Ultra-luminous X-ray sources and remnants of massive metal-poor stars

Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25<=mBH/Msun<=80, via direct collapse. We derive the number of massive BHs (NBH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (NULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between NULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our results.Comment: 21 pages, 8 figures, accepted for publication in MNRA

Graphene-based nanomaterials for tissue engineering in the dental field

The world of dentistry is approaching graphene-based nanomaterials as substitutes for tissue engineering. Apart from its exceptional mechanical strength, electrical conductivity and thermal stability, graphene and its derivatives can be functionalized with several bioactive molecules. They can also be incorporated into different scaffolds used in regenerative dentistry, generating nanocomposites with improved characteristics. This review presents the state of the art of graphene-based nanomaterial applications in the dental field. We first discuss the interactions between cells and graphene, summarizing the available in vitro and in vivo studies concerning graphene biocompatibility and cytotoxicity. We then highlight the role of graphene-based nanomaterials in stem cell control, in terms of adhesion, proliferation and differentiation. Particular attention will be given to stem cells of dental origin, such as those isolated from dental pulp, periodontal ligament or dental follicle. The review then discusses the interactions between graphene-based nanomaterials with cells of the immune system; we also focus on the antibacterial activity of graphene nanomaterials. In the last section, we offer our perspectives on the various opportunities facing the use of graphene and its derivatives in associations with titanium dental implants, membranes for bone regeneration, resins, cements and adhesives as well as for tooth-whitening procedure

Ultra-luminous X-ray sources and remnants of massive metal-poor stars

Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25 ≤mBH/M⊙≤ 80, via direct collapse. We derive the number of massive BHs (NBH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (NULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between NULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our result

Boundedness and Stability of Impulsively Perturbed Systems in a Banach Space

Consider a linear impulsive equation in a Banach space $$\dot{x}(t)+A(t)x(t) = f(t), ~t \geq 0,$$ $$x(\tau_i +0)= B_i x(\tau_i -0) + \alpha_i,$$ with $\lim_{i \rightarrow \infty} \tau_i = \infty$. Suppose each solution of the corresponding semi-homogeneous equation $$\dot{x}(t)+A(t)x(t) = 0,$$ (2) is bounded for any bounded sequence $\{ \alpha_i \}$. The conditions are determined ensuring (a) the solution of the corresponding homogeneous equation has an exponential estimate; (b) each solution of (1),(2) is bounded on the half-line for any bounded $f$ and bounded sequence $\{ \alpha_i \}$ ; (c) $\lim_{t \rightarrow \infty}x(t)=0$ for any $f, \alpha_i$ tending to zero; (d) exponential estimate of $f$ implies a similar estimate for $x$.Comment: 19 pages, LaTex-fil

The Star Formation History of the Disk of the Starburst galaxy M82

Spectroscopic, photometric and dynamical data of the inner 3 kpc part of the starburst galaxy M82 are analyzed in order to investigate the star formation history of the stellar disk. The long-slit spectra along the major axis are dominated by Balmer absorption lines in the region outside the nuclear starburst all the way up to ~3.5 scalelengths (mu_B=22 mag/arcsec**2). Single Stellar Population (SSP) spectra of age 0.4-1.0 Gyr match well the observed spectra in the 1-3 kpc zone, with a mean age of the stellar population marginally higher in the outer parts. The mass in these populations, along with that in the gas component, make up for the inferred dynamical mass in the same annular zone for a Kroupa initial mass function, with a low mass cut-off m_l=0.4 Msun. The observed ratio of the abundances of alpha elements with respect to Fe, is also consistent with the idea that almost all the stars in M82 disk formed in a burst of short duration (0.3 Gyr) around 0.8 Gyr ago. We find that the optical/near infrared colors and their gradients in the disk are determined by the reddening with visual extinction exceeding 1 mag even in the outer parts of the disk, where there is apparently no current star formation. The disk-wide starburst activity was most likely triggered by the interaction of M82 with its massive neighbor M81 around 1~Gyr ago. The properties of the disk of M82 very much resemble the properties of the disks of luminous compact blue galaxies seen at 0.2-1.0 redshift.Comment: 7 pages, Accepted for publication in Ap

Laryngectomized patients caregivers' life experience: A phenomenological study

Background: Laryngectomized patients often depend on their caregivers who have a central and difficult role in supporting them dealing with financial, social, and relational issues. In fact, they feel very responsible and committed, especially considering the time devoted to take care of their beloved. Besides, providing care induces caregivers high stress levels, emotional distress, anxiety and the fear of cancer recurrence or progress. Few studies investigated laryngectomized patients caregivers\u2019 life experience during both the whole course of illness and at the end of the treatment. Therefore, the purpose of our study was to explore, through a phenomenological approach, the lived-experience of primary family caregivers of laryngectomized patients undergoing radical surgery. Methods: Qualitative semi-structured and audiotaped interviews were held with 12 laryngectomized patients\u2019 primary family caregivers. Data were analysed using the descriptive phenomenological approach outlined by Colaizzi. Results: Three key themes emerged: the caregivers lived experience of illness; the change of caregivers\u2019 daily life and how they support their sick beloved. The experience of caregivers\u2019 lived relations changes from being a family member to a supportive carer, and the illness of their beloved negatively affects their psychological lived experience. Their perception of time and Quality of Life change as their perception of the future becomes uncertain. Finally, they feel guilty mainly because of the limited amount of time they can devote to their beloved. Conclusions: The study findings allowed to understand in depth how the presence of a laryngectomized person in the family may affect the life of the caregiver, even after the treatment phase. This suggests the need for healthcare professionals to support caregivers throughout the whole care journey and especially in dealing with the perception of time during the diagnosis and care phases. Further research should be conducted on factors contributing to time perception alteration and possible interventions to support caregivers to cope with it

AESOPUS 2.0: Low-Temperature Opacities with Solid Grains

In this study we compute the equation of state and Rosseland mean opacity from temperatures of T~30000 K down to T~400 K, pushing the capabilities of the AESOPUS code (Marigo et al., 2022; Marigo & Aringer, 2009) into the regime where solid grains can form. The GGchem code (Woitke et al. 2018) is used to solve the chemistry for temperatures less than ~3000 K. Atoms, molecules, and dust grains in thermodynamic equilibrium are all included in the equation of state. To incorporate monochromatic atomic and molecular cross sections, an optimized opacity sampling technique is used. The Mie theory is employed to calculate the opacity of 43 grain species. Tables of Rosseland mean opacities for scaled-solar compositions are provided. Based on our computing resources, opacities for other chemical patterns, as well as various grain sizes, porosity, and shapes, can be easily computed upon user request to the corresponding author.Comment: 14 pages, 8 figures, resubmitted to ApJ following moderate revisio

Sistema de classificação fuzzy para o risco de infestação por plantas daninhas considerando a sua variabilidade espacial.

Este artigo trata do problema de classificação do risco de infestação por plantas daninhas usando técnicas geoestatísticas, análise de imagens e modelos de classificação fuzzy. Os principais atributos utilizados para descrever a infestação incluem a densidade de sementes, bem como a sua extensão, a cobertura foliar e a agressividade das plantas daninhas em cada região. A densidade de sementes reflete a produção de sementes por unidade de área, e a sua extensão, a influência das sementes vizinhas; a cobertura foliar indica a extensão dos agrupamentos das plantas daninhas emergentes; e a agressividade descreve a porcentagem de ocupação de espécies com alta capacidade de produção de sementes. Os dados da densidade de sementes, da cobertura foliar e da agressividade para as diferentes regiões são obtidos a partir de simulação com modelos matemáticos de populações. Neste artigo propõe-se um sistema de classificação fuzzy utilizando os atributos descritos para inferir os riscos de infestação de regiões da cultura por plantas daninhas. Resultados de simulação são apresentados para ilustrar o uso desse sistema na aplicação localizada de herbicida

Metodologia para o mapeamento georeferenciado da aplicação de chuva artificial em área de plantio com base no uso de vasão computacional.

Nos últimos anos o monitoramento das condições das culturas agrícolas tem recebido atenção especial e uma maior ênfase tem sido colocada na identificação de deficiências nutricionais em plantas, na ocorrência de pragas e doenças, na classificação e quantificação de plantas daninhas e na otimização de impactos causados pelo uso excessivo de insumos. Neste contexto as práticas de agricultura de precisão vêm sendo valorizadas. Neste trabalho é apresentada uma metodologia que auxilia o mapeamento georeferenciado da aplicação de pesticidas em áreas de plantio com base no uso de visão computacional. A técnica é baseada no uso de imagens digitais para a contagem de gotas de chuva artificial por correlação de padrões no domínio da freqüência, no uso de krigeagem para a elaboração de mapas e no estabelecimento de um critério e análise sítio-específico que integra informações de descritores da distribuição de classes de gotas e sua distribuição