[en] Short communication

[en] According to recent studies (Amin et al 2008 Phys. Rev. Lett. 100 060503), the effect of a thermal bath may improve the performance of a quantum adiabatic search algorithm. In this paper, we compare the effects of such a thermal environment on the algorithm performance with those of a structured environment similar to the one encountered in systems coupled to an electromagnetic field that exists within a photonic crystal. Whereas for all the parameter regimes explored here, the algorithm performance is worsened by contact with a thermal environment, the picture appears to be different when one considers a structured environment. In this case we show that by tuning the environment parameters to certain regimes, the algorithm performance can actually be improved with respect to the closed system case. Additionally, the relevance of considering the dissipation rates as complex quantities is discussed in both cases. More specifically, we find that the imaginary part of the rates cannot be neglected with the usual argument that it simply amounts to an energy shift and in fact influences crucially the system dynamics.

[en] We propose a scheme to reversely construct a three-level Hamiltonian via the Rodrigues’ rotation formula and an auxiliary unitary transformation. The main goal of the scheme is designing feasible pulses to drive a three-level system to evolve rapidly from an arbitrary initial state to a desired final state. Numerical simulations demonstrate that the scheme is not only fast but also robust against the decoherence caused by fluctuations of control parameters and some dissipation factors. Besides, we apply the idea to implement a Hadamard gate in a three-level system, and the results show the present scheme is much faster compared with stimulated Raman adiabatic passage (STIRAP). Therefore, the scheme may be useful to find out an effective shortcut to the adiabatic passage in a three-level system. (letter)

[en] Two examples (nonstationary and stationary) of magnetic field generation in a fluid by processes without self-excitation, semidynamo processes, are considered, when Joule dissipation of a magnetic field created by some impressed emf is compensated for (fully or partially) by simple motion (V = const) of the medium. The resultant field greatly exceeds the field generated by emf action in a stationary medium

[en] In order to explain the inflated radii of some transiting extrasolar giant planets, we investigate a tidal heating scenario for the inflated planets WASP-4b, WASP-6b, WASP-12b, WASP-15b, and TrES-4. To do so, we assume that they retain a nonzero eccentricity, possibly by dint of continuing interaction with a third body. We calculate the amount of extra heating in the envelope that is then required to fit the radius of each planet, and we explore how this additional power depends on the planetary atmospheric opacity and on the mass of a heavy-element central core. There is a degeneracy between the core mass M_core and the heating E-dot_heating. Therefore, in the case of tidal heating, there is for each planet a range of {M_core, e ²/Q'_p} that can lead to the same radius, where Q'_p is the tidal dissipation factor and e is the eccentricity. With this in mind, we also investigate the case of the non-inflated planet HAT-P-12b, which can admit solutions combining a heavy-element core and tidal heating. A substantial improvement of the measured eccentricities of such planetary systems could simplify this degeneracy by linking the two unknown parameters {M_core, Q'_p}. Further independent constraints on either of these parameters would, through our calculations, constrain the other.

[en] The role of the clump lifetime τ_cl, logarithmically dependent on small scales, in determining the fluctuation level for forced, dissipative turbulence is reconsidered with the aid of an exactly solvable rapid-change model of passive advection. It is shown in mathematical detail that the common procedure of approximating the steady-state fluctuation level I by τ_clP, where P is the production rate or source of fluctuations, is invalid when a clean distinction can be made between energy-containing and inertial ranges. The correct result is I∼τ_DP, where τ_D is a macroscopic diffusion time that does not depend on the small scales. copyright 1997 American Institute of Physics

[en] In this paper it is calculated the specific heat (C_v) of Bateman-Caldirola-Kanai dissipative systems

[en] A nearly exact solution to the magnetohydrodynamic equations of a fluid of small resistivity describing the propagation of a helical magnetosonic wave parallel to the direction of a uniform magnetic field is given. Departures from an ideal magnetohydrodynamic situation in the context of the earth's magnetosphere seem to lead to a loss of charged particles from a given region. (author)

[en] Ljapunov theorem is applied in studies of stable equilibrium state of plasma

[en] The study was carried out to compare the dissipation of fluroxypyr in a Malaysian agricultural soil based on field experimentation and simulation using the PERSIST and VARLEACH model. A plot situated in an oil palm plantation near Sepang, Selangor, Malaysia was selected for the field exper ment. The plot was treated with fluroxypyr at the recommended dosage (72.5 g ha1). The soil samples from the field trial were collected and anal ses conducted in the laboratory according to the sampling schedule. Simulation of fluroxypyr persistence and leaching was also conducted using computer-run software, PERSIST and VARLEACH. The predicted data obtained using PERSIST for fluroxypyr was found to be higher than the observed data from field measurements. However, the predicted data for fluroxypyr using VARLEACH matched well with the observed data from the field trial. (author)