2,292 research outputs found
Energy conversion in isothermal nonlinear irreversible processes - struggling for higher efficiency
First we discuss some early work of Ulrike Feudel on structure formation in
nonlinear reactions including ions and the efficiency of the conversion of
chemical into electrical energy. Then we give some survey about energy
conversion from chemical to higher forms of energy like mechanical, electrical
and ecological energy. We consider examples of energy conversion in several
natural processes and in some devices like fuel cells. Further, as an example,
we study analytically the dynamics and efficiency of a simple "active circuit"
converting chemical into electrical energy and driving currents which is
roughly modeling fuel cells. Finally we investigate an analogous ecological
system of Lotka - Volterra type consisting of an "active species" consuming
some passive "chemical food". We show analytically for both these models that
the efficiency increases with the load, reaches values higher then 50 percent
in a narrow regime of optimal load and goes beyond some maximal load abrupt to
zero.Comment: 25 pages, 4 figure
Thermodynamics of hot dense H-plasmas: Path integral Monte Carlo simulations and analytical approximations
This work is devoted to the thermodynamics of high-temperature dense hydrogen
plasmas in the pressure region between and Mbar. In particular
we present for this region results of extensive calculations based on a
recently developed path integral Monte Carlo scheme (direct PIMC). This method
allows for a correct treatment of the thermodynamic properties of hot dense
Coulomb systems. Calculations were performed in a broad region of the
nonideality parameter and degeneracy parameter . We give a comparison with a few available results from
other path integral calculations (restricted PIMC) and with analytical
calculations based on Pade approximations for strongly ionized plasmas. Good
agreement between the results obtained from the three independent methods is
found.Comment: RevTex file, 21 pages, 5 ps-figures include
Entropy and Long range correlations in literary English
Recently long range correlations were detected in nucleotide sequences and in
human writings by several authors. We undertake here a systematic investigation
of two books, Moby Dick by H. Melville and Grimm's tales, with respect to the
existence of long range correlations. The analysis is based on the calculation
of entropy like quantities as the mutual information for pairs of letters and
the entropy, the mean uncertainty, per letter. We further estimate the number
of different subwords of a given length . Filtering out the contributions
due to the effects of the finite length of the texts, we find correlations
ranging to a few hundred letters. Scaling laws for the mutual information
(decay with a power law), for the entropy per letter (decay with the inverse
square root of ) and for the word numbers (stretched exponential growth with
and with a power law of the text length) were found.Comment: 8 page
X-ray/optical classification of cluster mergers and the evolution of the cluster merger fraction
We present the results of a simple but robust morphological classification of
a statis- tically complete sample of 108 of the most X-ray luminous clusters at
0.15 < z < 0.7 observed with Chandra. Our aims are to (a) identify the most
disturbed massive clusters to be used as gravitational lenses for studies of
the distant universe and as probes of particle acceleration mechanisms
resulting in non-thermal radio emission, (b) find cluster mergers featuring
subcluster trajectories that make them suitable for quantitative analyses of
cluster collisions, and (c) constrain the evolution with redshift of the
cluster merger fraction. Finally, (d) this paper represents the third public
release of clusters from the MACS sample, adding 24 clusters to the 46
published previously. To classify clusters by degree of relaxation, we use the
projected offset of the brightest cluster galaxy from the peak (or the global
centroid) of the X-ray emission as a measure of the segregation between the
intracluster gas and dark matter. Regarding (a), we identify ten complex
systems likely to have undergone multiple merger events in the recent past.
Regarding (b), we identify eleven systems likely to be post-collision, binary,
head-on mergers (BHOMs), as well as another six mergers that are possible BHOMs
but probably harder to interpret because of non-negligible impact parameters
and merger axes closer to our line of sight. Regarding (c), we find a highly
significant increase with redshift in the fraction of morphologically disturbed
clusters starting at z \sim 0.4, in spite of a detection bias in our sample
against very disturbed systems at high redshift. A larger sample of clusters
with high-quality X-ray data in particular at high redshift will be needed to
trace the evolutionary history of cluster growth and relaxation closer to the
primary epoch of cluster formation z \sim 1.Comment: Accepted to MNRA
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