58 research outputs found
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.
Kiloparsec-scale star formation law in M81 and M101 based on AKARI far-infrared observations
We assess the relationships between the surface densities of the gas and star
formation rate (SFR) within spiral arms of the nearby late-type spiral galaxies
M81 and M101. By analyzing these relationships locally, we derive empirically a
kiloparsec scale Kennicutt-Schmidt Law. Both M81 and M101 were observed with
the Far-Infrared Surveyor (FIS) aboard AKARI in four far-infrared bands at 65,
90, 140, and 160 um. The spectral energy distributions of the whole galaxies
show the presence of the cold dust component (Tc~20 K) in addition to the warm
dust component (Tw~60 K). We deconvolved the cold and warm dust emission
components spatially by making the best use of the multi-band photometric
capability of the FIS. The cold and warm dust components show power-law
correlations in various regions, which can be converted into the gas mass and
the SFR, respectively. We find a power-law correlation between the gas and SFR
surface densities with significant differences in the power law index N between
giant HII regions (N=1.0) and spiral arms (N=2.2) in M101. The power-law index
for spiral arms in M81 is similar (N=1.9) to that of spiral arms in M101.
Conclusions: The power-law index is not always constant within a galaxy. The
difference in the power-law index can be attributed to the difference in the
star formation processes on a kiloparsec scale. N~2 seen in the spiral arms in
M81 and M101 supports the scenario of star formation triggered by cloud-cloud
collisions enhanced by spiral density wave, while N~1 derived in giant HII
regions in M101 suggests the star formation induced by the Parker instability
triggered by high velocity HI gas infall. The present method can be applied to
a large galaxy sample for which the AKARI All Sky Survey provides the same 4
far-infrared band data.Comment: 12 pages, 8 figures, accepted for publication in A&
Angular Momentum Transport in Extended Galactic Disks
We demonstrate a significant difference in the angular momentum transport
properties of galactic disks between regions in which the interstellar medium
is single phase or two phase. Our study is motivated by observations of HI in
extended galactic disks which indicate velocity dispersions of nonthermal
origin, suggesting that turbulence in the gas may be contributing significantly
to the observed dispersion. To address this, we have implemented a shearing-box
framework within the FLASH code. The new code was used to perform local
simulations of galactic disks that incorporate differential rotation,
self-gravity, vertical stratification, hydrodynamics and cooling. These
simulations explore plausible mechanisms for driving turbulent motions via the
thermal and self-gravitational instabilities coupling to differential rotation.
Where a two-phase medium develops, gravitational angular momentum transporting
stresses are much greater, creating a possible mechanism for transferring
energy from galactic rotation to turbulence. In simulations where the disk
conditions do not trigger the formation of a two-phase medium, it is found that
perturbations to the flow damp without leading to a sustained mechanism for
driving turbulence. The differing angular momentum transport properties of the
single- and two-phase regimes of the disk suggest that a significant,
dynamically motivated division can be drawn between the two, even when this
division occurs far outside the star formation cutoff in a galactic disk.Comment: ApJ Letters accepted, 5 pages, 3 figur
Massless geodesics in as a superintegrable system
A Carter like constant for the geodesic motion in the
Einstein-Sasaki geometries is presented. This constant is functionally
independent with respect to the five known constants for the geometry. Since
the geometry is five dimensional and the number of independent constants of
motion is at least six, the geodesic equations are superintegrable. We point
out that this result applies to the configuration of massless geodesic in
studied by Benvenuti and Kruczenski, which are matched to
long BPS operators in the dual N=1 supersymmetric gauge theory.Comment: 20 pages, no figures. Small misprint is corrected in the Killing-Yano
tensor. No change in any result or conclusion
Adaptive Evolution of the Lactose Utilization Network in Experimentally Evolved Populations of Escherichia coli
Adaptation to novel environments is often associated with changes in gene regulation. Nevertheless, few studies have been able both to identify the genetic basis of changes in regulation and to demonstrate why these changes are beneficial. To this end, we have focused on understanding both how and why the lactose utilization network has evolved in replicate populations of Escherichia coli. We found that lac operon regulation became strikingly variable, including changes in the mode of environmental response (bimodal, graded, and constitutive), sensitivity to inducer concentration, and maximum expression level. In addition, some classes of regulatory change were enriched in specific selective environments. Sequencing of evolved clones, combined with reconstruction of individual mutations in the ancestral background, identified mutations within the lac operon that recapitulate many of the evolved regulatory changes. These mutations conferred fitness benefits in environments containing lactose, indicating that the regulatory changes are adaptive. The same mutations conferred different fitness effects when present in an evolved clone, indicating that interactions between the lac operon and other evolved mutations also contribute to fitness. Similarly, changes in lac regulation not explained by lac operon mutations also point to important interactions with other evolved mutations. Together these results underline how dynamic regulatory interactions can be, in this case evolving through mutations both within and external to the canonical lactose utilization network
Photography-based taxonomy is inadequate, unnecessary, and potentially harmful for biological sciences
The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009; Cianferoni & Bartolozzi 2016; Amorim et al. 2016). This question was again raised in a letter supported
by 35 signatories published in the journal Nature (Pape et al. 2016) on 15 September 2016. On 25 September 2016, the following rebuttal (strictly limited to 300 words as per the editorial rules of Nature) was submitted to Nature, which on
18 October 2016 refused to publish it. As we think this problem is a very important one for zoological taxonomy, this text is published here exactly as submitted to Nature, followed by the list of the 493 taxonomists and collection-based
researchers who signed it in the short time span from 20 September to 6 October 2016
Etnomatemáticas en artesanías de trenzado: un modelo metodológico para investigación
El área temática del Proyecto de Investigación, parte del cual exponemos en este artículo, es Etnomatemáticas. El propósito de investigación es la caracterización y valoración del conocimiento socio-cultural, implícito en la práctica diaria. En el contexto geográfico de Argentina, investigamos la matemática implícita en artesanías de trenzados, elaborando para esto un método propio de análisis etnomatemático. El instrumento metodológico MOMET que se crea para este estudio interpretativo formal de artesanías de trenzado tiene en cuenta dos aspectos: el producto final de la labor artesanal analizado en su complejidad global y el proceso que se lleva a cabo para realizarlo. La herramienta metodológica elaborada está constituida por dos componentes: un Método de análisis etnográfico (MET) y un Modelo de análisis matemático (MOM). El conjunto de los dos nos proporciona el instrumento metodológico MOMET, que permite la Modelización Etnomatemática de las artesanías de trenzado
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