294 research outputs found
A possible cosmological application of some thermodynamic properties of the black body radiation in dimensional Euclidean spaces
In this work we present the generalization of some thermodynamic properties
of the black body radiation (BBR) towards an dimensional Euclidean space.
For this case the Planck function and the Stefan-Boltzmann law have already
been given by Landsberg and de Vos and some adjustments by Menon and Agrawal.
However, since then no much more has been done on this subject and we believe
there are some relevant aspects yet to explore. In addition to the results
previously found we calculate the thermodynamic potentials, the efficiency of
the Carnot engine, the law for adiabatic processes and the heat capacity at
constant volume. There is a region at which an interesting behavior of the
thermodynamic potentials arise, maxima and minima appear for the BBR
system at very high temperatures and low dimensionality, suggesting a possible
application to cosmology. Finally we propose that an optimality criterion in a
thermodynamic framework could have to do with the nature of the universe.Comment: 9 pages, 8 figure
A simple model on the influence of the greenhouse effect on the efficiency of solar-to-wind energy conversion
In the present paper we study the Gordon and Zarmi model (Am. J. Phys., 57 (1989)995)for dealing with the earth’s wind energy as a solar-driven Carnot-like heat engine, incorporating the role of the greenhouse effect on the performance of this heat engine model, following the De Vos approach. We find that when the greenhouse effect is considered only at the low-temperature half part of the cycle, the efficiency of the conversion of solar energy into wind energy strongly depends on the greenhouse effect under both maximum-power and maximum-ecological-function
conditions. We also analyze the De Vos-van der Wel model corresponding to the so-called two-reservoir case and find that the efficiency of conversion of solar energy into wind energy under maximum ecological function reaches a reasonable value within the interval of values reported in the literature
Energy conversion theorems for some linear steady-states
One of the main issues that real energy converters present, when they produce
effective work, is the inevitable entropy production. Within the context of
Non-equilibrium Thermodynamics, entropy production tends to energetically
degrade man-made or living systems. On the other hand, it is also not useful to
think about designing an energy converter that works in the so-called minimum
entropy production regime since the effective power output and efficiency are
zero. In this manuscript, we establish some \textit{Energy Conversion Theorems}
similar to Prigogine's one with constrained forces, their purpose is to reveal
trade-offs between design and the so-called operation modes for
--linear isothermal energy converters. The objective
functions that give rise to those thermodynamic constraints show stability. A
two--meshes electric circuit was built as an example to demonstrate the
Theorems' validity. Likewise, we reveal a type of energetic hierarchy for power
output, efficiency and dissipation function when the circuit is tuned to any of
the operating regimes studied here: maximum power output (), maximum
efficient power (), maximum omega function (), maximum
ecological function (), maximum efficiency () and minimum
dissipation function ().Comment: 33 pages, 15 figures, 2 table
A statistical analysis of electric self-potential time series associated to two 1993 earthquakes in Mexico
Recent studies related with earthquake prediction involve statistical studies of the ground electric self-potential behavior. Published results about the complexity of this kind of processes encourage us to study the statistical behavior of the ground electric self-potential recorded in Guerrero state, Mexico. This region is characterized by high seismicity. The electric self-potential variations were recorded in the Acapulco station directly from the ground. The sampling period was four seconds and the data were stored from March to December of 1993. Two significant earthquakes (EQs) occurred near this station, 15 May and 24 October whose magnitudes were Mw=6.0 and Mw=6.6 respectively. A preliminary processing was carried out consisting of a moving average of the original time series in order to filter the very high frequencies and to complete short lacks of data and outliers. Then, a visual inspection of the complete filtered signal was performed to search some seismic electric signals (SES), which were ambiguously depicted. Subsequently, a detrending of µ=0 was applied with the windows of 3.3, 6.6 and 10 h. Later, the analysis of the spectral exponent β was made, showing changes during the total period examined, and the most evident changes occurred during the preparation mechanism of the Mw=6.6 EQ. Fifteen days before the 24 October EQ, a Brownian-noise like behavior was displayed (β≈2), having a duration of about two days. In addition a Higuchi fractal method and wavelet analysis were made confirming the presence of the β-anomaly
Multiscale entropy analysis of electroseismic time series
In this work we use the multiscale entropy method to analyse the variability of geo-electric time series monitored in two sites located in Mexico. In our analysis we consider a period of time from January 1995 to December 1995. We systematically calculate the sample entropy of electroseismic time series. Important differences in the entropy profile for several time scales are observed in records from the same station. In particular, a complex behaviour is observed in the vicinity of a <i>M</i>=7.4 EQ occurred on 14 September 1995. Besides, we also compare the changes in the entropy of the original data with their corresponding shuffled version
A first--order irreversible thermodynamic approach to a simple energy converter
Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
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