322 research outputs found
An automated design methodology of RF circuits by using Pareto-optimal fronts of EMsimulated inductors
A new design methodology for radiofrequency circuits is presented that includes electromagnetic (EM) simulation of the inductors into the optimization flow. This is achieved by previously generating the Pareto-optimal front (POF) of the inductors using EM simulation. Inductors are selected from the Pareto front and their S-parameter matrix is included in the circuit netlist that is simulated using an RF simulator. Generating the EM-simulated POF of inductors is computationally expensive, but once generated, it can be used for any circuit design. The methodology is illustrated both for a singleobjective and a multiobjective optimization of a low noise amplifierMinisterio de Economía y Competitividad TEC2013-45638-C3-3-R, TEC2013-40430-RJunta de Andalucía PIC12-TIC-1481Consejo Superior de Investigaciones Científicas 201350E05
Experimental vortex ratchet effect in nanostructured superconductors
Superconducting Nb thin films were grown on different arrays of triangle-shape metallic islands. The vortex lattice dynamics could be strongly modified by these asymmetric vortex traps. These asymmetric pinning potentials lead to a rectification effect on the vortex motion: Injecting an ac supercurrent on the sample yields a net dc vortex flow. This vortex ratchet ffect is adiabatic and reversible: The effect is frequency independent and the polarity of the dc voltage output could be tuned by the applied magnetic fields and the input ac currents
Vortex-lattice dynamics with channeled pinning potential landscapes
We have studied vortex-lattice dynamics as a function of driving force direction, in superconducting Nb films with periodic pinning arrays of magnetic dots. Square and rectangular symmetry arrays define channels that guide the vortex-lattice motion. We investigated the effect of the driving force direction on the commensurability between the vortex-lattice and dots array. We also studied the transverse depinning of the vortex-lattice as is moving longitudinally along channels. We found that transverse depinning forces are enhanced with respect to the static situation. The results are discussed in terms of the dynamical evolution of order in the vortex-lattice
Experimental adiabatic vortex ratchet effect in Nb films with asymmetric pinning trap
Nb films grown on top of an array of asymmetric pinning centers show a vortex ratchet effect. A net flow of vortices is induced when the vortex lattice is driven by fluctuating forces on an array of pinning centers without reflection symmetry. This effect occurs in the adiabatic regime and it could be mimiced only by reversible DC driven forces
Stellar populations of galaxies in the ALHAMBRA survey up to . II. Stellar content of quiescent galaxies within the dust-corrected stellar masscolour and the colourcolour diagrams
Our aim is to determine the distribution of stellar population parameters
(extinction, age, metallicity, and star formation rate) of quiescent galaxies
within the rest-frame stellar masscolour and colourcolour diagrams
corrected for extinction up to . These novel diagrams reduce the
contamination in samples of quiescent galaxies owing to dust-reddened galaxies,
and they provide useful constraints on stellar population parameters. We set
constraints on the stellar population parameters of quiescent galaxies
combining the ALHAMBRA multi-filter photo-spectra with our SED-fitting code
MUFFIT, making use of composite stellar population models. The extinction
obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from
the sample of red galaxies. The distributions of stellar population
parameters across these rest-frame diagrams are revealed after the dust
correction and are fitted by the LOESS method to reduce uncertainty effects.
Quiescent galaxy samples defined via classical diagrams are typically
contaminated by a % fraction of DSF galaxies. A significant part of the
galaxies in the green valley are actually obscured star-forming galaxies
(%). Consequently, the transition of galaxies from the blue cloud to
the red sequence, and hence the related mechanisms for quenching, seems to be
much more efficient and faster than previously reported. The rest-frame stellar
masscolour and colourcolour diagrams are useful for constraining
the age, metallicity, extinction, and star formation rate of quiescent galaxies
by only their redshift, rest-frame colours, and/or stellar mass. Dust
correction plays an important role in understanding how quiescent galaxies are
distributed in these diagrams and is key to performing a pure selection of
quiescent galaxies via intrinsic colours.Comment: (37 pages, 29 figures, accepted for publication in A&A
The ALHAMBRA survey: evolution of galaxy spectral segregation
We study the clustering of galaxies as a function of spectral type and
redshift in the range using data from the Advanced Large
Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) survey. The data
cover 2.381 deg in 7 fields, after applying a detailed angular selection
mask, with accurate photometric redshifts [] down to
. From this catalog we draw five fixed number density,
redshift-limited bins. We estimate the clustering evolution for two different
spectral populations selected using the ALHAMBRA-based photometric templates:
quiescent and star-forming galaxies. For each sample, we measure the real-space
clustering using the projected correlation function. Our calculations are
performed over the range Mpc, allowing us to find a
steeper trend for Mpc, which is especially clear for
star-forming galaxies. Our analysis also shows a clear early differentiation in
the clustering properties of both populations: star-forming galaxies show
weaker clustering with evolution in the correlation length over the analysed
redshift range, while quiescent galaxies show stronger clustering already at
high redshifts, and no appreciable evolution. We also perform the bias
calculation where similar segregation is found, but now it is among the
quiescent galaxies where a growing evolution with redshift is clearer. These
findings clearly corroborate the well known colour-density relation, confirming
that quiescent galaxies are mainly located in dark matter halos that are more
massive than those typically populated by star-forming galaxies.Comment: 14 pages, 9 figures, accepted by Ap
The ALHAMBRA survey: Accurate merger fractions by PDF analysis of photometric close pairs
Our goal is to develop and test a novel methodology to compute accurate close
pair fractions with photometric redshifts. We improve the current methodologies
to estimate the merger fraction f_m from photometric redshifts by (i) using the
full probability distribution functions (PDFs) of the sources in redshift
space, (ii) including the variation in the luminosity of the sources with z in
both the selection of the samples and in the luminosity ratio constrain, and
(iii) splitting individual PDFs into red and blue spectral templates to deal
robustly with colour selections. We test the performance of our new methodology
with the PDFs provided by the ALHAMBRA photometric survey. The merger fractions
and rates from the ALHAMBRA survey are in excellent agreement with those from
spectroscopic work, both for the general population and for red and blue
galaxies. With the merger rate of bright (M_B <= -20 - 1.1z) galaxies evolving
as (1+z)^n, the power-law index n is larger for blue galaxies (n = 2.7 +- 0.5)
than for red galaxies (n = 1.3 +- 0.4), confirming previous results.
Integrating the merger rate over cosmic time, we find that the average number
of mergers per galaxy since z = 1 is N_m = 0.57 +- 0.05 for red galaxies and
N_m = 0.26 +- 0.02 for blue galaxies. Our new methodology exploits
statistically all the available information provided by photometric redshift
codes and provides accurate measurements of the merger fraction by close pairs
only using photometric redshifts. Current and future photometric surveys will
benefit of this new methodology.Comment: Submitted to A&A, 15 pages, 15 figures, 6 tables. Comments are
welcome. Close pair systems available at
https://cloud.iaa.csic.es/alhambra/catalogues/ClosePairs
The ALHAMBRA survey : Estimation of the clustering signal encoded in the cosmic variance
The relative cosmic variance () is a fundamental source of
uncertainty in pencil-beam surveys and, as a particular case of count-in-cell
statistics, can be used to estimate the bias between galaxies and their
underlying dark-matter distribution. Our goal is to test the significance of
the clustering information encoded in the measured in the ALHAMBRA
survey. We measure the cosmic variance of several galaxy populations selected
with band luminosity at as the intrinsic dispersion in
the number density distribution derived from the 48 ALHAMBRA subfields. We
compare the observational with the cosmic variance of the dark
matter expected from the theory, . This provides an
estimation of the galaxy bias . The galaxy bias from the cosmic variance is
in excellent agreement with the bias estimated by two-point correlation
function analysis in ALHAMBRA. This holds for different redshift bins, for red
and blue subsamples, and for several band luminosity selections. We find
that increases with the band luminosity and the redshift, as expected
from previous work. Moreover, red galaxies have a larger bias than blue
galaxies, with a relative bias of . Our results
demonstrate that the cosmic variance measured in ALHAMBRA is due to the
clustering of galaxies and can be used to characterise the affecting
pencil-beam surveys. In addition, it can also be used to estimate the galaxy
bias from a method independent of correlation functions.Comment: Astronomy and Astrophysics, in press. 9 pages, 4 figures, 3 table
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