A novel concept is proposed: the use of shape memory
alloy (SMA) to reduce panel thermal deflection and flutter
responses. SMA has a unique ability to recover large
pre-strains completely when the alloy is heated above the
austenite finish temperature Af. The transformation
austenite start temperature As for nitinol can be anywhere
between -60 °F (-50 °C) and
+340 °F (+170 °C) by varying the nickel
content. During the recovery process, a large tensile recovery
stress occurs if the SMA is restrained. The shape memory effect
phenomenon is attributed to a change in crystal structure known as
a reversible austenite to martensite phase transformation. This
solid-solid phase transformation also gives a large increase
in Young's modulus and yield stress.
In this paper, a panel subject to the combined aerodynamic and
thermal loading is investigated. A nonlinear finite element
model based on the von Karman strain-displacement relation is
utilized to study the effectiveness of an SMA-embedded panel on
the flutter boundary, critical buckling temperature,
post-buckling deflection and free vibration. The study is
performed on an isotropic panel with embedded SMA. The
aerodynamic model is based on the first-order quasi-steady
piston theory. The dynamic pressure effect on the buckling and
post-buckling behaviour of the panel is investigated by
introducing the aerodynamic stiffness term, which changes the
critical buckling temperature. Panels with SMA embedded in
either the longer or shorter direction and either fully or
partially embedded are investigated for post-buckling behaviour.
Similarly, the influence of temperature elevation on the
flutter boundary and vibration frequencies is investigated.
Using the Stochastic Finite Element Method (SFEM) to perform reliability analysis of the free vibration of composite plates with material and fabrication uncertainties has received much attention lately. In this work the stochastic analysis is performed using the First Order Reliability Method (FORM-method 2) and the Second Order Reliability Method (SORM). The basic random variables include laminae stiffness properties and material density, as well as the randomness in ply orientation angles. Modeling of the composite behavior utilizes a nine-noded isoparametric Lagrangian element based on the third order shear deformation theory. The developed code utilizes MATLAB capabilities to derive the derivatives of the reduced stiffness and mass matrices symbolically with a considerable reduction in calculation time. Calculating the eigenvectors at the mean values of the variables proves to be a reasonable simplification which significantly increases solution speed. The stochastic finite element code is validated using available data in the literature, in addition to comparisons with results of the well-established Monte Carlo simulation technique with importance sampling. Results show that SORM is an excellent rapid tool in the stochastic analysis of free vibration of composite plates, when compared to the slower Monte Carlo simulation techniques.
Aim
Agomelatine (AGM) is the first melatonergic antidepressant. It suffers from low oral bioavailability (<5%) due to extensive hepatic metabolism. The current work aimed to develop an alternative AGM-loaded invasomes to enhance transdermal drug bioavailability.
Methodology
AGM-loaded invasomes were developed using two drug: lipid ratios (1:10 or 1:7.5), four terpene types (limonene, cineole, fenchone or citral) and two terpene concentrations (0.75% or 1.5%, w/v). They were characterized for drug entrapment efficiency (EE%), particle size (PS), zeta potential (ZP) and drug released percentages after 0.5h (Q
0.5h
) and 8h (Q
8h
). The optimum invasomes (I1, I2 and I4) were evaluated for morphology, drug-crystallinity, and ex-vivo drug flux. The variables influencing sonophoresis of the best achieved invasomal gel system (I2) were optimized including, ultrasound frequency (low, LFU or high, HFU), mode (pulsed or continuous), application period (10 min or 15 min) and duty cycle (50% or 100%). AGM pharmacokinetics were evaluated in rabbits following transdermal application of I2-LFU-C4 system, relative to AGM oral dispersion.
Results
The superiority of I2 invasomes [comprising AGM and phosphatidylcholine (1:10) and limonene (1.5% w/v)] was statistically revealed with respect to EE% (78.6%), PS (313 nm), ZP (−64 mV), Q
0.5h
(30.1%), Q
8h
(92%), flux (10.79 µg/cm2/h) and enhancement ratio (4.83). The optimum sonophoresis conditions involved application of LFU in the continuous mode for 15 min at a 100% duty cycle (I2-LFU-C4 system). The latter system showed significantly higher C
max
, and relative bioavailability (≈ 7.25 folds) and a similar T
max
(0.5 h).
Conclusion
I2-LFU-C4 is a promising transdermal system for AGM.
Ascobin (compound composed of ascorbic acid and citric acid) is considered one of exogenous protectants which may alleviate the harmful effects of salinity stress. Pot experiments were performed at the screen greenhouse of National Research Centre, Cairo, Egypt to study the effect of foliar treatment of two cultivars of wheat plant with different concentrations of ascobin (0, 200, 400 and 600 mg/l) on some biochemical parameters, antioxidant enzymes, element contents and amino acid constituents of two cultivars of wheat plant grown under different salinity levels (0.0, 3000 and 6000 mg/l) in 2011/2012 and 2012/2013. Salinity with different concentrations levels increased phenolic compounds contents of the two wheat cultivars. The activities of antioxidant enzymes (SOD, CAT, POD, PPO, AXP and GR) dramatically increased due to salinity stress. Amino acid content was increased in cultivar Sids 1, while the content was decreased in cultivar Giza 168 in all salinity treatments. Increments in the above mentioned parameters compared to the untreated plants at normal and stressed conditions. The magnitude of increments was much more pronounced in response to 600 mg/l of ascobin. It could be concluded that, foliar treatment of wheat cultivars with ascobin could partially alleviate the harmful effect of salinity especially at the lower levels of salinity of the two cultivars of wheat at most of the studied parameters.
A new nonlinear finite element model is provided for the nonlinear flutter response of shape memory alloy (SMA) hybrid composite plates under the combined effect of thermal and aerodynamic loads. The nonlinear governing equations for moderately thick rectangular plates are obtained using first-order shear-deformable plate theory, von Karman strain-displacement relations and the principle of virtual work. To account for the temperature dependence of material properties, the thermal strain is stated as an integral quantity of thermal expansion coefficient with respect to temperature. The aerodynamic pressure is modeled using the quasi-steady first-order piston theory. Newton-Raphson iteration method is employed to obtain the thermal post-buckling deflection, while the linearized updated mode method is implemented in predicting the limit-cycle oscillation at elevated temperatures. Numerical results are presented to show the thermal buckling and flutter characteristics of SMA hybrid composite plates, illustrating the effect of the SMA volume fraction and pre-strain value on the aero-thermo-mechanical response of such plates.
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