1,720,982 research outputs found
Progettazione e applicazione di strumenti computazionali per studiare le interfacce solide e i materiali per ridurre l'attrito
No full textL'attrito è la forza di resistenza al moto che si sviluppa tra due superfici che scorrono o rotolano l'una sull'altra. Si tratta di un fenomeno microscopico comune, la cui origine è da ricercare nelle forze di interazione adesive che si generano tra le superfici a contatto. Le dissipazioni dovute all'attrito causano ingenti costi energetici e ambientali in diversi settori, tra cui quello del trasporto e dell'industria. Si stima infatti che quasi un terzo dell'energia prodotta dai combustibili fossili per alimentare i veicoli venga spesa per vincere l'attrito. Si prevede che migliorare la tribologia delle superfici possa garantire una riduzione degli sprechi energetici pari al 40% entro i prossimi 15 anni.
Lo studio dell'attrito richiede una profonda comprensione dei fenomeni microscopici che si sviluppano a livello della superficie. Le simulazioni da principi primi consentono di studiare le proprietà elettroniche e chimiche dei materiali con un alto grado di accuratezza, fornendo un modo per comprendere gli eventi tribologici.
Nel corso degli anni, sono stati sviluppati diversi metodi basati sui calcoli a principi primi per studiare le proprietà dei materiali a livello atomico. Tra tutti, l’utilizzo di queste simulazioni in combinazione con un approccio high-throughput si sta diffondendo rapidamente negli ultimi decenni. Lo scopo di questo metodo consiste nel simulare migliaia di materiali in parallelo, in modo da selezionare tra essi un piccolo insieme di candidati con proprietà fisico-chimiche specifiche. L'obiettivo è accelerare la scoperta e la diffusione di nuovi materiali per la scienza e la tecnologia.
Questa tesi esplora l'implementazione e l'utilizzo di diverse tecniche computazionali innovative nell'ambito della tribologia. Il lavoro si concentra principalmente sulla descrizione di un software realizzato per automatizzare l'attività di ricerca in nanotribologia ed effettuare studi high-throughput sulle proprietà delle interfacce. Nella sua attuale implementazione, il software consente di combinare qualsiasi coppia di materiali cristallini, che possono differire sia per composizione sia per orientazione, e studiare le loro proprietà tribologiche, come l'adesione e lo shear strength. Il programma è stato utilizzato per studiare le proprietà tribologiche tra due superfici solide a contatto, effettuando uno screening sugli elementi della tavola periodica. Lo studio ha permesso di stimare la relazione tra adesione e resistenza di una interfaccia, permettendo inoltre di identificare un modo per stimare la modalità di failure dei materiali.
Un altro importante risultato di questo lavoro è la realizzazione di un modello teorico innovativo che combina la tradizionale tecnica GFMD alla dinamica molecolare a principi primi. Questo metodo ibrido migliora l'accuratezza delle simulazioni atomistiche tenendo conto del ruolo delle proprietà elastiche dei solidi e la propagazione di onde vibrazionali nel determinare l'attrito delle strutture atomiche. Il programma è stato utilizzato per calcolare le proprietà di attrito di una interfaccia diamante-diamante, considerando diversi gradi di passivazione delle superfici.
Infine, questo lavoro riporta uno studio condotto sulle proprietà lubrificanti del fosforene, un materiale innovativo bidimensionale a base di fosforo. Dapprima sono stati studiati due strati di fosforene a contatto. Ciò ha permesso di individuare la presenza di una fase super lubrificante per una particolare orientazione degli strati. Tale lavoro costituisce un primo importante passo nella possibile ideazione di lubrificanti a base di fosforene. Successivamente, è stata valutata la capacità del fosforene di lubrificare un substrato di ferro, confrontando i risultati ottenuti con calcoli effettuati per grafene e MoS2.Friction is the resistance force to motion between two surfaces that slide or roll over each other. It is a common microscopic phenomenon, the origin of which is to be found in the adhesive interaction forces that are generated between the surfaces in contact. Dissipations due to friction cause huge energy and environmental costs in various sectors, including transport and industry. In fact, it is estimated that nearly a third of the energy produced by fossil fuels to power vehicles is spent on overcoming friction. Improving the tribology of surfaces is expected to ensure a 40% reduction in energy waste within the next 15 years.
The study of friction requires a deep understanding of the microscopic phenomena that develop at the surface level. First principle simulations allow studying the electronic and chemical properties of materials with a high degree of accuracy, providing a way to understand tribological events.
Over the years, several methods based on first-principle calculations have been developed to study the properties of materials at the atomic level. Among all, the use of these simulations in combination with a high-throughput approach has been spreading rapidly in recent decades. This method aims to simulate thousands of materials in parallel to select from a small set of candidates with specific physicochemical properties from the initial pool. The goal is to accelerate the discovery and dissemination of new materials for science and technology.
This thesis explores the implementation and use of several innovative computational techniques in the field of tribology. The work mainly focuses on the description of a software designed to automate the research activity in nanotribology and carry out high-throughput studies on the properties of the interfaces. In its current implementation, the software allows you to combine any pair of crystalline materials, which can differ in both composition and orientation, and study their tribological properties, such as adhesion and shear strength. The program was used to study the tribological properties between two solid surfaces in contact by carrying out a screening on the elements of the periodic table. The study allows to estimate the relationship between adhesion and strength of an interface, also allowing to identify a way to assess the failure mode of materials.
Another important result of this work is the realization of an innovative theoretical model that combines the traditional GFMD technique with first-principle molecular dynamics. This hybrid method improves the accuracy of atomistic simulations by considering the role of the elastic properties of solids and the propagation of vibrational waves in determining the friction of atomic structures. The program was used to calculate the friction properties of a diamond-diamond interface, considering different degrees of surface passivation.
Finally, this work reports a study conducted on the lubricating properties of phosphorene, an innovative two-dimensional material based on phosphorus. First, two contact phosphorene layers were investigated. This made it possible to identify the presence of a super lubricating phase for a particular orientation of the layers. This work constitutes a first important step in the possible design of phosphorene-based lubricants. Subsequently, the ability of phosphorene to lubricate an iron substrate was evaluated, comparing the results obtained with calculations made for graphene and MoS2
NONGENOMIC REGULATION OF GLUTAMATERGIC NEUROTRANSMISSION IN HIPPOCAMPUS BY THYROID HORMONES
No full textThyroid hormones (THs) are well known for their genomic effects but recently attention has focused also on their nongenomic actions as rapid modulators of membrane receptors. Here we show that thyroxine (T4) and 3,3′,5′-l-triiodothyronine (T3) rapidly decrease N-methyl-d-aspartate (NMDA)-evoked currents in rat hippocampal cultures with potency in the micromolar range. The effect is not mediated by glutamate or glycine binding sites as an increase in agonist or glycine concentration does not alter TH potencies. Furthermore THs’ effect on NMDA receptors is independent of voltage and of subunit composition. The mechanism of THs’ antagonistic effect does not involve PKC phosphorylation of NMDA receptors since neither blocking nor stimulating PKC changed THs’ modulation. T3, but not T4, inhibits also kainate-evoked currents in hippocampal neurons in culture. In hippocampal pyramidal neurons in slice, T3, but not T4, significantly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) without affecting their amplitude and decay.In cultured rat cortical neurons THs prevented glutamate-induced neuronal death at concentrations similar to those effective on glutamatergic receptors. Taken together our data show for the first time that THs can rapidly affect ionotropic glutamatergic receptors in hippocampal neurons, an effect that could have an important role in their modulation of brain function in physiological and pathological states
IDRA-21, a positive AMPA receptor modulator, inhibits synaptic and extrasynaptic NMDA receptor mediated events in cultured cerebellar granule cells
No full textIDRA-21 (7-chloro-3-methyl-3,4-dihydro-2H-1-,2,4-benzothiadiazine 1,1-dioxide) reduces alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptors desensitisation in vitro and restores learning and cognitive impairment in vivo. In this study, we show that in cerebellar granule cells (CGCs) in culture IDRA-21 reduces N-methyl-D-aspartate receptor (NMDAR) whole-cell currents. The effect is neither competitive nor voltage-dependent. The reduction of NMDA currents is stronger at low glycine concentrations suggesting an interaction with this site. IDRA-21 shortens miniature excitatory postsynaptic currents mediated by NMDARs (NMDA-mEPSCs) in CGCs grown in low potassium with no effect oil peak amplitudes. By using fast glutamate application onto CGCs nucleated patches, we found that IDRA-21 decreases both decay time constant and amplitude of the current. Experiments performed oil recombinant NMDAR expressed in HEK 293 cells showed that IDRA-21 was more effective on NR1a-NR2B than NR1a-NR2A receptors highlighting a subunit selectivity of the drug. Our findings make light oil a novel target for IDRA-21: NMDA receptors function is negatively modulated and the different action at the level of extrasynaptic and synaptic receptors could be ascribed to a partial selectivity for NR2B subunits.IDRA-21 (7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide) reduces α-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptors desensitisation in vitro and restores learning and cognitive impairment in vivo. In this study, we show that in cerebellar granule cells (CGCs) in culture IDRA-21 reduces N-methyl-D-aspartate receptor (NMDAR) whole-cell currents. The effect is neither competitive nor voltage-dependent. The reduction of NMDA currents is stronger at low glycine concentrations suggesting an interaction with this site. IDRA-21 shortens miniature excitatory postsynaptic currents mediated by NMDARs (NMDA-mEPSCs) in CGCs grown in low potassium with no effect on peak amplitudes. By using fast glutamate application onto CGCs nucleated patches, we found that IDRA-21 decreases both decay time constant and amplitude of the current. Experiments performed on recombinant NMDAR expressed in HEK 293 cells showed that IDRA-21 was more effective on NR1a-NR2B than NR1a-NR2A receptors highlighting a subunit selectivity of the drug. Our findings make light on a novel target for IDRA-21: NMDA receptors function is negatively modulated and the different action at the level of extrasynaptic and synaptic receptors could be ascribed to a partial selectivity for NR2B subunits. © 2004 Elsevier Ltd. All rights reserved
Aromatic molecules as sustainable lubricants explored by ab initio simulations
Full text linkIn the pursuit of sustainable lubricant materials, the conversion of common
organic molecules into graphitic material has been recently shown to
effectively reduce friction of metallic interfaces. Aromatic molecules are
perfect candidates due to their inertness and possibility to form carbon-based
tribofilms. Among many promising possibilities, we selected a group of common
aromatic compounds and we investigated their capability to reduce the adhesion
of iron interface. Ab initio molecular dynamic simulations of the sliding
interface show that hypericin, a component of St. John's wort, effectively
separates the mating iron surfaces better than graphene. This phenomenon is due
to the size of the molecule, the reactivity of the moieties at its edges and
the possibility to stack several of these structures that can easily slide on
top of each other. The decomposition of the lateral groups of hypericin
observed in the dynamic simulations suggests that the clustering of several
molecules is possible, offering innovative paths to lubricate sliding contacts
with compounds not typically employed in tribology
Fast spiking interneuron control of seizure propagation in a cortical slice model of focal epilepsy
No full textIn different animal models of focal epilepsy, seizure-like ictal discharge propagation is transiently opposed by feedforward inhibition. The specific cellular source of this signal and the mechanism by which inhibition ultimately becomes ineffective are, however, undefined. We used a brain slice model to study how focal ictal discharges that were repetitively evoked from the same site, and at precise times, propagate across the cortex. We used Ca(2+) imaging and simultaneous single/dual cell recordings from pyramidal neurons (PyNs) and different classes of interneurons in rodents, including G42 and GIN transgenic mice expressing the green fluorescence protein in parvalbumin (Pv)-fast spiking (FS) and somatostatin (Som) interneurons, respectively. We found that these two classes of interneurons fired intensively shortly after ictal discharge generation at the focus. The inhibitory barrages that were recorded in PyNs occurred in coincidence with Pv-FS, but not with Som interneuron burst discharges. Furthermore, the strength of inhibitory barrages increased or decreased in parallel with increased or decreased firing in Pv-FS interneurons but not in Som interneurons. A firing impairment of Pv-FS interneurons caused by a membrane depolarization was found to precede ictal discharge onset in neighbouring pyramidal neurons. This event may account for the collapse of local inhibition that allows spatially defined clusters of PyNs to be recruited into propagating ictal discharges. Our study demonstrates that Pv-FS interneurons are a major source of the inhibitory barrages that oppose ictal discharge propagation and raises the possibility that targeting Pv-FS interneurons represents a new therapeutic strategy to prevent the generalization of human focal seizures
TribChem: A Software for the First-Principles, High-Throughput Study of Solid Interfaces and Their Tribological Properties
Full text linkHigh-throughput first-principlescalculations, based on solvingthe quantum mechanical many-body problem for hundreds of materialsin parallel, have been successfully applied to advance many materials-basedtechnologies, from batteries to hydrogen storage. However, this approachhas not yet been adopted to systematically study solid-solidinterfaces and their tribological properties. To this aim, we developedTribChem, an advanced software program based on the FireWorks platform,which is here presented and released. TribChem is constructed in amodular way, allowing for the separate calculation of bulk, surface,and interface properties. At present, the calculated interfacial propertiesinclude adhesion, shear strength, and charge redistribution. Furtherproperties can be easily added due to the general structure of themain workflow. TribChem contains a high-level interface class to store/retrieveresults from its own database and connect to public databases
Thyroid hormone (L-T3) directly modulates GABA and NMDA receptors in hippocampal cultures and slices.
No full textNot availabl
Modeling phosphorene and interacting with iron: lubricating effects compared to graphene
Full text linkPhosphorene, a single layer of black phosphorus, is attracting interest for several applications, among which tribology. Here, we investigate its possible use as a solid lubricant for iron-based materials by comparing its friction-reduction properties with MoS2 and graphene. Through first-principle calculations, we predict that phosphorene adheres more strongly to the native iron surface than the other considered 2D materials. The higher adhesion suggests that a stable and durable coverage of reactive surface regions can be obtained with phosphorene. Furthermore, our simulation uncovers the peculiar behavior of phosphorene to exfoliate into two atomic-thin layers upon interface intercalation. This capability makes phosphorene reduce the nano-asperity adhesion very efficiently thanks to the simultaneous passivation of the surface and countersurface. These results suggest that better performances could be obtained by phosphorene than other solid lubricants at low concentrations
Presenza di composti ad attivita’ ansiolitico-sedativa nella filera di produzione del parmigiano reggiano.
No full textDa tempo è stata descritta la presenza di sostanze ad attività sedativa nel latte tuttavia la loro struttura chimica è ancora oggetto di studio. Recentemente è stato isolato dall’s1-caseina un peptide denominato s1-CN-(f91-100) o s1-casozepina [1] mentre il nostro gruppo ha identificato nel latte altre sostanze non peptidiche ad attività benzodiazepino-simile [2]. Non è ancora noto, comunque, quali e quante sostanze presenti nel latte si ritrovano nei vari formaggi dopo i processi di produzione. Nel presente lavoro è stata valutata la presenza di composti ad attività benzodiazepino-simile nel parmigiano reggiano. In particolare è stata analizzata la filiera di produzione del parmigiano reggiano prelevando i seguenti campioni presso un’unica azienda in modo da escludere variabilità legate a fattori di alimentazione, ambiente, procedimento di produzione: fieno, latte intero, latte magro, siero, siero innesto, panna, cagliata, tosone e parmigiano reggiano. I campioni estratti con metanolo sono stati purificati mediante analisi HPLC a 0.8 ml/min utilizzando una colonna LiChrospher 100 RP-18 column (250x4.0 mm; 5 m) equilibrata con 80% di acqua/0.1% TFA e 20% di acetonitrile. I campioni sono stati analizzati a gradiente (0.5%) di acqua/0.1% TFA and acetonitrile dal 20 al 58% di acetonitrile. Per ogni campione sono state raccolte 75 frazioni, liofilizzate e testate per valutare la loro capacità di legarsi specificatamente al sito di riconoscimento centrale benzodiazepinico mediante dosaggio radioisotopici utilizzando come ligando marcato il [3H]RO 15-1788, antagonista benzodiazepinco. La concentrazione ottenuta per estrapolazione da una curva di competizione generata con autentico diazepam, viene espressa in ng diazepam equivalenti /g di campione. Nel tosone e nel parmigiano reggiano sono state rilevate piccole quantità di sostanze BDZ-simili (0,78 ± 0,12 e 0,86 ± 0,17 ng DE/g rispettivamente) mentre nel latte e nel siero la loro concentrazione risulta significativamente maggiore (117,75 ± 9,2 e 215 ± 15,7 ng DE/g rispettivamente). E’ interessante sottolineare che la concentrazione di tali sostanze nel fieno (14,8 ± 1,64 DE ng/g) è inferiore rispetto al latte, considerando che l’alimentazione della mucca è esclusivamente basata sul fieno si può ipotizzare che il contenuto che si ritrova nel latte sia anche il contributo di una sintesi endogena. L’attività ansiolitico-sedativa delle frazione isolate dal siero di latte è stata valutata sia in vitro su neuroni corticali con la tecnica elettrofisiologia del patch-clamp che in vivo.Bibliografia1. L. Miclo, E. Perrin, A. Driou, V. Papadopoulos et al. Characterization of a-casozepina, a tryptic peptide from bovine as1-caseina with benzodiazepine-like activity. FASEB J: 15, 1780-1782, 20012. R. Avallone, L. Corsi, M.L. Zeneroli and M. Baraldi. Presence of benzodiazepine-like molecules in food and their implication in the nutrition of cirrhotic patients. Innovative Food Science and Technologies: 2/3, 193-198, 200
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