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At least 1,189 records · Page 66Linked to original sources
PubMed2001

Energy dispersive analysis (EDX) of a degradable bioactive-glass coating on Ti6Al4V in-vivo.

The bioactive-glass coating of metallic substrates provides a gradually degrading interface which can be used to favor the bony integration of the implant by the physiologic processes of bone turn-over and remodeling. Twelve New Zealand White rabbits, about 2700 g of weight, were operated by the sagittal insertion of a bioactive-glass coated plate of Ti6Al4V. Retrievals were performed at 4, 8 and 12 weeks. Undecalcified specimens were embedded in methyl-metacrylate and sectioned at 100 microns of thickness. Blocks were grinded and had an electroconductive coating to be examined by scanning electron microscopy (SEM), back scattering electron microscopy (BSEM) and X-ray energy dispersive spectroscopy microanalysis (EDX). EDX allows to evaluate quantitatively the gradual process of coating degradation. Areas of 200 microns in square were analyzed at the interface between bone and coating to determine their elemental composition. Silicon was the key marker for the presence of the glass. Morphological analysis confirms that a tight apposition with bone can be obtained by utilizing the bioactive glass coating of metal. Results of energy dispersive analysis support the mechanism of a gradual degradation of the bioactive glass coating and its integration with bone, since the presence of silicon can be documented within the newly formed bone after the coating has disappeared.

Journal Article↗
PubMed2003

[Diagnosis of chronic prostatitis: 4 or 2 glass sample?].

Chronic pelvic pain syndrome is still an important clinical problem. The NIH-prostatitis classification introduced 1998 for diagnosis and treatment measures is based on extended microbiological analysis of urine, expressed prostate secretion (4-glass test), and ejaculate. We investigated if a simple urine analysis of an urine sample before and after prostatic massage (2-glass test) could replace the 4-glass test. 143 patients with the diagnosis chronic prostatitis were included in this prospective study. The results showed that the expensive and time consuming 4-glass test can be replaced by a simple 2-glass test. Extended examinations should only be performed in special cases.

Adult↗
PubMed2001

The relationship between fragility, configurational entropy and the potential energy landscape of glass-forming liquids.

Glass is a microscopically disordered, solid form of matter that results when a fluid is cooled or compressed in such a manner that it does not crystallize. Almost all types of materials are capable of glass formation, including polymers, metal alloys and molten salts. Given such diversity, general principles by which different glass-forming materials can be systematically classified are invaluable. One such principle is the classification of glass-formers according to their fragility. Fragility measures the rapidity with which a liquid's properties (such as viscosity) change as the glassy state is approached. Although the relationship between the fragility, configurational entropy and features of the energy landscape (the complicated dependence of energy on configuration) of a glass-former have been analysed previously, a detailed understanding of the origins of fragility is lacking. Here I use simulations to analyse the relationship between fragility and quantitative measures of the energy landscape for a model liquid whose fragility depends on its bulk density. The results reveal that fragility depends on changes in the vibrational properties of individual energy minima in addition to their total number and spread in energy. A thermodynamic expression for fragility is derived, which is in quantitative agreement with kinetic fragilities obtained from the liquid's diffusivity.

Journal Article↗
PubMed2005

Topological versus chemical ordering in network glasses at intermediate and extended length scales.

Atomic ordering in network glasses on length scales longer than nearest-neighbour length scales has long been a source of controversy. Detailed experimental information is therefore necessary to understand both the network properties and the fundamentals of glass formation. Here we address the problem by investigating topological and chemical ordering in structurally disordered AX2 systems by applying the method of isotopic substitution in neutron diffraction to glassy ZnCl2. This system may be regarded as a prototypical ionic network forming glass, provided that ion polarization effects are taken into account, and has thus been the focus of much attention. By experiment, we show that both the topological and chemical ordering are described by two length scales at distances greater than nearest-neighbour length scales. One of these is associated with the intermediate range, as manifested by the appearance in the measured diffraction patterns of a first sharp diffraction peak at 1.09(3) A(-1); the other is associated with an extended range, which shows ordering in the glass out to 62(4) A. We also find that these general features are characteristic of glassy GeSe2, a prototypical covalently bonded network material. The results therefore offer structural insight into those length scales that determine many important aspects of supercooled liquid and glass phenomenology.

Journal Article↗
PubMed2005

Electromagnetic vibration process for producing bulk metallic glasses.

It is known that the cooling rate from the liquid state is an important factor in the production of bulk metallic glasses. However, the effects of other factors such as electric and magnetic fields have not been thoroughly investigated. Here, we present a new method for producing bulk metallic glasses by using electromagnetic vibrations with simultaneous imposition of an alternating electric current and a magnetic field. This method was found to be effective in enhancing apparent glass-forming ability in Mg65-Cu25-Y10 (atomic percent) alloys. Indeed, larger bulk metallic glasses could be obtained by the electromagnetic vibration process under the same cooling conditions. We presume that disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state cause suppression of crystal nucleation. This electromagnetic vibration process should be effective in other bulk metallic glass systems if the clusters in the liquid state cause the crystal nucleation.

Alloys↗
PubMed2003

The effect of home-use fluoride gels on glass-ionomer, compomer and composite resin restorations.

The purpose of this study was to investigate the resistance to dissolution by two home-use fluoride gels on the surface integrity of glass-ionomer, resin modified glass-ionomer, compomer and composite resin restorations. Class V cavities prepared in extracted teeth were restored with a glass-ionomer (Fuji II), a resin modified glass-ionomer (Vitremenr), two compomers (Dyract and F-2000) and a composite resin (Z-100). Groups of five specimens of each material were treated for 24 h with one of the following: (i). distilled water, (ii). neutral fluoride gel and (iii). acidulated phosphate fluoride (APF) gel. Surface degradation of the restorations was studied using standard electron microscopy (SEM), rated according to specific criteria and statistically analysed by the Wilcoxon test (rank sums). Acidulated phosphate fluoride was found to have a significant effect on all examined materials, while minimal effects resulted from the neutral fluoride gel compared with the control group. The effect of home-use fluoride gels on glass-ionomer, compomer and composite resin restorations.

Acidulated Phosphate Fluoride↗
PubMed2000

Reconstruction of orbital floor fractures using bioactive glass.

INTRODUCTION: The management of orbital floor fractures continues to be debated. Bioactive glasses and glass-ceramics are in the new group of materials developed for the repair of bone defects which are beyond any innate healing capacity due to their size. OBJECTIVE: We compared the use of alloplastic implants (bioactive glass) with conventional autogenous grafts (cartilage--plus or minus Iyophilized dura) for the repair of orbital floor defects after trauma. MATERIAL AND METHODS: Twenty-eight patients having orbital floor fractures with persistent diplopia, enophthalmos, and/or infraorbital nerve paraesthesia were operated on from 1991 to 1995 at Turku University Central Hospital. Reconstruction was either with bioactive glass (S93P4) or autogenous cartilage implants. RESULTS: Postoperative tomograms in the 28 patients showed adequate maintenance of orbital and maxillary sinus volume without any evidence of resorption in either group. None of 14 patients in the study group had any evidence of dystopia or complications relating to implants follow-up. One had infraorbital nerve paraesthesia and another had entropion postoperatively. Among the 14 control subjects there were three cases of persistent diplopia, two of infraorbital nerve paraesthesia and one of enophthalmos. CONCLUSION: Bioactive glass implants are well-tolerated and seem to be a promising repair material for orbital floor fractures. Their use leads to less morbidity as no donor site operation is needed. Also it provides favourable healing as it is bioactive, biocompatible and causes new bone formation.

Adolescent↗
PubMed2006

Gel to glass transition in simulation of a valence-limited colloidal system.

We numerically study a simple model for thermoreversible colloidal gelation in which particles can form reversible bonds with a predefined maximum number of neighbors. We focus on three and four maximally coordinated particles, since in these two cases the low valency makes it possible to probe, in equilibrium, slow dynamics down to very low temperatures T. By studying a large region of T and packing fraction phi we are able to estimate both the location of the liquid-gas phase separation spinodal and the locus of dynamic arrest, where the system is trapped in a disordered nonergodic state. We find that there are two distinct arrest lines for the system: a glass line at high packing fraction, and a gel line at low phi and T. The former is rather vertical (phi controlled), while the latter is rather horizontal (T controlled) in the phi-T plane. Dynamics on approaching the glass line along isotherms exhibit a power-law dependence on phi, while dynamics along isochores follow an activated (Arrhenius) dependence. The gel has clearly distinct properties from those of both a repulsive and an attractive glass. A gel to glass crossover occurs in a fairly narrow range in phi along low-T isotherms, seen most strikingly in the behavior of the nonergodicity factor. Interestingly, we detect the presence of anomalous dynamics, such as subdiffusive behavior for the mean squared displacement and logarithmic decay for the density correlation functions in the region where the gel dynamics interferes with the glass dynamics.

Journal Article↗
PubMed2006

Dynamic light scattering in mixed alkali metaphosphate glass forming liquids.

We report the first ever photon correlation spectroscopy performed on single alkali and mixed alkali metaphosphate glasses at refractory temperatures above the glass transition. We find not only a significant decrease in the glass transition temperature but also a decrease in fragility for the mixed alkali composition as compared with the single akali glasses. We argue that structural relaxation in these polymeric oxide glasses is largely controlled by the cross linking cations and that the changes in fragility that we observed are a reflection of changes in the cooperativity of structural relaxation wrought by the substantial decrease in the ion mobility that accompanies the mixing of alkali ions.

Journal Article↗
PubMed2006

Densification of silica glass at ambient pressure.

We show that densification of silica glass at ambient pressure as observed in irradiation experiments can be attributed to defect generation and subsequent structure relaxation. In our molecular dynamics simulations, defects are created by randomly removing atoms, by displacing atoms from their nominal positions in an otherwise intact glass, and by assigning certain atom excess kinetic energy (simulated ion implantation). The former forms vacancies; displacing atoms and ion implantation produce both vacancies and "interstitials." Appreciable densification is induced by these defects after equilibration of the defective glasses. The structural and vibrational properties of the densified glasses are characterized, displaying resembling features regardless of the means of densification. These results indicate that relaxation of high free-energy defects into metastable amorphous structures enriched in atomic coordination serves as a common mechanism for densification of silica glass at ambient pressure.

Journal Article↗
PubMed2006

Glass transition in fullerenes: mode-coupling theory predictions.

We report idealized mode-coupling theory results for the glass transition of ensembles of model fullerenes interacting via phenomenological two-body potentials. Transition lines are found for C60, C70, and C96 in the temperature-density plane. We argue that the observed glass transition behavior is indicative of kinetic arrest that is strongly driven by the interparticle attraction in addition to excluded-volume repulsion. In this respect, these systems differ from most standard glass-forming liquids. They feature arrest that occurs at lower densities and that is stronger than would be expected for repulsion-dominated hard-sphere-like or Lennard-Jones-type systems. The influence of attraction increases with increasing the number of carbon atoms per molecule. However, unrealistically large fullerenes would be needed to yield behavior reminiscent of recently investigated model colloids with strong short-ranged attraction (glass-glass transitions and logarithmic decay of time-correlation functions).

Journal Article↗
PubMed2007

Theory of relaxation and elasticity in polymer glasses.

The recently developed activated barrier hopping theory of deeply supercooled polymer melts [K. S. Schweizer and E. J. Saltzman, J. Chem. Phys. 121, 1984 (2004)] is extended to the nonequilibrium glass state. Below the kinetic glass temperature T(g), the exact statistical mechanical relation between the dimensionless amplitude of long wavelength density fluctuations, S(0), and the thermodynamic compressibility breaks down. Proper extension of the theory requires knowledge of the nonequilibrium S(0) which x-ray scattering experiments find to consist of a material specific and temperature-independent quenched disorder contribution plus a vibrational contribution which varies roughly linearly with temperature. Motivated by these experiments and general landscape concepts, a simple model is proposed for S(0)(T). Deep in the glass state the form of the temperature dependence of the segmental relaxation time is found to depend sensitively on the magnitude of frozen in density fluctuations. At the (modest) sub-T(g) temperatures typically probed in experiment, an effective Arrhenius behavior is generically predicted which is of nonequilibrium origin. The change in apparent activation energy across the glass transition is determined by the amplitude of frozen density fluctuations. For values of the latter consistent with experiment, the theory predicts a ratio of effective activation energies in the range of 3-6, in agreement with multiple measurements. Calculations of the shear modulus for atactic polymethylmethacrylate above and below the glass transition temperature have also been performed. The present work provides a foundation for the formulation of predictive theories of physical aging, the influence of deformation on the alpha relaxation process, and rate-dependent nonlinear mechanical properties of thermoplastics.

Journal Article↗
PubMed1996

Identification and characterization of autosomal genes that interact with glass in the developing Drosophila eye.

The glass gene encodes a zinc finger, DNA-binding protein that is required for photoreceptor cell development in Drosophila melanogaster. In the developing compound eye, glass function is regulated at two points: (1) the protein is expressed in all cells' nuclei posterior to the morphogenetic furrow and (2) the ability of the Glass protein to regulate downstream genes is largely limited to the developing photoreceptor cells. We conducted a series of genetic screens for autosomal dominant second-site modifiers of the weal allele glass3, to discover genes with products that may regulate glass function at either of these levels. Seventy-six dominant enhancer mutations were recovered (and no dominant suppressors). Most of these dominant mutations are in essential genes and are associated with recessive lethality. We have assigned these mutations to 23 complementation groups that include multiple alleles of Star and hedgehog as well as single alleles of Delta, roughened eye, glass and hairy. Mutations in 18 of the complementation groups are embryonic lethals, and of these, 13 show abnormal adult retinal phenotypes in homozygous clones, usually with altered numbers of photoreceptor cells in some of the ommatidia.

Animals↗
PubMed2002

Holding power of bioabsorbable ciprofloxacin-containing self-reinforced poly-L/DL-lactide 70/30 bioactive glass 13 miniscrews in human cadaver bone.

Antibiotics-plus bioactive glass-containing bioabsorbable self-reinforced (SR) polylactide screws have been developed for antibacterial osteoconductive bone fixation. The aim of the present study was to test the pullout properties of these recently developed miniscrews. Ciprofloxacin-plus bioactive glass-containing SR-polylactide miniscrews (BC) were compared with miniscrews made of neat SR-polylactide (A), SR-polylactide with bioactive glass (B), and ciprofloxacin-containing SR-polylactide (C). BC miniscrews and their controls (A, B, C) (all of length 6.0 mm, core diameter 1.45 mm, thread diameter 2.0 mm) were applied to one pair of cadaveric fibulae. Pullout force was measured using a materials testing machine. We carried out 49-50 pullout tests for each implant type. The Mann-Whitney test and Student's t-test were used for statistical evaluation. The pullout force for BC miniscrews was 114.9 +/- 34.0 (SD) N. Pullout forces for control miniscrews were 162.7 +/- 37.8 N (A), 99.1 +/- 16.2 N (B), and 142.9 +/- 26.9 N (C). Differences between the four groups were statistically significant (p < 0.001). Ciprofloxacin-plus bioactive glass-containing polylactide miniscrews have good holding power to human cadaver fibulae. However, adding bioactive glass and ciprofloxacin components to neat SR-polylactide results in lower pullout values.

Absorbable Implants↗
PubMed2000

Correlation functions for glass-forming systems

We present a simple, linear, partial-differential equation for the density-density correlation function in a glass-forming system. The equation is written down on the basis of fundamental and general considerations of linearity, symmetry, stability, thermodynamic irreversibility and consistency with the equation of continuity (i.e. , conservation of matter). The dynamical properties of the solutions show a change in behavior characteristic of the liquid-glass transition as a function of one of the parameters (temperature). The equation can be shown to lead to the simplest mode-coupling theory of glasses and provides a partial justification of this simplest theory. It provides also a method for calculating the space dependence of the correlation functions not available otherwise. The results suggest certain differences in behavior between glassy solids and glass-forming liquids which may be accessible to experiment. A brief discussion is presented of how the method can be applied to other systems such as sandpiles and vortex glasses in type II superconductors.

Journal Article↗
PubMed2001

Glass transition of a particle in a random potential, front selection in nonlinear renormalization group, and entropic phenomena in Liouville and sinh-Gordon models.

We study via renormalization group (RG), numerics, exact bounds, and qualitative arguments the equilibrium Gibbs measure of a particle in a d-dimensional Gaussian random potential with translationally invariant logarithmic spatial correlations. We show that for any d>/=1 it exhibits a transition at T=T(c)>0. The low-temperature glass phase has a nontrivial structure, being dominated by a few distant states (with replica symmetry breaking phenomenology). In finite dimension this transition exists only in this "marginal glass" case (energy fluctuation exponent straight theta=0) and disappears if correlations grow faster (single ground-state dominance straight theta>0) or slower (high-temperature phase). The associated extremal statistics problem for correlated energy landscapes exhibits universal features which we describe using a nonlinear Kolmogorov (KPP) RG equation. These include the tails of the distribution of the minimal energy (or free energy) and the finite-size corrections, which are universal. The glass transition is closely related to Derrida's random energy models. In d=2, the connection between this problem and Liouville and sinh-Gordon models is discussed. The glass transition of the particle exhibits interesting similarities with the weak- to strong-coupling transition in Liouville (c=1 barrier) and with a transition that we conjecture for the sinh-Gordon model, with correspondence in some exact results and RG analysis. Glassy freezing of the particle is associated with the generation under RG of new local operators and of nonsmooth configurations in Liouville. Applications to Dirac fermions in random magnetic fields at criticality reveal a peculiar "quasilocalized" regime (corresponding to the glass phase for the particle), where eigenfunctions are concentrated over a finite number of distant regions, and allow us to recover the multifractal spectrum in the delocalized regime.

Journal Article↗
PubMed2002

Structural probe of a glass-forming liquid: generalized compressibility.

We introduce a structural quantity to probe the glass transition. This quantity is a linear generalized compressibility which depends solely on the positions of the particles. We have performed a molecular dynamics simulation on a glass-forming liquid consisting of a two-component mixture of soft spheres in three dimensions. As the temperature is lowered (or as the density is increased), the generalized compressibility drops sharply at the glass transition, with the drop becoming more and more abrupt as the measurement time increases. At our longest measurement times, the drop occurs approximately at the mode coupling temperature T(C). The drop in the linear generalized compressibility occurs at the same temperature as the peak in the specific heat. By examining the inherent structure energy as a function of temperature, we find that our results are consistent with the kinetic view of the glass transition in which the system falls out of equilibrium. We find no size dependence and no evidence for a second order phase transition, though this does not exclude the possibility of a phase transition below the observed glass transition temperature. We discuss the relation between the linear generalized compressibility and the ordinary isothermal compressibility, as well as the static structure factor.

Journal Article↗
PubMed2002

High-frequency dynamics of the glass former dibutylphthalate under pressure.

The high-frequency dynamics of a fragile molecular glass former (dibutylphthalate) was studied through inelastic x-ray scattering (IXS), as a function of pressure and temperature. The mesoscopic structural arrest associated with the glass transition process was tracked by following upon cooling the inelastic excitations at fixed Q points in the dispersion curves, at ambient pressure and 2 kbar. The application of pressure to this system induces an offset between the macroscopic glass transition temperature T(g) and the mesoscopic glass transition temperature, as determined from IXS. The concomitant fragility decrease of dibutylphthalate under pressure unveils that the stronger the glass former is, the more its mesoscopic dynamics differ from the macroscopic regime. This trend is interpreted as the signature of a nanoscopic inhomogeneous elastic network. Further aspects of this system are obtained when studying the temperature dependence of its nonergodicity factor f(Q)(T). The chemical specificity of the molecule is suggested to be responsible for the nonobservation of a critical temperature T(c) in dibutylphthalate up to approximately 300 K.

Journal Article↗