Search for: force
Total 1380 records
Article International Journal of Modern Physics B ; Volume 26, Issue 7 , 2012 ; 02179792 (ISSN) ; Darvishian, A ; Zohoor, H ; Ahmadian, M. T ; Sharif University of Technology
In the current paper, the effect of van der Waals (vdW) force on the static behavior and pull-in characteristics of nano/micromirrors under capillary force is investigated. At first, the dimensionless equation governing the static behavior of nano/micromirrors is obtained. The dependence of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that the existence of vdW force can considerably reduce the stability limits of the nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the vdW force applied to the mirror. Finally, analytical...
Article International Journal of Theoretical Physics ; Volume 51, Issue 6 , 2012 , Pages 1938-1945 ; 00207748 (ISSN) ; Tanhayi Ahari, M ; Tanhayi, M. R ; Tavakoli, F ; Sharif University of Technology
In this work we first obtain a trajectory of a freely falling charged particle in de Sitter space and then in the classical approach, the effect of electromagnetic self-force on particle's trajectory has been considered. Finally, some limits for the problem have been presented
Article Physica Status Solidi (B) Basic Research ; Volume 248, Issue 6 , 2011 , Pages 1437-1441 ; 03701972 (ISSN) ; Gutkin, M. Y ; Moeini Ardakani, S. S ; Sharif University of Technology
Behavior of a screw dislocation inside a nanotube (NT) is considered in the context of surface elasticity. The elastic fields as well as the image force acting over the dislocation are derived and analyzed in detail. In contrast with the result of classical elasticity, the screw dislocation is shown to be repelled by free surfaces and occupy two stable equilibrium positions near them. The image force strongly depends on the NT's inner and outer radii as well as surface elastic characteristics
Mechanical properties of graphene cantilever from atomic force microscopy and density functional theory, Article Nanotechnology ; Volume 21, Issue 18, Article number 185503 , 2010 ; 09574484 ; Iraji Zad, A. (Azam) ; Ahadian, M. M ; Sharif University of Technology
We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin–Müller–Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ~ 37, Ea ~ 0.7 TPa and a Hamakar constant of ~ 3 × 10 − 18 J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated...
Article Archive of Applied Mechanics ; Volume 87, Issue 11 , 2017 , Pages 1871-1889 ; 09391533 (ISSN) ; Heydari, M ; Behzad, M ; Sharif University of Technology
In this paper, the forced vibration of a cracked rotor with an open edge crack has been studied by a new continuous model for flexural vibration of cracked rotors proposed in Ebrahimi et al. (J Sound Vib 333:3522–3535, 2014). The cracked rotor behavior under the external excitation of gravity and unbalance forces is presented. Since the governing equation is linear, using the superposition principle the responses of the cracked rotor to the gravity and unbalance forces are calculated separately. Then, the total response is calculated by summing these two responses. Each of these two responses is found by using a modified Galerkin method. The effect of the crack in the presence of the gravity...
Discussing the Behavior of the Boundary Theory Caused by Kalb-Ramond Field Perturbation in the Bulk, Using AdS/CFT Correspondence, M.Sc. Thesis Sharif University of Technology ; Arfaei, Hessamaddin
In this thesis we have used the low energy effective action of the string theory to find an asymptotic Anti-de sitter metric with a non-vanishing H field. Then we have used the AdS/CFT correspondence to study the effects of the added Kalb_Ramond field on two calculations in the boundary theory. The first one was the calculation of the drag force exerted on a moving quark in the quark-gluon plasma. In the second calculation we observed the effect of the added field on the confinement-de confinement phase transition
Article AIP Conference Proceedings, 24 October 2010 through 27 October 2010, Paris ; Volume 1315 , 2010 , Pages 961-966 ; 0094243X (ISSN) ; 9780735408715 (ISBN) ; Gorjizadeh, A ; Mikaeil, R ; Sharif University of Technology
The application of sensor system is becoming more commonplace in improving productivity and reliability. Although measuring force signal have been widely used for monitoring of metal machining process that their application to stone cutting has not been well investigated. In this paper, the effect of machining parameter on force signal and tool wear was investigated. The result indicate that increasing of the depth of cut and spindle speed will increase the force and tool wear while increasing feed rate will increase force and decrease tool wear
Article Special Topics and Reviews in Porous Media ; Volume 1, Issue 1 , 2010 , Pages 39-47 ; 21514798 (ISSN) ; Kharrat, R ; Alipour Tabrizy, V ; Khosravi, M ; Ghotbi, C ; Sharif University of Technology
The drainage of oil under gravity forces is an efficient method because it can farther reduce the remaining oil saturation to below that obtained after water flooding. This paper describes a series of visual experiments under forced gas invasion with special attention to the effects of wettability. From oil production history and image analysis, we examine a threshold criterion for displacement stability that is consistent with the results of gradient percolation theory. The effect of the destabilized front velocity on oil recovery and residual saturation is investigated for both wettability conditions. Different recovery rates occur with different fluid morphologies, which depend on the...
Article Journal of Economic Studies ; Volume 47, Issue 1 , 2020 , Pages 1-19 ; Rahmati, M ; Sharif University of Technology
Emerald Group Publishing Ltd 2020
Purpose: The purpose of this study is to determine why female labor force participation in Iran has been less than 20 percent. Design/methodology/approach: The authors estimate a structural dynamic matching model of female participation using individual panel data in Iran. The study incorporates many factors such as wage, child cost, education, spouse employment and job market search parameters. Findings: The study finds that gender discrimination in job finding has the biggest effect in reducing the rate of women's participation. If all market differences disappear, the female participation rate will increase by 12 percentage points to almost 27 percent, which is still much lower than that...
Article Nonlinear Analysis: Hybrid Systems ; Volume 1, Issue 3 , 2007 , Pages 364-382 ; 1751570X (ISSN) ; Alasty, A ; Akbari, J ; Sharif University of Technology
In this paper, the effect of the Casimir force on pull-in parameters of cantilever type nanomechanical switches is investigated by using a distributed parameter model. In modeling of the electrostatic force, the fringing field effect is taken into account. The model is nonlinear due to the inherent nonlinearity of the Casimir and electrostatic forces. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The pull-in parameters of the switch are computed in three cases including nanoactuators...
Article CHISA 2006 - 17th International Congress of Chemical and Process Engineering, Prague, 27 August 2006 through 31 August 2006 ; 2006 ; 8086059456 (ISBN); 9788086059457 (ISBN) ; Yaghmaei, S ; Jafari, A ; Zamankhan, P ; Sharif University of Technology
Dynamic modeling and sensitivity analysis of atomic force microscope pushing force in nanoparticle manipulation on a rough substrate [electronic resource], Article Journal of Advanced Science, Engineering and Medicine ; 2013, Vol. 5, pp. 1-10 ; Mahboobi, Seyed Hanif ; Meghdari, Ali ; Sharif University of Technology
An Atomic Force Microscope (AFM) is a capable tool to manipulate nanoparticles by exerting pushing force on the nanoparticles located on the substrate. In reality, the substrate cannot be considered as a smooth surface particularly at the nanoscale. Hence, the particle may encounter a step on the substrate during a manipulation. In this study, dynamics of the nanoparticle on a stepped substrate and critical pushing force in the manipulation are investigated. There are two possible dynamic modes that may happen in the manipulation on the stepped substrate. In one mode, the nanoparticle may slide on the step edge and then climb up to the step which is a desired mode. Another possible mode is...
An exploration in acoustic radiation force experienced by cylindrical shells via resonance scattering theory, Article Ultrasonics ; Vol. 54, issue. 4 , April , 2014 , pp. 971-980 ; ISSN: 0041624X ; Behzad, M ; Sharif University of Technology
In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each...
Modeling of Pull-In Instability of Nano/Micromirrors Under the Combined Effect of Capillary and Casimir Forces, Article International Journal of Optomechatronics ; Volume 5, Issue 4 , Dec , 2011 , Pages 378-392 ; 15599612 (ISSN) ; Darvishian, A ; Ahmaidan, M. T ; Sharif University of Technology
In the current article the effect of the Casimir force on the static behavior and pull-in characteristics of nano/micromirrors under capillary force is investigated. At the first, the dimensionless equation governing the static behavior of nano/micromirrors is obtained. The dependency of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that the Casimir effect can considerably reduce the pull-in instability limits of the nano/micromirror. It is also found that rotation angle of the mirror under capillary force highly depends on the Casimir force applied to the mirror. Finally the...
Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010 ; Volume 3 , 2010 , Pages 619-626 ; 9780791849170 (ISBN) ; Khodabakhsh, M ; ASME Turkey Section ; Sharif University of Technology
A method for singularity reduction in a triangular 3-UPS mechanism is discussed. This mechanism usually has singularity near the origin. Changing the active joint angle can arrive at a suitable workspace near the origin without any singularity. Moreover, a 4-UPS mechanism, based on adding one additional leg to the 3-UPS mechanism, has a larger singular free workspace. Moreover, force analysis of two different mechanisms shows a reasonable and consistent force distribution between the different actuators. Singular free workspace is one of the characteristics which makes this mechanism ideal for haptic applications
A coupled model between torsion and bending in nano/micromirrors under the combined effect of Van der Waals force and capillary force, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011, Denver, CO ; Volume 11 , 2011 , Pages 523-529 ; 9780791854976 (ISBN) ; Darvishian, A ; Ahmadian, M. T ; ASME ; Sharif University of Technology
The coupling effect between torsion and bending in nano/micromirrors under the combined effect of capillary force and van der Waals (vdW) force is presented in this paper. At the first, the dimensionless equations governing the statical behavior of the nano/micromirror are obtained using the minimum total potential energy principle. Then the equations governing the pull-in state of the mirror are obtained using the implicit function theorem. The related results show that neglecting bending effect can lead to considerable overestimation in predicting the pull-in limits of the nano/micromirror under combined vdW and capillary forces. It is observed that vdW force reduces the pull-in angle and...
Mechanical properties of graphene cantilever from atomic force microscopy and density functional theory, Article Nanotechnology ; Volume 21, Issue 18 , 2010 ; 09574484 (ISSN) ; Iraji Zad, A ; Ahadian, M. M ; Sharif University of Technology
We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin-Müller-Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ∼ 37, Ea ∼ 0.7TPa and a Hamakar constant of ∼ 3 × 10 -18J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated from...
Critical ambient pressure and critical cooling rate in optomechanics of electromagnetically levitated nanoparticles, Article Journal of the Optical Society of America B: Optical Physics ; Volume 38, Issue 12 , 2021 , Pages 3652-3662 ; 07403224 (ISSN) ; Sharif University of Technology
The Optical Society 2021
The concept of critical ambient pressure is introduced in this paper. The particle escapes from its trap when the ambient pressure becomes comparable with or smaller than a critical value, even if the particle motion is cooled by one of the feedback cooling (or cavity cooling) schemes realized so far. The critical ambient pressure may be so small that it is not a limiting factor in ground-state cooling, but critical feedback cooling rates, which are also introduced in this paper, are limiting factors. The particle escapes from its trap if any of the feedback cooling rates (corresponding to the components of the particle motion) becomes comparable with or larger than its critical value. The...
M.Sc. Thesis Sharif University of Technology ; Alasti, Aria ; Vossoughi, Gholamreza
In this paper, controlling the cutting force of an end-milling process using a supervisory fuzzy controller has been investigated. The proposed control consists of an ordinary fuzzy controller and a fuzzy supervisor. In a machining process, there are several parameters which do not contribute to the force control system directly. Therefore an ordinary fuzzy force controller is suitable when these parameter have only small amount of variations. Since in practice this assumption is not valid, then a supervisory fuzzy controller has been added to the system. The designed fuzzy supervisor, inspects the dynamic behavior of the cutting force, estimates a pre-defined ‘sensitivity’ parameter and...
M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad
Considering the advantages and disadvantages of reported micropumps, we aimed to introduce a novel idea to diminish the disadvantages and promote the advantages of PiezoElectric micropumps. This novel idea operates based on a mercury slug actuation in a microchannel. This cyclic motion of the mercury slug which is similar to a piston, push the fluid in the microchannel and pump the flow. However, to bring this idea into the practice, a control system must be designed. This system contains: LABVIEW code, DAQ board & a switching Board. The pattern of actuating mercury is drawn in LABVIEW. DAQ Board produces electrical signals according to LABVIEW code. Switching board will transform the...