RESUMO
Seismological constraints obtained from receiver function (RF) analysis provide important information about the crust and mantle structure. Here, we explore the utility of the free-surface multiple of the P-wave (PP) and the corresponding conversions in RF analysis. Using earthquake records, we demonstrate the efficacy of PPs-RFs before illustrating how they become especially useful when limited data is available in typical planetary missions. Using a transdimensional hierarchical Bayesian deconvolution approach, we compute robust P-to-S (Ps)- and PPs-RFs with InSight recordings of five marsquakes. Our Ps-RF results verify the direct Ps converted phases reported by previous RF analyses with increased coherence and reveal other phases including the primary multiple reverberating within the uppermost layer of the Martian crust. Unlike the Ps-RFs, our PPs-RFs lack an arrival at 7.2 s lag time. Whereas Ps-RFs on Mars could be equally well fit by a two- or three-layer crust, synthetic modeling shows that the disappearance of the 7.2 s phase requires a three-layer crust, and is highly sensitive to velocity and thickness of intra-crustal layers. We show that a three-layer crust is also preferred by S-to-P (Sp)-RFs. While the deepest interface of the three-layer crust represents the crust-mantle interface beneath the InSight landing site, the other two interfaces at shallower depths could represent a sharp transition between either fractured and unfractured materials or thick basaltic flows and pre-existing crustal materials. PPs-RFs can provide complementary constraints and maximize the extraction of information about crustal structure in data-constrained circumstances such as planetary missions.
RESUMO
OBJECTIVE: To investigate the smoking habits and associated risk factors among Greek physicians. STUDY DESIGN: Cross-sectional survey of a randomly selected sample of Greek physicians. METHODS: A national sample of 1284 physicians (718 men, 566 women) participated in the study, which was conducted between September 2003 and June 2005. Data were collected through an anonymous self-completed questionnaire. Logistic regression was used to analyse the influence of different factors on the probability of a physician being a current or former smoker. RESULTS: Overall, 38.6% of the physicians (40% of men; 37% of women) currently smoked, 13.8% were former smokers, and 47.6% had never smoked. Eighty-three per cent of smokers reported starting smoking before the age of 25 years, with half of them during medical school (aged 19-24 years). Multivariate analyses revealed that physicians who were male, unmarried, divorced or widowed, surgeons or anaesthetists, and residents were more likely to be current smokers. Former smokers were more likely to be older, male and born in a rural area. Moreover, the odds of being a current or former smoker were significantly higher among physicians with a history of parents who smoked. The proportion of physicians who reported counselling patients (often or always) to stop smoking was lower among current smokers compared with those who never smoked or those who were former smokers (74.4% vs. 85.3% vs. 84.7%, P<0.0001). CONCLUSIONS: The prevalence of smoking among Greek physicians is exceedingly high and similar to that of the general population. More effective interventions that reduce smoking in the medical community should be implemented immediately so that physicians will be better able to fulfil their function as role models for the general population.
