Exogenous ascorbate improves antioxidant defense system and induces salinity tolerance in soybean seedlings

Germination, growth and antioxidant defense system were investigated under salinity stress and pre-treatment with ascorbate (ASC) in two soybean cultivars SAHAR and DPX. Sterilized seeds were soaked in distilled water or ASC solution (0, 400 mg L-1) for 4 hrs before they were sown in distilled water or NaCl solution (0, 12.5 and 50 mM). Salt stress reduced the growth of both cultivars through reduction in percentage of germination, shoot and root length and dry weight of seedling. ASC induced enhancement in growth of salt-stressed plants coupled with an increase in catalase and peroxidase activity in seedlings only in SAHAR cultivar, and an increase in superoxide dismutase activity in both cultivars. These findings led us to conclude that applied ASC counteracts the adverse effects of salt stress on growth of soybean; however, these effects were cultivar specific

Effect of mass diffusion on the damping ratio in micro-beam resonators

AbstractPresent investigation is focused on studying the effect of mass diffusion on the quality factor of the micro-beam resonators. Equation of motion is obtained using Hamilton’s principle and also the equations of thermo-diffusive elastic damping are established using two dimensional non-Fourier heat conduction and non-Fickian mass diffusion models. Free vibration of a clamped–clamped micro-beam with isothermal boundary conditions at both ends, and also a cantilever micro-beam with adiabatic boundary condition assumption at the free end, is studied using Galerkin reduced order model formulation for the first mode of vibration. Mass diffusion effects on the damping ratio are studied for the various micro-beam thicknesses and temperatures and the obtained results are compared with the results of a model in which the mass diffusion effect is ignored. In addition to the classic critical thickness of thermoelastic damping, a new critical thickness concerning mass diffusion is introduced

An experimental study for characterization of size-dependence in microstructures via electrostatic pull-in instability technique

This paper experimentally investigates the size-dependent effective Young's modulus (Eeff) of aluminum (Al) clamped-clamped microbeams using the electrostatic pull-in instability technique. This study presents an experimental characterization of the so-called “length scale parameter” in couple stress theory and surface elasticity. Eeff is retrieved from the measured pull-in voltage, of the clamped-clamped beams with different dimensions, via an electromechanically coupled equation. Measurement results show a strong size dependence of Eeff for the Al beams in small sizes. The Young's modulus increases monotonously as the beams become thinner. The experimental observations are consistent with the published modeling results of the size effects, in which couple stress theory and surface elasticity theory are taken into consideration. The presented experimental method has substantial advantages such as precise adjustable magnitude of the non-contacting force and a lower cost over the other approaches used for characterization of micro-/nanoelectromechanical systems. This simple and reproducible method can be extended for characterization of various materials with different sizes and boundary conditions

Eliminating of the Residual Stresses Effect in the Fixed-Fixed End Type MEMS Switches by Piezoelectric Layers

Abstract: In this paper, a novel method has been developed to eliminate the tensile or compressive residual stresses effects that have been created due to the fabrication sequence. In the developed model, the tensile or compressive residual stresses in the fixed-fixed end type MEM switches have been eliminated by using of two piezoelectric layers that have been located on the upper and lower surfaces of switch. The nonlinear governing differential equation of the fixed-fixed end type MEM switch has been derived by considering the piezoelectric layers and residual stresses. The pull-in voltage and the switching time have been calculated for different applied voltage to the piezoelectric layers. The results show that the both tensile and residual stresses can be eliminated by means of a small applied voltage to the piezoelectric layers

Modeling Open-Loop MEMS Tunneling Accelerometer Based on Circular Plate

In this paper open-loop MEMS tunneling accelerometer was modeled based on a clamped micro circular plate with a tip tunneling at its centre. Mechanical behavior of the micro plate was studied deriving governing equation based on classic Kirchhoff thin plate theory and it was discretized using Galerkin method. Dynamic response of the proposed accelerometer due to step and harmonic external excitation was studied and the magnitude of the applied acceleration was identified by measuring of the changing of tunneling current. Obtained results show that the proposed tunneling accelerometer very sensitive and it can be measure acceleration with very high resolution but very small gap of tip tunneling limit the range of measurable acceleration

Mechanical Behavior of a Thermal Micromirror Based on a Bimetallic Cantilever Beam

In this work mechanical behavior of a thermal micromirror based on a bimetallic cantilever microbeam was studied. The main target is to control the reflection of an incident ray in order to strick to a specific point. Tip slope of the bimetallic beam that is deflected due to temperature changes acts as an intermediary to relate the angle of the reflected ray and temperature changes. Governing equations to indicate the relation were derived and analytically solved. Required time of the system to the temperature changes was calculated. Detecting the position of the reflected ray is possible whereas deflection and consequently slope of the beam vary linearly with temperature. The proposed micromirror can be used as a thermal sensor whereas deflection varies linearly with temperature