Electron resonances in VLEED from Cu(111)

The sensitivity of the VLEED I–V curves to the shape and the position of the barrier is shown for the image- type surface barriers. For demonstration and comparison with experimental data the intensities of specularly reflected electron beams from Cu(111) are computed by dynamical theory of electron diffraction. Image plane position changes and modifications of the saturation shape of the surface barrier induce pronounced changes in the I–V curves calculated with the image-type barrier. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.     

The defocusing mechanism of isochronous resonances

We present a numerical study concerning the defocusing mechanism of isochronous resonance island chains in the presence of two permanent robust tori. The process is initialized and concluded through bifurcations of fixed points located on the robust tori. Our approach is based on a Hamiltonian system derived from the resonant normal form. Choosing a convenient parameter in this system, we are able to depict a comprehensive analysis of the dynamics of the problem.     

A relativistic study of the nucleon helicity amplitudes

Abstact: We perform a calculation of the relativistic transition form factors for the electromagnetic excitation of the nucleon resonances. We use as input the 3-quark wave functions obtained in a Constituent Quark Model with three-body forces in the hypercentral approach. With respect to the non relativistic calculations a significant contribution is obtained up to Q ²≃ 2 (GeV/c)². However, the low Q ²-behaviour exhibits a lack of strength, which may be connected with the need of taking into account explicitly further degrees of freedom beyond the three constituent quark ones. Received: 16 April 1998     

Diabatic instability of a solid deformed at high strain rates

Summary The model of a thermo-inelastic solid undergoing a very fast deformation is considered beyond the usual linear approximation. It is shown, via a stability analysis of small fluctuations, that a universal stability diagram in control parameter space exists exhibiting a complex topology but only hard-mode (acousticlike) instabilities, due to the hyperbolic nature of the governing equations. It turns out that an adiabatic homogeneous expansion against cohesion forces is no longer possible if a critical strain rate is exceeded, leading to spatial symmetry breaking towards fracture. The validity of this last result is thought to hold qualitatively irrespectively of the nature of the dissipation laws. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Effect of Strong Irradiation on Raman Magnetic Resonance in an AX Spin System

In Raman magnetic resonance an initially prepared multiple quantum coherence (MQC) in a spin system introduces all the possible single quantum (SQ) and multiple quantum (MQ) NMR signals when an irradiation is applied during the detection period. If the irradiation is weak, the induced signals include those MQs up to the very order of this given MQC, while in the strong irradiation case, those MQs beyond the very order of the given MQC will also appear. An analytical approach based on the product formalism is developed to predict the intensities and frequencies of these induced signals. The analysis provides a complete treatment to cover both cases of weak and strong irradiation. It is also demonstrated with an AX spin system. Experimental results are in qualitative agreement with the analysis.     

High resolution gamma-ray spectroscopy of the27Al(p,γ)28Si resonance reaction

High resolution gamma-ray spectra have been measured from the²⁷Al (p,γ)²⁸Si reaction for the resonances atE _p=2·482, 2·511 and 2·735 MeV at ϑ _pγ=0°, 30°, 55° and 90° using a Ge (Li) gamma spectrometer. From the spectra and the angular distributions the properties of the resonance states have been obtained. These states are the isobaric analogues of the levels at 4·69, 4·75 and 4·93MeV levels respectively in the parent nucleus A²⁸l.     

Strong and electromagnetic J/ψ and ψ(2S) decays into pion and kaon pairs

We discuss interference effects important for the form factors extraction in the vicinity of J/ψ andψ(2S)resonances in combination with resonance parameters determination.The implementation to the Monte Carlo event generator PHOKHARA of the J/ψ and ψ(2S)contributions to the muon,pion and kaon pairs production associated with a photon at next-to-leading order is also described.     

Tilted spin torque-driven ferromagnetic resonance in a perpendicular-analyzer magnetic trilayer

A theoretical study is presented on the current-driven ferromagnetic resonance in the magnetic trilayers. On the basis of the Landau-Lifshitz-Gilbert-Slonczewski equation, we derive the output dc voltage for arbitrary anisotropy in the free and pinned layers by the linearization method. As an example, the resonance spectra of the tilted-polarizer and perpendicular-analyzer trilayer show that the equilibrium position, the resonant linewidth and the resonant location can be tuned by changing the magnitude and the direction of spin torque. The effective damping can be minimized through adjusting the current and the pinned-layer magnetization direction.