167 research outputs found
Method for determination of the displacement field in patterned nanostructures by TEM/CBED analysis of split high-order Laue zone line profiles
No full textA method to extract accurate information on the displacement field distribution from split high-order Laue zones lines in a convergent-beam electron diffraction pattern of nanostructures has been developed. Starting from two-dimensional many beam dynamical simulation of HOLZ patterns, we assembled a recursive procedure to reconstruct the displacement field in the investigated regions of the sample, based on the best fit of a parametrized model. This recursive procedure minimizes the differences between simulated and experimental patterns, taken in strained regions, by comparing the corresponding rocking curves of a number of high-order Laue zone reflections. Due to its sensitivity to small displacement variations along the electron beam direction, this method is able to discriminate between different models, and can be also used to map a strain field component in the specimen. We tested this method in a series of experimental convergent-beam electron diffrac tion patterns, taken in a shallow trench isolation structure. The method presented here is of general validity and, in principle, it can be applied to any sample where not negligible strain gradients along the beam direction are present
TEM study of annealed Pt nanostructures grown by electron beam induced deposition
No full textIn this paper we report on the microstructural characterization of Pt nanostructures fabricated by electron beam-induced deposition in a dual beam system and subsequently annealed in furnace. The as-deposited natiostructures are made of a mixture of nanocrystalline Pt and amorphous carbon. We show by transmission electron microscopy and electron energy loss spectroscopy that the annealing in presence of oxygen at 550 degrees C for 30 min is able to remove the amorphous carbon from the nanostructure, leaving polycrystalline Pt grains. (c) 2006 Elsevier B.V. All rights reserved
Reactive hyperemia during short-term blood flow and pressure changes in the hypertensive forearm.
No full textThe aim of the present study was to further validate our method for the determination of minimal forearm vascular resistance after ischemia (13 min arterial occlusion and 1 min hand exercise) in patients with hypertension. This parameter, calculated as the ratio of mean blood pressure (intra-arterial recordings on the experimental side) to forearm blood flow (strain-gauge venous plethysmography), was measured basally and after either increasing (through unrelated vasodilators such as sodium nitroprusside or the calcium antagonist nicardipine in six mild-to-moderate uncomplicated hypertensives) or decreasing (norepinephrine, n = 4) flow without changes in systemic pressure. In spite of the divergent starting flow values, minimal postischemic forearm vascular resistance was unchanged, indicating a lack of relationship with functional arteriolar tone and the achievement of maximal dilatation. In two additional groups of patients, systemic arterial pressure was decreased by approximately equipotent oral doses of either nifedipine, a calcium antagonist (n = 6), or captopril, an angiotension converting enzyme inhibitor (n = 5). Under these conditions, minimal forearm vascular resistance was unchanged from pretreatment values, suggesting that local autoregulatory mechanisms were overridden during the reactive hyperemia, and that the vessel lumen was dependent on the distending pressure. Overall, the data show that our experimental conditions are suitable for measuring minimal forearm vascular resistance as a functional correlate of the morphological status of systemic arterioles in arterial hypertension
Nontypeable Haemophilus influenzae eludes complement-mediated killing seizing C4b-binding protein
No full textNontypeable Haemophilus influenzae (NTHi) is a Gram negative, non-capsulated coccobacillus commensal of the nasopharyngeal tract. Acting as an opportunistic pathogen is responsible for different pathologies such as exacerbation of COPD, Otitis Media and in worst cases meningitis and sepsis. Given the great genetic variability among NTHi strains, the greatest challenge in the formulation of a vaccine against NTHi is the identification of cross protective antigens. Under the Novartis legacy (now GSK), several antigens were identified thanks to a reverse vaccinology and proteomic approaches. The ability of antibodies raised against those antigens to induce complement-mediated killing was tested in Serum Bactericidal Assay against a large panel of NTHi clinical strains; interestingly 20% of tested strains results to be resistant. Moreover these strains were also capable to evade the complement-mediated killing induced by normal human serum itself. We determined the cause of NTHi serum resistance as the ability to avoid C3 deposition on the bacterial surface, escaping the complement classical and lectin pathways activation. Like other bacterial pathogens NTHi is able to evade the C3 deposition seizing C4BP from the bloodstream. We assessed the ability of the resistant strains to bind C4BP, in comparison to sensitive strains, performing serum resistance assay, flow cytometry analysis and confocal microscopy. From literature it is known that binding of C4BP can be dependent on the decoration of the LOS. Therefore, a correlation between the Phosphorylcholyne (ChoP) expression and C4BP binding was investigated. We identified by Western blot and flow cytometry assay a negative correlation between ChoP expression and C4BP binding. Only sensitive strains resulted to decorate the LOS with ChoP. The essential role of C4BP in determining NTHi serum resistance was further confirmed depleting C4BP from the human serum. In absence of C4BP resistant strains became sensitive to killing. Finally, through a combined approach of co-immunoprecipitation technique and mass spectrometry, we identified Outer Membrane Protein P2 (Omp P2) as the putative protein responsible for the C4BP binding. Being Omp P2 a ubiquitous porin protein, well documented in literature, with highly conserved and highly variable extracellular domains, structural differences in this protein could be responsible for the different ability of the strains to bind C4BP determining then different susceptibility
Sviluppo di tecnologie innovative in fonderia
No full textSand casting is the most ancient metal forming process, but it is still one of the more useful manufacturing process. On the other hand, aluminum is a quite new material, and he established itself in the industry for its intrinsic characteristics like lightness, corrosion resistance, machinability, formability, thermal and electric conductivity, and more. The increasing use of aluminum in the most advanced fields, like aerospace, naval, electric, chemical, push quality to higher levels, and it involves optimizing the methods developed during the years and the use of appropriate process control tool.
The aim of this work is to review techniques and methods already known in academic world, to adopt them correctly in a real manufacturing process. The principal industrial interface has been Castalia, a company specialized in making big aluminum components by sand casting. Big attention is focused on thermal analysis: it is very useful like process control tool and to obtain experimental data on the solidification conditions of the casting. These information are very important to estimate the microstructural and metallurgical characteristics of the component.
The principal themes are:
Liquid metal treatments: grain refinement and eutectic structure modify make it possible to increase many casting properties, both on foundry process and final casting characteristics. Thermal analysis is used to control the treatments efficency and to estimate the impact of different cooling rates on microstructure.
Mold material: the final casting characteristics depend from the properties and quality of the mold. Advanced image analysis instruments are used to characterize foundry sands end the effect of the sand reclamation.
Directional solidification: Changing of the cooling rate in some zones of the casting is useful to avoid aluminum microshrinkage problems during solidification. Chills can be used to increase cooling rate in the zones where feeding could be a problem. Exothermal powders could be put on the feeder surface to keep them hotter for long times.Nonostante il processo di fonderia in sabbia sia la tecnica più antica di formatura dei metalli, ancora oggi è uno dei processi produttivi più utilizzati. D’altro canto l’alluminio è un materiale abbastanza nuovo, che si è imposto industrialmente per le sue caratteristiche intrinseche quali leggerezza, resistenza alla corrosione, lavorabilità, formabilità, conduttività termica ed elettrica, aspetto estetico e altri ancora. Il progressivo impiego nei settori più avanzati quali l’aerospaziale, il navale, l’elettrico ed il chimico, spinge verso una qualità dei getti sempre più alta, che comporta l’ottimizzazione dei metodi sviluppati negli anni e l’uso di opportuni strumenti di controllo del processo.
Lo scopo di questo lavoro è stato quello di rivedere metodi e tecniche già note a livello accademico, in modo da poterle applicare correttamente in un processo produttivo reale. In particolare, l’interfaccia industriale principale è stata Castalia, azienda specializzata nella realizzazione di grossi manufatti in alluminio mediante un processo di fonderia in sabbia - resina. Molta attenzione è stata data all’analisi termica, utilizzabile sia come strumento di controllo del processo, sia per ottenere informazioni sperimentali sulle modalità di solidificazione del getto, le quali diventano molto importanti per stimare le caratteristiche microstrutturali e metallurgiche del componente.
Volendo riassumere le principali tematiche affrontate si ricorda:
Trattamenti sulla lega liquida: l’affinazione del grano e la modifica della struttura eutettica permettono di incrementare diverse proprietà del getto, sia inerenti al processo fusorio che alle caratteristiche finali del getto. L’analisi termica è stata utilizzata per controllare l’efficacia dei trattamenti e per valutare l’impatto delle diverse velocità di raffreddamento sulla microstruttura.
Materiali di formatura: le caratteristiche finali di un getto dipendono fortemente dalla qualità e dalle proprietà della forma. Avanzati strumenti di analisi di immagine sono stati sfruttati per caratterizzare le sabbie da fonderia e l’effetto del trattamento di rigenerazione.
Direzionalità della solidificazione: per evitare problematiche legate al ritiro dell’alluminio in fase di solidificazione, può essere utile modificare la velocità di raffreddamento in alcuni punti del getto. Le conchiglie di raffreddamento vengono utilizzate per accelerare la solidificazione nei punti in cui l’alimentazione può essere più difficoltosa, mentre polveri esotermiche possono essere poste sopra le materozze per mantenerle calde più a lungo
Strain field reconstruction in shallow trench isolation structures by CBED and LACBED
No full textUsing a combination of the CBED and the LACBED techniques in the transmission electron microscopy (TEM), we have investigated the strain field in the silicon active region of a shallow trench isolation structure, underlying a TiSi2 layer. Starting from the analysis of the deformation in a sample, thinned for TEM analysis, we have reconstructed the displacement field, simulating the split HOLZ lines visible in the experimental CBED patterns. From the comparison between the experimental LACBED patterns, taken in a suitable sample orientation to evidence the stressors distribution in the polycrystalline silicide layer, and the corresponding dynamically simulated ones, we have reproduced the strain field in the unthinned, bulk sample. (c) 2006 Elsevier B.V. All rights reserved
Transmission Electron Microscopy characterization and sculpting of sub-1 nm Si-O-C freestanding nanowires grown by electron beam induced deposition
No full textThe authors present a transmission electron microscopy characterization and sculpting of freestanding Si-O-C nanowires, fabricated by electron beam induced deposition from a tetraethylorthosilicate precursor, in a dual beam system. Electron energy loss spectroscopy and near edge structure analyses performed on as deposited wires show the formation of amorphous silicon dioxide with extra oxygen and carbon content. Subsequent electron beam sculpting by 200 keV transmission electron microscope irradiation decreases carbon and oxygen contents leaving the silicon oxidation state unchanged and narrows Si-O-C wire width to less than 1 nm. (c) 2006 American Institute of Physics
The interference by nicardipine and diltiazem on alpha-adrenergic receptor-mediated vasoconstriction in isolated human subcutaneous arterioles
No full textThe effects of nicardipine and diltiazem on alpha-adrenergic receptor-mediated vasoconstriction in isolated human subcutaneous arterioles was studied. Arterioles were mounted in a myograph and stimulated at 50% of maximal contraction with norepinephrine. The vasoconstrictor responses to an unrelated agonist, endothelin, was used for comparison. The percentage of decrement in tension produced by nicardipine or diltiazem was the parameter evaluated. Both calcium channel blockers caused an equipotent and dose-dependent relaxation of the vasoconstrictor responses to norepinephrine and endothelin I. The equipotent alpha-adrenolytic effect exerted by nicardipine and diltiazem in subcutaneous arterioles contrasts with the preferential antagonism by local nicardipine in the forearm. This suggests that the interaction between alpha-adrenergic receptor activation and structurally unrelated calcium channel blockers is affected by the regional and functional characteristics of the vessels under stud
Calcium entry blockade and agonist-mediated forearm vasoconstriction in hypertensive patients. Difference between nicardipine and verapamil.
No full textThe interference by nicardipine and verapamil with the response to vasoactive stimuli, such as lower body negative pressure and angiotensin II, has been evaluated in the forearm of hypertensive patients. Forearm blood flow was monitored during the intraarterial infusion of either drug at rates equieffective on basal flow. Nicardipine blunted the peak forearm vasoconstrictor action of lower body negative pressure and a comparable result was obtained when angiotensin II was administered intraarterially. In spite of a comparable increase in forearm flow, nicardipine was more potent than verapamil in inhibiting vasoconstriction following both stimuli. Thus, nicardipine suppressed regional vascular reactivity, probably by blockade of the influx of extracellular calcium, in response to receptor activation, since both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. However, the results of the comparison with an unrelated calcium entry blocker, such as verapamil, may suggest that nicardipine, and possibly other dihydropiridine derivatives, preferentially antagonize agonist-mediated vasoconstriction in the human forearm
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