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Mechanical analysis of cutout piezoelectric nonlocal nanobeam including surface energy effects
Mohamed A Eltaher,Fatema-Alzahraa Omar,Waleed S. Abdalla,Abdallah M. Kabeel,Amal E. Alshorbagy 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.1
This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long–range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin–Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler–Bernoulli nanobeam are derived by Hamilton’s principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell’s equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2≤α≤0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).
Mechanical behaviors of piezoelectric nonlocal nanobeam with cutouts
Mohamed A. Eltaher,Fatema-Alzahraa Omar,Azza M. Abdraboh,Waleed S. Abdalla,Amal E. Alshorbagy 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.2
This work presents a modified continuum model to explore and investigate static and vibration behaviors of perforated piezoelectric NEMS structure. The perforated nanostructure is modeled as a thin perforated nanobeam element with Euler.Bernoulli kinematic assumptions. A size scale effect is considered by included a nonlocal constitutive equation of Eringen in differential form. Modifications of geometrical parameters of perforated nanobeams are presented in simplified forms. To satisfy the Maxwell's equation, the distribution of electric potential for the piezoelectric nanobeam model is assumed to be varied as a combination of a cosine and linear functions. Hamilton's principle is exploited to develop mathematical governing equations. Modified numerical finite model is adopted to solve the equation of motion and equilibrium equation. The proposed model is validated with previous respectable work. Numerical investigations are presented to illustrate effects of the number of perforated holes, perforation size, nonlocal parameter, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric nanobeams.
Diagnosis of Clostridium difficile infection in patients with hospital-acquired diarrhea
Ibrahim Afifi, Salwa Selim,Gomaa, Fatma Alzahraa M.,Fathi, Lamia Fouad,Rasslan, Fatma Salah,Hamdy, Ahmed Mohamed The Microbiological Society of Korea 2018 미생물학회지 Vol.54 No.3
Clostridium difficile infection (CDI) is a rapidly emerging infection that may have devastating consequences. Prompt and accurate diagnosis is crucial for management and control. The aim of this study was to determine the incidence of C. difficile associated diarrhea among hospitalized patients, and to compare different diagnostic laboratory methods for detection of toxin producing strains in clinical specimens. The study was conducted at a university hospital in Cairo during the period from May 2013 till June 2015. Subjects were under antibiotic therapy and presented with hospital-acquired diarrhea. Four hundred and sixty-five stool specimens were processed by different microbiological methods. C. difficile was recovered in culture in 51 of stool specimens. Of these, 86.3% to 98% were positive for toxin production by 2 different methods. This study showed that antibiotic intake is the major risk factor for development of hospital-acquired diarrhea. We evaluated different microbiological methods for diagnosis of C. difficile. We recommend the use of toxigenic culture as a gold standard for microbiological diagnosis of C. difficile.
Mostafa Maha,Hasanin Ahmed,Mostafa Mahmoud,Taha Mai Y,Elsayad Mohamed,Haggag Fatma Alzahraa,Taalab Omar,Rady Ashraf,Abdelhamid Bassant 대한마취통증의학회 2021 Korean Journal of Anesthesiology Vol.74 No.4
Background: Elderly population are at increased risk of spinal anesthesia-induced hypotension increasing their risk for postoperative morbidity and mortality. This study aimed to compare the hemodynamic effects of prophylactic infusion of norepinephrine (NE) versus phenylephrine (PE) in elderly patients undergoing hip fracture surgery under spinal anesthesia. Methods: Elderly patients scheduled for hip fracture surgery were randomized to receive either NE infusion (8 µg/min) (NE group, n = 31) or PE infusion (100 µg/min) (PE group, n = 31) after spinal anesthesia. Outcomes included mean heart rate, mean blood pressure, cardiac output, incidence of spinal anesthesia-induced hypotension, incidence of bradycardia, and incidence of hypertension. Results: Sixty-two patients with a mean age of 71 ± 6 years were included in the final analysis (31 patients in each group). The NE group showed a higher mean heart rate and cardiac output than the PE group. The NE group had a lower incidence of reactive bradycardia (10% vs. 36%, P = 0.03) and hypertension (3% vs. 36%, P = 0.003) than the PE group. No study participant developed hypotension, and the mean blood pressure was comparable between the two groups. Conclusions: Both NE and PE infusions effectively prevented spinal anesthesia-induced hypotension in elderly patients undergoing hip fracture surgery. However, NE provided more hemodynamic stability than PE; maintaining the heart rate, higher cardiac output, less reactive bradycardia, and hypertension.