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The Evolution of Dental Materials over the Past Century: Silver and Gold to Tooth Color and Beyond.
The field of dental materials has undergone more of a revolution than an evolution over the past 100 y. The development of new products, especially in the past half century, has occurred at a staggering pace, and their introduction to the market has been equally impressive. The movement has mostly come in the area of improved esthetics, marked by the gradual replacement of dental amalgam with dental composite and all-metal and porcelain-fused-to-metal indirect restorations with reinforced dental ceramics, all made possible by the rapid improvements in dental adhesive materials. This article covers the time course of dental materials development over the past century in which the Journal of Dental Research has been published. While there have been advances in nearly all materials used in the field, this article focuses on several areas, including dental amalgam, dental composites and light curing, dental adhesives and dental cements, ceramics, and new functional repair materials. A few short statements on future advances will be included at the end
Effect of Pulp Protection Technique on the Clinical Performance of Amalgam Restorations: Three-Year Results
This study evaluated the influence of the pulp protection technique on clinical performance of amalgam restorations after three years, with particular reference to post-operative sensitivity and secondary caries. One hundred and twenty (120) Class II amalgam restorations (68 premolars, 52 molars; 78 MOD, 42 OD/MO) were placed
in 30 participants (four restorations per participant).The restorations were divided into four groups according to the pulp protection technique used: copal varnish; 2% neutral sodium fluoride; adhesive resin and no pulp protection. The parameters evaluated were post-operative sensitivity, staining of the dental structure, tooth
vitality, partial or total loss of the restoration and
secondary caries. One hundred and eight (108)restorations were available for evaluation after three years. No partial or total loss of restorations had occurred; all teeth were vital, no tooth structure staining or secondary caries was detected in any of the restored teeth. Post-operative sensitivity was observed only in two restorations
at baseline and at seven-days. The three year clinical performance of teeth restored with a high copper dispersed phase amalgam was not affected by the choice of pulp protection technique
Evaluation of laminated structures for sports mouthguards
Most of the past studies have concentrated on the properties of mouthguard materials rather than their ability to protect the underlying substructure. Previous work has indicated that the incorporation of a shook absorbing layer into the sports mouthguard reduces the likelihood of injury to the head, neck and oral cavity of the wearer, The purpose of this study is to develop an optimum laminated structure that protects an easily deformable structure during an impact.
Dropweight impact tests were conducted on a series of moulded samples which were circularly clamped and force-time and displacement-time plots obtained, Single thickness specimens of ethylene vinyl acetate (EVA), 1-5mm thick were compared with laminated structures of EVA, incorporating 1mm thick layers of polymethylmethacrylate (PMMA) and a silicone or synthetic rubber up to a thickness of 5mm. It was observed that the multi-layered structures exhibited less deformation thereby transmitting less of the harmful effects through the laminate. It was concluded that laminated systems for mouthguards using different materials appear to offer better protection to the wearer
The Effect of Website Interactivity on Political Involvement:The Moderating Role of Political Cynicism
This study examines the extent to which interactive communication on political websites affects various forms of citizens’ involvement in politics, and the moderating role of political cynicism in this relationship. Based on the outcomes of a laboratory experiment with a single-factor (interactivity: low vs. medium vs. high interactivity) between-subjects design, we found that interactive political websites have a positive effect on citizen involvement, and this effect is particularly present for websites with high levels of interactivity. We also demonstrate that interactivity effects are, to some extent, contingent on citizens’ political cynicism. For higher levels of political cynicism, deviations in the level of interactivity make less of a difference in their impact on political involvement
Redox effects on the excited-state lifetime in chlorosomes and bacteriochlorophyll c oligomers
Oligomers of [E,E] BChl CF (8, 12-diethyl bacteriochlorophyll c esterified with farnesol (F)) and [Pr,E] BChl CF (analogously, M methyl, Pr propyl) in hexane and aqueous detergent or lipid micelles were studied by means of steady-state absorption, time-resolved fluorescence, and electron spin resonance spectroscopy. The maximum absorption wavelength, excited-state dynamics, and electron spin resonance (EPR) linewidths are similar to those of native and reconstituted chlorosomes of Chlorobium tepidum. The maximum absorption wavelength of oligomers of [E,E] BChl CF was consistently blue-shifted as compared to that of [Pr,E] BChl CF oligomers, which is ascribed to the formation of smaller oligomers with [E,E] BChl CF than [Pr,E] BChl CF. Time-resolved fluorescence measurements show an excited-state lifetime of 10 ps or less in nonreduced samples of native and reconstituted chlorosomes of Chlorobium tepidum. Under reduced conditions the excited-state lifetime increased to tens of picoseconds, and energy transfer to BChl a or long-wavelength absorbing BChl c was observed. Oligomers of [E,E] BChl CF and [Pr,E] BChl CF in aqueous detergent or lipid micelles show a similar short excited-state lifetime under nonreduced conditions and an increase up to several tens of picoseconds upon reduction. These results indicate rapid quenching of excitation energy in nonreduced samples of chlorosomes and aqueous BChl c oligomers. EPR spectroscopy shows that traces of oxidized BChl c radicals are present in nonreduced and absent in reduced samples of chlorosomes and BChl c oligomers. This suggests that the observed short excited-state lifetimes in nonreduced samples of chlorosomes and BChl c oligomers may be ascribed to excited-state quenching by BChl c radicals. The narrow EPR linewidth suggests that the BChl c are arranged in clusters of 16 and 6 molecules in chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, respectively
Принципы построения сетевых систем обнаружения вторжений на базе ПЛИС
The common principles of FPGA-based NIDS (Network Intrusion Detection
Systems) construction are investigated. The main requirements and characteristics of
such systems are discussed. The generalized structure of a reconfigurable NIDS is
described
spFRET Using Alternating Excitation and FCS Reveals Progressive DNA Unwrapping in Nucleosomes
AbstractAccessibility to DNA wrapped in nucleosomes is essential for nuclear processes such as DNA transcription. Large conformational changes in nucleosome structure are required to facilitate protein binding to target sites within nucleosomal DNA. Transient unwrapping of DNA from nucleosome ends can provide an intrinsic exposure of wrapped DNA, allowing proteins to bind DNA that would otherwise be occluded in the nucleosome. The molecular details underlying these mechanisms remain to be resolved. Here we show how DNA unwrapping occurs progressively from both nucleosome ends. We performed single-pair fluorescence resonance energy transfer (spFRET) spectroscopy with alternating laser excitation (ALEX) on nucleosomes either in free solution or confined in a gel after PAGE separation. We combined ALEX-spFRET with a correlation analysis on selected bursts of fluorescence, to resolve a variety of unwrapped nucleosome conformations. The experiments reveal that nucleosomes are unwrapped with an equilibrium constant of ∼0.2–0.6 at nucleosome ends and ∼0.1 at a location 27 basepairs inside the nucleosome, but still remain stably associated. Our findings, obtained using a powerful combination of single-molecule fluorescence techniques and gel electrophoresis, emphasize the delicate interplay between DNA accessibility and condensation in chromatin
Inclinations of small quiet-Sun magnetic features based on a new geometric approach
High levels of horizontal magnetic flux have been reported in the quiet-Sun
internetwork, often based on Stokes profile inversions. Here we introduce a new
method for deducing the inclination of magnetic elements and use it to test
magnetic field inclinations from inversions. We determine accurate positions of
a set of small, bright magnetic elements in high spatial resolution images
sampling different photospheric heights obtained by the Sunrise balloon-borne
solar observatory. Together with estimates of the formation heights of the
employed spectral bands, these provide us with the inclinations of the magnetic
features. We also compute the magnetic inclination angle of the same magnetic
features from the inversion of simultaneously recorded Stokes parameters. Our
new, geometric method returns nearly vertical fields (average inclination of
around 14 deg with a relatively narrow distribution having a standard deviation
of 6 deg). In strong contrast to this, the traditionally used inversions give
almost horizontal fields (average inclination of 75+-8 deg) for the same small
magnetic features, whose linearly polarised Stokes profiles are adversely
affected by noise. The almost vertical field of bright magnetic features from
our geometric method is clearly incompatible with the nearly horizontal
magnetic fields obtained from the inversions. This indicates that the amount of
magnetic flux in horizontal fields deduced from inversions is overestimated in
the presence of weak Stokes signals, in particular if Stokes Q and U are close
to or under the noise level. By combining the proposed method with inversions
we are not just improving the inclination, but also the field strength. This
technique allows us to analyse features that are not reliably treated by
inversions, thus greatly extending our capability to study the complete
magnetic field of the quiet Sun.Comment: 12 pages, 9 figures, 1 table; Accepted for publication in Astronomy &
Astrophysic
Stokes imaging polarimetry using image restoration: A calibration strategy for Fabry-P\'{e}rot based instruments
context: The combination of image restoration and a Fabry-P\'{e}rot
interferometer (FPI) based instrument in solar observations results in specific
calibration issues. FPIs generally show variations over the field-of-view,
while in the image restoration process, the 1-to-1 relation between pixel space
and image space is lost, thus complicating any correcting for such variations.
aims: We develop a data reduction method that takes these issues into account
and minimizes the resulting errors. methods: By accounting for the time
variations in the telescope's Mueller matrix and using separate calibration
data optimized for the wavefront sensing in the MOMFBD image restoration
process and for the final deconvolution of the data, we have removed most of
the calibration artifacts from the resulting data. results: Using this method
to reduce full Stokes data from CRISP at the SST, we find that it drastically
reduces the instrumental and image restoration artifacts resulting from cavity
errors, reflectivity variations, and the polarization dependence of flatfields.
The results allow for useful scientific interpretation. Inversions of restored
data from the sunspot AR11029 using the Nicole inversion code, reveal
strong (~10 km/s) downflows near the disk center side of the umbra.
conclusions: The use of image restoration in combination with an FPI-based
instrument leads to complications in the calibrations and intrinsic limitations
to the accuracy that can be achieved. We find that for CRISP, the resulting
errors can be kept mostly below the polarimetric accuracy of ~10^-3. Similar
instruments aiming for higher polarimetric and high spectroscopic accuracy,
will, however, need to take these problems into account. keywords: Techniques:
image processing, polarimetric, imaging spectroscopy, Sun: surface magnetism,
sunspots, activityComment: Astronomy and Astrophysics (accepted
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