5,652 research outputs found
On the Origin of the Type Ia Supernova Width-Luminosity Relation
Brighter Type Ia supernovae (SNe Ia) have broader, more slowly declining
B-band light curves than dimmer SNe Ia. We study the physical origin of this
width-luminosity relation (WLR) using detailed radiative transfer calculations
of Chandrasekhar mass SN Ia models. We find that the luminosity dependence of
the diffusion time (emphasized in previous studies) is in fact of secondary
relevance in understanding the model WLR. Instead, the essential physics
involves the luminosity dependence of the spectroscopic/color evolution of SNe
Ia. Following maximum-light, the SN colors are increasingly affected by the
development of numerous Fe II/Co II lines which blanket the B-band and, at the
same time, increase the emissivity at longer wavelengths. Because dimmer SNe Ia
are generally cooler, they experience an earlier onset of Fe III to Fe II
recombination in the iron-group rich layers of ejecta, resulting in a more
rapid evolution of the SN colors to the red. The faster B-band decline rate of
dimmer SNe Ia thus reflects their faster ionization evolution.Comment: 6 pages, submitted to Ap
Gingival crevicular fluid alkaline phosphatase activity in relation to pubertal growth spurt and dental maturation: A multiple regression study
Introduction: The identification of the onset of the pubertal growth spurt has major clinical implications when dealing with orthodontic treatment in growing subjects.
Aim: Through multivariate methods, this study evaluated possible relationships between the gingival crevicular fluid (GCF) alkaline phosphatase (ALP) activity and pubertal growth spurt and dentition phase.
Materials and methods: One hundred healthy growing subjects (62 females, 38 males; mean age, 11.5±2.4 years) were enrolled into this doubleblind, prospective, cross-sectional-design study. Phases of skeletal maturation (pre - pubertal, pubertal, post - pubertal) was assessed using the cervical vertebral maturation method. Samples of GCF for the ALP activity determination were collected at the mesial and distal sites of the mandibular central incisors. The phases of the dentition were recorded as intermediate mixed, late mixed, or permanent. A multinomial multiple logistic regression model was used to assess relationships of the enzymatic activity to growth phases and dentition phases.
Results: The GCF ALP activity was greater in the pubertal growth phase as compared to the pre - pubertal and post - pubertal growth phases. Significant adjusted odds ratios for the GCF ALP activity for the pre - pubertal and post - pubertal subjects, in relation to the pubertal group, were 0.76 and 0.84, respectively. No significant correlations were seen for the dentition phase.
Conclusions: The GCF ALP activity is a valid candidate as a non - invasive biomarker for the identification of the pubertal growth spurt irrespective of the dentition phase
Radiographic growth indicators: The issue of diagnostic reliability and clinical feasibility
The use of radiographic growth indicators, such as the hand-and-wrist maturation (HWM) and cervical vertebral maturation (CVM)methods, has been recommended in previous clinical trials on the skeletal effects obtained by functional treatment in growing ClassII patients. The concept behind the use of indicators resides in the identification of the pubertal growth spurt in individual patients allowing the delivery of the treatment at this specific stage of skeletal maturation when the mandible response is expected to be maximum growth. Interestingly, while many of the former types of investigations reported a poor correlation between the stages of growth indicators (mainly the CVM) and mandibular growth spurt, most of the latter type of investigations reported clinically relevant favorable effects when the growth indicators are used. It is perhaps that investigations are still missing the relevant piece of evidence.The first critical issue relates to the correlation between two variables (i.e., stages of maturation and mandibular growth) that does not imply diagnostic accuracy, as it has been extensively reported for the case of dental maturation. The other relevant issue relates to the clinical feasibility of the repetition of the recording when dealing with invasive methods based on X-rays, irrespective of whether the methods are accurate. Meanwhile, more opportunity will be given by the use of non-invasive (serum or GCF) biomarkers. According to all these considerations, more reports will be necessary to elucidate the role of the growth indicators in orthodontics fully
Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?
B-band light-curve rise times for eight unusually well-observed nearby Type
Ia supernovae (SNe) are fitted by a newly developed template-building
algorithm, using light-curve functions that are smooth, flexible, and free of
potential bias from externally derived templates and other prior assumptions.
From the available literature, photometric BVRI data collected over many
months, including the earliest points, are reconciled, combined, and fitted to
a unique time of explosion for each SN. On average, after they are corrected
for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five
SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single
parent population (a hypothesis not favored by statistical tests), the rms
intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52
-0.25 days -- a first measurement of this dispersion. The corresponding global
mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by
intrinsic variance. This value is ~2 days shorter than two published averages
that nominally are twice as precise, though also based on small samples. When
comparing high-z to low-z SN luminosities for determining cosmological
parameters, bias can be introduced by use of a light-curve template with an
unrealistic rise time. If the period over which light curves are sampled
depends on z in a manner typical of current search and measurement strategies,
a two-day discrepancy in template rise time can bias the luminosity comparison
by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2
tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte
The Persistence of Memory, or How the X-Ray Spectrum of SNR 0509-67.5 Reveals the Brightness of its Parent Type Ia Supernova
We examine the dynamics and X-ray spectrum of the young Type Ia supernova
remnant 0509-67.5 in the context of the recent results obtained from the
optical spectroscopy of its light echo. Our goal is to estimate the kinetic
energy of the supernova explosion using Chandra and XMM-Newton observations of
the supernova remnant, thus placing the birth event of 0509-67.5 in the
sequence of dim to bright Type Ia supernovae. We base our analysis on a
standard grid of one-dimensional delayed detonation explosion models, together
with hydrodynamic and X-ray spectral calculations of the supernova remnant
evolution. From the remnant dynamics and the properties of the O, Si, S, and Fe
emission in its X-ray spectrum we conclude that 0509-67.5 was originated ~400
years ago by a bright, highly energetic Type Ia explosion similar to SN 1991T.
Our best model has a kinetic energy of 1.4x10E51 erg and synthesizes 0.97 Msun
of 56Ni. These results are in excellent agreement with the age estimate and
spectroscopy from the light echo. We have thus established the first connection
between a Type Ia supernova and its supernova remnant based on a detailed
quantitative analysis of both objects.Comment: 10 pages, 9 figures, plus an exclusive astro-ph-only Appendix; ApJ in
press, companion paper to Rest et al. 0
Treatment effects of fixed functional appliances alone or in combination with multibracket appliances: A systematic review and meta-analysis
"Abstract Objective: To assess skeletal and dentoalveolar effects of fixed
functional appliances, alone or in combination with multibracket appliances
(comprehensive treatment), on Class II malocclusion in pubertal and postpubertal patients. Materials and Methods: Literature survey was conducted using the Medline, SCOPUS, LILACS, and SciELO databases and The Cochrane Library, and through a manual search. The studies retrieved had to have a matched untreated control group. No restrictions were set regarding the type of fixed appliance, treatment length, or to the cephalometric analysis used. Data extraction was mostly predefined at the protocol stage by two authors. Supplementary mandibular elongation was used for the meta-analysis. Results: Twelve articles qualified for the final analysis of which eight articles were on pubertal patients and four were on postpubertal patients. Overall supplementary total mandibular longationsas mean (95 confidence interval) were 1.95 mm (1.47 to 2.44) and 2.22 mm (1.63to 2.82) among pubertal patients and -1.73 mm (-2.60 to -0.86) and 0.44 mm (-0.78 to 1.66) among postpubertal patients, for the functional and comprehensive treatments, respectively. For pubertal subjects, maxillary growth restraint was also reported. Nevertheless, skeletal effects alone would not account for the whole Class II correction even in pubertal subjects with dentoalveolar effects always present. Conclusions: Fixed functional treatment is effective in treating Class II malocclusion with skeletal effects when performed during the pubertal growth phase, very few data are available on postpubertal patients.
Can differences in the nickel abundance in Chandrasekhar mass models explain the relation between brightness and decline rate of normal Type Ia Supernovae?
The use of Type Ia supernovae as distance indicators relies on the
determination of their brightness. This is not constant, but it can be
calibrated using an observed relation between the brightness and the properties
of the optical light curve (decline rate, width, shape), which indicates that
brighter SNe have broader, slower light curves. However, the physical basis for
this relation is not yet fully understood. Among possible causes are different
masses of the progenitor white dwarfs or different opacities in
Chandrasekhar-mass explosions. We parametrise the Chandrasekhar-mass models
presented by Iwamoto et al (1999), which synthesize different amounts of Ni,
and compute bolometric light curves and spectra at various epochs. Since
opacity in SNe Ia is due mostly to spectral lines, it should depend on the mass
of Fe-peak elements synthesized in the explosion, and on the temperature in the
ejecta. Bolometric light curves computed using these prescriptions for the
optical opacity reproduce the relation between brightness and decline rate.
Furthermore, when spectra are calculated, the change in colour between maximum
and two weeks later allows the observed relation between M_B(Max) and
Dm_{15}(B) to be reproduced quite nicely. Spectra computed at various epochs
compare well with corresponding spectra of spectroscopically normal SNeIa
selected to cover a similar range of Dm_{15}(B) values.Comment: 25 pages, including 6 figures. Accepted for publication in Ap
Outcome stability of orthopaedic treatment of skeletal Class III malocclusion: A study of prognostic agreement between three models
Introduction: Long-term stability of the treatment outcome of skeletal Class III malocclusion is always not achievable, thereforeseveral prediction models of stability of orthopaedic treatment of the Class III malocclusion have been proposed.
Aim: This cross-sectional study was aimed at the evaluation of the prognostic agreement and association between three differentprediction models based on skeletal parameters recorded on lateral cephalograms.
Materials and methods: A total of 75 subjects (34 females and 41 males, age range 7-11, mean age 9.1±1.2years) having skeletal ClassIII malocclusion were included in the study. Prediction models reported by Baccetti et al. 2004 (prediction model 1), Moon et al.2005 (prediction model 2) and Yoshida et al. 2006 (prediction model 3), were considered. Percentage agreement and unweighted kappa coefficient evaluated the agreement between the prediction models in terms of stable or unstable cases. Multiple regressions were run to evaluate the association between the absolute scores obtained from each of the prediction model (prediction scores).
Results: Percentage agreement ranged from 77.3% (models 2 and 3) to 89.3%, (models 1 and 2) and corresponding unweighted kappa coefficients ranged from 0.099 (models 1 and 3) to 0.205 (models 2 and 3). The prediction score from model 3 was significantly associated with those from both the other models; on the contrary, prediction scores from models 1 and 2 were not significantly associated.
Conclusions: Agreement in terms of stability or instability outcome derived from these models is only partial and not satisfactory,even though significant association between the prediction scores denotes a common biological meaning of the models
- âŠ