10 research outputs found
PS210. Surgical Restoration of Flow Following Prolonged Ischemia Inhibits Neuromuscular Recovery in a Porcine (Sus Scrofa) Model of Extremity Vascular Injury
Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in General and Comparative Endocrinology 176 (2012): 472-480, doi:10.1016/j.ygcen.2011.12.034.Axolotls (Ambystoma mexicanum) are aquatic salamanders that are widely used in
research. Axolotls have been bred in laboratories for nearly 150 years, yet little is known
about the basic biology of reproduction in these animals. We investigated the effects of
changing day length, time of year, and food availability on levels of circulating estradiol
and androgens in adult female and male axolotls, respectively. In addition, we examined
the effects of these variables on the mass of ovaries, oviducts, and eggs in females and
on mass of testes in males relative to each individual's body weight, to calculate a form
of gonadosomatic index (GSI). In both sexes, GSI was not correlated with levels of
circulating steroids. In female axolotls, estradiol levels were influenced by food
availability, changes in day length, and season, even when animals were held at a
constant temperature and day length was decorrelated with calendar date. In addition,
the mass of ovaries, oviducts, and eggs varied seasonally, peaking in the winter months
and declining during the summer months, even though our animals were not breeding
and shedding eggs. In males, levels of androgens appeared to vary independently of
external conditions, but GSI varied dramatically with changes in day length. These
results suggest that reproduction in axolotls may vary seasonally, as it does in many
other ambystomid species, although both male and female axolotls are capable of
reproducing several times each year. The physiological basis of this ability remains
enigmatic, given the indications of seasonality contained in our data.The work described here would not have been possible without funding from the National
Science Foundation (IOS 0817785), fellowships from the Marine Biological Laboratory,
and undergraduate research support from Michigan State University
Branched Surgical Grafts for Aortic Reconstruction in Connective Tissue Disorder Patients: The Emerging Standard for Repair
Preoperative Smoking Cessation is Essential in Preventing Early Graft Failure after Infrainguinal Bypass Surgery
Branched Surgical Grafts for Aortic Reconstruction in Connective Tissue Disorder Patients: The Emerging Standard for Repair
Hispanic ethnicity is associated with increased costs after carotid endarterectomy and carotid stenting in the United States
Attrition Rate in Military General Surgery GME and Effect on Quality of Military Programs
Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies
Flare frequency distributions represent a key approach to addressing one of
the largest problems in solar and stellar physics: determining the mechanism
that counter-intuitively heats coronae to temperatures that are orders of
magnitude hotter than the corresponding photospheres. It is widely accepted
that the magnetic field is responsible for the heating, but there are two
competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To
date, neither can be directly observed. Nanoflares are, by definition,
extremely small, but their aggregate energy release could represent a
substantial heating mechanism, presuming they are sufficiently abundant. One
way to test this presumption is via the flare frequency distribution, which
describes how often flares of various energies occur. If the slope of the power
law fitting the flare frequency distribution is above a critical threshold,
as established in prior literature, then there should be a
sufficient abundance of nanoflares to explain coronal heating. We performed
600 case studies of solar flares, made possible by an unprecedented number
of data analysts via three semesters of an undergraduate physics laboratory
course. This allowed us to include two crucial, but nontrivial, analysis
methods: pre-flare baseline subtraction and computation of the flare energy,
which requires determining flare start and stop times. We aggregated the
results of these analyses into a statistical study to determine that . This is below the critical threshold, suggesting that Alfv\'en
waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The
Astrophysical Journal on 2023-05-09, volume 948, page 7