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Search Results: 1 - 10 of 4289 matches for " Yolanda Gomez "
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A VLA Archive Observation of the Youngest Known Galactic Supernova Remnant G1.9+0.3
Yolanda Gomez,Luis F. Rodriguez
Physics , 2009,
Abstract: We present the analysis of an unpublished VLA archive observation made at 1.49 GHz in 1989 toward the supernova remnant G1.9+0.3, the youngest such Galactic object known. This observation agrees with the time evolution in angular size previously reported. We derive an expansion rate of 0.46 +- 0.11 % per year and an age of 220+45-70 yr for the remnant by comparing the 1985 and 1989 images.
A Cluster of Compact Radio Sources in NGC 2024 (Orion B)
Luis F. Rodriguez,Yolanda Gomez,Bo Reipurth
Physics , 2003, DOI: 10.1086/378953
Abstract: We present deep 3.6 cm radio continuum observations of the H II region NGC 2024 in Orion B obtained using the Very Large Array in its A-configuration, with $0\rlap.{''}2$ angular resolution. We detect a total of 25 compact radio sources in a region of $4' \times 4'$. We discuss the nature of these sources and its relation with the infrared and X-ray objects in the region. At least two of the radio sources are obscured proplyds whose morphology can be used to restrict the location of the main ionizing source of the region. This cluster of radio sources is compared with others that have been found in regions of recent star formation.
Compact radio sources in the vicinity of the ultracompact HII region G78.4+2.6
Citlali Neria,Yolanda Gomez,Luis F. Rodriguez
Physics , 2010,
Abstract: Using the Very Large Array (VLA) at 3.6~cm we identify four new compact radio sources in the vicinity of the cometary HII region G78.4+2.6 (VLA~1). The four compact radio sources (named VLA~2 to VLA~5), have near-infrared counterparts, as seen in the 3.6 $\mu$m Spitzer image. One of them (VLA~5) clearly shows evidence of radio variability in a timescale of hours. We explore the possibility that these radio sources are associated with pre-main sequence (PMS) stars in the vicinity of the UC HII region G78.4+2.6. Our results favor the smaller distance value of 1.7 kpc for G78.4+2.6. In addition to the detection of the radio sources in the vicinity of G78.4+2.6, we detected another group of five sources which appear located about 3' to the northwest of the HII region. Some of them exhibit extended emission.
Expansion parallax of the planetary nebula IC 418
Lizette Guzman,Laurent Loinard,Yolanda Gomez,Christophe Morisset
Physics , 2009, DOI: 10.1088/0004-6256/138/1/46
Abstract: In this paper, we present radio continuum observations of the planetary nebula IC 418 obtained at two epochs separated by more than 20 years. These data allow us to show that the angular expansion rate of the ionization front in IC 418 is 5.8 $\pm$ 1.5 mas yr$^{-1}$. If the expansion velocity of the ionization front is equal to the expansion velocity of the gas along the line of sight as measured by optical spectroscopy, then the distance to IC 418 must be 1.1 $\pm$ 0.3 kpc. Recent theoretical predictions appropriate for the case of IC 418, however, suggest that the ionization front may be expanding about 20% faster than the material. Under this assumption, the distance to IC 418 would increase to 1.3 $\pm$ 0.4 kpc.
On the Size of the Non-Thermal Component in the Radio Emission from Cyg OB2 #5
Luis F. Rodriguez,Yolanda Gomez,Laurent Loinard,Amy J. Mioduszewski
Physics , 2010,
Abstract: Cyg OB2 #5 is a contact binary system with variable radio continuum emission. This emission has a low-flux state where it is dominated by thermal emission from the ionized stellar wind and a high-flux state where an additional non-thermal component appears. The variations are now known to have a period of 6.7 +/- 0.2 yr. The non-thermal component has been attributed to different agents: an expanding envelope ejected periodically from the binary, emission from a wind-collision region, or a star with non-thermal emission in an eccentric orbit around the binary. The determination of the angular size of the non-thermal component is crucial to discriminate between these alternatives. We present the analysis of VLA archive observations made at 8.46 GHz in 1994 (low state) and 1996 (high state), that allow us to subtract the effect of the persistent thermal emission and to estimate an angular size of 0.02 arcseconds for the non-thermal component. This compact size favors the explanation in terms of a star with non-thermal emission or of a wind-collision region.
A Microscopical Description of Giant Gravitons II: The AdS_5 x S^5 Background
Bert Janssen,Yolanda Lozano,Diego Rodriguez-Gomez
Physics , 2003, DOI: 10.1016/S0550-3213(03)00532-7
Abstract: In this article we continue with the microscopical investigation of giant graviton configurations in AdS_m x S^n spacetimes, initiated in hep-th/0207199. Using dualities and a Matrix theory derivation we propose an action that describes multiple Type IIB gravitons. This action contains multipole moment couplings to the Type IIB background potentials. Using these couplings, we study, from the microscopical point of view, the giant graviton and dual giant graviton configurations in the AdS_5 x S^5 background. In both cases the gravitons expand into a non-commutative 3-sphere, that is defined as an S^1-bundle over a fuzzy 2-sphere. When the number of gravitons is large we find perfect agreement with the Abelian, macroscopical description of giant gravitons in this spacetime, given in the literature.
A distance estimate based on angular expansion for the planetary nebula NGC 6881
Lizette Guzman-Ramirez,Yolanda Gomez,Laurent Loinard,Daniel Tafoya
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.18609.x
Abstract: In this paper, we report on high angular resolution radio observations of the planetary nebula NGC 6881 obtained with the Very Large Array at a wavelength of 6 cm. The emission appears to be the superposition of a roundish core and a point-symmetric bipolar structure elongated along a position angle of about 145$^\circ$. This is strongly reminiscent of the morphology seen in H$\alpha$ and [NII] images. A comparison between VLA observations obtained in 1984 and 1994 clearly reveals the expansion of the core of the nebula, at a rate of 2.1 $\pm$ 0.7 mas yr$^{-1}$. Assuming that the expansion velocity in the plane of the sky (determined from these measurements) and the expansion velocity along the line of sight (estimated from optical spectroscopy available in the literature) are equal, we find a distance to NGC 6881 of 1.6 $\pm$ 0.5 kpc $\pm$ 0.3 kpc, where the first error reflects the uncertainty on the expansion, and the second error comes from the potential difference between pattern and material speeds. This distance is compatible with (but does not necessarily imply) an association of NGC 6881 with the nearby HII region Sh 2-109 and, more generally, the Cygnus star-forming region.
Ih Current Is Necessary to Maintain Normal Dopamine Fluctuations and Sleep Consolidation in Drosophila
Alicia Gonzalo-Gomez, Enrique Turiegano, Yolanda León, Isabel Molina, Laura Torroja, Inmaculada Canal
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0036477
Abstract: HCN channels are becoming pharmacological targets mainly in cardiac diseases. But apart from their well-known role in heart pacemaking, these channels are widely expressed in the nervous system where they contribute to the neuron firing pattern. Consequently, abolishing Ih current might have detrimental consequences in a big repertoire of behavioral traits. Several studies in mammals have identified the Ih current as an important determinant of the firing activity of dopaminergic neurons, and recent evidences link alterations in this current to various dopamine-related disorders. We used the model organism Drosophila melanogaster to investigate how lack of Ih current affects dopamine levels and the behavioral consequences in the sleep:activity pattern. Unlike mammals, in Drosophila there is only one gene encoding HCN channels. We generated a deficiency of the DmIh core gene region and measured, by HPLC, levels of dopamine. Our data demonstrate daily variations of dopamine in wild-type fly heads. Lack of Ih current dramatically alters dopamine pattern, but different mechanisms seem to operate during light and dark conditions. Behaviorally, DmIh mutant flies display alterations in the rest:activity pattern, and altered circadian rhythms. Our data strongly suggest that Ih current is necessary to prevent dopamine overproduction at dark, while light input allows cycling of dopamine in an Ih current dependent manner. Moreover, lack of Ih current results in behavioral defects that are consistent with altered dopamine levels.
Evaluation of the Fungicidal Activity of Leaves Powders and Extracts of Fifteen Mexican Plants Against Fusarium oxysporum f.sp. gadioli (Massey) Snyder and Hansen
Claudia Garduno Pizana,Laura Leticia Barrera Necha,Ma. Yolanda Rios Gomez
Plant Pathology Journal , 2010,
Abstract: Fusarium oxysporum f. sp. gladioli represent one of the problems of greater importance in the culture of gladiolus. The resistance of this fungus to the fungicides has stimulated the search of new alternatives control measures. The natural plant extracts used in the study were safer to the environment and effective in the control of the plant pathogen tested. The present paper describes the in vitro fungicidal or fungistatic effect of powders (20 mg mL-1) and of aqueou, methanol and hexane extracts (5%) of 15 plant species on the development of F. oxysporum f. sp. gladioli on artificial growth media and volatile compound identification. Twelve plant species showed antifungal activity. The hexane extract of Chenopodium ambrosioides (by its fungicidal activity), the methanol extract with Spondias purpurea and Psidium guajava, as well as the aqueous extract of L. esculenta and Guazuma ulmifolia inhibited the mycelia growth with a percentage superior to 50%. Also, the powders of Byrsonima crassifolia diminished the percentage germination and sporulation of the pathogen. All the species presented antifungal activity in form of methanol extract. The 80% of the plant powders increased the rate of mycelial growth of the fungus. By chromatography of gases and spectrometry of masses, 90 volatile compounds in the powders and extracts were identified that showed activity on the fungus. The majority of the compounds were fatty acids (18.8%), monoterpenes (4.2%), sesquiterpenes (23.6%) and phenolic compound (6.3%). The high chemical diversity of the analyzed plant species, differentially affected the development of the fungus, either for the individual compounds or for synergism of some of them.
H91$α$ Radio Recombination Line and 3.5 cm Continuum Observations of the Planetary Nebula NGC 3242
Luis F. Rodriguez,Yolanda Gomez,J. Alberto Lopez,Ma. Teresa Garcia-Diaz,David M. Clark
Physics , 2009,
Abstract: We present high sensitivity H91$\alpha$ and 3.5 cm radio continuum observations toward the planetary nebula NGC 3242. The electron temperature determined assuming local thermodynamic equilibrium is consistent within $\sim$10% with that derived from optical lines and the Balmer discontinuity. The line emission and the continuum emission have very similar spatial distribution, suggesting that at this wavelength there is no other continuum process present in a significant manner. In particular, we conclude that emission from spinning dust is not important at this wavelength. In this radio recombination line the nebula presents a radial velocity structure consistent with that obtained from observations of optical lines.
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