Synchronisation Induced by Repulsive Interactions in a System of van der Pol Oscillators

We consider a system of identical van der Pol oscillators, globally coupled through their velocities, and study how the presence of competitive interactions affects its synchronisation properties. We will address the question from two points of view. Firstly, we will investigate the role of competitive interactions on the synchronisation among identical oscillators. Then, we will show that the presence of an intermediate fraction of repulsive links results in the appearance of macroscopic oscillations at that signal's rhythm, in regions where the individual oscillator is unable to synchronise with a weak external signal

Spectrum and Statistical Entropy of AdS Black Holes

Popular approaches to quantum gravity describe black hole microstates differently and apply different statistics to count them. Since the relationship between the approaches is not clear, this obscures the role of statistics in calculating the black hole entropy. We address this issue by discussing the entropy of eternal AdS black holes in dimension four and above within the context of a midisuperspace model. We determine the black hole eigenstates and find that they describe the quantization in half integer units of a certain function of the Arnowitt-Deser-Misner (ADM) mass and the cosmological constant. In the limit of a vanishing cosmological constant (the Schwarzschild limit) the quantized function becomes the horizon area and in the limit of a large cosmological constant it approaches the ADM mass of the black holes. We show that in the Schwarzschild limit the area quatization leads to the Bekenstein-Hawking entropy if Boltzmann statistics are employed. In the limit of a large cosmological constant the Bekenstein-Hawking entropy can be recovered only via Bose statistics. The two limits are separated by a first order phase transition, which seems to suggest a shift from "particle-like" degrees of freedom at large cosmological constant to geometric degrees of freedom as the cosmological constant approaches zero.Comment: 14 pages. No figures. Some references added. Version to appear in Phys. Rev.

Potential of a New Technique for Remote Sensing of Hydrocarbon Accumulations and Blind Uranium Deposits: Buried Lif Thermoluminescence Dosimeters

Buried thermoluminescence dosimeters may be useful in remote sensing of petroleum and natural gas accumulations and blind uranium deposits. They act as integrating detectors that smooth out the effects of environmental variations that affect other measuring systems and result in irregularities and poor repeatability in measurements made during gas and radiometric surveys

Braneworlds and Dark Energy

In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5 braneworld when conformal matter fields propagate in five dimensions. We show that conformal fields of weight -4 are associated with stable geometries which describe the dynamics of inhomogeneous dust, generalized dark radiation and homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded in the compact AdS5 orbifold. We discuss aspects of the radion stability conditions and of the localization of gravity in the vicinity of the brane.Comment: 12 pages, latex, 3 eps figures. Talk given at the Seventh Workshop on Quantum Field Theory under the Influence of External Conditions, IEEC, CSIC and University of Barcelona, Barcelona, Catalonia, Spain, 5-9 September 2005. Revised version published in the workshop proceedings, J. Phys. A: Mathematical and General. Typos corrected and some changes introduced for clarit

Circadian Rhythms and Stride-to-Stride Fluctuations: Is there a connection ?

Several physiological systems exhibit rhythmic changes over the course of 24h. A disruption in the CR is thought to represent a risk to the human’s health (e.g., cardiac risk, diabetes). Aging and neurological diseases are known to be characterized by an increased likelihood of circadian disruption. Recently, balance and gait have been shown to exhibit diurnal variations, suggesting a possible influence of CR. Gait is also characterized by a certain level of stride-to-stride fluctuations. In addition, a breakdown in the temporal structure of these fluctuations has recently been associated with aging and neurological diseases. Therefore, it is likely that a circadian disruption may affect the stride-to-stride fluctuations over a 24h period. The present study aims 1) to understand how stride-to-stride fluctuations vary throughout a day and; 2) to examine the effects of chronotype in stride-to-stride fluctuations. Three participants completed the Morningness-Eveningness Questionnaire to determine their chronotype. Then, they walked for 15min at 2h intervals (8am-8pm) and the mean and temporal structure of stride time were determined. Our preliminary data exhibit that a certain cycle emerges for daily fluctuations of the temporal structure of stride time. Furthermore, these daily fluctuations look to be chronotype-specific. This very preliminary data show promise regarding the hypothesis that stride-to-stride fluctuations in gait are influenced by circadian rhythms. If verified, such a finding may bring new insights of a potential increased risk of falling in older adults at specific times of the day that can be targeted of interventions