719 research outputs found
Phase diagram of Fe-doped Ni-Mn-Ga ferromagnetic shape-memory alloys
We have studied the effect of Fe addition on the structural and magnetic
transitions in the magnetic shape memory alloy Ni-Mn-Ga by substituting
systematically each atomic species by Fe. Calorimetric and AC susceptibility
measurements have been carried out in order to study the magnetic and
structural transformation properties. We find that the addition of Fe modifies
the structural and magnetic transformation temperatures. Magnetic transition
temperatures are displaced to higher values when Fe is substituted into
Ni-Mn-Ga, while martensitic and premartensitic transformation temperatures
shift to lower values. Moreover, it has been found that the electron per atom
concentration essentially governs the phase stability in the quaternary system.
However, the observed scaling of transition temperatures with differs
from that reported in the related ternary system Ni-Mn-Ga.Comment: 8 pages, 8 figures. Accepted for publication in the Physical Review
Detailed Interstellar Polarimetric Properties of the Pipe Nebula at Core Scales
We use R-band CCD linear polarimetry collected for about 12000 background
field stars in 46 fields of view toward the Pipe nebula to investigate the
properties of the polarization across this dark cloud. Based on archival 2MASS
data we estimate that the surveyed areas present total visual extinctions in
the range 0.6 < Av < 4.6. While the observed polarizations show a well ordered
large scale pattern, with polarization vectors almost perpendicularly aligned
to the cloud's long axis, at core scales one see details that are
characteristics of each core. Although many observed stars present degree of
polarization which are unusual for the common interstellar medium, our analysis
suggests that the dust grains constituting the diffuse parts of the Pipe nebula
seem to have the same properties as the normal Galactic interstellar medium.
Estimates of the second-order structure function of the polarization angles
suggest that most of the Pipe nebula is magnetically dominated and that
turbulence is sub-Alvenic. The Pipe nebula is certainly an interesting region
where to investigate the processes prevailing during the initial phases of low
mass stellar formation.Comment: 20 pages, 23 figures, Accepted for The Astrophysical Journa
The Current Status of the Distribution Range of the Western Pine Beetle, Dendroctonus brevicomis (Curculionidae: Scolytinae) in Northern Mexico
Abstract The distribution range of the western pine beetle Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) is supported only by scattered records in the northern parts of Mexico, suggesting that its populations may be marginal and rare in this region. In this study, we review the geographical distribution of D. brevicomis in northern Mexico and perform a geometric morphometric analysis of seminal rod shape to evaluate its reliability for identifying this species with respect to other members of the Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae) complex. Our results provide 30 new records, with 26 distributed in the Sierra Madre Occidental and 4 in the Sierra Madre Oriental. These records extend the known distribution range of D. brevicomis to Durango and Tamaulipas states in northern Mexico. Furthermore, we find high geographic variation in size and shape of the seminal rod, with conspicous differences among individuals from different geographical regions, namely west and east of the Great Basin and between mountain systems in Mexico.
Key words: seminal rod shape, geometric morphometry, Dendroctonus frontalis comple
Crowdfunding, una solución de financiamiento alternativo para el sistema de emprendimiento e innovación. Análisis de las implicaciones tributarias en el Ecuador
For decades, both the financial system and the stock market system have been the conventional financing mechanisms for those who have wanted to undertake or guarantee their investment. However, these sectors have imposed their regulations limiting, in many cases, their accessibility. Thus, an alternative financing mechanism known as crowdfunding (CF) arises; a way that has made it possible, especially, to carry out donation and investment projects. Crowdfunding has experienced strong growth worldwide; however, in Ecuador it is totally new; As of the creation of the Organic Law on Entrepreneurship and Innovation and its Regulations in 2020, the institution of duly regulated and accredited collaborative fund platforms or –crowdfunding– is allowed; However, due to its recent implementation, its impact has not been evaluated. This article aims to analyze the benefits and risks inherent in the use of crowdfunding and the tax implications for promoters and investors; and, the effectiveness of this financing mechanism in order to guarantee the sustainability of the entrepreneurship and innovation system for microenterprises and SMEs in Ecuador, through a detailed review and analysis of Ecuadorian legislation.Durante décadas, tanto el sistema financiero como el sistema bursátil han sido los mecanismos de financiamiento convencionales para quienes han querido emprender o garantizar su inversión. No obstante, estos sectores han impuesto sus regulaciones limitando, en muchos casos, su accesibilidad. Es así que, surge un mecanismo de financiamiento alternativo conocido como crowdfunding (CF)[1]; una vía que ha permitido, especialmente, llevar a cabo proyectos de donación e inversión. El crowdfunding ha experimentado un fuerte crecimiento a nivel mundial; sin embargo, en el Ecuador es totalmente nuevo; a partir de la creación de la Ley Orgánica de Emprendimiento e Innovación y su Reglamento en el 2020 se permite la institución de plataformas de fondos colaborativos o –crowdfunding– debidamente reguladas y acreditadas; No obstante, por su reciente implementación, su impacto no ha podido ser evaluado El presente artículo pretende analizar los beneficios y riesgos inherentes por el uso del crowdfunding y las implicaciones tributarias para los promotores e inversores; y, la eficacia de este mecanismo de financiamiento con la finalidad de garantizar la sostenibilidad del sistema de emprendimiento e innovación para microempresas y PYMES[2] en el Ecuador a través de una revisión y análisis pormenorizado de la legislación ecuatoriana.
[1] Crowdfunding. CF, en adelante nos referiremos al crowdfunding con las siglas CF.
[2] PYMES. Pequeñas y medianas empresas en cuanto al volumen de ingresos, patrimonio y número de empleados
On the behavior of site effects in central Mexico (the Mexican volcanic belt – MVB), based on records of shallow earthquakes that occurred in the zone between 1998 and 2011
The Mexican volcanic belt (MVB) is a seismogenic zone that transects the
central part of Mexico with an east–west orientation. The seismic risk and
hazard of this seismogenic zone has not been studied in detail due to the
scarcity of instrumental data as well as because seismicity in the
continental regime of central Mexico is not too frequent. However, it is
known that there are precedents of large earthquakes (<i>M</i><sub>w</sub> > 6.0)
that have taken place in this zone. The valley of Mexico City (VM) is the
sole zone, within the MVB, that has been studied in detail. Studies have
mainly focused on the ground amplification during large events such as the
1985 subduction earthquake that occurred off coast of Michoacán. The
purpose of this article is to analyze the behavior of site effects in the MVB
zone based on records of shallow earthquakes (data not reported before) that
occurred in the zone between 1998 and 2011. We present a general overview of
site effects in the MVB, a classification of the stations in order to reduce
the uncertainty in the data when obtaining attenuation parameters in future
works, as well as some comparisons between the information presented here and
that presented in previous studies.
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A regional evaluation of site effects and Fourier acceleration spectrum
(FAS) shape was estimated based on 80 records of 22 shallow earthquakes
within the MVB zone. Data of 25 stations were analyzed. Site effects were
estimated by using the horizontal-to-vertical spectral ratio (HVSR)
methodology. The results show that seismic waves are less amplified in the
northeast sites of the MVB with respect to the rest of the zone and that it
is possible to classify two groups of stations: (1) stations with negligible
site amplification (NSA) and (2) stations with significant site amplification
(SSA). Most of the sites in the first group showed small (<3)
amplifications while the second group showed amplifications ranging from 4
to 6.5 at frequencies of about 0.35, 0.75, 15 and 23 Hz. With these groups
of stations, average levels of amplification were contrasted for the first
time with those caused by the subduction zone earthquakes. With respect to
the FAS shapes, most of them showed similarities at similar epicentral
distances. Finally, some variations of site effects were found when compared
to those obtained in previous studies on different seismicity regions. These
variations were attributed to the location of the source.
<br><br>
These aspects help to advance the understanding about the amplification
behavior and of the expected seismic risk on central Mexico due to large
earthquakes within the MVB seismogenic zone
Plasma gradient modified scaffolds to generate a chemoattractant surface
A gradient of plasma polymerization of pyrrole was generated to model a chemoattractant surface; it was obtained by changing the polymerization time to manipulate the thickness and the deposited layer. The polymerization was generated with a power of 30W on a cylindrical vacuum reactor, the coverslip was polymerized covered by a cavity with a surface exposed of 0.7 cm every 35 min., the cells seeded were liver stellate cells (Ito); it was evaluated against a coverslip with continuous plasma polymerization of pyrrole (Ppy). The results show similar protein secretions, but cells proliferation was selective in the surface gradient regions
Young starless cores embedded in the magnetically dominated Pipe Nebula
The Pipe Nebula is a massive, nearby dark molecular cloud with a low
star-formation efficiency which makes it a good laboratory to study the very
early stages of the star formation process. The Pipe Nebula is largely
filamentary, and appears to be threaded by a uniform magnetic field at scales
of few parsecs, perpendicular to its main axis. The field is only locally
perturbed in a few regions, such as the only active cluster forming core B59.
The aim of this study is to investigate primordial conditions in low-mass
pre-stellar cores and how they relate to the local magnetic field in the cloud.
We used the IRAM 30-m telescope to carry out a continuum and molecular survey
at 3 and 1 mm of early- and late-time molecules toward four selected starless
cores inside the Pipe Nebula. We found that the dust continuum emission maps
trace better the densest regions than previous 2MASS extinction maps, while
2MASS extinction maps trace better the diffuse gas. The properties of the cores
derived from dust emission show average radii of ~0.09 pc, densities of
~1.3x10^5 cm^-3, and core masses of ~2.5 M_sun. Our results confirm that the
Pipe Nebula starless cores studied are in a very early evolutionary stage, and
present a very young chemistry with different properties that allow us to
propose an evolutionary sequence. All of the cores present early-time molecular
emission, with CS detections toward all the sample. Two of them, Cores 40 and
109, present strong late-time molecular emission. There seems to be a
correlation between the chemical evolutionary stage of the cores and the local
magnetic properties that suggests that the evolution of the cores is ruled by a
local competition between the magnetic energy and other mechanisms, such as
turbulence.Comment: Accepted for publication in ApJ. 15 pages, 5 figures, 9 table
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