Showing 741 - 750 of 4695 Items
Optical proxy for phytoplankton biomass in the absence of photophysiology: Rethinking the absorption line height
Date: 2013-01-01
Creator: Collin S. Roesler
Andrew H. Barnard
Access: Open access
- The pigment absorption peak in the red waveband observed in phytoplankton and particulate absorption spectra is primarily associated with chlorophyll-a and exhibits much lower pigment packaging compared to the blue peak. The minor contributions to the signature by accessory pigments can be largely removed by computing the line height absorption at 676 nm above a linear background between approximately 650 nm and 715 nm. The line height determination is also effective in removing the contributions to total or particulate absorption by colored dissolved organic matter and non-algal particles, and is relatively independent of the effects of biofouling. The line height absorption is shown to be significantly related to the extracted chlorophyll concentration over a large range of natural optical regimes and diverse phytoplankton cultures. Unlike the in situ fluorometric method for estimating chlorophyll, the absorption line height is not sensitive to incident irradiance, in particular non-photochemical quenching. The combination of the two methods provides a combination of robust phytoplankton biomass estimates, pigment based taxonomic information and a means to estimate the photosynthetic parameter, , the irradiance at which photosynthesis transitions from light limitation to light saturation. © 2013 The Authors. E K
Statement by Anonymous (Paula) collected by Erika Bjorum on October 5, 2018 [part 1]
Date: 2018-10-05
Creator: Anonymous (Paula)
Access: Open access
- Transcription of statement includes parts 1 and 2, recorded on October 5 and October 9, 2018. This statement was given privately.
Statement by Sarah Mary (Anne) McCarron collected by Rachel George on May 1, 2014
Date: 2014-05-01
Creator: Sarah Mary McCarron
Access: Open access
Statement by Sandra Pictou collected by Marcie Lister on October 16, 2014
Date: 2014-10-16
Creator: Sandra Pictou
Access: Open access
Interview with Jenna Burton (Class of 1994) by Emma Kellogg
Date: 2019-05-31
Creator: Jenna Burton
Access: Open access
- Jenna Burton (Class of 1994) describes the process of making friends through Hyde Hall and the sailing team. She also speaks about her experience being part of the Kappa Sigma fraternity and becoming its first female president. Burton reminisces about the hurdles and triumphs of starting the women’s rugby team and discusses the camaraderie and support she found within the team. Additionally, Burton talks about her on-campus job as a Resident Assistant, her Biology major, and reflects on working with Safe Space to critically examine the College’s sexual harassment policy. Finally, she touches on some of her favorite memories, like long brunches in Thorne Dining Hall and broom hockey on the quad.
A semester-long project-oriented biochemistry laboratory based on Helicobacter pylori urease
Date: 2015-09-01
Creator: Kate R. Farnham
Danielle H. Dube
Access: Open access
- Here we present the development of a 13 week project-oriented biochemistry laboratory designed to introduce students to foundational biochemical techniques and then enable students to perform original research projects once they have mastered these techniques. In particular, we describe a semester-long laboratory that focuses on a biomedically relevant enzyme-Helicobacter pylori (Hp) urease-the activity of which is absolutely required for the gastric pathogen Hp to colonize the human stomach. Over the course of the semester, students undertake a biochemical purification of Hp urease, assess the success of their purification, and investigate the activity of their purified enzyme. In the final weeks of the semester, students design and implement their own experiments to study Hp urease. This laboratory provides students with an understanding of the importance of biochemistry in human health while empowering them to engage in an active area of research.
Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition: Evidence from CFC-12 measurements in Antarctic firn air and ice cores
Date: 2010-06-18
Creator: M. Aydin
S. A. Montzka
M. O. Battle
M. B. Williams
W. J., De Bruyn
J. H. Butler
K. R. Verhulst
C. Tatum
B. K. Gun
D. A. Plotkin
B. D. Hall
E. S. Saltzman
Access: Open access
- In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition. © Author(s) 2010.
Bio-optical discrimination of diatoms from other phytoplankton in the surface ocean: Evaluation and refinement of a model for the Northwest Atlantic
Date: 2018-11-01
Creator: Sasha J. Kramer
Collin S. Roesler
Heidi M. Sosik
Access: Open access
- Diatoms dominate global silica production and export production in the ocean; they form the base of productive food webs and fisheries. Thus, a remote sensing algorithm to identify diatoms has great potential to describe ecological and biogeochemical trends and fluctuations in the surface ocean. Despite the importance of detecting diatoms from remote sensing and the demand for reliable methods of diatom identification, there has not been a systematic evaluation of algorithms that are being applied to this end. The efficacy of these models remains difficult to constrain in part due to limited datasets for validation. In this study, we test a bio-optical algorithm developed by Sathyendranath et al. (2004) to identify diatom dominance from the relationship between ratios of remote sensing reflectance and chlorophyll concentration. We evaluate and refine the original model with data collected at the Martha's Vineyard Coastal Observatory (MVCO), a near-shore location on the New England shelf. We then validated the refined model with data collected in Harpswell Sound, Maine, a site with greater optical complexity than MVCO. At both sites, despite relatively large changes in diatom fraction (0.8–82% of chlorophyll concentration), the magnitude of variability in optical properties due to the dominance or non-dominance of diatoms is less than the variability induced by other absorbing and scattering constituents of the water. While the original model performance was improved through successive re-parameterizations and re-formulations of the absorption and backscattering coefficients, we show that even a model originally parameterized for the Northwest Atlantic and re-parameterized for sites such as MVCO and Harpswell Sound performs poorly in discriminating diatom-dominance from optical properties.
Natural and experimental evolution of sexual conflict within Caenorhabditis nematodes
Date: 2015-05-22
Creator: Michael F. Palopoli
Colin Peden
Caitlin Woo
Ken Akiha
Megan, Ary
Lori Cruze
Jennifer L. Anderson
Patrick C. Phillips
Access: Open access
- Background: Although males and females need one another in order to reproduce, they often have different reproductive interests, which can lead to conflict between the sexes. The intensity and frequency of male-male competition for fertilization opportunities is thought to be an important contributor to this conflict. The nematode genus Caenorhabditis provides an opportunity to test this hypothesis because the frequency of males varies widely among species with different mating systems. Results: We find evidence that there is strong inter- and intra-sexual conflict within C. remanei, a dioecious species composed of equal frequencies of males and females. In particular, some C. remanei males greatly reduce female lifespan following mating, and their sperm have a strong competitive advantage over the sperm of other males. In contrast, our results suggest that both types of conflict have been greatly reduced within C. elegans, which is an androdioecious species that is composed of self-fertilizing hermaphrodites and rare males. Using experimental evolution in mutant C. elegans populations in which sperm production is blocked in hermaphrodites (effectively converting them to females), we find that the consequences of sexual conflict observed within C. remanei evolve rapidly within C. elegans populations experiencing high levels of male-male competition. Conclusions: Together, these complementary data sets support the hypothesis that the intensity of intersexual conflict varies with the intensity of competition among males, and that male-induced collateral damage to mates can evolve very rapidly within populations.
Complete mitochondrial genomes of the human follicle mites Demodex brevis and D. folliculorum: Novel gene arrangement, truncated tRNA genes, and ancient divergence between species
Date: 2014-12-16
Creator: Michael F. Palopoli
Samuel Minot
Dorothy Pei
Alicia Satterly
Julie, Endrizzi
Access: Open access
- Background: Follicle mites of the genus Demodex are found on a wide diversity of mammals, including humans. surprisingly little is known, however, about the evolution of this association. Additional sequence information promises to facilitate studies of Demodex variation within and between host species. Here we report the complete mitochondrial genome sequences of two species of Demodex known to live on humans-Demodex brevis and D. folliculorum-which are the first such genomes available for any member of the genus. We analyzed these sequences to gain insight into the evolution of mitochondrial genomes within the Acariformes. We also used relaxed molecular clock analyses, based on alignments of mitochondrial proteins, to estimate the time of divergence between these two species. Results: Both Demodex genomes shared a novel gene order that differs substantially from the ancestral chelicerate pattern, with transfer RNA (tRNA) genes apparently having moved much more often than other genes. Mitochondrial tRNA genes of both species were unusually short, with most of them unable to encode tRNAs that could fold into the canonical cloverleaf structure. indeed, several examples lacked both D- and T-arms. Finally, the high level of sequence divergence observed between these species suggests that these two lineages last shared a common ancestor no more recently than about 87 mya. Conclusions: Among Acariformes, rearrangements involving tRNA genes tend to occur much more often than those involving other genes. The truncated tRNA genes observed in both Demodex species would seem to require the evolution of extensive tRNA editing capabilities and/or coevolved interacting factors. The molecular machinery necessary for these unusual tRNAs to function might provide an avenue for developing treatments of skin disorders caused by Demodex. The deep divergence time estimated between these two species sets a lower bound on the time that Demodex have been coevolving with their mammalian hosts, and supports the hypothesis that there was an early split within the genus Demodex into species that dwell in different skin microhabitats.