Articoli di riviste: "Force"

1

Mandelkern, Matthew, e Jonathan Phillips. "Sticky situations: 'Force' and quantifier domains". Semantics and Linguistic Theory 28 (27 novembre 2018): 474. http://dx.doi.org/10.3765/salt.v28i0.4431.

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When do we judge that someone was forced to do what they did? One relatively well-established finding is that subjects tend to judge that agents were not forced to do actions when those actions violate norms. A surprising discovery of Young & Phillips 2011 is that this effect seems to disappear when we frame the relevant ‘force’-claim in the active rather than passive voice ('X forced Y to φ' vs. 'Y was forced to φ by X'). Young and Phillips found a similar contrast when the scenario itself shifts attention from Y (the forcee) to X (the forcer). We propose that these effects can be (at least partly) explained by way of the role of attention in the setting of quantifier domains which in turn play a role in the evaluation of ‘force’- claims. We argue for this hypothesis by way of an experiment which shows that sequences of active vs. passive ‘force’-claims display the characteristic “stickiness” of quantifier domain expansion, using a paradigm which we argue provides a useful general paradigm for testing quantifier domain hypotheses. Finally, we sketch a semantics for ‘force’ which we argue is suitable for capturing these effects.

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Mihalka, Michael. "NATO Response Force: Rapid? Responsive? A Force?" Connections: The Quarterly Journal 04, n. 2 (2005): 67–79. http://dx.doi.org/10.11610/connections.04.2.09.

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3

Perveen, Asma, M. Rahman e Y. S. Wong. "Modeling of Vertical Micro Grinding". Key Engineering Materials 625 (agosto 2014): 463–68. http://dx.doi.org/10.4028/www.scientific.net/kem.625.463.

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Due to the small feed rate used in micro-machining, ploughing force needs to be considered in addition to the chip formation force. A new analytical model has been proposed to calculate cutting forces of micro-grinding process based on the process configuration, work piece material properties, and micro-grinding tool topography. The proposed approach allows the calculation of cutting force comprising both the chip formation force and ploughing forcec considering single grain interaction.

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Marquardt, Jens, Karoline Steinbacher e Miranda Schreurs. "Driving force or forced transition?" Journal of Cleaner Production 128 (agosto 2016): 22–33. http://dx.doi.org/10.1016/j.jclepro.2015.06.080.

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5

Spakovszky, Z. S. "Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors". Journal of Turbomachinery 122, n. 4 (1 febbraio 2000): 761–68. http://dx.doi.org/10.1115/1.1312801.

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A new analytical model to predict the aerodynamic forces in axial flow compressors due to asymmetric tip-clearance is introduced. The model captures the effects of tip-clearance induced distortion (i.e., forced shaft whirl), unsteady momentum-induced tangential blade forces, and pressure-induced forces on the spool. Pressure forces are shown to lag the tip-clearance asymmetry, resulting in a tangential (i.e., whirl-inducing) force due to spool pressure. This force can be of comparable magnitude to the classical Alford force. Prediction and elucidation of the Alford force is also presented. In particular, a new parameter denoted as the blade loading indicator is deduced. This parameter depends only on stage geometry and mean flow and determines the direction of whirl tendency due to tangential blade loading forces in both compressors and turbines. All findings are suitable for incorporation into an overall dynamic system analysis and integration into existing engine design tools. [S0889-504X(00)01604-4]

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Spandan, Vamsi, Daniel Putt, Rodolfo Ostilla-Mónico e Alpha A. Lee. "Fluctuation-induced force in homogeneous isotropic turbulence". Science Advances 6, n. 14 (aprile 2020): eaba0461. http://dx.doi.org/10.1126/sciadv.aba0461.

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Understanding force generation in nonequilibrium systems is a notable challenge in statistical physics. We uncover a fluctuation-induced force between two plates immersed in homogeneous isotropic turbulence using direct numerical simulations. The force is a nonmonotonic function of plate separation. The mechanism of force generation reveals an intriguing analogy with fluctuation-induced forces: In a fluid, energy and vorticity are localized in regions of defined length scales. When varying the distance between the plates, we exclude energy structures modifying the overall pressure on the plates. At intermediate plate distances, the intense vorticity structures (worms) are forced to interact in close vicinity between the plates. This interaction affects the pressure in the slit and the force between the plates. The combination of these two effects causes a nonmonotonic attractive force with a complex Reynolds number dependence. Our study sheds light on how length scale–dependent distributions of energy and high-intensity vortex structures determine Casimir forces.

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Ahmed, Rizwan, Christian Maria Firrone e Stefano Zucca. "Design and Calibration of a Tri-Directional Contact Force Measurement System". Applied Sciences 11, n. 2 (19 gennaio 2021): 877. http://dx.doi.org/10.3390/app11020877.

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In low pressure turbine stages, adjacent blades are coupled to each other at their tip by covers, called shrouds. Three-dimensional periodic contact forces at shrouds strongly affect the blade vibration level as energy is dissipated by friction. To validate contact models developed for the prediction of nonlinear forced response of shrouded blades, direct contact force measurement during dynamic tests is mandatory. In case of shrouded blades, the existing unidirectional and bi-directional contact force measurement methods need to be improved and extended to a tri-directional measurement of shroud contact forces for a comprehensive and more reliable validation of the shroud contact models. This demands an accurate and robust measurement solution that is compatible with the nature and orientation of the contact forces at blade shrouds. This study presents a cost effective and adaptable tri-directional force measurement system to measure static and dynamic contact forces simultaneously in three directions at blade shrouds during forced response tests. The system is based on three orthogonal force transducers connected to a reference block that will eventually be put in contact with the blade shroud in the test rig. A calibration process is outlined to define a decoupling matrix and its subsequent validation is demonstrated in order to evaluate the effectiveness of the measurement system to measure the actual contact forces acting on the contact.

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8

Yamanaka, Kazushi, e Eisuke Tomita. "Lateral Force Modulation Atomic Force Microscope for Selective Imaging of Friction Forces". Japanese Journal of Applied Physics 34, Part 1, No. 5B (30 maggio 1995): 2879–82. http://dx.doi.org/10.1143/jjap.34.2879.

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9

Gilroy, Paul. "“Rhythm in the Force of Forces”". Critical Times 2, n. 3 (1 dicembre 2019): 370–95. http://dx.doi.org/10.1215/26410478-7862525.

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Abstract This essay is addressed to discrepancies between musical and political time. It uses the death of Hugh Masekela to consider the changing pattern of intergenerational relationships and the place of music within local and transnational freedom movements. The impact of technological change on the mediation of political solidarity is then examined through two principal examples: the elaboration of generic racial identity and the weaponization of culture and information by the alt-right and its fellow travelers.

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10

Kassenov, L. G., B. H. Zhanbusinova e S. S. Sagintayev. "CAN THE FRICTION FORCE BE THE DRIVING FORCE?" BULLETIN Series of Physics & Mathematical Sciences 71, n. 3 (30 settembre 2020): 111–17. http://dx.doi.org/10.51889/2020-3.1728-7901.15.

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Friction is one of the types of interaction between bodies. It occurs when two bodies touch. The forces acting between the surfaces of contacting solids are called dry friction forces. They are always directed tangentially to the touching surfaces and are divided into the forces of friction at rest, sliding and rolling. The friction forces depend on many factors that accompany the movement of bodies in the presence of friction. In this regard, the description of friction forces is possible only with the help of empirically found approximate laws, which are often quite rough. The rest friction force is a variable value, it can change from zero to a certain maximum value. By applying a force to the body that exceeds the maximum resting friction force, we will move the body from its place, and it will begin to move. The article considers examples of motion in which the friction force can be mistakenly interpreted as a driving force. The nature of the forces of friction at rest and rolling is considered from the perspective of modern physical materials science.

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11

Szcześniak, Wacław, e Magdalena Ataman. "The Krylov problem in the case of a beam on Vlasov inertial foundation". AUTOBUSY – Technika, Eksploatacja, Systemy Transportowe 19, n. 6 (30 giugno 2018): 728–36. http://dx.doi.org/10.24136/atest.2018.165.

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The paper deals with vibrations of the elastic beam caused by the moving force traveling with uniform speed. The function defining the pure forced vibrations (aperiodic vibrations) is presented in a closed form. Dynamic deflection of the beam caused by moving force is compared with the static deflection of the beam subjected to the force , and compressed by axial forces . Comparing equations (9) and (13), it can be concluded that the effect on the deflection of the speed of the moving force is the same as that of an additional compressive force . Selected problems of stability of the beam on the Winkler foundation and on the Vlasov inertial foundation are discussed. One can see that the critical force of the beam on Vlasov foundation is greater than in the case of Winkler's foundation. Numerical examples are presented in the paper

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12

Khudjaev, Mukhiddin, Anvar Rizaev, Gulomjon Pirnazarov e Musallam Mirzaeva. "Simulation of forced vibration of a wedge pair under the impact of variable force". E3S Web of Conferences 413 (2023): 02051. http://dx.doi.org/10.1051/e3sconf/202341302051.

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The forced oscillations of a wedge pair under the effect of a variable force are investigated in the article. The general solution to the differential equation of forced oscillations of a wedge pair is chosen in the form depending on some unknown function. An equation for this function is obtained for the cosine form of the virtual displacement of the wedge under longitudinal displacement. This equation is obtained on the basis of the principle of virtual work of inertial forces, elastic forces, and external dynamic forces with virtual displacement. As a result, the solution to the differential equation of forced vibrations of a wedge pair under a variable longitudinal external force was obtained, and calculations were performed on the basis of the obtained solution. Research methods are based on the principle of virtual displacement, the method of mathematical modeling, and the analytical method of their solutions.

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13

Leib, Raz, Amir Karniel e Ilana Nisky. "The effect of force feedback delay on stiffness perception and grip force modulation during tool-mediated interaction with elastic force fields". Journal of Neurophysiology 113, n. 9 (maggio 2015): 3076–89. http://dx.doi.org/10.1152/jn.00229.2014.

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During interaction with objects, we form an internal representation of their mechanical properties. This representation is used for perception and for guiding actions, such as in precision grip, where grip force is modulated with the predicted load forces. In this study, we explored the relationship between grip force adjustment and perception of stiffness during interaction with linear elastic force fields. In a forced-choice paradigm, participants probed pairs of virtual force fields while grasping a force sensor that was attached to a haptic device. For each pair, they were asked which field had higher level of stiffness. In half of the pairs, the force feedback of one of the fields was delayed. Participants underestimated the stiffness of the delayed field relatively to the nondelayed, but their grip force characteristics were similar in both conditions. We analyzed the magnitude of the grip force and the lag between the grip force and the load force in the exploratory probing movements within each trial. Right before answering which force field had higher level of stiffness, both magnitude and lag were similar between delayed and nondelayed force fields. These results suggest that an accurate internal representation of environment stiffness and time delay was used for adjusting the grip force. However, this representation did not help in eliminating the bias in stiffness perception. We argue that during performance of a perceptual task that is based on proprioceptive feedback, separate neural mechanisms are responsible for perception and action-related computations in the brain.

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14

Williams, John M., Taejoon Han e Thomas P. Beebe. "Determination of Single-Bond Forces from Contact Force Variances in Atomic Force Microscopy". Langmuir 12, n. 5 (gennaio 1996): 1291–95. http://dx.doi.org/10.1021/la950500j.

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15

Setúbal, Fábio Antônio do Nascimento, Sérgio de Souza Custódio Filho, Newton Sure Soeiro, Alexandre Luiz Amarante Mesquita e Marcus Vinicius Alves Nunes. "Force Identification from Vibration Data by Response Surface and Random Forest Regression Algorithms". Energies 15, n. 10 (20 maggio 2022): 3786. http://dx.doi.org/10.3390/en15103786.

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Several dynamic projects and fault diagnosis of mechanical structures require the knowledge of the acting external forces. However, the measurement of such forces is often difficult or even impossible; in such cases, an inverse problem must be solved. This paper proposes a force identification method that uses the response surface methodology (RSM) based on central composite design (CCD) in conjunction with a random forest regression algorithm. The procedure initially required the finite element modal model of the forced structure. Harmonic analyses were then performed with varied parameters of forces, and RSM generated a dataset containing the values of amplitude, frequency, location of forces, and vibration acceleration at several points of the structure. The dataset was used for training and testing a random forest regression model for the prediction of any location, amplitude, and frequency of the force to be identified with information on only the vibration acquisition at certain points of the structure. Numerical results showed excellent accuracy in identifying the force applied to the structure.

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16

Zellers, Kerith K., e M. Susan Hallbeck. "The Effects of Gender, Wrist and Forearm Position on Maximum Isometric Power Grasp Force, Wrist Force, and their Interactions". Proceedings of the Human Factors and Ergonomics Society Annual Meeting 39, n. 10 (ottobre 1995): 543–47. http://dx.doi.org/10.1177/154193129503901001.

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The interaction of power grasp force and wrist force has not been previously examined. This research not only examined the effect of task (wrist force in flexion and extension with and without simultaneous power grasp force), but the effects of gender, wrist position, and forearm position on maximal static exertions. Gender, wrist position, and task were found to significantly affect both power grasp and wrist forces. Females averaged 59.5% of male power grasp force and 51% of male wrist force. Power grasp force was significantly greater in neutral and extended wrist positions than flexed wrist positions while a neutral wrist position generated significantly greater wrist forces than both extended and flexed wrist positions. Due to synergistic conflicts, grasp force during simultaneous wrist extension force was significantly less than grasp force during simultaneous wrist flexion force (60%) and grasp force only tasks (58%). Wrist extension forces were found to exceed flexion forces which contrasts with previous research studies. In addition, wrist forces during simultaneous grasp force did not differ from wrist forces with fingers relaxed.

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17

Niita, Shusaku, Taichi Sato, Hiroki Ota e Katsuaki Nagahashi. "TuC-2-4 AERODYNAMIC EXCITATION FORCE GENERATED BY ROTATING FAN AND ITS REACTION FORCES". Proceedings of JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment : IIP/ISPS joint MIPE 2015 (2015): _TuC—2–4–1—_TuC—2–4–3. http://dx.doi.org/10.1299/jsmemipe.2015._tuc-2-4-1.

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Liu, Ming, Shan Cao e Shuliang Cao. "Numerical analysis for interphase forces of gas-liquid flow in a multiphase pump". Engineering Computations 35, n. 6 (6 agosto 2018): 2386–402. http://dx.doi.org/10.1108/ec-04-2018-0161.

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Purpose The modeling of interphase forces plays a significant role in the numerical simulation of gas–liquid flow in a rotodynamic multiphase pump, which deserves detailed study. Design/methodology/approach Numerical analysis is conducted to estimate the influence of interphase forces, including drag force, lift force, virtual mass force, wall lubrication force and turbulent dispersion force. Findings The results show that the magnitude of the interphase forces can be sorted by: drag force > virtual mass force > lift force > turbulent dispersion force > wall lubrication force. The relations between interphase forces and velocity difference of gas–liquid flow and also the interphase forces and gas volume fraction are revealed. The distribution characteristics of interphase forces in the passages from impeller inlet to diffuser outlet are illustrated and analyzed. According to the results, apart from the drag force, the virtual mass force, lift force and turbulent dispersion force are required, whereas wall lubrication force can be neglected for numerical simulation of gas–liquid flow in a rotodynamic multiphase pump. Compared with the conventional numerical method which considers drag force only, the relative errors of predicted pressure rise and efficiency based on the proposed numerical method in account of four major forces can be reduced by 4.95 per cent and 3.00 per cent, respectively. Originality value The numerical analysis reveals the magnitude and distribution of interphase forces inside multiphase pump, which is meaningful for the simulation and design of multiphase pump.

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19

Rowell, Robert M., M. Ram Gudavalli e Steven Silverman. "A pilot study of the effect of force feedback training on students learning flexion-distraction chiropractic technique*". Journal of Chiropractic Education 33, n. 2 (27 dicembre 2018): 100–105. http://dx.doi.org/10.7899/jce-18-5.

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Objective: We compared traditional training alone and with the addition of force feedback training for learning flexion-distraction chiropractic technique. Methods: Participants were randomly allocated to two groups (traditional or traditional plus force feedback training). Students' forces were measured before training and after force feedback training. Students rated the helpfulness of the training and the comfort of the force transducer. Results: Thirty-one students were enrolled. Both groups delivered similar forces at baseline. Group 1 students' subsequent force measurements were higher after force feedback training. Group 2 students' forces were unchanged. Group 2 students were trained with force feedback for week 2 of the class, and forces were higher after feedback and similar to those in group 1. Students rated the training as very or somewhat helpful. Students also experienced discomfort as a patient and a student-doctor due to the force transducer that was used. Students who received force feedback training learned to deliver higher forces, which were closer to the forces delivered by experienced doctors of chiropractic. Students who did not receive force feedback continued to deliver lower forces. Conclusion: Force feedback helped students deliver forces closer to the desired force level and to learn this delivery faster than students who were not trained with force feedback.

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Ren, Haojie, Shixiao Fu, Chang Liu, Mengmeng Zhang, Yuwang Xu e Shi Deng. "Hydrodynamic Forces of a Semi-Submerged Cylinder in an Oscillatory Flow". Applied Sciences 10, n. 18 (14 settembre 2020): 6404. http://dx.doi.org/10.3390/app10186404.

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This work experimentally investigated the performance of hydrodynamic forces on a semi-submerged cylinder under an oscillatory flow. To generate the equivalent oscillatory flow, the semi-submerged cylinder is forced to oscillate in several combinations of different periods and amplitudes. The mean downward lift force was observed to be significant and the fluctuating lift forces show dominant frequency is twice that of oscillatory flow and amplitude that is the same as the mean lift force. Based on this main hydrodynamic feature, a novel empirical prediction formula for the lift forces on semi-submerged cylinder under oscillatory flow is proposed where the lift forces expression is proportional to the square of oscillatory flow velocity. This novel empirical formula directly assigns the fluctuating lift force with frequency twice of oscillatory flow and the amplitude that is the same as the mean lift force. This assignment of empirical lift force formula reduces parameters required to determine a dynamic lift force but is demonstrated to well predict the fluctuating lift force. The lift coefficient can reach 1.5, which is larger than the typical value 1.2 of the drag coefficient for a fully submerged cylinder with infinite depth. Moreover, relationships among hydrodynamic coefficients, Keulegan-Carpenter (KC) number, Stokes number and Froude number are studied. With the increase of KC number, the Froude number has a more significant influence on the distribution of hydrodynamic coefficients. As Froude number is increasing, the drag coefficient shows a nonlinear decay (KC < 20) but a linear increase (KC > 20), while the added mass coefficients show a nonlinear (KC < 20) and a linear (KC > 20) increase trend. The present work can provide useful references for design of the relevant marine structures and serve as the useful guideline for future research.

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HOVER, F. S., A. H. TECHET e M. S. TRIANTAFYLLOU. "Forces on oscillating uniform and tapered cylinders in cross flow". Journal of Fluid Mechanics 363 (25 maggio 1998): 97–114. http://dx.doi.org/10.1017/s0022112098001074.

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Forces are measured at both ends of rigid cylinders with span 60 cm, performing transverse oscillations within an oncoming stream of water, at Reynolds number Re≈3800. Forced harmonic motions and free vibrations of uniform and tapered cylinders are studied. To study free motions, a novel force-feedback control system has been developed, consisting of: (a) a force transducer, which measures forces on a section of a cylinder moving forward at constant speed; (b) a computer using the measured force signal to drive in real time a numerical simulation of an equivalent mass-dashpot-spring system; (c) a servomotor and linear table which impose, also in real time, the numerically calculated motion on the cylinder section. The apparatus allows very low equivalent system damping and strict control of the parametric values and structure of the equivalent system.Calculation of the cross-correlation coefficient between forces at the two ends of the uniform cylinder reveals five distinct regimes as a function of the nominal reduced velocity Vrn: two regimes, for low and high values of Vrn, and far away from the value of VrS corresponding to the Strouhal frequency, show small correlation; two regimes immediately adjacent to, but excluding, VrS show strong correlation, close to 1; surprisingly, there is a regime containing the Strouhal frequency, within which correlation is low. Free vibrations with a 40[ratio ]1 tapered cylinder show that the regime of low correlation, containing the Strouhal frequency, stretches to higher reduced velocities, while lock-in starts at lower reduced velocities.When comparing the amplitude and phase of the lift coefficient measured for free and then for forced vibrations, we obtain close agreement, both for tapered and uniform cylinders. When comparing the cross-correlation coefficient, however, we find that it is much higher in the forced oscillations, especially for the uniform cylinder. Hence, although the force magnitude and phase may be replicated well in forced vibrations, the correlation data suggest that differences exist between free and forced vibration cases.

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Kulik, Andrzej J., Małgorzata Lekka, Kyumin Lee, Grazyna Pyka-Fościak e Wieslaw Nowak. "Probing fibronectin–antibody interactions using AFM force spectroscopy and lateral force microscopy". Beilstein Journal of Nanotechnology 6 (15 maggio 2015): 1164–75. http://dx.doi.org/10.3762/bjnano.6.118.

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The first experiment showing the effects of specific interaction forces using lateral force microscopy (LFM) was demonstrated for lectin–carbohydrate interactions some years ago. Such measurements are possible under the assumption that specific forces strongly dominate over the non-specific ones. However, obtaining quantitative results requires the complex and tedious calibration of a torsional force. Here, a new and relatively simple method for the calibration of the torsional force is presented. The proposed calibration method is validated through the measurement of the interaction forces between human fibronectin and its monoclonal antibody. The results obtained using LFM and AFM-based classical force spectroscopies showed similar unbinding forces recorded at similar loading rates. Our studies verify that the proposed lateral force calibration method can be applied to study single molecule interactions.

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FUJII, Masatoshi. "Surface Forces Measurement by Atomic Force Microscopy". Journal of the Japan Society of Colour Material 72, n. 1 (1999): 34–42. http://dx.doi.org/10.4011/shikizai1937.72.34.

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Hao, Huang Wen. "Electrostatic and contact forces in force microscopy". Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 9, n. 2 (marzo 1991): 1323. http://dx.doi.org/10.1116/1.585188.

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Mltropolsky, Yu A., e A. M. Samoilenko. "Forced oscillations of systems with impulse force". International Journal of Non-Linear Mechanics 20, n. 5-6 (gennaio 1985): 419–26. http://dx.doi.org/10.1016/0020-7462(85)90018-6.

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Sheets, Kevin, Ji Wang, Wei Zhao, Rakesh Kapania e Amrinder S. Nain. "Nanonet Force Microscopy for Measuring Cell Forces". Biophysical Journal 111, n. 1 (luglio 2016): 197–207. http://dx.doi.org/10.1016/j.bpj.2016.05.031.

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Yang, R., R. Miller e P. J. Bryant. "Atomic force profiling by utilizing contact forces". Journal of Applied Physics 63, n. 2 (15 gennaio 1988): 570–72. http://dx.doi.org/10.1063/1.340089.

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O'Shea, Sean J. "Oscillatory Forces in Liquid Atomic Force Microscopy". Japanese Journal of Applied Physics 40, Part 1, No. 6B (30 giugno 2001): 4309–13. http://dx.doi.org/10.1143/jjap.40.4309.

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San Francisco Section of the Americ, Joint Committee on Lateral Forces,. "Earthquake forces for the lateral force code". Structural Design of Tall Buildings 9, n. 1 (marzo 2000): 49–64. http://dx.doi.org/10.1002/(sici)1099-1794(200003)9:1<49::aid-tal130>3.0.co;2-x.

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Flamarion, Marcelo V., e Efim Pelinovsky. "Solitary Wave Interactions with an External Periodic Force: The Extended Korteweg-de Vries Framework". Mathematics 10, n. 23 (1 dicembre 2022): 4538. http://dx.doi.org/10.3390/math10234538.

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In this work we asymptotically and numerically studied the interaction of large amplitude solitary waves with an external periodic force using the forced extended Korteweg-de Vries equation (feKdV). Regarding these interactions, we found three types of regimes depending on the amplitude of the solitary wave and how its speed and the speed of the external force are related. A solitary wave can remain steady when its crest and the crest of the external force are in phase, it can bounce back and forth remaining close to its initial position when its speed and the external force speed are near resonant, or it can move away from its initial position without reversing its direction. Additionally, we verified that the numerical results agreed qualitatively well within the asymptotic approximation theory for external broad forces.

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Biegus, Antoni, e Dariusz Czepiżak. "Equivalent stabilizing force of members parabolically compressed by longitudinally variable axial force". MATEC Web of Conferences 262 (2019): 09004. http://dx.doi.org/10.1051/matecconf/201926209004.

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The EN 1993-1-1 model of equivalent stabilizing force qd and Rd of bracings conservatively assumes that the braced member is compressed with a force constant along its length. This assumption is incorrect since the axial force distribution varies along the length of the braced member. As a result, the braced member generates equivalent stabilizing forces different from equivalent force qd and Rd acc. to EN 1993-1-1. This paper presents parametric studies of the equivalent stabilizing forces of the braced, compression top chord of roof trusses. The girder’s top chord is compressed parabolically by a variable axial force. The values of the axial compressive forces is: Nsupp in the support zone of truss and Nspan in the central zone of truss. Parametric analyses of the equivalent stabilizing force and the stress of the purlins and the bracings depending on axial forces Nsupp and Nspan in the braced member were carried out. The investigated problem is illustrated with exemplary calculations of the equivalent force in trusses.

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Li, Ming, e Rong Qing Xu. "A New Method for Detecting Jet Impact Force of Laser Cavity". Key Engineering Materials 552 (maggio 2013): 463–69. http://dx.doi.org/10.4028/www.scientific.net/kem.552.463.

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Based on the deflection effect resulted from deformation, a new experiment device for measuring the jet impact force of laser cavity is developed. The device has been used in experiment and the typical signal of jet impact force was obtained. The variational characteristic of the force with time was given. The result shows that during the experiment the target material sustains three forces. In order of time, the first force is the laser ablation force, and the other two forces are jet impact forces. The first jet impact force is greater than the ablation force and the second jet impact force is smaller than the first jet impact force.

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Sundararajan, Sriram, e Bharat Bhushan. "Topography-induced contributions to friction forces measured using an atomic force/friction force microscope". Journal of Applied Physics 88, n. 8 (2000): 4825. http://dx.doi.org/10.1063/1.1310187.

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Inui, Nobuyuki, Yumi Katsura e Masaki Yamanishi. "Retention of Relative Force in the Scaling of a Serial Force Pattern with an Attenuated-Force Tap". Perceptual and Motor Skills 92, n. 1 (febbraio 2001): 301–8. http://dx.doi.org/10.2466/pms.2001.92.1.301.

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The present study was designed to examine the retention of relative force in the scaling of a serial force pattern in a finger-tapping sequence using an attenuated tap. On practice trials, 12 undergraduate students tapped a force plate connected to strain gauges that gave them feedback about the force. On test trials, participants recalled the force pattern (200 gm-200 gm-200 gm-100 gm) and the intertap interval (400 msec.) practiced during the practice period without the feedback (recalled task). Then, they adaptively produced a halved (halved task) or doubled force profile (doubled task) at the fixed intertap interval. Analyses showed that mean peak forces at the first three tap positions of the tapping sequence undershot the expected forces across all tasks. Hence, the ratios of the forces in Serial Positions 1 4, 2:4, and 3:4 were considerably lower than 2.0. This is a contextual effect suggesting that the last attenuated tap affected the first three taps of the tapping sequence Thus, because the relative force of movements appears to be a weaker invariant feature than sequencing and relative timing for generalized motor program theory of Schmidt and Lee, this finding does not support the relative force for a generalized motor program.

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35

SRINIVASAN, K., D. V. SENTHILKUMAR, R. SURESH, K. THAMILMARAN e M. LAKSHMANAN. "EXPERIMENTAL REALIZATION OF STRANGE NONCHAOTIC ATTRACTORS IN A NONLINEAR SERIES LCR CIRCUIT WITH NONSINUSOIDAL FORCE". International Journal of Bifurcation and Chaos 19, n. 12 (dicembre 2009): 4131–63. http://dx.doi.org/10.1142/s0218127409025262.

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Abstract (sommario):

We have identified several prominent routes, namely, fractalization, fractalization followed by intermittency, intermittency and Heagy–Hammel routes, for the birth of strange nonchaotic attractors (SNAs) in a quasiperiodically forced electronic system with nonsinusoidal (square wave) force as one of the quasiperiodic forces [Senthilkumar et al., 2008]. In addition, a new bubbling route has also been identified in this circuit. Although some of these prominent routes have been reported experimentally [Thamilmaran et al., 2006] in a quasiperiodically forced electronic circuit with both the forcings as sinusoidal forces, experimental identification of all these routes is reported here in a quasiperiodically forced electronic circuit with one of the forcings as a nonsinusoidal (square wave) force. The birth of SNAs by these routes are characterized from both the experimental and numerical data by the maximal Lyapunov exponents and their variance, Poincaré maps, Fourier amplitude spectra, spectral distribution functions and the distribution of finite-time Lyapunov exponents.

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36

Szekeres, Alexander, M. Ham e J. Jeswiet. "Force Measurement in Pyramid Shaped Parts with a Spindle Mounted Force Sensor". Key Engineering Materials 344 (luglio 2007): 551–58. http://dx.doi.org/10.4028/www.scientific.net/kem.344.551.

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Abstract (sommario):

Forces are measured in Single Point Incremental Forming with a spindle mounted sensor. Results for AA3003 aluminum cones and pyramids are shown. Forces are measured for parts with a 75° forming angle, at which shear cracks are expected to occur. Forces in the three directions are measured on the spindle with force spikes being observed when the tool changes direction at pyramid corners, and reductions in force when stepping between contours. There is also a force variation as the forming tool moves along the pyramid wall. A comparison is made between the forces measured for cones and pyramids.

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37

Johnson, Peter, Hugh McLoone e Steve Arms. "Developing Miniature Force-Sensing Technologies for Measuring the Forces Applied to a Computer Mouse". Proceedings of the Human Factors and Ergonomics Society Annual Meeting 44, n. 37 (luglio 2000): 629–32. http://dx.doi.org/10.1177/154193120004403722.

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Abstract (sommario):

Force-sensing technologies, 1.4 − 2.5 mm thick, were developed to measure the forces applied to the button and sides of a computer mouse. A force-sensing computer mouse was developed, built and tested for force measurement accuracy. The force-sensing technology could accurately measure the forces applied to the sides of a mouse and identify the location of force application. The force-sensing technology also accurately measured the forces applied to the mouse button with slight measurement errors at low forces. The force-sensing technologies developed in this study were made from commercially available materials, were relatively low cost and will be readily exportable to different mouse designs. These force-sensing technologies should assist manufacturers, designers and researchers in better understanding how various hand held devices and tools are gripped and operated.

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38

Meiss, Richard A., e Ramana M. Pidaparti. "Mechanical state of airway smooth muscle at very short lengths". Journal of Applied Physiology 96, n. 2 (febbraio 2004): 655–67. http://dx.doi.org/10.1152/japplphysiol.00388.2003.

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Abstract (sommario):

Although the shortening of smooth muscle at physiological lengths is dominated by an interaction between external forces (loads) and internal forces, at very short lengths, internal forces appear to dominate the mechanical behavior of the active tissue. We tested the hypothesis that, under conditions of extreme shortening and low external force, the mechanical behavior of isolated canine tracheal smooth muscle tissue can be understood as a structure in which the force borne and exerted by the cross bridge and myofilament array is opposed by radially disposed connective tissue in the presence of an incompressible fluid matrix (cellular and extracellular). Strips of electrically stimulated tracheal muscle were allowed to shorten maximally under very low afterload, and large longitudinal sinusoidal vibrations (34 Hz, 1 s in duration, and up to 50% of the muscle length before vibration) were applied to highly shortened (active) tissue strips to produce reversible cross-bridge detachment. During the vibration, peak muscle force fell exponentially with successive forced elongations. After the episode, the muscle either extended itself or exerted a force against the tension transducer, depending on external conditions. The magnitude of this effect was proportional to the prior muscle stiffness and the amplitude of the vibration, indicating a recoil of strained connective tissue elements no longer opposed by cross-bridge forces. This behavior suggests that mechanical behavior at short lengths is dominated by tissue forces within a tensegrity-like structure made up of connective tissue, other extracellular matrix components, and active contractile elements.

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39

Kinoshita, Hiroshi, Lars Bäckström, J. Randall Flanagan e Roland S. Johansson. "Tangential Torque Effects on the Control of Grip Forces When Holding Objects With a Precision Grip". Journal of Neurophysiology 78, n. 3 (1 settembre 1997): 1619–30. http://dx.doi.org/10.1152/jn.1997.78.3.1619.

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Abstract (sommario):

Kinoshita, Hiroshi, Lars Bäckström, J. Randall Flanagan, and Roland S. Johansson. Tangential torque effects on the control of grip forces when holding objects with a precision grip. J. Neurophysiol. 78: 1619–1630, 1997. When we manipulate small objects, our fingertips are generally subjected to tangential torques about the axis normal to the grasp surface in addition to linear forces tangential to the grasp surface. Tangential torques can arise because the normal force is distributed across the contact area rather than focused at a point. We investigated the effects of tangential torques and tangential forces on the minimum normal forces required to prevent slips (slip force) and on the normal forces actually employed by subjects to hold an object in a stationary position with the use of the tips of the index finger and thumb. By changing the location of the object's center of gravity in relation to the grasp surface, various levels of tangential torque (0–50 N⋅mm) were created while the subject counteracted object rotation. Tangential force (0–3.4 N) was varied by changing the weight of the object. The flat grasp surfaces were covered with rayon, suede, or sandpaper, providing differences in friction in relation to the skin. Under zero tangential force, both the employed normal force and the slip force increased in proportion to tangential torque with a slope that reflected the current frictional condition. Likewise, with pure tangential force, these forces increased in proportion to tangential force. The effects of combined tangential torques and tangential forces on the slip force were primarily additive, but there was a significant interaction of these variables. Specifically, the increase in slip force for a given increment in torque decreases as a function of tangential force. A mathematical model was developed that successfully predicted slip force from tangential torque, tangential force, and an estimate of coefficient of static friction in the digit-surface interface. The effects of combined tangential torques and forces on the employed normal force showed the same pattern as the effects on the slip force. The safety margin against frictional slips, measured as the difference between the employed normal force and the slip force, was relatively small and constant across all tangential force and torque levels except at small torques (<10 N⋅mm). There was no difference in safety margin between the digits. In conclusion, tangential torque strongly influences the normal force required for grasp stability. When controlling normal force, people take into account, in a precise fashion, the slip force reflecting both tangential force and tangential torque and their interaction as well as the current frictional condition in the object-digit interface.

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40

Böddeker, Thomas J., Stefan Karpitschka, Christian T. Kreis, Quentin Magdelaine e Oliver Bäumchen. "Dynamic force measurements on swimming Chlamydomonas cells using micropipette force sensors". Journal of The Royal Society Interface 17, n. 162 (gennaio 2020): 20190580. http://dx.doi.org/10.1098/rsif.2019.0580.

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Abstract (sommario):

Flagella and cilia are cellular appendages that inherit essential functions of microbial life including sensing and navigating the environment. In order to propel a swimming microorganism they displace the surrounding fluid by means of periodic motions, while precisely timed modulations of their beating patterns enable the cell to steer towards or away from specific locations. Characterizing the dynamic forces, however, is challenging and typically relies on indirect experimental approaches. Here, we present direct in vivo measurements of the dynamic forces of motile Chlamydomonas reinhardtii cells in controlled environments. The experiments are based on partially aspirating a living microorganism at the tip of a micropipette force sensor and optically recording the micropipette’s position fluctuations with high temporal and sub-pixel spatial resolution. Spectral signal analysis allows for isolating the cell-generated dynamic forces caused by the periodic motion of the flagella from background noise. We provide an analytic, elasto-hydrodynamic model for the micropipette force sensor and describe how to obtain the micropipette’s full frequency response function from a dynamic force calibration. Using this approach, we measure the amplitude of the oscillatory forces during the swimming activity of individual Chlamydomonas reinhardtii cells of 26 ± 5 pN, resulting from the coordinated flagellar beating with a frequency of 49 ± 5 Hz. This dynamic micropipette force sensor technique generalizes the applicability of micropipettes as force sensors from static to dynamic force measurements, yielding a force sensitivity in the piconewton range. In addition to measurements in bulk liquid environment, we study the dynamic forces of the biflagellated microswimmer in the vicinity of a solid/liquid interface. As we gradually decrease the distance of the swimming microbe to the interface, we measure a significantly enhanced force transduction at distances larger than the maximum extent of the beating flagella, highlighting the importance of hydrodynamic interactions for scenarios in which flagellated microorganisms encounter surfaces.

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41

Martin, Bernard J., Thomas J. Armstrong, James A. Foulke, Sivakumaran Natarajan, Edward Klinenberg, Elaine Serina e David Rempel. "Keyboard Reaction Force and Finger Flexor Electromyograms during Computer Keyboard Work". Human Factors: The Journal of the Human Factors and Ergonomics Society 38, n. 4 (dicembre 1996): 654–64. http://dx.doi.org/10.1518/001872096778827288.

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Abstract (sommario):

This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a comfortable speed. A linear fit of EMG force data for each person and finger was calculated during static fingertip loading. An average r2 of .71 was observed for forces below 50% of the maximal voluntary contraction (MVC). These regressions were used to characterize EMG data in force units during the typing task. Averaged peak reaction forces measured during typing ranged from 3.33 N (thumb) to 1.84 N (little finger), with an overall average of 2.54 N, which represents about 10% MVC and 5.4 times the key switch make force (0.47 N). Individual peak or mean finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r2 for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained using EMG averaged across all fingers. For 5 of the participants the force computed from EMG was within ±20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants the difference between EMG estimated force and the reaction force was less than 13% MVC. It is suggested that the difference between EMG and finger force partly results from the amount of muscle load not captured by the measured applied force.

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42

Ehrsson, H. Henrik, Anders Fagergren, Roland S. Johansson e Hans Forssberg. "Evidence for the Involvement of the Posterior Parietal Cortex in Coordination of Fingertip Forces for Grasp Stability in Manipulation". Journal of Neurophysiology 90, n. 5 (novembre 2003): 2978–86. http://dx.doi.org/10.1152/jn.00958.2002.

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Abstract (sommario):

Grasp stability during object manipulation is achieved by the grip forces applied normal to the grasped surfaces increasing and decreasing in phase with increases and decreases of destabilizing load forces applied tangential to the grasped surfaces. This force coordination requires that the CNS anticipates the grip forces that match the requirements imposed by the self-generated load forces. Here, we use functional MRI (fMRI) to study neural correlates of the grip-load force coordination in a grip-load force task in which six healthy humans attempted to lift an immovable test object held between the tips of the right index finger and thumb. The recorded brain activity was compared with the brain activity obtained in two control tasks in which the same pair of digits generated forces with similar time courses and magnitudes; i.e., a grip force task where the subjects only pinched the object and did not apply load forces, and a load force task, in which the subjects applied vertical forces to the object without generating grip forces. Thus neither the load force task nor the grip force task involved coordinated grip-load forces, but together they involved the same grip force and load force output. We found that the grip-load force task was specifically associated with activation of a section of the right intraparietal cortex, which is the first evidence for involvement of the posterior parietal cortex in the sensorimotor control of coordinated grip and load forces in manipulation. We suggest that this area might represents a node in the network of cortical and subcortical regions that implement anticipatory control of fingertip forces for grasp stability.

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43

Hichert, Mona, e Dick H. Plettenburg. "Ipsilateral Scapular Cutaneous Anchor System: An alternative for the harness in body-powered upper-limb prostheses". Prosthetics and Orthotics International 42, n. 1 (20 marzo 2017): 101–6. http://dx.doi.org/10.1177/0309364617691624.

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Abstract (sommario):

Background: Body-powered prosthesis users frequently complain about the poor cosmesis and comfort of the traditional shoulder harness. The Ipsilateral Scapular Cutaneous Anchor System offers an alternative, but it remains unclear to what extent it affects the perception and control of cable operation forces compared to the traditional shoulder harness. Objective: To compare cable force perception and control with the figure-of-nine harness versus the Ipsilateral Scapular Cutaneous Anchor System and to investigate force perception and control at different force levels. Study design: Experimental trial. Methods: Ten male able-bodied subjects completed a cable force reproduction task at four force levels in the range of 10–40 N using the figure-of-nine harness and the Anchor System. Perception and control of cable operating forces were quantified by the force reproduction error and the force variability. Results: In terms of force reproduction error and force variability, the subjects did not behave differently when using the two systems. The smallest force reproduction error and force variability were found at the smallest target force level of 10 N. Conclusion: The Anchor System performs no differently than the traditional figure-of-nine harness in terms of force perception and control, making it a viable alternative. Furthermore, users perceive and control low operation forces better than high forces. Clinical relevance The Ipsilateral Scapular Cutaneous Anchor System offers an alternative for the traditional harness in terms of cable operation force perception and control and should therefore be considered for clinical use. Low cable operation forces increase the perception and control abilities of users.

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44

Wei, Baochen, e Feng Gao. "Output force capacity polytope approach for actuator forces selection of three degrees of freedom excavating manipulator". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, n. 11 (2 dicembre 2013): 2007–17. http://dx.doi.org/10.1177/0954406213512629.

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Abstract (sommario):

Output force or velocity polytopes are usually used as an index of the manipulability of robot. This paper discusses the relationship between the actuator force and the variation of the output force capacity polytope and proposes the output force capacity polytope method for the selection of actuator forces of a three degrees of freedom excavating manipulator with the requirement that the output force on the end effector is a set of all possible forces rather than a single force. In this paper, the method to calculate capacity polytope is introduced with the consideration of gravity effect. With the concept that the required output force space should be within the output capacity polytope, the output force capacity polytope approach for selecting actuator forces is proposed.

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45

Ataman, M. "Amplification Factors in the Case of Beam Under Moving Force – Theoretical Analysis". Archives of Civil Engineering 65, n. 1 (1 marzo 2019): 83–96. http://dx.doi.org/10.2478/ace-2019-0006.

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AbstractThe impact of a moving load speed on the dynamic overload of beams, assuming that the track of the load has no unevenness, is examined. First the problem of a visco-elastic beam on a Winkler foundation subjected to a force moving at a constant speed will be solved. Using the Bubnov-Galerkin method, the deflections of the beam, and then the bending moments and shear forces will be determined. The solution of the problem will be obtained both for the case of a forced vibration and the case of a free vibration after the moving force has left the beam. Using these solutions, dynamic amplification factors will be determined for the deflections, bending moments, and shear forces, which are different for the two cases.The magnitude of the amplification factors increases and decreases alternately as a function of the speed. In the case of a single force on a beam, the dynamic overloads are limited, and do not exceed 60%. There is no resonance phenomenon in the beam subjected to the single moving force. The dynamic amplification factors determined in this way can be used as correction coefficients when designing engineering structures subjected to moving loads by static methods.

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46

De Corato, M., e V. Garbin. "Capillary interactions between dynamically forced particles adsorbed at a planar interface and on a bubble". Journal of Fluid Mechanics 847 (21 maggio 2018): 71–92. http://dx.doi.org/10.1017/jfm.2018.319.

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Abstract (sommario):

We investigate the dynamic interfacial deformation induced by micrometric particles exerting a periodic force on a planar interface or on a bubble, and the resulting lateral capillary interactions. Assuming that the deformation of the interface is small, neglecting the effect of viscosity and assuming point particles, we derive analytical formulas for the dynamic deformation of the interface. For the case of a planar interface the dynamic point force simply generates capillary waves, while for the case of a bubble it excites shape oscillations, with a dominant deformation mode that depends on the bubble radius for a given forcing frequency. We evaluate the lateral capillary force acting between two particles, by superimposing the deformations induced by two point forces. We find that the lateral capillary forces experienced by dynamically forced particles are non-monotonic and can be repulsive. The results are applicable to micrometric particles driven by different dynamic forcing mechanisms such as magnetic, electric or acoustic fields.

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47

Zhang, Zhijian, Youping Chen e Dailin Zhang. "Development and Application of a Tandem Force Sensor". Sensors 20, n. 21 (23 ottobre 2020): 6042. http://dx.doi.org/10.3390/s20216042.

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Abstract (sommario):

In robot teaching for contact tasks, it is necessary to not only accurately perceive the traction force exerted by hands, but also to perceive the contact force at the robot end. This paper develops a tandem force sensor to detect traction and contact forces. As a component of the tandem force sensor, a cylindrical traction force sensor is developed to detect the traction force applied by hands. Its structure is designed to be suitable for humans to operate, and the mechanical model of its cylinder-shaped elastic structural body has been analyzed. After calibration, the cylindrical traction force sensor is proven to be able to detect forces/moments with small errors. Then, a tandem force sensor is developed based on the developed cylindrical traction force sensor and a wrist force sensor. The robot teaching experiment of drawer switches were made and the results confirm that the developed traction force sensor is simple to operate and the tandem force sensor can achieve the perception of the traction and contact forces.

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48

Harada, Takashi, e Podi Liu. "Internal and External Forces Measurement of Planar 3-DOF Redundantly Actuated Parallel Mechanism by Axial Force Sensors". ISRN Robotics 2013 (9 ottobre 2013): 1–8. http://dx.doi.org/10.5402/2013/593606.

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Abstract (sommario):

This paper proposes a method for measuring the internal and external forces of a planar 3-DOF (degree of freedom) redundantly actuated parallel mechanism. The internal forces, force acts inside the endplate and mechanism constraint force, and the external forces, forces act on the endplate and thrusts by actuators, were measured simultaneously using the axial forces of the rods. Kinetostatic equations of the parallel mechanism were used to derive algorithms for measuring the internal and external forces. A link axis force sensor was developed using a strain gauge sensor. To verify the actual internal force of the endplate, a force sensor was also installed on the endplate. A real-time system for measuring the forces of the parallel mechanism was developed using RT-Linux. The external and internal forces were measured accurately.

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49

Tokatli, Ozan, e Volkan Patoglu. "Non-Overshooting Force Control of Series Elastic Actuators". Solid State Phenomena 166-167 (settembre 2010): 421–26. http://dx.doi.org/10.4028/www.scientific.net/ssp.166-167.421.

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Abstract (sommario):

Whenever mechanical devices are used to interact with the environment, accurate control of the forces occurring at the interaction surfaces arises as an important challenge. Traditionally, force controlled systems utilize stiff force sensors in the feedback loop to measure and regulate the interaction forces. Series elastic actuation (SEA) is an alternative approach to force control, in which the deflection of a compliant element (orders of magnitude less stiff than a typical force sensor) placed between motor and the environment is controlled to regulate the interaction forces. The use of SEAs for force control is advantageous, since this approach possesses inherent robustness without the need for high-precision force sensors/actuators and allows for the accurate control of the force exerted by the actuator through position control of the deflection of a compliant coupling element. Here, a non-overshooting force controller is proposed to be embedded into the control structure of SEAs. Such controller architecture ensures safe operations of SAEs by making sure that the force applied to the environment are always bounded from above by the reference forces commanded to the controller.

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50

Zhang, Zixin, e Michael Braun. "Smoothness-based forces for deformable models: a long-range force and a corner fitting force". Computers in Biology and Medicine 33, n. 1 (gennaio 2003): 91–112. http://dx.doi.org/10.1016/s0010-4825(02)00028-8.

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