Urban heat island in southern Europe: The case study of Hania, Crete

One of the most common assumptions in the study of neutron star models and their oscillations is that the pressure is isotopic, however, there are arguments that this may not be correct. Thus in the present paper we make a first step towards studying the nonradial oscillations of neutron stars with an anisotropic pressure. We adopt the so-called Cowling approximation where the spacetime metric is kept fixed and the oscillation spectrum for the first few fluid modes is obtained. The effect of the anisotropy on the frequencies is apparent, although with the present results it might be hard to distinguish it from the changes in the frequencies caused by different equations of state.

Nonradial oscillations of anisotropic neutron stars in the Cowling approximation

Application of artificial neural networks for the spatial estimation of wind speed in a coastal region with complex topography

On the physics of power, energy and economics of renewable electric energy sources - Part I

Observational studies indicate that large earthquakes are sometimes preceded by phases of accelerated seismic release (ASR) characterized by cumulative Benioff strain following a power law timeto-failure relation with a term (tf - t)m, where tr is the failure time of the large event and observed values of m are close to 0.3. We discuss properties of ASR and related aspects of seismicity patterns associated with several theoretical frameworks. The subcritical crack growth approach developed to describe deformation on a crack prior to the occurrence of dynamic rupture predicts great variability and low asymptotic values of the exponent m that are not compatible with observed ASR phases. Statistical physics studies assuming that system-size failures in a deforming region correspond to critical phase transitions predict establishment of long-range correlations of dynamic variables and power-law statistics before large events. Using stress and earthquake histories simulated by the model of BEN-ZION (1996) for a discrete fault with quenched heterogeneities in a 3-D elastic half space, we show that large model earthquakes are associated with nonrepeating cyclical establishment and destruction of long-range stress correlations, accompanied by nonstationary cumulative Benioff strain release. We then analyze results associated with a regional lithospheric model consisting of a seismogenic upper crust governed by the damage rheology of LYAKHOVSKY et al. (39) over a viscoelastic substrate. We demonstrate analytically for a simplified 1-D case that the employed damage rheology leads to a singular power-law equation for strain proportional to (t f - t)-1/3, and a nonsingular power-law relation for cumulative Benioff strain proportional to (t f - t)-1/3,A simple approximate generalization of the latter for regional cumulative Benioff strain is obtained by adding to the result a linear function of time representing a stationary background release. To go beyond the analytical expectations, we examine results generated by various realizations of the regional lithospheric model producing seismicity following the characteristic frequency-size statistics, Gutenberg-Richter power-law distribution, and mode switching activity. We find that phases of ASR exist only when the seismicity preceding a given large event has broad frequency-size statistics. In such cases the simulated ASR phases can be fitted well by the singular analytical relation with m = -1/3, the nonsingular equation with m = 0.2, and the generalized version of the latter including a linear term with m = 1/3. The obtained good fits with all three relations highlight the difficulty of deriving reliable information on functional forms and parameter values from such data sets. The activation process in the simulated ASR phases is found to be accommodated both by increasing rates of moderate events and increasing average event size, with the former starting a few years earlier than the latter. The lack of ASR in portions of the seismicity not having broad frequency-size statistics may explain why some large earthquakes are preceded by ASR and other are not. The results suggest that observations of moderate and large events contain two complementary end-member predictive signals on the time of future large earthquakes. In portions of seismicity following the characteristic earthquake distribution, such information exists directly in the associated quasi-periodic temporal distribution of large events. In portions of seismicity having broad frequency-size statistics withrandom or clustered temporal distribution of large events, the ASR phases have predictive information. The extent to which natural seismicity may be understood in terms of these end-member cases remains to be clarified. Continuing studies of evolving stress and other dynamic variables in model calculations combined with advanced analyses of simulated and observed seismicity patterns may lead to improvements in existing forecasting strategies.

Accelerated Seismic Release and Related Aspects of Seismicity Patterns on Earthquake Faults

We present a stationary axisymmetric solution belonging to Carter's family [A] of spaces and representing an anisotropic fluid configuration

Anisotropic fluids in the case of stationary and axisymmetric spaces of general relativity

We define the notion of a surface of revolution in the curved spaces of General Relativity and we present the corresponding Einstein's equations in the case of an anisotropic fluid with bulk and shear viscosity and heat conduction. We indicate a method of integration and some particular solutions.

Rotating fluids in General Relativity

We present a stationary axisymmetric solution belonging to Carter's family [A] of spaces and representing an anisotropic fluid configuration.

Anisotropic fluids in the case of stationary and axisymmetric spaces of General Relativity

In this paper the wind field of the broader area of Chania is statistically analyzed. This analysis is based over one year's hourly averaged measurements of the wind speed and direction, obtained from a network of five Automated Meteorological Stations operating in the greater area of Chania. Firstly, a descriptive statistical analysis of wind speed and direction is performed, which includes the availability of data, the calculation of mean wind speeds, monthly and diurnal variations along with the distribution by wind direction. The Weibull distribution function has been fitted to the available data and its two parameters were identified using the maximum likelihood estimation method. The hourly and monthly wind speeds are found to have remarkable variations.

Analysis of the Wind Field at the Broader Area of Chania, Crete

Observational studies from rock fractures to earthquakes indicate that fractures and many large earthquakes are preceded by accelerating seismic release rates (accelerated seismic deformation). This is characterized by cumulative Benioff strain that follows a power law time-to-failure relation of the form C(t) = K + A(Tf – t)m, where Tf is the failure time of the large event, and m is of the order of 0.2-0.4. More recent theoretical studies have been related to the behavior of seismicity prior to large earthquakes, to the excitation in proximity of a spinodal instability. These have show that the power-law activation associated with the spinodal instability is essentially identical to the power-law acceleration of Benioff strain observed prior to earthquakes with m = 0.25-0.3. In the present study, we provide an estimate of the generic local distribution of cracks, following the Wackentrapp-Hergarten-Neugebauer model for mode I propagation and concentration of microcracks in brittle solids due to remote stress. This is a coupled system that combines the equilibrium equation for the stress tensor with an evolution equation for the crack density integral. This inverse type result is obtained through the equilibrium equations for a solid body. We test models for the local distribution of cracks, with estimation of the stress tensor in terms of the crack density integral, through the Nash-Moser iterative method. Here, via the evolution equation, these estimates imply that the crack density integral grows according to a (Tf – t)0.3-law, in agreement with observations.

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T. Papakostas

Papers

Anisotropic fluids in the case of stationary and axisymmetric spaces of general relativity

Rotating fluids in General Relativity

Anisotropic fluids in the case of stationary and axisymmetric spaces of General Relativity

Analysis of the Wind Field at the Broader Area of Chania, Crete

A first principles approach to understand the physics of precursory accelerating seismicity