Dust-to-gas ratio resurgence in circumstellar disks due to the formation of giant planets: the case of HD 163296

The amount of dust present in circumstellar disks is expected to steadily decrease with age due to the growth from micron-sized particles to planetesimals and planets. Mature circumstellar disks, however, can be observed to contain significant amounts of dust and possess high dust-to-gas ratios. Using HD 163296 as our case study, we explore how the formation of giant planets in disks can create the conditions for collisionally rejuvenating the dust population, halting or reversing the expected trend. We combine N-body simulations with statistical methods and impact scaling laws to estimate the dynamical and collisional excitation of the planetesimals due to the formation of HD 163296's giant planets. We show that this process creates a violent collisional environment across the disk that can inject collisionally produced second-generation dust into it, significantly contributing to the observed dust-to-gas ratio. The spatial distribution of the dust production can explain the observed local enrichments in HD 163296's inner regions. The results obtained for HD 163296 can be extended to any disk with embedded forming giant planets and may indicate a common evolutionary stage in the life of such circumstellar disks. Furthermore, the dynamical excitation of the planetesimals could result in the release of transient, non-equilibrium gas species like H2O, CO2, NH3 and CO in the disk due to ice sublimation during impacts and, due to the excited planetesimals being supersonic with respect to the gas, could produce bow shocks in the latter that could heat it and cause a broadening of its emission lines.Comment: 18 pages, 9 figures, 2 tables. Accepted for publication on The Astrophysical Journa

A new perspective on the irregular satellites of Saturn - II Dynamical and physical origin

The origin of the irregular satellites of the giant planets has been long debated since their discovery. Their dynamical features argue against an in-situ formation suggesting they are captured bodies, yet there is no global consensus on the physical process at the basis of their capture. In this paper we explore the collisional capture scenario, where the actual satellites originated from impacts occurred within Saturn's influence sphere. By modeling the inverse capture problem, we estimated the families of orbits of the possible parent bodies and the specific impulse needed for their capture. The orbits of these putative parent bodies are compared to those of the minor bodies of the outer Solar System to outline their possible region of formation. Finally, we tested the collisional capture hypothesis on Phoebe by taking advantage of the data supplied by Cassini on its major crater, Jason. Our results presented a realistic range of solutions matching the observational and dynamical data.Comment: 26 Pages, 21 Figure

Optical mapping of neuronal activity during seizures in zebrafish

Mapping neuronal activity during the onset and propagation of epileptic seizures can provide a better understanding of the mechanisms underlying this pathology and improve our approaches to the development of new drugs. Recently, zebrafish has become an important model for studying epilepsy both in basic research and in drug discovery. Here, we employed a transgenic line with pan-neuronal expression of the genetically-encoded calcium indicator GCaMP6s to measure neuronal activity in zebrafish larvae during seizures induced by pentylenetretrazole (PTZ). With this approach, we mapped neuronal activity in different areas of the larval brain, demonstrating the high sensitivity of this method to different levels of alteration, as induced by increasing PTZ concentrations, and the rescuing effect of an anti-epileptic drug. We also present simultaneous measurements of brain and locomotor activity, as well as a high-throughput assay, demonstrating that GCaMP measurements can complement behavioural assays for the detection of subclinical epileptic seizures, thus enabling future investigations on human hypomorphic mutations and more effective drug screening methods. Notably, the methodology described here can be easily applied to the study of many human neuropathologies modelled in zebrafish, allowing a simple and yet detailed investigation of brain activity alterations associated with the pathological phenotype

Comportamentos Afetivo-motivacionais e de Autorregulação em Pré-escolares Nascidos Prematuros e com Baixo Peso: Avaliação e Intervenção em Estratégias Metacognitivas

Comportamentos afetivo-motivacionais relacionados à metacognição de regulação na idade pré-escolar podem mediar o desempenho de crianças em risco de problemas no desenvolvimento, como nos casos de prematuridade e baixo peso ao nascimento (PTBP), tema desta pesquisa, realizada com 3 estudos. No Estudo 1, aplicou-se o Checklist para Avaliação do Comportamento Afetivo-Motivacional Infantil (ACAMI) em 15 crianças do G1-PTBP, durante uma prova cognitiva assistida (CATM, com fases Sem Ajuda-SAJ, Assistência-ASS, Manutenção-MAN, Transferência-TRF), mostrando diferenças significativas nos comportamentos não-facilitadores em todas as fases do CATM, especialmente no Engajamento na Tarefa e Estados Emocionais, quando comparadas com 15 crianças nascidas a termo (G2-AT), aos 5 anos de idade. Os resultados corroboram a literatura relacionando fatores afetivo-motivacionais e desempenho cognitivo, e a prematuridade e o baixo peso com riscos para problemas de comportamento. No Estudo 2, 34 crianças do G1-PTBP (17) e do G2-AT (17) responderam a 2 subtestes da de uma prova metacognitiva assistida - Application of Cognitive Functions Scale (ACFS). Os comportamentos durante a ACFS foram registrados pela Behavior Observation Rating Scale (BORS). Ambos os grupos, na fase SAJ, tiveram dificuldades em verbalizar estratégias mnemônicas; usando mais frequentemente a estratégia de Repetição. Mas, tiveram aumento significativo na média de acertos nos 2 subtestes, comparando-se as fases SAJ e MAN. Na BORS, houve diferenças significativas a favor do G2-AT em Autorregulação, Persistência e Tolerância à Frustração, confirmando a diferença entre os grupos. O Estudo 3 analisou os efeitos de um programa de promoção de estratégias metacognitivas (PPEM) no desempenho linguístico, acadêmico, cognitivo, metacognitivo e comportamental das crianças PTBP, em delineamento quase-experimental. No pré-teste, 17 crianças do G1-PTBP e 17 do G2-AT foram avaliadas no desempenho: a) cognitivo tradicional (Raven-MPC) e assistido (CATM e ACAMI); b) metacognitivo assistido (ACFS); c) linguístico receptivo (TVIP) e expressivo (LAVE); d) acadêmico (IAR); e) problemas de comportamento (CBCL-1½-5 anos). Foram submetidas ao PPEM 13 crianças do G1-PTBP (15 sessões, 2 vezes/semana), intervindo-se em: (a) autorregulação comportamental, (b) aprendizagem social e (c) sequência e padrões cognitivos. G1-PTBP (13) e G2-AT (16) passaram pelo pós-teste. No seguimento (após 6 meses), G1-PTBP (9) respondeu as provas assistidas: cognitiva (CATM) e metacognitiva (ACFS). No pré-teste, G2-AT foi significativamente melhor em: repertório pré-alfabetização (IAR); comportamentos internalizantes (CBCL); cognição (CATM - níveis de mediação), nos comportamentos afetivo-motivacionais (ACAMI) e na metacognição de regulação (autorregulação, persistência e tolerância à frustração- ACFS). Após a aplicação do PPEM, houve efeito compensatório, ficando sem diferenças em: problemas de comportamento, repertório pré-alfabetização, níveis de mediação e autorregulação. No seguimento, G1-PTBP melhorou nos comportamentos afetivo-motivacionais (ACAMI). O PPEM permitiu o desenvolvimento de habilidades básicas para escolarização, nesse grupo de risco para fracasso escolar. Como Apêndice, um capítulo de livro ilustra 2 casos do G1-PTBP, destacando o papel dos comportamentos afetivo-motivacionais e de autorregulação, como fatores de risco e de proteção capazes de mediar os efeitos potenciais do risco ao desenvolvimento. Palavras-chave: Educação Metacognitiva; Pré-escolares; Nascimento prematur

Signaling response to transient redox stress in human isolated T cells: Molecular sensor role of syk kinase and functional involvement of IL2 receptor and L-selectine

Reactive oxygen species (ROS) are central effectors of inflammation and play a key role in cell signaling. Previous reports have described an association between oxidative events and the modulation of innate immunity. However, the role of redox signaling in adaptive immunity is still not well understood. This work is based on a novel investigation of diamide, a specific oxidant of sulfhydryl groups, and it is the first performed in purified T cell tyrosine phosphorylation signaling. Our data show that ex vivo T cells respond to –SH group oxidation with a distinctive tyrosine phosphorylation response and that these events elicit specific cellular responses. The expression of two essential T-cell receptors, CD25 and CD62L, and T-cell cytokine release is also affected in a specific way. Experiments with Syk inhibitors indicate a major contribution of this kinase in these phenomena. This pilot work confirms the presence of crosstalk between oxidation of cysteine residues and tyrosine phosphorylation changes, resulting in a series of functional events in freshly isolated T cells. Our experiments show a novel role of Syk inhibitors in applying their anti-inflammatory action through the inhibition of a ROS-generated reaction

Acute haemolysis in childhood falciparum malaria

Acute haemolysis associated with clinical episodes of high-level Plasmodium falciparum parasitaemia was studied in 20 children from an holoendemic area (coastal Tanzania). The change in blood haemoglobin (Hb) concentration ranged from -46 to +5 g/L during the 72-h observation period and was linearly related to maximum parasitaemia. Balance studies between loss of blood Hb, increase in plasma Hb and appearance of Hb in the urine indicated that extravascular clearance of red cells was the predominant mode of erythrocyte clearance. Most subjects, however, showed minor signs of intravascular haemolysis. The plasma Hb was ≪1% of blood Hb and haemoglobinuria was detected in 14/20 children but the excretion of Hb in urine was \u3c0.5% of total Hb loss. Haemoglobinuria was, however, a marker of severe haemolysis, since the maximum blood Hb loss in children without haemoglobinuria was 10 g/L. Erythrocyte-bound opsonins known to induce erythrophagocytosis, i.e., complement C3c fragments and autologous IgG, were increased in all patients. In the patients with major haemolysis, the changes correlated to the haemolysis over time. Hence, a similar mechanism for predominantly extravascular erythrocyte clearance may be operative in acute malarial anaemia, normal erythrocyte senescence and other forms of acute haemolysis

Probing the origin of the dark material on Iapetus

Among the icy satellites of Saturn, Iapetus shows a striking dichotomy between its leading and trailing hemispheres, the former being significantly darker than the latter. Thanks to the VIMS imaging spectrometer on-board Cassini, it is now possible to investigate the spectral features of the satellites in Saturn system within a wider spectral range and with an enhanced accuracy than with previously available data. In this work, we present an application of the G-mode method to the high resolution, visible and near infrared data of Phoebe, Iapetus and Hyperion collected by Cassini/VIMS, to search for compositional correlations. We also present the results of a dynamical study on the efficiency of Iapetus in capturing dust grains travelling inward in Saturn system to evaluate the viability of Poynting-Robertson drag as the physical mechanism transferring the dark material to the satellite. The results of spectroscopic classification are used jointly with the ones of the dynamical study to describe a plausible physical scenario for the origin of Iapetus' dichotomy. Our work shows that mass transfer from the outer Saturnian system is an efficient mechanism, particularly for the range of sizes hypothesised for the particles composing the newly discovered outer ring around Saturn. Both spectral and dynamical data indicate Phoebe as the main source of the dark material. However, we suggest a multi-source scenario where now extinct prograde satellites and the disruptive impacts that generated the putative collisional families played a significant role in supplying the original amount of dark material.Comment: 20 pages, 4 tables, 11 figures, major revision (manuscript extended and completed, figures added and corrected, new results added), minor revision and finalization of author list, moderate revision (update of the manuscript following reviewer's feedback and discovery of the new Saturnian outer ring