A Simple Technique to Passively Gravity-Balance Articulated Mechanisms

1995 ◽  
Vol 117 (4) ◽  
pp. 655-658 ◽  
Author(s):  
T. Rahman ◽  
R. Ramanathan ◽  
R. Seliktar ◽  
W. Harwin
Keyword(s):  
Simple Technique ◽  
Restoring Force ◽  
Simple Method ◽  
Nonlinear Restoring Force ◽  
Articulated Mechanisms ◽  
Gravitational Moment

A simple method to counter the effects of gravity in articulated mechanisms is proposed. The scheme uses kinematics and linear springs to produce a nonlinear restoring force to oppose the gravitational moment. The method equilibrates a rotational mechanism for all postures. A solution for one link is obtained then general equations for n links are derived. The method is simpler than previous schemes and has applications in robotics, orthotics and a host of everyday mechanisms.

Nonparametric nonlinear restoring force and excitation identification with Legendre polynomial model and data fusion

2021 ◽  
pp. 147592172199474
Author(s):  
Bin Xu ◽  
Ye Zhao ◽  
Baichuan Deng ◽  
Yibang Du ◽  
Chen Wang ◽  
...  
Keyword(s):  
Data Fusion ◽  
Legendre Polynomial ◽  
Structural Parameters ◽  
Polynomial Model ◽  
Magnetorheological Damper ◽  
Dynamic Responses ◽  
Identification Accuracy ◽  
Restoring Force ◽  
Nonlinear Restoring Force ◽  
Dynamic Loadings

Identification of nonlinear restoring force and dynamic loadings provides critical information for post-event damage diagnosis of structures. Due to high complexity and individuality of structural nonlinearities, it is difficult to provide an exact parametric mathematical model in advance to describe the nonlinear behavior of a structural member or a substructure under strong dynamic loadings in practice. Moreover, external dynamic loading applied to an engineering structure is usually unknown and only acceleration responses at limited degrees of freedom of the structure are available for identification. In this study, a nonparametric nonlinear restoring force and excitation identification approach combining the Legendre polynomial model and extended Kalman filter with unknown input is proposed using limited acceleration measurements fused with limited displacement measurements. Then, the performance of the proposed approach is first illustrated via numerical simulation with multi-degree-of-freedom frame structures equipped with magnetorheological dampers mimicking nonlinearity under direct dynamic excitation or base excitation using noise-polluted measurements. Finally, a dynamic experimental study on a four-story steel frame model equipped with a magnetorheological damper is carried out and dynamic response measurement is employed to validate the effectiveness of the proposed method by comparing the identified dynamic responses, nonlinear restoring force, and excitation force with the test measurements. The convergence and the effect of initial estimation errors of structural parameters on the final identification results are investigated. The effect of data fusion on improving the identification accuracy is also investigated.

Soft X-ray emission from an anharmonic collisional nanoplasma by a laser–nanocluster interaction

2021 ◽  
Vol 87 (3) ◽  
Author(s):  
R. Nemati Siahmazgi ◽  
S. Jafari
Keyword(s):  
Electric Field ◽  
Laser Beam ◽  
Resonant Frequency ◽  
Restoring Force ◽  
Cluster Radius ◽  
X Ray ◽  
Nonlinear Restoring Force ◽  
Cluster Temperature ◽  
Argon Clusters ◽  
Helium Neon

The purpose of the present paper is to investigate the generation of soft X-ray emission from an anharmonic collisional nanoplasma by a laser–nanocluster interaction. The electric field of the laser beam interacts with the nanocluster and leads to ionization of the cluster atoms, which then produces a nanoplasma. Because of the nonlinear restoring force in an anharmonic nanoplasma, the fluctuations and heating rate of, as well as the power radiated by, the electrons in the nanocluster plasma will be notably different from those arising from a linear restoring force. By comparing the nonlinear restoring force state (which arises from an anharmonic cluster) with that of the linear restoring force (in harmonic clusters), the cluster temperature specifically changes at the resonant frequency relative to the linear restoring force, while the variation of the anharmonic cluster radius is almost identical to that of the harmonic cluster radius. In addition, it is revealed that a sharp peak of X-ray emission arises after some picoseconds in deuterium, helium, neon and argon clusters.

A (Relatively) Simple Method to Visualize Single Molecules

2011 ◽  
Vol 19 (1) ◽  
pp. 8-8
Author(s):  
Stephen W. Carmichael ◽  
Julio M. Fernandez
Keyword(s):  
Fluorescence Microscopy ◽  
Simple Technique ◽  
Zero Mode ◽  
Single Molecules ◽  
Simple Method ◽  
Expensive Equipment ◽  
Freely Moving ◽  
Good For

Fluorescence microscopy can be used to study certain single molecules in solution or attached to a surface. Two conflicting challenges to overcome are: (1) to image freely moving molecules for long times and (2) to image immobilized single molecules when there is a highly fluorescent background. The fact that these two goals are inversely related is illustrated by epifluorescence, which is good for observing freely diffusing molecules but poor for detecting single molecules, whereas the reverse is true for zero-mode waveguides. Plus, these and other techniques require elaborate (read: expensive) equipment with computerized controls. Sabrina Leslie, Alexander Fields, and Adam Cohen have developed an ingenious (relatively) simple technique that can image freely moving single molecules.

Harmonic Oscillations of Nonlinear Two-Degree-of-Freedom Systems

1955 ◽  
Vol 22 (1) ◽  
pp. 107-110
Author(s):  
T. C. Huang
Keyword(s):  
Nonlinear System ◽  
Degrees Of Freedom ◽  
Forced Oscillations ◽  
Viscous Damping ◽  
Free Oscillations ◽  
Response Curves ◽  
Harmonic Oscillations ◽  
Restoring Force ◽  
Nonlinear Restoring Force ◽  
Two Degree Of Freedom

Abstract In this paper an investigation is made of equations governing the oscillations of a nonlinear system in two degrees of freedom. Analyses of harmonic oscillations are illustrated for the cases of (1) the forced oscillations with nonlinear restoring force, damping neglected; (2) the free oscillations with nonlinear restoring force, damping neglected; and (3) the forced oscillations with nonlinear restoring force, small viscous damping considered. Amplitudes of oscillations and frequency equations are derived based on the mathematically justified perturbation method. Response curves are then plotted.

scholarly journals A new autogenous mobile system driven by vibration without impacts, excited by an impulse periodic force

2018 ◽  
Vol 148 ◽  
pp. 04005 ◽  
Author(s):  
The-Hung Duong ◽  
Van-Du Nguyen ◽  
Ngoc-Tuan La
Keyword(s):  
Duffing Oscillator ◽  
Mobile Systems ◽  
Main Body ◽  
Rectilinear Motion ◽  
Mobile System ◽  
Restoring Force ◽  
Periodic Force ◽  
Nonlinear Restoring Force ◽  
Novel Structure ◽  
Excitation Force

This report describes a new proposed design for autogenous mobile systems which can move without any external mechanisms such as legs or wheels. A Duffing oscillator with a cubic spring, which is excited by an impulse periodic force, is utilized to drive the whole system. The rectilinear motion of the system is performed employing the periodically oscillation of the internal mass interacting without collisions with the main body. Utilizing the nonlinear restoring force of the cubic spring, the system can move in desired directions. When the ratio between the excitation force and the friction force is smaller than 2.5, backward or forward motion can be easily achieved by applying an excitation force in the same desired direction. Different from other vibro-impact drifting devices, no impact needed to drive the new proposed system. This novel structure allows to miniaturize the device as well as to simplify the control algorithm thus can significantly expand applicability of the proposed system.

A SIMPLE METHOD FOR THE ASSAY OF SMALL AMOUNTS OF ANTIDIURETIC HORMONE

1959 ◽  
Vol 37 (10) ◽  
pp. 1215-1225 ◽  
Author(s):  
J. Hunter ◽  
H. Kalant ◽  
J. C. Ogilvie
Keyword(s):  
Antidiuretic Hormone ◽  
Simple Technique ◽  
Nacl Solution ◽  
Albino Rat ◽  
Simple Method ◽  
Water Load ◽  
True Value ◽  
Statistical Precision ◽  
Urine Production ◽  
Animal Material

A reliable, sensitive, and simple technique is described for the assay of antidiuretic hormone in amounts between 25 and 130 μunits. The assay animal is a conscious albino rat weighing between 150 and 250 g. On the day of assay it is tranquillized with an injection of perphenazine. Specially designed cannulae, implanted on the day before the assay, provide unimpaired access to the stomach and bladder, permitting the maintenance of hydration and continuous urine collection without disturbance of the animal. Material to be assayed is injected intravenously. Water load is maintained by manual injection of 0.5-ml quantities of 0.05% NaCl solution at intervals dependent upon the rate of urine production. A useful index for expression of the response is described, which is related to both the intensity and the duration of antidiuresis. Assay of an artificial unknown by this method gave a result within 6% of the true value, and an excellent statistical precision (λ = 0.143).

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