298 research outputs found
Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity
We have measured the magnetic penetration depth of the recently discovered
binary superconductor MgB_2 using muon spin rotation and low field
-susceptibility. From the damping of the muon precession signal we find the
penetration depth at zero temperature is about 85nm. The low temperature
penetration depth shows a quadratic temperature dependence, indicating the
presence of nodes in the superconducting energy gap.Comment: 4 pages 3 figure
Surface effects in multiband superconductors. Application to MgB
Metals with many bands at the Fermi level can have different band dependent
gaps in the superconducting state. The absence of translational symmetry at an
interface can induce interband scattering and modify the superconducting
properties. We dicuss the relevance of these effects to recent experiments in
MgB
Experiencia en el tratamiento quirúrgico del angiofibroma nasal juvenil en Hospital de Especialidades No 2 Lic. Luis Donaldo Colosio Murrieta. Instituto Mexicano del Seguro Social de Ciudad Obregón, Sonora
Objective: To present our experience and assess the recurrence of juvenile nasopharyngeal angiofibroma after a surgical
treatment (open versus endoscopic approach) in the country’s northwestern Department of Otorhinolaryngology.
Materials and methods: An observational, retrospective, analytical study. The medical records of patients diagnosed
with juvenile nasopharyngeal angiofibroma, who were treated at the Department of Otorhinolaryngology – Head and Neck
Surgery of this institution from 2014 to 2017, were reviewed.
Results: A total of 19 patients diagnosed with juvenile nasopharyngeal angiofibroma underwent a surgical procedure, out
of which 14 had an open surgery and 5 an endoscopic one. Recurrence accounted for 50 % and 40 %, respectively, which
was not statistically significant (p = 0.88). However, other variables were compared, such as the need for admission to the
Intensive Care Unit (ICU), which was represented by 71 % in the case of the open approach and 20 % for the endoscopic
approach, where a significant difference was found (p = 0.04).
Conclusions: The study shows no statistically significant advantage of the endoscopic approach versus the open approach,
but demonstrates less need for ICU admissions, which would reduce healthcare costs
Electronic structure of MgB: X-ray emission and absorption studies
Measurements of x-ray emission and absorption spectra of the constituents of
MgB are presented. The results obtained are in good agreement with
calculated x-ray spectra, with dipole matrix elements taken into account. The
comparison of x-ray emission spectra of graphite, AlB, and MgB in the
binding energy scale supports the idea of charge transfer from to
bands, which creates holes at the top of the bonding bands and
drives the high-TComment: final version as published in PR
Upper critical field for underdoped high-T_c superconductors. Pseudogap and stripe--phase
We investigate the upper critical field in a stripe--phase and in the
presence of a phenomenological pseudogap. Our results indicate that the
formation of stripes affects the Landau orbits and results in an enhancement of
. On the other hand, phenomenologically introduced pseudogap leads to a
reduction of the upper critical field. This effect is of particular importance
when the magnitude of the gap is of the order of the superconducting transition
temperature. We have found that a suppression of the upper critical field takes
place also for the gap that originates from the charge--density waves.Comment: 7 pages, 5 figure
Spectral Line Selection for HMI: A Comparison of Fe I 6173 and Ni I 6768
We present a study of two spectral lines, Fe I 6173 Angstroms and Ni I 6768
Angstroms, that were candidates to be used in the Helioseismic and Magnetic
Imager (HMI) for observing Doppler velocity and the vector magnetic field. The
line profiles were studied using the Mt. Wilson Observatory, the Advanced
Stokes Polarimeter and the Kitt Peak McMath telescope and one meter Fourier
transform spectrometer atlas. Both Fe I and Ni I profiles have clean continua
and no blends that threaten instrument performance. The Fe I line is 2% deeper,
15% narrower and has a 6% smaller equivalent width than the Ni I line. The
potential of each spectral line to recover pre-assigned solar conditions is
tested using a least-squares minimization technique to fit Milne-Eddington
models to tens of thousands of line profiles that have been sampled at five
spectral positions across the line. Overall, the Fe I line has a better
performance than the Ni I line for vector magnetic field retrieval. We selected
the Fe I spectral line for use in HMI due to its better performance for
magnetic diagnostics while not sacrificing velocity information
Non-linear numerical simulations of magneto-acoustic wave propagation in small-scale flux tubes
We present results of non-linear, 2D, numerical simulations of
magneto-acoustic wave propagation in the photosphere and chromosphere of
small-scale flux tubes with internal structure. Waves with realistic periods of
three to five minutes are studied, after applying horizontal and vertical
oscillatory perturbations to the equilibrium model. Spurious reflections of
shock waves from the upper boundary are minimized thanks to a special boundary
condition. This has allowed us to increase the duration of the simulations and
to make it long enough to perform a statistical analysis of oscillations. The
simulations show that deep horizontal motions of the flux tube generate a slow
(magnetic) mode and a surface mode. These modes are efficiently transformed
into a slow (acoustic) mode in the vA < cS atmosphere. The slow (acoustic) mode
propagates vertically along the field lines, forms shocks and remains always
within the flux tube. It might deposit effectively the energy of the driver
into the chromosphere. When the driver oscillates with a high frequency, above
the cut-off, non-linear wave propagation occurs with the same dominant driver
period at all heights. At low frequencies, below the cut-off, the dominant
period of oscillations changes with height from that of the driver in the
photosphere to its first harmonic (half period) in the chromosphere. Depending
on the period and on the type of the driver, different shock patterns are
observed.Comment: 22 pages 6 color figures, submitted to Solar Physics, proceeding of
SOHO 19/ GONG 2007 meeting, Melbourne, Australi
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Bioquímica y proteómica vegetal y agrícola
En la presente comunicación se resume lo que ha sido la actividad investigadora del grupo “Bioquímica y
Proteómica Vegetal y Agrícola” (PAI AGR-164) en los últimos tres años (2005-2007). Nuestro interés y objetivo
científico se ha centrando en el estudio de los cambios adaptativos y reacciones de defensa y de
resistencia/tolerancia de las plantas a estreses de tipo biótico (hongos fitopatógenos y plantas parásitas) y
abiótico (metales pesados, sequía). Dichos estudios se han llevado a cabo tanto con sistemas modelo
(Arabidopsis thaliana y Medicago truncatula), como con especies de interés agronómico (garbanzo, girasol,
guisante, maíz) o forestal (encina, alcornoque y pino). En los proyectos de investigación abordados se ha
utilizado, en gran medida, una aproximación de proteómica, y también técnicas de bioquímica clásica y
transcriptómica. La proteómica constituye, hoy en día, una línea prioritaria en cualquier investigación
biológica, suministrando, en el área de la biología vegetal, y en combinación con las técnicas clásicas de
bioquímica y las de transcriptómica, información relevante sobre diferentes aspectos básicos y aplicados
relacionados con especies de interés agronómico y forestal, como es el de la respuesta a estreses, y la
caracterización de genotipos (poblaciones, mutantes, líneas transgénicas). Además, hay aspectos, como el de
las modificaciones postraduccionales, que sólo pueden ser abordados experimentalmente mediante una
estrategia de proteómica. Nuestro grupo ha iniciado recientemente una nueva línea, dirigida a estudiar el
proteoma redox en Arabidopsis y su implicación en la respuesta a patógeno
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