40,223 research outputs found
Interactions and star formation activity in Wolf-Rayet galaxies
We present the main results of the PhD Thesis carried out by
L\'opez-S\'anchez (2006), in which a detailed morphological, photometrical and
spectroscopical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was
realized. The main aims are the study of the star formation and O and WR
stellar populations in these galaxies and the role that interactions between
low surface companion objects have in the triggering of the bursts. We analyze
the morphology, stellar populations, physical conditions, chemical abundances
and kinematics of the ionized gas, as well as the star-formation activity of
each system.Comment: 16 pages, 15 figure
Mesoscopic Coulomb drag, broken detailed balance and fluctuation relations
When a biased conductor is put in proximity with an unbiased conductor a drag
current can be induced in the absence of detailed balance. This is known as the
Coulomb drag effect. However, even in this situation far away from equilibrium
where detailed balance is explicitly broken, theory predicts that fluctuation
relations are satisfied. This surprising effect has, to date, not been
confirmed experimentally. Here we propose a system consisting of a capacitively
coupled double quantum dot where the nonlinear fluctuation relations are
verified in the absence of detailed balance.Comment: 4 pages, 3 figure
Scattering theory of nonlinear thermoelectric transport
We investigate nonlinear transport properties of quantum conductors in
response to both electrical and thermal driving forces. Within scattering
approach, we determine the nonequilibrium screening potential of a generic
mesoscopic system and find that its response is dictated by particle and
entropic injectivities which describe the charge and entropy transfer during
transport. We illustrate our model analyzing the voltage and thermal
rectification of a resonant tunneling barrier. Importantly, we discuss
interaction induced contributions to the thermopower in the presence of large
temperature differences.Comment: 5 pages, 3 figures; slightly shortened version to fulfill the
journal's requirement
Dynamical Coulomb blockade of thermal transport
The role of energy exchange between a quantum system and its environment is
investigated from the perspective of the Onsager conductance matrix. We
consider the thermoelectric linear transport of an interacting quantum dot
coupled to two terminals under the influence of an electrical potential and a
thermal bias. We implement in our model the effect of coupling to
electromagnetic environmental modes created by nearby electrons within the
P(E)-theory of dynamical Coulomb blockade. Our findings relate the lack of some
symmetries among the Onsager matrix coefficients with an enhancement of the
efficiency at maximum power and the occurrence of the heat rectification
phenomenon.Comment: 9 pages, 7 figure
Detecting synchronization in spatially extended discrete systems by complexity measurements
The synchronization of two stochastically coupled one-dimensional cellular
automata (CA) is analyzed. It is shown that the transition to synchronization
is characterized by a dramatic increase of the statistical complexity of the
patterns generated by the difference automaton. This singular behavior is
verified to be present in several CA rules displaying complex behavior.Comment: 4 pages, 2 figures; you can also visit
http://add.unizar.es/public/100_16613/index.htm
MIMO PID Controller Tuning Method for Quadrotor Based on LQR/LQG Theory
In this work, a new pre-tuning multivariable PID (Proportional Integral Derivative)
controllers method for quadrotors is put forward. A procedure based on LQR/LQG (Linear Quadratic
Regulator/Gaussian) theory is proposed for attitude and altitude control, which suposes a considerable
simplification of the design problem due to only one pretuning parameter being used. With the aim to
analyze the performance and robustness of the proposed method, a non-linear mathematical model of
the DJI-F450 quadrotor is employed, where rotors dynamics, together with sensors drift/bias properties
and noise characteristics of low-cost commercial sensors typically used in this type of applications are
considered. In order to estimate the state vector and compensate bias/drift effects in the measures,
a combination of filtering and data fusion algorithms (Kalman filter and Madgwick algorithm for attitude
estimation) are proposed and implemented. Performance and robustness analysis of the control system
is carried out by employing numerical simulations, which take into account the presence of uncertainty
in the plant model and external disturbances. The obtained results show the proposed controller design
method for multivariable PID controller is robust with respect to: (a) parametric uncertainty in the plant
model, (b) disturbances acting at the plant input, (c) sensors measurement and estimation errors
Two new species of Ammothea (Pycnogonida, Ammotheidae) from Antarctic waters
Two new species of the genus Ammothea are
described from Elephant Island and the South Shetlands
Islands, Antarctica. The material was captured during the
Polarstern cruise XXIII/8 to the Antarctic Peninsula area.
The main features of Ammothea pseudospinosa n. sp. are a
proboscis distinctly trilobulated distally with a constriction
at 2/3 of its length and dimorphism between the propodi of
the anterior (first and second) and posterior (third and
fourth) legs, and a trunk: proboscis length ratio of about
1.5. The main features of Ammothea childi n. sp. are a
cylindrical proboscis, longer than trunk length, and adults
with functional chelifores. These species are compared
with their closest congeners from the Southern Ocean:
A. pseudospinosa n. sp. with Ammothea spinosa and
Ammothea allopodes;A. childi n. sp. withAmmothea gigantea,
Ammothea bicorniculata and Ammothea hesperidensis
Colossendeis species (Pycnogonida: Colossendeidae) collected during the Italica XIX cruise to Victoria Land (Antarctica), with remarks on some taxonomic characters of the ovigers
The pycnogonid fauna of the genus Colossendeis collected during the Italica XIX cruise to Victoria Land (Ross Sea, Antarctica) was studied. A total of 19 specimens of six species were collected: Colossendeis australis (6), C. wilsoni (3), C. scotti (2), C. robusta (3), C. lilliei (2) and C. megalonyx (3). In the present contribution the observed variability of all collected Colossendeis species is described and illustrated. The previously synonymised C. lilliei is considered a different species from C. robusta. The observations made in this study lead us to discuss a controversy about the total number of oviger segments in this genus. Despite the currently established 10-segmented status, a short basal element is here considered to be a possible 11th segment. A detailed SEM study of the last oviger segment is carried out in all collected species, showing some intraspecific and the interspecific variability in the structures examined (shape and number of rows of compound spines, morphology of terminal claw, etc.). Finally, we discuss the taxonomic value of these characters of the last strigilis segment for distinguishing the Colossendeis species, and their possible utility in establishing internal phylogenetic relationships in future contributions
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