2,269 research outputs found
Cartilage on the Move: Cartilage Lineage Tracing During Tadpole Metamorphosis
The reorganization of cranial cartilages during tadpole metamorphosis is a set of complex processes. The fates of larval cartilage-forming cells (chondrocytes) and sources of adult chondrocytes are largely unknown. Individual larval cranial cartilages may either degenerate or remodel, while many adult cartilages appear to form de novo during metamorphosis. Determining the extent to which adult chondrocytes/cartilages are derived from larval chondrocytes during metamorphosis requires new techniques in chondrocyte lineage tracing. We have developed two transgenic systems to label cartilage cells throughout the body with fluorescent proteins. One system strongly labels early tadpole cartilages only. The other system inducibly labels forming cartilages at any developmental stage. We examined cartilages of the skull (viscero- and neurocranium), and identified larval cartilages that either resorb or remodel into adult cartilages. Our data show that the adult otic capsules, tecti anterius and posterius, hyale, and portions of Meckel\u27s cartilage are derived from larval chondrocytes. Our data also suggest that most adult cartilages form de novo, though we cannot rule out the potential for extreme larval chondrocyte proliferation or de- and re-differentiation, which could dilute our fluorescent protein signal. The transgenic lineage tracing strategies developed here are the first examples of inducible, skeleton-specific, lineage tracing in Xenopus
High-Resolution Near Infrared Spectroscopy of HD 100546: II. Analysis of variable rovibrational CO emission lines
We present observations of rovibrational CO in HD 100546 from four epochs
spanning January 2003 through December 2010. We show that the equivalent widths
of the CO lines vary during this time period with the v=1-0 CO lines
brightening more than the UV fluoresced lines from the higher vibrational
states. While the spectroastrometric signal of the hot band lines remains
constant during this period, the spectroastrometric signal of the v=1--0 lines
varies substantially. At all epochs, the spectroastrometric signals of the UV
fluoresced lines are consistent with the signal one would expect from gas in an
axisymmetric disk. In 2003, the spectroastrometric signal of the v=1-0 P26 line
was symmetric and consistent with emission from an axisymmetric disk. However,
in 2006, there was no spatial offset of the signal detected on the red side of
the profile, and in 2010, the spectroastrometric offset was yet more strongly
reduced toward zero velocity. A model is presented that can explain the
evolution of the equivalent width of the v=1-0 P26 line and its
spectroastrometric signal by adding to the system a compact source of CO
emission that orbits the star near the inner edge of the disk. We hypothesize
that such emission may arise from a circumplanetary disk orbiting a gas giant
planet near the inner edge of the circumstellar disk. We discuss how this idea
can be tested observationally and be distinguished from an alternative
interpretation of random fluctuations in the disk emission.Comment: 18 pages, 10 figure
Structural Properties, Order-Disorder Phenomena and Phase Stability of Orotic Acid Crystal Forms
Orotic acid (OTA) is reported to exist in the anhydrous (AH), monohydrate (Hy1) and dimethylsulfoxide monosolvate (SDMSO) forms. In this study we investigate the (de)hydration/desolvation behavior, aiming at an understanding of the elusive structural features of anhydrous OTA by a combination of experimental and computational techniques, namely, thermal analytical methods, gravimetric moisture (de)sorption studies, water activity measurements, X-ray powder diffraction, spectroscopy (vibrational, solid-state NMR), crystal energy landscape and chemical shift calculations. The Hy1 is a highly stable hydrate, which dissociates above 135°C and loses only a small part of the water when stored over desiccants (25°C) for more than one year. In Hy1, orotic acid and water molecules are linked by strong hydrogen bonds in nearly perfectly planar arranged stacked layers. The layers are spaced by 3.1 Å and not linked via hydrogen-bonds. Upon dehydration the X-ray powder diffraction and solid-state NMR peaks become broader indicating some disorder in the anhydrous form. The Hy1 stacking reflection (122) is maintained, suggesting that the OTA molecules are still arranged in stacked layers in the dehydration product. Desolvation of SDMSO, a non-layer structure, results in the same AH phase as observed upon dehydrating Hy1. Depending on the desolvation conditions different levels of order-disorder of layers present in anhydrous OTA are observed, which is also suggested by the computed low energy crystal structures. These structures provide models for stacking faults as intergrowth of different layers is possible. The variability in anhydrate crystals is of practical concern as it affects the moisture dependent stability of AH with respect to hydration
High-Resolution Near Infrared Spectroscopy of HD 100546: I. Analysis of Asymmetric Ro-Vibrational OH Emission Lines
We present observations of ro-vibrational OH and CO emission from the Herbig
Be star HD 100546. The emission from both molecules arises from the inner
region of the disk extending from approximately 13 AU from the central star.
The velocity profiles of the OH lines are narrower than the velocity profile of
the [O I] 6300 Angstrom line indicating that the OH in the disk is not
cospatial with the O I. This suggests that the inner optically thin region of
the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO
emission lines, the OH lines are highly asymmetric. We show that the average CO
and average OH line profiles can be fit with a model of a disk comprised of an
eccentric inner wall and a circular outer disk. In this model, the vast
majority of the OH flux (75%) originates from the inner wall, while the vast
majority of the CO flux (65%) originates on the surface of the disk at radii
greater than 13 AU. Eccentric inner disks are predicted by hydrodynamic
simulations of circumstellar disks containing an embedded giant planet. We
discuss the implications of such a disk geometry in light of models of planet
disk tidal interactions and propose alternate explanations for the origin of
the asymmetry
Forensics Leadership: An Isocratean Vision
Contemporary forensic students and educators owe much to the leaders of the latter half of the twentieth century who rediscovered the educational benefits of speech competition, founded several collegiate programs and professional organizations, and established numerous tournaments and perfect-ed their management in a time of great technological change and challenge. A long list of noteworthy women and men who sacrificed inordinate amounts of time, money, often careers and professional standing, and more, for the benefit of forensic activity deserve recognition, appreciation and honor. The spirit of sacrifice that characterized the founding generation of leaders and those who immediately followed is in many ways, in many places, the reason for the existence of forensic activity today. A discussion of leadership in the forensics community must begin with gratitude.
Leader is a title worn by forensic professionals from the executive level of national organizations to an assistant coach at Mount Nowhere College in the hills of Georgia. Leading students on the educational journey of understanding and practicing rhetoric is a noble task that both unifies and divides. At the same time that forensic educators are drawn together by purpose, we are often scattered by directional differences of interpretation, opinion and philosophy. While diversity of perspective represents one of the greatest strengths of the forensics community, a transcendent sense of identity and direction is necessary for meeting the challenges of the future. Leadership requires a clear vision, especially now
The Times, They Were A-Changin\u27: Exploring the Interstate Oratorical Contests of the 1960s
Since 1874, a handful of American college classrooms have hosted generations of students practicing the art of oratory. Throughout the intervening decades, students involved in the Interstate Oratory Contest have, to varying degrees, addressed the compelling social, political, economic and educational issues of their time. When one considers the shifting socio-political landscape of the 1960s, this decade seems a far cry from the rhetorical contexts that gave rise to speeches for the previous nine decades. Did stock issues give way to Woodstock issues? An analysis of the Interstate Oratory winning orations from the 1960s raises numerous questions. To what extent do the speeches reflect the emerging notion of student empowerment? How are the compelling social movements of the day, such as the Civil Rights Movement, the Women\u27s Movement, and the Anti-War Movement, reflected in the discourse of the decade? Do the 1960s\u27 orations signal the generic properties observed by previous researchers
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