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At least 1,693 records · Page 94Linked to original sources
PubMed2003

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence.

The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.

Journal Article↗
PubMed2000

Viscous solutions, networks and the glass transition in high sugar galactomannan and kappa-carrageenan mixtures.

Small-deformation rotational oscillation was used to examine the effect of small additions of galactomannan and kappa-carrageenan on the vitrification of glucose syrup at a total level of solids of 83%. The method of reduced variables allowed construction of composite curves covering the glass transition and glassy state (from 10(5) to 10(9.5) Pa) over a wide frequency range (up to 15 orders of magnitude). The combined WLF/free volume framework was employed to determine the rheological glass transition temperature (T(g)), fractional free volume and thermal expansion coefficient of the samples. It was found that the WLF-predicted glass transition temperature matched the cross over of experimental modulus traces in the passage from the glass transition (GG') to the glassy state (GG"). This coincides with the mechanistic transformation from free volume effects to the Arrhenius-type phenomena, thus ascribing physical significance to the rheological T(g). The T(g) value of 83% glucose syrup at a scan rate of 2 degrees C min(-1) was -25.3 degrees C. Replacing, for example, 1% glucose syrup with guar gum shifted the T(g) of the mixture to -19.7 degrees C. Network formation via the K(+)-supported junction zones of the kappa-carrageenan chains further increased the T(g) to about -1 degrees C. It appears that the low rates of relaxation processes and diffusion mobility in the presence of a polysaccharide network accelerate the collapse of the free volume thus inducing vitrification of the high sugar/polysaccharide mixture at high temperatures.

Carbohydrates↗
PubMed2001

Role of acid attack in the in vitro bioactivity of a glass-ceramic of the 3CaO.P2O5-CaO.SiO2-CaO.MgO.2SiO2 system.

A non-bioactive glass-ceramic (GC13) that contains hydroxyapatite (Ca5(PO4)3OH), diopside (CaMg(SiO3)2) and althausite (Mg2 PO4OH) as crystalline phases has been obtained by thermal treatment of a parent bioactive glass (G13) of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5CaF2. To induce bioactivity, GC13 was chemically treated with 1 M HCl for different periods of time. After chemical etching the in vitro studies showed formation of an apatite-like surface layer. In this article the influence of etching time both on the surface composition of the glass-ceramic and on the growth rate of the apatite layer is studied. It is concluded that the presence of hydroxyapatite in the glass-ceramic, associated to microstructural fluctuations, can favour apatite deposition in vitro.

Apatites↗
PubMed2003

Glass ionomer as an expander of allograft in revision arthroplasty of the hip.

The use of glass ionomer as a bone graft expander was investigated in an in vivo model of revision hip arthroplasty. Bone grafts of pure allograft and allograft + glass ionomer particles in a 50:50 by weight mixture were implanted in an ovine hemi-arthroplasty model. Post-operative assessments of locomotor function, radiographic appearance and quantitative changes in mineralisation around the graft were made at 2, 4 and 6 months. Post-mortem assessments of radiographic and histologic appearance of the grafts were made at 6 months. No significant differences were noted in any of the measured or assessed parameters between the two graft types. The glass ionomer particles seemed to be well tolerated within the matrix of new bone, smaller sized particles appearing to be better incorporated than larger ones. The use of particles of glass ionomer as a bone graft expander, in this in vivo model of revision hip arthroplasty, would therefore appear to offer no detriment in performance over pure allograft in the short to medium term.

Acrylic Resins↗
PubMed2001

Effect of molecular weight and glass transition on relaxation and release behaviour of poly(DL-lactic acid) tablets.

Different molecular weight grades of poly(DL-lactic acid) were applied as release controlling excipients in tablets for oral drug administration. The role of molecular weight and glass transition in the mechanism of water-induced volume expansion and drug release of PDLA tablets was investigated. Modulated differential scanning calorimetry (MDSC) was used to determine the glass transition temperature of both dry and hydrated PDLA samples. The absorption rate and total amounts of sorbed water by the polymer were determined by dynamic vapour sorption (DVS). Expansion behaviour of PDLA tablets was measured using thermal mechanical analysis (TMA). At 95% relative humidity all molecular weight grades of PDLA sorbed 1.1-1.3% w/w water, as was determined with DVS. MDSC showed glass transition temperature reductions of 10-11 degrees C for all molecular weight grades of PDLA in water. Volume expansion studies using TMA showed that the molecular relaxation time and equilibrium porosity of the tablets increased with molecular weight. The mean relaxation time increased exponentially with the temperature interval T(g)-T. The onset temperature of shape recovery of hydrated tablets was approximately 8 degrees C lower than for dry samples. Drug release was only slightly affected by molecular weight. It is concluded that volume expansion of compressed PDLA tablets is related to the glass transition behaviour, originates from water-induced and thermally stimulated shape memory behaviour and is therefore highly dependent on the molecular weight of PDLA.

Lactic Acid↗
PubMed2003

Kauzmann's paradox and the glass transition.

Kauzmann showed that the entropy of a liquid decreases rapidly on cooling towards the kinetic glass transition temperature and extrapolates to unreasonable values at lower temperature. The temperature where the extrapolated liquid entropy meets the crystal entropy is now called the Kauzmann temperature. Thermodynamics, with Planck's statement of the third law, shows that the entropy of a liquid cannot be less than the entropy of a glass with the same enthalpy. This is the thermodynamic condition violated by the Kauzmann extrapolation and it suggests a thermodynamic glass transition. Simulations show that, for the simple models studied and regardless of how the liquid entropy is extrapolated, the Kauzmann temperature cannot be reached because the entropy of glasses with the same enthalpy as the liquid is greater than that of the crystal.

Crystallization↗
PubMed2002

Efficacy of virtual glasses in audio-visual sexual stimulation during penile color duplex Doppler ultrasonography.

OBJECTIVE: To examine whether audio-visual sexual stimulation (AVSS) with virtual glasses is effective in improving the recording of penile hemodynamics during penile color duplex Doppler ultrasonography. PATIENTS AND METHODS: A total of 64 consecutive patients with erectile dysfunction underwent penile color duplex Doppler ultrasonography after intracavernosal injection of 10-20 microg prostaglandin El and subsequent genital stimulation. AVSS with virtual glasses and earphones was applied when peak systolic velocities (PSV) were less than 35 cm/s or end diastolic velocities (EDV) were more than 5 cm/s. PSV, EDV and the resistive index of both cavernosal arteries were continuously monitored. Clinical erectile response was assessed with visual inspection and manual palpation. RESULTS: AVSS with virtual glasses was performed on 40 of 64 patients. AVSS improved the clinical erectile response in 26 (65%) of 40 patients. Doppler ultrasonography without AVSS identified 11 (27.5%), 5 (12.5%), and 24 (60%) patients with arteriogenic, veno-occlusive, and mixed-type impotence, respectively. However, after real-time AVSS 15 (37.5%), 7 (17.5%), 8 (20%), and 10 (25%) patients demonstrated non-vasculogenic, arteriogenic, veno-occlusive, and mixed-type impotence, respectively. Real-time AVSS improved the Doppler wave forms in 65% of cases. CONCLUSION: AVSS with virtual glasses improves the recording of physiologic erectile response and may be used as a valuable tool during penile color duplex Doppler ultrasonography.

Adult↗
PubMed2001

[Larval history of glass eels, Anguilla anguilla (Linné, 1758) in migration in coastal and estuary areas (Adour, Gulf of Gascogne) as revealed by otolith test].

The embryonic past of glass eels was studied from the interpretation of microstructures registered on otoliths. The aim of this work is to put in evidence possible seasonal modifications of the growth of otoliths so that differences between otoliths of glass eels caught off marine and estuarine environment. So during the season 1999-2000, from November till March, otolith sampling was realised in the southwestern part of France, in an estuarine and coastal zone. We observed a spatial and temporal evolution of proportions of the three various types of otoliths taken into account. Glass eels sampled at sea sometimes have a mark on their otoliths indicating the transition in the estuary, especially at the end of the fishing season. Measures of growth marks of otoliths showed that there were no seasonal differences during phases of the transoceanic migration and the crossing of the continental shelf. The radius of otoliths of glass eels sampled at sea was significantly smaller than those sampled in estuary. These results translated homogeneous environmental modifications met by the various larvae groups during the oceanic crossing and during the principal migration season as well as a turn over of these groups during the transition between marine and continental environment.

Anguilla↗
PubMed2002

Approach to ground-glass opacification of the lung.

There area number of diseases that present with ground-glass opacification of the lung as a primary manifestation on chest radiography and thin-section computed tomography (CT). These diseases cannot be clearly categorized into the classic classification scheme of airspace and interstitial disease because there are features of both categories seen in the imaging and histologic findings. Ground-glass opacification has, therefore, been categorized as nonspecific by many radiologists. The fact that both the airspaces and interstitial tissues are often involved should have little importance when evaluating radiographs or high-resolution CT (HRCT) images. The role of the radiologist is evolving and is becoming more significant in the clinical evaluation of a patient presenting with so-called interstitial lung disease. In this article, an approach is described that hopefully will lead to an effective and narrow differential diagnosis when a radiologist is confronted with ground-glass opacification. The critical features in evaluating such cases include: (1) the duration of clinical symptoms; (2) the presence or absence of lung fibrosis, especially honeycombing; (3) the patient's history of smoking; and (4) the distribution of the disease. Each of these features is considered in this article in conjunction with the diseases that lead to ground-glass opacification. The recent thinking regarding nonspecific interstitial pneumonia and usual interstitial pneumonia also is discussed.

Acute Disease↗
PubMed2003

The structure of a metallic glass system using EXELFS and EXAFS as complementary probes.

The short-range atomic order around all three constituent atoms in a prototypical bulk metallic glass (BMG) system was probed in a complementary way, using extended X-ray absorption fine structure for neighborhood of the higher atomic number elements, and extended energy loss fine structure (EXELFS) for the lower atomic number ones. The Pd(x)Ni((80-x))P((20)) system is a prototype for a whole class of BMG formers which are 80% transition metal and 20% metalloid. We find that the structure of these BMGs could be explained in terms of those of glasses at the end of the BMG range, namely, Pd(60)Ni(20)P(20) and Pd(30)Ni(50)P(20). The binary phosphide crystals near [Formula: see text] and 80 are found to be simulate very well the local atomic structure of Pd(30)Ni(50)P(20) and Pd(60)Ni(20)P(20) glasses, respectively. The best glass former in this series, Pd(40)Ni(40)P(20), is best described by a weighted average of Pd(30)Ni(50)P(20) and Pd(60)Ni(20)P(20) structures.

Journal Article↗
PubMedDate not supplied

Glass on clothing and shoes of members of the general population and people suspected of breaking crimes.

The outer clothing and footwear of 122 people attending a university gymnasium and a private gymnasium were searched for fragments of glass. Both the surfaces and the pockets of the clothing and the uppers and soles of the footwear were searched. New Zealand forensic glass cases have been reviewed to determine the amount of non-matching glass present on the clothing of people who are suspected of breaking crimes. Data from 114 suspects who had no matching glass on their clothing and shoes were accumulated. Statistical modelling techniques have been applied to the data collected.

Journal Article↗
PubMed2001

Evaluation of three-dimensional microchannel glass biochips for multiplexed nucleic acid fluorescence hybridization assays.

Three-dimensional, flow-through microchannel glass substrates have a potential for enhanced performance, including increased sensitivity and dynamic range, over traditional planar substrates used in medium-density microarray platforms. This paper presents a methodology for the implementation of multiplexed nucleic acid hybridization fluorescence assays on microchannel glass substrates. Fluorescence detection was achieved, in a first instance, using conventional low-magnification microscope objective lenses, as imaging optics whose depth-of-field characteristics match the thickness of the microchannel glass chip. The optical properties of microchannel glass were shown, through experimental results and simulations, to be compatible with the quantitative detection of heterogeneous hybridization events taking place along the microchannel sidewalls, with detection limits for oligonucleotide targets in the low-attomole range.

Base Sequence↗
PubMed1989

Thimble glass frit nebulizer for atomic spectrometry.

A thimble-shaped glass frit nebulizer has been developed for atomic spectrometry. The thimble glass frit was pressurized internally by gases such as helium (He) or argon (Ar) while the test solution was applied externally to the frit. The pressurized gas exited through the pores of the glass frit and shattered the thin liquid film flowing on the surface of the thimble-shaped device to form small droplets. A small spray chamber surrounded the nebulizer to remove the large droplets. Small droplets were then introduced into inductively coupled plasmas (ICP) sustained in either Ar or He. To reduce the memory effect noted in the frit-type nebulizers, a clean-out system was also devised. Detection limits, signal-to-background ratios (S/B), precision, memory effects, noise power spectra (NPS), and particle size distributions measured with the new nebulizer were compared to those of disk and cylindrical glass frit nebulizers and the commonly used pneumatic nebulizer for Ar ICP atomic emission spectrometry (AES). Analytical performance was also measured for He ICP by using frit-type nebulizers and an ultrasonic nebulizer.

Nebulizers and Vaporizers↗
PubMed2004

Effect of fractionation on the forensic elemental analysis of glass using laser ablation inductively coupled plasma mass spectrometry.

Laser ablation (LA) is a powerful analytical technique for solid microsampling. Its coupling with ICPMS has been shown to offer good precision and accuracy for the elemental analysis of glass fragments. Fractionation in LA poses one of the major challenges to using this technique for in situ trace elemental profiling of glass evidence. The aim of this work was to study the effect of elemental fractionation on the forensic application of elemental analysis of glass samples by LA-ICPMS. Two different approaches were used to evaluate the fractionation: fractionation index and U/Th ratios. The resulting fractionation index values indicate low fractionation for the majority of elements evaluated, ranging between 0.8 and 1.2. The U/Th ratio suggests a higher fractionation at the beginning of the ablation process. To evaluate whether fractionation affects the quantification of glass samples by LA-ICPMS, a comparison of LA results with solution ICPMS analysis was conducted. The distribution of particle sizes during the ablation under different conditions and laser systems was also measured to evaluate the fractionation. The standard reference materials NIST 612, 610, and 1831 were analyzed in triplicate by both methods (n = 55) along with a set of 10 casework samples originating from different automobiles.

Journal Article↗
PubMed2005

Doping of glass with lithium ion.

Doping of glass with lithium ion can be accomplished by exposing the glass to a solution of organic solvent containing a soluble lithium ion salt, such as LiBr and a small amount of water. Under such conditions, the activity of solvated Li+ is very high causing it to partition into the hydrated glass surface. Laser-induced breakdown spectroscopy and atomic absorption spectroscopy have been used to monitor the partitioning between glass and organic phase, respectively.

Journal Article↗
PubMedDate not supplied

Phosphate glass as a phosphate source in high cell density Escherichia coli fermentations.

Polyphosphate glass (sodium hexametaphosphate, sodium polyphosphate, glassy) was identified and tested as a source of phosphate that supports growth of recombinant Escherichia coli to cell densities over 110 g dry wt/L. Polyphosphate glasses cost no more than sodium and potassium phosphates, are more soluble than any other inorganic phosphate source, and do not form metallophosphate precipitates when mixed with other nutrients in proportions found in fermentation medias. Using a typical fermentation medium, 40% higher cell densities were obtained using polyphosphate glass rather than orthophosphate. Polyphosphate glasses will allow more flexibility in designing and executing high cell density fermentations.

Cell Division↗
PubMed2005

Short-range structure and cation bonding in calcium-aluminum metaphosphate glasses.

Comprehension of short- and medium-range order of phosphate glasses is a topic of interest, due to the close relation between network structure and mechanical, thermal, and optical properties. In this work, the short-range structure of glasses (1 - x)Ca(PO(3))(2).xAl(PO(3))(3) with 0 < or = x < or = 0.47 was studied using solid-state nuclear magnetic resonance spectroscopy, Raman spectroscopy, density measurements, and differential scanning calorimetry. The bonding between a network modifier species, Al, and the network forming phosphate groups was probed using high-resolution nuclear magnetic resonance spectroscopy of (27)Al and (31)P. Changes in the compositional behavior of the density, glass transition temperature, PO(2) symmetric vibrations, and Al coordination number were verified at around x = 0.30. (31)P NMR spectra show the presence of phosphorus in Q(2) sites with nonbridging oxygens (NBOs) coordinated by Ca ions and also Q(2) sites with one NBO coordinated by Al (namely, Q(2)(1Al)). The changes in the properties as a function of x can be understood by considering the mean coordination number measured for Al and the formation of only Q(2) and Q(2)(1Al) species. It is possible to calculate that a network formed only by Q(2)(1Al) phosphates can just exist up to the upper limit of x = 0.48. Above this value, Q(2)(2Al) species should appear, imposing a major reorganization of the network. Above x = 0.30 the network undergoes a progressive reorganization to incorporate Al ions, maintaining the condition that only Q(2)(1Al) species are formed. These observations support the idea that bonding principles for cationic species inferred originally in binary phosphate glasses can also be extended to ternary systems.

Journal Article↗
PubMed1998

Effect of Crystallinity on the Glass Transition Temperature of Starch.

The glass transition temperature (T(g)) of potato and wheat starches, stored for several periods after gelatinization, was measured by differential scanning calorimetry (DSC), and the relative crystallinity of the starches was measured by X-ray diffractometry. T(g) of stored starches was higher than that of starches without storage, and the T(g) increment of starches gelatinized at 120 degrees C was higher than that of starches gelatinized at 60 degrees C. The water content at which the glass transition of a starch occurs at 25 degrees C was estimated from DSC data, and it increased linearly with relative crystallinity in two groups that differed in the gelatinization method. These results also showed the quantitative relationship between T(g) and retrogradation. In addition, these results suggested that the glass transition of starch could be interpreted in the same way as the glass transition of cross-linked synthetic polymers.

Journal Article↗