Instrument for mimicking fast cooling conditions of polymers: Design and case studies on polypropylene

Abstract The complete understanding of polymers crystallization kinetic in real industrial processes is fundamental for designing materials towards specific applications. Hereby, we propose a method for fast cooling preparation of polymers by means of air and water sprays, which presents several enhancements with respect to previous similar devices. The new device was built in order to fulfill safety and cleaning standards required in an industrial environment. Furthermore, the small dimensions and the limited costs enable its implementation in any laboratory. Moreover, preliminary results on selected isotactic-polypropylenes (iPP) were obtained in a cooling range from 0.01 to a few thousand °C/s, in order to validate the present method by comparison with previous literature results and to highlight the large range of studies that can be carried out with this set-up. Ex-situ analysis with WAXS, DSC and AFM techniques were performed to characterize such prepared samples

Analysis of Composite Space Structures Subjected to Loading Factor

Reinforced structures are mandatory in the space structures on which the lightweight is the main project parameter. The coupling between simple thin-walled plate and different systems of ribs or beams along one or more directions make it possible to meet the requirements of lightness and strength. During the project phase a structure is usually analysed via Finite Element Method (FEM), where different approaches can be used but the pointed out one common essential characteristic, a mesh discretization of a continuous domain into a set of discrete subdomains, usually called elements. Three main finite elements (FEs) are widely used in the commercial code, but only the Solid (3D) FE represents more faithfully the behaviour of a real structure. The solid FE models require a large number of degrees of freedoms (DOFs) and therefore the analyses are computational expensive [1]. For these reason that usually the reduced models are used as substitute of solid models. The reduced models are made using shell (2D) and beam (1D) FEs, and they are suitable to build a reinforced structure, in fact the shell are used for the skin and the beam for the stringers. The present work uses a refined 1D model based on the Carrera Unified Formulation (CUF) [2] to analyse space structures made coupling skin and stringers. Thanks to its refined cinematic the present model can be used to represent both skin and stringers. The whole structure is obtained connecting simple one-dimensional structures using a new approach called Component-Wise (CW) [3]. This is possible because the unknowns are only displacements. Free-vibration analysis of isotropic and composite space structures with non-structural masses and loading factor are considered. A space vehicle is inspired to Arian 5 with a central body, on which the cryogenic fuel and the payload are accommodated, and two lateral boosters, on which solid fuel is stored. The results show the quasi-3D capabilities of the present 1D CUF model and the coupling with the CW approach provide accurate results nearest to solid FE results than the classical refined FEs models. In conclusion the present 1D refined model appears suitable for the analysis of reinforced thin-walled structures, it provides accurate results with the benefit to reduce the computational costs with respect to the classical refined FE approaches. References [1] E. Carrera, E. Zappino and T. Cavallo. Accurate free vibration analysis of launcher structures using refined 1D models. International Journal of Aeronautical and Space Sciences,vol. 16(2) 206-222, 2015. [2] E. Carrera, G. Giunta and M. Petrolo. Beam Structures: Classical and Advanced Theories. Jhon Wiley & Sons Ltd, 2011. [3] E. Carrera, A. Pagani and M. Petrolo. Component-wise Method Applied to Vibration of Wing Structures. J Appl Mech, vol. 80(4), 041012-1-041012-15, 2013

Fractionated stereotactic conformal radiotherapy for large benign skull base meningiomas

<p>Abstract</p> <p>Purpose</p> <p>to assess the safety and efficacy of fractionated stereotactic radiotherapy (FSRT) for large skull base meningiomas.</p> <p>Methods and Materials</p> <p>Fifty-two patients with large skull base meningiomas aged 34-74 years (median age 56 years) were treated with FSRT between June 2004 and August 2009. All patients received FSRT for residual or progressive meningiomas more than 4 centimeters in greatest dimension. The median GTV was 35.4 cm³(range 24.1-94.9 cm³), and the median PTV was 47.6 cm³(range 33.5-142.7 cm³). Treatment volumes were achieved with 5-8 noncoplanar beams shaped using a micromultileaf collimator (MLC). Treatment was delivered in 30 daily fractions over 6 weeks to a total dose of 50 Gy using 6 MV photons. Outcome was assessed prospectively.</p> <p>Results</p> <p>At a median follow-up of 42 months (range 9-72 months) the 3-year and 5-year progression-free survival (PFS) rates were 96% and 93%, respectively, and survival was 100%. Three patients required further debulking surgery for progressive disease. Hypopituitarism was the most commonly reported late complication, with a new hormone pituitary deficit occurring in 10 (19%) of patients. Clinically significant late neurological toxicity was observed in 3 (5.5%) patients consisting of worsening of pre-existing cranial deficits.</p> <p>Conclusion</p> <p>FSRT as a high-precision technique of localized RT is suitable for the treatment of large skull base meningiomas. The local control is comparable to that reported following conventional external beam RT. Longer follow-up is required to assess long term efficacy and toxicity, particularly in terms of potential reduction of treatment-related late toxicity.</p

Surface-enhanced nucleation in immiscible polypropylene and polyethylene blends: The effect of polyethylene chain regularity

In blends where polyethylene (PE) is the minor component dispersed in an isotactic-polypropylene (PP) matrix, an enhancement of the crystallization rate of PE was found when the crystallization temperature of the matrix phase is increased by means of a self-nucleation protocol. Such an effect is interpreted as the result of the epitaxial nucleation of PE droplet domains at the interface with the PP matrix (Macromolecules, 2021, 54, 19, 9100–9112). This study extends the findings on immiscible blends of a PP matrix and various industrially produced PE grades as the dispersed phase. Eight different PEs with varying molecular architecture, and thus density and melting temperatures, were mixed with PP in a 20/80 PE/PP weight ratio. The possible existence of surface nucleation was probed by applying a self-nucleation thermal protocol to the PP matrix and recording the concomitant variation of PE crystallization temperature (Tc). Different behaviours are observed for various PEs. In particular, those with relatively high density display a clear increase in crystallization temperature, over 3.0 °C, when the Tc of the matrix is increased (i.e., as PP lamellar thickness increased), indicating an efficient surface nucleation mechanism. Metallocene-made LLDPE also shows a small increase, about 1.7 °C, while PEs with lower densities, below 927 kg/m3, metallocene PEs or LDPE display no meaningful change in Tc with matrix self-nucleation. It was demonstrated that a threshold value of chain regularity is required to trigger the surface nucleation of PE on PP. Only polymers with a density above approximately 920 kg/m3 and melting temperatures exceeding about 115 °C can efficiently nucleate onto the PP substrate. It is postulated that the presence of a high amount of branches or comonomers along the PE chains hinders the epitaxial matching between PE and PP.This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 860221. AJM acknowledges funding from the Basque Government through grant IT1503-22

A workflow to generate physical 3D models of cerebral aneurysms applying open source freeware for CAD modeling and 3D printing

Objectives: 3D anatomical models are becoming a new frontier in surgery for planning and simulation on an individualized patient specific basis. Since 1999, 3D cerebral aneurysms models for neurosurgery have been proposed. The possibility of reproducing in a realistic 3D fashion the malformation with the surrounding vascular structures, provides important preoperative information for the treatment strategy. The same models can be used for training and teaching.Unfortunately stereolitography is often burdened by high costs and long times of production. These factors limit the possibility to use 3D models to plan surgeries in an easy daily fashion. Patients and methods: Our study enrolled 5 patients harboring cerebral aneurysms. DICOM data of each aneurysm were elaborated by an open source freeware to obtain CAD molds. Afterwards, the 3D models were produced using a fused deposition or a stereolitography printer. Results: Models were evaluated by Neurosurgeons in terms of quality and usefulness for surgical planning. Costs and times of production were recorded. Conclusions: Models were reliable, economically affordable and quick to produce. Keywords: Stereolitography, Cerebral aneurysms, 3D printing, Surgical planning, Aneurysm model

Hypopigmentation as a diagnostic clue in primary extramammary Paget disease: Case report and short literature review

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