22,587 research outputs found
SwSt 1: an O-rich planetary nebula around a C-rich central star
The hydrogen-deficient carbon-rich [WCL] type central star HD167362 and its
oxygen-rich planetary nebula (PN) SwSt~1 are investigated. The nebular
chemistry might indicate a recent origin for the carbon-rich stellar spectrum.
Its stellar and nebular properties might therefore provide further
understanding of the origin of the [WCL] central star class. The UV-IR stellar
spectra are modelled with state of the codes and show ~40kK central star with a
wind and a C/O~3, indicative of efficient third dredge-up. The synthetic
stellar flux distribution is used to model the high density, compact PN, which
has a solar C/O ratio, is still enshrouded by 1200K and 230K dust shells and,
reported here for the first time, in molecular hydrogen. Although it appears
that the change in C/O ratio has been recent, the published spectroscopy since
1895 has been re-examined and no clear spectral change is seen. If an event
occurred that has turned it into a hydrogen-deficient central star, it did not
happen in the last 100 years.Comment: 31 pages, 19 figures (some are gif files), MNRAS in pres
Tracheocutaneous fistula in patients undergoing supracricoid partial laryngectomy: the role of chronic aspiration
The aim of the present retrospective controlled study was to analyse and compare risk factors for tracheocutaneous fistula in patients who received tracheostomy after supracricoid partial laryngectomy with those who received tracheostomy for other causes. We enrolled 39 patients with tracheocutaneous fistulas who were divided into two groups. The first received temporary tracheostomy for supracricoid partial laryngectomies (n = 21), while the control group consisted of patients who received temporary tracheostomy for other causes (n = 18). Risk factors believed to play a role in the pathogenesis of tracheocutaneous fistula were examined including advanced age, cardiopathy, local infections, radiotherapy, elevated body mass index, malnutrition, decannulation time and aspiration grade. The Leipzig and Pearson scale score was significantly higher in the supracricoid partial laryngectomy group (p = 0.006 and 0.031 for univariate and multivariate analyses, respectively). The penetration/aspiration scale score was significantly higher in the supracricoid partial laryngectomy group as determined by univariate analysis (p = 0.014). The decannulation time was significantly lower in the supracricoid partial laryngectomy group (p = 0.004 and 0.0004 for univariate and multivariate analyses, respectively). The number of surgical closures for tracheocutaneous fistula was significantly higher in the supracricoid partial laryngectomy group by univariate analysis (p = 0.027). These results suggest that chronic aspiration and related cough may be important pathogenic factors for tracheocutaneous fistula and could be responsible for the significantly higher rates of closure failure in patients after supracricoid partial laryngectomy
Simulations of viscous shape relaxation in shuffled foam clusters
We simulate the shape relaxation of foam clusters and compare them with the
time exponential expected for Newtonian fluid. Using two-dimensional Potts
Model simulations, we artificially create holes in a foam cluster and shuffle
it by applying shear strain cycles. We reproduce the experimentally observed
time exponential relaxation of cavity shapes in the foam as a function of the
number of strain steps. The cavity rounding up results from local rearrangement
of bubbles, due to the conjunction of both a large applied strain and local
bubble wall fluctuations
Polynomial growth of volume of balls for zero-entropy geodesic systems
The aim of this paper is to state and prove polynomial analogues of the
classical Manning inequality relating the topological entropy of a geodesic
flow with the growth rate of the volume of balls in the universal covering. To
this aim we use two numerical conjugacy invariants, the {\em strong polynomial
entropy } and the {\em weak polynomial entropy }. Both are
infinite when the topological entropy is positive and they satisfy
. We first prove that the growth rate of the volume of
balls is bounded above by means of the strong polynomial entropy and we show
that for the flat torus this inequality becomes an equality. We then study the
explicit example of the torus of revolution for which we can give an exact
asymptotic equivalent of the growth rate of volume of balls, which we relate to
the weak polynomial entropy.Comment: 22 page
Cyclic loading and load to failure of lithium disilicate endocrowns:Influence of the restoration extension in the pulp chamber and the enamel outline
Clinical performance of direct composite resin versus indirect restorations on endodontically treated posterior teeth:A systematic review and meta-analysis
STATEMENT OF PROBLEM: High-level evidence concerning the restoration of endodontically treated posterior teeth by means of direct composite resin or indirect restorations is lacking. PURPOSE: The purpose of this systematic review and meta-analysis was to analyze the current literature on the direct and indirect restoration of endodontically treated posterior teeth. MATERIAL AND METHODS: Databases MEDLINE, CENTRAL, and EMBASE were screened. Risk of bias was assessed by using the ROB2 tool for RCTs and the ROBINS-I tool for prospective and retrospective clinical studies. Randomized clinical trials (RCTs) and prospective and retrospective studies comparing direct composite resin and indirect restorations on endodontically treated posterior teeth were included. Outcomes were tooth and restoration survival. A meta-analysis was conducted for tooth retention and restorative success. RESULTS: Twenty-two studies were included (2 RCTs, 3 prospective, and 17 retrospective). Over the short term (2.5 to 3 years), low-quality evidence suggested no difference in tooth survival. For the prospective and retrospective clinical trials, the overall risk of bias was serious to critical from the risk of confounding because of a difference in restorative indication: Direct restorations were fabricated when one marginal ridge remained or when tooth prognosis was unfavorable. For short-term restorative success, low-quality evidence suggested no difference between the direct and indirect restorations. CONCLUSIONS: For the short term (2.5 to 3 years), low-quality evidence suggests no difference in tooth survival or restoration quality. To assess the influence of the type of restoration on the survival and restorative success of endodontically treated posterior teeth, clinical trials that control for the amount of coronal tooth tissue and other baseline characteristics are needed
V605 Aql: The Older Twin of Sakurai's Object
New optical spectra have been obtained with VLT/FORS2 of the final helium
shell flash (FF) star, V605 Aql, which peaked in brightness in 1919. New models
suggest that this star is experiencing a very late thermal pulse. The evolution
to a cool luminous giant and then back to a compact hot star takes place in
only a few years. V605 Aql, the central star of the Planetary Nebula (PN), A58,
has evolved from T5000 K in 1921 to 95,000 K today. There are
indications that the new FF star, Sakurai's Object (V4334 Sgr), which appeared
in 1996, is evolving along a similar path. The abundances of Sakurai's Object
today and V605 Aql 80 years ago mimic the hydrogen deficient R Coronae Borealis
(RCB) stars with 98% He and 1% C. The new spectra show that V605 Aql has
stellar abundances similar to those seen in Wolf-Rayet [WC] central stars of
PNe with ~55% He, and ~40% C. The stellar spectrum of V605 Aql can be seen even
though the star is not directly detected. Therefore, we may be seeing the
spectrum in light scattered around the edge of a thick torus of dust seen
edge-on. In the present state of evolution of V605 Aql, we may be seeing the
not too distant future of Sakurai's Object.Comment: 12 pages, 1 figure, ApJ Letters in pres
Migraine and cluster headache show impaired neurosteroids patterns
Background: Perturbation of neuronal excitability contributes to migraine. Neurosteroids modulate the activity of γ-aminobutyric acid A and N-methyl-d-aspartate receptors, and might be involved in the pathogenesis of migraine. Here, we measured plasma levels of four neurosteroids, i.e., allopregnanolone, epiallopregnanolone, dehydroepiandrosterone and deydroepiandrosterone sulfate, in patients affected by episodic migraine, chronic migraine, or cluster headache. Methods: Nineteen female patients affected by episodic migraine, 51 female patients affected by chronic migraine, and 18 male patients affected by cluster headache were recruited to the study. Sex- and age-matched healthy control subjects (31 females and 16 males) were also recruited. Patients were clinically characterized by using validated questionnaires. Plasma neurosteroid levels were measured by liquid chromatography-tandem mass spectrometry. Results: We found disease-specific changes in neurosteroid levels in our study groups. For example, allopregnanolone levels were significantly increased in episodic migraine and chronic migraine patients than in control subjects, whereas they were reduced in patients affected by cluster headache. Dehydroepiandrosterone and dehydroepiandrosterone sulfate levels were reduced in patients affected by chronic migraine, but did not change in patients affected by cluster headache. Conclusion: We have shown for the first time that large and disease-specific changes in circulating neurosteroid levels are associated with chronic headache disorders, raising the interesting possibility that fluctuations of neurosteroids at their site of action might shape the natural course of migraine and cluster headache. Whether the observed changes in neurosteroids are genetically determined or rather result from exposure to environmental or intrinsic stressors is unknown. This might also be matter for further investigation because stress is a known triggering factor for headache attacks in both migraineurs and cluster headache patients
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