On the relevance of bubbles and potential flows for stellar convection

Recently Pasetto et al. have proposed a new method to derive a convection theory appropriate for the implementation in stellar evolution codes. Their approach is based on the simple physical picture of spherical bubbles moving within a potential flow in dynamically unstable regions, and a detailed computation of the bubble dynamics. Based on this approach the authors derive a new theory of convection which is claimed to be parameter free, non-local and time-dependent. This is a very strong claim, as such a theory is the holy grail of stellar physics. Unfortunately we have identified several distinct problems in the derivation which ultimately render their theory inapplicable to any physical regime. In addition we show that the framework of spherical bubbles in potential flows is unable to capture the essence of stellar convection, even when equations are derived correctly.Comment: 14 pages, 3 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society. (Comments and criticism are welcomed

Semi-empirical white dwarf initial-final mass relationships: A thorough analysis of systematic uncertainties due to stellar evolution models

Using the most recent results about white dwarfs (WDs) in ten open clusters, we revisit semiempirical estimates of the initial-final mass relation (IFMR) in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the WD cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.Facultad de Ciencias Astronómicas y Geofísica

Semi-empirical white dwarf initial-final mass relationships: a thorough analysis of systematic uncertainties due to stellar evolution models

Using the most recent results about white dwarfs in 10 open clusters, we revisit semi-empirical estimates of the initial-final mass relation in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the white dwarf cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.Comment: 53 pages, including 6 figures and 5 tables. Revised and accepted for publications in Ap

Giant liver cyst associated with cholelithiasis: literature review and state of art

Liver lesions subject to laparoscopic resection are one of the frontiers conquered in surgery today. Even when dealing with surgery, which is often complex, the increase in demand from patients has increased, bringing more and more learning and dexterity to surgery teams with the increasing development of technology. To analytically evaluate the method, based on the most recent publications in the literature, with possible indications and reporting a recently successfully operated case, highlighting the safety, results and fundamental technical aspects. The relevant works from the last 15 years were identified and analyzed in the LILACS and PUBMED databases until August 2023, using the descriptors “ liver resection ”, “ laparoscopic surgery ” and “ liver surgery ”. We don't We found prospective and double-blind studies in the databases, with available data coming from case series, case-control studies and some multicenter studies and meta-analyses. Laparoscopic hepatectomy is a safe surgery and is very standardized in execution, even for major liver resections, with a low morbidity and mortality rate. As an oncological surgical method, it is gaining more and more space without compromising oncological radicality and with advantages for patients.  with specific liver diseases. Benign lesions are the best indicated and performed, especially adenoma and cystic lesions, which in the hands of experienced teams have very good results and videolaparoscopic surgery can be considered today as standard treatment

On the relevance of bubbles and potential flows for stellar convection

Recently Pasetto et al. have proposed a new method to derive a convection theory appropriate for the implementation in stellar evolution codes. Their approach is based on the simple physical picture of spherical bubbles moving within a potential flow in dynamically unstable regions, and a detailed computation of the bubble dynamics. Based on this approach, the authors derive a new theory of convection which is claimed to be parameter-free, non-local and time-dependent. This is a very strong claim, as such a theory is the holy grail of stellar physics. Unfortunately, we have identified several distinct problems in the derivation which ultimately render their theory inapplicable to any physical regime. In addition, we show that the framework of spherical bubbles in potential flows is unable to capture the essence of stellar convection, even when equations are derived correctly.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Spacers in the treatment of hip joint infections: numerical analysis of their durability

Hip spacers are temporary implants having a geometry similar to the femoral component of a hip prosthesis, and they are manufactured with antibiotic-impregnated bone cement. The use of spacers in two stage revisions is the most effective treatment to eradicate infections and to avoid limb shortening. The most frequent complication associated with spacers is fatigue failure, for which doctors recommend patients to stay at rest. In this work, several spacer designs are analyzed in order to determine the feasibility of doing activities like walking, standing up or sitting down while performing the antibiotics treatment. Designs combine both different neck diameters and the presence/absence of an internal, stainless steel reinforcement. By means of computational simulations based on the finite element method, stress fields are calculated for various hip spacer designs under several load and fixing conditions. For this purpose, a 3D model of human femur is generated by processing tomographic images with segmentation techniques and inverse engineering. The results allow us to estimate the life expectancy of each design, by considering the fatigue behavior of the bone cement. Only the introduction of a reinforcement with a proper diameter into the bone cement matrix could assure the integrity of the spacer along the treatment period.Fil: Weiss, Brenda Anahí. Universidad Nacional de Entre Ríos. Facultad de Ingeniería. Departamento de Física Química. Laboratorio de Biomecánica Computacional; ArgentinaFil: Vanrell, Sebastián Rodrigo. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; ArgentinaFil: Berli, Marcelo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Ubal, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Di Paolo, José. Universidad Nacional de Entre Ríos. Facultad de Ingeniería. Departamento de Física Química. Laboratorio de Biomecánica Computacional; Argentin

Semi-empirical white dwarf initial-final mass relationships: A thorough analysis of systematic uncertainties due to stellar evolution models

Using the most recent results about white dwarfs (WDs) in ten open clusters, we revisit semiempirical estimates of the initial-final mass relation (IFMR) in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the WD cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.Facultad de Ciencias Astronómicas y Geofísica

Impact of convective boundary mixing on the TP-AGB

The treatment of convective boundaries remains an important source of uncertainty within stellar evolution, with drastic implications for the thermally-pulsing stars on the Asymptotic Giant Branch (AGB). Various sources are taken as motivation for the incorporation of convective boundary mixing during this phase, from s-process nucleosynthesis to hydrodynamical models. In spite of the considerable evidence in favour of the existence of convective boundary mixing on the pre-AGB evolution, this mixing is not universally included in models of TP-AGB stars. The aim of this investigation is to ascertain the extent of convective boundary mixing, which is compatible with observations when considering full evolutionary models. Additionally, we investigate a theoretical argument that has been made that momentum-driven overshooting at the base of the pulse-driven convection zone should be negligible. We show that, while the argument holds,estimations based on the picture of turbulent entrainment suggest that mixing is possible at both convective boundaries. We demonstrate that additional mixing at convective boundaries during core-burning phases prior to the thermally-pulsing Asymptotic Giant Branch has an impact on the later evolution, changing the mass range at which the third dredge-up and hot-bottom burning occur, and thus also the final surface composition. In addition, an effort has been made to constrain the efficiency of convective boundary mixing at the different convective boundaries, using observational constraints. Our study suggests a strong tension between different constraints that makes it impossible to reproduce all observables simultaneously within the framework of an exponentially decaying overshooting. This result calls for a reassessment of both the models of convective boundary mixing and the observational constraints.Instituto de Astrofísica de La Plat

Phytochemical study of Muehlenbeckia platyclada (F. Muell) leaves

Medicinal plants have active substances with therapeutic potential that have been used in the treatment of various diseases in humans since the most primitive populations. The use of those plants establishes a direct relationship with the theme of planetary health as it allows to relate the health of the planet's natural systems and the health of human civilization. The plant species Muehlenbeckia platyclada, belonging to the Polygonaceae family, is important in traditional medicine, presenting antinociceptive and analgesic activities proven in several studies. The general objective of the current study is to understand the chemical and phytochemical characteristics of M. platyclada. From the leaves, the humidity and total ash contents were quantified as well as phytochemical prospecting was carried out. An aqueous extract and four ethanolic extracts of different concentrations were prepared from the leaves of the plant drug. Total phenol and flavonoid levels were quantified and the presence of antioxidant activity was verified. As a result: The sum of total ash and humidity content produced a value of 96.39%. It was possible to observe that the reactions for tannins, flavonoids, coumarins, terpenoids/steroids, and saponins were positive while anthraquinones and alkaloids were negative. The average phenol contents ranged from 1.83 to 8.53mg/100g (of organic plant material), concerning the extracting solvents (p < 0.05). The extracting liquid that provided the highest yield of phenols and flavonoids was 50% ethanol, using the hot and cold extraction method. Regarding antioxidant activity, the effective concentration (EC50) for rutin (positive control) was 5.50mg/mL and ranged from 14.30±0.10 to 65.66±7.79 mg/mL, being identified the aqueous extract as the one with the greatest activity. Phytochemical prospecting and investigation into antioxidant activity allow the classification of the studied plant as a potential anti-inflammatory and antitumor agent

Análise comparativa entre o conversor boost tradicional e o conversor boost entrelaçado utilizando a técnica de mppt P&O para sistemas fotovoltaicos / Comparative analysis between traditional boost converter and interleaved boost converter using mppt P&O technique for photovoltaic systems

 Este trabalho apresenta um estudo comparativo entre dois conversores CC-CC elevadores de tensão utilizados em sistemas fotovoltaicos conectados à rede elétrica. Os sistemas fotovoltaicos apresentam baixa eficiência e um nível de tensão que deve ajustado para aplicações em conexão com a rede. Os conversores elevadores de tensão são os responsáveis pela adequação do nível de tensão e devem apresentar uma boa eficiência e resposta ao sistema fotovoltaico. Dentre os conversores elevadores de tensão os mais empregados em sistemas fotovoltaicos são eles o conversor boost convencional e o conversor boost entrelaçado. Para fins de análise comparativa neste trabalho foi implementado via simulação estes dois conversores juntamente com a técnica de rastreamento de máxima potência Perturba e Observa (P&O). Foram analisadas a eficiência dos conversores, a dinâmica do sistema e a rastreabilidade