Planet Populations as a Function of Stellar Properties

Exoplanets around different types of stars provide a window into the diverse environments in which planets form. This chapter describes the observed relations between exoplanet populations and stellar properties and how they connect to planet formation in protoplanetary disks. Giant planets occur more frequently around more metal-rich and more massive stars. These findings support the core accretion theory of planet formation, in which the cores of giant planets form more rapidly in more metal-rich and more massive protoplanetary disks. Smaller planets, those with sizes roughly between Earth and Neptune, exhibit different scaling relations with stellar properties. These planets are found around stars with a wide range of metallicities and occur more frequently around lower mass stars. This indicates that planet formation takes place in a wide range of environments, yet it is not clear why planets form more efficiently around low mass stars. Going forward, exoplanet surveys targeting M dwarfs will characterize the exoplanet population around the lowest mass stars. In combination with ongoing stellar characterization, this will help us understand the formation of planets in a large range of environments.Comment: Accepted for Publication in the Handbook of Exoplanet

Ontogenesis of immunocytochemically demonstrable somatotrophs in the adenohypophyseal pars distalis of the developing chick embryo

Growth hormone (GH)-containing cells in the hypophyseal pars distalis of the chick embryo were identified immunohistochemically using anti-chicken GH sera. GH cells are first demonstrable in Rathke's Pouch as early as Day 4.5 of incubation. By Day 9.5, when the two lobes (rostral and caudal) of the pars distalis are easily recognized, GH cells are confined exclusively to the caudal lobe. Although the number of GH cells increases gradually during embryonic development, there is a statistically significant difference between Days 10.5 and 12.5 in both the cellular density and the percentage of somatotrophs. GH cells, which contain coarse granules evenly distributed throughout the cytoplasm, varied in diameter from 9.3 μm on Day 4.5 to 11.8 μm on Day 20.5, while the nuclear diameter of these cells increased from 2.8 μm on Day 4.5 to 4.9 μm on Day 20.5. There was a statistically significant difference in the nuclear/cytoplasmic ratio between Days 4.5 and 13.5 and between Days 13.5 and 20.5 of incubation. Aspects of the regulation of growth hormone synthesis and secretion in the chick embryo are discussed. © 1987.link_to_subscribed_fulltex

Two-Step Solid Lipid Extrusion as a Process to Modify Dissolution Behavior

Extrudates based on varying ratios of the triglyceride tripalmitin and the hydrophilic polymer polyethylene glycol as matrix formers were produced as oral dosage forms with controlled release characteristics. The extrudates were processed below the melting points of the excipients and contained the hydrophobic model drug chloramphenicol. The influence of the ratio of the matrix formers on drug dissolution was investigated, with an increase in the water-soluble polymer content increasing the drug release rate. In addition, the effect of varying the extrusion process on the extrudate structure and drug dissolution was investigated. Two-step extrusion was performed, which comprised an initial extrusion step of drug and one matrix component followed by milling these extrudates and a second extrusion step for the milled extrudates mixed with the second matrix component. Initial extrusion with polyethylene glycol led to increased dissolution rates, while initial extrusion with tripalmitin led to decreased dissolution rates compared to the dissolution characteristics of extrudates containing the same composition produced by one-step extrusion. Thus, two-step solid lipid extrusion can successfully be used as a process to modify the dissolution behavior of extrudates