550 research outputs found
Stellar populations in the Carina region: The Galactic plane at l = 291
Previous studies of the Carina region have revealed its complexity and
richness as well as a significant number of early-type stars. In many cases,
these studies only concentrated on the central region or were not homogeneous.
This latter aspect, in particular, is crucial because very different ages and
distances for key clusters have been claimed in recent years. The aim of this
work is to study in detail an area of the Galactic plane in Carina. We analyze
the properties of different stellar populations and focus on a sample of open
clusters and their population of YSOs and highly reddened early stars. We also
studied the stellar mass distribution in these clusters and the possible
scenario of their formation. Finally, we outline the Galactic spiral structure
in this direction. We obtained photometric data for six young open clusters
located in Carina at l = 291, and their adjacent stellar fields, which we
complemented with spectroscopic observations of a few selected targets. We also
culled additional information from the literature. Our results provide more
reliable estimates of distances, color excesses, masses, and ages of the
stellar populations in this direction. We estimate the basic parameters of the
studied clusters and find that they identify two overdensities of young stellar
populations. We find evidence of PMS populations inside them, with an apparent
coeval stellar formation in the most conspicuous clusters. We also discuss
apparent age and distance gradients in the direction NW-SE. We study the mass
distributions of several clusters in the region. They consistently show a
canonical IMF slope. We discover and characterise an abnormally reddened
massive stellar population. Spectroscopic observations of ten stars of this
latter population show that all selected targets were massive OB stars. Their
location is consistent with the position of the Car-Sag spiral arm.Comment: 15 pages, 13 figure
Phase conjugation by four-wave mixing of statistical beams
A study of the influence of the spatial structure and statistics of the pump beams in the phase-conjugation process is made, showing that the reflectivity varies along the phase-conjugation mirror when the phase factor in the coupling equations that describe the process is not constant. The mutual coherence function of the generated field is calculated from the mutual reflectivity of the mirror for two commonly used statistics for the partially coherent pump beams. Finally, the influence of diffractional effects is also analyzed, showing that, in general, the fidelity of the process is degraded. © 1990 The American Physical Society.This work was supported by the Comision Interministerial de Ciencia y Tecnologia under Grant No. PB 0278. G. Lera acknowledges a grant from the Ministerio de Educacion y Ciencia.Peer Reviewe
Impact of the covid-19 pandemic on teacher quality of life: A longitudinal study from before and during the health crisis
Background: Prior to the COVID-19 pandemic, teachers were already reporting a low quality of life (QoL) perception, with a significant impact on mental and physical health due to various stress factors associated with work overload. The objective of this study was to evaluate the QoL impact on Chilean teachers before and during the COVID-19 pandemic. The analysis was performed following a longitudinal design on a sample of 63 Chilean teachers in pre-pandemic and COVID-19 pandemic timeframes. QoL perception, along with teachers’ sociodemographic data, was evaluated via the Short-Form 36 Health Survey (SF-36) questionnaire. Sociodemographic variables presented no significant variations in pre-pandemic and pandemic comparisons. QoL, however, showed a significant decrease during the pandemic compared to the pre-pandemic measurement (p < 0.01). In each gender, there were significant differences between pre-pandemic and pandemic timeframes, with a greater impact among women in the mental and physical component summary variables and seven of the eight QoL scales (p < 0.01). Between age categories, people under 45 presented significant differences (p < 0.05) between pre-pandemic and pandemic timeframes in all summary dimensions and measurements. In conclusion, Chilean teachers’ QoL perception has been affected by the COVID-19 pandemic. These findings could be related to work overload due to teleworking or feelings of uncertainty, loneliness, and fear that the pandemic and its associated confinements will worsen
Stellar populations in the Carina region : The Galactic plane at l = 291°
Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very di erent ages and distances for key clusters have been claimed in recent years.
Aims. The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina.We analyze the properties of di erent stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction.
Methods. We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS.We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction.
Results. We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB-V ~ 0.1-0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the mass distributions of the covered clusters and several others in the region (which we took form the literature). They consistently show a canonical IMF slope (the Salpeter one). We discover and characterise an abnormally reddened massive stellar population, scattered between 6.6 and 11 kpc. Spectroscopic observations of ten stars of this latter population show that all selected targets were massive OB stars. Their location is consistent with the position of the Carina-Sagittarius spiral arm.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
Spectral performance of SKA log-periodic antennas I: Mitigating spectral artefacts in SKA1-LOW 21 cm cosmology experiments
This paper is the first in a series of papers describing the impact of
antenna instrumental artefacts on the 21-cm cosmology experiments to be carried
out by the low frequency instrument (SKA1-LOW) of the Square Kilometre Array
telescope (SKA), i.e., the Cosmic Dawn (CD) and the Epoch of Reionization
(EoR). The smoothness of the passband response of the current log-periodic
antenna being developed for the SKA1-LOW is analyzed using numerical
electromagnetic simulations. The amplitude variations over the frequency range
are characterized using low-order polynomials defined locally, in order to
study the impact of the passband smoothness in the instrument calibration and
CD/EoR Science. A solution is offered to correct a fast ripple found at 60~MHz
during a test campaign at the SKA site at the Murchison Radio-astronomy
Observatory, Western Australia in September 2015 with a minor impact on the
telescope's performance and design. A comparison with the Hydrogen Epoch of
Reionization Array antenna is also shown demonstrating the potential use of the
SKA1-LOW antenna for the Delay Spectrum technique to detect the EoR
Endoscopic submucosal dissection for the treatment of early esophageal and gastric cancer - initial experience of a western center
BACKGROUND: Endoscopic submucosal dissection is a new Japanese technique characterized by en-bloc resection of the entire lesion irrespective of size, with lower local recurrence when compared to endoscopic mucosal resection. OBJECTIVE: To evaluate the feasibility, early results and complications of the endoscopic submucosal dissection technique for treating early gastric and esophageal cancer at the Endoscopic Unit of Clinics Hospital and Cancer Institute of the São Paulo University. MATERIALS AND METHODS: Twenty patients underwent endoscopic resection using the endoscopic submucosal dissection technique for early gastric or esophageal cancer. The patients were evaluated prospectively as to the executability of the technique, the short-term results of the procedure and complications. RESULTS: Sixteen gastric adenocarcinoma lesions and six esophageal squamous carcinoma lesions were resected. In the stomach, the mean diameter of the lesions was 16.2 mm (0.6-3.5 mm). Eight lesions were type IIa + IIc, four were type IIa and four IIc, with thirteen being well differentiated and three undifferentiated. Regarding the degree of invasion, five were M2, seven were M3, two were Sm1 and one was Sm2. The mean duration of the procedures was 85 min (20-160 min). In the esophagus, all of the lesions were type IIb, with a mean diameter of 17.8 mm (6-30 mm). Regarding the degree of invasion, three were M1, one was M2, one was M3 and one was Sm1. All had free lateral and deep margins. The mean time of the procedure was 78 min (20-150 min). CONCLUSION: The endoscopic submucosal dissection technique was feasible in our service with a high success rate
Simulations of primary beam effects on the cosmic bispectrum phase observed with the Hydrogen Epoch of Reionization Array
The 21~cm transition from neutral Hydrogen promises to be the best
observational probe of the Epoch of Reionisation. The main difficulty in
measuring the 21 cm signal is the presence of bright foregrounds that require
very accurate interferometric calibration. Closure quantities may circumvent
the calibration requirements but may be, however, affected by direction
dependent effects, particularly antenna primary beam responses. This work
investigates the impact of antenna primary beams affected by mutual coupling on
the closure phase and its power spectrum. Our simulations show that primary
beams affected by mutual coupling lead to a leakage of foreground power into
the EoR window, which can be up to orders magnitude higher than the
case where no mutual coupling is considered. This leakage is, however,
essentially confined at ~~Mpc for triads that include 29~m
baselines. The leakage magnitude is more pronounced when bright foregrounds
appear in the antenna sidelobes, as expected. Finally, we find that triads that
include mutual coupling beams different from each other have power spectra
similar to triads that include the same type of mutual coupling beam,
indicating that beam-to-beam variation within triads (or visibility pairs) is
not the major source of foreground leakage in the EoR window
Stellar populations in the Carina region : The Galactic plane at l = 291°
Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very di erent ages and distances for key clusters have been claimed in recent years.
Aims. The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina.We analyze the properties of di erent stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction.
Methods. We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS.We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction.
Results. We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB-V ~ 0.1-0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the mass distributions of the covered clusters and several others in the region (which we took form the literature). They consistently show a canonical IMF slope (the Salpeter one). We discover and characterise an abnormally reddened massive stellar population, scattered between 6.6 and 11 kpc. Spectroscopic observations of ten stars of this latter population show that all selected targets were massive OB stars. Their location is consistent with the position of the Carina-Sagittarius spiral arm.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
Development of a few TW Ti:Sa laser system at 100 Hz for proton acceleration
[EN] We report the development of a table-top high peak power Titanium:Sapphire (Ti:Sa) CPA laser working at 100 Hz capable of delivering 205 mJ, 55 fs pulses. Every amplification stage is pumped by Nd-doped solid-state lasers and fully powered by diodes. Thermal effects in the Ti:Sa amplifiers are compensated passively with optics. This system is intended to be used for proton acceleration experiments at high repetition rates.Centro para el Desarrollo Tecnológico Industrial (CDTI, Spain) within the INNPRONTA program, Grant no. IPT-20111027.Lera, R.; Bellido-Millán, PJ.; Sánchez, I.; Mur, P.; Seimetz, M.; Benlloch Baviera, JM.; Roso, L.... (2019). Development of a few TW Ti:Sa laser system at 100 Hz for proton acceleration. Applied Physics B. 125(1):1-8. https://doi.org/10.1007/s00340-018-7113-8S181251P. Zeitoun, G. Faivre, S. Sebban, T. Mocek, A. Hallou, M. Fajardo, D. Aubert, P. Balcou, F. Burgy, D. Douillet, S. Kazamias, G. de Lachèze-Murel, T. Lefrou, S. le Pape, P. Mercère, H. Merdji, A.S. Morlens, J.P. Rousseau, C. Valentin, Nature 431(7007), 426–429 (2004)V. Malka, S. Fritzler, E. Lefebvre, M.-M. Aleonard, F. Burgy, J.-P. Chambaret, J.-F. Chemin, K. Krushelnick, G. Malka, S.P.D. Mangles, Z. Najmudin, M. Pittman, J.-P. Rousseau, J.-N. Scheurer, B. Walton, A.E. Dangor, Science 298(5598), 1596–1600 (2002)H. Daido, M. Nishiuchi, A.S. Pirozhkov, Rep. Progress Phys. 75(5), 056401 (2012)A. Macchi, M. Borghesi, M. Passoni, Rev. Mod. Phys. 85, 751–793 (2013)T. Tajima, J.M. Dawson, Phys. Rev. Lett. 43, 267–270 (1979)M. Noaman-ul Haq, H. Ahmed, T. Sokollik, L. Yu, Z. Liu, X. Yuan, F. Yuan, M. Mirzaie, X. Ge, L. Chen, J. Zhang, Phys. Rev. Accel. Beams 20, 041301 (2017)D. Strickland, G. Mourou, Opt. Commun. 53(3), 219–221 (1985)G. Cheriaux, B. Walker, L.F. Dimauro, P. Rousseau, F. Salin, J.P. Chambaret, Opt. Lett. 21(6), 414–416 (1996)P. Tournois, Opt. Commun. 140(4), 245–249 (1997)R. Soulard, A. Brignon, S. Raby, E. Durand, R. Moncorgé, Appl. Phys. B 106(2), 295–300 (2012)J. Liu, L. Ge, L. Feng, H. Jiang, H. Su, T. Zhou, J. Wang, Q. Gao, J. Li, Chin. Opt. Lett. 14(5), 051404 (2016)A. Maleki, M.K. Tehrani, H. Saghafifar, M.H.M. Dindarlu, H. Ebadian, Laser Phys. 26(2), 025003 (2016)R. Lera, F. Valle-Brozas, S. Torres-Peiró, A.R. de-la Cruz, M. Galán, P. Bellido, M. Seimetz, J.M. Benlloch, L. Roso, Appl. Opt. 55(33), 9573–9576 (2016)R. Lausten, P. Balling, J. Opt. Soc. Am. B 20(7), 1479–1485 (2003)I. Nam, M. Kim, T.H. Lee, S.W. Lee, H. Suk, Curr. Appl. Phys. 15(4), 468–472 (2015)E. Treacy, IEEE J. Quantum Electron. 5(9), 454–458 (1969)A. Trisorio, S. Grabielle, M. Divall, N. Forget, C.P. Hauri, Opt. Lett. 37(14), 2892–2894 (2012)Y.-H. Cha, Y.-W. Lee, S.M. Nam, J.M. Han, Y.J. Rhee, B.D. Yoo, B.C. Lee, Y.U. Jeong, Appl. Opt. 46(28), 6854–6858 (2007)P. Bellido, R. Lera, M. Seimetz, A.R. de la Cruz, S. Torres-Peiró, M. Galán, P. Mur, I. Sánchez, R. Zaffino, L. Vidal, A. Soriano, S. Sánchez, F. Sánchez, M. Rodríguez-Álvarez, J. Rigla, L. Moliner, A. Iborra, L. Hernández, D. Grau-Ruiz, A. González, J. García-Garrigos, E. Díaz-Caballero, P. Conde, A. Aguilar, L. Roso, J. Benlloch, J. Instrum. 12(05), T05001 (2017
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