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Effects of a flexible joint on instability of a free-free jointed bipartite beam under the follower and transversal forces

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第9期10卷 1252-1262页

作者： saied IRANI Omid KAVIANIPOUR Department of Aerospace Engineering K.N.Toosi University of Technology

This paper deals with the problem of the instability regions of a free-free flexible jointed bipartite beam under the follower and transversal forces as a realistic simulation of a two-stage aerospace structure. The aim of this study is to analyze the effects of the characteristics of a flexible joint on the beam instability to use maximum bearable propulsion force. A parametric study is conducted to investigate the effects of the stiffness and the location of the joint on the critical follower force by the Ritz method and the Newmark method, then to research the vibrational properties of the structure. It has been shown that the nature of instability is quite unpredictable and dependent on the stiffness and the location of the joint. The increase of the follower force or the transversal force will increase the vibration of the model and consequently cause a destructive phenomenon in the control system of the aerospace structure. Furthermore, this paper introduces a new concept of the parametric approach to analyze the characteristics effects of a flexible two-stage aerospace structure joint design.

关键词： Two stage to orbit launch vehicle (TSTO LV) Beam instability Follower force Ritz's method Newmark's method

Unveiling the hidden connection:Investigating the relationship between shared leadership and missed nursing care

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International Journal of Nursing Sciences 2025年第1期12卷 12-18,I0001页

作者： Amal Diab Ghanem Atalla Naglaa Abdelaziz Mahmoud Elseesy Ayman Mohamed El-Ashry Samia Mohamed Sobhi Mohamed Ebaa Marwan Felemban Abdulhafith Alharbi Nervana Abdelrahman saied Gheith Sabrein Mahmoud khalifa khattab Department of Nursing Administration Faculty of NursingAlexandria UniversityAlexandriaEgypt Department of Public Health Nursing Faculty of NursingKing Abdulaziz UniversityJeddahAl-QurayyatSaudi Arabia Department of Nursing Collage of Applied Medical SciencesAl-QurayyatJouf UniversityAl-QurayyatSaudi Arabia Department of Psychiatric and Mental Health Nursing College of NursingUniversity of HailHailSaudi Arabia Department of Nursing Administration Faculty of NursingMansoura UniversityMansouraEgypt

Objectives:This study examined the levels of shared leadership and missed nursing care and their relationship among nurses in ***:A cross-sectional survey was *** February to April 2024,340 nurses worked in all inpatient care units at Alexandria Main University *** Shared Leadership and Missed Nursing Care Survey was used for ***:The overall score of shared leadership was(72.62±4.30),which imitates a high perception of shared leadership among nurses;the dimension of delegation achieved the highest average mean score(3.66±0.26),followed by collaboration(3.64±0.31),the vision dimension scored the lowest mean score(3.59±0.33).The elements of missed nursing care had a total score of(46.72±5.69),and the dimension of secondary care achieved the highest average mean score(3.74±0.31).The reasons for missed nursing care had a total mean score of(22.40±1.59),and the dimension of labor resources achieved the highest average mean score(3.20±0.22).Male nurses,less than 30 years old,married,held a bachelor’s degree in nursing sciences,less than five years of experience in the nursing profession,and less than five years of experience in the current working unit had higher total scores of the shared leadership and lower total scores of missed nursing care(P<0.001).A negative correlation existed between shared leadership and two dimentisons(the elements of nursing care[r=-0.383],the reasons for missing nursing care[r=-0.047])(P<0.001).Conclusions:The study’s findings can help as a theoretical underpinning for nursing leaders to stand in an environment that reduces the incidence of missed nursing care by encouraging teamwork,responsibility,workload management,and empowerment among nurses.

关键词： Missed nursing care Nurses Nursing administration research Shared leadership

Asperity-based modification on theory of contact mechanics and rubber friction for self-affine fractal surfaces

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Friction 2021年第6期9卷 1707-1725页

作者： Anahita EMAMI Seyedmeysam KHALEGHIAN saied TAHERI Texas State University 601 University DriveSan MarcosTexas 78666USA Virginia Polytechnic Institute and State University 460 Old Turner Street BlacksburgBlacksburgVirginia 24061USA

Modeling the real contact area plays a key role in every tribological process,such as friction,adhesion,and *** between two solids does not necessarily occur everywhere within the apparent contact *** the multiscale nature of roughness,Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough *** this theory,he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate *** this assumption gives an accurate pressure distribution at the interface for complete contact,when no gap exists between two surfaces,it results in an overestimation of elastic energy stored in the material for partial contact,which typically occurs in many practical *** issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics *** paper proposes a different approach to correct the overestimation of vertical displacement in Persson’s contact theory for rough surfaces with self-affine fractal *** results are compared with the correction factor proposed by *** main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics,material properties,sliding velocity,and normal load to correct the *** method is also implemented in the theory of rubber *** results of the corrected friction model are compared with *** results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model.

关键词： contact area rubber friction self-affine fractals tribology surface roughness

Bifurcation in a 3-DOF Airfoil with Cubic Structural Nonlinearity

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Chinese Journal of Aeronautics 2011年第3期24卷 265-278页

作者： saied IRANI Hamid SARRAFZADEH Mohammad Reza AMOOZGAR Department of Aerospace Engineering K.N.Toosi University of Technology

Limit cycle oscillations （LCOs） as well as nonlinear aeroelastic analysis of a 3-DOF aeroelastic airfoil motion with cubic restoring moments in the pitch degree of freedom are investigated. Aeroelastic equations of an airfoil with control surface in an incompressible potential flow are presented in the time domain. The harmonic balance （HB） method is utilized to calculate the LCO frequency and amplitude for the airfoil. Also the semi-analytical method has revealed the presence of stable and unstable limit cycles, along with stability reversal in the neighborhood of a Hopf bifurcation. The system response is determined by nu- merically integrating the governing equations using a standard Runge-Kutta algorithm and the obtained results are compared with the HB method. Also the results by the third order HB （HB3） method for control surface are consistent with the other numerical solution. Finally, by combining the numerical and the HB methods, types of bifiarcation, be it supercritical, subcritical, or diver- gent flutter area are identified.

关键词： flutter bifurcation cubic nonlinearity limit cycle oscillations harmonic balance method

A technical survey on tire-road friction estimation

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Friction 2017年第2期5卷 123-146页

作者： Seyedmeysam KHALEGHIAN Anahita EMAMI saied TAHERI Center for Tire Research(CenTiRe) Department of Mechanical Engineering Virginia Tech Blacksburg VA 24061 United States Department of Biomedical Engineering and Mechanics Virginia Tech Blacksburg VA 24061 United States

Lack of driver's knowledge about the abrupt changes in pavement's friction and poor performance of the vehicle's stability,traction,and ABS controllers on the low friction surfaces are the most important factors affecting car *** to its direct relation to vehicle stability,accurate estimation of tire-road friction is of interest to all vehicle and tire *** studies have been conducted in this field and researchers have used different tools and have proposed different *** literature survey introduces different approaches,which have been widely used to estimate the friction or other related parameters,and covers the recent literature that contains these *** emphasize of this review paper is on the algorithms and studies,which are more popular and have been repeated several *** focus has been divided into two main groups:experiment-based and model-based *** of these main groups has several sub-categories,which are explained in the next few *** summary tables are provided in which the overall feature of each approach is reviewed that gives the reader the general picture of different algorithms,which are widely used in friction estimation studies.

关键词： tire-road friction friction estimation model-based approach experiment-based approach

Corrosion Behavior and Biocompatibility of Hydroxyapatite Coating on H_2SO_4 Passivated 316L SS for Human Body Implant

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Acta Metallurgica Sinica(English Letters) 2013年第4期26卷 409-415页

作者： Ali Parsapour saied Nouri Khorasani Mohammad Hossein Fathi Biomaterials Research Center Department of Chemical Engineering Isfahan University of Technology Department of Materials Engineering Isfahan University of Technology

The aim of this studies at simultaneous improvement of the corrosion behavior and biocompatibility of metallic implant and bone Osseointegration simultaneously. Stainless steel 316L （SS） was used as metallic substrate and after surface treatment with 15 vol.% sulfuric acid, it was coated with hydroxyapatite coating employing plasma - spraying process. Structure characterization techniques including XRD, SEM and EDX were also utilized to investigate the microstructure, morphology, and crystallinity of the coating. Electrochemical potentiodynamic tests were performed in two types of physiological solutions in order to determine and compare the corrosion resistance behavior of the coated and uncoated specimens as an indication of biocompatibility. The results indicate that the surface treatment and hydroxyapatite coating improve the corrosion resistance behavior of SS. The corrosion current density of the surface treated and the hydroxyapatite coated SS also decrease. These also show that surface treated and hydroxyapatite coated SS can be used as human body implants with the goals of corrosion resistance improvement （biocompatibility） and bone osseointegration.

关键词： Surface treatment Hydroxyapatite coating Corrosion behavior Plasma spray Stainless steel 316L Human body implant

Synthesis and characterization of a new magnetic bromochromate hybrid nanomaterial with triethylamine surface modified iron oxide nanoparticles

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Chinese Chemical Letters 2014年第6期25卷 919-922页

作者： Rahmatollah Rahimi Ali Maleki saied Maleki Department of Chemistry Iran University of Science and Technology

We describe a novel method for the synthesis a new magnetic bromochromate hybrid nanomaterial, Fe3O4@SiO2@TEA@[CrO3Br], as a catalyst. The physical properties, morphology and magnetic investigations of magnetic bromochromate hybrid nanomaterials are identified by transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and vibrating sample magnetometer （VSM） techniques. Fourier transform infrared （FT-IR）, elemental analysis, X-ray fluorescence （XRF）, X-ray diffraction （XRD） were also used for structural identification. The quantity of chromium is approximately 0.38%, which confirms to the immobilization amount of [CrO3Br]- and is equal to 0.007 mol/100 g.

关键词： Magnetic nanoparticles Fe3O4 Bromochromate

Effect of Surface Treatment and Metallic Coating on Corrosion Behavior and Biocompatibility of Surgical 316L Stainless Steel Implant

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Journal of Materials Science & Technology 2012年第2期28卷 125-131页

作者： Ali Parsapour saied Nouri Khorasani Mohammad Hossein Fathi Department of Materials Engineering Isfahan University of Technology Department of Chemical Engineering Isfahan University of Technology

Surface engineering technology is a suitable method for coatings on the metal surfaces or performing surface modification treatment, which can improve corrosion resistance and biocompatibility of metals. In this research, corrosion behavior of Nb coating on H2SO4 and HNO3 treated AISI stainless steel 316L （SS） was evaluated. Nb coating was carried out using physical vapor deposition process on the SS. Characterization techniques including scanning electron microscopy （SEM） and energy dispersive X-ray （EDX） technique were used to investigate the microstructure and morphology of the coated and treated SS. Electrochemical potentiodynamic tests were performed in two types of physiological solutions and compared with the pristine SS specimens. Cyclic polarization tests were performed to evaluate resistivity against pitting. Experimental results indicate that Nb coating and surface treatment of the SS had a positive effect on improvement of corrosion behavior. The decrease in corrosion current densities was significant for coated and treated specimens. The corrosion current density was much lower than the values obtained for pristine specimens.

关键词： 316L stainless steel Corrosion behavior Nb coating Surface treatment

Propagation and aperture of staged hydraulic fractures in unconventional resources in toughness-dominated regimes

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第2期10卷 249-258页

作者： Ali Taghichian Hamid Hashemalhoseini Musharraf Zaman saied Beheshti Zavareh Department of Civil Engineering Isfahan University of Technology Mewbourne School of Petroleum and Geological Engineering Sarkeys Energy CenterUniversity of Oklahoma Department of Mining Engineering Isfahan University of Technology

Simultaneous multistage hydraulic fracturing of unconventional gas shale in parallel multilateral wells is an effective technique to raise the connectivity of the reservoir to the wellbore and improve reservoir permeability for an economical production. However, this technique should be accompanied with some optimization procedures to obtain an efficiently fractured reservoir with the highest production and the lowest cost. In unconventional hydraulic fracturing, fracture deviation/collapse and trapping are familiar phenomena which occur when a non-optimized fracturing pattern is used. These problems occur respectively when stress shadow size has not been considered in optimization and fracturing pressure is higher than the available pressure in the sealed section. Therefore, in an optimized hydraulic fracturing,having straight fractures with no deviation or collapse needs consideration of stress shadow effect(SSE).Apart from that, having efficiently propagated fractures to the extent of the reservoir without any fracture trap requires consideration of stress intensity factor(SIF) and aperture. SSE was studied and published by the authors in 2014. For the case of SIF, investigating any change in mode I SIF and aperture with different influencing variables such as fracture geometry and pattern are studied in the current research work. Three different fracturing techniques are assumed as multistage fracturing, simultaneous single-stage fracturing, and simultaneous multistage fracturing techniques. Since obtaining SIF for threedimensional fractures is a challenging issue, a stress ratio technique is used for calculation of SIF ratios of different fracturing scenarios compared to the case of a single fracture. Therefore, changes of SIF for different fracturing schemes are estimated and analyzed to understand whether or not a fracturing scheme is efficient and all the spaced perforations are activated and change to hydraulic fractures.

关键词： Hydraulic fracturing Stress intensity factor(SIF) Aperture Numerical analysis Gas shale