Polytechnic University of Milan

About: Polytechnic University of Milan is a education organization based out in Milan, Italy. It is known for research contribution in the topics: Computer science & Finite element method. The organization has 18231 authors who have published 58416 publications receiving 1229711 citations. The organization is also known as: PoliMi & L-NESS.

High mechanical performance of fibre reinforced cementitious composites: the role of “casting-flow induced” fibre orientation

Abstract: Governing the dispersion and the orientation of fibres in concrete through a suitably balanced set of fresh state properties and a carefully designed casting procedure, is a feasible and cost-effective way to achieve a superior mechanical performance of fibre reinforced cementitious composites, which may be required by the intended application, even keeping the fibre content at relatively low values (e.g. around 1% by volume). In this paper the possibility of pursuing the above said “integrated” approach has been addressed in the framework of larger project focused on developing a deflection-hardening FRCC (DHFRCC), reinforced with 100 kg/m3 (1.27% by volume) of short steel fibres (13 mm long and 0.16 mm in diameter). The material has to be employed to manufacture thin (30 mm) roof elements, without any kind of conventional reinforcement, which have been anticipated to work, as simply supported beams, over a 2.5 m span. The study hence paves the way to the possibility of exploiting at an industrial level the correlation among fresh state performance, fibre dispersion and hardened state properties of self consolidating steel fibre reinforced concrete to achieve enhanced structural performance tailored to the specific application.

Photosynthetic light harvesting by carotenoids: detection of an intermediate excited state.

Abstract: We present the first direct evidence of the presence of an intermediate singlet excited state (Sx) mediating the internal conversion from S2 to S1 in carotenoids. The S2 to Sx transition is extremely fast and is completed within approximately 50 femtoseconds. These results require a reassessment of the energy transfer pathways from carotenoids to chlorophylls in the primary step of photosynthesis.

Topological Phase Transition in non-Hermitian Quasicrystals.

Abstract: The discovery of topological phases in non-Hermitian open classical and quantum systems challenges our current understanding of topological order. Non-Hermitian systems exhibit unique features with no counterparts in topological Hermitian models, such as failure of the conventional bulk-boundary correspondence and non-Hermitian skin effect. Advances in the understanding of the topological properties of non-Hermitian lattices with translational invariance have been reported in several recent studies; however little is known about non-Hermitian quasicrystals. Here we disclose topological phases in a quasicrystal with parity-time (PT) symmetry, described by a non-Hermitian extension of the Aubry-Andre-Harper model. It is shown that the metal-insulating phase transition, observed at the PT symmetry breaking point, is of topological nature and can be expressed in terms of a winding number. A photonic realization of a non-Hermitian quasicrystal is also suggested.

Controlling competing photochemical reactions stabilizes perovskite solar cells

Abstract: Metal halide perovskites have become a popular material system for fabricating photovoltaics and various optoelectronic devices. However, long-term reliability must be assured. Instabilities are manifested as light-induced ion migration and segregation, which can lead to material degradation. Discordant reports have shown a beneficial role of ion migration under illumination, leading to defect healing. By combining ab initio simulations with photoluminescence measurements under controlled conditions, we demonstrate that photo-instabilities are related to light-induced formation and annihilation of defects acting as carrier trap states. We show that these phenomena coexist and compete. In particular, long-living carrier traps related to halide defects trigger photoinduced material transformations, driving both processes. Defect formation can be controlled by blocking under-coordinated surface sites, which act as a defect reservoir. By use of a passivation strategy we are thus able to stabilize the perovskite layer, leading to improved optoelectronic material quality and enhanced photostability in solar cells. The photo-instability of perovskite solar cells is investigated and controlled by the use of a passivation strategy.

Structural synthesis of 'parallel' robots generating spatial translation

Abstract: Presents a tool, based on the mathematical group theory, for the synthesis of new parallel structure robots. By the kinematic principle of displacement subgroups intersection a family of 3 degrees of freedom robots for pure spatial translation movements is conceived. One of the many possible implementations is also given as an example. >