2,445 research outputs found
Stellar population analysis on local infrared-selected galaxies
To study the stellar population of local infrared galaxies, which contain
star-forming galaxies, composite galaxies, LINERs, and Seyfert 2s. We also want
to find whether infrared luminosity and spectral class have any effects on
their stellar populations. The sample galaxies are selected from the main
galaxy sample of SDSS-DR4 and then cross-correlated with the IRAS-PSCz catalog.
We fit our spectra (stellar absorption lines and continua) using the spectral
synthesis code STARLIGHT on the base of the templates of Simple Stellar
Population and the spectra of star clusters.Among the 4 spectral classes,
LINERs present the oldest stellar populations, and the other 3 sub-samples all
present substantial young and intermediate age populations and very few old
populations. The importance of young populations decreases from star-forming,
composite, Seyfert 2 to LINER. As to different infrared luminosity bins, ULIGs
& LIGs (log(11) present younger populations than
starbursts and normal galaxies. However, the dominant contributors to mass are
old populations in all sample galaxies. The fittings by using the spectra of
star clusters with different ages and metallicities as templates also give
consistent results. The dominated populations in star-forming and composite
galaxies are those with metallicity , while LINERs and Seyfert 2s
are more metal-rich. The normal galaxies are more metal-rich than the ULIGs &
LIGs and starbursts for the star-forming galaxies within different infrared
luminosity bins. Additionally, we also compare some synthesis results with
other parameters obtained from the MPA/JHU catalog.Comment: 13 pages, 11 figures, accepted for publication by A&
Comparing six evolutionary population synthesis models through spectral synthesis on galaxies
We compare six popularly used evolutionary population synthesis (EPS) models
(BC03, CB07, Ma05, GALEV, GRASIL, Vazdekis/Miles) through fitting the full
optical spectra of six representative types of galaxies (star-forming and
composite galaxies, Seyfert 2s, LINERs, E+A and early-type galaxies), which are
taken from the Sloan Digital Sky Survey (SDSS). Throughout our paper, we use
the simple stellar populations (SSPs) from each EPS model and the software
STARLIGHT to do our fits. Our main results are: Using different EPS models the
resulted numerical values of contributed light fractions change obviously, even
though the dominant populations are consistent. The stellar population
synthesis does depend on the selection of age and metallicity, while it does
not depend on the stellar evolution track much. The importance of young
populations decreases from star-forming, composite, Seyfert 2, LINER to
early-type galaxies, and E+A galaxies lie between composite galaxies and
Seyfert 2s in most cases. We conclude that different EPS models do derive
different stellar populations, so that it is not reasonable to directly compare
stellar populations estimated from different EPS models. To get reliable
results, we should use the same EPS model for the compared samples.Comment: 13 pages, 4 figures, accepted for publication in A&
A new approach for identifying non-pathogenic mutations. An analysis of the cystic fibrosis transmembrane regulator gene in normal individuals
Given q as the global frequency of the alleles causing a disease, any allele with a frequency higher than q minus the cumulative frequency of the previously known disease-causing mutations (threshold) cannot be the cause of that disease. This principle was applied to the analysis of cystic fibrosis transmembrane conductance regulator (CFTR) mutations in order to decide whether they are the cause of cystic fibrosis. A total of 191 DNA samples fl-om random individuals from Italy, France, and Spain were investigated by DGGE (denaturing gradient gel electrophoresis) analysis of all the coding and proximal non-coding regions of the gene. The mutations detected by DGGE were identified by sequencing. The sample size was sufficient to select essentially all mutations with a frequency of at least 0.01. A total of 46 mutations was detected, 20 of which were missense mutations. Four new mutations were identified: 1341+28 C/T, 2082 C/T, L1096R, and I1131V. Thirteen mutations (125 G/C, 875+40 A/G, TTGAn, IVS8-6 5T, IVS8-6 9T, 1525-61 A/G, M470V, 2693 T/G, 3061-65 C/A, 4002 A/G, 4521 G/A, IVS8 TG10, IVS8 TG12) were classified as non-CF-causing alleles on the basis of their frequency. The remaining mutations have a cumulative frequency far exceeding q; therefore, most of them cannot be CF-causing mutations. This is the first random survey capable of detecting all the polymorphisms of the coding sequence of a gene
The star formation histories of red and blue low surface brightness disk galaxies
We study the star formation histories (SFH) and stellar populations of 213
red and 226 blue nearly face-on low surface brightness disk galaxies (LSBGs),
which are selected from the main galaxy sample of Sloan Digital Sky Survey
(SDSS) Data Release Seven (DR7). We also want to compare the stellar
populations and SFH between the two groups. The sample of both red and blue
LSBGs have sufficient signal-to-noise ratio in the spectral continua. We obtain
their absorption-line indices (e.g. Mg_2, H\delta_A), D_n(4000) and stellar
masses from the MPA/JHU catalogs to study their stellar populations and SFH.
Moreover we fit their optical spectra (stellar absorption lines and continua)
by using the spectral synthesis code STARLIGHT on the basis of the templates of
Simple Stellar Populations (SSPs). We find that red LSBGs tend to be relatively
older, higher metallicity, more massive and have higher surface mass density
than blue LSBGs. The D_n(4000)-H\delta_A plane shows that perhaps red and blue
LSBGs have different SFH: blue LSBGs are more likely to be experiencing a
sporadic star formation events at the present day, whereas red LSBGs are more
likely to form stars continuously over the past 1-2 Gyr. Moreover, the fraction
of galaxies that experienced recent sporadic formation events decreases with
increasing stellar mass. Furthermore, two sub-samples are defined for both red
and blue LSBGs: the sub-sample within the same stellar mass range of 9.5 <=
log(M_\star/M_\odot) <= 10.3, and the surface brightness limiting sub-sample
with \mu_0(R) <= 20.7 mag arcsec^{-2}. They show consistent results with the
total sample in the corresponding relationships, which confirm that our results
to compare the blue and red LSBGs are robust.Comment: 9 pages, 7 figures, 2 tables, Accepted for publication in A&
Quantum Cryptanalysis on Contracting Feistel Structures and Observation on Related-key Settings
In this paper we show several quantum chosen-plaintext attacks (qCPAs) on contracting Feistel structures.
In the classical setting, a -branch -round contracting Feistel structure can be shown to be PRP-secure when is even and , meaning it is secure against polynomial-time chosen-plaintext attacks.
We propose a polynomial-time qCPA distinguisher on the -branch -round contracting Feistel structure, which solves an open problem by Dong et al.
In addition, we show a polynomial-time qCPA that recovers the keys of the -branch -round contracting Feistel structure when each round function has the form for a public random function . This is applicable to the Chinese block cipher standard {\texttt{SM4}}, which is a special case where .
Finally, in addition to quantum attacks under single-key setting, we also show related-key quantum attacks on balanced Feistel structures in the model that adversaries can only control part of the key difference in quantum superposition.
Our related-key attacks on balanced Feistel structures can easily be extended to ones on contracting Feistel structures
Origin and fate of a bloom of Skeletonema costatum during a winter upwelling/downwelling sequence in the Ría de Vigo (NW Spain)
Original research paperThe onset, development and decay of a winter bloom of the marine diatom Skeletonema costatum
was monitored during a 10 d period in the coastal upwelling system of the Rı´a de Vigo (NW Spain).
The succession of upwelling, relaxation and downwelling-favorable coastal winds with a frequency
of 10 –20 d is a common feature of the NW Iberian shelf. The onset of the bloom occurred during an
upwelling-favorable 1⁄2 wk period under winter thermal inversion conditions. The subsequent 1⁄2 wk
coastal wind relaxation period allowed development of the bloom (gross primary production reached
8gCm–2 d–1) utilizing nutrients upwelled during the previous period. Finally, downwelling during
the following 1⁄2 wk period forced the decay of the bloom through a combination of cell sinking and
downward advection.Financial support came from the Spanish Ministerio de Ciencia y Tecnologı´a (MCyT) grant REN2000-0880-C02-01 and Xunta de Galicia grant PGIDT01MAR40201PN; a fellowship from the MCyT and the I3P-CSIC Program.Versión del editor0,98
Algebraic Cryptanalysis of Curry and Flurry using Correlated Messages
In \cite{BPW}, Buchmann, Pyshkin and Weinmann have described two families of
Feistel and SPN block ciphers called Flurry and Curry
respectively. These two families of ciphers are fully parametrizable and have
a sound design strategy against basic statistical attacks; i.e. linear and
differential attacks. The encryption process can be easily described by a set
of algebraic equations. These ciphers are then targets of choices for
algebraic attacks. In particular, the key recovery problem has been reduced to
changing the order of a Groebner basis \cite{BPW,BPWext}. This attack -
although being more efficient than linear and differential attacks - remains
quite limited. The purpose of this paper is to overcome this limitation by
using a small number of suitably chosen pairs of message/ciphertext for
improving algebraic attacks. It turns out that this approach permits to go one
step further in the (algebraic) cryptanalysis of Flurry and
\textbf{Curry}. To explain the behavior of our attack, we have established an
interesting connection between algebraic attacks and high order differential
cryptanalysis \cite{Lai}. From extensive experiments, we estimate that our
approach, that we can call an ``algebraic-high order
differential cryptanalysis, is polynomial when the Sbox is a power function.
As a proof of concept, we have been able to break Flurry -- up to
rounds -- in few hours
Current-carrying cosmic string loops 3D simulation: towards a reduction of the vorton excess problem
The dynamical evolution of superconducting cosmic string loops with specific
equations of state describing timelike and spacelike currents is studied
numerically. This analysis extends previous work in two directions: first it
shows results coming from a fully three dimensional simulation (as opposed to
the two dimensional case already studied), and it now includes fermionic as
well as bosonic currents. We confirm that in the case of bosonic currents,
shocks are formed in the magnetic regime and kinks in the electric regime. For
a loop endowed with a fermionic current with zero-mode carriers, we show that
only kinks form along the string worldsheet, therefore making these loops
slightly more stable against charge carrier radiation, the likely outcome of
either shocks or kinks. All these combined effects tend to reduce the number
density of stable loops and contribute to ease the vorton excess problem. As a
bonus, these effects also may provide new ways of producing high energy cosmic
rays.Comment: 11 pages, RevTeX 4 format, 8 figures, submitted to PR
Performance of the Muon Identification at LHCb
The performance of the muon identification in LHCb is extracted from data
using muons and hadrons produced in J/\psi->\mu\mu, \Lambda->p\pi and
D^{\star}->\pi D0(K\pi) decays. The muon identification procedure is based on
the pattern of hits in the muon chambers. A momentum dependent binary
requirement is used to reduce the probability of hadrons to be misidentified as
muons to the level of 1%, keeping the muon efficiency in the range of 95-98%.
As further refinement, a likelihood is built for the muon and non-muon
hypotheses. Adding a requirement on this likelihood that provides a total muon
efficiency at the level of 93%, the hadron misidentification rates are below
0.6%.Comment: 17 pages, 10 figure
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