1,464 research outputs found
Quantum Monte Carlo calculations of the dimerization energy of borane
Accurate thermodynamic data are required to improve the performance of chemical hydrides that are potential hydrogen storage materials. Boron compounds are among the most interesting candidates.
However, different experimental measurements of the borane dimerization energy resulted in a rather wide range ( 1234.3 to 1239.1) \ub1 2 kcal/mol. Diffusion Monte Carlo (DMC) simulations usually recover more than 95% of the correlation energy, so energy differences rely less on error cancellation than other methods. DMC energies of BH3, B2H6, BH3 CO, CO, and BH2+ allowed us to predict the borane dimerization energy, both via the direct process and indirect processes such as the dissociation of BH3CO. Our De = 1243.12(8) kcal/mol, corrected for the zero point energy evaluated by considering the anharmonic contributions, results in a borane dimerization energy of 1236.59(8) kcal/mol. The process via the dissociation of BH3CO gives 1234.5(2) kcal/mol. Overall, our values suggest a slightly less De than the most recent W4 estimate De = 1244.47 kcal/mol [A. Karton and J. M. L. Martin, J. Phys. Chem. A 111, 5936 2007)]. Our results show that reliable thermochemical data for boranes can be predicted by fixed node (FN)-DMC calculations
Effect of alloying elements on the Sr modification of Al-Si cast alloys
Strontium-based modifier alloys are commonly adopted to modify the eutectic silicon in aluminum-silicon casting alloys by changing the silicon shape from an acicular to a spherical form. Usually, the modifier alloy necessary to properly change the silicon shape depends on the silicon content, but the alloying elements’ content may have an influence. The AlSr10 master alloy’s modifying effect was studied on four Al-Si alloys through the characterization of microstructural and mechanical properties (micro-hardness and impact tests). The experimental results obtained on gravity cast samples highlighted the interdependence in the modification of silicon between the Si content and the alloying elements. After modification, a higher microstructural homogeneity characterized by a reduction of up to 22.8% in the size of intermetallics was observed, with a generalized reduction in secondary dendritic arm spacing. The presence of iron-based polygonal-shaped intermetallics negatively affects Sr modification; coarser silicon particles tend to grow close to α-Fe. The presence of casting defects such as bifilm reduces Sr modification’s beneficial effects, and little increase in absorbed impact energy is observed in this work
Residual stress analysis applied to HPDC aluminium components: a case study
High-Pressure Die Casting (HPDC) is a casting process largely diffused in the aluminium foundries. By HPDC is possible to obtain aluminium castings with thin walls and high specific mechanical properties in short cycle times. Aluminium HPDC castings are commonly intended for the automotive sector: engine, covers, engine blocks and more in general the powertrain. In recent years, one of the most important focus in the automotive sector is decreasing the powertrain weight, acting on stock allowances in certain parts of the casting. This reduction can affect the dimensional features and in turn the residual stress inside the casting. Despite that, it is possible to obtain beneficial compression states into the castings by mean of post-process operations, such as shot-blasting, to reduce or remove residual stresses by mean of heat treatments. Residual stresses can be assessed by an X-Ray residual stress measurement device, a nondestructive technique that allows observing the process parameters effect into the casting.
In this work, after a detailed analysis of the residual stress measurement available for aluminium castings, a powertrain component realized in aluminium alloy EN AC 46000 was analysed. These analyses involved both dimensional response and related residual stresses in the as-cast state and the shot-blasted-state on a valve cover, to understand and prevent the residual stress states into the aluminium castings
Smart City : condividere per innovare (e con il rischio di escludere?)
Il contributo ha ad oggetto il tema delle smart cities da un punto di vista giuridico, analizzando le criticit\ue0 che emergono dal diritto positiv
Role of synthetic parameters on the structural and optical properties of N,Sn-copromoted nanostructured TiO2: A combined Ti K-edge and Sn L2,3-edges X-ray absorption investigation
Dual-readout Calorimetry
The RD52 Project at CERN is a pure instrumentation experiment whose goal is
to understand the fundamental limitations to hadronic energy resolution, and
other aspects of energy measurement, in high energy calorimeters. We have found
that dual-readout calorimetry provides heretofore unprecedented information
event-by-event for energy resolution, linearity of response, ease and
robustness of calibration, fidelity of data, and particle identification,
including energy lost to binding energy in nuclear break-up. We believe that
hadronic energy resolutions of {\sigma}/E 1 - 2% are within reach for
dual-readout calorimeters, enabling for the first time comparable measurement
preci- sions on electrons, photons, muons, and quarks (jets). We briefly
describe our current progress and near-term future plans. Complete information
on all aspects of our work is available at the RD52 website
http://highenergy.phys.ttu.edu/dream/.Comment: 10 pages, 10 figures, Snowmass White pape
Colata per gravità di un FGM in lega di alluminio: ottimizzazione del trattamento termico e proprietà finali
Le leghe di alluminio sono largamente utilizzate nel settore dell’autoveicolo per produrre ad esempio blocchi motore, coperchi punterie,
pistoni, grazie all’ottima correlazione tra resistenza meccanica e leggerezza che le contraddistingue. In particolare, i pistoni sono
soggetti a fratture per fatica vista la loro duale richiesta di resistenza alla fatica termica e di duttilità lungo l’intero volume del pezzo. I
FGM (Functionally Graded Materials) sono materiali compositi avanzati ideati per garantire una graduale variazione di proprietà e composizione
lungo il volume del materiale stesso. In questo lavoro, la lega per pistoni EN AC 48000 è impiegata insieme alla lega EN AC
42100 per la realizzazione di un FGM, con l’obiettivo di ottenere una variazione di proprietà lungo il volume del pezzo che garantisca
le caratteristiche meccaniche ottimali per un pistone. Le proprietà finali richieste vengono ottenute per mezzo di trattamento termico
T6 con solubilizzazione a 530°C ed invecchiamento artificiale a 175°C fornendo caratteristiche meccaniche apprezzabili
Medical-grade silicone coated with rhamnolipid R89 is effective against Staphylococcus spp. Biofilms
Staphylococcus aureus and Staphylococcus epidermidis are considered two of the most important pathogens, and their biofilms frequently cause device-associated infections. Microbial biosurfactants recently emerged as a new generation of anti-adhesive and anti-biofilm agents for coating implantable devices to preserve biocompatibility. In this study, R89 biosurfactant (R89BS) was evaluated as an anti-biofilm coating on medical-grade silicone. R89BS is composed of homologues of the mono- (75%) and di-rhamnolipid (25%) families, as evidenced by mass spectrometry analysis. The antimicrobial activity against Staphylococcus spp. planktonic and sessile cells was evaluated by microdilution and metabolic activity assays. R89BS inhibited S. aureus and S. epidermidis growth with minimal inhibitory concentrations (MIC99) of 0.06 and 0.12 mg/mL, respectively and dispersed their pre-formed biofilms up to 93%. Silicone elastomeric discs (SEDs) coated by R89BS simple adsorption significantly counteracted Staphylococcus spp. biofilm formation, in terms of both built-up biomass (up to 60% inhibition at 72 h) and cell metabolic activity (up to 68% inhibition at 72 h). SEM analysis revealed significant inhibition of the amount of biofilm-covered surface. No cytotoxic effect on eukaryotic cells was detected at concentrations up to 0.2 mg/mL. R89BS-coated SEDs satisfy biocompatibility requirements for leaching products. Results indicate that rhamnolipid coatings are effective anti-biofilm treatments and represent a promising strategy for the prevention of infection associated with implantable devices
Gestione delle conchiglie nella colata in gravità e possibili vie per migliorarne prestazioni e durata
La colata in gravità è una tecnologia di largo impiego nelle fonderie di alluminio: seppur ben nota è ancora attuale. Nonostante molte ricerche negli ultimi anni si siano focalizzate sullo studio di processi ad elevata produttività come la pressocolata, vi è ancora una larga serie di prodotti che viene ottenuta tramite colata in gravità , grazie a cui è possibile ottenere getti con difettosità ridotta e proprietà meccaniche superiori.
Nonostante la colata in gravità sia una tecnologia che non è possibile definire innovativa, l’evoluzione subita dai componenti in termini di geometria, dimensioni e volumi, ha imposto un aumento della produttività a fronte di una riduzione delle tolleranze accettabili. Questi cambiamenti hanno inficiato sulla vita delle conchiglie in acciaio, utensili che si usurano sempre più facilmente.
Per ottimizzare il processo produttivo è necessario introdurre su questa tecnologia già conosciuta degli elementi innovativi. In questo studio è presentato lo stato dell’arte dei metodi per aumentare la vita delle conchiglie nella colata in gravità con particolare attenzione all’effetto della rugosità superficiale della conchiglia e del metodo di verniciatura sulla resistenza ad usura ed alla metallizzazione
dell’acciaio. L’alluminio fuso infatti, durante il processo di colata, interagisce con l’acciaio di cui è costituita la conchiglia, producendo usura da erosione e metallizzazione delle superfici con cui entra in contatto.
Per limitare il danneggiamento della conchiglia si utilizzano comunemente delle vernici, al fine di creare una barriera tra i due materiali. Tuttavia il processo di verniciatura spesso viene effettuato basandosi su principi qualitativi e troppo spesso semi-quantitativi. Questo studio vuole investigare in modo più approfondito le fasi da seguire per l’ottenimento di una verniciatura ottimale, andando a utilizzare differenti vernici commerciali e valutandone la loro resistenza sia dal punto di vista sia della finitura superficiale della conchiglia che della resistenza alle alte temperature, simulando le condizioni d’uso reali della conchiglia, attraverso prove di usura e prove di immersione in alluminio fuso
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