OALib Journal期刊

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匹配条件: “Alexandru Marcu” ,找到相关结果约1288条。
Power Spectral Distribution of the BL Lacertae Object S5 0716+714
Gabriela-Raluca Mocanu,Alexandru Marcu
Physics , 2011, DOI: 10.1002/asna.201111645
Abstract: Observational data in the BVRI bands of the variable BL Lacertae Object S5 0716+714 is discussed from the point of view of its Power Spectral Distribution (PSD). Analysis of the noise properties exhibited by the source. Assessment of the validity of a turbulent model. We fitted a model of the type $P(f) = \beta f^{-\alpha} + \gamma$ to the data for two null hypothesis and calculated the Bayesian p parameter for the fits. Different theoretical models are discussed and applied to these data and a special focus is placed on the MagnetoRotational Instability (MRI). The $P(f) = \beta f^{-\alpha}$ fit provides slopes with values ranging from 0.376 to 2.237, with medium values for each band of $\bar{\alpha}_B = 1.756$, $\bar{\alpha}_V = 1.704$, $\bar{\alpha}_R = 1.780$ and $\bar{\alpha}_I = 1.272$ respectively. An interval for the calculated effective $\alpha_{SS}$ parameter is obtained to be $[0.18,1.72]\cdot 10^{-2}$, corresponding to the order of magnitude previously inferred through both observational and numerical investigations. Structure function analysis, fractal dimension analysis and DFT analysis (all performed in other studies) plus our own analysis establish that the source is turbulent in a nontrivial way, i.e. there is "intrinsic" noise superimposed on the deterministic behavior of the source. We propose that embedding a weakly stochastic magnetic field component in the MRI (MagnetoRotational Instability) framework and taking into account stochastic reconnection of magnetic field lines might explain microvariability in AGN objects.
Sausage Mode Propagation in a Thick Magnetic Flux Tube
Anabele-Linda Pardi,Istvan Ballai,Alexandru Marcu,Beniamin Orza
Physics , 2013, DOI: 10.1007/s11207-013-0380-y
Abstract: The aim of this paper is to model the propagation of slow magnetohydrodynamic (MHD) sausage waves in a thick expanding magnetic flux tube in the context of the quiescent (VAL C) solar atmosphere. The propagation of these waves is found to be described by the Klein-Gordon equation. Using the governing MHD equations and the VAL C atmosphere model we study the variation of the cut-off frequency along and across the magnetic tube guiding the waves. Due to the radial variation of the cut-off frequency the flux tubes act as low frequency filters for waves.
Appearance of an accretion disk perturbed by fractional Brownian Motion density
Gabriela Mocanu,Norbert Magyar,Anabele Pardi,Alexandru Marcu
Physics , 2014,
Abstract: This paper aims to investigate/map the effects that perturbations applied to an accretion disk might produce on the registered Light Curves (LC). The case of accretion disks around supermassive active black holes (AGNs) is studied with the goal to explain some of the statistical properties of the observed IntraDay Variability (IDV). The region producing optical IDV is perturbed by allowing it to develop a mass density of a fractional Brownian Motion-like type. The light curves and spectral slopes are calculated and compared to observational data for different Hurst parameters. The spectral slopes of the simulated light curves vary in the range $(0.4,2.5)$. The agreement with observational data shows that a magnetized disk subjected to stochastic perturbations can produce some of the features observed in the light curves.
Romanian Migration to the Community of Madrid (Spain): Patterns of Mobility and Return
Silvia Marcu
International Journal of Population Research , 2011, DOI: 10.1155/2011/258646
Abstract: The article analyzes the process by which Romanian immigrants to the Autonomous Community of Madrid (Spain) return to their country. Starting with the empirical reality and the theoretical focuses on human mobility as a form of transnationalism, the article emphasises on the characteristics which distinguish the Romanian collective from other collectives of immigrants living in Spain; circular migration that creates work networks. The paper reflects how the intensive mobility contributes to a process that is continuous and partial—hardly ever final. The first part of the article presents the phases of Romanian migration to the Autonomous Community of Madrid. It then delves into the process by which Romanians return to their country of origin, while detailing those factors that influence their decision. The conclusions point towards a renewal of studies on mobility within the framework of the European Union that links the border dynamic with the migration process. 1. Introduction The fall of the Iron Curtain (1989) meant the first exercise of freedom along with the fall of the totalitarian system for the people of Eastern Europe. A people without a tradition of international migration were to experience foreign viewpoints that were directly inspired by the models that were closest at hand, the careers of those exiled by communist governments. This new mobility was to be noted in the global tendencies of migration worldwide. Throughout the past two decades, the migration of Romanians within Europe has been closely linked to the policies of the European Community. As of the 1990s, Spain became one of the destinations of Romanian emigration. While it was slow at first, as of 2002, with the opening of the EC borders as a result of the Schengen Treaty allowing free circulation of Romanians, emigration from Romania became greater. The flow of Romanians towards Spain intensified in 2007 when Romania entered the EU. Madrid has continued to be the Autonomous Community where the majority of Romanians have settled in Spain. Networks that favored intense cyclical mobility between Romania and Spain were formed, which has made it impossible to closely follow the annual, monthly, and even daily movement by Romanians. Between 2007 and 2009, Spain and other EU countries imposed a moratorium that prevented Romanians and Bulgarians from freely entering the labour market. After 2009, Spain lifted the moratorium and allowed free circulation for Romanians and Bulgarians (The moratorium on the free circulation of Romanian and Bulgarian workers within Spanish territory lasted
Del este al oeste. La migración de rumanos en la Unión Europea: Evolución y características
Marcu, Silvia;
Migraciones internacionales , 2009,
Abstract: after the collapse of the totalitarian regimes in eastern europe and the consequent opening of borders and initiation of political and economic transitions, a wave of emigration flowed out of those countries to the european union. this article analyzes the flows of temporary labor migrants from romania to europe from 1990 to the present. it attempts to offer an initial x-ray that is needed for further consideration, analysis, and debate. the first part analyzes the country's recent situation. this background is key for understanding why romania has experienced strong emigration in recent years. next, the socio demographic structure and labor trends are examined, which clearly shows the size, characteristics, and stages of migration during the transition. in the third section, romania, now a part of the eu, is situated within trends in both immigration and emigration.
20 a os después. Nuevos valores en la sociedad civil de la Rumanía postcomunista 20 a os después. Nuevos valores en la sociedad civil de la Rumanía postcomunista
Silvia Marcu
Política y Sociedad , 2010, DOI: -
Abstract: El artículo presenta la influencia de los cambios ocurridos en la estructura de la sociedad civil rumana, en los últimos 20 a os. Analiza la aparición de la nueva Rumanía social, a partir de una sociedad civil débil, con una clase intelectual en declive. Además de indagar en los cambios políticos y sociales, y su reflejo en la sociedad rumana, el artículo detecta y analiza los mecanismos y modelos de “éxito”, tal como los percibe y fomenta el pueblo rumano. Se evidencia que a falta de confianza en la actuación del Estado, la población crea sus propias estrategias de supervivencia. The article presents the influence of the changes happened in the structure of the Rumanian civil society, in the last 20 years. It analyzes the appearance of the new social Rumania, from a weak civil society, with an intellectual class in decline. Besides investigating in the political and social changes and their reflection in the Rumanian society, to the article it detects and it analyzes the mechanisms and models of “success”, it perceives as them and it foments the Rumanian town. The article evidence that for want of confidence in the action of the State, the population creates own strategies of survival.
Cellular bystander effects and radiation hormesis
Loredana MARCU
Analele Universitatii din Oradea, Fascicula Biologie , 2009,
Abstract: Bystander effects describe the effects of extracellular mediators from irradiated cells on neighbouring non-irradiated cells resulting in radiation-induced effects in unirradiated cells. Although the underlying mechanisms are largely unknown, it is widely recognised that two types of cellular communication (i.e. via gap junctions and/or release of molecular messengers into the extracellular environment) play an essential role. Additionally, the effects can be significantly modulated by parameters such as cell type, cell-cycle stage and cell density. Some of the common bystander effects or biological end points which are evidenced after low-dose irradiation are: chromosomal instability, cell killing and delayed cell death, mutagenesis, micronucleus formation, gene and protein expression changes. Through these end points it is likely that bystander effects can be both detrimental and beneficial. By increasing mutation levels of cells bystander effects increase the likelihood of genetic defects and in turn cancer. On the other hand by removing damaged cells from the population and preventing the growth of cancer cells, bystander effects are beneficial.Radiation hormesis is a term used to relate the beneficial effects of small doses of radiation on living cells, whether plant, animal or human. Experiments on bacteria, plants and animals have demonstrated that several biological mechanisms are stimulated by low dose radiation, such as: protein synthesis, gene activation, detoxication of free radicals and stimulation of the immune system. These mechanisms were also observed in humans.The present review paper is a compilation of the most recent data on bystander effects and the possible implications of cellular response to radiation on cell growth and development.
Science education: the need for an interdisciplinary approach
Loredana MARCU
Analele Universitatii din Oradea, Fascicula Biologie , 2007,
Abstract: With today's evolving science and technology, there is a desperate need for retailoring science education. Whether biology or physics, chemistry or computing, mathematics or engineering, one should seek for interaction between disciplines not only at research level but also at teaching levels. The term 'interdisciplinary' is increasingly gaining meaning for the new generation of researchers and educators as the novel approaches to all areas of science are based on multidisciplinary methods. Fields such as medical physics, biochemistry, computational biology, bioengineering, physical chemistry, just to mention some, are a valid proof of the need for interaction between sciences. Often students are confused regarding their future, as they are not aware of the applicative side of their chosen discipline. Furthermore, both undergraduate and postgraduate students encounter frequent gaps in their knowledge because of the lack of coordination and interaction between disciplines. These hiccups in the educational system could be overcome through a better organization of curriculum. An example of interdisciplinary approach in science education is medical physics. A medical physicist must have a multidisciplinary vision of physics, otherwise the goals of this developing area are not met. The aim of the present talk is to illustrate the branching science of medical physics, the need for its correlation with molecular biology, chemistry, computing, mathematics and technology, and to underline its ultimate goal: to be of service, as an adjuvant field, to the novel areas of medicine.
Del este al oeste. La migración de rumanos en la Unión Europea: Evolución y características
Silvia Marcu
Migraciones internacionales , 2009,
Abstract: Después del desplome de los regímenes totalitarios en el este de Europa, con la consecuente apertura de fronteras y el inicio de las transiciones políticas y económicas, se produjo una ola migratoria de estos países hacia los de la Unión Europea. En el presente artículo analizo, en especial, los flujos de inmigración temporal laboral de rumanos en Europa a partir de 1990 y hasta nuestros días. Se pretende ofrecer una radiografía inicial, necesaria para la reflexión y posterior análisis y debate. En la primera parte se analiza la situación reciente del país, clave que ayudará a comprender el porqué de la fuerte migración procedente de Rumania en los últimos a os. A continuación se estudia la estructura sociodemográfica y las trayectorias laborales, haciendo evidentes las dimensiones, características y etapas de las migraciones en el período de transición. En la tercera parte se sitúa a Rumania, ya integrada en la Unión Europea, entre las tendencias de emigración e inmigración.
La movilidad transfronteriza de rumanos en Espa a en tiempos de crisis
Marcu, Silvia
Revista Internacional de Sociologia , 2013,
Abstract: This article seeks to analyze the mobility of Romanians within Spain, taking into account the current economic crisis that is affecting labor markets in Spain and Romania, and its impact upon people. Using the discourse of Romanian immigrants as a reference, the paper examines their mobility experiences as Europeans who have a right to free circulation but not to work in the enlarged European Union (EU). To carry out this research, I utilize the qualitative method of in-depth interviews with 80 Romanian immigrants engaged in labor mobility between the two countries. The empirical approach suggests that migrant may have varying perceptions concerning place and mobility according to their migratory stage and the current economic circumstances. In the theoretical field, the article emphasizes the contribution of mobility to improve knowledge on migration and its conclusions points toward understanding the process of mobility in the enlarged EU. El artículo analiza la movilidad de rumanos en Espa a, en el contexto de la crisis económica que afecta a los mercados de trabajo de Espa a y Rumanía. Tomando como referencia la percepción de los inmigrantes rumanos, el estudio aborda sus experiencias de movilidad como ciudadanos europeos en la Unión Europea (UE) ampliada, con derechos de libre circulación pero no de trabajo. Para realizar la investigación se utilizó la técnica cualitativa de la entrevista en profundidad, llevándose a cabo 80 entrevistas a rumanos que practican la movilidad laboral entre los dos países. El trabajo empírico sugiere que las percepciones de los migrantes sobre la movilidad se interpretan según las etapas migratorias y las circunstancias económicas actuales. En el ámbito teórico el artículo destaca la contribución de la movilidad al conocimiento sobre la inmigración, y sus conclusiones apuntan hacia la comprensión del proceso de movilidad en la UE ampliada.

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