437 research outputs found
Differential Scanning Calorimetry (dsc) Analyses Of Esthetic Nickel-Titanium Wires As-Received And After Clinical Use
Introduction: The demand for esthetic orthodontics has increased rapidly over the past few decades, and much progress has been made in the development of esthetic clear and translucent brackets for labial orthodontics. However, the majority of wires used with these clear brackets are still the traditional alloys. Recently, American Orthodontics (Sheboygan, WI) and Opal (Ultradent; South Jordan, UT) have released epoxy resin coated nickel-titanium archwires that give a tooth-colored appearance. American Orthodontics has released EverWhite and Opal has released Via Pearl. The goal of this study was to compare the thermal properties of these new archwires with their uncoated counterparts before and after clinical use via differential scanning calorimetry (DSC).
Materials and Methods: Four types of nickel-titanium orthodontic archwires were evaluated in this study. The four types consisted of two epoxy coated wires and two comparable control wires of the same .016 x 0.022 inch dimension. The transformation temperatures and phase transformations of these wires were determined in the as-received condition and after 4 to 12 weeks in the oral cavity by differential scanning calorimetry. In addition, the amount of coating lost for each coated archwire after clinical use was determined using a scanned image of the wire and matlab software.
Results: There were no statistically significant differences in thermal properties when comparing archwires before and after clinical use. However, significant differences were observed between the as-received uncoated and coated counterparts from both manufacturers. Both wire types lost a significant amount of esthetic coating after use, but the Opal Via Pearl wire maintained significantly more coating compared to the EverWhite type.
Conclusions: The significant differences between as-received uncoated and coated wires from the same manufacturer indicate that these wires may perform differently in clinical situations contrary to the manufacturers\u27 claims. In addition, improvements to the coating processes or alternative wires are needed to provide a more esthetic archwire with limited coating loss
An investigation into the mechanical and aesthetic properties of new generation coated nickel-titanium wires in the as-received state and after clinical use
SUMMARYBACKGROUND/OBJECTIVES: The purpose of this study was to compare the mechanical, structural, and aesthetic properties of two types of aesthetic coated nickel-titanium (NiTi) wires compared with comparable regular NiTi wires in the as-received state and after clinical use. MATERIALS/METHODS: Sixty one subjects were randomly assigned to four groups (N = 61), two groups of coated wires and two groups of comparable, non-coated controls (n = 15/group). The period in the mouth ranged from 4 to 12 weeks after insertion. In total, 121 wires (61 retrieved and 60 as-received) were used in the study. The percentages of coating retention and loss were extrapolated from scans. A brief survey of five questions with three choices was given to all patients. Differential scanning calorimetry (DSC) and three-point bending tests were done on as-received and used wires. RESULTS: The surface characterization by the percentage of resin remaining indicated that most wires in both test groups lost a significant amount of coating. A patient survey indicated that this was a noticeable feature for patients. DSC analysis of the wires indicated that the metallurgical properties of the coated wires were not similar to the uncoated wires in the as-received condition. Three-point bending results indicate a wide variation in test results with large standard deviations among all the groups. LIMITATIONS: The extent of coating loss requires investigating, as do the biological properties of the detached coating. CONCLUSIONS: Both wires lost a significant amount of aesthetic coating after varying periods in the mouth. The metallurgical testing of these findings may indicate that these wires perform differently in the mout
Quantum Atomic Matter Near Two-Dimensional Materials in Microgravity
Novel two-dimensional (2D) atomically flat materials, such as graphene and
transition-metal dichalcogenides, exhibit unconventional Dirac electronic
spectra. We propose to effectively engineer their interactions with cold atoms
in microgravity, leading to a synergy between complex electronic and atomic
collective quantum phases and phenomena. Dirac materials are susceptible to
manipulation and quantum engineering via changes in their electronic properties
by application of strain, doping with carriers, adjustment of their dielectric
environment, etc. Consequently the interaction of atoms with such materials,
namely the van der Waals / Casimir-Polder interaction, can be effectively
manipulated, leading to the potential observation of physical effects such as
Quantum Reflection off atomically thin materials and confined Bose-Einstein
Condensate (BEC) frequency shifts.Comment: 11 pages, 3 figures; discussion and references adde
Molecular packing structure of fibrin fibers resolved by X-ray scattering and molecular modeling
Fibrin is the major extracellular component of blood clots and a proteinaceous hydrogel used as a versatile biomaterial. Fibrin forms branched networks built of laterally associated double-stranded protofibrils. This multiscale hierarchical structure is crucial for the extraordinary mechanical resilience of blood clots, yet the structural basis of clot mechanical properties remains largely unclear due, in part, to the unresolved molecular packing of fibrin fibers. Here the packing structure of fibrin fibers is quantitatively assessed by combining Small Angle X-ray Scattering (SAXS) measurements of fibrin reconstituted under a wide range of conditions with computational molecular modeling of fibrin protofibrils. The number, positions, and intensities of the Bragg peaks observed in the SAXS experiments were reproduced computationally based on the all-atom molecular structure of reconstructed fibrin protofibrils. Specifically, the model correctly predicts the intensities of the reflections of the 22.5 nm axial repeat, corresponding to the half-staggered longitudinal arrangement of fibrin molecules. In addition, the SAXS measurements showed that protofibrils within fibrin fibers have a partially ordered lateral arrangement with a characteristic transverse repeat distance of 13 nm, irrespective of the fiber thickness. These findings provide fundamental insights into the molecular structure of fibrin clots that underlies their biological and physical properties. This journal i
Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
We present results from monitoring the multi-waveband flux, linear
polarization, and parsec-scale structure of the quasar PKS 1510-089,
concentrating on eight major gamma-ray flares that occurred during the interval
2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at
optical wavelengths, although the flux ratio of the two wavebands varied by an
order of magnitude. The optical polarization vector rotated by 720 degrees
during a 5-day period encompassing six of these flares. This culminated in a
very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of
emission passed through the highest-intensity, stationary feature (the "core")
seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate
down the jet at an apparent speed of 22c and emit strongly at gamma-ray
energies as a months-long X-ray/radio outburst intensified. We interpret these
events as the result of the knot following a spiral path through a mainly
toroidal magnetic field pattern in the acceleration and collimation zone of the
jet, after which it passes through a standing shock in the 43 GHz core and then
continues downstream. In this picture, the rapid gamma-ray flares result from
scattering of infrared seed photons from a relatively slow sheath of the jet as
well as from optical synchrotron radiation in the faster spine. The 2006-2009.7
radio and X-ray flux variations are correlated at very high significance; we
conclude that the X-rays are mainly from inverse Compton scattering of infrared
seed photons by 20-40 MeV electrons.Comment: 10 pages of text + 5 figures, to be published in Astrophysical
Journal Letters in 201
Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
Precision astrometry at microarcsecond accuracy has application to a wide
range of astrophysical problems. This paper is a study of the science questions
that can be addressed using an instrument that delivers parallaxes at about 4
microarcsec on targets as faint as V = 20, differential accuracy of 0.6
microarcsec on bright targets, and with flexible scheduling. The science topics
are drawn primarily from the Team Key Projects, selected in 2000, for the Space
Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities
of this mission to illustrate the importance of the next level of astrometric
precision in modern astrophysics. SIM PlanetQuest is currently in the detailed
design phase, having completed all of the enabling technologies needed for the
flight instrument in 2005. It will be the first space-based long baseline
Michelson interferometer designed for precision astrometry. SIM will contribute
strongly to many astronomical fields including stellar and galactic
astrophysics, planetary systems around nearby stars, and the study of quasar
and AGN nuclei. SIM will search for planets with masses as small as an Earth
orbiting in the `habitable zone' around the nearest stars using differential
astrometry, and could discover many dozen if Earth-like planets are common. It
will be the most capable instrument for detecting planets around young stars,
thereby providing insights into how planetary systems are born and how they
evolve with time. SIM will observe significant numbers of very high- and
low-mass stars, providing stellar masses to 1%, the accuracy needed to
challenge physical models. Using precision proper motion measurements, SIM will
probe the galactic mass distribution and the formation and evolution of the
Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS
Exoplanet Science Priorities from the Perspective of Internal and Surface Processes for Silicate and Ice Dominated Worlds
The geophysics of extrasolar planets is a scientific topic often regarded as
standing largely beyond the reach of near-term observations. This reality in no
way diminishes the central role of geophysical phenomena in shaping planetary
outcomes, from formation, to thermal and chemical evolution, to numerous issues
of surface and near-surface habitability. We emphasize that for a balanced
understanding of extrasolar planets, it is important to look beyond the natural
biases of current observing tools, and actively seek unique pathways to
understand exoplanet interiors as best as possible during the long interim
prior to a time when internal components are more directly accessible. Such
pathways include but are not limited to: (a) enhanced theoretical and numerical
modeling, (b) laboratory research on critical material properties, (c)
measurement of geophysical properties by indirect inference from imprints left
on atmospheric and orbital properties, and (d) the purpose-driven use of Solar
System object exploration expressly for its value in comparative planetology
toward exoplanet-analogs. Breaking down barriers that envision local Solar
System exploration, including the study of Earth's own deep interior, as
separate from and in financial competition with extrasolar planet research, may
greatly improve the rate of needed scientific progress for exoplanet
geophysics. As the number of known rocky and icy exoplanets grows in the years
ahead, we expect demand for expertise in 'exogeoscience' will expand at a
commensurately intense pace. We highlight key topics, including: how water
oceans below ice shells may dominate the total habitability of our galaxy by
volume, how free-floating nomad planets may often attain habitable subsurface
oceans supported by radionuclide decay, and how deep interiors may critically
interact with atmospheric mass loss via dynamo-driven magnetic fields
Highly Volcanic Exoplanets, Lava Worlds, and Magma Ocean Worlds:An Emerging Class of Dynamic Exoplanets of Significant Scientific Priority
Highly volcanic exoplanets, which can be variously characterized as 'lava
worlds', 'magma ocean worlds', or 'super-Ios' are high priority targets for
investigation. The term 'lava world' may refer to any planet with extensive
surface lava lakes, while the term 'magma ocean world' refers to planets with
global or hemispherical magma oceans at their surface. 'Highly volcanic
planets', including super-Ios, may simply have large, or large numbers of,
active explosive or extrusive volcanoes of any form. They are plausibly highly
diverse, with magmatic processes across a wide range of compositions,
temperatures, activity rates, volcanic eruption styles, and background
gravitational force magnitudes. Worlds in all these classes are likely to be
the most characterizable rocky exoplanets in the near future due to
observational advantages that stem from their preferential occurrence in short
orbital periods and their bright day-side flux in the infrared. Transit
techniques should enable a level of characterization of these worlds analogous
to hot Jupiters. Understanding processes on highly volcanic worlds is critical
to interpret imminent observations. The physical states of these worlds are
likely to inform not just geodynamic processes, but also planet formation, and
phenomena crucial to habitability. Volcanic and magmatic activity uniquely
allows chemical investigation of otherwise spectroscopically inaccessible
interior compositions. These worlds will be vital to assess the degree to which
planetary interior element abundances compare to their stellar hosts, and may
also offer pathways to study both the very young Earth, and the very early form
of many silicate planets where magma oceans and surface lava lakes are expected
to be more prevalent. We suggest that highly volcanic worlds may become second
only to habitable worlds in terms of both scientific and public long-term
interest.Comment: A white paper submitted in response to the National Academy of
Sciences 2018 Exoplanet Science Strategy solicitation, from the NASA Sellers
Exoplanet Environments Collaboration (SEEC) of the Goddard Space Flight
Center. 6 pages, 0 figure
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