Search results for "Amplitude"

Comparison of different methods for presenting variable amplitude loading fatigue results

2004

This paper discusses eight methods for presenting fatigue test results for variable amplitude loading and their comparison with constant amplitude loading. While the maximum amplitude method compares constant and variable amplitude loading results by the Woehler and Gassner curves, all other seven methods try to transform the variable amplitude results into the Woehler curve by applying different equations. The advantage of the maximum amplitude method is the direct comparison of the maximum amplitude of the spectrum with the yield strength and with the high-cycle fatigue strength, which is an important step in structural design. Among the other methods, the best results were obtained by fo…

Unraveling of an original mechanism of hypometria in human using a new myohaptic device — The Wristalyzer

2009

We report a novel form of hypometria in a patient presenting a spinocerebellar ataxia type 2 (SCA2; 32 repeats; Age: 44). We investigated fast pointing (FP) and fast reversal (FR) single-joint movements performed under artificial damping conditions using our myohaptic device called Wristalyzer, which allows an instantaneous regulation of the mechanical characteristics of a wrist manipulandum. The wristalyzer controller has a range of motion from −1 rad to +1 rad. The inertia of the motor/handgrip is 0.004 kg × m2. Movements were studied in free mode and with damping either at 0.1 Nms/rad or 0.2 Nms/rad. Subjects performed sets of FP movements and FR movements over 3 distances (targets: 0.2,…

Model Dependence of Nucleon Resonance Parameters

2004

Nucleon resonance parameters as mass, width, branching ratios and electromagnetic helicity amplitudes cannot be determined in a model independent way. The best way to obtain such elementary quantities is in terms of a partial wave analysis and a separation of resonance and background. In this work we have concentrated on the extraction of the e.m. helicity amplitudes A l p and A312 from electric and magnetic multipole analyses that were obtained from different groups with different techniques. We make a comparison of our results for the resonances P11(1440), 013(1520) and s11(1535). The variation that we find can be considered as a measure of the model uncertainty in these quantities.

Optical phonons and electron-phonon interaction in quantum wires.

1993

A unified macroscopic continuum theory for the treatment of optical-phonon modes in quantum-wire structures is established. The theory is based on a Lagrangian formalism from which the equations of motion are rigorously derived. They consist of four coupled second-order differential equations for the vibrational amplitude and electrostatic potential. The matching boundary conditions are obtained from the fundamental equations. It is shown that no incompatibility exists between mechanical and electrostatic matching boundary conditions when a correct mathematical treatment of the problem is given. The particular case of a GaAs quantum wire buried in AlAs, where the phonons can be considered c…

Spurious Singularities in Quasipotential Amplitudes

1973

Analysis of the γγ→DD¯ reaction and the DD¯ bound state

2021

In this work, we investigate the reaction of $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}D\overline{D}$, taking into account the $S$-wave $D\overline{D}$ final state interaction. By fitting to the $D\overline{D}$ invariant mass distributions measured by the Belle and BABAR Collaborations, we obtain a good reproduction of the data by means of a $D\overline{D}$ amplitude that produces a bound $D\overline{D}$ state with isospin $I=0$ close to threshold. The error bands of the fits indicate, however, that more precise data on this reaction are needed to be more assertive about the position and width of such a state.

Time-optimal control of spin-1/2 particles with dissipative and generalized radiation-damping effects

2013

We analyze the time-optimal control of spin-1/2 particles with bounded field amplitudes in the presence of dissipative and radiation damping effects. Using tools of geometric optimal control theory, we determine different optimal syntheses for specific values of the system parameters. We show the nontrivial role of the effective radiation damping effect on the optimal control law.

Multiphoton-ionization transition amplitudes and the Keldysh approximation.

1989

The Keldysh approximation to treat the multiphoton ionization of atoms is reconsidered. It is shown that, if one consistently uses the hypothesis under which the approximation should be valid (essentially, that of a weak, short-range binding potential), a Keldysh-like term results as an approximation to the first term of a uniformly convergent series in powers of the binding potential. No cancellation occurs when higher-order terms are taken into account. This result allows one to consider the Keldysh approximation as a well-defined theoretical model, without implying, however, that it is adequate to describe multiphoton ionization of real atoms.

Optimal control of the signal-to-noise ratio per unit time of a spin 1/2 particle: The crusher gradient and the radiation damping cases

2015

We show to which extent the signal to noise ratio per unit time of a spin 1/2 particle can be maximized. We consider a cyclic repetition of experiments made of a measurement followed by a radio-frequency magnetic field excitation of the system, in the case of unbounded amplitude. In the periodic regime, the objective of the control problem is to design the initial state of the system and the pulse sequence which leads to the best signal to noise performance. We focus on two specific issues relevant in nuclear magnetic resonance, the crusher gradient and the radiation damping cases. Optimal control techniques are used to solve this non-standard control problem. We discuss the optimality of t…

Reduction to finite dimensions of continuous systems having only a few amplified modes

2008

In the approach of Guckenheimer and Knobloch the amplitudes of trajectories on the unstable manifold 0 are the pivotal quantities. This places a certain restriction on the applicability of this approach, as only neighbourhoods of 0 of the unstable manifold of 0 are accessible, which have a one-to-one projection into their tangent at 0, the linear space spanned by the amplified modes. This restriction may be lifted, using the arc lengths of trajectories instead.