1,323 research outputs found

    Dust formation in the winds of AGBs: the contribution at low metallicities

    Get PDF
    We present new models for the evolution of stars with mass in the range 1Msun < M < 7.5Msun, followed from the pre-main-sequence through the asymptotic giant branch phase. The metallicity adopted is $Z=3*10^{-4} (which, with an alpha-enhancement of +0.4, corresponds to [Fe/H]=-2). Dust formation is described by following the growth of dust grains of various types as the wind expands from the stellar surface. Models with mass M>3Msun experience Hot Bottom Burning, thus maintaining the surface C/O below unity. Unlike higher Z models, the scarcity of silicon available in the envelope prevents the formation of silicates in meaningful quantities, sufficient to trigger the acceleration of the wind via radiation pressure on the dust grains formed. No silicate formation occurs below a threshold metallicity of Z=10^{-3}. Low--mass stars, with M< 2.5Msun become carbon stars, forming solid carbon dust in their surroundings. The total dust mass formed depends on the uncertain extent of the inwards penetration of the convective envelope during the Third Dredge--Up episodes following the Thermal Pulses. Carbon grains have sizes 0.08 micron < a_C < 0.12 micron and the total amount of dust formed (increasing with the mass of the star) is M_C=(2-6)*10^{-4}Msun. Our results imply that AGB stars with Z=3*10^{-4} can only contribute to carbon dust enrichment of the interstellar medium on relatively long timescales, > 300 Myr, comparable to the evolutionary time of a 3Msun star. At lower metallicities the scarcity of silicon available and the presence of Hot Bottom Burning even in M< 2Msun, prevents the formation of silicate and carbon grains. We extrapolate our conclusion to more metal--poor environments, and deduce that at Z < 10^{-4} dust enrichment is mostly due to metal condensation in supernova ejecta.Comment: 13 pages, 8 figures, accepted for publication on MNRA

    Aquaculture and Restoration: Perspectives from Mediterranean Sea Experiences

    Get PDF
    In this paper, the different possibilities and innovations related to sustainable aquaculture in the Mediterranean area are discussed, while different maricultural methods, and the role of Integrated Multi-Trophic Aquaculture (IMTA) in supporting the exploitation of the ocean’s resources, are also reviewed. IMTA, and mariculture in general, when carefully planned, can be suitable for environmental restoration and conservation purposes. Aquaculture, especially mariculture, is a sector that is progressively increasing in parallel with the increase in human needs; however, several problems still affect its development, mainly in relation to the choice of suitable sites, fodder production, and the impact on the surrounding environment. A current challenge that requires suitable solutions is the implementation of IMTA. Unfortunately, some criticisms still affect this approach, mostly concerning the commercialization of new products such as invertebrates and seaweeds, notwithstanding their environmentally friendly character. Regarding the location of a suitable site, mariculture plans are currently displaced from inshore to offshore, with the aim of reducing the competition for space with other human activities carried out within coastal waters. Moreover, in open water, waste loading does not appear to be a problem, but high-energy waters increase maintenance costs. Some suggestions are given for developing sustainable mariculture in the Mediterranean area, where IMTA is in its infancy and where the scarce nutrients that characterize offshore waters are not suitable for the farming of both filter feeder invertebrates and macroalgae. From the perspective of coupling mariculture activity with restoration ecology, the practices suggested in this review concern the implementation of inshore IMTA, creating artificially controlled gardens, as well as offshore mussel farming coupled with artificial reefs, while also hypothesizing the possibility of the use of artificially eutrophized areas

    Congenital Glioblastoma multiforme and eruptive disseminated Spitz nevi

    Get PDF
    Background: Glioblastoma multiforme (GBM) is the deadliest malignant primary brain tumor in adults. GBM develops primarily in the cerebral hemispheres but can develop in other parts of the central nervous system. Its congenital variant is a very rare disease with few cases described in literature. Case presentation: We describe the case of a patient with congenital GBM who developed eruptive disseminated Spitz nevi (EDSN) after chemotherapy. Few cases of EDSN have been described in literature and this rare clinical variant, which occurs predominantly in adults, is characterized by multiple Spitz nevi in the trunk, buttocks, elbows and knees. There is no satisfactory treatment for EDSN and the best therapeutic choice is considered the clinical observation of melanocytic lesions. Conclusion: We recommend a close follow-up of these patients with clinical observation, dermoscopy and reflectance confocal microscopy (RCM). However, we suggest a surgical excision of the lesions suspected of being malignant

    Conformational disorder in phosphopeptides: solution studies by CD and NMR techniques

    Get PDF
    In the last few years intrinsically disordered proteins (IDPs) have received great attention from the scientific community as they participate in several important biological processes and diseases. The intrinsic disorder and flexibility of IDPs grant them a number of advantages with respect to ordered proteins, such as conformational plasticity to bind several targets, a large interaction surface, involvement in high specificity/low affinity interactions, enhanced binding kinetics. It is assumed that post-translational modifications such as phosphorylation can stimulate structural rearrangement in IDPs and facilitate their binding to partners. To better understand at a structural level the multifaceted mechanisms that govern molecular recognition processes involving IDPs, we designed, synthesized by solid phase methods, and structurally characterized unstructured peptides. These molecules contain a putative disordered module, flanked at either the N- or C-terminal ends by a different phosphorylated amino acid (serine or threonine) to mimick the effects of phosphorylation. The absence of an ordered state in the designed peptides was proved experimentally by CD and NMR conformational studies that were carried out under different solution conditions

    Fundaments for managing process in care practices

    Get PDF
    Apresenta-se uma reflexão sobre elementos que estruturam o processo de trabalho em saúde e o agir do enfermeiro. Abordam-se o processo de trabalho em saúde, as tecnologias em saúde e o gerenciamento do cuidado como construtos que fundamentam a reflexão, com o objetivo de auxiliar na ampliação da visibilidade dos atos do enfermeiro. Ressalta-se a importância da utilização desses fundamentos para o exercício de práticas do cuidado nos processos gerenciais.El presente trabajo constituye una reflexión sobre los elementos que estructuran el proceso del trabajo en salud y el actuar del enfermero. Se aborda el proceso del trabajo en salud, las tecnologías en salud y el gerenciamiento del cuidado como constructores que fundamentan la reflexión, con el objetivo de ayudar a la ampliación de la visibilidad de los actos del enfermero. Se resalta la importancia de la utilización de estos fundamentos en el ejercicio de las prácticas del cuidado en los procesos gerenciales.A reflection on the elements that structure the process of the nurse's work with health and his/her action. The study deals with health work, technologies in health and the management of care as pillars that serve as bases for the reflection, with the aim of helping the enlargement of the visibility of the nurse's acts. The importance of those fundaments for the exercise of care practices in the managing processes is highlighted
    • …
    corecore