1,721,000 research outputs found
Pressure Effects on Water Dynamics by Time-Resolved Optical Kerr Effect
Full text linkDespite water being the most common and most widely studied substance in the world, it still presents unknown aspects. In particular, water shows several thermodynamic and dynamical anomalies in the liquid and supercooled metastable phases, and the natures of these phases are still hotly debated. Here, we report measurements of water using the optical Kerr effect as a function of pressure along two isotherms, at 273 K from 0.1 to 750 MPa and at 297 K from 0.1 to 1350 MPa, reaching the supercooled metastable phase. The structural relaxation and the low frequency vibrational dynamics of water show a peculiar pressure dependence similar to that of other dynamical properties. The data analysis suggests the presence in the water phase diagram of a crossover area that divides two regions characterized by different dynamic regimes, which appear to be related to two liquid forms, one dominated by the high density water and the other by the low density water
Superheating and Homogeneous Melting Dynamics of Bulk Ice
No full textHomogeneous melting of crystals is a complex multistep process involving the formation of transient states at temperatures considerably higher than the melting point. The nature and persistence of these metastable structures are intimately connected to the melting process, and a precise definition of the temporal boundaries of these phenomena is not yet available. We set up a specifically designed experiment to probe by transient infrared absorption spectroscopy the entire dynamics, ranging from tens of picoseconds to microseconds, of superheating and melting of an ice crystal. In spite of a large excess of energy provided, only about 30% of the micrometric crystal liquefies in the first 20-25 ns because of the long persistence of the superheated metastable phase that extends for more than 100 ns. This behavior is ascribed to the population of low-energy states that trap a large amount of energy, favoring the formation of a metastable, likely plastic, ice phase
Pressure Dependence of Hydrogen-Bond Dynamics in Liquid Water Probed by Ultrafast Infrared Spectroscopy
Full text linkClarifying the structure/dynamics relation of water hydrogen-bond network has been the aim of extensive research over many decades. By joining anvil cell high-pressure technology, femtosecond 2D infrared spectroscopy, and molecular dynamics simulations, we studied, for the first time, the spectral diffusion of the stretching frequency of an HOD impurity in liquid water as a function of pressure. Our experimental and simulation results concordantly demonstrate that the rate of spectral diffusion is almost insensitive to the applied pressure. This behavior is in contrast with the previously reported pressure-induced speed up of the orientational dynamics, which can be rationalized in terms of large angular jumps involving sudden switching between two hydrogen-bonded configurations. The different trend of the spectral diffusion can be, instead, inferred considering that the first solvation shell preserves the tetrahedral structure with pressure and the OD stretching frequency is only slight perturbed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Change in work management for facilities services : Tenaris-Dalmine case of information system implementation
No full textLAUREA MAGISTRALEIl fine principale della tesi è la costituzione di un framework di analisi per mappare il processo di cambiamento verso un nuovo sistema informativo di gestione degli interventi di manutenzione relativi ai servizi di Facility Management. Il caso studio di applicazione di tale framework è la realtà aziendale di TenarisDalmine.
Il lavoro si sviluppa in due parti: una prima parte teorica ed una seconda parte di applicazione pratica.
La prima parte considera il fenomeno del cambiamento attraverso una prospettiva iniziale di carattere generale. Successivamente, lo studio assume una connotazione più specifica: cambiamento inteso come implementazione del sistema informativo nelle organizazzioni. Alla fine di questa fase avviene la costituzione del framework di analisi dell’implementazione del sistema informativo per il Facility Management.
Nella seconda fase, si applica il framework di analisi alla realtà aziendale. Il fine è quello di studiare da vicino il processo di cambiamento che ha portato ad un nuovo modello di gestione delle attività manutentive grazie all’implementazione del sistema informativo.
A seguito dell’implementazione, i risultati mostrano prima di tutto alcuni radicali miglioramenti della capacità di controllo della commessa di Facility Management.
In secondo luogo, si appura la vera natura del sistema informativo: uno strumento per la creazione di nuova conoscenza.The main purpose of the work is the establishment of an analytical framework aiming to map the change process towards a new information system for management of maintenance activities relating to Facility Management services. The case study of the application of this framework is the business reality of TenarisDalmine.
The work is divided into two parts: the first theoretical part and the second part of practical application.
The first part considers the change phenomenon through an initial general perspective. Subsequently, the study takes a more specific connotation: change understood as information system implementation within organizations. Finally, the creation of the framework of analysis for information system implementation concerning Facility Management takes place in this phase.
In the second part of the work, the application of the analytical framework to the business reality takes place. The aim is to study the process of change that leads to a new management model of maintenance activities based on the newly-implemented information system.
After the implementation, the results show several radical improvements of the control capability of Facility Management commission.
Then, the true nature of the information system arises: a tool able to create new knowledge
Picosecond optical parametric generator and amplifier for large temperature-jump
No full textAn optical parametric generator and amplifier producing 15 ps pulses at wavelengths tunable around 2 μm, with energies up to 15 mJ/pulse, has been realized and characterized. The output wavelength is chosen to match a vibrational combination band of water. By measuring the induced birefringence changes we prove that a single pulse is able to completely melt samples of ice in the 10−6 cm3 volume range, both at room pressure (263 K) and at high pressure (298 K, 1 GPa) in a sapphire anvil cell. This source opens the possibility of studying melting and freezing processes by spectroscopic probes in water or water solutions in a wide range of conditions as found in natural environments
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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