Modified continuum model for stability analysis of asymmetric FGM double-sided NEMS: Corrections due to finite conductivity, surface energy and nonlocal effect

Finite conductivity, surface energy and nonlocal effect can influence the electromechanical performance of micro/nano-electromechanical systems (MEMS/NEMS). However, these factors are yet ignored on stability analysis of MEMS/NEMS fabricated from functionally graded materials (FGM). In this paper, dynamic stability of double-sided NEMS fabricated from non-symmetric FGM is investigated incorporating finite conductivity, surface energy and nonlocal effect. The Gurtin-Murdoch model and Eringen's elasticity are employed to consider the surface energy and nonlocal effect, respectively. Effect of finite conductivity of FGM on electrostatic and Casimir attractions is incorporated via relative permittivity and plasma frequency of the material. The stability analysis of the nanostructure is conducted by plotting time history and phase portraits. Moreover, bifurcation analysis is conducted to investigate the stability of the fixed points of the nano-structure. The validity of the proposed model is examined by comparing the results of the present study with those reported in the literature. The impact of various parameters i.e. finite conductivity, nonlocal parameter, surface stresses and material characteristics on the dynamic instability of the NEMS are addressed. (C) 2015 Elsevier Ltd. All rights reserved

Thermodynamic and environmental analysis of a fuel cell power system used in a building in ahvaz

Herein, a fuel cell power system that works in CHP mode has been considered to provide electrical, heating, cooling and domestic hot water loads of buildings. The buildings tolerate hot summers and mild winters during their operation life. In previous research, the PEM fuel cell system was designed and number of fuel cell stacks to provide the required energy of the building was estimated. As a complementary investigation, the thermodynamic and environmental analysis of the mentioned system has been conducted in this research. Results have shown that for a 12 fuel cell stacks at a nominal capacity of 8.5 kW, the mass production of monoxide carbon, monoxide nitrogen and dioxide carbon are equal to 1272.621 (kg/year), 1609.056 (kg/year) and 26107.23 (kg/year), respectively. The mass production values are acceptable since it is within limitation ranges mentioned by many environmental protocols

The effect of breast self-examination training on knowledge, attitude and practice of women working in Shahrekord universities in 2010

Background and aim: Delay in diagnosis of breast cancer is still a main cause of death among disease women. However, preventive procedures to solve this problem are less than expectation. The success rate in the treatment of breast can be directly related to early diagnose and breast self –examination is one of the ways to detect the disease early. This study was aimed to examine the effect of education on knowledge, attitude and performance of employed women about breast self-examination. Methods: In this quasi-experimental study, 50 employee women randomly selected of Shahrekord University randomly. Participants during 2 weeks, in 2 sections and each session 2 hours performed self –examination. The rate of knowledge, attitude, and performance of participants before and after education using a questionnaires and check list were evaluated and compared. Results: Based on the results, the mean scores of subjects from 33.5±18.4 to 68.9± 9/2 increased (p<0.001). The mean scores for attitude increased from 74.5± 14.7 to 82.2±10.2 and the mean score for function from 41.5±30.8 before training to 84.8± 7.8 after training (p<0.001). Before training, %30 and after training, %84 of the wards under research breast self-examination performed. BSE McNamar test showed a significant difference before and after training breast self-examination (p<0.001). Conclusion: According to the present study, educational programs designed to enhance the knowledge, attitude and function and representation it through social media and health care centers is commend to provide opportunities for the use of screening methods

Microstructure-dependent dynamic behavior of torsional nano-varactor

Experiments depict that the physico-mechanical response of miniature devices is microstructure-dependent. However, the classic continuum theory cannot correctly predict the microstructure-dependency. In this paper, the strain gradient theory is employed to examine the dynamic behavior and instability characteristics of miniature varactor with trapezoidal geometry. The governing equation of the varactor is obtained incorporating the effects of Coulomb force, van der Waals (vdW) attraction, squeeze film damping and structural damping. The influences of microstructure on the dynamic instability of equilibrium points are studied by plotting the phase portrait and bifurcation diagrams. It is found that increase in the microstructure parameter enhances the torsional stability. In the presence of the applied voltage, the phase portrait shows the saddle-node bifurcation while for free-standing varactor a subcritical pitchfork bifurcation is observe

Modeling the stability of freestanding cnt probe/sensor in the vicinity of graphene layers considering casimir dispersion force

Carbon nanotube (CNT) is one the most important nano-elements in fabrication of probes, sensors and other ultrasmall devices that have a wide usage in engineering and medicine. In this paper, the deflection and instability of a freestanding CNT probe/sensor in the vicinity of the graphene layers are investigated. A nano-scale continuum model in conjunction with Euler beam theory is employed to obtain nonlinear constitutive equation of freestanding CNT by considering the effect of Casimir dispersion force. A numerical finite difference method is employed to solve the nonlinear governing equation. © 2006-2014 Asian Research Publishing Network (ARPN)

Electromechanical instability of nanobridge in ionic liquid electrolyte media: influence of electrical double layer, dispersion forces and size effect

In this paper, the electromechanical response and instability of the nanobridge immersed in ionic electrolyte media is investigated. The electrochemical force field is determined using double-layer theory and linearized Poisson–Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions are incorporated considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). The strain gradient elasticity is employed to model the size-dependent structural behavior of the nanobridge. To solve the nonlinear constitutive equation of the system, three approaches, e.g., the Rayleigh–Ritz method, Lumped parameter model and the numerical solution method are employed. Impacts of the dispersion forces and size effect on the instability characteristics as well as the effects of ion concentration and potential ratio are discussed. © 2015, Indian Association for the Cultivation of Science

Modeling the effect of microstructure on the coupled torsion/bending instability of rotational nano-mirror in Casimir regime

t has been well-established that the physical performance of nano-devices might be affected by the microstructure. Herein, a 2-degree-of-freedom model based on the modified couple stress elasticity is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nano-electromechanical mirror. The governing equation of the mirror is derived incorporating the effects of electrostatic Coulomb and corrected Casimir forces with the consideration of the finite conductivity of interacting surfaces. Effect of microstructure-dependency on the instability parameters are determined as a function of the microstructure parameter, bending/torsion coupling ratio, vacuum fluctuation parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the mirrors especially those with long rotational beam elements. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nano-mirror

Optimization of baffle spacingon heat transfer, pressure drop and estimated price in a shell-and-tube heat exchanger

In this paper for a given heat duty, study of the effects of baffle spacing on three parameters mentioned above is considered in a STHX with single segmental baffles and staggered tubes layout in Iran, Arvand petrochemical. A program in EES (Engineering Equations Solver) software is used for this purpose to solve governing equations; moreover, Aspen B-JAC and HTFS+softwares are used for considering estimated total price. At first the simulated results obtained from this program is compared to the experimental data for two cases of baffle spacing. The effects of baffle spacing are considered from 4 to 24 inches over overall heat transfer coefficient (OHTC) to pressure drop ratio (U/Δp ratio). The results show that U/Δp ratio is low when baffle spacing is minimum (4 inches) because pressure drop is high; however, heat transfer coefficient is very significant. And in this case estimated total price increases 7 percent. Then with the increase of baffle spacing, pressure drop rapidly decreases and OHTC also decreases, but the decrease of OHTC is lower than pressure drop, so (U/Δp) ratio increases. After increasing baffles more than 12 inches, variation in pressure drop is gradual and approximately constant and OHTC decreases; Consequently, U/Δp ratio decreases again. If baffle spacing reaches to 24 inches, STHX will have minimum pressure drop, but OHTC decreases, so required heat transfer surface increases and U/?p ratio decreases. After baffle spacing more than 12 inches, variation of both estimated price and shell side pressure drop is negligible. So optimum baffle spacing is suggested between 8 to 12 inches (43 to 63 percent of inside shell diameter) for a sufficient heat duty, low cost and low pressure drop. © IDOSI Publications, 2012

Modeling the coupled effects of surface layer and size effect on the static and dynamic instability of narrow nano-bridge structure

For modeling the electromechanical behavior of nano-bridge structures with slender narrow-width beam elements, not only the simultaneous effects of surface layer and size dependency should be taken into account but also corrected force models should be considered. In this paper, the instability of a narrow-width nano-bridge is studied based on strain gradient theory and Gurtin–Murdoch surface elasticity. The mid-plane stretching is incorporated in the governing equation as well as corrected force distribution. Using Rayleigh–Ritz method, a parametric analysis is conducted to examine the impacts of surface layer, size dependence, dispersion forces and structural damping on static and dynamic instability voltage of the nano-bridge. © 2016, The Brazilian Society of Mechanical Sciences and Engineering

Using HPM for approximating the instability of narrow bio-sensor used in bio-electronic, biology and cancer detection

Recently biosensors become one of the most components in evaluating live systems and medical applications. These applications are detection of cancers, DNA, tumors, cells, bio-enzymes etc. In this paper, we investigate the instability of narrow bio nano electro mechanical system (bio-NEMS) sensor. The proposed HPM is employed to solve nonlinear constitutive equation of cantilever beam-type bio-sensor. An analytical solution is obtained in terms of convergent series with easily computable components. The basic design parameters such as critical cantilever tip deflection of the bio-sensor are comp uted. The analytical results agree well with numerical solutions and those from the literature. © IDOSI Publications, 2012