1,124 research outputs found
A study of primary teeth restored by intracoronal restorations in children participating in an undergraduate teaching programme at Cork University Dental School and Hospital, Ireland
Aim: To study the outcomes for restored primary molar teeth; to examine outcomes in relation to tooth type involved, intracoronal restoration complexity and to the material used. Materials and methods: Design: Retrospective study of primary molar teeth restored by intracoronal restorations. A series of restored primary molar teeth for children aged 6-12 years was studied. The principal outcome measure was failure of initial restoration (re-restoration or extraction). Three hundred patient records were studied to include three equal groups of primary molar teeth restored with amalgam, composite or glass ionomer, respectively. Restorative materials, the restoration type, simple (single surface) or complex (multi-surface) restoration, and tooth notation were recorded. Subsequent interventions were examined. Data were coded and entered into a Microsoft Excel database and analysis undertaken using SPSS v.18. Statistical differences were tested using the c2 test of statistical significance. Results: Of the 300 teeth studied, 61 restoration failures were recorded with 11 of those extracted. No significant differences were found between outcomes for upper first, upper second, lower first or lower second primary molars. Outcomes for simple primary teeth restored by intracoronal restorations were significantly better than those for complex intracoronal restorations (P = 0.042). Teeth originally restored with amalgam accounted for 19.7% of the 61 failures, composite for 29.5%, while teeth restored with glass ionomer represented 50.8% of all restoration failures. The differences were significant (P = 0.012). Conclusions: The majority (79.7%) of the 300 restored primary teeth studied were successful, and 3.7% teeth were extracted. Restorations involving more than one surface had almost twice the failure rate of single surface restorations. The difference was significant. Significant differences in failure rates for the three dental materials studied were recorded. Amalgam had the lowest failure rate while the failure rate with glass ionomer was the highest
Metallicity gradients in the Sagittarius dwarf spheroidal Galaxy
Metallicity gradients in the Sagittarius dwarf Galaxy (Sgr) are investigated
by using infrared photometric data from the 2MASS survey. To search for
metallicity effects, the giant branch in a field situated near the Center of
the Sgr is compared to the giant branch in a field situated near its southern
edge. The contamination of Sgr giant branch by foreground Galactic stars is
canceled by statistical subtraction of diagrams symmetrical in Galactic
latitude. After subtraction it is possible to reconstruct the Sgr giant branch
with excellent accuracy. The giant branch in the two fields have similar slopes
but are shifted in color. Even after correction for the differential reddening
between the fields, the shift in color between the branch remains, and is very
significant. This variation in the color of the giant branch corresponds to a
metallicity variation of about -0.25 Dex. The existence of a metallicity
gradient in Sgr may indicate that there are two different stellar population in
Sgr. One has low metallicity, and another one of higher metallicity has a
smaller spatial extension.Comment: 7 pages, 8 figures, A&A in pres
N-body Models of Extended Clusters
We use direct N-body simulations to investigate the evolution of star
clusters with large size-scales with the particular goal of understanding the
so-called extended clusters observed in various Local Group galaxies, including
M31 and NGC6822. The N-body models incorporate a stellar mass function, stellar
evolution and the tidal field of a host galaxy. We find that extended clusters
can arise naturally within a weak tidal field provided that the tidal radius is
filled at the start of the evolution. Differences in the initial tidal
filling-factor can produce marked differences in the subsequent evolution of
clusters and the size-scales that would be observed. These differences are more
marked than any produced by internal evolution processes linked to the
properties of cluster binary stars or the action of an intermediate-mass black
hole, based on models performed in this work and previous work to date. Models
evolved in a stronger tidal field show that extended clusters cannot form and
evolve within the inner regions of a galaxy such as M31. Instead our results
support the suggestion many extended clusters found in large galaxies were
accreted as members of dwarf galaxies that were subsequently disrupted. Our
results also enhance the recent suggestion that star clusters evolve to a
common sequence in terms of their size and mass.Comment: 12 pages, 8 figures, accepted by MNRA
The influence of stellar-dynamical ejections and collisions on the relation between the maximum-star and star-cluster-mass
We perform the largest currently available set of direct N-body calculations
of young star cluster models to study the dynamical influence, especially
through the ejections of the most massive star in the cluster, on the current
relation between the maximum-stellar-mass and the star-cluster-mass. We vary
several initial parameters such as the initial half-mass radius of the cluster,
the initial binary fraction, and the degree of initial mass segregation. Two
different pairing methods are used to construct massive binaries for more
realistic initial conditions of massive binaries. We find that lower mass
clusters (<= 10^2.5 Msun) do not shoot out their heaviest star. In the case of
massive clusters (>= 1000 Msun), no most-massive star escapes the cluster
within 3 Myr regardless of the initial conditions if clusters have initial
half-mass radii, r_0.5, >= 0.8 pc. However, a few of the initially smaller
sized clusters (r_0.5 = 0.3 pc), which have a higher density, eject their most
massive star within 3 Myr. If clusters form with a compact size and their
massive stars are born in a binary system with a mass-ratio biased towards
unity, the probability that the mass of the most massive star in the cluster
changes due to the ejection of the initially most massive star can be as large
as 20 per cent. Stellar collisions increase the maximum-stellar-mass in a large
number of clusters when clusters are relatively dense (M_ecl >= 10^3 Msun and
r_0.5 = 0.3 pc) and binary-rich. Overall, we conclude that dynamical effects
hardly influence the observational maximum-stellar-mass -- cluster mass
relation.Comment: 16 pages, 8 figures, 5 tables, accepted for publication in MNRA
Improving the Relative Calculations of Volta Potential Differences Acquired from Scanning Kelvin Probe Force Microscopy (SKPFM) from Comparing an Inert Material to First-Principle Calculations
An improved relative scaling of Volta potential differences (VPD) acquired from scanning Kelvin probe force microscopy (SKPFM) was developed by quantifying the probe work function. In corrosion studies, SKPFM has been used to identify local nobility of complex metallic systems and provide theoretical corrosion initiation sites. However, large variability in measured VPD values for metallic phases has led to controversy in their interpretation. Tracking changes of the probe work function has been shown to decrease the variability seen in SKPFM results. To quantify the work function of SKPFM probes, the measured VPD of an inert gold standard was compared to the work function theoretically calculated by density functional theory (DFT) first-principles. For proof of concept, a stainless steel sample joined by a Cu-Ag-Ti brazing material was characterized by SKPFM with three different types of probes
Monte Carlo Simulations of Star Clusters - VII. The globular cluster 47 Tuc
We describe Monte Carlo models for the dynamical evolution of the massive
globular cluster 47 Tuc (NGC 104). The code includes treatments of two-body
relaxation, most kinds of three- and four-body interactions involving
primordial binaries and those formed dynamically, the Galactic tide, and the
internal evolution of both single and binary stars. We arrive at a set of
initial parameters for the cluster which, after 12Gyr of evolution, gives a
model with a fairly satisfactory match to surface brightness and density
profiles, the velocity dispersion profile, the luminosity function in two
fields, and the acceleration of pulsars. Our models appear to require a
relatively steep initial mass function for stars above about turnoff, with an
index of about 2.8 (where the Salpeter mass function has an index of 2.35), and
a relatively flat initial mass function (index about 0.4) for the lower main
sequence. According to the model, the current mass is estimated at 0.9 million
solar masses, of which about 34% consists of remnants. We find that primordial
binaries are gradually taking over from mass loss by stellar evolution as the
main dynamical driver of the core. Despite the high concentration of the
cluster, core collapse will take at least another 20Gyr.Comment: 16 pages, 16 figures, revised version submitted to MNRA
AMI galactic plane survey at 16 GHz - II. Full data release with extended coverage and improved processing
The Arcminute Microkelvin Imager Galactic Plane Survey (AMIGPS) provides
mJy-sensitivity, arcminute-resolution interferometric images of the northern
Galactic plane at 16 GHz. The first data release covered between latitudes of ; here we present a second data release, extending the coverage to
and including
high-latitude extensions to cover the Taurus and California giant molecular
cloud regions, and the recently discovered large supernova remnant G159.6+7.3.
The total coverage is now 1777 deg and the catalogue contains 6509 sources.
We also describe the improvements to the data processing pipeline which
improves the positional and flux density accuracies of the survey.We thank the staff of the Mullard Radio Astronomy Observatory for their invaluable assistance in the commissioning and operation of AMI, which is supported by Cambridge University and the Science and Technologies Facilities Council. YCP acknowledges support from a CCT/Cavendish Laboratory studentship and a Trinity College Junior Research Fellowship. CR and TZJ acknowledge support from Science and Technology Facilities Council studentships.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv172
Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies
Scanning Kelvin probe force microscopy (SKPFM) is used in corrosion studies to quantify the relative nobility of different microstructural features present within complex metallic systems and thereby elucidate possible corrosion initiation sites. However, Volta potential differences (VPDs) measured via SKPFM in the literature for metal alloys exhibit large variability, making interpretation and application for corrosion studies difficult. We have developed an improved method for referencing SKPFM VPDs by quantifying the closely related work function of the probe relative to an inert gold standard whose modified work function is calculated via density functional theory (DFT). By measuring and tracking changes in the probe vs. gold VPD, this method compensates for some of the complex effects that cause changes in an individual probe\u27s work function. Furthermore, it provides a path toward direct, quantitative comparison of SKPFM results obtained by different researchers. Application of this method to a Cu-Ag-Ti eutectic braze of a steel sample imaged with multiple SKPFM probes of differing compositions led to enhanced repeatability both within and among probe types, as well as enabled the calculation of modified work function values for each of the microstructural constituents present
Dwarf elliptical galaxies in Centaurus A group: stellar populations in AM 1339-445 and AM 1343-452
We study the red giant populations of two dE galaxies, AM 1339-445 and AM
1343-452, with the aim of investigating the number and luminosity of any upper
asymptotic giant branch (AGB) stars present. The galaxies are members of the
Centaurus A group (D~3.8 Mpc) and are classified as outlying (R~350 kpc)
satellites of Cen A. The analysis is based on near-IR photometry for individual
red giant stars, derived from images obtained with ISAAC on the VLT. The
photometry, along with optical data derived from WFPC2 images retrieved from
the HST science archive, enable us to investigate the stellar populations of
the dEs in the vicinity of the red giant branch (RGB) tip. In both systems we
find stars above the RGB tip, which we interpret as intermediate-age upper-AGB
stars. The presence of such stars is indicative of extended star formation in
these dEs similar to that seen in many, but not all, dEs in the Local Group.
For AM 1339-445, the brightest of the upper-AGB stars have Mbol~-4.5 while
those in AM 1343-452 have Mbol~-4.8 mag. These luminosities suggest ages of
approximately 6.5+/-1 and 4+/-1 Gyr as estimates for the epoch of the last
episode of significant star formation in these systems. In both cases the
number of upper-AGB stars suggests that ~15% of the total stellar population is
in the form of intermediate-age stars, considerably less than is the case for
outlying dE satellites of the Milky Way such as Fornax and LeoI.Comment: 18 pages, 19 figures, A&A accepted; high resolution version available
from: http://www.eso.org/~mrejkuba/CenA_dEs_I.pd
Spectroscopic versus Photometric Metallicities: Milky Way Dwarf Spheroidal Companions as a Test Case
Aims. The method of deriving photometric metallicities using red giant branch
stars is applied to resolved stellar populations under the common assumption
that they mainly consist of single-age old stellar populations. We explore the
effect of the presence of mixed-age stellar populations on deriving photometric
metallicities. Methods. We use photometric data sets for the five Galactic
dwarf spheroidals Sculptor, Sextans, Carina, Fornax, and Leo II in order to
derive their photometric metallicity distribution functions from their resolved
red giant branches using isochrones of the Dartmouth Stellar Evolutionary
Database. We compare the photometric metallicities with published spectroscopic
metallicities based on the analysis of the near-infrared Ca triplet (Ca T),
both on the metallicity scale of Carretta & Gratton and on the scale defined by
the Dartmouth isochrones. In addition, we compare the photometric metallicities
with published spectroscopic metallicities based on spectral synthesis and
medium-resolution spectroscopy, and on high resolution spectra where available.
Results. The mean properties of the spectroscopic and photometric metallicity
samples are comparable within the intrinsic scatter of each method although the
mean metallicities of dSphs with pronounced intermediate-age population
fractions may be underestimated by the photometric method by up to a few tenths
of dex in [Fe/H]. The star-by-star differences of the spectroscopic minus the
photometric metallicities show a wide range of values along the fiducial
spectroscopic metallicity range, with the tendency to have systematically lower
photometric metallicities for those dwarf spheroidals with a higher fraction of
intermediate-age populations. Such discrepancies persist even in the case of
the purely old Sculptor dSph, where one would na\"ively expect a very good
match when comparing with medium or low resolution metallicity measurements.
Overall, the agreement between Ca T metallicities and photometric metallicities
is very good in the metallicity range from ~ -2 dex to ~ -1.5 dex. We find that
the photometric method is reliable in galaxies that contain small (less than
15%) intermediate-age stellar fractions. Therefore, in the presence of
mixed-age stellar populations, one needs to quantify the fraction of the
intermediate-age stars in order to assess their effect on determining
metallicities from photometry alone. Finally, we note that the comparison of
spectroscopic metallicities of the same stars obtained with different methods
reveals similarly large discrepancies as the comparison with photometric
metallicities.Comment: 17 pages, 12 figures; A&A accepte
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