Showing 1361 - 1370 of 5831 Items
Spatially variable syn- and post-orogenic exhumation of the Appalachian Mountains from apatite and zircon (U-Th)/He thermochronology
Date: 2020-01-01
Creator: Luke Coughtry Basler
Access: Open access
- We present zircon and apatite (U-Th)/He (ZHe, closure temperature = 150-200ºC; AHe, closure temperature = 45-80ºC) results from two study regions in the Appalachians Mountains to investigate the timing, rates, and spatial trends of exhumation during Alleghanian orogenesis, Atlantic rifting, and post-rift passive margin conditions. Within West Virginia and Virginia, 10 ZHe dates along an across-orogen transect display an eastward younging trend, from ~425 million years (Ma) in the western Appalachian Plateau province, to ~250-300 Ma in the central Valley-Ridge fold-thrust belt, and 163 ± 29 Ma in the eastern Piedmont. Inverse thermal modeling of ZHe data using external geologic constraints indicates: (1) Pre-depositional cooling signatures within Pennsylvanian Appalachian Plateau rocks, suggesting provenance from recycled Taconic or Acadian basin strata, (2) Rapid Alleghanian (250-300 Ma) cooling in the Valley and Ridge province, indicating syn-orogenic uplift and exhumation, followed by a protracted period of stable syn-rift thermal conditions from ~250-150 Ma, and (3) Rapid rift-induced cooling in the Piedmont province, likely caused by rift-flank uplift and the post-rift lessening of the geothermal gradient. Within the Northern Appalachians of Vermont, four metamorphic samples yield averaged AHe dates of 100-120 Ma. Inverse thermal modeling indicates stable thermal conditions from 90 Ma to the present, limiting cooling driven by the recently recognized Northern Appalachian lithospheric thermal anomaly to < 20ºC. Modeling also indicates steady mid-Cretaceous (120-90 Ma) cooling (70 to 30ºC) coeval with passage over the Great Meteor Hotspot, although cooling rates are slower than would be expected during hotspot-induced thermal doming.
Bowdoin College - Medical School of Maine Catalogue (1914-1915)
Date: 1915-01-01
Access: Open access
- Bowdoin College Bulletin no. 55
Bowdoin College Catalogue (1927-1928)
Date: 1928-01-01
Access: Open access
- Bowdoin College Bulletin no. 169
The use of Hardy-Weinberg Equilibrium in clonal plant systems
Date: 2016-02-01
Creator: Vladimir Douhovnikoff, Matthew Leventhal
Access: Open access
- Traditionally population genetics precludes the use of the same genetic individual more than once in Hardy-Weinberg (HW) based calculations due to the model's explicit assumptions. However, when applied to clonal plant populations this can be difficult to do, and in some circumstances, it may be ecologically informative to use the ramet as the data unit. In fact, ecologists have varied the definition of the individual from a strict adherence to a single data point per genotype to a more inclusive approach of one data point per ramet. With the advent of molecular tools, the list of facultatively clonal plants and the recognition of their ecological relevance grows. There is an important risk of misinterpretation when HW calculations are applied to a clonal plant not recognized as clonal, as well as when the definition of the individual for those calculations is not clearly stated in a known clonal species. Focusing on heterozygosity values, we investigate cases that demonstrate the extreme range of potential modeling outcomes and describe the different contexts where a particular definition could better meet ecological modeling goals. We emphasize that the HW model can be ecologically relevant when applied to clonal plants, but caution is necessary in how it is used, reported, and interpreted. We propose that in known clonal plants, both genotype (GHet) and ramet (RHet) based calculations are reported to define the full range of potential values and better facilitate cross-study comparisons.
Interview with John Warner by Brien Williams
Date: 2009-03-31
Creator: John W. Warner
Access: Audio recording permanently restricted
- Biographical NoteJohn William Warner was born February 18, 1927, to John W. Warner and Martha Budd Warner. He grew up in Washington, D.C. and was graduated from Woodrow Wilson High School in 1945. He enlisted in the Navy after high school and is a veteran of World War II. After leaving the service he attended Washington & Lee University in Lexington, Virginia, graduating in 1949. He attended law school at the University of Virginia but left to serve in the Marines during the Korean War; subsequently, he received his law degree from George Washington University in 1953, served as a law clerk and became an assistant U.S. attorney before going into private practice in 1960, when he also served as a member of Richard Nixon’s advance staff during the 1960 presidential campaign. He married Catherine Conover Mellon in 1967 and they had three children before divorcing in 1973. In 1969, Warner was appointed undersecretary of the Navy, and then in 1972 he rose to be secretary of the Navy, a post he held for two years. President Ford appointed him director of the American Revolution Bicentennial Administration. In 1976, he married Elizabeth Taylor; they divorced in 1982. In 1978, Warner ran unsuccessfully in the Virginia Republican primary for the U.S. Senate; however, when the nominee was killed in a plane crash, he was asked to step in with only ten weeks until the election. Warner managed a narrow victory, earning the nickname “Landslide Johnny,” and remained in the Senate for thirty years, eventually retiring in 2009 as Virginia’s second longest serving senator. At the time of this interview he was a partner at the firm Hogan & Hartson, now Hogan Lovells. SummaryInterview includes discussion of: Warner’s entry into politics in 1960 as a member of then Vice President Nixon’s advance staff; opening Nixon’s Washington, D.C. office in 1968; serving as undersecretary, and later secretary, of the navy; working on the nation’s bicentennial; the 1978 Virginia Senate race; an anecdote about Warner and Mike Mansfield serving in the military; majority and minority leaders descriptions; the role of the filibuster in the Senate and how it has evolved; Mitchell’s Elizabeth Taylor joke and sense of humor in general; how the Republican caucus regarded Mitchell; an anecdote about Washington and Jefferson discussing the role of the Senate in the bicameral system; George Mitchell’s interest in environmental issues and the Clean Air Act; the ISTEA transportation bill; projects, or “pork”; the Gulf War Resolution; Mitchell’s views on military spending and awarding of shipbuilding contracts; BRAC proceedings and the Loring Air Force Base closure; the pendulum of political power; the political shift in 1980 with Reagan’s election; Reagan’s economic policies; how the culture of the Senate has changed; the increased importance of fund-raising; former House members in the Senate; Maine senators and distinguished careers; the Gang of Fourteen; Warner’s role in electing Bill Frist to majority leader; the Clintons’ attempt at health care reform; Warner’s role in encouraging Dole to run for majority leader; Hillary Clinton as a senator; Mitchell’s career since leaving the Senate; the challenges Mitchell faces as special envoy for the Middle East; Warner’s thoughts on leaving the Senate, and his plans for the future at the firm Hogan Lovells.
Does differential receptor distribution underlie variable responses to a neuropeptide in the lobster cardiac system?
Date: 2021-08-02
Creator: Audrey J. Muscato, Patrick Walsh, Sovannarath Pong, Alixander Pupo, Roni J., Gross, Andrew E. Christie, J. Joe Hull, Patsy S. Dickinson
Access: Open access
- Central pattern generators produce rhythmic behaviors independently of sensory input; however, their outputs can be modulated by neuropeptides, thereby allowing for functional flexibility. We investigated the effects of C-type allatostatins (AST-C) on the cardiac ganglion (CG), which is the central pattern generator that controls the heart of the American lobster, Homarus americanus, to identify the biological mechanism underlying the significant variability in individual responses to AST-C. We proposed that the presence of multiple receptors, and thus differential receptor distribution, was at least partly responsible for this observed variability. Using transcriptome mining and PCR-based cloning, we identified four AST-C receptors (ASTCRs) in the CG; we then characterized their cellular localization, binding potential, and functional activation. Only two of the four receptors, ASTCR1 and ASTCR2, were fully functional GPCRs that targeted to the cell surface and were activated by AST-C peptides in our insect cell expression system. All four, however, were amplified from CG cDNAs. Following the confirmation of ASTCR expression, we used physiological and bioinformatic techniques to correlate receptor expression with cardiac responses to AST-C across individuals. Expression of ASTCR1 in the CG showed a negative correlation with increasing contraction amplitude in response to AST-C perfusion through the lobster heart, suggesting that the differential expression of ASTCRs within the CG is partly responsible for the specific physiological response to AST-C exhibited by a given individual lobster.
Bowdoin College Catalogue (1942-1943)
Date: 1943-01-01
Access: Open access
- Bowdoin College Bulletin no. 266