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Search Results: 1 - 10 of 34695 matches for " Alejandro González-Samaniego "
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Testing assumptions and predictions of star-formation theories
Alejandro González-Samaniego,Enrique Vázquez-Semadeni,Ricardo F. González,Jongsoo Kim
Physics , 2013, DOI: 10.1093/mnras/stu400
Abstract: (Abridged). We present numerical simulations of isothermal, MHD, supersonic turbulence, designed to test various hypotheses frequently assumed in star formation(SF) theories. We consider three simulations, each with a different combination of physical size, rms sonic Mach number, and Jeans parameter, but chosen as to give the same value of the virial parameter and to conform with Larson's scaling relations. As in the non-magnetic case: we find no simultaneously subsonic and super-Jeans structures in our MHD simulations. We find that the fraction of small-scale super-Jeans structures increases when self gravity is turned on, and that the production of gravitationally unstable dense cores by turbulence alone is very low. This implies that self-gravity is in general necessary not only to induce the collapse of Jeans-unstable cores, but also to form them. We find that denser regions tend to have more negative values of the velocity divergence, implying a net inwards flow towards the regions' centers. We compare the results from our simulations with the predictions from the recent SF theories by Krumholz & McKee, Padoan & Nordlund, and Hennebelle & Chabrier, using the expressions recently provided by Federrath & Klessen. We find that none of these theories reproduces the dependence of the SFEff with Ms observed in our simulations in the MHD case. The SFEff predicted by the theories ranges between half and one order of magnitude larger than what we observe in the simulations in both the HD and the MHD cases. We conclude that the type of flow used in simulations like the ones presented here and assumed in recent SF theories, may not correctly represent the flow within actual clouds, and that theories that assume it does may be missing a fundamental aspect of the flow. We suggest that a more realistic regime may be that of hierarchical gravitational collapse.
Simulations of isolated dwarf galaxies formed in dark matter halos with different mass assembly histories
A. González-Samaniego,P. Colín,V. Avila-Reese,A. Rodríguez-Puebla,O. Valenzuela
Physics , 2013, DOI: 10.1088/0004-637X/785/1/58
Abstract: We present high-resolution N-body/hydrodynamics simulations of dwarf galaxies formed in isolated CDM halos with the same virial mass, Mv~2.5x10^10 Msun at z=0, in order to (1) study the mass assembly histories (MAHs) of the halo, stars, and gas components, and (2) explore the effects of the halo MAHs on the stellar/baryonic assembly of the simulated dwarfs and on their z~0 properties. Overall, the simulated dwarfs are roughly consistent with observations. Our main results are: a) The stellar-to-halo mass ratio is ~0.01 and remains roughly constant since z~1 (the stellar MAHs follow closely the halo MAHs), with a smaller value at higher z's for those halos that assemble their mass later. b) The evolution of the galaxy gas fraction, fg, is episodic and higher, most of the time, than the stellar fraction. When fg decreases (increases), the gas fraction in the halo typically increases (decreases), showing that the SN driven outflows play an important role in regulating the gas fractions -and hence the SFR- of the dwarfs. However, in most cases, an important fraction of the gas escapes the virial radius, Rv; at z=4 the total baryon fraction inside Rv is 1.5-2 times smaller than the universal one, while at z=0 is 2-6 times smaller, with the earlier assembled halos ejecting more gas. c) The SF histories are episodic with changes in the SFRs of factors 2-10 on average. d) Although the dwarfs formed in late assembled halos show more extended SF histories, their z~0 SFRs are still below the ones measured for local isolated dwarfs. e) The effects of baryons on Mv are such that at almost any time Mv is 10-20% smaller than the corresponding Mv obtained in pure N-body simulations. Our results suggest that rather than increasing the strength of the SN-driven outflows, processes that reduce the SF efficiency even more will help to solve the potential issues faced by the CDM-based simulations of dwarfs.
The specific star formation rate and stellar mass fraction of low-mass central galaxies in cosmological simulations
V. Avila-Reese,P. Colín,A. González-Samaniego,O. Valenzuela,C. Firmani,H. Velázquez,D. Ceverino
Physics , 2011, DOI: 10.1088/0004-637X/736/2/134
Abstract: (Abridged) By means of high-resolution cosmological simulations in the context of the LCDM scenario, the specific star formation rate (SSFR=SFR/Ms, Ms is the stellar mass)--Ms and stellar mass fraction (Fs=Ms/Mh, Mh is the halo mass)--Ms relations of low-mass galaxies (2.5< Mh/10^10 Msun <50 at redshift z=0) at different epochs are predicted. The Hydrodynamics ART code was used and some variations of the sub-grid parameters were explored. Most of simulated galaxies, specially those with the highest resolutions, have significant disk components and their structural and dynamical properties are in reasonable agreement with observations of sub-M* field galaxies. However, the SSFRs are 5-10 times smaller than the averages of several (compiled and homogenized here) observational determinations for field blue/star-forming galaxies at z<0.3 (at low masses, most of observed field galaxies are actually blue/star-forming). This inconsistency seems to remain even at z~1.5 though less drastic. The Fs of simulated galaxies increases with Mh as semi-empirical inferences show, but in absolute values the former are ~5-10 times larger than the latter at z=0; this difference increases probably to larger factors at z~1-1.5. The inconsistencies reported here imply that simulated low-mass galaxies (0.2
Red de mercadeo y rentabilidad de flor de corte en el Valle de Mexicali, Baja California, México
Samaniego-Gámez, Blancka Yesenia;Cano-García, Gloria Virginia;Colinas-León, María Teresa Beryl;Sánchez-Abarca, Carlos;Manzo-González, Alejandro;
Revista mexicana de ciencias agrícolas , 2012,
Abstract: cut flower commercialization for baja california contributed during 2004 with more than 122 million pesos, considering flower seed and cut flower production. most of cut flowers produced in state of baja california norte is for export market, by this reason local market means an opportunity for introducing quality products at market prices from national companies. mexicali city, by being near usa and together with its population economic wealth thanks to profitability of cotton and orchards production in mexicali valley, is one or the main producer region in the country. by this reason and thanks to great amount of flower shops located in the region the aim of describing marketing network and profitability for cut flower in mexicali valley is proposed. market study and diagnose to make foda analysis were developed, defining strategies in order to seize economic potential. actual distribution networks and marketing system consist in moving cut flowers from production centers, córdoba, veracruz and coatepec de harinas district, state of mexico, up to mexicali valley, baja california, keeping quality and optimum vase life for final customer, also proper planning for production chain due not covered demand along year it is required, the population has economical potential and tradition to give flowers guaranteeing good profitability. roses (rosa gigantea and r. chinensis l.), asian lilies (lilium spp.), chrysanthemum [dendranthema x grandiflorum (ramat) kitamura c. v. polaris white], carnation (dianthus caryophyllus), gerbera (gerbera jamesonii h. bolux ex hook f.) and oriental lilies (lilium spp.) are species with more consumers' interest.
La filosofía mexicana durante el régimen liberal: redes intelectuales y equilibrios políticos
Estrella González, Alejandro;
Signos filosóficos , 2010,
Abstract: basing myself on the tools that the sociology of philosophy -specially in works of pierre bourdieu and randall collins- this article tries to reconstruct the solidarity and opposition relations among intellectuals nets in liberal mexico (18671910). i understand that the philosophical agents are organized in intellectuals genealogies in oppositions againts others, definining a common field where individuals take of positions happen. the reconstruction of this field is not complete if we do not identify the specific conections between that nets and the political area; ties that introduce exogenous authority ways to resolve intellectuals struggels.
Energy Subsidies in Argentina Lead to Inequalities and Low Thermal Efficiency
Alejandro D. González
Energies , 2009, DOI: 10.3390/en20300769
Abstract: Natural gas is the main energy resource for buildings in Argentina. Since 2002, subsidies have kept the prices of this fuel between 9 and 26 times lower than regular prices in other countries. The lowest prices are the result of climate-related subsidies. In cold areas, heating uses several times more energy than locations in Europe with a similar climate. A potential for consumption reductions of up to 70% suggests a very low building thermal performance. The main barriers to finding a solution are the heavy subsidies and public unawareness. Users, government officials, and construction professionals do not identify the very low thermal efficiency. Energy policies to encourage improvements are proposed.
La vida social de los objetos etnográficos y su desalmada mercantilización
González Villarruel, Alejandro;
Alteridades , 2010,
Abstract: this article will examine the original material culture of the mixtec in the coast of oaxaca. the main axis will be the social life of things, the meaning of the ornament for the mixtec and how they value their knowledge. i will try to answer transcendental questions like the way in which the objects relate to the persons and how the objects reveal the social relations of the ones who make them. this is a work on the material culture of a mexican ethnic group that has organized a transnational commercial project within a global context.
La impugnación de la credibilidad de testigos en el sistema penal acusatorio
Decastro González,Alejandro;
Revista Opinión Jurídica , 2008,
Abstract: this paper explains the procedure of impeachment of the credibility of the witness in the colombian accusatory criminal system established by the law 906 of 2004, analyzing some of its problematic aspects from a procedural and probative perspective; it exposes the mistakes of the concept 'impeachment' in our environment and its relation to good judgment.
Las ambigüedades de la "historia desde abajo" de E. P. Thompson: las herramientas del historiador entre la forma, el compromiso político y las disposiciones sociales
Estrella González, Alejandro;
Signos históricos , 2009,
Abstract: this article out a formal and sociological criticism of the theorical model of "history from below" by e. p. thompson. understood as a reflexivity exercise about social history results, it pursues these aims. first, to discuss the identity between "history from below" and a specific historical subject matter, with the objective to show that "history from below" is a theoretical model which can go beyond its context of production, and work in different research contexts of production, and work in different research contexts. secondly, to discuss the autonomy of this model ant to point out that its contents, although they are formalized, they still refer to external logics of intelectual fields; for example: political commitments historian made or social disposition he has incorporated. to value this ambiguity essential to "history from below" model, i reconstruct the filters and mediations thorough it achieves a polifony that make possible to speck several species at the same time.
Antonio Caso y las redes filosóficas mexicanas: sociología de la creatividad intelectual
Estrella González, Alejandro;
Revista mexicana de sociología , 2010,
Abstract: on the basis of the sociological tools offered by randall collins for the analysis of the production and circulation of philosophical objects, this article seeks to measure the creativity of the work of mexican thinker antonio caso. to this end, the author analyzes caso's social and intellectual career within the framework of late 19th and early 20th philosophical networks, as well as the teacher-disciple genealogy that emanated from him, the end of which announced the new configuration of a mexican philosophical field that emerged in the 1930s and 1940s.
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