Applied Physics

New analytical methodology in the temporal structure of urban noise was proposed • Average errors less than one decibel in all acoustics indicators were found • General purpose could be found for the study of pollution related with road traffic a b s t r a c t Editor: P. Kassomenos

An area of current interest and topic of multiple publications is the assessment of uncertainty in estimating long-term indicators from measurements made for periods of time of less than 1 year. In this work, these prior investigations have been used as a starting point.

Previous studies concerning the categorisation method have been based on short daytime measurements. These studies demonstrated urban-noise stratification in the daytime. Nevertheless, legislation and standards refer to noise estimation throughout the day. This paper presents the first attempt to apply the categorisation method to indicators obtained through long-term measurements. The study was conducted in Plasencia, Extremadura (Spain) which has approximately 41,500 inhabitants. First, we conducted a stratification of the roads using the categorisation method. Second, long-term measurements (approximately one week) were conducted at different sampling locations across different categories of streets. The results were analysed by category. Moreover, the profile of the noise-level variation was analysed during the day. The results revealed a stratification of sound levels measured across the different categories. Furthermore, we found health risks due to the noise levels in this town. Short-term measurements were also conducted to complete the categorisation method suitability analysis.

In this paper, the stabilisation times for all 24 h of the day are analysed for 12 measurement stations located in the Spanish town of Malaga and throughout 5 years (2007-2011) of sampling environmental noise levels. For the results to be generalised to sound level measurements made in other streets or cities where there have been no long-term measurements, this study was developed for different road types and urban shapes. This distinction was made according to the types of roads indicated in other studies in which a statistically significant relationship was found between noise levels and the road type. The final objective of the study is to determine the capacity to estimate and approximate the real equivalent hourly noise level (L Aeq,1h ) from the integration of a number of consecutive minutes (shortterm measurements) less than 60 (L Aeq,1h ≈L Aeq,T being T≤60 min). Clearly, this strategy would save time and resources by making measurements of reduced duration. In summary and according to this analysis, a short-time measurement of 15 min is adequate to work with 90 % confidence levels and errors of ±2 dB, with 80 % confidence levels and errors of ±1 dB, and 50 % confidence levels and errors of ±0.5 dB. However, it is necessary to consider the measurement hour period to achieve these levels of confidence due to the high variability throughout the day.

We discuss a novel generic mechanism for controlling the ratchet effect through the breaking of relevant symmetries. We review previous works on ratchets where directed transport is induced by the breaking of standard temporal symmetries f (t) = −f (t + T/2) and f (t) = f (−t) (or f (t) = −f (−t)). We find that in seemingly unrelated systems the average velocity (or the current) of particles (or solitons) exhibits common features. We show that, as a consequence of Curie's symmetry principle, the average velocity (or the current) is related to the breaking of the symmetries of the system. This relationship allows us to control the transport in a systematic way. The qualitative agreement between the present analytical predictions and previous experimental, numerical, and theoretical results leads us to suggest that for the given breaking of the temporal symmetries there is an optimal wave form for a given time-periodic force. Also, we comment on how this mechanism can be applied to the case where a ratchet effect is induced by breaking of spatial symmetries. Finally, we conjecture that the ratchet potential underlying biological motor proteins might be optimized according to the breaking of the relevant symmetries.

The suppressory effects of localized heterogeneous periodic pulses on the chaotic behaviour of sinusoidally coupled nonlinear pendula are studied. We assume that when the pendula are driven synchronously, i.e., all driving pulses have the same waveform, the chains display chaotic dynamics. It is shown that decreasing the impulse transmitted by the pulses of a minimal number of pendula results in regularization with the whole array exhibiting frequency synchronization over a wide range of coupling periods. These findings demonstrate that decreasing the impulse transmitted by localized external forces can tame chaos and lead to frequency-locked states in networks of periodically coupled dissipative systems.

The onset is demonstrated of spatiotemporal chaos arising from the competition between sine-Gordon-breather and kink-antikink-pair solitons by reshaping of a sinusoidal force. After introducing soliton collective coordinates, Melnikov's method is applied to the resulting effective equation of motion to deduce the parameter-space regions of the ac force where chaotic instabilities are induced. The analysis reveals that the chaotic threshold amplitude when altering solely the pulse shape presents a minimum when the transmitted impulse is maximal, the remaining parameters being held constant. The universality of the results is shown by studying the behaviour of the Lyapunov exponent from a simple recursion relation which models an unstable limit cycle. Computer simulations of the sine-Gordon system show good agreement with the theoretical predictions. Additionally, it is found that the reshaping-induced order M chaos route is especially rich, including transitions from a two-breather state to a spatially uniform, periodic oscillatory state. The appearance of this spatially uniform state is explained by means of geometrical resonance analysis.

Spatiotemporal chaos arising from the competition between sine-Gordonbreather and kink-antikink-pair solitons by reshaping an ac force is demonstrated. After introducing soliton collective coordinates, Melnikov's method is applied to the resulting effective equation of motion to estimate the parameterspace regions of the ac force where homoclinic bifurcations are induced. The analysis reveals that the chaos-order threshold exhibits sensitivity to small changes in the force shape. Computer simulations of the sine-Gordon system show good agreement with these theoretical predictions.

We study the structural stability of the Helmholtz oscillator under changes of the shape of periodic nonlinear perturbations. In particular, we determine the order-chaos threshold by means of Melnikov's method for the case of periodic perturbations given in terms of Jacobian elliptic functions. Computer simulations confirm our theoretical predictions.

In this work the theoretical model of multidimensional physical systems, representable as chains of nonlinearly coupled chaotic pendula subjected to harmonic excitations, is formulated and its nonlinear dynamics and synchronization characteristics are studied by means of a numerical approach. Some considerations on the role of the main system parameters are drawn. Dynamic perturbations, due for example to background interactions or to intrinsic pathological imperfections of the chain, are also taken into account. Their effect is analyzed with reference to two distinct situations: uniform application to all the pendula and localized application to the extremities of the chain.

We present theoretical and numerical evidence for a new route, strange nonchaotic behavior ←→ chaos, in two-period quasiperiodically driven dynamical systems by solely changing the excitation waveform. A characteristic signature of this route is the existence of a sequence of intervals over a wide range of waveforms for which only strange non-chaotic attractors or chaos appear, alternatingly. We also found that the largest nontrivial Lyapunov exponent passes through zero linearly near each transition point, which confirms and extends the scaling behavior previously reported for other control parameters.

A general energy-based theory of autoresonance (self-sustained resonance) in low-dimensional nonautonomous systems is presented. The equations that together govern the autoresonance solutions and excitations are derived with the aid of a variational principle concerning the power functional. These equations provide a feedback autoresonance-controlling mechanism. The theory is applied to Duffing-like systems to obtain exact analytical expressions for autoresonance excitations and solutions which explain all the phenomenological and approximate results arising from a previous (adiabatic) approach to autoresonance phenomena in such systems. The theory is also applied to obtain new, general, and exact properties concerning autoresonance phenomena in a broad class of dissipative and Hamiltonian systems, including (as a particular case) Duffing-like systems.

It is demonstrated that the oscillations in the width of the momentum distribution of atoms moving in a phase-modulated standing light field, as a function of the modulation amplitude λ, are correlated with the variation of the chaotic layer width in energy of an underlying effective pendulum. The maximum effect of dynamical localization and the nearly perfect delocalization are associated with the maxima and minima, respectively, of the chaotic layer width. It is also demonstrated that kinetic energy is conserved as an almost adiabatic invariant at the minima of the chaotic layer width, and that the system is accurately described by delta-kicked rotors at sufficiently large zeros of the Bessel functions J 0 (λ) and J 1 (λ). Numerical calculations of kinetic energy and Lyapunov exponents confirm all the theoretical predictions.

We present analytical and numerical results concerning the inhibition of chaos in a single driven Josephson junction by means of an additional weak resonant perturbation. From Melnikov analysis, we theoretically find parameter-space regions, associated with the chaos-suppressing perturbation, where chaotic states can be suppressed. In particular, we test analytical expressions for the intervals of initial phase difference between the two excitations for which chaotic dynamics can be eliminated. All the theoretical predictions are in overall good agreement with numerical results obtained by simulation.

It is shown that the dissipative chaotic dynamics of a charged particle in the field of a wave packet with an arbitrary but finite number of harmonics can be reliably suppressed by judiciously varying the constant phase of the main harmonic, ϕ0, while keeping null the corresponding constant phases of the remaining harmonics. The dependence of the chaotic threshold on the wave packet parameters is predicted theoretically (Melnikov method) and confirmed numerically (Lyapunov exponents). In particular, it is shown that ϕ0 is effective at suppressing the chaotic behavior existing when ϕ0 = 0 over a wide range of values of the wave packet width, while the remaining parameters are kept constant.

The extent of chaos and the suppressory role of Coulomb repulsion in the chaotic dynamics associated with nonsteady finite-amplitude electroconvection is revisited in the context of dynamical systems. Specifically, it is theoretically demonstrated that the threshold value of the charge density taming the heteroclinic chaos associated with laminar chaotic mixing depends on the sinusoidal perturbation's frequency of the fluid velocity field, which is at variance with the fixed threshold value previously reported [Chacón et al., 1994]. Additionally, the consideration of time-periodic multiharmonic perturbations reveals the great complexity of the chaotic mixing scenario.

This special issue of Physica Scripta contains papers presented at the 1st International Meeting on Applied Physics (APHYS-2003), held in Badajoz (Spain), from 13th to 18th October 2003, and more specifically, selected papers presented during the conference sessions mainly on Applied Optics, Laser Physics, Ultrafast Phenomena, Optical Materials, Semiconductor Materials and Devices, Optoelectronics, Quantum Electronics and Applied Solid State Physics-Chemistry. APHYS-2003 was born as an attempt to create a new international forum on Applied Physics in Europe. Since Applied Physics is not really a branch of Physics, but the application of all the branches of Physics to the broad realms of practical problems in Science, Engineering and Industry, this conference was a truly multi and inter-disciplinary event. The organizers called for papers relating Physics with other sciences such as Biology, Chemistry, Information Science, Medicine, etc, or relating different Physics areas, and aimed...