Terrestrial-type planet formation: Comparing different types of initial conditions

To study the terrestrial-type planet formation during the post oligarchic growth, the initial distributions of planetary embryos and planetesimals used in N-body simulations play an important role. Most of these studies typically use ad hoc initial distributions based on theoretical and numerical studies. We analyze the formation of planetary systems without gas giants around solar-type stars focusing on the sensitivity of the results to the particular initial distributions of planetesimals and embryos. The formation of terrestrial planets in the habitable zone (HZ) and their final water contents are topics of interest. We developed two different sets of N-body simulations from the same protoplanetary disk. The first set assumes ad hoc initial distributions for embryos and planetesimals and the second set obtains these distributions from the results of a semi-analytical model which simulates the evolution of the gaseous phase of the disk. Both sets form planets in the HZ. Ad hoc initial conditions form planets in the HZ with masses from $0.66M_{\oplus}$ to $2.27M_{\oplus}$. More realistic initial conditions obtained from a semi-analytical model, form planets with masses between $1.18M_{\oplus}$ and $2.21M_{\oplus}$. Both sets form planets in the HZ with water contents between 4.5% and 39.48% by mass. Those planets with the highest water contents respect to those with the lowest, present differences regarding the sources of water supply. We suggest that the number of planets in the HZ is not sensitive to the particular initial distribution of embryos and planetesimals and thus, the results are globally similar between both sets. However, the main differences are associated to the accretion history of the planets in the HZ. These discrepancies have a direct impact in the accretion of water-rich material and in the physical characteristics of the resulting planets.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 9 figure

Chemical composition of Earth-like planets

Models of planet formation are mainly focused on the accretion and dynamical processes of the planets, neglecting their chemical composition. In this work, we calculate the condensation sequence of the different chemical elements for a low-mass protoplanetary disk around a solar-type star. We incorporate this sequence of chemical elements (refractory and volatile elements) in our semi-analytical model of planet formation which calculates the formation of a planetary system during its gaseous phase. The results of the semi-analytical model (final distributions of embryos and planetesimals) are used as initial conditions to develope N-body simulations that compute the post-oligarchic formation of terrestrial-type planets. The results of our simulations show that the chemical composition of the planets that remain in the habitable zone has similar characteristics to the chemical composition of the Earth. However, exist differences that can be associated to the dynamical environment in which they were formed.Comment: 3 pages, 4 figures - Accepted for publication in the Bolet\'in de la Asociaci\'on Argentina de Astronom\'ia, vol.5

The role of hydrogeology to achieve the water security

[Abstract] The concept of water security focuses on the objective of water management in society. However, in urban environments -where requirements related to water supply, floods, important rains, rising water tables, pollution problems, among others-, the lack of data and information appropriate to the scale of work, and even the inappropriate use of methodologies, attempt against any attempt to improve this capacity of the population to deal with critical situations. Even in the cities, it is more evident that the challenge of achieving a balance between the supply of water -finite, vulnerable and variable-, and an offer - tirelessly growing, of multiple users and interdependent-, forces us to “rethink” the hydrological cycle as a dynamic environmental system and with it, to add an interdisciplinary approach to hydrology. This paper presents the methodologies, results and conclusions that have served as the basis for improving knowledge of aquifer systems in the cities of Esperanza and Santa Fe (Argentina). The first supports its supply with groundwater, which is essential to protect the resource and the collection works. In the second case, the interrelation between surface and underground water is complex and requires that hydrodynamics of the system as a whole should be considered to define the best technological alternatives for urban infrastructure and the management of floods. The advances achieved point to the importance of science, as an engine that generates effective solutions for society to achieve the goals of sustainable development and water security.[Resumen] El concepto de seguridad hídrica focaliza el objetivo de la gestión del agua en la sociedad. Sin embargo, en los ambientes urbanos -donde deben atenderse requerimientos relacionados al abastecimiento de agua, inundaciones, lluvias intensas, ascenso del nivel freático, problemas de contaminación, entre otros-, la falta de datos e información adecuadas a la escala de trabajo, e incluso el uso inapropiado de metodologías, atentan contra cualquier intento de mejorar esta capacidad de la población para hacer frente a las situaciones críticas. Incluso en las ciudades es más evidente que el desafío de lograr el equilibrio entre la oferta de agua –finita, vulnerable y variable-, y una oferta -incansablemente creciente, de múltiples usuarios e interdependiente-, obliga a “re pensar” el ciclo hidrológico como un sistema ambiental dinámico y con ello, a sumar a la Hidrología un enfoque interdisciplinar. En este trabajo se presentan las metodologías, resultados y conclusiones que han servido de base para mejorar el conocimiento de los sistemas acuíferos de las ciudades de Esperanza y Santa Fe (Argentina). La primera sustenta su abastecimiento con aguas subterráneas, con lo cual es indispensable la protección del recurso y las obras de captación. En el segundo caso, la interrelación entre el agua superficial y la subterránea es compleja y requiere que hidrodinámica del sistema en su conjunto deba ser considerada para definir las mejores alternativas tecnológicas de la infraestructura urbana y el manejo de las inundaciones. Los avances logrados señalan la importancia de la ciencia, como motor que genera soluciones efectivas para que la sociedad alcance las metas del desarrollo sostenible y la seguridad hídric

Retroneumoperitoneo secundario a dilatación endoscópica de anastomosis colorrectal: ¿permite un manejo conservador?

Background The incidence of anastomotic stricture varies due to the different definitions given to the condition. In most cases they are asymptomatic, and if there are symptoms, they are usually those of a partial intestinal obstruction. Case report The case is presented of an 80 year old patient who underwent a lower anterior resection for rectal neoplasm. After ileostomy closure, he presented with subocclusive symptoms caused by stenosis of colorectal anastomosis. This stenosis was managed with endoscopic dilations, and one of these dilations produced an anastomotic perforation with pneumoperitoneum, retropneumoperitoneum, and pneumothorax. Once the patient was clinically and haemodynamically stable, the perforation was treated with conservative measures, resolving the complication satisfactorily. Conclusions The literature describes several management options for colorectal anastomoses strictures, such as surgical resection, rubber dilators, endoscopic dilation, all of which might produce colonic perforation. Its management ranges from conservative measures to surgical intervention

Devastadora complicación tras tratamiento con aflibercept

Background The use of a new chemotherapy as adjuvant treatment of colorectal cancer is not free of complications. Monoclonal antibodies are associated with bleeding and intestinal perforations. Objective To report the case of a patient who developed a serious complication after treatment with an antiangiogenic drug for colorectal neoplasm. Clinical case The case is presented of a 42-year-old male operated on due to subocclusive rectal cancer with metástasis at the time of diagnosis. Sixteen months after surgery during second-line adjuvant therapy, an intestinal perforation was observed with haemorrhage and intestinal leak to retroperitoneum and left lower extremity. Despite intensive medical and surgical treatment this complication had fatal consequences. Conclusions Future research should be directed at obtaining biomarkers for the specific use of antiangiogenic agents in order to decrease the rate of adverse factors

Fascitis necrosante clostridial asociada a neoplasia colónica perforada: importancia de un diagnóstico precoz

La gangrena espontánea por Clostridium septicum es una entidad poco frecuente con una alta mortalidad que se asocia a pacientes neoplásicos y/o inmunodeprimidos. Caso clínico: Presentamos un caso de gangrena clostridial en un paciente con neoplasia de colon ascendente perforada a retroperitoneo. Discusión-conclusiones: Aunque es poco común deberemos pensar en una infección clostridial en pacientes sépticos y sospecha de neoplasia colónica. En ausencia de diagnóstico y tratamiento precoz, el pronóstico es fatal. Introduction Spontaneous gangrene due to Clostridium septicum is a low frequency pathology with a high mortality rate. It is related to neoplasic and/or immunodeficient patients. Case report We present the case of a patient who presented clostridial gangrene associated with a perforated colon neoplasm. Discussion-conclusions Although it is not very common it must supposed a clostridial infection in septic patients with colon neoplasm suspect. If diagnosis and treatment are delayed the prognostic of the patient is fatal

Tratamiento de la base apendicular por laparoscopia mediante el uso de endograpadoras: análisis de nuestros resultados;

Objective The objective of this study is to analyse the results in our centre as regards the closure of the appendix stump in laparoscopic appendectomy using an endo-stapler. Material and methods A retrospective analysis, collecting the demographic, clinical, and surgical technique variables, was conducted on laparoscopic appendectomies with section of the appendix base with an endo-stapler performed between January 2013 and March 2015. Results A total of 239 patients were included in the analysis. Complications were recorded in 41 patients, with a re-admission rate of 5%, and 2.5% of patients received further surgery. The mean post-surgical stay was 3.64 days. Discussion and conclusions The endo-stapler is a suitable technique in the closure of the appendix stump, as regards post-surgical hospital stay and complications. Despite the advantages of its use, the employment of other techniques, such as endo-loops, should be evaluated in non-complicated appendectomies

The scattering of small bodies in planetary systems: constraints on the possible orbits of cometary material

The scattering of small bodies by planets is an important dynamical process in planetary systems. We present an analytical model to describe this process using the simplifying assumption that each particle's dynamics is dominated by a single planet at a time. As such the scattering process can be considered as a series of three body problems during each of which the Tisserand parameter with respect to the relevant planet is conserved. This constrains the orbital parameter space into which a particle can be scattered. Such arguments have previously been applied to the process by which comets are scattered to the inner Solar System from the Kuiper belt. Our analysis generalises this for an arbitrary planetary system. For particles scattered from an outer belt directly along a chain of planets, based on the initial value of the Tisserand parameter, we find that it is possible to (i) determine which planets can eject the particles from the system, (ii) define a minimum stellar distance to which particles can be scattered, and (iii) constrain range of particle inclinations (and hence the disc height) at different distances. Applying this to the Solar System, we determine that the planets are close to optimally separated for scattering particles between them. Concerning warm dust found around stars that also have Kuiper belt analogues, we show that, if there is to be a dynamical link between the outer and inner regions, then certain architectures for the intervening planetary system are incapable of producing the observations. Furthermore we show that for certain planetary systems, comets can be scattered from an outer belt, or with fewer constraints, from an Oort cloud analogue, onto star-grazing orbits, in support of a planetary origin to the metal pollution and dustiness of some nearby white dwarfs

Planetesimal fragmentation and giant planet formation: the role of planet migration

In the standard model of core accretion, the cores of the giant planets form by the accretion of planetesimals. In this scenario, the evolution of the planetesimal population plays an important role in the formation of massive cores. Recently, we studied the role of planetesimal fragmentation in the in situ formation of a giant planet. However, the exchange of angular momentum between the planet and the gaseous disk causes the migration of the planet in the disk. In this new work, we incorporate the migration of the planet and study the role of planet migration in the formation of a massive core when the population of planetesimals evolves by planet accretion, migration, and fragmentatio

The Size Distributions of Asteroid Families in the SDSS Moving Object Catalog 4

Asteroid families, traditionally defined as clusters of objects in orbital parameter space, often have distinctive optical colors. We show that the separation of family members from background interlopers can be improved with the aid of SDSS colors as a qualifier for family membership. Based on an ~88,000 object subset of the Sloan Digital Sky Survey Moving Object Catalog 4 with available proper orbital elements, we define 37 statistically robust asteroid families with at least 100 members using a simple Gaussian distribution model in both orbital and color space. The interloper rejection rate based on colors is typically ~10% for a given orbital family definition, with four families that can be reliably isolated only with the aid of colors. About 50% of all objects in this data set belong to families, and this fraction varies from about 35% for objects brighter than an H magnitude of 13 and rises to 60% for objects fainter than this. The fraction of C-type objects in families decreases with increasing H magnitude for H > 13, while the fraction of S-type objects above this limit remains effectively constant. This suggests that S-type objects require a shorter timescale for equilibrating the background and family size distributions via collisional processing. The size distributions for 15 families display a well-defined change of slope and can be modeled as a "broken" double power-law. Such "broken" size distributions are twice as likely for S-type familes than for C-type families, and are dominated by dynamically old families. The remaining families with size distributions that can be modeled as a single power law are dominated by young families. When size distribution requires a double power-law model, the two slopes are correlated and are steeper for S-type families.Comment: 50 pages, 16 figures, accepted for publication in Icaru