Search results for "conica"

Costruzione omologica e rappresentazione digitale di una sezione conica

2012

La trattazione del luogo geometrico conica assume carattere di grande generalità nell’applicazione dei metodi della Scienza della Rappresentazione. Lo studio teorico e pratico delle proprietà di questa curva trova contributi fin dai tempi antichi delineando, nel corso dei secoli, diversi approcci culturali che tracciano momenti salienti dell’evoluzione del pensiero geometrico/matematico. Risulta affascinante osservare che l’interesse profuso in questo campo di indagine ha delineato vari aspetti legati alla concezione e alla generazione delle linee curve deducendone le proprietà intrinseche. Si espone un’inedita via risolutiva, attraverso procedimenti omologici, per la costruzione del profil…

Aspetti storici delle curve relative ad un triangolo: dalla conica per 9 punti alla cubica per 21 punti

Fra le numerose tematiche legate alla cosiddetta “Geometria del triangolo”, di cui si occuparono nel corso dell’Ottocento eminenti matematici, sicuramente quella relativa alla conica dei nove punti è una delle più interessanti. Tale conica è la naturale generalizzazione del cerchio dei nove punti scoperto nel 1822 da Feuerbach. Nel 1844 Jacob Steiner in un articolo apparso in italiano in una piccola rivista romana, generalizza il cerchio di Feuerbach relativo ad un triangolo al concetto di conica dei nove punti, luogo dei centri del fascio di coniche per i tre vertici del triangolo e per un ulteriore punto interno o esterno al triangolo. Nel 1862 Eugenio Beltrami riguarda la conica dei nove…

Testing jet geometries and disc-jet coupling in the neutron star LMXB 4U 0614 + 091 with the internal shocks model

2020

Multi-wavelength spectral energy distributions of Low Mass X-ray Binaries in the hard state are determined by the emission from a jet, for frequencies up to mid-infrared, and emission from the accretion flow in the optical to X-ray range. In the last years, the flat radio-to-mid-IR spectra of Black Hole (BH) X-ray binaries was described using the internal shocks model, which assumes that the fluctuations in the velocity of the ejecta along the jet are driven by the fluctuations in the accretion flow, described by the X-ray Power Density Spectrum (PDS). In this work we attempt to apply this model for the first time to a Neutron Star (NS) LMXB, i.e. 4U 0614+091. We used the multi-wavelength d…

Ultrafast ring-opening/closing and deactivation channels for a model spiropyran-merocyanine system.

2011

The photochemistry of a model merocyanine-spiropyran system was analyzed theoretically at the MS-CASPT2//SA-CASSCF(14,12) level. Several excited singlet states were studied in both the closed spiropyran and open merocyanine forms, and the paths to the different S(1)/S(0) conical intersections found were analyzed. After absorption of UV light from the spiropyran form, there are two possible ultrafast routes to efficient conversion to the ground state; one involves the rupture of the C(spiro)-O bond leading to the open form and the other involves the lengthening of the C(spiro)-N bond with no photoreaction. From the merocyanine side the excited state can reach a very broad S(1)/S(0) conical i…

Weak intermolecular interactions promote blue luminescence of protonated 2,2′-dipyridylamine salts

2014

In this work we demonstrate that protonation and π-stacking can be exploited to convert non-luminescent 2,2′-dipyridylamine into blue-emitting derivatives. We have synthesized a series of luminescent 2,2′-dipyridylamine (dpa) salts, i.e., (dpaH)X·nSolv (dpa = 2,2′-dipyridylamine, X = HF2, n = 0.5, Solv = H2O 1; X = Cl, n = 2, Solv = H2O 2; X = Br, n = 2, Solv = H2O 3; X = I n = 1, Solv = H2O 4a; X = I n = 1, Solv = CHCl34b), (dpaH)2[SiF6]·H2O 5 and (dpaH)X (X = I36; SbF67; BF48) and characterized their emission properties, both in the solid-state and in solution. To rationalize our observations and relate the luminescence properties to the structure in the solid state and in solution, we ha…

On the use of reduced active space in CASSCF calculations

2014

Abstract The complete active space self-consistent field (CASSCF) method is one of the most used approaches to explore theoretically non-adiabatic photochemical processes in medium-size molecular systems. It is also frequently utilized in direct dynamics studies because this method offers a reliable description of the electronic state mixing in the regions of surface crossings (conical intersections). In this context, however, the large computational demand required to perform such on-the-fly molecular dynamics simulations using CASSCF as the electronic structure method means that only relatively small active space can be handled (typically not more than 10 electrons distributed in 10 orbit…

Polymer Brushes on Flat and Curved Substrates: Scaling Concepts and Computer Simulations

2007

The scaling concepts for isolated flexible macromolecules in good solvent grafted with one chain end to a flat surface (polymer mushrooms) as well as for layers of many overlapping end-grafted chain molecules (polymer brushes) are introduced. Monte Carlo attempts to test these concepts are briefly reviewed. Then the extension of these concepts to polymer brushes grafted to the interior of a cylinder surface is discussed. Molecular Dynamics results on chain average linear dimensions in the direction normal to the grafting surface and in axial direction are described, as well as distribution functions for the density of end monomers and of all monomers of the chains. It is argued that under t…

New and less known Orthoptera (Insecta) from the island of Socotra (Yemen)

2009

A list of nine species of Orthoptera collected on Socotra is reported. Three of them were previously unrecorded on the island (Trigonidium cicindeloides, Paratettix subpustulatus and Acrotylus insubricus) and one (Ochrilidia socotrae n.sp.) was undescribed. Further systematic notes on Glomeremus pileatus, G. mediopictus, Pyrgomorpha conica tereticornis, Acrotylus incarnatus and Sphingonotus insularis are included. The East African Acrotylus meruensis, previously considered synonym of A. incarnatus, is proposed as a valid species, distinct from the latter.

Parole e immagini riflesse nei romanzi di Consolo.

2013

Il saggio evidenzia l'originalità della sperimentazione stilistica di Consolo ed esamina la costruzione iconologica di due romanzi storici, "Il sorriso dell’ignoto marinaio" e "Lo spasimo di Palermo". L’adozione di una prospettiva iconica è la strategia retorica con cui lo scrittore siciliano formalizza procedimenti di irradiazione metaforica e di correlazione analogica. L’intensità problematica dell’invenzione storica si dispone in una rete complessa di simmetrie e antitesi tra segni pittorici e narrativi, e si articola come flusso metonimico di immagini in grado di rifigurare materiali e forme del Romanzo moderno. The study highlights the originality of Consolo's stylistic experimentation…

Scenery Flow, Conical Densities, and Rectifiability

2015

We present an application of the recently developed ergodic theoretic machinery on scenery flows to a classical geometric measure theoretic problem in Euclidean spaces. We also review the enhancements to the theory required in our work. Our main result is a sharp version of the conical density theorem, which we reduce to a question on rectifiability.