Search results for "GLASS"
showing 10 items of 1153 documents
Clinical guidelines for diagnosing and managing ocular manifestations in children with mucopolysaccharidosis.
2011
The mucopolysaccharidoses (MPS) are a group of rare lysosomal storage disorders characterized by the accumulation of glycosaminoglycans in several tissues and organs. This accumulation results in an array of clinical manifestations and premature death in severe cases. Ocular problems are very common in children with MPS and may involve the cornea, sclera, trabecular meshwork, retina, optic nerve and also the posterior visual pathways. The aims of this study are to give an overview of ocular problems in MPS and to provide clinical guidelines for paediatric ophthalmologists for early diagnosis and management of ocular manifestations in children with MPS. Diagnostic problems may arise in child…
Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy
2007
Abstract We report the results of a broadband (10−2–107 Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric rel…
Effect of a filler on the dielectric properties of an epoxy resin
1983
The effect of aluminum hydroxide upon the dielectric properties of an epoxy resin has been studied in a wide frequency and temperature range. An interfacial polarization effect, known as the Maxwell–Wagner–Sillars polarization is evidenced for the filled resin, which shows a higher permittivity, a higher dielectric loss, and a β transition with a larger relaxation time. The glass transition temperature is, on the contrary, mostly unaffected by the presence of the filler.
Dielectric spectroscopy measurements of the sub-Tg relaxations in amorphous ethyl cellulose: A relaxation magnitude study
2005
Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion.
Dielectric spectroscopy analysis of EVA-silicate nanocomposite insulating materials
2005
Nanocomposite materials show promising results for applications as electrical insulation. Among several materials presently under investigation, previous works indicate that polypropylene and ethylene-vinilacetate filled by nanosilicates present lower content of space charge and higher electric strength. However, efforts are needed to explain nanocomposite behaviour and characterize their electrical, thermal and mechanical properties. In this paper, the results of broad-band dielectric spectroscopy performed on ethylene-vinylacetate copolymer filled by layered micro and nanosized silicates are reported. The nanofillers consist of montmorillonite and fluorohectorite, that is, natural and syn…
Proton glass behavior and hopping conductivity in solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite.
1991
Measurements of the dielectric permittivity are reported for solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite at frequencies 10 −2 Hz T c the dielectric response is dominated by ac and dc conduction. The 40% sample exhibits pure relational behavior indicative of a transition into an orientational glass state
Simulation of the glass transition in polymeric systems: Evidence for an underlying phase transition?
1998
Abstract The bond fluctuation model of polymer chains on sc lattices with an energy that favours long bonds can describe the slowing down of supercooled melts that approach the glass transition in qualitative similarity with various experiments. In this paper we focus on the question of whether there exists a correlation length that increases to large values when the temperature is lowered towards the glass transition. Two types of analysis are presented: firstly density oscillations near hard walls become long range, and the resulting correlation length becomes larger than the gyration radius, secondly oscillations in the pair correlation function in real space also become long range, and …
Phase Transition in Niobophosphate Glass-Ceramic
2011
Phase transition during crystallization of glass to glass-ceramic in system P2O5-CaO-Nb2O5-Na2O was studied. Several heating rates were compared – 1, 2, 5, 11 and 20°Cmin-1. DTA, XRD, FTIR and Raman analyses were performed. Niobophosphate glass-ceramic is found to form utterly different crystalline phases depending on maximal heating temperature, heating rate and time of maximal temperature maintenance. Crystallization temperatures of the same phases are strongly dependent on heating rate, while crystallinity of obtained phases is not. At lower temperatures poorly crystalline phosphates (Ca3(PO4)2, Ca10Na(PO4)7, Ca2P2O7) and niobates (NaNbO3 and Nb2O5) are identified. At higher temperatures…
The kinetics of phase transitions in vitreous chalcogenide semiconductors As10.2Se89.8 and As9Se90Bi in early stage of physical ageing process
2013
The kinetics of glass transition in selenide glasses As10.2Se89.8 and As9Se90Bi in early stage of physical ageing process has been investigated by parallel differential scanning calorimetry (DSC) and exoelectron emission (EEE). It has been found that the glass transition process occurring in investigated glasses is evidenced by peaks on EEE intensity and DSC curves. Admixture of bismuth causes a distinct lowering of the temperature of glass transitions process both in the surface layer and in the volume. The addition of Bi causes a decrease in the value of the activation energy for glass transition process in both the volume and in the surface layer, thus reducing the thermal stability of i…
Phase Behavior and Microscopic Transport Processes in Binary Metallic Alloys: Computer Simulation Studies
2009
In a binary liquid mixture, different kinds of phase transitions can occur that are associated with various mass transport phenomena in the liquid. First, there is the possibility that the liquid undergoes a liquid-liquid demixing transition [1]. Near the critical point of this transition, a slowing down of dynamic properties is observed which is characterized, e.g., by a vanishing interdiffusion coefficient at the critical point [2, 3]. Another possible phase transition is a first-order transition of the liquid into a crystalline structure. In this case, crystal nucleation and growth are limited by the diffusive transport in the liquid [1, 4]. In a binary liquid, crystal nucleation process…