An optical and infrared study of the reflection nebulae GGD-30 and GGD-31

CCD images and near-IR observations of the nebular objects GGD 30 and GGD 31 are presented. The data have been used to study the morphology and physical nature of the nebulosities. GGD 30 is a reflection nebula illuminated by a low mass PMS star of estimated luminosity almost-equal-to 2.3 L.. The CCD images reveal that the illuminating star is likely to be double with a separation between components of 4", corresponding to a projected linear separation of 2000 AU. A stream arises from one of the stellar components; our data do not show, however, evidence of shock-excited material. GGD 31 is a reflection nebula showing a rather complex morphology. It has a dark cavity within the nebulosity and there are two nebular streams arising from the illuminating star and surrounding the cavity. The estimated luminosity of the star is almost-equal-to 10 L.. In addition, the region around GGD 30 has been surveyed in the near-IR and also searched for IRAS point sources. A further PMS object is present in the GGD 30 region. Finally, a peculiar near-IR object has been detected. The object seems to be a late type oxygen-rich star with very extreme colours, H - K = 4.47, K - L' = 4.49, and L' - M' = 1.19 mag

Prethermalization and Persistent Order in the Absence of a Thermal Phase Transition

We numerically study the dynamics after a parameter quench in the one-dimensional transverse-field Ising model with long-range interactions ($\propto 1/r^\alpha$ with distance $r$), for finite chains and also directly in the thermodynamic limit. In nonequilibrium, i.e., before the system settles into a thermal state, we find a long-lived regime that is characterized by a prethermal value of the magnetization, which in general differs from its thermal value. We find that the ferromagnetic phase is stabilized dynamically: as a function of the quench parameter, the prethermal magnetization shows a transition between a symmetry-broken and a symmetric phase, even for those values of $\alpha$ for which no finite-temperature transition occurs in equilibrium. The dynamical critical point is shifted with respect to the equilibrium one, and the shift is found to depend on $\alpha$ as well as on the quench parameters.Comment: 6 pages, 4 figure

The impact of significant input of fine sediment on benthic fauna at tributary junctions: a case study of the Bermejo-Paraguay River confluence, Argentina

This study examines the morphological features, suspended sediment inputs and hydraulic conditions within a large river in association with ecological patterns before and after a tributary confluence. In order to examine these effects, the macroinvertebrate distributions from three reaches of the Paraguay and Bermejo Rivers (Paraguay-Argentina) are investigated. The Bermejo River is a tributary that supplies significant quantities of fine sediment to the Paraguay River, primarily in suspension. Two reaches were examined on the Paraguay River, upstream and downstream of the Bermejo River junction, with the third study reach located on the Bermejo River, upstream of the confluence with the Paraguay River. The results provide clear evidence that a significantly increased loading of fine sediment at a river confluence has effects on the distribution and potential movement of benthic invertebrates in the lotic environment by representing physical barriers at affected sites. These effects may be important at both local and regional scales, and such increases in suspended sediment (especially associated with anthropogenic change) may thus pose a major threat to ecosystem integrity that has been historically underestimated

Multiple-time correlation functions for non-Markovian interaction: Beyond the Quantum Regression Theorem

Multiple time correlation functions are found in the dynamical description of different phenomena. They encode and describe the fluctuations of the dynamical variables of a system. In this paper we formulate a theory of non-Markovian multiple-time correlation functions (MTCF) for a wide class of systems. We derive the dynamical equation of the {\it reduced propagator}, an object that evolve state vectors of the system conditioned to the dynamics of its environment, which is not necessarily at the vacuum state at the initial time. Such reduced propagator is the essential piece to obtain multiple-time correlation functions. An average over the different environmental histories of the reduced propagator permits us to obtain the evolution equations of the multiple-time correlation functions. We also study the evolution of MTCF within the weak coupling limit and it is shown that the multiple-time correlation function of some observables satisfy the Quantum Regression Theorem (QRT), whereas other correlations do not. We set the conditions under which the correlations satisfy the QRT. We illustrate the theory in two different cases; first, solving an exact model for which the MTCF are explicitly given, and second, presenting the results of a numerical integration for a system coupled with a dissipative environment through a non-diagonal interaction.Comment: Submitted (04 Jul 04

Determinación de agua en alcoholes usando como reactivo un tiocianocomplejo del cobalto

En el presente trabajo se propone un método cuantitativopara la determinación de agua en etanol, basado en las variaciones de intensidad del color azul que presentan las soluciones hidroalcohólicas del complejo tetratiocianocobaltato(II) de potasio.El compuesto de coordinación se prepara triturando intimamente en un mortero cantidades estequiométricas desulfato de cobalto(II) y tiocianato de potasio. El complejoobtenido se extrae con etanol, y el sulfato de potasioremanente es insoluble en este medio. El extracto alcohólicofiltrado se evapora lentamente y los cristales azulesobtenidos se mantienen en desecador conteniendo ácido sulfúrico.El objetivo del presente trabajo es desarrollar un métodocuantitativo usando la espectrofotometría molecular, para determinar la concentración de agua en alcoholes hidratados.Esta técnica es de aplicación a limitadas cantidades de agua en alcohol etílico (3,6 -11,2 %) pues a mayores concentracionesde agua en la solución complejo-etanol, se descompone el complejo, liberando el ión cobalto(II) que colorea de rosado la solución

Infección por Chlamydia Trachomatis, candida albicans y neisseria gonorrhoeae en mujeres embarazadas

The frequency of cervical and vaginal infection with Chlamydia trachomatis, Neisseria gonorrhoeae and Candida albicans was studied in 198 pregnant women in their last trimester. The diagnosis was made culturing endocervicaí and vaginal specimens by standard procedures. The percentages of infection were: 21% for C. albicans, 3.5% C. trachomatis and 0.5% N. gonorrhoeae. The diagnosis of chamydial infections in gynecologic and pregnant patients is emphasized.Se estudiaron 198 mujeres en el último trimestre de la gestación con el fin de conocer la frecuencia de la infección por Chlamydia trachomatis, Neisseria gonorrhoeae y Candida albicans diagnosticada empleando cultivos de muestras endocervicales y vaginales. Los porcentajes de infección con los diferentes microorganismos fueron: C. albicans 21%, C. trachomatis 3,5% y N. gonorrhoeae 0,5%. Se destaca la importancia de la investigación de la infección por C. trachomatis, en pacientes ginecológicas, en embarazadas, y como parte del estudio preconcepcional

Invasion process of Limnoperna fortunei (Bivalvia: Mytilidae): the case of Uruguay river and emissaries of the Esteros del Iberá Wetland, Argentina

Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland.Facultad de Ciencias Naturales y Muse

Invasion process of Limnoperna fortunei (Bivalvia: Mytilidae): the case of Uruguay river and emissaries of the Esteros del Iberá Wetland, Argentina

Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland.Facultad de Ciencias Naturales y Muse

Docencia Universitaria: un nuevo enfoque

In the fourth century before christ, Aristóteles characterized the teacher function when he said that the student's mind was a "blank slate" and that the role of the teacher was to full it, making students memorize the contents that he expose in his teaching lecture. The topic of their signatures were selected by them with their judgement. This point of view determined a passive attitutide from the studen towards the different fields of knowledge, and it distiguished the education as dogmatic, authoritarian, and no critical, where the professor was mithicized as the erudite foolproof of the knowledge.Hacia el siglo cuarto antes de Cristo, Aristóteles caracterizó la función docente al decir que la mente del alumno era una “tabula rasa” y que el papel del maestro no era otro que el de llenarla, haciendo que los alumnos memorizaran los contenidos que éste exponía en su cátedra magistral. Los temas de las asignaturas eran seleccionados por él con el criterio de su autoridad. Este punto de vista determinó una actitud pasiva del alumno frente a los distintos campos del conocimiento y caracterizó a la educación como dogmática, autoritaria y acrítica donde se mitificaba al maestro creyéndole el sabedor infalible del conocimiento

Benefits of probiotic administration on growth and performance along metamorphosis and weaning of Senegalese sole (Solea senegalensis)

Suitable nutrition at first feeding in marine fish larvae is an important factor for successful larval and juvenile rearing. In this way probiotic supplementation may contribute to better face the habitual stress of metamorphosis and weaning at early sole stages. The aimof this study was to optimize Shewanella putrefaciens Pdp11 administration to Senegalese sole (Solea senegalensis) at early stages of development. For this purpose, we studied the influence of a short pulse of S. putrefaciens Pdp11 (10–30 dah) on growth performance, gut microbiota modulation, digestive enzymes activities and body composition. These probiotic bacteria were incorporated using Artemia as live vector (2.5 × 10 7 cfu mL −1 ) and supplied to sole specimens in a co-feeding regime (Gemma, Skretting) by triplicate. S. putrefaciens Pdp11 colonized larval gut being present from23 to 119 dah. Probiotic supply significantly modulated larval and fry gut microbiota. A PCA analysis including all the parameters analyzed strongly associated S. putrefaciens Pdp11 presence with a higher fish growth, a higher digestive proteolytic activity level and a fish body composition modulation along S. senegalensis rearing. In addition less size variability was obtained frommetamorphosis until the end of weaning. In conclusion a short pulse of S. putrefaciens Pdp11 (10– 30 dah) seems sufficient to obtain a suitable microbial modulation involved in a better growth performance and body composition that suggests a great potential for sole aquaculture production.En prens