1,847 research outputs found
Strain-driven elastic and orbital-ordering effects on thickness-dependent properties of manganite thin films
We report on the structural and magnetic characterization of (110) and (001)
La2/3Ca1/3MnO3 (LCMO) epitaxial thin films simultaneously grown on (110) and
(001)SrTiO3 substrates, with thicknesses t varying between 8 nm and 150 nm. It
is found that while the in-plane interplanar distances of the (001) films are
strongly clamped to those of the substrate and the films remain strained up to
well above t=100 nm, the (110) films relax much earlier. Accurate determination
of the in-plane and out-of-plane interplanar distances has allowed concluding
that in all cases the unit cell volume of the manganite reduces gradually when
increasing thickness, approaching the bulk value. It is observed that the
magnetic properties (Curie temperature and saturation magnetization) of the
(110) films are significantly improved compared to those of (001) films. These
observations, combined with 55Mn-nuclear magnetic resonance data and X-ray
photoemission spectroscopy, signal that the depression of the magnetic
properties of the more strained (001)LCMO films is not caused by an elastic
deformation of the perovskite lattice but rather due to the electronic and
chemical phase separation caused by the substrate-induced strain. On the
contrary, the thickness dependence of the magnetic properties of the less
strained (110)LCMO films are simply described by the elastic deformation of the
manganite lattice. We will argue that the different behavior of (001) and
(110)LCMO films is a consequence of the dissimilar electronic structure of
these interfaces.Comment: 16 pages, 15 figure
Quasars Clustering at z approx 3 on Scales less sim 10 h^{-1} Mpc
We test the hypothesis whether high redshift QSOs would preferentially appear
in small groups or pairs, and if they are associated with massive, young
clusters. We carried out a photometric search for \Ly emitters on scales
Mpc, in the fields of a sample of 47 known
QSOs. Wide and narrow band filter color-magnitude diagrams were generated for
each of the fields. A total of 13 non resolved objects with a
significant color excess were detected as QSO candidates at a redshift similar
to that of the target. All the candidates are significantly fainter than the
reference QSOs, with only 2 of them within 2 magnitudes of the central object.
Follow-up spectroscopic observations have shown that 5, i.e., about 40% of the
candidates, are QSOs at the same redshift of the target; 4 are QSOs at
different z (two of them probably being a lensed pair at z = 1.47); 2
candidates are unresolved HII galaxies at z0.3; one unclassified and one
candidate turned out to be a CCD flaw. These data indicate that at least 10% of
the QSOs at z3 do have companions.
We have also detected a number of resolved, rather bright \Ly Emitter
Candidates. Most probably a large fraction of them might be bright galaxies
with [OII] emission, at z 0.3. The fainter population of our
candidates corresponds to the current expectations. Thus, there are no strong
indication for the existence of an overdensity of \Ly galaxies brighter than m
25 around QSOs at 3.Comment: 29 pages, 8 figures, tar gzip LaTex file, accepted to appear in Ap
Impact damage mitigation using bioinspired CFRP laminate architectures
Carbon fibre reinforced polymers (CFRP) are widely used in advanced applications due to their high performance and low weight. However, when exposed to some conditions, as shear, dynamic and impact loading, they may develop interlaminar damages. One of the most common and dangerous solicitations that they must face in service is low velocity impact (LVI) events. To improve damage tolerance to LVI events, three new bioinspired CFRP laminates were developed and tested in the present work to assess and compare their behaviour to the one presented by a typical aeronautic standard laminate. All these studied laminates, having approximately the same thickness of 4 mm, were produced by vacuum bag infusion and observed under deflexion and scanning electron microscopes (SEM) for assessing their processing quality. Interlaminar shear strength (ILSS) and LVI tests were performed in order to evaluate their delamination resistance and impact response. LVI tests were performed for all laminates at the three different impact energy levels of 13.5 J, 25 J and 40 J. Those tests have shown that the bioinspired hybrid laminate (HYB) and all bioinspired ones presented higher interlaminar shear strength and energy absorption for the 40 J impact energy than the standard CFRP laminate (LS), respectively.FCT projeto do Programa MIT Portugal "IAMAT – Introduction of advanced materials technologies into new product development for the mobility industries
The evolution of Balmer jump selected galaxies in the ALHAMBRA survey
We present a new color-selection technique, based on the Bruzual & Charlot
models convolved with the bands of the ALHAMBRA survey, and the redshifted
position of the Balmer jump to select star-forming galaxies in the redshift
range 0.5 < z < 1.5. These galaxies are dubbed Balmer jump Galaxies BJGs. We
apply the iSEDfit Bayesian approach to fit each detailed SED and determine
star-formation rate (SFR), stellar mass, age and absolute magnitudes. The mass
of the haloes where these samples reside are found via a clustering analysis.
Five volume-limited BJG sub-samples with different mean redshifts are found to
reside in haloes of median masses slightly
increasing toward z=0.5. This increment is similar to numerical simulations
results which suggests that we are tracing the evolution of an evolving
population of haloes as they grow to reach a mass of at z=0.5. The likely progenitors of our samples at z3 are Lyman
Break Galaxies, which at z2 would evolve into star-forming BzK galaxies,
and their descendants in the local Universe are elliptical galaxies.Hence, this
allows us to follow the putative evolution of the SFR, stellar mass and age of
these galaxies. From z1.0 to z0.5, the stellar mass of the volume
limited BJG samples nearly does not change with redshift, suggesting that major
mergers play a minor role on the evolution of these galaxies. The SFR evolution
accounts for the small variations of stellar mass, suggesting that star
formation and possible minor mergers are the main channels of mass assembly.Comment: 14 pages, 10 figures. Submitted to A&A. It includes first referee's
comments. Abstract abridged due to arXiv requirement
Phenology and Biomass Production of Adapted and Non-Adapted Tropical Corn Populations in Central Iowa
Biofuel production in the midwestern United States has largely focused on corn (Zea mays L.) grain for ethanol production and more recently, corn stover for lignocellulosic ethanol. Tropical corn refers to corn adapted from tropical regions. Growing tropical germplasm in temperate environments is not attractive for grain yield, but shows promise for biomass production through taller and more vigorous plants with thick stems and long leaves. The comparison between tropical corn populations and their temperate adapted counterparts with a focus on biomass production has not yet been explored under Iowa growing conditions. This study refines the accuracy of the leaf collar method, and characterizes the adaptation of the populations by evaluating crop development and biomass production. Therefore, field trials were established in central Iowa during the 2014 and 2015 growing seasons. Adapted and non-adapted versions of three populations, Tuxpeño, Suwan, and Tuson, were planted at three dates to evaluate their phenology and potential for biomass production under midwestern U.S. conditions. Plant height correlated well with vegetative development and total biomass. Adapted tropical corn had advanced grain development, while non-adapted tropical corn had advanced vegetative development and greater biomass yield. Non-adapted tropical corn flowered later, had 22% greater total biomass on average (4.6 Mg ha–1 greater than adapted), and had 43% greater non-grain biomass on average, up to 20 Mg ha–1 (6 Mg ha–1 greater than adapted), while adapted populations yielded more grain. Non-adapted tropical corn has a high potential as feedstock for Gen2 biofuels in central Iowa
The Ionized Gas Kinematics of the LMC-Type Galaxy NGC 1427A in the Fornax Cluster
NGC 1427A is a LMC-like irregular galaxy in the Fornax cluster with an
extended pattern of strong star formation around one of its edges, which is
probably due to some kind of interaction with the cluster environment. We
present H-alpha velocities within NGC 1427A, obtained through long-slit
spectroscopy at seven different positions, chosen to fall on the brightest HII
regions of the galaxy. Due to its location very near the center of the cluster
this object is an excellent candidate to study the effects that the cluster
environment has on gas-rich galaxies embedded in it. The rotation of NGC 1427A
is modeled in two different ways. The global ionized gas kinematics is
reasonably well described by solid-body rotation, although on small scales it
shows a chaotic behaviour. In this simple model, the collision with a smaller
member of the cluster as being responsible for the peculiar morphology of NGC
1427A is very unlikely, since the only candidate intruder falls smoothly into
the general velocity pattern of the main galaxy. In a more elaborate model, for
which we obtain a better solution, this object does not lie in the same plane
of NGC 1427A, in which case we identify it as a satellite bound to the galaxy.
These results are discussed in the context of a normal irregular versus one
interacting with some external agent. Based on several arguments and
quantitative estimates, we argue that the passage through the hot intracluster
gas of the Fornax cluster is a very likely scenario to explain the
morphological properties of NGC 1427A.Comment: 31 pages, LaTeX2e, uses aas2pp4.sty and psfig.sty, including 7
Postscript figures; accepted for publication in ApJ, Vol. 530, February 200
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