1,721,212 research outputs found
L'effetto Raman di noncoincidenza della seconda armonica del modo vibrazionale di stretching C=O dell'acetone
No full textLa separazione spettrale tra i momenti primi della componente anisotropa ed isotropa della banda Raman associata ad un modo vibrazionale avente un elevato valore della derivata del momento di dipolo elettrico, cioè il cosiddetto effetto di noncoincidenza (NCE), è un’osservabile accessibile per via spettroscopica che rivela l’occorrenza di accoppiamenti vibrazionali di risonanti za tra molecole adiacenti all’interno di un liquido molecolare, vedi [1] e referenze ivi allegate.
In pubblicazioni antecedenti abbiamo riportato risultati sperimentali e di simulazione sull’effetto di noncoincidenza NCE(3) del modo vibrazionale di stretching 3 dell’acetone (C=O) in funzione della sua diluizione in miscele chimiche ed isotopiche [2-3].
Il presente lavoro si concentra sull’effetto di noncoincidenza NCE(23) della seconda armonica 23, il quale manifesta una separazione spettrale tra i momenti primi dei picchi anisotropi ed isotropi di entità comparabile a NCE(3), ma di segno opposto, causato dal picco isotropo 23 a circa 3413.9 cm-1 e dal picco anisotropo 23 a circa 3407.5 cm-1 [3].
Questo contributo scientifico presenta l’attuale stato dello studio sperimentale e di simulazione sul NCE(23).
Bibliografia
[1] Torii H., “Computational methods for analyzing the intermolecular resonant vibrational interactions in liquids and the noncoincidence effect of vibrational spectra”, in Novel Approaches to the Structure and Dynamics of Liquids: Experiments, Theories and Simulations, Samios J. and Durov V.A. (Eds.), Kluver, pp. 343-360 (2004).
[2] M. Musso, M.G. Giorgini, H. Torii, R. Dorka, D. Schiel, A. Asenbaum, D. Keutel, K.L. Oehme, J. Molec. Liquids 2006, 125, 115.
[3] M. Musso, M.G. Giorgini, H. Torii, J. Molec. Liquids 2009, 147, 37
L'organizzazione strutturale di liquidi dipolari in soluzioni elettrolitiche rivelata dall'effetto di noncoincidenza Raman: il caso ddelle soluzioni d Li+/Carbonato di Propilene (PC) e Li+/(PC+DMC)
No full textNegli ultimi anni sono state raccolte svariate evidenze che indicano che l’effetto di noncoincidenza (NCE), ovvero la separazione spettrale fra il profilo anisotropo ed isotropo di una banda Raman totalsimmetrica, costituisca un osservabile spettroscopico intimamente correlato con la struttura microscopica di un liquido molecolare. Nell’ambito di una estesa attività spettroscopica rivolta a stabilire questa correlazione, abbiamo recentemente indagato le alterazioni che NCE della banda (C=O) di solventi carbonilici subisce come conseguenza della presenza di ioni alcalini ed alcalino terrosi in soluzioni elettrolitiche [1,2]. L’uso congiunto di calcoli quanto chimici ci ha permesso di stabilire in modo inequivocabile una correlazione fra il valore negativo di NCE osservato per questa banda in una soluzione Li+/acetone e la struttura delle specie clusterizzate Mm+(acetone)n presenti nelle soluzioni elettrolitiche e di giustificare il progressivo aumento del valore negativo di NCE della banda (C=O) con l’aumento della densità di carica dello ione Mm+.
Per la rilevanza rivestita dal Carbonato di Propylene (PC) come solvente nello sviluppo di batterie secondarie per la sua elevata permettività elettrica (=64) abbiamo esteso lo studio di NCE a soluzioni elettrolitiche Li+/PC. Il valore di NCE che per la banda (C=O) di PC puro risulta piccolo e positivo (NCE=5 cm-1), e cambia in modo molto evidente in soluzione Li+/PC (xLi+=0.09), diventando negativo e molto grande (NCEexper. =-41 cm-1 ), come atteso, per la formazione di clusters Li+(PC)n. I calcoli quanto chimici dello spettro Raman anisotropo ed isotropo della banda (C=O) condotto per svariati clusters Li+/(PC)n (n=2, 3, e 4) indicano che l’osservazione di un valore negativo così elevato di NCE è compatibile solo con la formazione della specie con n=4 (NCEcalc(n=2)=....., NCEcalc (n=3), NCEcalc (n=4) = -35 cm-1) in cui i quattro gruppi C=O puntano tetraedricamente verso lo ione Li+ (gruppo di punti Td).
Abbiamo esteso questo tipo di indagine ad altri solventi carbolinilici come dietil (DEC) ed etil-metil (EC) carbonato che sono usati spesso come co-solventi nelle batterie al litio per ridurre la viscosità della soluzione elettrolitica Li/PC. Risultati preliminari condotti su una soluzione equimolare di PC/DEC sembrano indicare una solvatazione preferenziale di Li+ da parte del PC.
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Bibliografia
[1] M. G. Giorgini, H. Torii, M. Musso, G. P. Venditti, J. Phys. Chem. B 112, 7506 (2008).
[2] M. G. Giorgini, H. Torii, M. Musso, Phys. Chem. Chem. Phys. 12, 183 (2010)
The structural organization of organic eklectrolytic solutions probed by the Raman noncoincidence effect: experimental and quantum chemical results
No full textThe structural organization of organic electrolytic solutions probed by the Raman noncoincidence effect: experimental and quantum chemical results.
M. G. Giorgini1, H. Torii2, M. Musso3
1 Dipartimento di Chimica Fisica ed Inorganica, Università di Bologna, Viale del
Risorgimento 4, I-40136 Bologna, Italy.
2 Department of Chemistry, School of Education, Shizuoka University, 836
Ohya, Shizuoka 422-8529, Japan.
3 Fachbereich Materialforschung und Physik, Abteilung Physik und Biophysik,
Universität Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria
Electrolytic solutions (M+X/Solvent) are of noteworthy importance in both technological [1] and biological solvation processes [2]. The mobility of ions and their activity within a solution strongly depend on its structure at molecular level and then on the specific interactions between ions and between ions and solvent molecules. Ion pairs (M+--X) and solvent clusters M+(S)n formation is expected as a consequence of these interactions. Recently we have investigated the liquid structure of electrolytic solutions of mono-valent (M+ = Li+, Na+) salts in carbonyl solvents by making use of the Raman noncoincidence effect (NCE) of the solvent (C=O) band and, with the joint use of ab initio molecular orbital quantum-chemical calculations, we have been able to assess the formation of cluster species M+(S)n [3]. NCE, i.e. the difference between the spectral first moments, M, of the anisotropic and isotropic profiles of a Raman band of a totally symmetric vibrational mode, is indicated as a reliable probe of the liquid organization. We have found [3] that the observed large and negative NCE of the (C=O) band is a consequence of the formation of clusters species M+(S)n made of n C=O groups of solvent molecules (S) pointing towards the M+ cation in a tetrahedral (n = 4, Li+) and octahedral (n = 6, Na+) organization. Now we have extended these investigations to electrolytic solutions of bi-valent cations, Mg2+, Ca2+, Sr2+, and Ba2+, to shed light on the effect of the increased strength of the electric field on NCE and assess, on a quantum chemical basis, the formation of M2+(S)n clusters. Our observations indicate a remarkable increase of the negative NCE (34.2 cm-1 in Mg2+/acetone and 21.1 cm-1 in Ba2+/acetone solutions, in Figure 1a) as compared with those found in the singly charged ions (e.g., –16.0 cm-1 in Na+/acetone) [3].
The NCE calculated for the species (acetone)nMg2+ with n = 3, 4 and 6 suggests the formation, in the Mg2+/acetone solution, of the n = 6 cluster species (NCE= 35.1 cm-1) in which six carbonyl groups are pointing towards the Mg2+ ion in an octahedral organization, as illustrated in Figure 1b.
1. J. McBreen, H.S. Lee, X. Q. Yang, X. Sun, J. Power Sources 89, 163 (2000).
2. D. Vaden, J. M. Lisy, Chem. Phys. Lett. 408, 54 (2005).
3. M. G. Giorgini, H. Torii, G. Venditti, M. Musso, J. Phys. Chem B, 112, 7506 (2008).
Figure 1. a) Isotropic and anisotropic Raman profiles of the (C=O) band of acetone/M2+ solutions with M = Mg, Ca, Ba (in red, blue, and green, respectively), where B and C indicate the “bulk” and “cluster” components of the band, and those of neat liquid acetone (in black); b) Cluster of six acetone molecules pointing towards the Mg2+ ion in an octahedral organization
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
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
"Metodi di ricerca basato sulle caratteristiche geometriche delle orbite per sky search in sistemi GPS"
No full text"Theoretical Analysis of S-curve for GNSS System"
No full textThe GPS system improvement and the Galileo system development will increase the signal availability and therefore the GNSS system-based applications. The great evolution of GNSS based application will imply the growth of precise and fast navigation systems. The performances of GNSS systems are mostly influenced by the accuracy of the synchronization modules. In fact, loss of fine tracking means a less precise position estimation. In urban environment the receiver measurement is usually affected by errors, especially caused by multipath fading. For this cause could be useful to analyze the performances of different methodologies to solve this problem proposed in literature. In this paper, a theoretical model valid for the analysis of synchronization performances in GNSS receivers in a urban environment is proposed. The proposed model is studied under the presence of two important cause of disturbances, named gaussian noise and multipath, in the received signal. In general the S-curve is shown in the ideal case, without any source of noise. A model can permit to recognise the presence of different type of noise that act on the received signal. The validation of the method will be made comparing results derived from signals from a simulated environment with the theoretical model. Performed tests have pointed out the validity of the theoretical model in a real case
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