Articles de revues : « Forced responce »

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McCuaig Edge, Heather, Samantha Carlucci et Diane Lu. « Rôle de la Direction de la protection de la santé de la Force dans la réponse des Forces armées canadiennes à la pandémie de COVID-19 ». Relevé des maladies transmissibles au Canada 46, n^o 09 (3 septembre 2020) : 314–17. http://dx.doi.org/10.14745/ccdr.v46i09a05f.

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

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Setúbal, Fábio Antônio do Nascimento, Sérgio de Souza Custódio Filho, Newton Sure Soeiro, Alexandre Luiz Amarante Mesquita et Marcus Vinicius Alves Nunes. « Force Identification from Vibration Data by Response Surface and Random Forest Regression Algorithms ». Energies 15, n^o 10 (20 mai 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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Ahmed, Rizwan, Christian Maria Firrone et Stefano Zucca. « Design and Calibration of a Tri-Directional Contact Force Measurement System ». Applied Sciences 11, n^o 2 (19 janvier 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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Yang, B. D., et C. H. Menq. « Characterization of Contact Kinematics and Application to the Design of Wedge Dampers in Turbomachinery Blading : Part 2—Prediction of Forced Response and Experimental Verification ». Journal of Engineering for Gas Turbines and Power 120, n^o 2 (1 avril 1998) : 418–23. http://dx.doi.org/10.1115/1.2818139.

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In the second part of this paper, the application of the proposed dual-interface model to the prediction of the forced response of a blade constrained by wedge dampers will be presented. When considering cyclic loading, the induced friction forces and contact normal loads are combined so as to determine the effective stiffness and damping of the friction interfaces over a cycle of motion. The harmonic balance method is then used to impose the approximate stiffness and damping of the friction interfaces to a linear structure model of the blade. This approach results in a set of nonlinear algebraic equations that can be solved to yield the forced response of the blade excited by harmonic external forces. The predicted forced response can then be used to optimize a given damper design, namely to determine the dynamic weight at which the maximum reduction of resonant response is obtained. In order to illustrate the capacity of the proposed method and to examine its accuracy, the forced response of a test beam is examined. The prediction is also compared with the results of lab tests to validate the proposed dual-interface friction force model.

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Otsuru, Yoshihide, Yuichi Kurita, Koji Kawaguchi, Minoru Hattori, Hiroyuki Egi, Hideki Ohdan, Kazuyuki Nagata et Toshio Tsuji. « Palpation force display by enhancing the force response of a surgical training phantom ». Abstracts of the international conference on advanced mechatronics : toward evolutionary fusion of IT and mechatronics : ICAM 2015.6 (2015) : 19–20. http://dx.doi.org/10.1299/jsmeicam.2015.6.19.

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Nikolic, M., E. P. Petrov et D. J. Ewins. « Coriolis Forces in Forced Response Analysis of Mistuned Bladed Disks ». Journal of Turbomachinery 129, n^o 4 (15 août 2006) : 730–39. http://dx.doi.org/10.1115/1.2720866.

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The problem of estimating the mutual interaction of the effects of Coriolis forces and of blade mistuning on the vibration characteristics of bladed disks is addressed in this paper. The influence of different degrees of mistuning on forced response and amplification factors are studied in the presence of Coriolis forces and then compared to their non-Coriolis counterparts using a computationally inexpensive, yet representative, model of a bladed disk. The primary objective of the study reported in this paper is to establish whether current mistuned bladed disk analyses should incorporate Coriolis effects in order to represent accurately all the significant factors that affect the forced response levels.

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KANEKO, Yasutomo, Kazushi MORI, Toshio WATANABE et Hiroharu OOYAMA. « ICOPE-15-1006 Study on forced response of grouped steam turbine vanes ». Proceedings of the International Conference on Power Engineering (ICOPE) 2015.12 (2015) : _ICOPE—15——_ICOPE—15—. http://dx.doi.org/10.1299/jsmeicope.2015.12._icope-15-_3.

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Yang, B. D., et C. H. Menq. « Modeling of Friction Contact and Its Application to the Design of Shroud Contact ». Journal of Engineering for Gas Turbines and Power 119, n^o 4 (1 octobre 1997) : 958–63. http://dx.doi.org/10.1115/1.2817082.

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Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroudlike contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between stick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response of a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.

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Kan, Xuanen, et Bo Zhao. « Vibration Characteristics of a Mistuned Bladed Disk considering the Effect of Coriolis Forces ». Shock and Vibration 2016 (2016) : 1–9. http://dx.doi.org/10.1155/2016/4656032.

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To investigate the influence of Coriolis force on vibration characteristics of mistuned bladed disk, a bladed disk with 22 blades is employed and the effects of different rotational speeds and excitation engine orders on the maximum forced response are discussed considering the effects of Coriolis forces. The results show that if there are frequency veering regions, the largest split of double natural frequencies of each modal family considering the effects of Coriolis forces appears at frequency veering region. In addition, the amplitude magnification factor considering the Coriolis effects is increased by 1.02% compared to the system without considering the Coriolis effects as the rotating speed is 3000 rpm, while the amplitude magnification factor is increased by 2.76% as the rotating speed is 10000 rpm. The results indicate that the amplitude magnification factor may be moderately enhanced with the increasing of rotating speed. Moreover, the position of the maximum forced response of bladed disk may shift from one blade to another with the increasing of the rotational speed, when the effects of Coriolis forces are considered.

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Li, Xiang Guang, Qin Wen Huang, Yun Hui Wang, Yu Bin Jia et Zhi Bin Wang. « The Response of Electrostatic MEMS Structure under Mechanical Shock and Electrostatic Forces ». Applied Mechanics and Materials 427-429 (septembre 2013) : 120–23. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.120.

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For MEMS devices actuated by electrostatic force, unexpected failure modes can be hardly predicted when the electrostatic force coupled with the shock. A response model is established when a micro cantilever subjected to electrostatic force and mechanical shock. First, based on the theory of transverse forced vibration in vibration mechanics, the equation of motion under shock and electrostatic fore is presented. Then the reduced order model is gained after simplifying by mode superposition method. The computing results indicate that: the shock amplitude and duration are the key factors to affect the reliability of the device; the shock load and electrostatic forces make the threshold voltage much lower than the anticipated value. The micro cantilever may collapse to the substrate even at a voltage far lower than the pull-in voltage. This early dynamic pull-in instability may cause some failures such as short circuit, adhesion or collision damage.

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Jahng, Junghoon, Eric O. Potma et Eun Seong Lee. « Nanoscale spectroscopic origins of photoinduced tip–sample force in the midinfrared ». Proceedings of the National Academy of Sciences 116, n^o 52 (11 décembre 2019) : 26359–66. http://dx.doi.org/10.1073/pnas.1913729116.

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When light illuminates the junction formed between a sharp metal tip and a sample, different mechanisms can contribute to the measured photoinduced force simultaneously. Of particular interest are the instantaneous force between the induced dipoles in the tip and in the sample, and the force related to thermal heating of the junction. A key difference between these 2 force mechanisms is their spectral behavior. The magnitude of the thermal response follows a dissipative (absorptive) Lorentzian line shape, which measures the heat exchange between light and matter, while the induced dipole response exhibits a dispersive spectrum and relates to the real part of the material polarizability. Because the 2 interactions are sometimes comparable in magnitude, the origin of the chemical selectivity in nanoscale spectroscopic imaging through force detection is often unclear. Here, we demonstrate theoretically and experimentally how the light illumination gives rise to the 2 kinds of photoinduced forces at the tip–sample junction in the midinfrared. We comprehensively address the origin of the spectroscopic forces by discussing cases where the 2 spectrally dependent forces are entwined. The analysis presented here provides a clear and quantitative interpretation of nanoscale chemical measurements of heterogeneous materials and sheds light on the nature of light–matter coupling in optomechanical force-based spectronanoscopy.

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PRAJINA N V, PRAJINA N. V., et T. D. JOHN T D JOHN. « Multi Response Optimization of Cutting Forces in End Milling Using Response Surface Methodology and Desirability Function ». International Journal of Scientific Research 2, n^o 5 (1 juin 2012) : 126–30. http://dx.doi.org/10.15373/22778179/may2013/45.

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Bucher, Izhak, et Moshe Rosenstein. « Determination of External Forces—Application to the Calibration of an Electromagnetic Actuator ». Journal of Vibration and Acoustics 128, n^o 5 (10 avril 2005) : 545–54. http://dx.doi.org/10.1115/1.2346699.

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A new method to estimate time-varying external forces acting upon a vibrating structure is presented in this paper. The method is developed for a force-calibrating device which is designed to be rigid in the operating frequency band and, therefore, it was believed that simple force-gauges should recover the applied forces. It has been observed that the inertia of the vibrating calibration device distorts the estimated force, even when the excitation is only one-third of the first natural frequency. Unlike traditional methods, the frequency response need not be inverted, alternatively a smoothed, Lagrange multiplier based estimation method is formed. With the proposed method, an electromagnetic excitation device can be calibrated such that the electromagnetic forces can be compared with theoretical estimates. The unique features of the proposed method are: (a) Compensation for inertia forces; (b) incorporation of measured reaction forces in a mixed analytical and experimentally obtained model; (c) possible independence on elastic stiffness forces; and (d) closed form, integral equations. New equations relating the externally applied forces and various measurable physical parameters are established, for example: The dependency upon the air-gap, current, and magnetic flux can be found.

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Paulson, T. J., et D. P. Abrams. « Correlation between Static and Dynamic Response of Model Masonry Structures ». Earthquake Spectra 6, n^o 3 (août 1990) : 573–91. http://dx.doi.org/10.1193/1.1585587.

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The paper presents correlations between response of the same structural system subjected to either dynamic shaking or static lateral forces. Two one-quarter scale test structures were constructed with identical designs and were tested in the laboratory using two different methods. The first structure was subjected to simulated earthquake motions on a shaking table while the second structure was forced to displace through the same history at static rates using computer controlled servohydraulic actuators. Characteristics of dynamic lateral force distributions are examined first and followed by a description of techniques used for the static loading experiment. Correlations are made between observed response of the statically and dynamically tested twin structures to suggest differences in strength, stiffness and energy dissipation that may arise with each test method.

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Saito, Akira, et Tatsuya Suzuki. « Forced response vibration analysis of induction motor stators induced by electromagnetic forces ». IFAC-PapersOnLine 55, n^o 27 (2022) : 155–59. http://dx.doi.org/10.1016/j.ifacol.2022.10.504.

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Moe, G., et Z. J. Wu. « The Lift Force on a Cylinder Vibrating in a Current ». Journal of Offshore Mechanics and Arctic Engineering 112, n^o 4 (1 novembre 1990) : 297–303. http://dx.doi.org/10.1115/1.2919870.

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This paper reports an extensive program of forced and free vibration tests on a single circular cylinder moving mainly perpendicularly to a uniform current. For both free and forced vibration tests, two cases were investigated: one in which the cylinder was restrained in the in-line direction and the other in which it was supported on suitable springs. The cross-flow vibrational response and hydrodynamic forces on the cylinder were measured. Large variations of motion frequency in the “lock-in” range were found from the free vibration tests. This leads to two different definitions of reduced velocity, namely, a so-called nominal reduced velocity based on one reference frequency and the true reduced velocity based on the actual vibration frequency. When different results are compared, the true reduced velocity should be used. The forced vibration tests showed, as may be expected, that the transverse force in the “lock-in” range on the average will add energy to the cylinder at moderate motion amplitudes and subtract energy at large amplitudes. Some conditions resulting in a steady-state vibration of a flexibly mounted cylinder were analyzed. The actual force traces also show very large and apparently random deviations from the average force amplitude. The results from the forced and the free vibration tests are consistent with each other if the true reduced velocity and reduced amplitude are the same.

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Rosenfeld, Dekel, Shira Landau, Yulia Shandalov, Noa Raindel, Alina Freiman, Erez Shor, Yaron Blinder, Herman H. Vandenburgh, David J. Mooney et Shulamit Levenberg. « Morphogenesis of 3D vascular networks is regulated by tensile forces ». Proceedings of the National Academy of Sciences 113, n^o 12 (7 mars 2016) : 3215–20. http://dx.doi.org/10.1073/pnas.1522273113.

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Understanding the forces controlling vascular network properties and morphology can enhance in vitro tissue vascularization and graft integration prospects. This work assessed the effect of uniaxial cell-induced and externally applied tensile forces on the morphology of vascular networks formed within fibroblast and endothelial cell-embedded 3D polymeric constructs. Force intensity correlated with network quality, as verified by inhibition of force and of angiogenesis-related regulators. Tensile forces during vessel formation resulted in parallel vessel orientation under static stretching and diagonal orientation under cyclic stretching, supported by angiogenic factors secreted in response to each stretch protocol. Implantation of scaffolds bearing network orientations matching those of host abdominal muscle tissue improved graft integration and the mechanical properties of the implantation site, a critical factor in repair of defects in this area. This study demonstrates the regulatory role of forces in angiogenesis and their capacities in vessel structure manipulation, which can be exploited to improve scaffolds for tissue repair.

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Vuksanović Herceg, Iva, Vukašin Kuč, Veljko M. Mijušković et Tomislav Herceg. « Challenges and Driving Forces for Industry 4.0 Implementation ». Sustainability 12, n^o 10 (21 mai 2020) : 4208. http://dx.doi.org/10.3390/su12104208.

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Industry 4.0 has been a major force framing the societal, economic and technological environment after 2010. Exposed to ongoing digital transformation, companies are able to exploit opportunities offered by Industry 4.0, and are forced to manage immanent risks and barriers. However, studies on opportunities and challenges relevant for the implementation of Industry 4.0 for companies are scarce. In response to this literature gap, the aim of this exploratory research is to provide a deeper analysis of the level of digital transformation of companies in Serbia based on a digital maturity model, and examine their managers’ opinions on the most important driving forces and implementation barriers. The paper uses exploratory research design based on a survey responded to by 122 high-level managers within the Serbian manufacturing sector. Findings show that, contrary to expectations, digitally transforming enterprises do not see human resources as a driving force, but rather as an obstacle to Industry 4.0 implementation, when they lack necessary competences and skills. Resistance to change caused by Industry 4.0 implementation is not seen as an important barrier. On the other hand, efficiency factors represent the main driving force, while the lack of competences and financial resources represent the greatest barriers to Industry 4.0 implementation.

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Gao, Shuxiang, et Ying Ye. « Acute Vascular Response of Hand to Force and Vibration ». Vibration 5, n^o 1 (2 mars 2022) : 153–64. http://dx.doi.org/10.3390/vibration5010010.

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This study aimed to investigate the acute effect of grip and feed exertions on the vascular system at the fingers during exposure to hand-arm vibration (HAV), and to identify which active hand force situation would have the most effect on finger vascular function. A total of 12 individuals attended the test, and each of them were subjected to eight sets of force-and-vibration situations: four with combinations of forces and vibration, and four control ones with only hand forces applied. The vibration stimulus was applied on the right hand at 2.75 m/s2 with a frequency of 125 Hz for three minutes, during which the application of grip and feed forces were set at either 10 N or 50 N. The weakening of the finger vascular function was reflected by a reduction in the finger blood flow (FBF) and finger skin temperature (FST). They were tested on both hands at fixed intervals before, during and after the exposure for in-time measurement. Hand forces resulted in clear reductions in FBF and FST in exposed right fingers whether the force was exerted solely or combined with vibration. The greater the hand force (especially grip force), the stronger the vascular response, while the additional reductions in FBF and FST from vibration were not significant. In the non-exposed left fingers, no significant changes in finger circulation occurred in response to force or vibration. Generally, vibration-induced acute finger vasoconstriction was affected by the hand forces, in which hand force seemed to play a more important part than vibration. A larger grip force would lead to a greater loss in the digital circulation than feed force. Thus, the level of hand force exerted on the tool handle should be limited to reduce the risk of harm from HAV.

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Tagarev, Todor, et Valeri Ratchev. « Evolving Models of Using Armed Forces in Domestic Disaster Response and Relief ». Information & ; Security : An International Journal 40, n^o 2 (2018) : 167–80. http://dx.doi.org/10.11610/isij.4012.

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Kenyon, J. A., J. H. Griffin et N. E. Kim. « Sensitivity of Tuned Bladed Disk Response to Frequency Veering ». Journal of Engineering for Gas Turbines and Power 127, n^o 4 (1 mars 2004) : 835–42. http://dx.doi.org/10.1115/1.1924486.

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A continuous method is presented for representing the mode interaction that occurs in frequency veering in terms of the nominal sector modes of a cyclic symmetric bladed disk model constrained at a reference interblade phase angle. Using this method, the effect of frequency veering on the mode shapes can be considered in the context of the generalized forces exciting the system and the modal response of the bladed disk. It is shown that in a blade-dominated family of modes, the transfer of modal energy to the disk in the veering results in a lower generalized force exciting the mode as well as reduced response amplitude in the blade. For the disk-dominated modes, the sharing of modal energy with the blades can lead to the disk being excited by aerodynamic loading. These effects can have important implications for predicting and interpreting forced response in bladed disks. Numerical examples are provided to illustrate these concepts.

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Yao, Donghui, Yongsheng Ren, Yuhuan Zhang et Bole Ma. « Nonlinear Dynamics of Cutting Process considering Higher-Order Deformation of Composite Cutting Tool ». Shock and Vibration 2021 (2 décembre 2021) : 1–23. http://dx.doi.org/10.1155/2021/8699218.

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In this paper, the nonlinear dynamic analysis of the cutting process of composite cutting tool is performed. The cutting tool is simplified to a nonplanar bending rotating shaft. The higher-order bending deformation, structural damping, and gyroscopic effect of cutting tool are considered. It is assumed that cutting tool is subjected to a regenerative two-dimensional cutting force containing the first and second harmonic components. Based on the Hamilton principle, the motion equation of nonlinear chatter of the cutting system is derived. The nonlinear ordinary differential equations in the generalized coordinates are obtained by Galerkin method. In order to analyze the nonlinear dynamic response of cutting process, the multiscale method is used to derive the analytical approximate solution of the forced response for the cutting system under periodic cutting forces. In the forced response analysis, four cases including primary resonance and superharmonic resonance, i.e., Ω ¯ = ω 1 , Ω ¯ = ω 2 , 2 Ω ¯ = ω 1 , and 2 Ω ¯ = ω 2 , are considered. The influences of ratio of length to diameter, structural damping, cutting force, and ply angle on primary resonance and superharmonic resonance are investigated. The results show that nonlinearity due to higher-order bending deformation significantly affects the dynamic behavior of the milling process and that the effective nonlinearity of the cutting system is of hard type. Multivalued resonance curves and jump phenomenon are presented. The influences of various factors, such as ratio of length to diameter, ply angle, structural damping, cutting force, and rotating speed, are thoroughly discussed.

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Huang, Shu Ke, Dan Chen Zhou, Jian Hui Liu, Jin Teng et Ning Li. « Amplitude Frequency Response Characteristics of Fe-Based Damping Alloy Simple Beams under Forced Vibrations ». Advanced Materials Research 328-330 (septembre 2011) : 1072–76. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1072.

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The amplitude frequency response characteristics of simple beams made by Fe-Mn damping alloy, Fe-Cr-Mo damping alloy and 0.45C-steel under forced vibrations were studied using forced vibration measurement instrument. The results indicated that at forced vibration condition, the damping behaviors of Fe-Mn and Fe-Cr-Mo alloy beams were that the resonance amplitude and the resonance frequency range were reduced. The higher the exciting force was, the better the damping capacity of Fe-Mn alloy beam was, so it was suitable for the environment where higher vibrating force and shock existed. Whatever the exciting force was high or low, the damping capacity of Fe-Cr-Mo alloy beam was higher than 0.45C-steel, so it was more suitable for the environment where the strain amplitude changed in a wide range.

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Kan, Xuanen, Zili Xu, Bo Zhao et Jize Zhong. « Effect of coriolis force on forced response magnification of intentionally mistuned bladed disk ». Journal of Sound and Vibration 399 (juillet 2017) : 124–36. http://dx.doi.org/10.1016/j.jsv.2017.03.002.

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Yuen, Steeve Chung Kim, Gerald Nurick, Sylvester Piu et Gadija Ebrahim. « Response of Filled Thin-Walled Square Tubes to Axial Impact Load ». Applied Mechanics and Materials 566 (juin 2014) : 586–92. http://dx.doi.org/10.4028/www.scientific.net/amm.566.586.

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This paper presents the results of an investigation into the response of thin-walled square (60x60 mm and 76x76 mm) tubes made from mild steel filled with four different fillers; aluminium foam (Cymat 7%), two types of aluminium honeycomb and polyurethane foam to quasi-static and dynamic axial impact load. The energy absorption characteristics of the foam-filled tubes are compared to that of a hollow tube, through efficiency calculations. The tubular structures are subjected to axial impact load generated by drop masses of 320 kg and 390 kg released from a height ranging between 2.1 m to 4.1 m. Footage from a high speed camera is used to determine the average crush forces exerted by each specimen. The results show that the fillers have insignificant effects on the initial peak forces based on the quasi-static results but increase the overall mean crushed force. The findings also indicate that the fillers affect at times the size of the lobe formed thus compromising the energy absorption capacity of the tube.

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Tho, Nguyen Chi, Nguyen Tri Ta et Do Van Thom. « New Numerical Results from Simulations of Beams and Space Frame Systems with a Tuned Mass Damper ». Materials 12, n^o 8 (23 avril 2019) : 1329. http://dx.doi.org/10.3390/ma12081329.

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In working processes, mechanical systems are often affected by both internal and external forces, which are the cause of the forced vibrations of the structures. They can be destroyed if the amplitude of vibration reaches a high enough value. One of the most popular ways to reduce these forced vibrations is to attach tuned mass damper (TMD) devices, which are commonly added at the maximum displacement point of the structures. This paper presents the computed results of the free vibration and the vibration response of the space frame system under an external random load, which is described as a stationary process with white noise. Static and dynamic equations are formed through the finite element method. In addition, this work also establishes artificial neural networks (ANNs) in order to predict the vibration response of the first frequencies of the structure. Numerical studies show that the data set of the TMD device strongly affects the first frequencies of the mechanical system, and the proposed artificial intelligence (AI) model can predict exactly the vibration response of the first frequencies of the structure. For the forced vibration problem, we can find optimal parameters of the TMD device and thus obtain minimum displacements of the structure. The results of this work can be used as a reference when applying this type of structure to TMD devices.

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Ismail, Al Emran, Muhd Hafeez Zainulabidin, Mohd Nazrul Roslan, Abdul Latif Mohd Tobi et Nik Hisyamudin Muhd Nor. « Effect of Velocity on the Impact Resistance of Woven Jute Fiber Reinforced Composites ». Applied Mechanics and Materials 465-466 (décembre 2013) : 1277–81. http://dx.doi.org/10.4028/www.scientific.net/amm.465-466.1277.

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is present project investigated the impact penetration response of woven jute fiber reinforced composites subjected to wide range of low impact velocities. Hand layout woven jute fibers are thermally compressed to ensure no internal defects formed in the composites. Six layers of woven jutes are stacked together using different fiber orientations [0/q/0]s. Low impact velocities are used ranging between 5 – 20 m/s. Force-time, force-displacement and energy-time curves are obtained automatically during the impact tests. The results are then discussed with considering the composite fragmentations and failure mechanisms. It is found that 00composite orientations capable to absorb sufficiently impact energy for 5 m/s but not for velocity greater than 10 m/s. When fiber orientations used between 15 – 450, the composite impact resistance increased indicating two significant peak forces. These peak forces represent different type of failure mechanisms occurred during the striker progresses.

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Obara, Kazuo, Koji Nobe, Hiromi Nobe, Michael S. Kolodney, Primal De Lanerolle et Richard J. Paul. « Effects of microtubules and microfilaments on [Ca2+]i and contractility in a reconstituted fibroblast fiber ». American Journal of Physiology-Cell Physiology 279, n^o 3 (1 septembre 2000) : C785—C796. http://dx.doi.org/10.1152/ajpcell.2000.279.3.c785.

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We used a reconstituted fiber formed when 3T3 fibroblasts are grown in collagen to characterize nonmuscle contractility and Ca2+ signaling. Calf serum (CS) and thrombin elicited reversible contractures repeatable for >8 h. CS elicited dose-dependent increases in isometric force; 30% produced the largest forces of 106 ± 12 μN ( n = 30), which is estimated to be 0.5 mN/mm2 cell cross-sectional area. Half times for contraction and relaxation were 4.7 ± 0.3 and 3.1 ± 0.3 min at 37°C. With imposition of constant shortening velocities, force declined with time, yielding time-dependent force-velocity relations. Forces at 5 s fit the hyperbolic Hill equation; maximum velocity ( V max) was 0.035 ± 0.002 Lo/s. Compliance averaged 0.0076 ± 0.0006 Lo/Fo. Disruption of microtubules with nocodazole in a CS-contracted fiber had no net effects on force, V max, or stiffness; force increased in 8, but decreased in 13, fibers. Nocodazole did not affect baseline intracellular Ca2+ concentration ([Ca2+]i) but reduced (∼30%) the [Ca2+]i response to CS. The force after nocodazole treatment was the primary determinant of stiffness and V max, suggesting that microtubules were not a major component of fiber internal mechanical resistance. Cytochalasin D had major inhibitory effects on all contractile parameters measured but little effect on [Ca2+]i.

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Liu, Xiaohui, Haobo Liang, Guangyun Min, Chuan Wu et Mengqi Cai. « Investigation on the Nonlinear Vibration Characteristics of Current-Carrying Crescent Iced Conductors under Aerodynamic Forces, Ampere’s Forces, and Forced Excitation Conditions ». Discrete Dynamics in Nature and Society 2021 (12 octobre 2021) : 1–22. http://dx.doi.org/10.1155/2021/5009209.

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Aiming at the problem of nonlinear vibration of current-carrying iced conductors, the aerodynamic forces are introduced into the previous vibration equation of current-carrying conductors that only considered Ampere’s forces. At the same time, on this basis, a forced excitation load is further introduced to study the influence of dynamic wind on the nonlinear vibration characteristics of current-carrying iced conductors, and a new current-carrying iced conductors system under the combined action of Ampere’s forces, forced excitation, and aerodynamic forces has been established, and the improved theoretical modeling of current-carrying iced transmission lines made the model more in line with practical engineering. Firstly, the model of current-carrying iced conductors was established, and then the vibration equation of the model was derived. And the vibration equation was transformed into a finite dimensional ordinary differential equation by using the Galerkin method. The amplitude-frequency response functions of the nonlinear forced primary resonances and super-harmonic and subharmonic resonances of the system are derived by using the multiscale method. Through numerical calculation, the influence of current-carrying, spacing, wind velocity, tension, and excitation amplitude on the response amplitude when the primary resonance of the system appears is analyzed, and the difference between the two working conditions (considering the aerodynamic forces and without considering aerodynamic forces) is compared. The influence of the variation of current-carrying i on the response amplitude of super-harmonic and subharmonic resonances and the stability of the steady-state solution of forced primary resonance was analyzed. The results show that the response amplitude and the nonlinearilty of system under the action of aerodynamic forces are smaller and weaker than without the action of aerodynamic forces; the variation of line parameters has a certain influence on the response amplitude of conductor and the nonlinearity of system; the response amplitudes of the primary resonance, super-harmonic resonance, and subharmonic resonance increase with the increase in the excitation amplitudes, and the resonance peak is offset towards the negative value of the tuning parameter σ, showing the characteristics of soft spring, and the response amplitudes are accompanied by complex nonlinear dynamic behaviors such as the multivalue and jump phenomenon. The change of current-carrying i has an obvious effect on the nonlinearity of the system. The nonlinear and response amplitudes of the system are also enhanced with the increase in wind velocity. The stability of the system is judged when the primary resonance occurs, and it is found that the response amplitude shows synchronization and the out-of-step phenomenon with the change of tuning parameters. The research results obtained in this paper would help to further improve the theoretical modeling about current-carrying iced lines, and the research of line parameters can give a certain reference value to practical engineering, and it will have a positive effect on the safe operation of high-voltage transmission lines.

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Libersat, F., S. Zill et F. Clarac. « Single-unit responses and reflex effects of force-sensitive mechanoreceptors of the dactyl of the crab ». Journal of Neurophysiology 57, n^o 5 (1 mai 1987) : 1601–17. http://dx.doi.org/10.1152/jn.1987.57.5.1601.

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This paper examines the responses and reflex effects of force-sensitive mechanoreceptors of the most distal leg segment, the dactyl, of the leg of the crab, Carcinus maenas. The goals of these studies are to establish the potential activities and functions of these receptors in posture and locomotion. The responses of force-sensitive mechanoreceptors to imposed mechanical stimuli depended upon their location on the dactyl. A distal group of receptors is located on a specialized region, the dactyl tip, which is composed solely of epicuticle. Another group of receptors is distributed throughout more proximal regions of the dactyl where the cuticle is completely calcified. Both groups of receptors showed vigorous responses to imposed bending forces. When bending forces were applied as step functions at the dactyl, tip distal receptors showed only phasic responses to all levels of force application. Receptors located at more proximal positions on the dactyl showed phasic responses to low levels of step applied forces and phasicotonic discharges at higher levels of force. Increasing levels of force produced a sigmoid increase in the tonic firing of these units. When bending forces were applied using ramp functions, receptors of the distal group responded with an intense initial discharge followed by firing at a constant rate throughout both force application and release. This response was not related to the velocity of force application. In contrast, receptors located more proximally responded directionally to force application and release. Proximal receptors also effectively encoded the velocity of force application. Responses of these two groups of receptors also differed when vibrations were applied at the dactyl tip: proximal receptors only followed vibrational stimuli up to 50 Hz, whereas distal receptors showed 1:1 responses at vibrations as high as 95 Hz. Mechanoreceptors of the dactyl also responded intensely to bending forces resulting from resisted contractions of the animal's own muscles. No responses were obtained from unresisted movements of the leg. Stimulation of force-sensitive mechanoreceptors of the dactyl produced intra- and interleg reflex discharges in motor neurons to leg muscles. Mechanical bending of the dactyl or electrical stimulation of dactyl nerves in which force-sensitive mechanoreceptors were recorded produced strong tonic excitation of motors neurons to the levator muscles of the same leg.(ABSTRACT TRUNCATED AT 400 WORDS)

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Tang, D. M., et E. H. Dowell. « On the Threshold Force for Chaotic Motions for a Forced Buckled Beam ». Journal of Applied Mechanics 55, n^o 1 (1 mars 1988) : 190–96. http://dx.doi.org/10.1115/1.3173628.

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The effects of higher modes on the chaotic oscillations of a buckled beam under forced external excitation are studied. Of principal interest are the threshold force required for chaotic motions and the influence of damping on the system response. A comparison is also presented of results from numerical simulations with experimental data.

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Mitra, Anirban, Prasanta Sahoo et Kashinath Saha. « Large Amplitude Forced Vibration Analysis of Stiffened Plates Under Harmonic Excitation ». International Journal of Manufacturing, Materials, and Mechanical Engineering 1, n^o 2 (avril 2011) : 62–98. http://dx.doi.org/10.4018/ijmmme.2011040105.

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Large amplitude forced vibration behaviour of stiffened plates under harmonic excitation is studied numerically incorporating the effect of geometric non-linearity. The forced vibration analysis is carried out in an indirect way in which the dynamic system is assumed to satisfy the force equilibrium condition at peak excitation amplitude. Large amplitude free vibration analysis of the same system is carried out separately to determine the backbone curves. The mathematical formulation is based on energy principles and the set of governing equations for both forced and free vibration problems derived using Hamilton’s principle. Appropriate sets of coordinate functions are formed by following the two dimensional Gram-Schmidt orthogonalization procedure to satisfy the corresponding boundary conditions of the plate. The problem is solved by employing an iterative direct substitution method with an appropriate relaxation technique and when the system becomes computationally stiff, Broyden’s method is used. The results are furnished as frequency response curves along with the backbone curve in the dimensionless amplitude-frequency plane. Three dimensional operational deflection shape (ODS) plots and contour plots are provided in a few cases.

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Saniee, Avva, Kihyuck Kwak, Nicolas Quizon, Haewon Sohn, Javier Manzella-Lapeira, Prasida Holla, Jinghua Lu et al. « Human germinal center B cells are intrinsically able to discriminate antigen affinity and with T cell help express plasma cell transcription factors ». Journal of Immunology 200, n^o 1_Supplement (1 mai 2018) : 107.17. http://dx.doi.org/10.4049/jimmunol.200.supp.107.17.

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Abstract The selection of GC B cells that express high affinity B cell receptors (BCRs) is driven by the ability of B cells to both signal through the BCR and to extract antigen and present it to follicular helper T cells (T FH cells). Using anti-kappa antibodies of low (KD=3.9×10 −7 ) versus high (KD=2.4×10 −9 ) affinities attached to membranes as surrogate antigens, we show that LZ GC B cells are able to discriminate between these and responded only to the high affinity antigen. In contrast, naïve B cells responded to both high and low affinity antigens. LZ GC B cells engaged membrane associated surrogate antigens through highly dynamic F-actin and ezrin-rich pod-like structures that concentrated BCRs at their contact points. Using DNA-based mechanical force nano-sensors we observed robust pulling forces localized to the contact sites of the pods with the membrane. In contrast, naïve B cells formed flat stable contacts with the membranes and showed only defuse weak pulling forces. GC B cells optimally express transcription factors that drive plasma cell differentiation, namely IRF-4 and PRDM-1, in response to antigen in combination with T FH help while naïve B cells increased IRF-4 and PRDM-1 transcription in response to T FH alone and less so to antigen alone. Thus, LZ GC B cells appear to be intrinsically capable of antigen affinity discrimination and with the acquisition of T FH help BCR-activated LZ GC B cells differentiate into plasma cells.

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Bar-Avi, Patrick. « Dynamic Response of Risers Conveying Fluid ». Journal of Offshore Mechanics and Arctic Engineering 122, n^o 3 (2 mars 2000) : 188–93. http://dx.doi.org/10.1115/1.1286517.

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Riser conveying fluid is one category in a wide research area known as moving continua dynamic that was the subject to many research studies in the past 50 yr. The structure investigated in this paper is assumed to be a flexible pipe having a geometry of a simple catenary with a buoyancy force at the top. The riser is modeled as a beamlike continuous system subjected to wave, current, and wind forces. The derivation of the partial differential equation of motion included the following aspects: nonlinearities due to geometry, i.e., large displacements as well as wave drag force, fluid internal and external pressure, and internal fluid velocity and acceleration. The wave forces are approximated via Morison’s equation, where the drag force is proportional to the square of the relative velocity between the riser and the waves. All forces are calculated at the instantaneous position of the riser, causing the equation to be highly nonlinear. The nonlinear partial differential equation of motion is then solved numerically. Finite difference approximation code that was imbedded in ACSL software is used. The equation of motion is solved to evaluate the riser’s response to different environmental conditions and other physical parameters such as internal pressure and fluid velocity and acceleration. [S0892-7219(00)00203-X]

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Cha, Myeounghoon, Jennifer Ling, Guang-Yin Xu et Jianguo G. Gu. « Shear mechanical force induces an increase of intracellular Ca2+in cultured Merkel cells prepared from rat vibrissal hair follicles ». Journal of Neurophysiology 106, n^o 1 (juillet 2011) : 460–69. http://dx.doi.org/10.1152/jn.00274.2011.

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Merkel cells have been proposed to play a role in mechanical transduction of light touch in mammals. In the present study, Merkel cells were prepared from upper segments of rat vibrissal hair follicles and maintained in culture. Reponses of these cells to shear mechanical forces were examined by Ca2+imaging technique. Shear forces of ≥0.8 dyn/cm2that were delivered to the cells by the application of normal bath solution significantly increased intracellular Ca2+levels ([Ca2+]i) in some of these cells, and up to 30% cells responded to 1.6 dyn/cm2shear force applied for 20 s. Gd3+(100 μM), a compound widely used to inhibit mechanically activated channels, abolished shear force-induced increases of [Ca2+]iin these cells. Reduction of extracellular Ca2+concentration from 2 mM to 0.2 mM also abolished shear force-induced increases of [Ca2+]iin these cells. In addition to shear force, we found that many shear force-responding cells also responded to hypotonic solution. However, the response to hypotonic solution was not abolished by Gd3+(100 μM). We also found that all shear force-responding cells responded to ATP (100 μM) with large increases of [Ca2+]i. The responses to ATP remained in the presence of Gd3+. Taken together, our results suggest that Merkel cells in culture are sensitive to shear force stress, osmotic, and chemical stimuli and that shear force-induced increases of [Ca2+]imay be mediated by the activation of mechanically activated channels.

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Ma, Yong Jie, Yi Du Zhang et Xiao Ci Zhao. « Cutting Force Model of Aluminum Alloy 2014 in Turning with ANOVA Analysis ». Applied Mechanics and Materials 42 (novembre 2010) : 242–45. http://dx.doi.org/10.4028/www.scientific.net/amm.42.242.

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In the present study, aluminum alloy 2014 was selected as workpiece material, cutting forces were measured under turning conditions. Cutting parameters, the depth of cut, feed rate, the cutting speed, were considered to arrange the test research. Mathematical model of turning force was solved through response surface methodology (RSM). The fitting of response surface model for the data was studied by analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to cutting force values. The turning force coefficients in the model were calibrated with the test results, and the suggested models of cutting forces adequately map within the limits of the cutting parameters considered. Experimental results suggested that the most cutting force among three cutting forces was main cutting force. Main influencing factor on cutting forces was obtained through cutting force models and correlation analysis. Cutting force has a significant influence on the part quality. Based on the cutting force model, a few case studies could be presented to investigate the precision machining of aluminum alloy 2014 thin walled parts.

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Xu, Jiang Lin, et Zhi Sun. « Prestress Force Identification Based on Forced Vibration Tests of Eccentrically Prestressed Concrete Beam ». Advanced Materials Research 479-481 (février 2012) : 733–38. http://dx.doi.org/10.4028/www.scientific.net/amr.479-481.733.

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The measurement of residue prestress force is one main issue for condition and performance assessment of prestressed concrete beam bridge. This paper proposes a vibration based parameter estimation technique for this purpose. Under given form external excitation, beam velocity responses at multiple points are collected firstly. The prestress force of the beam is then identified based on the minimization of the least square difference between the measured response and the baseline response. A numerical study on a beam of variant length, subjected to a constant prestress force with variant eccentricity, is conducted to show the effect of prestress force and the effect of bending moment due to eccentricity on fundamental frequency of the beam. The results show that this vibration based method for prestress force identification is both theoretically feasible and practically workable.

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Kim. « Formula for Equivalent Impulsive Force to Predict Vibrational Response of High-frequency Staircases ». Journal of Korean Society of Steel Construction 27, n^o 2 (2015) : 181. http://dx.doi.org/10.7781/kjoss.2015.27.2.181.

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LiZhong, Xu, et Fu XiaoRui. « Electromechanical Coupled Forced Responses for Microplate ». Advances in Mechanical Engineering 6 (1 janvier 2014) : 857015. http://dx.doi.org/10.1155/2014/857015.

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The electromechanical coupled forced response of the microplate subjected to electrostatic force is investigated. Using electromechanical coupled dynamic equations and the mode superposition method, the forced responses of the microplate to voltage excitation and load excitation are analyzed, respectively. Based on this, the coupled forced responses of the micrplate to voltage and load excitations are obtained. Beat vibration caused by the coupled response is investigated and the condition that the beat vibration occurs is determined.

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Sun, Zhe, Luis A. Martinez-Lemus, Michael A. Hill et Gerald A. Meininger. « Extracellular matrix-specific focal adhesions in vascular smooth muscle produce mechanically active adhesion sites ». American Journal of Physiology-Cell Physiology 295, n^o 1 (juillet 2008) : C268—C278. http://dx.doi.org/10.1152/ajpcell.00516.2007.

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Integrin-mediated mechanotransduction in vascular smooth muscle cells (VSMCs) plays an important role in the physiological control of tissue blood flow and vascular resistance. To test whether force applied to specific extracellular matrix (ECM)-integrin interactions could induce myogenic-like mechanical activity at focal adhesion sites, we used atomic force microscopy (AFM) to apply controlled forces to specific ECM adhesion sites on arteriolar VSMCs. The tip of AFM probes were fused with a borosilicate bead (2∼5 μm) coated with fibronectin (FN), collagen type I (CNI), laminin (LN), or vitronectin (VN). ECM-coated beads induced clustering of α5- and β3-integrins and actin filaments at sites of bead-cell contact indicative of focal adhesion formation. Step increases of an upward ( z-axis) pulling force (800∼1,600 pN) applied to the bead-cell contact site for FN-specific focal adhesions induced a myogenic-like, force-generating response from the VSMC, resulting in a counteracting downward pull by the cell. This micromechanical event was blocked by cytochalasin D but was enhanced by jasplakinolide. Function-blocking antibodies to α5β1- and αvβ3-integrins also blocked the micromechanical cell event in a concentration-dependent manner. Similar pulling experiments with CNI, VN, or LN failed to induce myogenic-like micromechanical events. Collectively, these results demonstrate that mechanical force applied to integrin-FN adhesion sites induces an actin-dependent, myogenic-like, micromechanical event. Focal adhesions formed by different ECM proteins exhibit different mechanical characteristics, and FN appears of particular relevance in its ability to strongly attach to VSMCs and to induce myogenic-like, force-generating reactions from sites of focal adhesion in response to externally applied forces.

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Ratchev, Valeri, et Todor Tagarev. « Policy and Legal Frameworks of Using Armed Forces for Domestic Disaster Response and Relief ». Information & ; Security : An International Journal 40, n^o 2 (2018) : 137–66. http://dx.doi.org/10.11610/isij.4011.

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Wheat, H. E., L. M. Salo et A. W. Goodwin. « Cutaneous Afferents From the Monkeys Fingers : Responses to Tangential and Normal Forces ». Journal of Neurophysiology 103, n^o 2 (février 2010) : 950–61. http://dx.doi.org/10.1152/jn.00502.2009.

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Control of tangential force plays a key role in everyday manipulations. In anesthetized monkeys, forces tangential to the skin were applied at a range of magnitudes comparable to those used in routine manipulations and in eight different directions. The paradigm used enabled separation of responses to tangential force from responses to the background normal force. For slowly adapting type I (SAI) afferents, tangential force responses ranged from excitatory through no response to suppression, with both a static and dynamic component. For fast adapting type I (FAI) afferents, responses were dynamic and excitatory only. Responses of both afferent types were scaled by tangential force magnitude, elucidating the neural basis for previous human psychophysical scaling data. Most afferents were direction selective with a range of preferred directions and a range in sharpness of tuning. Both the preferred direction and the degree of tuning were independent of the background normal force. Preferred directions were distributed uniformly over 360° for SAI afferents, but for FAI afferents they were biased toward the proximo-ulnar direction. Afferents from all over the glabrous skin of the distal segment of the finger responded; there was no evident relationship between the position of an afferent's receptive field on the finger and its preferred direction or its degree of tuning. Nor were preferred directions biased either toward or away from the receptive field center. In response to the relatively large normal forces, some afferents saturated and others did not, regardless of the positions of their receptive fields. Total afferent response matched human psychophysical scaling functions for normal force.

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Macpherson, J. M. « Changes in a postural strategy with inter-paw distance ». Journal of Neurophysiology 71, n^o 3 (1 mars 1994) : 931–40. http://dx.doi.org/10.1152/jn.1994.71.3.931.

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1. The purpose of this study was to examine the effect of changing initial stance conditions on the postural response of the cat to horizontal plane translations of the support surface. Cats were trained to stand, unrestrained, on a moveable force platform. The platform was translated linearly in each of 16 directions in the horizontal plane, with a ramp-and-hold displacement. The animal's response was quantified in terms of the forces exerted at the ground. The trajectory of the center of mass (CoM) was computed from the forces. 2. Stance length was varied along the longitudinal (sagittal) axis by adjusting the distance between the forepaw and hindpaw force plates. Translation perturbations of the platform were recorded at stance distances varying from 66 to 110% of the preferred stance distance. 3. Changing stance distance had a significant effect on the amplitude and direction of the active forces exerted by the cat both during quiet stance and during the response to platform translation. At long stance distances, each limb exerted a force outward, along the diagonals during quiet stance. The response to translation was characterized by an invariance in the direction of force exerted against the ground, a strategy that was described previously. At short stance distances, quiet stance forces were more laterally directed. The force constraint strategy was usually not observed for the response to translation. Nevertheless, the cats were equally effective at all stance distances in restoring the position of the center of mass after translation of the support surface. 4. There was no discrete boundary between the presence and absence of the force constraint, suggesting that the strategy for exerting forces against the support surface is characterized by a continuum of response, from a bimodal, or anisotropic distribution of force vectors on the one extreme, to a uniform, or isotropic distribution on the other. Arguments are developed to suggest that the force constraint strategy may be useful in stabilizing the vertebral column during the response to platform translation, to allow linear translation of the CoM rather than bending of the trunk.

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Diaz, S. E., et L. A. San Andre´s. « Air Entrainment Versus Lubricant Vaporization in Squeeze Film Dampers : An Experimental Assessment of Their Fundamental Differences ». Journal of Engineering for Gas Turbines and Power 123, n^o 4 (1 octobre 1998) : 871–77. http://dx.doi.org/10.1115/1.1383258.

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Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in air-breathing engines and process gas compressors. However, SFDs are prone to develop a flow regime where the ingestion of air leads to the formation of a bubbly lubricant. This pervasive phenomenon lacks proper physical understanding and sound analytical modeling, although actual practice demonstrates that it greatly reduces the damper force response. Measurements of film pressures in a test SFD describing circular centered orbits at whirl frequencies varying from 0 to 100 Hz are presented for fully flooded and vented discharge operating conditions. The experiments demonstrate that operation with low levels of external pressurization, moderate to large whirl frequencies, and lubricant discharge to ambient leads to the entrapment of air within the damper film lands. The experiments also elucidate fundamental differences in the generation of film pressures and forces for operation in a flooded condition that evidences vapor cavitation. Damping forces for the vented end with air entrainment are just 15 percent of the forces measured for the flooded damper. Further measurements at constant whirl frequencies demonstrate that increasing the lubricant pressure supply retards the onset of air entrainment. Classical fluid film cavitation models predict well the pressures and forces for the lubricant vapor cavitation condition. However, prevailing models fail to reproduce the dynamic forced response of vented (open-ended) SFDs where air entrainment makes a foamy lubricant, which limits severely the damper film pressures and forces.

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Stern, Menachem, Chukwunonso Arinze, Leron Perez, Stephanie E. Palmer et Arvind Murugan. « Supervised learning through physical changes in a mechanical system ». Proceedings of the National Academy of Sciences 117, n^o 26 (16 juin 2020) : 14843–50. http://dx.doi.org/10.1073/pnas.2000807117.

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Mechanical metamaterials are usually designed to show desired responses to prescribed forces. In some applications, the desired force–response relationship is hard to specify exactly, but examples of forces and desired responses are easily available. Here, we propose a framework for supervised learning in thin, creased sheets that learn the desired force–response behavior by physically experiencing training examples and then, crucially, respond correctly (generalize) to previously unseen test forces. During training, we fold the sheet using training forces, prompting local crease stiffnesses to change in proportion to their experienced strain. We find that this learning process reshapes nonlinearities inherent in folding a sheet so as to show the correct response for previously unseen test forces. We show the relationship between training error, test error, and sheet size (model complexity) in learning sheets and compare them to counterparts in machine-learning algorithms. Our framework shows how the rugged energy landscape of disordered mechanical materials can be sculpted to show desired force–response behaviors by a local physical learning process.

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Yu, H. Y., et Sanboh Lee. « Time-harmonic elastic singularities and oscillating indentation of layered solids ». IMA Journal of Applied Mathematics 85, n^o 4 (8 juin 2020) : 542–63. http://dx.doi.org/10.1093/imamat/hxaa017.

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Abstract A new approach is proposed for obtaining the dynamic elastic response of a multilayered elastic solid caused by axisymmetric, time-harmonic elastic singularities. The method for obtaining the elastodynamic Green’s functions of the point force, double forces and center of dilatation is presented. For this purpose, the boundary conditions in an infinite solid at the plane passing through the singularity are derived first by using Helmholtz potentials. Then the Green’s function solution for layered solids is obtained by solving a set of simultaneous linear algebraic equations using the boundary conditions for both the singularities and for the layer interfaces. The application of the point force solution for the oscillating normal indentation problem is also given. The solution of the forced normal oscillation is formulated by integrating the point force Green’s function over the contact area with unknown surface traction. The dual integral equations of the unknown surface traction are established by considering the boundary conditions on the contact surface of the multilayered solid, which can be converted into a Fredholm integral equation of the second kind and solved numerically.

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Wei, S. T., et C. Pierre. « Localization Phenomena in Mistuned Assemblies with Cyclic Symmetry Part II : Forced Vibrations ». Journal of Vibration and Acoustics 110, n^o 4 (1 octobre 1988) : 439–49. http://dx.doi.org/10.1115/1.3269548.

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The effects of disorder on the forced response of nearly periodic structures with cyclic symmetry are investigated. The force model adopted here is relevant to blade assemblies. Perturbation methods for the forced response are developed to gain a physical insight into the effects of mistuning. The study shows that the internal coupling between component systems is the key parameter governing the sensitivity to mistuning and that localized forced vibrations do occur in the disordered assembly for weak internal coupling. However, although both localized free and forced vibrations occur for finite or large values of the mistuning to coupling ratio, the deflection patterns for these two types of localized vibrations are different. Also, for the forced response, the degree of localization does not necessarily increase as this ratio increases—a fundamental difference from localized free modes. An important conclusion is that the common periodicity assumption for cyclic structures may lead to qualitative errors for the forced response of weakly coupled systems when small mistuning is present.

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Kan, Xuanen, et Zili Xu. « Vibration localization for a rotating mistuning bladed disk with the Coriolis effect by a state-space decoupling method ». Proceedings of the Institution of Mechanical Engineers, Part G : Journal of Aerospace Engineering 233, n^o 3 (29 novembre 2017) : 1011–20. http://dx.doi.org/10.1177/0954410017744238.

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Slight deviations of blades due to manufacturing tolerances can cause mistuning of bladed disk leading to localized vibration, which can accelerate fatigue. Moreover, the rotating blades are subjected to the Coriolis effect and the influence of the Coriolis force on the natural frequencies of high-speed rotational bladed disks such as those of an aero-engine become more apparent. In this paper, the effect of Coriolis force on the forced response localization of a mistuned bladed disk are investigated, for conditions where the natural frequency located in the first and second modal families of the bladed disk. Mistuning is introduced by varying the Young’s modulus of each blade. Due to the asymmetric Coriolis matrix, it is not possible to directly decouple the system. A state-space decoupling method is developed to decouple the system to effectively calculate the forced response of bladed disk with the consideration of the Coriolis effect. The results show that response localization factor is increased by 13.09% considering the Coriolis force compared to the system without considering the Coriolis effect, in the case of where the first modal family is considered. In addition, the response localization factor with the consideration of the Coriolis force is decreased by 30.85% compared to the system without considering the Coriolis force, when the second modal family is considered. It indicates that the forced response localization with the consideration of the Coriolis effect will be changed obviously with the rotational speed increasing, when the concerning natural frequency is located in the first and second modal families. Furthermore, the effect of Coriolis force causes changes in the resonant frequencies and resonant amplitude, but does not introduce additional resonant peaks for the case of the mistuned bladed disk.

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Pan, Chudong, et Ling Yu. « Identification of external forces via truncated response sparse decomposition under unknown initial conditions ». Advances in Structural Engineering 22, n^o 15 (28 juin 2019) : 3161–75. http://dx.doi.org/10.1177/1369433219859479.

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When structural dynamic design for smart control and health monitoring is executed, imposed excitations on structures are one of most important issues in structural engineering. Identification of structural excitations, such as force reconstruction, moving force identification, and so on, has drawn increasing attentions in the last decades. Assumption of known initial conditions is a precondition for existing deterministic force reconstruction methods. However, initial conditions are often unknown and hard to be estimated. To address this problem, a novel truncated response sparse decomposition method is proposed for calculating the external forces under unknown initial conditions. The truncated response sparse decomposition involves two basic steps, that is, response sparse decomposition and force estimation. First, a collection of basis vectors is defined for expressing unknown forces. Unknown initial conditions are represented in modal space. Structural responses induced by both external forces and initial conditions are then normalized as potential response features to form an image dictionary, which is adapted to decompose the measured responses via sparse regularization. Second, the response features with lower decomposed amplitudes and small scaling factors are eliminated from the decomposed results. The remaining features are used for estimating the external forces. In order to assess the accuracy and the feasibility of the proposed force reconstruction method, some numerical simulations on a planar truss structure and a series of experimental studies are carried out. The illustrated results show the robustness and the applicability of the proposed method for addressing the force reconstruction problem under unknown initial conditions. Some related issues are discussed as well.

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