130,678 research outputs found
Minimal Active Space: NOSCF and NOSI in Multistate Density Functional Theory
No full textIn this Perspective, we introduce a minimal active space (MAS) for the lowest N
eigenstates of a molecular system in the framework of a multistate density functional
theory (MSDFT), consisting of no more than N2 nonorthgonal Slater determinants. In
comparison with some methods in wave function theory in which one seeks to expand the ever increasing size of an active space to approximate the wave functions,
it is possible to have an upper bound in MSDFT because the auxiliary states in a
MAS are used to represent the exact N-dimensional matrix density D(r). In analogy
to Kohn-Sham DFT, we partition the total Hamiltonian matrix functional H[D] into
an orbital-dependent part, including multistate kinetic energy and Coulomb-exchange energy plus an external potential energy, and a correlation matrix density functional Ec[D]. The latter accounts for the part of correlation
energy not explicitly included in the minimal active space. However, a major difference from Kohn-Sham DFT is that state interactions are necessary to represent the
N-matrix density D(r) in MSDFT, rather than a non-interacting reference state for the
scalar ground-state density. Two computational approaches are highlighted. We
first derive a set of non-orthogonal multistate self-consistent-field (NOSCF) equations
for the variational optimization of H[D]. We introduce the multistate correlation po tential, as the functional derivative of Ec[D], which includes both correlation effects
within the MAS and that from the correlation matrix functional. Alternatively, we
describe a non-orthogonal state interaction (NOSI) procedure, in which the determi nant functions are optimized separately. Both computational methods are useful for
determining the exact eigenstate energies and for constructing variational diabatic
states, provided that the universal correlation matrix functional is known. It is hoped
that this discussion would stimulate developments of approximate multistate density
functionals both for the ground and excited states
Alterations of the cortico-cortical network in sensori-motor areas of dystrophin deficient mice.
No full textThe dystrophin defective mdx mouse, acknowledged model of Duchenne Muscular Dystrophy (DMD), bears outstanding alterations of the cortical architecture, that could be responsible for the cognitive impairment often accompanying this pathological condition. Using a retrograde tract tracing technique to label neurons in Golgi-like fashion, we investigated the fine anatomical organization of associative cortico-cortical projections in mdx mice. While the absolute number of associative pyramidal neurons was significantly higher in mdx than in control animals, the ratio between the number of supra- and infragranular cortico-cortical cells was substantially unmodified. Basal dendrites of layer 2/3 pyramidal neurons displayed longer terminal branches in mdx compared to controls. Finally, the density of dendritic spines was significantly lower in mdx animals. The anomalies of associative cortico-cortical projections provide potential groundwork on the neurobiological bases of cognitive involvement in DMD and value the role of cortical microcircuitry alterations as possible source of interference with peripheral motor impairment
Strategie emergenti nel business vitivinicolo: un’analisi comparata tra Italia e Australia
No full textObiettivo della presente ricerca è l’esame di due sistemi di offerta nel settore vitivinicolo, quello del vino italiano analizzato in termini comparati con il modello di business del vino australiano. Questa scelta si giustifica per due principali ragioni:
• la consapevolezza che mancano, o sono comunque molto limitati, contributi di carattere scientifico che studiano i sistemi vitivinicoli (e più in generali i sistemi rurali) attraverso una comparazione a livello internazionale; ciò rende particolarmente preziosi quegli studi che propongano benchmark di settori/territori considerando non solo variabili macro-economiche, ma anche differenze nei comportamenti imprenditoriali dei diversi attori protagonisti;
• l'opportunità per il gruppo di lavoro dell’Università di Siena di aver già effettuato, in collaborazione con studiosi stranieri (Zanni ed., 2004), ricerche su dei cluster del vino all’estero (USA, Argentina, Germania, Francia); l’estensione dell’analisi ai cluster del vino australiani rappresenta, quindi, il naturale proseguimento di questa ricerca su scala internazionale.
L'approccio di analisi proposto è di tipo economico-aziendale seppur rivolto a tre differenti unità di analisi ritenute tutte al contempo rilevanti per la comprensione dei processi di creazione del valore su scala locale: sistemi di offerta nazionali; reti di attori che agiscono su scala locale; singole imprese protagoniste. Per cogliere l’interrelazione tra questi diversi aspetti in un quadro interpretativo unitario dei processi di sviluppo delle imprese vitivinicole articoleremo la nostra indagine per semplificazioni successive (con una logica “ad imbuto” che passa dagli aspetti macro di settore fino alle problematiche a livello di singole aree operative delle imprese).
In particolare, la ricerca intende approfondire quattro questioni che assumono importanza critica nello sviluppo delle imprese e dei sistemi locali vitivinicoli e, più in generale, dei distretti agroalimentari, osservati in ottica comparata:
1. il valore del luogo d’origine nelle strategie competitive che approfondiremo attraverso un riesame della letteratura specialistica (§ 1);
2. le differenze nei caratteri strutturali delle filiere vitivinicole in Australia e Italia, nonché nei sistemi di organizzazione dell’offerta su scala nazionale e locale (§§ 2 e 3);
3. le specificità delle imprese protagoniste e dei loro comportamenti strategici che, sulla base della ricerca empirica svolta in Toscana, evidenzia differenti modalità di gestione del rapporto impresa-territorio (§ 4);
4. il diverso approccio al business da parte degli imprenditori vitivinicoli australiani rispetto a quelli italiani (§ 5).
Sotto il profilo metodologico lo studio si è articolato in tre fasi principali:
• Approfondimento della letteratura e analisi delle fonti documentali (analisi desk). Sono state approfondite, attraverso lo studio di fonti di tipo economico-statistico, le caratteristiche strutturali dei settori vitivinicolo in Italia e in Australia. Questa fase è stata propedeutica all'individuazione dei sistemi locali successivamente indagati.
• Ricerca sul campo (analisi field). La ricerca sul campo è consistita nello studio dei caratteri strutturali dei cluster del vino individuati durante la fase desk, attraverso la raccolta di dati forniti da
• organizzazioni operanti sul territorio (Consorzi di tutela, camere di commercio, associazioni di categoria, ecc.) ed interviste dirette. In questo modo, le informazioni raccolte da fonti documentali sono state arricchite e approfondite da quelle ricevute dagli operatori del più circoscritto territorio di indagine. Per quanto riguarda l’Australia, nel maggio 2005 è stata effettuata una missione di studio finalizzata ad incontrare gli attori protagonisti dei sistemi locali rurali prescelti; durante gli incontri sono stati somministrate agli interlocutori delle interviste destrutturate per raccogliere le informazioni necessarie a stilare dei casi aziendali. Le interviste sono state somministrate sia alle imprese che operano lungo le filiere produttive, sia ad attori terzi (media, fornitori di servizi, attori istituzionali, ecc.) che sembrano assumere un ruolo importante nell'ambito dei processi di creazione del valore del sistema. Nel caso dei tre cluster toscani analizzati (Chianti Classico senese, Brunello di Montalcino, Chianti Colli Aretini) nell’estate 2005 sono state intervistate 50 imprese sulla base di un questionario semistrutturato .
• Elaborazione dei dati e prima diffusione dei risultati. I dati ottenuti sono stati sistematizzati attraverso un'elaborazione statistica basata su tabelle di contingenza in modo da evidenziare delle differenze nei comportamenti a livello aziendale e territoriale. I case-study realizzati, sono stati letti alla luce del modello interpretativo di riferimento ed esaminati in ottica comparata. I primi risultati di questa ricerca sono stati anticipati in due convegni internazionali (Mattiacci-Nosi-Zanni 2005; Zanni & Nosi 2005b)
Non-specific interaction of pre-fibrillar amyloid aggregates with glutamatergic receptors results in Ca2+ increase in primary neuronal cells
No full textIt is widely reported that the Ca2+ increase following nonspecific cell membrane permeabilization is among the earliest biochemical modifications in cells exposed to toxic amyloid aggregates. However, more recently receptors with Ca2+ channel activity such as α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl D-aspartate (NMDA), ryanodine, and inositol 1,4,5-trisphosphate receptors have been proposed as mediators of the Ca2+ increase in neuronal cells challenged with β-amyloid peptides. We previously showed that prefibrillar aggregates of proteins not associated with amyloid diseases are toxic to exposed cells similarly to comparable aggregates of disease-associated proteins. In particular, prefibrillar aggregates of the prokaryotic HypF-N were shown to be toxic to different cultured cell lines by eliciting Ca2+ and reactive oxygen species increases. This study was aimed at assessing whether NMDA and AMPA receptor activations could be considered a generic feature of cell interaction with amyloid aggregates rather than a specific effect of some aggregated protein. Therefore, we investigated whether NMDA and AMPA receptors were involved in the Ca2+ increase following exposure of rat cerebellar granule cells to HypF-N prefibrillar aggregates. We found that the intracellular Ca2+increase was associated with the early activation of NMDA and AMPA receptors, although some nonspecific membrane permeabilization was also observed at longer times of exposure. This result matched a significant co-localization of the aggregates with both receptors on the plasma membrane. Our data support the possibility that glutamatergic channels are generic sites of interaction with the cell membrane of prefibrillar aggregates of different peptides and proteins as well as the key structures responsible for the resulting early membrane permeabilization to Ca2+
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
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