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

Detection and Characterization of Extrasolar Planets through Mean-motion Resonances. II. The Effect of the Planet’s Orbital Eccentricity on Debris Disk Structures

Structures observed in debris disks may be caused by gravitational interaction with planetary or stellar companions. These perturbed disks are often thought to indicate the presence of planets and offer insights into the properties of both the disk and the perturbing planets. Gaps in debris disks may indicate a planet physically present within the gap, but such gaps can also occur away from the planet's orbit at mean-motion resonances (MMRs), and this is the focus of our interest here. We extend our study of planet-disk interaction through MMRs, presented in an earlier paper, to systems in which the perturbing planet has moderate orbital eccentricity, a common occurrence in exoplanetary systems. In particular, a new result is that the 3:1 MMR becomes distinct at higher eccentricity, while its effects are absent for circular planetary orbits. We also only consider gravitational interaction with a planetary body of at least 1 Jupiter mass. Our earlier work shows that even a 1 Earth mass planet can theoretically open an MMR gap; however, given the narrow gap that can be opened by a low-mass planet, its observability would be questionable. We find that the widths, locations, and shapes of two prominent structures, the 2:1 and 3:1 MMRs, could be used to determine the mass, semimajor axis, and eccentricity of the planetary perturber and present an algorithm for doing so. These MMR structures can be used to narrow the position and even determine the planetary properties (such as mass) of any inferred but as-yet-unseen planets within a debris disk. We also briefly discuss the implications of eccentric disks on brightness asymmetries and their dependence on the wavelengths with which these disks are observed.Comment: 20 pages, 10 figures, 1 tabl

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

Corrosion behavior of bulk amorphous and crystalline Zr-based alloys in simulated body fluid with and without additions of protein

The main aim of the present study has been to investigate the electrochemical behavior of, and oxide film formation on, the bulk amorphous Zr55Cu30Ni5Al10 alloy and the crystalline counterpart in simulated body fluid. Different analytical methods, e.g., polarization and electrochemical impedance measurements, were used to compare the results of the samples when exposed to, phosphate buffered saline (PBS), with or without the addition of protein (albumin). Moreover, the influence of pH on the corrosion behavior of the materials was also investigated. Pitting corrosion was observed to exist on both amorphous and crystalline samples after exposure to the PBS solution, but the passivity region was much smaller for the crystalline material. The addition of protein to the PBS solution improved passive behavior and led to higher pitting potential in the case of the crystalline samples, while the pitting corrosion potential decreased slightly in the case of the amorphous samples. Furthermore, a decrease in the pH level accelerates the dissolution rate of both materials when exposed to the PBS environment, however, in the presence of albumin the pitting corrosion potential increased in the case of both materials. </p