1,721,072 research outputs found
Rilassometria 1H-NMR per la caratterizzazione di legni integri e degradati
No full textLa caratterizzazione del legno riveste un particolare ruolo negli studi volti alla conservazione di manufatti lignei di interesse storico-artistico-archeologico. Le proprietà meccaniche del legno dipendono dalla specie, dal contenuto d’acqua, dalla direzione delle fibre, dalla porosità, dalla distribuzione dei pori e, in generale, da un insieme di condizioni che non sempre sono facilmente misurabili e controllabili. Di particolare interesse sono i metodi di indagine non invasivi e non distruttivi; tra questi si sta affermando la Risonanza Magnetica Nucleare (NMR) [1,2].
In questo lavoro metodi di Rilassometria 1H-NMR, messi a punto per il tessuto osseo [3], sono stati applicati allo studio di diverse tipologie lignee. I FID (Free Induction Decay) ottenuti sono la somma di due componenti: una componente approssimativamente gaussiana o “di tipo solido”, ascrivibile alle macromolecole, e una componente esponenziale o “di tipo liquido”, ascrivibile all’acqua.
Le curve di distribuzione dei tempi di rilassamento della componente longitudinale della magnetizzazione nucleare dei nuclei 1H, ottenute separatamente per le due componenti in campioni di legno stagionato, mostrano inattese regolarità, che da un lato permettono di classificare i campioni in funzione della specie e dall’altro suggeriscono fenomeni di accoppiamento e/o di scambio tra i nuclei di idrogeno dell’acqua e quelli macromolecolari. Le variazioni dei tempi di rilassamento osservate in campioni degradati possono essere rilevanti nell’ottica della determinazione di parametri atti alla valutazione dello stato conservativo di macromolecole biologiche.
Conifera, Latifoglia, Tempi di rilassamento, Macromolecole biologiche
[1] A. Maccotta. P. Fantazzini, C. Garavaglia, I. Donato, P. Perzia, M. Brai, F. Morreale, Preliminary 1H NMR study on archaeological waterlogged wood, ANNALI DI CHIMICA 95: 117-124 (2005).
[2] A. Maccotta, M. Brai, P. Fantazzini, G. Veronesi, Classificabilità di essenze lignee mediante rilassometria e imaging NMR, XCI Congresso Nazionale SIF, Catania, 26 Sett. – 1 Ott. 2005, p.192.
[3] P. Fantazzini, V. Bortolotti, R.J.S. Brown, M. Camaiti, C. Garavaglia, R. Viola, G. Giavaresi, Two 1H-NMR Methods to Measure Internal Porosity of Bone Trabeculae: by Solid-Liquid Signal Separation and by Longitudinal Relaxation, J. Appl. Phys., 95: 339-343 (2004)
Radiation quality discrimination by continuous and pulse ESR techniques
No full textThe biological damages produced by ionizing radiations in tissues and cells depend on the radiation quality, besides on the dose. The discrimination of the radiation quality, which is related to the linear energy transfer (LET), interests various fields such as radiobiology, astronautic space research, radiotherapy research and accidental dosimetry.
In this work we have applied continuous wave ESR (cw-ESR) and pulse ESR techniques to ammonium tartrate samples with the aim of developing procedures able to discriminate radiation quality whose knowledge is fundamental for rabiobiological considerations. We have chosen the ammonium tartrate because it is a promising compound for the measurement of the absorbed ionizing radiation dose [1, 2, 3]. The compound is particularly competitive to standard alanine in the detection of ionizing radiation other than high energy gamma photons, such as low energy X photons, electrons, protons, thermal neutrons.
At the same time cw-ESR and the Electron Spin Echo (ESE) decay techniques and Double Electron-Electron Resonance (DEER) can be used to obtain from average to local distributions of spins. CW-ESR is particular suited for the determination of total spin (macroscopic) concentration, whereas ESE is suited for the determination of local concentration. A new insight into the knowledge of the complex distribution of free radicals inside the dosimeters can be obtained by DEER. This technique is very useful for our purpose because it is able to measure distance between radicals in solids in the range of approximately 1.5-8 nm by analyzing the dipolar coupling between two electron spins.
In this work we analyze the spatial distributions of the free radicals produced after exposure of ammonium tartrate dosimeters to various radiation beams (21 MeV protons, 60Co γ-photons, thermal neutrons).
By measuring the differences between the local radical concentrations and the macroscopic one, and the distributions of radical-radical distances obtained with DEER, this study has given details on the differences between the distributions of radicals created by the radiation-matter energy transfer for the different ionizing radiations.
Differences and analogies are discussed in terms of differences and analogies in the LET and type of particles involved.
References
[1] S. K. Olsson, S. Bagherian, E. Lund, G. A. Carlsson, A. Lund, Appl. Radiat. Isot. 1999, 50, 95565.
[2] M. Brustolon, A. Zoleo and A. Lund, J. Magn. Reson., 1999, 137, 389-396.
[3] A. Bartolotta, M. C. D'Oca, M. Brai, V. Caputo, V. De Caro, L. I. Giannola, Phys. Med. Biol., 2001, 46, 461-471
Analysis of the spatial distribution of free radicals in ammonium tartrate by pulse EPR techniques
No full textUsing pulse electron paramagnetic resonance (EPR) on a series of L(+)-ammonium tartrate (AT) dosimeters exposed to radiations with different linear energy transfer (LET), we assessed the ability of pulse EPR spectroscopy to discriminate the quality of various radiation beams such as (60)Co gamma-ray photons,, protons and thermal neutrons at various doses by analyzing the local radical distributions produced by the different beams. We performed two types of pulse EPR investigations: two-pulse electron spin echo decay obtained by varying the microwave power, and a double electron-electron resonance (DEER) study. Both methods provide information about the dipolar interactions among the free radicals and about their spatial distributions. The first method provided information on the instantaneous diffusion and hence the microscopic concentration of the radicals that is compared with the macroscopic one obtained by CW-EPR. The DEER spectra yielded the distributions of distances between pairs of radicals two to five crystal cells apart produced by the same radiation event, a result reported here for the first time. The inter-radical distributions given by the DEER results have been simulated by modeling the radical distributions according to the details of the matter-radiation interactions for the various beams. The results of both types of pulse experiments are strongly dependent: on the radiation quality. This was also observed for samples giving indistinguishable CW-EPR spectral profiles. We conclude that the pulse EPR measurements can be valuable tools for distinguishing the LET of the radiation beams, an important parameter for radiobiological considerations
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
Rilassometria NMR applicata allo studio della statua lignea di San Nicola di Mira (XVI secolo) al museo Diocesano di Palermo
No full textIn un recente studio condotto mediante Rilassometria NMR del nucleo 1H su legni moderni stagionati è stato mostrato che è possibile separare la curva di rilassamento della componente longitudinale della magnetizzazione nucleare dei nuclei 1H meno mobili (componente “solida”), attribuibili alle macromolecole, da quella dei nuclei a maggior mobilità (componente “liquida”), attribuibili all’acqua. Oltre a permettere di verificare la proporzionalità diretta tra ampiezza della componente liquida del segnale e massa d’acqua, l’analisi delle curve di rilassamento mediante distribuzioni quasi-continue del tempo di rilassamento longitudinale T1 permette di classificare le essenze lignee esaminate, mettendo in evidenza variazioni regolari di tale tempo nel passare da latifoglie a conifere. Alcune regolarità osservate possono essere giustificate assumendo un modello di scambio a due siti, con un tempo di scambio solido-liquido di qualche decina di ms. La stessa analisi, condotta su campioni di legno della statua di San Nicola di Mira (XVI secolo) recentemente restaurata e collocata presso il Museo Diocesano di Palermo, mostra che anche per il legno antico, sebbene fortemente degradato, valgono le stesse regolarità, ma con valori per i tempi di rilassamento e per il tempo di scambio solido-liquido che sono circa la metà di quelli osservati per il legno moderno. Si avanza l’ipotesi che questa accelerazione nei processi di rilassamento e di scambio sia associabile all’aumento del contributo paramagnetico, legato alla presenza di radicali liberi nel legno degradato, messo in evidenza in uno studio parallelo mediante EPR. Per il legno antico trattato non valgono le regolarità osservate per il legno non trattato, sia esso moderno od antico. Le regolarità riscontrate suggeriscono che la Rilassometria NMR possa essere utilizzata in futuro per analisi non distruttive volte alla classificazione delle essenze ed alla diagnosi del degrado di legni di interesse storico-artistico-archeologico
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