676 research outputs found
Gas and Dust Emission at the Outer Edge of Protoplanetary Disks
We investigate the apparent discrepancy between gas and dust outer radii
derived from millimeter observations of protoplanetary disks. Using 230 and 345
GHz continuum and CO J=3-2 data from the Submillimeter Array for four nearby
disk systems (HD 163296, TW Hydrae, GM Aurigae, and MWC 480), we examine models
of circumstellar disk structure and the effects of their treatment of the outer
disk edge. We show that for these disks, models described by power laws in
surface density and temperature that are truncated at an outer radius are
incapable of reproducing both the gas and dust emission simultaneously: the
outer radius derived from the dust continuum emission is always significantly
smaller than the extent of the molecular gas disk traced by CO emission.
However, a simple model motivated by similarity solutions of the time evolution
of accretion disks that includes a tapered exponential edge in the surface
density distribution (and the same number of free parameters) does much better
at reproducing both the gas and dust emission. While this analysis does not
rule out the disparate radii implied by the truncated power-law models, a
realistic alternative disk model, grounded in the physics of accretion,
provides a consistent picture for the extent of both the gas and dust.Comment: 9 pages, 2 figures, accepted for publication in Ap
Imaging fetal anatomy.
Due to advancements in ultrasound techniques, the focus of antenatal ultrasound screening is moving towards the first trimester of pregnancy. The early first trimester however remains in part, a 'black box', due to the size of the developing embryo and the limitations of contemporary scanning techniques. Therefore there is a need for images of early anatomical developmental to improve our understanding of this area. By using new imaging techniques, we can not only obtain better images to further our knowledge of early embryonic development, but clear images of embryonic and fetal development can also be used in training for e.g. sonographers and fetal surgeons, or to educate parents expecting a child with a fetal anomaly. The aim of this review is to provide an overview of the past, present and future techniques used to capture images of the developing human embryo and fetus and provide the reader newest insights in upcoming and promising imaging techniques. The reader is taken from the earliest drawings of da Vinci, along the advancements in the fields of in utero ultrasound and MR imaging techniques towards high-resolution ex utero imaging using Micro-CT and ultra-high field MRI. Finally, a future perspective is given about the use of artificial intelligence in ultrasound and new potential imaging techniques such as synchrotron radiation-based CT to increase our knowledge regarding human development
Leisure of family as a pedagogical problem
The pedagogical value of family leisure forms is that they actively involve and intensively use various communication mechanisms: family - children, family - family, children - children, children - teenagers - adults. The simultaneity of these contacts gives the family leisure emotional appeal, sincerity, warmth. Intra-family leisure relationships are already in themselves rehabilitative function, actively influencing the creation of a favorable psychological climate in the family.Педагогическая ценность семейных досуговых форм состоит в том, что в них активно включены и интенсивно задействованы различные механизмы общения: семья - дети, семья - семья, дети - дети, дети - подростки - взрослые. Одновременность этих контактов придает семейному досугу эмоциональную привлекательность, душевность, теплоту. Внутрисемейные досуговые отношения уже сами по себе несут реабилитирующую функцию, активно воздействуют на создание благоприятного психологического климата в семье
New highlights on stroma–epithelial interactions in breast cancer
Although the stroma in which carcinomas arise has been previously regarded as a bystander to the clonal expansion and acquisition of malignant characteristics of tumor cells, it is now generally acknowledged that stromal changes are required for the establishment of cancer. In the present article, we discuss three recent publications that highlight the complex role the stroma has during the development of cancer and the potential for targeting the stroma by therapeutic approaches
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