1,147 research outputs found

    Mid Infrared Photometry of Mass-Losing AGB Stars

    Get PDF
    We present ground-based mid-infrared imaging for 27 M-, S- and C-type Asymptotic Giant Branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal is to establish relations between the IR colors, the effective temperature TeffT_{eff}, the luminosity LL and the mass loss rate MË™\dot M, for improving the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are obtained through distance compilations, and by applying previously-derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are: i) Values of LL and MË™\dot M for C stars fit relations previously established by us, with Miras being on average more evolved and mass losing than Semiregulars. ii) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. iii) A larger reddening characterizes C-rich Miras and post-AGBs. In this case, part of the excess is due to AGB models overestimating TeffT_{eff} for C-stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. iv) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8 -- 20 ÎĽ\mum region, usually Mira variables (1/3 of our sample). Most Semiregular and post-AGB stars studied here remained remarkably constant in mid-IR over the last twenty years.Comment: Accepted for publication in the Astronomical Journal - 35 pages (in preprint), 9 figures, 5 table

    Production and characterization of polyethylene terephthalate nanoparticles

    Get PDF
    Microplastic (MP) pollution represents one of the biggest environmental problems that is further exacerbated by the continuous degradation in the marine environment of MPs to nanoplastics (NPs). The most diffuse plastics in oceans are commodity polymers, mainly thermoplastics widely used for packaging, such as polyethylene terephthalate (PET). However, the huge interest in the chemical vector role of micro/nanoplastics, their fate and negative effects on the environment and human health is still under discussion and the research is still sparse due also to the difficulties of sampling MPs and NPs from the environment or producing NPs in laboratory. Moreover, the research on MPs and NPs pollution relies on the availability of engineered nanoparticles similar to those present in the marine environment for toxicological, transport and adsorption studies in biological tissues as well as for wastewater remediation studies. This work aims to develop an easy, fast and scalable procedure for the production of representative model nanoplastics from PET pellets. The proposed method, based on a simple and economic milling process, has been optimized considering the peculiarities of the polymer. The results demonstrated the reliability of the method for preparing particle suspensions for aquatic microplastic research, with evident advantages compared to the present literature procedures, such as low cost, the absence of liquid nitrogen, the short production time, the high yield of the process, stability, reproducibility and polydisperse size distribution of the produced water dispersed nanometric PET

    The challenge of perioperative pain management in opioid-tolerant patients

    Get PDF
    The increasing number of opioid users among chronic pain patients, and opioid abusers among the general population, makes perioperative pain management challenging for health care professionals. Anesthesiologists, surgeons, and nurses should be familiar with some pharmacological phenomena which are typical of opioid users and abusers, such as tolerance, physical dependence, hyperalgesia, and addiction. Inadequate pain management is very common in these patients, due to common prejudices and fears. The target of preoperative evaluation is to identify comorbidities and risk factors and recognize signs and symptoms of opioid abuse and opioid withdrawal. Clinicians are encouraged to plan perioperative pain medications and to refer these patients to psychiatrists and addiction specialists for their evaluation. The aim of this review was to give practical suggestions for perioperative management of surgical opioid-tolerant patients, together with schemes of opioid conversion for chronic pain patients assuming oral or transdermal opioids, and patients under maintenance programs with methadone, buprenorphine, or naltrexone

    Fused Filament Fabrication and Computer Numerical Control Milling in Cultural Heritage Conservation

    Get PDF
    This paper reports a comparison between the advantages and disadvantages of fused filament fabrication (FFF) and computer numerical control (CNC) milling, when applied to a specific case of conservation of cultural heritage: the reproduction of four missing columns of a 17th-century tabernacle. To make the replica prototypes, European pine wood (the original material) was used for CNC milling, while polyethylene terephthalate glycol (PETG) was used for FFF printing. Neat materials were chemically and structurally characterized (FTIR, XRD, DSC, contact angle measurement, colorimetry, and bending tests) before and after artificial aging, in order to study their durability. The comparison showed that although both materials are subject to a decrease in crystallinity (an increase in amorphous bands in XRD diffractograms) and mechanical performance with aging, these characteristics are less evident in PETG (E = 1.13 +/- 0.01 GPa and sigma = 60.20 +/- 2.11 MPa after aging), which retains water repellent (ca = 95.96 +/- 5.56 degrees) and colorimetric ( increment E = 2.6) properties. Furthermore, the increase in flexural strain (%) in pine wood, from 3.71 +/- 0.03% to 4.11 +/- 0.02%, makes it not suitable for purpose. Both techniques were then used to produce the same column, showing that for this specific application CNC milling is quicker than FFF, but, at the same time, it is also much more expensive and produces a huge amount of waste material compared to FFF printing. Based on these results, it was assessed that FFF is more suitable for the replication of the specific column. For this reason, only the 3D-printed PETG column was used for the subsequent conservative restoration

    Historically Accurate Reconstruction of the Materials and Conservation Technologies Used on the Facades of the Artistic Buildings in Lecce (Apulia, Italy)

    Get PDF
    The protection of the stone surfaces of the buildings of the city of Lecce (Apulia, Italy) represents an ancient practice, which has always allowed the conservation of the historical-artistic heritage of the city, which nowadays is an international touristic and cultural destination. The identification of ancient recipes, materials and methodologies for the protection of historical buildings plays an important role in establishing correct protocols in order to ensure the durability of stone surfaces over time. This work presents a historically accurate reconstruction of the materials and conservation technologies used on the facades of the artistic buildings in Lecce. Several historical buildings, both civil and religious, have been selected in order to investigate the treatments applied on their facades and to know the traditions spread in the past in the field of building conservation in the Salento territory. Thanks to non-invasive or micro-destructive techniques (optical microscopy, ATR-FTIR spectroscopy, pyrolysis–gas chromatography–mass spectrometry), the characteristic molecular markers of the materials and the products of degradation have been identified, deepening the knowledge of the mechanisms of deterioration and interaction between the stone material, the surface finish and the surrounding environment. The paper is a valuable tool for the knowledge of ancient traditions and the planning of proper restoration works

    Recycling of organic fraction of municipal solid waste as an innovative precursor for the production of bio-based epoxy monomers

    Get PDF
    This paper reports the preparation of newly synthesized bio-epoxy monomers, suitable for replacing petrochemical-derived epoxy resins. An original green method able to produce epoxy monomers starting from neat carbohydrates, waste flours, and even from the organic fraction of municipal solid waste (OFMSW), was here proposed. Hence, for the first time, the epoxidation of carbohydrates was attained only through the exposition to UV and ozone radiation, without using any organic solvent to carry out the reaction. Besides the innovation in the epoxidation method, this work explored the possibility of valorizing waste materials, by recycling carbohydrate scraps; in particular, the exposition of waste flours and municipal solid waste to UV and ozone and their consequent epoxidation allowed obtaining green precursors for the production of a bio-based epoxy resin. Applicability and suitability of the synthesized compounds for epoxy monomers were investigated by curing experiments with a selected amount of a model cycloaliphatic amine-type hardener, i.e. isophorodiamine (IPDA)

    Natural convection from multiple horizontal cylinders arranged side by side

    Get PDF
    Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Steady laminar free convection in air from a row of parallel circular cylinders, is studied numerically. SIMPLE-C algorithm is used for the solution of the mass, momentum, and energy transfer governing equations. Simulations are performed for 10- cylinder assemblies with inter-cylinder spacings from 0.6 to 5 cylinder-diameters and Rayleigh numbers from 101 to 105. It is found that the thermal performance of the whole assembly increases as the Rayleigh number increases, and has a peak at an optimum separation distance among the cylinders which decreases with increasing the Rayleigh number.cs201

    Buoyancy-induced heat transfer from an inclined tube-array

    Get PDF
    Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.No abstract available, please open full text articleSteady laminar free convection in air from an inclined array of parallel circular cylinders, is studied numerically. SIMPLE-C algorithm is used for the solution of the mass, momentum, and energy transfer governing equations. Simulations are performed for tube-arrays consisting of 3 to 7 cylinders equally-spaced at a center-to-center separation distance of 2 cylinder-diameters, tilting angles from 0° to 90° (which correspond to the vertical and horizontal settings, respectively), and Rayleigh numbers in the range between 102 and 106. It is found that the thermal performance of the whole array increases (a) with increasing both the Rayleigh number and the tilting angle, and (b) as the number of cylinders either decreases at small inclinations or increases at large inclinations.cs201
    • …
    corecore