3,220 research outputs found
Room temperature ferromagnetic-like behavior in Mn-implanted and post-annealed InAs layers deposited by Molecular Beam Epitaxy
We report on the magnetic and structural properties of Ar and Mn implanted
InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and
the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling
Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn
implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs
lattice, like in a diluted magnetic semiconductor (DMS). All of these samples
show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit
room-temperature magnetism. According to PIXE measurements the Mn atoms are no
longer substitutional. When the same set of experiments were performed with As
as implantation ion all of the layers present diamagnetism without exception.
This indicates that the appearance of room-temperature ferromagnetic-like
behavior in the Mn-InAs-RTA layer is not related to lattice disorder produce
during implantation, but to a Mn reaction produced after a short thermal
treatment. X-ray diffraction patterns (XRD) and Rutherford Back Scattering
(RBS) measurements evidence the segregation of an oxygen deficient-MnO2 phase
(nominally MnO1.94) in the Mn-InAs-RTA epitaxial layers which might be on the
origin of room temperature ferromagnetic-like response observed.Comment: 16 pages, 5 figures. Acepted in J. Appl. Phy
The central parsecs of M87: jet emission and an elusive accretion disc
We present the first simultaneous spectral energy distribution (SED) of M87
core at a scale of 0.4 arcsec () across the electromagnetic
spectrum. Two separate, quiescent, and active states are sampled that are
characterized by a similar featureless SED of power-law form, and that are thus
remarkably different from that of a canonical active galactic nuclei (AGN) or a
radiatively inefficient accretion source. We show that the emission from a jet
gives an excellent representation of the core of M87 core covering ten orders
of magnitude in frequency for both the active and the quiescent phases. The
inferred total jet power is, however, one to two orders of magnitude lower than
the jet mechanical power reported in the literature. The maximum luminosity of
a thin accretion disc allowed by the data yields an accretion rate of , assuming 10% efficiency. This power
suffices to explain M87 radiative luminosity at the jet-frame, it is however
two to three order of magnitude below that required to account for the jet's
kinetic power. The simplest explanation is variability, which requires the core
power of M87 to have been two to three orders of magnitude higher in the last
200 yr. Alternatively, an extra source of power may derive from black hole
spin. Based on the strict upper limit on the accretion rate, such spin power
extraction requires an efficiency an order of magnitude higher than predicted
from magnetohydrodynamic simulations, currently in the few hundred per cent
range.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
The introduction of real numbers in secondary education. An institutional analysis of textbooks
In this paper we analyse the introduction of irrational and real numbers in secondary textbooks, and specifically the propositions on how these should be taught, in a sample of Brazilian textbooks used in state schools and approved by the Ministry of Education. The analyses discussed in this paper follow an institutional perspective (using Chevallard's Anthropological Theory of Didactics). Our results indicate that the notion of irrational number is generally introduced on the basis of the decimal representation of numbers, and that the mathematical need for the construction of the field of real numbers remains unclear in the textbooks. It seems that textbooks used in secondary teaching institutions develop mathematical organisations which focus on the practical block
Crack-Depth Prediction in Steel Based on Cooling Rate
One criterion for the evaluation of surface cracks in steel welds is to analyze the depth of the crack, because it is an effective indicator of its potential risk. This paper proposes a new methodology to obtain an accurate crack-depth prediction model based on the combination of infrared thermography and the 3D reconstruction procedure. In order to do this, a study of the cooling rate of the steel is implemented through active infrared thermography, allowing the study of the differential thermal behavior of the steel in the fissured zone with respect to the nonfissured zone. These cooling rate data are correlated with the real geometry of the crack, which is obtained with the 3D reconstruction of the welds through a macrophotogrammetric procedure. In this way, it is possible to analyze the correlation between cooling rate and depth through the different zones of the crack. The results of the study allow the establishment of an accurate predictive depth model which enables the study of the depth of the crack using only the cooling rate data. In this way, the remote measure of the depth of the surface steel crack based on thermography is possible
Wide range group delay tuning in lossy fiber ring resonators
22nd International Conference on Optical Fiber Sensors, OFS 2012, Beijing, China, 15-19 Oct. 2012We demonstrate theoretically and experimentally that a wide-range tuning of group delay values can be achieved in a\ud
lossy fiber ring resonator. The tuning mechanism relies simply on varying the loss/coupling ratio in the resonator. This\ud
simple structure may be used advantageously in different regimes for many sensing configurations, both for achieving\ud
extremely high sensitivity enhancements (by working close to critical coupling, where the group index becomes\ud
extremely large) or suppression of undesired refractive index effects (e.g. Kerr effect), by working in the under-coupled\ud
regime
Interaction Effects on the Magneto-optical Response of Magnetoplasmonic Dimers
The effect that dipole-dipole interactions have on the magneto-optical (MO)
properties of magnetoplasmonic dimers is theoretically studied. The specific
plasmonic versus magnetoplasmonic nature of the dimer's metallic components and
their specific location within the dimer plays a crucial role on the
determination of these properties. We find that it is possible to generate an
induced MO activity in a purely plasmonic component, even larger than that of
the MO one, therefore dominating the overall MO spectral dependence of the
system. Adequate stacking of these components may allow obtaining, for specific
spectral regions, larger MO activities in systems with reduced amount of MO
metal and therefore with lower optical losses. Theoretical results are
contrasted and confirmed with experiments for selected structures
On the generalised Chaplygin gas: worse than a big rip or quieter than a sudden singularity?
Although it has been believed that the models with generalised Chaplygin gas
do not contain singularities, in a previous work we have studied how a big
freeze could take place in some kinds of phantom generalised Chaplygin gas. In
the present work, we study some types of generalised Chaplygin gas in order to
show how different sorts of singularities could appears in such models, in the
future or in the past. We point out that: (i) singularities may not be
originated from the phantom nature of the fluid, and (ii) if initially the
tension of the brane in a brane-world Chaplygin model is large enough then an
infrared cut off appears in the past.Comment: 19 pages, 6 figures. Discussion expanded and references added.
Version to appear in the International Journal of Modern Physics
Molecular gas in the northern nucleus of Mrk273: Physical and chemical properties of the disk and its outflow
Aiming to characterise the properties of the molecular gas in the
ultraluminous infrared galaxy Mrk273 and its outflow, we used the NOEMA
interferometer to image the dense gas molecular tracers HCN, HCO+, HNC, HOC+
and HC3N at 86GHz and 256GHz with angular resolutions of 4.9x4.5 arcsec
(3.7x3.4 kpc) and 0.61x0.55 arcsec (460x420 pc). We also modelled the flux of
several H2O lines observed with Herschel using a radiative transfer code that
includes excitation by collisions as well as by far-infrared photons. The disk
of the Mrk273 north nucleus has two components with decoupled kinematics. The
gas in the outer parts (1.5 kpc) rotates with a south-east to north-west
direction, while in the inner disk (300 pc) follows a north-east to south-west
rotation. The central 300 pc, which hosts a compact starburst region, is filled
with dense and warm gas, contains a dynamical mass of (4-5)x10^9M_sun, a
luminosity of L'_HCN=(3-4)x10^8 K km/s pc^2, and a dust temperature of 55 K. At
the very centre, a compact core with R~50 pc has a luminosity of
L_IR=4x10^11L_sun (30% of the total infrared luminosity), and a dust
temperature of 95 K. The core is expanding at low velocities ~50-100 km/s,
probably affected by the outflowing gas. We detect the blue-shifted component
of the outflow, while the red-shifted counterpart remains undetected in our
data. Its cold and dense phase reaches fast velocities up to ~1000 km/s, while
the warm outflowing gas has more moderate maximum velocities of ~600 km/s. The
outflow is detected as far as 460 pc from the centre in the northern direction,
and has a mass of dense gas <8x10^8M_sun. The difference between the position
angles of the inner disk (~70 degree) and the outflow (~10 degree) indicates
that the outflow is likely powered by the AGN, and not by the starburst.
Regarding the chemistry, we measure an extremely low HCO+/HOC+ ratio of 10+-5
in the inner disk of Mrk273.Comment: Accepted for publication in A&A. 21 pages, 17 figures, 7 tables, and
a lot of interesting tex
First detection of the 448 GHz H2O transition in space
We present the first detection of the ortho-H2O 4_23-3_30 transition at 448
GHz in space. We observed this transition in the local (z = 0.010) luminous
infrared (IR) galaxy ESO 320-G030 (IRAS F11506-3851) using the Atacama Large
Millimeter/submillimeter Array (ALMA). The water 4_23-3_30 emission, which
originates in the highly obscured nucleus of this galaxy, is spatially resolved
over a region of ~65 pc in diameter and shows a regular rotation pattern
compatible with the global molecular and ionized gas kinematics. The line
profile is symmetric and well fitted by a Gaussian with an integrated flux of
37.0 +- 0.7 Jy km s-1 . Models predict this water transition as a potential
collisionally excited maser transition. On the contrary, in this galaxy, we
find that the 4_23-3_30 emission is primarily excited by the intense far-IR
radiation field present in its nucleus. According to our modeling, this
transition is a probe of deeply buried galaxy nuclei thanks to the high dust
optical depths (tau_100{\mu}m > 1, N_H > 1e24 cm-2) required to efficiently
excite it.Comment: Accepted for publication in A&A Letters; 4 pages, 5 figure
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