1,720,985 research outputs found
ANAEROBIC THRESHOLD AND KERNEL ESTIMATORS
No full textThe transition threshold from aerobic to anaerobic metabolism of athletes practising endurance sports is identified with the deflection point in the graph of cardiac frequency versus velocity. A parametric statistical background was provided (Calderoni et al., 1990) by assuming a transition from linear to parabolic regression. By interpreting the threshold as a jump-point for the first derivative of a continuous regression curve, the use of one-sided kernel estimators can be a useful explorative treatment. Here Müller’s theory of such kernels is summarized and simulations are discussed for this type of application
Absence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentials
No full textWe prove the absence of the absolutely continuous spectrum for the operator -d(2)/dx(2) + Sigma(j epsilon Z)alpha delta'(x - j) + fx, > 0 and alpha not equal 0, by means of the crystal momentum representation and the Howland's criterion for Floquet-type operators
Gevrey formal power series of Wannier-Stark ladders
No full textWe consider time-independent Schrodinger equations in one dimension with both periodic and Stark potentials. By means of an iterative procedure we obtain a formal power series for the Wannier-Stark ladders. In the case of strongly singular periodic potentials we prove that such a formal power series is of Gevrey type
Two level systems driven by a stochastic perturbation
No full textHere we consider a two level system driven by an external harmonic field whose amplitude is perturbed by a white noise term. In the limit of small splitting, dynamical localization, i.e. coherent destruction of tunneling, is proved for times of the order of 1/epsilon, where epsilon is the two-level splitting. The same type of localization is proved if the driving field is simply the white noise
Absence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentials
No full textWe correct here the proof of the boundedness of the coupling term X given by us in a previous paper (1995 J. Phys. A: Math. Gen. 28 1101-6)
Wannier ladders and perturbation theory
No full textFollowing Avron we consider the Stark effect for Bloch electrons in the case of a finite number of gaps. We prove that the ladders of resonances are given by the Wannier decoupled-band approximation and the perturbation theory. The Fermi golden rule yields the width behaviour of Buslaev and Dmitrieva
Horn of singularities for the Stark-Wannier ladders
No full textWe prove that the small field asymptotic behaviour of the Stark-Wannier ladders near the real direction is generically highly singular. This result is in agreement with the conjecture of a chaotic behaviour of the lifetime of the states because of infinitely many crossings
Dynamical localization for two-level systems periodically driven
No full textHere, we consider a two-level system driven by an external periodic field. We show that the coherent destruction of tunnelling, as proved by Grossmann and co-workers (1991 Phys. Rev. Lett. 67 516; 1992 Europhys. Lett. 18 571) in the case of a monochromatic field, also appears for any periodic driving field given by an even regular function with zero mean value and satisfying a technical condition on the zeros of this function
- …
