787 research outputs found
Methods for Caries Prevention in Children Reported by Dentists from a Brazilian Community
Objective: To describe the dental practice patterns related to caries prevention in children aged 6-18 years and associated factors. Material and Methods: Dentists (n=162) from Araraquara, Brazil, completed two paper questionnaires: (1) one about characteristics of their practice and their patient population; and (2) a translated version of the âAssessment of Caries Diagnosis and Caries Treatmentâ Questionnaire from the National Dental Practice-Based Research Network. Regression analyses were used for data analysis (p<0.05). Results: Dentists reported using in-office fluoride (IOF) and dental sealants (DS) in 74.2% and 45.1% of their pediatric patients, respectively. Regression analysis showed that female dentists (p=0.035 for DS; p=0.044 for IOF; p=0.011 for non-prescription fluoride rinse), those with advanced degrees (p=0.032 for prescription of fluoride), those who graduated from a private dental school (p=0.018 for chlorhexidine rinse), those who provided caries prevention regimens (p<0.001 for DS; p=0.004 for IOF; p=0.013 for non-prescription fluoride rinse), those with a greater percentage of patients interested in a caries prevention regimen (p=0.007 for non-prescription fluoride rinse), those working in a private practice model (p=0.047 for prescription of fluoride) were more likely to recommend some type of preventive methods to their pediatric patients. Conclusion: Dentists reported recommending IOF to most of their pediatric patients. Certain dentistsâ, practicesâ, and patientsâ characteristics were associated to some caries prevention regimens recommended by dentists
Soil methane sink capacity response to a long-term wildfire chronosequence in Northern Sweden
Boreal forests occupy nearly one fifth of the terrestrial land surface and are recognised as globally important regulators of carbon (C) cycling and greenhouse gas emissions. Carbon sequestration processes in these forests include assimilation of CO2 into biomass and subsequently into soil organic matter, and soil microbial oxidation of methane (CH4). In this study we explored how ecosystem retrogression, which drives vegetation change, regulates the important process of soil CH4 oxidation in boreal forests. We measured soil CH4 oxidation processes on a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. Across these islands the build-up of soil organic matter was observed to increase with time since fire disturbance, with a significant correlation between greater humus depth and increased net soil CH4 oxidation rates. We suggest that this increase in net CH4 oxidation rates, in the absence of disturbance, results as deeper humus stores accumulate and provide niches for methanotrophs to thrive. By using this gradient we have discovered important regulatory controls on the stability of soil CH4 oxidation processes that could not have not been explored through shorter-term experiments. Our findings indicate that in the absence of human interventions such as fire suppression, and with increased wildfire frequency, the globally important boreal CH4 sink could be diminished
Two formation channels of UCDs in Hickson Compact Groups
The formation of ultra-compact dwarf galaxies (UCDs) is believed to be
interaction driven, and UCDs are abundant in the cores of galaxy clusters,
environments that mark the end-point of galaxy evolution. Nothing is known
about the properties of UCDs in compact groups of galaxies, environments where
most of galaxy evolution and interaction is believed to occur and where UCDs in
intermediate state of evolution may be expected. The main goal of this study is
to detect and characterize, for the first time, the UCD population of compact
groups. For that, 2 groups in different evolutionary stages, HCG 22 and HCG 90,
were targeted with VLT/FORS2/MXU. We detect 16 and 5 objects belonging to HCG
22 and HCG 90, respectively, covering the magnitude range -10.0 > M_R > -11.5
mag. Their colours are consistent with old ages covering a broad range in
metallicities. Photometric mass estimates put 4 objects in HCG 90 and 9 in HCG
22 in the mass range of UCDs (>2x10^6 M_Sun) for an assumed age of 12 Gyr.
These UCDs are on average 2-3 times larger than typical Galactic GCs, covering
a range of 2 >~ r_h >~ 21 pc. The UCDs in HCG 22 are more concentrated around
the central galaxy than in HCG 90, at the 99% confidence level. They cover a
broad range in [alpha/Fe] abundances from sub- to super-solar. The spectra of 3
UCDs show tentative evidence for intermediate age stellar populations. We
calculate the specific frequency (S_N) of UCDs for both groups, finding that
HCG 22 has about three times higher S_N than HCG 90. The ensemble properties of
the detected UCDs supports 2 co-existing formation channels: a star cluster
origin and an origin as tidally stripped dwarf nuclei. Our results imply that
the UCDs detected in both groups do not, in their majority, originate from
relatively recent galaxy interactions. Most of the detected UCDs have likely
been brought into the group with their host galaxies.[abridged]Comment: Accepted for publication at A&A, 17 pages, 9 figures + 2 additional
figure
Diffuse light and building history of the galaxy cluster Abell 2667
We have searched for diffuse intracluster light in the galaxy cluster Abell
2667 (z=0.233) from HST images in three filters. We have applied to these
images an iterative multi-scale wavelet analysis and reconstruction technique,
which allows to subtract stars and galaxies from the original images. We detect
a zone of diffuse emission south west of the cluster center (DS1), and a second
faint object (ComDif), within DS1. Another diffuse source (DS2) may be
detected, at lower confidence level, north east of the center. These sources of
diffuse light contribute to 10-15% of the total visible light in the cluster.
Whether they are independent entities or are part of the very elliptical
external envelope of the central galaxy remains unclear. VLT VIMOS integral
field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif
but do not allow to compute a redshift. A hierarchical substructure detection
method reveals the presence of several galaxy pairs and groups defining a
similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The
analysis of archive XMM-Newton and Chandra observations shows X-ray emission
elongated in the same direction. The X-ray temperature map shows the presence
of a cool core, a broad cool zone stretching from north to south and hotter
regions towards the north east, south west and north west. This possibly
suggests shock fronts along these directions produced by infalling material.
These various data are consistent with a picture in which diffuse sources are
concentrations of tidal debris and harassed matter expelled from infalling
galaxies by tidal stripping and undergoing an accretion process onto the
central cluster galaxy; as such, they are expected to be found along the main
infall directions.Comment: Accepted for publication in Astronomy and Astrophysic
Pre-senescence Harvest of Switchgrass Inhibits Xylose Utilization by Engineered Yeast
Proper timing of switchgrass harvest for bioenergy is important to maximize yield and optimize end use conversion. Proposed windows range from peak biomass to the following spring after overwintering in the field. There are various pros and cons associated with harvest timing: earlier harvests maximize yield but can remove nutrients from the field that may require replacement, while later harvests have reduced biomass yields due to weathering but maximize nutrient resorption in belowground tissues. Switchgrass composition changes during the harvest period, with losses of potential fermentation nutrients (amino acids and minerals), and sources of pretreatment-derived inhibitors (soluble sugars), which could affect downstream conversion by microorganisms. For this work we investigated whether switchgrass harvest could be timed to maximize beneficial impacts on fermentation. Switchgrass samples were harvested from five replicate field plots in Wisconsin, roughly every 2â3 weeks from peak biomass (Aug. 20) until after the killing frost (Nov. 7). Cell wall composition showed little consistent variation with harvest date while bulk biomass analysis showed a relative increase in cell wall content (lignin and structural sugars) and loss of extractives (minerals, protein, soluble sugars, and others). Following high or low severity AFEX pretreatment and high solids enzymatic hydrolysis (6% glucan loading), two field replicates were fermented using Saccharomyces cerevisiae 424A, a strain engineered to utilize xylose in addition to glucose. For both pretreatment severities, S. cerevisiae 424A grown in hydrolysates from the three earlier harvests utilized only a small fraction of available xylose, while almost complete utilization occurred within 96 hr for the last three harvest dates. Detailed analysis of the hydrolysate low molecular weight aromatics did not indicate any compounds potentially responsible for the inhibition, with most of the observed variation in their concentration due to pretreatment severity. Amino acid composition also did not appear to be limiting. Current indications point to a plant-generated compound that degrades during senescence, which future work will attempt to identify. Ultimately this work demonstrates that, although an attractive option to maximize yield, harvesting switchgrass before it begins senescing could have a negative effect on downstream conversion processes
The specific frequencies of ultra-compact dwarf galaxies
We aim at quantifying the specific frequency of UCDs in a range of
environments and at relating this to the frequency of globular clusters (GCs)
and potential progenitor dwarf galaxies. Are the frequencies of UCDs consistent
with being the bright tail of the GC luminosity function (GCLF)? We propose a
definition for the specific frequency of UCDs,
S_{N,UCD}=N_{UCD}*10^{0.4*(M_{V,host}-M_{V,0})}*c_{w}. The parameter M_{V,0} is
the zeropoint of the definition, chosen such that the specific frequency of
UCDs is the same as those of globular clusters, S_{N,GC}, if UCDs follow a
simple extrapolation of the GCLF. The parameter c_{w} is a correction term for
the GCLF width sigma. We apply our definition of S_{N,UCD} to results of
spectroscopic UCD searches in the Fornax, Hydra and Centaurus galaxy clusters,
two Hickson Compact Groups, and the Local Group. This includes a large database
of 180 confirmed UCDs in Fornax. We find that the specific frequencies derived
for UCDs match those of GCs very well, to within 10-50%. The ratio
{S_{N,UCD}}/{S_{N,GC}} is 1.00 +- 0.44 for the four environments Fornax, Hydra,
Centaurus, and Local Group, which have S_{N,GC} values. This good match also
holds for individual giant galaxies in Fornax and in the Fornax
intracluster-space. The error ranges of the derived UCD specific frequencies in
the various environments then imply that not more than 50% of UCDs were formed
from dwarf galaxies. We show that such a scenario would require >90% of
primordial dwarfs in galaxy cluster centers (<100 kpc) to have been stripped of
their stars. We conclude that the number counts of UCDs are fully consistent
with them being the bright tail of the GC population. From a statistical point
of view there is no need to invoke an additional formation channel.Comment: 11 pages, 6 figures, A&A accepted. Press release
http://www.aanda.org/index.php?option=com_content&task=view&id=788&Itemid=27
12 mode, WDM, MIMO-free orbital angular momentum transmission
Simultaneous MIMO-free transmission of 12 orbital angular momentum (OAM) modes over a 1.2 km air-core fiber is demonstrated. WDM compatibility of the system is shown by using 60, 25 GHz spaced WDM channels with 10 GBaud QPSK signals. System performance is evaluated by measuring bit error rates, which are found to be below the soft FEC limit, and limited by inter-modal crosstalk. The crosstalk in the system is analyzed, and it is concluded that it can be significantly reduced with an improved multiplexer and de-multiplexer
Antlia Dwarf Galaxy: Distance, quantitative morphology and recent formation history via statistical field correction
We apply a statistical field correction technique originally designed to
determine membership of high redshift galaxy clusters to Hubble Space Telescope
imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local
Group. Using the tip of the red giant branch standard candle method coupled
with a simple Sobel edge detection filter we find a new distance to Antlia of
1.31 +/- 0.03 Mpc. For the first time for a Local Group Member, we compute the
concentration, asymmetry and clumpiness (CAS) quantitative morphology
parameters for Antlia from the distribution of resolved stars in the HST/ACS
field, corrected with a new method for contaminants and complement these
parameters with the Gini coefficient (G) and the second order moment of the
brightest 20 per cent of the flux (M_20). We show that it is a classic dwarf
elliptical (C = 2.0, A = 0.063, S = 0.077, G = 0.39 and M_20 = -1.17 in the
F814W band), but has an appreciable blue stellar population at its core,
confirming on-going star-formation. The values of asymmetry and clumpiness, as
well as Gini and M_20 are consistent with an undisturbed galaxy. Although our
analysis suggests that Antlia may not be tidally influenced by NGC 3109 it does
not necessarily preclude such interaction.Comment: Accepted for publication in MNRA
A large population of ultra-compact dwarf galaxies in the Hydra I cluster
We performed a large spectroscopic survey of compact, unresolved objects in
the core of the Hydra I galaxy cluster (Abell 1060), with the aim of
identifying ultra-compact dwarf galaxies (UCDs), and investigating the
properties of the globular cluster (GC) system around the central cD galaxy NGC
3311. We obtained VIMOS medium resolution spectra of about 1200 candidate
objects with apparent magnitudes 18.5 < V < 24.0 mag, covering both the bright
end of the GC luminosity function and the luminosity range of all known UCDs.
By means of spectroscopic redshift measurements, we identified 118 cluster
members, from which 52 are brighter than M_V = -11.0 mag, and can therefore be
termed UCDs. The brightest UCD in our sample has an absolute magnitude of M_V =
-13.4 mag (corresponding to a mass of > 5 x 10^7 M_sun) and a half-light radius
of 25 pc. This places it among the brightest and most massive UCDs ever
discovered. Most of the GCs/UCDs are both spatially and dynamically associated
to the central cD galaxy. The overall velocity dispersion of the GCs/UCDs is
comparable to what is found for the cluster galaxies. However, when splitting
the sample into a bright and a faint part, we observe a lower velocity
dispersion for the bright UCDs/GCs than for the fainter objects. At a dividing
magnitude of M_V = -10.75 mag, the dispersions differ by more than 200 km/s,
and up to 300 km/s for objects within 5 arcmin around NGC 3311. We interpret
these results in the context of different UCD formation channels, and conclude
that interaction driven formation seems to play an important role in the centre
of Hydra I.Comment: 18 pages, 17 figures, accepted for publication in A&
The use of happiness research for public policy
Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator
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