Search results for "amorphous"
showing 10 items of 790 documents
Il management dell’ipersensibilità dentinale: dalla ricerca alla clinica
2014
Obiettivi. Scopo di questo lavoro è presentare le più recenti acquisizioni in tema di epidemiologia, diagnosi, eziopatogenesi e management clinico dell’ipersensibilità dentinale. Vengono inoltre descritti i prodotti disponibili per il suo trattamento e gli studi sperimentali e clinici condotti per valutarne l’efficacia. Materiali e metodi. Attraverso la banca dati Medline/Pubmed sono stati selezionati i lavori originali, le revisioni della letteratura e le linee guida pubblicate in lingua inglese e in italiano sull’argomento dal 2009 al 2013. Altre fonti sono state selezionate dai riferimenti bibliografici individuati. Risultati e conclusioni. Il management dell’ipersensibilità prevede il c…
Effects of fluoride versus amorphous calcium phosphate solutions on enamel microhardness of white spot lesions: An in-vitro study
2019
Background Development of white spot lesions around orthodontic fixed orthodontic appliances is a common finding, especially in patients with poor oral hygiene. One of the conservative interventions for regression of these lesions is using chemical solutions. The current study aimed to compare the effectiveness of fluoride and amorphous calcium phosphate (ACP) on microhardness improvement of affected enamel. Material and Methods Forty-five intact human incisor teeth were selected and randomly divided into 3 groups of 15. Fluoride group, ACP group and artificial saliva group (control group). Inducing of white spot lesion was done by PH-cycling model. Samples of the first and second group wer…
NanoSIMS: insights into the organization of the proteinaceous scaffold within Hexactinellid sponge spicules.
2010
The giant basal spicules (GBS) from Monorhaphis chuni (Porifera [sponges], Hexactinellida) represent the largest biosilica structures on Earth and can reach lengths of 300 cm (diameter of 1.1 cm). The amorphous silica of the inorganic matrix is formed enzymatically by silicatein. During this process, the enzyme remains trapped inside the lamellar-organized spicules. In order to localize the organic silicatein scaffold, the inside of a lamella has been analyzed by nano-secondary ion mass spectrometry (NanoSIMS). It is shown that the GBSs are composed of around 245 concentrically arranged individual siliceous lamellae. These surround an internal siliceous axial cylinder. The lamellae adjacent…
Studies on atomic layer deposition of IRMOF-8 thin films
2015
Deposition of IRMOF-8 thin films by atomic layer deposition was studied at 260–320 C. Zinc acetate and 2,6-naphthalenedicarboxylic acid were used as the precursors. The as-deposited amorphous films were crystallized in 70% relative humidity at room temperature resulting in an unknown phase with a large unit cell. An autoclave with dimethylformamide as the solvent was used to recrystallize the films into IRMOF-8 as confirmed by grazing incidence x-ray diffraction. The films were further characterized by high temperature x-ray diffraction (HTXRD), field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), time-of-flight elastic recoil detection analysis (TOF-…
Growth of Ice Particles by Accretion and Ice Particle Melting
2010
In Chapter 13, we discussed the growth of snow crystals by vapor diffusion, and in Chapter 14, we described the manner with which snow crystals interact with other snow crystals and with drops. In this chapter, we shalllook closer at the growth of ice particles by the accretion of supercooled drops, at the formation of snow flakes by the collision of snow crystals, and also consider the physics of melting of individual ice particles.
Vacuum-ultraviolet absorption of amorphous SiO2: intrinsic disorder and role of silanol groups
2008
We present a study on the vacuum-ultraviolet VUV absorption properties of amorphous SiO2 a-SiO2 with high concentrations of silanol groups Si-OH . We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from 7.5 to 8.1 eV, was attributed to Si-OH group absorption, while the second, in the range from 8.1 to 8.25 eV, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in a-SiO2 was determined as well. The intrinsic absorption was found to be affected by the Si-OH concentration: high silanol group contents allow lower values of the Urbach energy. This result is interpreted in terms of a reduction in th…
Sturctural disorder and silanol groups content in amorphous SiO2
2009
We present a study on the features of the Urbach edge in amorphous silicon dioxide a-SiO2 . The effects of temperature on the absorption edge in the range from 4 to 300 K were studied in both materials having negligible dry, 1017 cm−3 and significant wet, 1019 cm−3 silanol groups contents. Remarkable differences in the values and in the temperature dependence of the Urbach energy in the dry and wet samples were observed. These differences are interpreted as a consequence of a drastic reduction in the degree of disorder in wet materials, which turn out to be characterized by an electronic structure more similar to that of crystalline quartz. Furthermore, our results indicate that silanol gro…
Amorphous semiconducting passive film-electrolyte junctions revisited. The influence of a non homogeneous density of state on the differential admitt…
2006
Abstract An analysis of the electronic properties of amorphous semiconductor-electrolyte junction is reported for passive films grown on Nb in alkaline solution and in a large range of thickness (~20nm ÷ ~250nm). A modelling of electronic density of state (DOS) has been carried out by fitting EIS spectra, at different potentials and in a range of frequencies (0.1 Hz ≤ f ≤100 kHz), and differential admittance (DA) data of a-Nb 2 O 5 /El interface. The fitting of EIS and DA curves was performed by using the theory of amorphous semiconductor Schottky barrier and a non-homogeneous DOS distribution.