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This paper develops a higher order refined beam model with a parabolic shear strain function for vibration analysis of porous nanocrystalline nanobeams based on nonlocal couple stress theory. Nanocrystalline nanobeam is composed from three phases which are nano-grains, nano-voids and interface. Nano-voids or porosities inside the material have a stiffness-softening impact on the nanobeam. Nonlocal elasticity theory of Eringen is applied in analysis of nanocrystalline nanobeams for the first time. Also, modified couple stress theory is employed to capture grains rigid rotations. The governing equations obtained from Hamilton's principle are solved applying an analytical approach which satisfies various boundary conditions. The reliability of present approach is verified by comparing obtained results with those provided in literature. Finally the influences of nonlocal parameter, couple stress, grain size, porosities and shear deformation on the vibration characteristics of nanocrystalline nanobeams are explored. [ABSTRACT FROM AUTHOR]

In this article, the size-dependent and porosity-dependent vibrational behavior of magneto-electro-elastic functionally graded (MEE-FG) nanoscale beams on two-parameter elastic substrate is presented via a third-order shear deformation beam model. Porosity-dependent material coefficients of the nanobeam are compositionally graded throughout the thickness according to a modified power-law model. Incorporation of small size effect is carried out based on Eringen’s nonlocal elasticity theory. Through Hamilton’s principle, derivation of nonlocal governing equations is performed. After analytically solving these equations, the influences of porosity, elastic foundation, magnetic potential, applied voltage, scale coefficient, material gradation and slenderness ratio on the frequencies of the porous MEE-FG nanobeams are examined. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Some studies have reported erectile dysfunction in patients receiving lithium through a mechanism that has not yet been defined. The aim of the present study was to verify the effect of acute lithium administration on the nonadrenergic noncholinergic (NANC)- and endothelium-mediated relaxation of rat isolated corpus cavernosum. Materials and methods: The isolated rat corporeal strips were precontracted with phenylephrine hydrochloride (7.5μM) and electrical field stimulation (EFS) was applied at different frequencies (2, 5, 10, and 15Hz) to obtain NANC-mediated relaxation or relaxed by adding cumulative doses of acetylcholine (10nM–1mM) to obtain endothelium-dependent relaxation in the presence or absence of lithium (0.3, 0.5, 1, and 5mM). Also, effects of combining lithium (0.3mM) with 30nM and 0.1nM l-NAME (an NO synthase inhibitor) on NANC- and acetylcholine-mediated relaxation was investigated, respectively. Moreover, effects of combining lithium (1mM) with 0.1mM and 10μM l-arginine (a precursor of NO) on NANC- and endothelium-mediated relaxation was assessed, respectively. Also, the effect of lithium (1mM) on relaxation to sodium nitroprusside (SNP; 1nM–1mM), an NO donor, was investigated. Results: The NANC-mediated relaxation was significantly (P <0.001) reduced by 1 and 5mM, but not by 0.3 and 0.5mM lithium. Lithium significantly (P <0.001) attenuated the maximum response to acetylcholine in a concentration-dependent manner. Combination of lithium (0.3mM) with 30 and 0.1nM l-NAME, which separately had a minimum effect on NANC- and endothelium-mediated relaxation, significantly (P <0.001) reduced the NANC- and endothelium-mediated relaxation, respectively. Although l-arginine at 10μM and 0.1mM did not alter the relaxant responses to acetylcholine and EFS, it improved the inhibition by lithium (1mM) of relaxant responses to acetylcholine and EFS, respectively. Also, SNP produced similar concentration-dependent relaxations from both groups. Discussion: Our experiments indicated that lithium likely by interfering with NO pathway in both endothelium and nitrergic nerve can result in impairment of both the endothelium- and NANC-mediated relaxation of rat corpus cavernosum. [Copyright &y& Elsevier]

Abstract: Background: The protective effect of hypothyroidism against ischemic or toxic conditions has been shown in various tissues. We investigated the effect of propylthiouracil (PTU)/methimazole (MMI)-induced hypothyroidism and acute local effect of MMI on the outcome of lethal ischemia in random-pattern skin flaps. Materials and methods: Dorsal flaps with caudal pedicles were elevated at midline and flap survival was measured at the seventh day after surgery. The first group, as control, received 1 mL of 0.9% saline solution in the flap before flap elevation. In groups 2 and 3, hypothyroidism was induced by administration of either PTU 0.05% or MMI 0.04% in drinking water. The next four groups received local injections of MMI (10, 20, 50, or 100 μg/flap) before flap elevation. Local PTU injection was ignored due to insolubility of the agent. Results: Hypothyroidism was induced in chronic PTU- and MMI-treated groups, and animals in these groups showed significant increase in their flap survival, compared to control euthyroid rats (79.47% ± 10.49% and 75.48% ± 12.93% versus 52.26% ± 5.75%, respectively, P < 0.01). Acute local treatment of skin flaps with MMI failed to significantly affect the flap survival. Conclusion: This study demonstrates for the first time that hypothyroidism improves survival of random-pattern skin flaps in rats. [Copyright &y& Elsevier]

Background: Despite its apparent anti-apoptotic effect, lithium impairs endothelium-dependent vasorelaxation in various tissues. In this study, we assessed the effect of lithium treatment on ischemic skin flap survival and its interaction with nitric oxide pathway. Materials and Methods: Seventy-six male Sprague-Dawley rats were randomly assigned into 13 groups. For skin flap surgery, dorsal skin flap measuring 8 × 2 cm was elevated on the midline. After local injections (if needed), the cranial pedicle was cut and flap was sutured back. Flap survival was assessed after 7 d. Animals in the chronic lithium group received lithium chloride in tap water for 4 wk preoperatively and 7 d postoperatively. Acute lithium groups received 3 nmol, 10 nmol and 3 μmol/flap lithium locally. In another experiment, interaction with nitric oxide synthase inhibitor L-NAME as well as nitric oxide precursor L-arginine was studied, and the effect of ischemic preconditioning on skin flap survival in lithium treated rats was investigated. Results: Chronic lithium group had mean flap survival value of 32.6% ± 5.2% (mean ± SD), which was significantly lower than normal subjects (52.7% ± 6.1%, P < 0.001), while acute local lithium treatment had no effect. In chronic lithium group, systemic L-NAME (10 mg/kg, 30 min before flap elevation) failed to significantly decrease the survival, while sub-effective systemic L-arginine (100 mg/kg) and ischemic preconditioning significantly increased flap survival (P < 0.001 and P < 0.01, respectively). Conclusions: We conclude that long-term lithium treatment impairs the skin tolerance to ischemia in rats, which seems to be nitric oxide mediated. This effect is prevented by ischemic preconditioning or L-arginine treatment. The results suggest that skin-involving interventions should be applied more cautiously in patients who are on lithium treatment. [Copyright &y& Elsevier]