Debris Disks: Probing Planet Formation

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at >>5au. Hot dust in the region planets are commonly found (<5au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018

The Effect of Instruction on Students’ Knowledge and Attitude towards Breast

Background and Objectives: Breast self examination (BSE) is an easy and inexpensive method to screen breast cancer and unlike Mammography, BSE performing is widely possible in developing countries. The incidence rate of breast cancer is higher in developed countries but it is being increased in developing countries such as Iran as a result of lifestyle change and reproductive pattern similar to those in western countries thus affecting Iranian women at a younger age and at advanced stages. Due to the fact that BSE should perform monthly after the age 20, the aim of the present study was to determine instruction effect on students’ knowledge and attitude of female students upon BSE.Methods: 174 students were selected by cluster random sampling and questionnaires were completed by interview. After that an instructional program was planned for them with the model being presented through live lecture. Finally the same questionnaires were completed again after 4 months by interview. The data were then analyzed by S.P.S.S software (ver10)Results: The mean scores of students’ knowledge and attitude were significantly increased after education. (p<0.001). Conclusion: These findings showed that Iranian students' knowledge of BSE is inadequate. It may be due to two causes: 1. there is no formal instructional programs about awareness of breast cancer for this age group in Iran.2. As the students are unmarried and very young, they may rarely refer to health care centers. The importance of BSE has been highlighted and it is recommended that BSE instruction be put in the students’ curriculum