of the NaA zeolite matrix play a very important role in water transport through the membrane. These sites act both as water sorption and transport sites. Surface diffusion of water occurs in an activated fashion through these sites. The precise nanoporous structure of the zeolite cage helps in a partial molecular sieving of the large solvent molecules leading to high separation factors. A comparison between experimental flux and calculated flux using Stephan Maxwell (S.M.) correlation was made and a linear trend was found to exist for water flux through the membrane with UDMH concentration.