Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GLASSES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed2002

Rearrangements in hard-sphere glasses under oscillatory shear strain.

We investigate particle rearrangements in colloidal glasses subjected to oscillatory shear strain by the technique of light scattering (LS) echo. LS echo directly follows the motion of the particles through peaks (echoes) in the intensity autocorrelation function; the height of the peak measures the reversible motion in the sample. Polydisperse hard-sphere poly-methylmethacrylate particles were used to avoid crystallization under shear. The yielding behavior is monitored through irreversible particle rearrangements at several volume fractions in the glass phase region. At high volume fractions the glasses are found to yield at strains as high as 15% while the irreversible rearrangements have a more gradual onset with strain for low volume fraction glasses. The behavior of high order echoes at long times is related to the effects of shear on the frozen-in fluctuations of the glass.

Journal Article↗
PubMed2003

Fracture behavior of Lennard-Jones glasses.

The fracture behavior of binary Lennard-Jones (LJ) glasses is studied by extensive molecular dynamics simulations. These LJ glasses represent a nonbond limit of polymer network glasses. We determine that the low strain behavior of the LJ and polymer glasses is similar. Two different LJ glasses are fractured under tensile strain without any preexisting crack. Void formation and resulting growth as strain increases is the mechanism through which the system fails. Void formation initiates at the yield strain of varepsilon (y) approximately 0.09, which is approximately the same strain at which the yielding behavior is first observed in cross-linked network models of polymer adhesives. The yield stress increased only by small amounts with increased strain rate and with increased system size (from N=30 000 atoms to 120 000 atoms). Within the ranges tested, the stress-strain behavior of these systems is independent of the temperature drop during quench and the initial molecular configuration.

Journal Article↗
PubMed2004

Dynamics in colloidal liquids near a crossing of glass- and gel-transition lines.

Within the mode-coupling theory for ideal glass transitions, the mean-squared displacement and the correlation function for density fluctuations are evaluated for a colloidal liquid of particles interacting with a square-well potential for states near the crossing of the line for transitions to a gel with the line for transitions to a glass. It is demonstrated how the dynamics is ruled by the interplay of the mechanisms of arrest due to hard-core repulsion and due to attraction-induced bond formation as well as by a nearby higher-order glass-transition singularity. Application of the universal relaxation laws for the slow dynamics near glass-transition singularities explains the qualitative features of the calculated time dependence of the mean-squared displacement, which are in accord with the findings obtained in molecular-dynamics simulation studies by Zaccarelli et al. [Phys. Rev. E 66, 041402 (2002)]. Correlation functions found by photon-correlation spectroscopy in a micellar system by Mallamace et al. [Phys. Rev. Lett. 84, 5431 (2000)] can be interpreted qualitatively as a crossover from gel to glass dynamics.

Journal Article↗
PubMed2004

Nonergodic states of charged colloidal suspensions: repulsive and attractive glasses and gels.

Two types of isotropic disordered nonergodic states exist in colloidal suspensions: glasses and gels. The difference between the two is that the nonergodicity, or elasticity, of gel stems from the existence of a percolated network, while that of glass stems from caging effects. Despite this clear difference in the origin of nonergodicity, it is not straightforward to distinguish the two states in a clear manner. Taking a Laponite suspension as an explicit example, we propose a general phase diagram for charged colloidal systems. It follows that a transition from the glass to the gel state can be induced by changing the interparticle interactions from predominantly repulsive to attractive. This originates from the competition between electrostatic Coulomb repulsion and van der Waals attraction. If the repulsion dominates, the system forms a Wigner glass, while in a predominantly attractive situation it forms a gel. In the intermediate region, where both repulsive and attractive interactions play roles, it may form an attractive glass.

Journal Article↗
PubMed2005

Correlation of fragility of supercooled liquids with elastic properties of glasses.

We present a detailed analysis of correlations between fragility and other parameters of glass-forming systems. The analysis shows the importance of the ratio between the instantaneous bulk and shear modulus of glass-forming systems, or their Poisson ratio, for structural alpha relaxation and fast dynamics. In particular, for simple glass formers, the bulk to shear modulus ratio in the glassy state correlates with fragility in the liquid state and is inversely proportional to the intensity of the boson peak. A simple relationship between the temperature dependence of the viscosity of liquids at high temperatures and near the glass transition is used to rationalize these correlations. We argue that the ratio of the moduli controls the high-temperature activation energy of the structural relaxation and in this way affects the fragility. The ratio also defines the amplitude of the structural relaxation (i.e., the nonergodicity parameter) and the latter influences the strength of the boson peak. These observations might explain the puzzling correlation observed between the fragility and fast dynamics in glass-forming systems.

Journal Article↗
PubMed2005

Structural relaxation in the glass transition region of water.

We perform molecular dynamics (MD) simulations using the extended simple-point-charge (SPC/E) model for water to study the structural relaxation through the glass transition region. We follow the same standard protocol used in differential scanning calorimetry experiments. Specifically, we cool liquid configurations at different cooling rates to produce a glass, and then we heat the glass back to the liquid state. We also study aging effects in the glass before heating. We find that MD simulations can reproduce the phenomenology observed in experiments. We review the Tool-Narayanaswamy-Moynihan (TNM) phenomenological approach, introduced to describe the behavior of the specific heat upon heating glass to the liquid phase. The TNM approach requires, as an ansatz, an expression for the temperature dependence of the relaxation time. We compare the simulation results with the prediction of the TNM approach supplemented with two well-known expressions for the relaxation time: the Narayanaswamy-Moynihan (NM) and the Adam-Gibbs-Scherer (AGS) expressions. We find that, in the case of slow cooling rates, our simulations are well represented by the TNM approach, but only if the AGS expression is adopted. We also find that the TNM approach fails in the case of fast cooling rates for both NM and AGS expressions. Several attempts to provide more freedom to the fitting procedure by allowing the fitting parameters to depend on temperature, cooling, and/or heating rates do not improve the agreement between the simulation data and the TNM predictions.

Journal Article↗
PubMed2004

Spin anisotropy and slow dynamics in spin glasses.

We report on an extensive study of the influence of spin anisotropy on spin glass aging dynamics. New temperature cycle experiments allow us to compare quantitatively the memory effect in four Heisenberg spin glasses with various degrees of random anisotropy and one Ising spin glass. The sharpness of the memory effect appears to decrease continuously with the spin anisotropy. Besides, the spin glass coherence length is determined by magnetic field change experiments for the first time in the Ising sample. For three representative samples, from Heisenberg to Ising spin glasses, we can consistently account for both sets of experiments (temperature cycle and magnetic field change) using a single expression for the growth of the coherence length with time.

Journal Article↗
PubMed2004

Gravity-induced aging in glasses of colloidal hard spheres.

The influence of gravity on the long-time behavior of the mean squared displacement in glasses of polydisperse colloidal hard spheres was studied by means of real-space fluorescent recovery after photobleaching. We present, for the first time, a significant influence of gravity on the mean squared displacements of the particles. In particular, we observe that systems which are glasses under gravity (with a gravitational length on the order of tens of micrometers) show anomalous diffusion over several decades in time if the gravitational length is increased by an order of magnitude. No influence of gravity was observed in systems below the glass transition density. We show that this behavior is caused by gravity dramatically accelerating aging in colloidal hard sphere glasses. This behavior explains the observation that colloidal hard sphere systems which are a glass on Earth rapidly crystallize in space.

Journal Article↗
PubMed2004

Energy landscape picture of overaging and rejuvenation in a sheared glass.

Molecular simulations and an energy landscape analysis are used to investigate the effects of shear on aging in a glass. Shear beyond the yield point is shown to change the state of a glass such that it resembles (but is not identical to) a different stage in the aging process. A cycle of large strain rejuvenates the glass by relocating the system to shallower energy minima, while a cycle of small strain overages the glass by relocating the system to deeper energy minima. The balance between overaging and rejuvenation is controlled by how well the glass was initially annealed.

Journal Article↗
PubMed2006

Phase separating bulk metallic glass: a hierarchical composite.

Phase separating systems present a unique opportunity for designing composites with hierarchical microstructure at different length scales. We report here our success in synthesizing phase separating metallic glasses exhibiting the entire spectrum of microstructural possibilities expected from a phase separating system. In particular, we report novel core shell and hierarchical structures of spherical glassy droplets, resulting from critical wetting behavior and limited diffusion. We also report synthesis of a bulk phase separating glass in a metallic glass system. The combination of unique core shell and hierarchical structures in metallic glass systems opens a new avenue for the microstructure design of metallic glasses.

Journal Article↗
PubMed2005

The effect of bioactive glass ceramics on the expression of bone-related genes and proteins in vitro.

Using biodegradable bone substitutes in alveolar ridge augmentation avoids second-site surgery for autograft harvesting. Considerable efforts have been undertaken to develop rapidly resorbable bone substitute materials with a higher degree of biodegradability than tricalcium phosphate (TCP). This study examines the effect of novel biodegradable glass ceramics on the expression of bone-related genes and proteins by human bone-derived cells (HBDC) and compares this behavior with that of TCP. Test materials used were alpha-TCP, a surface-treated glass ceramic GB9N with crystalline phase Ca(2)KNa(PO(4))(2) and a small amount of amorphous silica phosphate; AP40 - a glass ceramic based on crystalline phases of apatite and wollastonite; and a glass ceramic Mg5 composed of 20.6% CaO, 58.5% P(2)O(5), 14.4% Na(2)O, 4.1% MgO and 2.4% CaF(2) (wt%). HBDC were grown on the substrata for 3, 5, 7, 14 and 21 days, counted and probed for various bone-related mRNAs and proteins (type I collagen (Col I), osteocalcin (OC), osteopontin (OP), osteonectin (ON), alkaline phosphatase (ALP) and bone sialoprotein (BSP)). The substrata supported continuous cellular growth for 21 days. By day 21, GB9N had the highest number of HBDC. GB9N induced significantly enhanced expression of Col I, ALP, OP, OC and ON mRNA at 3 days; of OP, OC and ON mRNA and protein at 7 and 14 days; and of ALP, OP and OC mRNA and Col I, ALP, BSP, ON and OP protein at 21 days. Since all novel glass ceramics supported cellular proliferation together with expression of bone-related genes and proteins at least as much as TCP, these ceramics can be regarded as potential bone substitutes. GB9N had the most effect on osteoblastic differentiation, thus suggesting that this material may possess a higher potency to enhance osteogenesis than TCP.

Absorbable Implants↗
PubMed2005

Bone healing in surgically created defects treated with either bioactive glass particles, a calcium sulfate barrier, or a combination of both materials. A histological and histometric study in rat tibias.

OBJECTIVE: The purpose of this study was to histologically analyze the influence of bioactive glass and/or a calcium sulfate barrier on bone healing in surgically created defects in rat tibias. MATERIAL AND METHODS: Sixty-four rats were divided into 4 groups: C (control), CS (calcium sulfate), BG (bioactive glass), and BG/CS (bioactive glass/calcium sulfate). A surgical defect was created in the tibia of each animal. In Group CS, a calcium sulfate barrier was placed to cover the defect. In Group BG the defect was filled with bioactive glass. In Group BG/CS, it was filled with bioactive glass and protected by a barrier of calcium sulfate. Animals were sacrificed at 10 or 30 days post-operative. The formation of new bone in the cortical area of the defect was evaluated histomorphometrically. RESULTS: At 10 days post-operative, Group C presented significantly more bone formation than Groups CS, BG, or BG/CS. No statistically significant differences were found between the experimental groups. At 30 days post-operative, Group C demonstrated significantly more bone formation than the experimental groups. Groups CS and BG/CS showed significantly more bone formation than Group BG. No statistically significant differences were found between Group CS and BG/CS. CONCLUSIONS: (a) the control groups had significantly more bone formation than the experimental groups; (b) at 10 days post-operative, no significant differences were found between any of the experimental groups; and (c) at 30 days post-operative, the groups with a calcium sulfate barrier had significantly more bone formation than the group that used bioactive glass only.

Animals↗
PubMed2005

Direct experimental evidence of a growing length scale accompanying the glass transition.

Understanding glass formation is a challenge, because the existence of a true glass state, distinct from liquid and solid, remains elusive: Glasses are liquids that have become too viscous to flow. An old idea, as yet unproven experimentally, is that the dynamics becomes sluggish as the glass transition approaches, because increasingly larger regions of the material have to move simultaneously to allow flow. We introduce new multipoint dynamical susceptibilities to estimate quantitatively the size of these regions and provide direct experimental evidence that the glass formation of molecular liquids and colloidal suspensions is accompanied by growing dynamic correlation length scales.

Journal Article↗
PubMed1999

Replacement for 30-milliliter flat-bottomed, glass-stoppered, round bottles used in VDRL antigen preparation.

When the flat-bottomed, glass-stoppered, round bottle traditionally used to make VDRL antigen was discontinued, an appropriate substitute was needed. Although many laboratories have switched to one of the other nontreponemal tests for syphilis serology screening, the VDRL test remains the only approved procedure for testing spinal fluids of patients with possible neurosyphilis. We tested 25-ml glass-stoppered, convex-bottomed Erlenmeyer flasks to determine if these could be used as appropriate substitutes. We tested 52 reactive sera and 54 nonreactive sera by using one reference antigen prepared in the traditional flat-bottomed bottles and five antigens prepared in the Erlenmeyer flasks. Results with all serum samples were comparable. We also tested two lots of a commercial antigen plus an additional lot of reference antigen. Again there was no difference in the reactivity of the antigens. Therefore, we conclude that 25-ml glass-stoppered Erlenmeyer flasks can be used as an appropriate substitute for glass-stoppered, flat-bottomed, round glass bottles in the making of VDRL antigen.

Cardiolipins↗
PubMed1979

Vision screening of adolescents and their use of glasses.

Vision screening was performed in over 11 000 16-year-olds who were taking part in the National Child Development Study. For distance vision 75% had normal acuity, 9% a minor defect, and 16% a more severe unilateral or bilateral defect. For near vision 85% had normal vision, 8% a minor defect, and 7% a unilateral or bilateral defect. Few children (62) with normal distant vision had defects in near vision, though many more (607) had both poor distant vision and poor near vision. Vision defects were more common in girls than in boys and occurred more often in adolescents from non-manual than manual families. Athough 18% of children had been prescribed glasses for current use, a third did not have their glasses available at the examination: 27% of the children prescribed glasses had normal unaided distant visual acuity or only a minor defect, and they constituted 42% of those who were not wearing their glasses. Further investigation is needed into the criteria on which glasses are prescribed for children and into the reasons for which they are not worn.

Adolescent↗
PubMed1993

Importance of ground-glass attenuation in chronic diffuse infiltrative lung disease: pathologic-CT correlation.

PURPOSE: To correlate areas of ground-glass attenuation at computed tomography (CT) with findings at open lung biopsy in chronic diffuse lung disease. MATERIALS AND METHODS: The cases of 26 patients were included on the basis of (a) extensive areas of ground-glass attenuation as the predominant (n = 17) or exclusive (n = 9) abnormality at CT in the absence of honeycombing and (b) histologic evaluation at open lung biopsy. Severity of ground-glass attenuation was scored in the lobe sampled at biopsy, with separate analysis of associated lung changes. RESULTS: Correlation of CT with histologic findings at the 37 biopsy sites demonstrated that ground-glass attenuation corresponded to inflammation in 24 (65%) cases and to fibrosis in 13 (54%) cases. Eleven of the 13 patients (85%) with fibrosis had traction bronchiectasis or bronchiolectasis. These findings were not present in any of the patients with inflammation. CONCLUSION: In patients with chronic diffuse infiltrative lung disease, areas of ground-glass attenuation not associated with traction bronchiectasis or bronchiolectasis are a reliable indicator of inflammation.

Biopsy↗
PubMed1996

Bronchioloalveolar carcinoma: focal area of ground-glass attenuation at thin-section CT as an early sign.

PURPOSE: To assess an early thin-section computed tomographic (CT) finding of the localized formation of bronchioloalveolar carcinoma (BAC). MATERIALS AND METHODS: From October 1994 to September 1995, four consecutive patients with biopsy-proved BAC were studied. Thin-section CT (n=4), radiographic (n=4), pathologic (n=4), and positron emission tomographic (n=2) findings were analyzed. RESULTS: Chest radiographs showed focal areas of poorly defined nodules (n=2) and poorly defined opacity (n=2). At thin-section CT, lesions appeared as isolated areas of ground-glass attenuation (n=2) and mixed areas of ground-glass attenuation and consolidation (n=2). The areas of ground-glass attenuation were 1.8-11 cm in longest diameter. A focal, isolated area of ground-glass attenuation changed into mixed areas with consolidation at serial CT in one patient. Mucinous and nonmucinous BACs were observed in two patients each. Positron emission tomography showed false-negative results for malignancy. CONCLUSION: Focal areas of ground-glass attenuation at CT could be an early sign of localized BAC.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1997

Source of error on A-aDO2 calculated from blood stored in plastic and glass syringes.

We studied the effects of time delay on blood gases, pH, and base excess in blood stored in glass and plastic syringes on ice and the effects of resulting errors on calculated alveolar-to-arterial PO2 difference (A-aDO2). Matched samples of dog whole blood were tonometered with gas mixtures of 5% CO2-12% )2-83% N2 (mixture A), 10% CO2-5% O2-85% N2 (mixture B), and 2.88% CO2-4% O2-93.12% N2 (mixture C). Tonometered blood samples were transferred to 5-ml glass (5G), 5-ml plastic (5P), and 3-ml plastic (3P) syringes and stored on ice. Blood gases were measured every 1 h up to 6 h. In 5G, PO2 progressively decreased in blood tonometered with mixture A but rose in blood tonometered with mixtures B and C. O2 saturation progressively fell in all cases. In 5G, blood PCO2 progressively rose regardless of which gas mixture was used, and pH as well as base excess progressively fell. The rise in PO2 was faster in plastic than in glass syringes, and O2 saturation always rose in plastic syringes. Differences between storage in plastic and glass syringes on PO2 change were greatest when initial blood PO2 was highest (mixture A). At the highest PO2, O2 exchange was faster in 3P than in 5P. The rise of PCo2 was just as fast in plastic as in glass syringes, but in both the rise in PCO2 was faster at a higher initial PCO2 (mixture B) than in lower initial PCO2 (mixtures B and C). Rates of PO2 and PCO2 change in matched samples were significantly faster in 3P than in 5P. Errors due to rises in PCO2 and PO2 cause additive errors in calculated A-aDO2, and when blood is stored in plastic syringes for > 1 h significant errors result. Errors are greater in normoxic blood, in which estimated A-aDO2 decreased by > 10 Torr after 6 h on ice in plastic syringes, than in hypoxic blood.

Animals↗