On Some Peculiar Aspects of Axial Motions of Closed Loops of String in the Presence of a Singular Supply of Momentum

2004 ◽  
Vol 71 (4) ◽  
pp. 541-545 ◽  
Author(s):  
Oliver M. O’Reilly ◽  
Peter C. Varadi
Keyword(s):  
Arbitrary Number ◽  
Coulomb Friction ◽  
Closed Loop ◽  
Exact Expression ◽  
Material Point ◽  
Linear Momentum ◽  
Axial Motion ◽  
Closed Loops ◽  
External Constraint ◽  
Mass Spring

We consider the dynamics of a closed loop of inextensible string which is undergoing an axial motion. At each instant, one material point of the string is in contact with a singular supply of linear momentum (also known as an external constraint). Several peculiar features of this problem which have not been previously discussed are presented. These include the possible presence of an arbitrary number of kinks, the vanishing nature of the singular supply of momentum, and the critical nature of the tension in the string. When the linear momentum is supplied by a mass-spring-dashpot system, we are also able to establish an exact expression for the frequency of the resulting vibrations, prove that dissipation cannot be present, show that these vibrations only occur for discrete speeds of axial motion, and establish that Coulomb friction is absent.

THE GEOMETRIC PHASE AND THE SCHWINGER TERM IN SOME MODELS

1992 ◽  
Vol 07 (21) ◽  
pp. 5045-5083 ◽  
Author(s):  
H. GROSSE ◽  
E. LANGMANN
Keyword(s):  
Parameter Space ◽  
Geometric Phase ◽  
Closed Loop ◽  
Parallel Transport ◽  
Quantum Mechanical System ◽  
Second Quantization ◽  
Closed Loops ◽  
Gauge Transformations ◽  
Canonical Anticommutation Relations ◽  
Inequivalent Representations

We discuss the quantization of fermions interacting with external fields and observe the occurrence of equivalent as well as inequivalent representations of the canonical anticommutation relations. Implementability of gauge and axial gauge transformations leads to generators which fulfil an algebra of current with a Schwinger term. This term can be written as a cocycle and leads to the boson-fermion correspondence. Transport of a quantum-mechanical system along a closed loop of parameter space may yield a geometric phase. We discuss models for which nonintegrable phase factors are obtained from the adiabatic parallel transport. After second quantization, one obtains, in addition, a Schwinger term. Depending on the type of transformation, a subtle relationship between these two obstructions can occur. We indicate finally how we may transport density matrices along closed loops in parameter space.

scholarly journals Flowering Buds of Globular Proteins: Transpiring Simplicity of Protein Organization

2002 ◽  
Vol 3 (6) ◽  
pp. 525-534 ◽  
Author(s):  
Igor N. Berezovsky ◽  
Edward N. Trifonov
Keyword(s):  
Protein Evolution ◽  
Closed Loop ◽  
Globular Proteins ◽  
Polymer Physics ◽  
Basic Unit ◽  
Amino Acid Residues ◽  
Sequence Motifs ◽  
Closed Loops ◽  
Physical Necessity ◽  
Functional Complexity

Structural and functional complexity of proteins is dramatically reduced to a simple linear picture when the laws of polymer physics are considered. A basic unit of the protein structure is a nearly standard closed loop of 25–35 amino acid residues, and every globular protein is built of consecutively connected closed loops. The physical necessity of the closed loops had been apparently imposed on the early stages of protein evolution. Indeed, the most frequent prototype sequence motifs in prokaryotic proteins have the same sequence size, and their high match representatives are found as closed loops in crystallized proteins. Thus, the linear organization of the closed loop elements is a quintessence of protein evolution, structure and folding.

Constraint Wrench Formulation for Closed-Loop Systems Using Two-Level Recursions

2007 ◽  
Vol 129 (12) ◽  
pp. 1234-1242 ◽  
Author(s):  
Himanshu Chaudhary ◽  
Subir Kumar Saha
Keyword(s):  
Lagrange Multipliers ◽  
Spanning Tree ◽  
Closed Loop ◽  
Equations Of Motion ◽  
Constraint Forces ◽  
Minimal Set ◽  
Closed Loops ◽  
Closed Loop Systems ◽  
Subsystem Level ◽  
Body Level

In order to compute the constraint moments and forces, together referred here as wrenches, in closed-loop mechanical systems, it is necessary to formulate a dynamics problem in a suitable manner so that the wrenches can be computed efficiently. A new constraint wrench formulation for closed-loop systems is presented in this paper using two-level recursions, namely, subsystem level and body level. A subsystem is referred here as the serial- or tree-type branches of a spanning tree obtained by cutting the appropriate joints of the closed loops of the system at hand. For each subsystem, unconstrained Newton–Euler equations of motion are systematically reduced to a minimal set in terms of the Lagrange multipliers representing the constraint wrenches at the cut joints and the driving torques/forces provided by the actuators. The set of unknown Lagrange multipliers and the driving torques/forces associated to all subsystems are solved in a recursive fashion using the concepts of a determinate subsystem. Next, the constraint forces and moments at the uncut joints of each subsystem are calculated recursively from one body to another. Effectiveness of the proposed algorithm is illustrated using a multiloop planar carpet scraping machine and the spatial RSSR (where R and S stand for revolute and spherical, respectively) mechanism.

Coulomb Friction Limit Cycles in Elastic Positioning Systems

1999 ◽  
Vol 121 (2) ◽  
pp. 298-301 ◽  
Author(s):  
A. Bonsignore ◽  
G. Ferretti ◽  
G. Magnani
Keyword(s):  
Coulomb Friction ◽  
Closed Loop ◽  
Tracking Error ◽  
Pole Placement ◽  
Stick Slip ◽  
Positioning Systems ◽  
Relay Control ◽  
Pure Coulomb ◽  
Pole Placement Controller ◽  
Motor Velocity

The state space control of a positioning system affected by torsional elasticity at the gearbox is considered, using a motor position transducer only. An output feedback, pole placement controller is used, with an additional integral action on the tracking error to cancel it at steady state. Both experiments and simulations point out that large oscillations may appear for some sets of closed-loop poles which yields, in contrast to stick-slip cycles, instantaneous motor velocity reversals. It is shown that such oscillations are induced by “pure” Coulomb friction. The period of the oscillations is predicted precisely following the Tsypkin’s relay control theory and also by the approximate describing function method. The latter also allows understanding of how oscillations depend on observer and feedback control design and on plant parameters; thus we are able to derive guidelines for the design of an oscillation free closed-loop system.

Efficient Parallel Computer Simulation of the Motion Behaviors of Closed-Loop Multibody Systems

2007 ◽  
Author(s):  
Shanzhong Duan ◽  
Andrew Ries
Keyword(s):  
Parallel Computing ◽  
Multibody Systems ◽  
Closed Loop ◽  
High Efficiency ◽  
Equations Of Motion ◽  
Parallel Computer ◽  
Constraint Forces ◽  
Computing Systems ◽  
Closed Loops

This paper presents an efficient parallelizable algorithm for the computer-aided simulation and numerical analysis of motion behaviors of multibody systems with closed-loops. The method is based on cutting certain user-defined system interbody joints so that a system of independent multibody subchains is formed. These subchains interact with one another through associated unknown constraint forces fc at the cut joints. The increased parallelism is obtainable through cutting joints and the explicit determination of associated constraint forces combined with a sequential O(n) method. Consequently, the sequential O(n) procedure is carried out within each subchain to form and solve the equations of motion while parallel strategies are performed between the subchains to form and solve constraint equations concurrently. For multibody systems with closed-loops, joint separations play both a role of creation of parallelism for computing load distribution and a role of opening a closed-loop for use of the O(n) algorithm. Joint separation strategies provide the flexibility for use of the algorithm so that it can easily accommodate the available number of processors while maintaining high efficiency. The algorithm gives the best performance for the application scenarios for n>>1 and n>>m, where n and m are number of degree of freedom and number of constraints of a multibody system with closed-loops respectively. The algorithm can be applied to both distributed-memory parallel computing systems and shared-memory parallel computing systems.

scholarly journals INTESTINAL OBSTRUCTION

1913 ◽  
Vol 17 (3) ◽  
pp. 307-324
Author(s):  
G. H. Whiffle ◽  
H. B. Stone ◽  
B. M. Bernheim
Keyword(s):  
Intestinal Mucosa ◽  
Intestinal Tract ◽  
Closed Loop ◽  
Toxic Substance ◽  
Great Part ◽  
Essential Factor ◽  
Closed Loops ◽  
Toxic Material ◽  
Closed Duodenal Loop

The blood of closed duodenal loop dogs is not toxic to normal dogs. The blood of dogs that have been fatally poisoned with duodenal loop fluid is likewise non-toxic to normal dogs. The mucosa of closed or drained duodenal loops contains a toxic substance quite similar to the toxic material found in the lumen of the closed loops. This toxic substance is absorbed from the mucosa itself and not from the lumen of the drained loops. The same is probably true of the closed loops which have an intact mucosa. It seems highly probable that the poison is formed by the mucosa and is in great part absorbed directly from it by the blood. Normal intestinal mucosa contains no toxic substance nor can it neutralize in vitro the toxic substance produced in the closed loops. There is no evidence that the toxic material when given intravenously is excreted by the intestine or held by the intestinal mucosa in any demonstrable form. The toxic substance is not absorbed from the normal intestinal tract. Destruction of the mucosa in a closed loop by means of sodium fluoride prevents the formation of the toxic substance. This fact furnishes the final proof that the mucosa is the essential factor in the elaboration of the poisonous material.

Stability Switches in a Neutral Delay Differential Equation with Application to Real-Time Dynamic Substructuring

2006 ◽  
Vol 5-6 ◽  
pp. 79-84 ◽  
Author(s):  
Y.N. Kyrychko ◽  
K.B. Blyuss ◽  
A. Gonzalez-Buelga ◽  
S.J. Hogan ◽  
David J. Wagg
Keyword(s):  
Real Time ◽  
Closed Loop ◽  
Numerical Models ◽  
Closed Loop System ◽  
Neutral Delay ◽  
Time Dynamic ◽  
Dynamic Substructuring ◽  
Delay Differential ◽  
Mass Spring ◽  
Theoretical Results

In this paper delay differential equations approach is used to model a real-time dynamic substructuring experiment. Real-time dynamic substructuring involves dividing the structure under testing into two or more parts. One part is physically constructed in the lab- oratory and the remaining parts are being replaced by their numerical models. The numerical and physical parts are connected via an actuator. One of the main difficulties of this testing technique is the presence of delay in a closed loop system. We apply real-time dynamic sub- structuring to a nonlinear system consisting of a pendulum attached to a mass-spring-damper. We will show how a delay can have (de)stabilising effect on the behaviour of the whole system. Theoretical results agree very well with experimental data.

Simulation of a Closed-Loops Assembly Line

2012 ◽  
Vol 502 ◽  
pp. 127-132 ◽  
Author(s):  
L.P. Ferreira ◽  
E. Ares ◽  
G. Peláez ◽  
A. Resano ◽  
C.J. Luis-Pérez ◽  
...  
Keyword(s):  
Assembly Line ◽  
Closed Loop ◽  
Discrete Event ◽  
Specific Class ◽  
Production Lines ◽  
Closed Loops ◽  
Event Simulation ◽  
Automobile Assembly ◽  
Loop Network ◽  
The Impact

The aim of the work presented in this paper describes the development of a decision support system based on a discrete-event simulation model of an automobile assembly line. The model focuses at a very specific class of production lines with a four closed-loop network configuration. One key characteristic in the closed-loop system is that the number of pallets inside the first three loops has been made constant. The impact of the number of pallets circulating on the first three closed-loops and of the proportion of four-door car bodies on the performance of the production line has been thoroughly investigated. This has been translated into the number of cars produced per hour, in order to improve the availability of the entire manufacturing system.

Microelectromechanical Hybrid Gyroscope Design of Closed-Loop Detection Circuit Based on FPGA

2013 ◽  
Vol 562-565 ◽  
pp. 172-177
Author(s):  
Dun Zhu Xia ◽  
Cheng Yu ◽  
Shou Rong Wang ◽  
Hong Sheng Li
Keyword(s):  
Closed Loop ◽  
Rotation Frequency ◽  
Digital Design ◽  
Closed Loops ◽  
Noise Interference ◽  
Scale Factors ◽  
Detection Circuit ◽  
Loop Detection ◽  
Sinusoidal Functions ◽  
Cross Axis

This paper presents a new microelectromechanical hybrid gyroscope (MHG) with three equilibrium rings. This structure can eliminate the error caused by the double rotation frequency of the driving shaft successfully. The MHG kinematic equations with three equilibrium rings are derived in this paper. Meanwhile, a new digital design and simulation of the MHG closed-loop detection circuit are proposed based on FPGA. The noise interference is weakened by using differential mode signal detection and the resources of FPGA are decreased by the loop diode demodulation in this paper. The cross axis coupling of the decoupled system is about 2.4%. The phase margin is 70deg and the magnitude margin is 22db after correction. The transcient response simulation is tested when the inputs are sinusoidal functions. The bandwidth and scale factors of x-axis and y-axis closed loops are analyzed in the paper. The bandwidth can reach about 70Hz and the scale factors of x-axis and y-axis closed loops are 0.1467V/o/s and -0.1467V/o/s respectively.

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