1,182 research outputs found
Effect of ultrasound on the setting characteristics of glass ionomer cements studied by Fourier Transform Infrared Spectroscopy
Objective: To investigate the effect of ultrasound (US) application on the setting of glass ionomer cement (GIC) by using Attenuated Total Reflectance Fourier Transform Infrared (ATR/FTIR) spectrometer. Methods: Two conventional GICs, Fuji IX Fast and Ketac Molar were studied. US application was started at 30 s or 40 s after mixing and was applied for times between 15 and 55 s on samples of two different thicknesses. The samples were analysed using ATR/FTIR.Results: US accelerated the curing process in both cements, US needed to be applied for more than 15 s. Both Fuji IX and Ketac Molar showed increased setting on increasing the US application duration from 15 s to 55 s. Increased setting of the GICs was produced when US application started 40 s after mixing rather than 30 s after mixing. Conclusions: The significant findings of the study include that US application accelerated the setting processes, by accelerating the formation of the acid salts. The salt formation increased with increase time of US application. The effect of application of US to setting GICs is influenced by time of the start of application of the US. The effects appear to material specific, with Ketac Molar showing a greater effect than Fuji IX
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Neural processing of imminent collision in humans
Detecting a looming object and its imminent collision is imperative to survival. For most humans, it is a fundamental aspect of daily activities such as driving, road crossing and participating in sport, yet little is known about how the brain both detects and responds to such stimuli. Here we use functional magnetic resonance imaging to assess neural response to looming stimuli in comparison with receding stimuli and motion-controlled static stimuli. We demonstrate for the first time that, in the human, the superior colliculus and the pulvinar nucleus of the thalamus respond to looming in addition to cortical regions associated with motor preparation. We also implicate the anterior insula in making timing computations for collision events
Trades in complex Hadamard matrices
A trade in a complex Hadamard matrix is a set of entries which can be changed
to obtain a different complex Hadamard matrix. We show that in a real Hadamard
matrix of order all trades contain at least entries. We call a trade
rectangular if it consists of a submatrix that can be multiplied by some scalar
to obtain another complex Hadamard matrix. We give a
characterisation of rectangular trades in complex Hadamard matrices of order
and show that they all contain at least entries. We conjecture that all
trades in complex Hadamard matrices contain at least entries.Comment: 9 pages, no figure
Ribosomal RNA Synthesis in Chronic Lymphocytic Leukaemia
Lymphocytes from patients with chronic lymphocytic leukaemia make large amounts of stable, rapidly labelled high molecular weight RNA, but ribosomal RNA methylation is normal. However, fewer ribosomes are available for protein synthesis than in normal lymphocytes
Noise Sensitivity and Diminished Health: Testing Moderators and Mediators of the Relationship
The concept of noise sensitivity emerged in public health and psychoacoustic research to help explain individual differences in reactions to noise. Noise sensitivity has been associated with health problems, but the mechanisms underlying this relationship have yet to be fully examined. Participants (n = 1102) were residents of Auckland, New Zealand, who completed questionnaires and returned them through the post. Models of noise sensitivity and health were tested in the analyses using bootstrapping methods to examine indirect effects. Results indicated that gender and noise exposure were not significant moderators in the model. Perceived stress and sleep problems were significant mediators of the relationship between noise sensitivity and subjective health complaints, even after controlling for the influence of neuroticism. However, the relationship between noise sensitivity and mental health complaints (anxiety and depression) was accounted for by the variance explained by neuroticism. Overall, this study provides considerable understanding of the relationship between noise sensitivity and health problems and identifies areas for further research in the field
DO GLASS IONOMER CEMENTS MATURE APPRECIABLY? A CRITICAL REVIEW
Introduction: The earliest glass ionomer cement (GIC)
had low strength when tested after 24 hours. However,
after long periods, strength increased. This was initially
thought to be a property of all GICs, but some later
materials either did not increase or got weaker. Objectives:
This review aims at determining whether changes in the
chemical composition of the glass component of GICs do
result in different strength changes or whether other
formulation changes are also responsible. In addition, it
aims at evaluating changes in other non-mechanical
properties, such as abrasion and erosion. Materials and
methods: Search engines were used to find relevant
references included in Ovid SP, Pubmed and Index
Copernicus.Results and discussion: In experimental GICs
strength, changes have an inverse correlation with initial
(24 hours) strength. For commercial GICs, no such
relationship is found. High phosphorus contents result in
large increases in strength from initial low strength values.
Other properties also show maturation changes. In
particular, both resistance to abrasion and erosion increase
in the relatively few GICs tested, including some which do
not show strength increases. Conclusions: GICs have the
potential to improve their properties when matured for
periods longer than 24 hours, however this property is
dependent on glass composition
A versatile high resolution objective for imaging quantum gases
We present a high resolution objective lens made entirely from catalog
singlets that has a numerical aperture of 0.36. It corrects for aberrations
introduced by a glass window and has a long working distance of 35mm, making it
suitable for imaging objects within a vacuum system. This offers simple high
resolution imaging for many in the quantum gas community. The objective
achieves a resolution of 1.3{\mu}m at the design wavelength of 780nm, and a
diffraction-limited field of view of 360{\mu}m when imaging through a 5mm
window. Images of a resolution target and a pinhole show quantitative agreement
with the simulated lens performance. The objective is suitable for
diffraction-limited imaging on the D2 line of all the alkalis by changing only
the aperture diameter, retaining numerical apertures above 0.32. The design
corrects for window thicknesses of up to 15mm if the singlet spacings are
modified
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