1,587 research outputs found
Diffusion Monte Carlo simulations of gas phase and adsorbed D2-(H2)n clusters
No full textWe have computed ground state energies and analyzed radial distributions for several gas phase and adsorbed D2(H2)nand HD(H2)nclusters. An external model potential designed to mimic ionic adsorption sites inside porous materials is used [M. Mella and E. Curotto, J. Phys. Chem. A 121, 5005 (2017)]. The isotopic substitution lowers the ground state energies by the expected amount based on the mass differences when these are compared with the energies of the pure clusters in the gas phase. A similar impact is found for adsorbed aggregates. The dissociation energy of D2from the adsorbed clusters is always much higher than that of H2from both pure and doped aggregates. Radial distributions of D2and H2are compared for both the gas phase and adsorbed species. For the gas phase clusters, two types of hydrogen-hydrogen interactions are considered: one based on the assumption that rotations and translations are adiabatically decoupled and the other based on nonisotropic four-dimensional potential. In the gas phase clusters of sufficiently large size, we find the heavier isotopomer more likely to be near the center of mass. However, there is a considerable overlap among the radial distributions of the two species. For the adsorbed clusters, we invariably find the heavy isotope located closer to the attractive interaction source than H2, and at the periphery of the aggregate, H2molecules being substantially excluded from the interaction with the source. This finding rationalizes the dissociation energy results. For D2-(H2)nclusters with nâ ¥12, such preference leads to the desorption of D2from the aggregate, a phenomenon driven by the minimization of the total energy that can be obtained by reducing the confinement of (H2)12. The same happens for (H2)13, indicating that such an effect may be quite general and impact on the absorption of quantum species inside porous materials
Exciplexes with Ionic Dopants: Stability, Structure and Experimental Relevance of M+(2P)Hen(M=Sr, Ba)
No full textM+(2P)4Hen species, possibly involved in the post 2P ← 2S excitation dynamics of Sr+ and Ba+ in cold 4He gas or droplets, are studied employing both high level ab initio calculations to determine the potential energy curves (PEC) and diffusion Monte Carlo (DMC) to obtain information on their ground state structure and energetics. PEC for the excited M+(2P)He dimers were obtained using MRCI calculations with extended basis sets. Potential energy surfaces (PES) for M+( 2P)Hen were built with the DIM model including spin-orbit coupling via a perturbative procedure. DMC simulations indicated several exciplexes (n > 2) to be stable against He dissociation whatever the ion state, a finding that is at variance with what was previously suggested for Ba+(2P1/2) due to the repulsive nature of the interaction potential obtained in [ Phys. Rev. A 2004, 69, 042505 ]. Our results, instead, support the suggestion made in [ J. Chem. Phys. 2012, 137, 051102 ] for the existence of Ba+(2P1/2)He n exciplexes emitted following the excitation of the barium cation solvated into He droplets. In the 2P1/2 state, the Ba ion also shows a peculiar behavior as a function of n with respect to the location and binding strength of the attached He atoms compared to Sr+. Although the latter forms the usual equatorial He ring, Ba+ deviates from this geometry for 1 ≤ n ≤ 4, with the radial distribution functions strongly depending on the number of solvent atoms. Finally, a putative species is proposed to explain the emission band at 523 nm that follows D1 or D2 excitation of Ba+ in superfluid bulk helium
#-Minimal models of uniruled 3-folds
No full textWI study varieties with a big linear system of uniruled surfaces with applications to special classification and classical problem
Structural properties of hydrophilic polymeric chains bearing covalently-linked hydrophobic substituents: Exploring the effects of chain length, fractional loading and hydrophobic interaction strength with coarse grained potentials and Monte Carlo simulations
No full textChemical and physical properties of polymeric species in solution strongly depend on their structure, which can be modulated by covalently linking substituents of different solubility. In this work, the effect of changing the interaction strength and fractional loading of hydrophobic substituents on semi-flexible hydrophilic polymers of varying chain length is studied by means of Monte Carlo simulations and coarse grained model potentials. The latter are chosen in order to provide a more factual representation of a chain in diluted solution, introducing substituent flexibility and realistic torsional and bending potentials. Upon increasing the number and the interaction strength of the substituents, our results indicate a less steep rise of the chain gyration radius and "end to end" distance for the chain length than predicted for an unsubstituted polymer in an almost good solvent. Moreover, a "disordered to compact" structural transition appears. In parallel, the formation of hydrophobic nuclei and the consequent appearance of flexible polymer loops grafted to the semi-rigid cores is witnessed. The core formation resembles a nucleation phenomenon, where the change in the interaction between the substituents modulates the free energy surface for the aggregation process similarly to the change in chemical potential. Interestingly, it has been found that a single chain containing a sufficiently high number of interacting substituents may give rise to the formation of multiple cores, suggesting that the chain stiffness may play a role in defining the structure of the free energy minimum. (C) 2010 Elsevier Ltd. All rights reserved
L’integrazione tra CSR e shareholder value
No full textLa necessità che l’impresa debba prendere in considerazione e soddisfare in modo equilibrato i bisogni e gli interessi di tutti gli stakeholder era già stata ampiamente evidenziata dagli economisti afferenti alla scuola comportamentista (Simon, 1961; Cyert, March, 1955). In tal senso, soprattutto con riferimento alle imprese di dimensioni medio-grandi, la creazione di valore, tipica finalità riferita agli stockholder, deve farsi rientrare nel processo di ottimizzazione di una funzione obiettivo più ampia e complessa, che deriva da un “compromesso politico” di finalità di diverse classi di stakeholders. In particolare, tale funzione deve essere compatibile con le esigenze dell’ambiente esterno, tenendo conto dell’influenza delle radici culturali in un contesto di Corporate Social Responsibility (CSR) (Mella, Gazzola, 2005).
La grave crisi finanziaria che ha investito, dapprima, gli Stati Uniti e, in seguito, i paesi europei e i numerosi scandali, degli anni recenti, per corruzione dei manager e falsi in bilancio, hanno reso necessaria un’integrazione sempre più profonda tra l’obiettivo della shareholder value e le practices in termini di CSR, in passato maggiormente diffuse nel contesto europeo.
La presenza di interessi contrapposti, sia all’interno che all’esterno dell’impresa, genera la possibilità che si creino situazioni di conflitto tra i gruppi portatori di tali interessi; il profitto stesso dipende dalla misura in cui sono soddisfatti gli interessi contrapposti e dal modo in cui è data risoluzione ai conflitti interni ed esterni. In presenza di una funzione obiettivo multidimensionale, il principio di razionalità nelle scelte d’impresa deve essere adattato proprio per tenere conto del sistema dei vincoli posti dagli stakeholder.
Le motivazioni di questa integrazione profonda tra gli interessi degli shareholder e quelli degli altri stakeholder rivelano sia che l’impresa assume connotati sempre più importanti, in particolare nelle comunità locali a garanzia del tessuto sociale e lavorativo, sia l’influenza sempre più forte dell’immagine aziendale che si riflette inevitabilmente sulle scelte degli investitori e dei consumatori in primis e su quelle di tutti gli altri stakeholder.
Questo studio si pone l’obiettivo di descrivere come si possano individuare principi di management responsabile che, pur derivando da culture diverse, se legati insieme, consentono una più significativa comprensione del comportamento delle imprese moderne. L’analisi della letteratura proposta a livello internazionale sarà corredata dai risultati ottenuti da una ricerca empirica estesa a imprese italiane, dai tipici connotati culturali latini
Systems Thinking. Intelligence in action.
No full textThe core belief underlying this book is that the most useful and effective models to strengthen our intelligence are system ones, developed following the logic of Systems Thinking. Such models can explore complexity, dynamics, and change, and it is the author s view that intelligence depends on the ability to construct models of this nature. The book is designed to allow the reader not only to acquire simple information on Systems Thinking but above all to gradually learn the logic and techniques that make this way of thinking an instrument for the improvement of intelligence. In order to aid the learning and practice of the Systems Thinking discipline, the author has abandoned a rigid formal language for a more discursive style. He writes in the first person, with an ample number of citations and critical analyses, and without ever giving in to the temptation to use formal mathematics
Birational geometry of quartic 3-folds II: the importance of being Q-factorial
No full textThe paper explores the birational geometry of terminal quartic 3-folds. In doing this I develop a new approach to study maximal singularities with positive dimensional centers. This allows to determine the pliability of a Q-factorial quartic with ordinary double points, and it shows the importance of Q-factoriality in the context of birational geometry of uniruled 3-folds
Morphisms of projective varieties from the viewpoint of Minimal Model Theory
No full textDescription of results and techniques in the MMP applied to biregular and birational geometr
Contractions on a manifold polarized by an ample vector bundle
No full textA complex manifold X of dimension n together with an ample vector bundle E on it will be called a generalized polarized variety. The adjoint bundle of the pair (X,E) is the line bundle KX + det(E). We study the positivity (the nefness or ampleness) of the adjoint bundle in the case r := rank(E) = (n - 2). If r ≥ (n - 1) this was previously done in a series of papers by Ye and Zhang, by Fujita, and by Andreatta, Ballico and Wisniewski. If KX + detE is nef then, by the Kawamata-Shokurov base point free theorem, it supports a contraction; i.e. a map π : X → W from X onto a normal projective variety W with connected fiber and such that KX + det(E) = π*H, for some ample line bundle H on W. We describe those contractions for which dimF ≤ (r - 1). We extend this result to the case in which X has log terminal singularities. In particular this gives Mukai's conjecture 1 for singular varieties. We consider also the case in which dimF = r for every fiber and π is birational. ©1997 American Mathematical Society
Separating hydrogen isotopologues via kinetic quantum sieving: Understanding important pore characteristics for an efficient separation
No full textThe potential performance of porous membranes in separating hydrogen isotopologues has been explored employing model systems and quanto-mechanical calculations including both zero-point energy and a numerically exact description of tunneling effects along the reaction coordinate. Membranes have been modeled as cylindrically pierced impenetrable wall, whereas diatomic molecules are described as dumbells composed of hard-sphere atoms. With the relative energetics of diatomics confined into cylindrical pores suggesting that differences in the adiabatic energy profiles between isotopologues for pore radii lower than 2.1 & Aring; should favor transport of heavier species, we investigated the selectivity for the latter process when membranes are 2.0 & Aring; thick. Chosen a pore radius, the results suggest that non-interacting pores represent the best compromise between selectivity and permeance, the addition of attraction between the membrane walls and molecular projectiles improving permeance while markedly depressing selectivity. A repulsive interaction with the pore inner surface, instead, reduced both properties. Finally, sieving molecules through a double membrane layer was found to marginally impact on the separation properties, which could be improved, at best, by 25% with a careful selection of the inter-membrane distance. Our results appear useful for the process of designing more effective sieving systems to separate di-deuterium molecules from its lighter counterparts
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