Showing 1801 - 1850 of 5840 Items
Parole lievitanti: La panificazione spirituale di S. Caterina di Bologna This record is embargoed.
- Embargo End Date: 2027-05-19
Date: 2022-01-01
Creator: Katherine Aiello McKee
Access: Embargoed
The development of begging calls in Yellow Warblers
Date: 2015-05-01
Creator: Jackson F Bloch
Access: Open access
- Nestling birds use begging calls to solicit resources from adults. Efficient transmission of calls is necessary for motivating parental feeding and outcompeting siblings. However, ambient acoustic masking and costs such as predation may influence the structure of the calls. While many interspecific comparisons of begging behavior have been made, the ontogeny of calls is understudied. In this study, Yellow Warbler (Setophaga petechia) begging calls were recorded and analyzed at different stages of nestling development to document changes in acoustic structure and gain insight into the selective forces that influence call development. Begging calls increased in peak frequency, frequency range, and amplitude during the 5-day recording period. Call duration did not change with age. Call structure did not differ between nestlings living in distinct acoustic environments. As begging calls increase in amplitude with age, perhaps due to increased food needs and competition from nestmates, nestlings may compensate for increased predation risk by increasing the peak frequency of the calls. Higher frequency calls attenuate more quickly than do low frequency calls and fall outside the frequency range of maximum hearing sensitivity for some potential predators. Previous studies on warbler begging have shown that nestlings of ground-nesting warblers, which are subject to higher rates of predation, beg at higher frequencies than do nestlings of tree-nesting warblers. This study supports the hypothesis that changes to begging call structure during development mirror the differences in call structure of species under different predation risks.
Phenotypic divergence between sites in photosynthetic thermal response despite low genetic differentiation in Gulf of Maine Ascophyllum nodosum This record is embargoed.
- Embargo End Date: 2028-05-18
Date: 2023-01-01
Creator: Olivia Bronzo-Munich
Access: Embargoed
“Something most girls don’t do” An Ethnographic Study of Women in Extreme Sports
Date: 2022-01-01
Creator: Jacqueline Boben
Access: Open access
- Extreme sports, like skateboarding, whitewater kayaking, and skiing, have historically been male-dominated. As women’s participation in these sports grows, my research asks: how do women navigate sports spaces and cultures that have for so long been defined by men? To answer this question, I draw on ethnographic research on communities of skateboarders, whitewater kayakers and skiers conducted during the summer of 2021 in Bozeman, Montana. I found that the specific landscapes where these extreme sports take place are often conceptualized by participants as more masculine spaces. Within these spaces and communities, women participants often leverage gender performances associated with masculinity to gain entry into these male-dominated communities. Performing in more masculine ways mitigates feelings of hypervisibility, while also helping to build connections to established members of the community. More than simply fitting in, women find that these gendered performances also help them to build competence in the sport. At the same time, women are transforming skateboarding, whitewater kayaking, and skiing through their participation by creating opportunities for more dynamic and fluid gender performances.
Theories of Thanks: Affect Studies, Reciprocity, and Theoretical Perspectives on Gratitude This record is embargoed.
- Embargo End Date: 2027-05-19
Date: 2022-01-01
Creator: Clayton James Wackerman
Access: Embargoed
Church Space as Queer Place? LGBTQ+ Placemaking, Assimilation, and Subversion within Progressive Faith-Based Spaces in Maine
Date: 2023-01-01
Creator: Salina Chin
Access: Open access
- In popular discourse, understandings of queerness and religiosity as antithetical proliferate. However, the political involvement of Portland, Maine’s First Parish Unitarian-Universalist Church in Maine’s queer political movement points to a more complex relationship between the LGBTQ+ community and progressive religious institutions. Through participant observation, archival research, and semi-structured interviews with nine LGBTQ+ community members and informants, I reveal the crucial role of Portland’s First Parish Unitarian-Universalist Church in Maine’s queer political movement from the late 1980s into the present day. On the one hand, progressive faith-based spaces across Maine provide safe spaces for queer political organizing. On the other hand, “ephemeral placemaking” in progressive faith-based spaces represents an assimilationist political strategy that stresses LGBTQ+ respectability. Thus, I argue that queer placemaking in progressive faith-based spaces reflects both subversive and assimilationist politics. LGBTQ+ activists utilize ephemeral placemaking strategies within progressive faith-based spaces to challenge political opposition from the religious Right while also reinforcing what Mikulak (2019) terms “godly homonormativity”: the normalization of LGBTQ+ identity and the upholding of heteronormativity by emphasizing respectability and monogamy. My analysis of queer political organizing within progressive faith-based spaces “queers” religion and LGBTQ+ politics, disrupting dominant narratives of religion as homophobic and LGBTQ+ politics as radical.
The Photocatalytic Degradation of 17α-ethynylestradiol (EE2) and Related Estrogens Access to this record is restricted to members of the Bowdoin community. Log in here to view.
- Restriction End Date: 2028-06-01
Date: 2023-01-01
Creator: Kevin Jairre Fleshman
Access: Access restricted to the Bowdoin Community
Stretch Feedback in the Lobster Heart: Experimental and Computational Analysis
Date: 2016-05-01
Creator: Katelyn J Suchyta
Access: Open access
Identity Formation in the Lebanese-American Christian Diaspora
Date: 2024-01-01
Creator: Matthew Cesar Audi
Access: Open access
- Since the late 1800s, people have immigrated to the United states from Lebanon and Syria, and the community’s racial and ethnic position within the United States has been contested ever since. Previous research emphasizes that while people from the Middle East and North Africa (MENA) are legally classified as “white” on the U.S. Census. However, many people from the region do not identify as white, and they often face discrimination or threats of violence. For people of Arab and Christian backgrounds this is further complicated because they are a part of the majority through their religion, but part of a minority through their ethnic background. In addition, media depictions of MENAs tend to be homogenizing and stereotypical. This thesis attempts to fill a gap in literature on Christian Lebanese American identities by conducting ethnographic interviews with Lebanese-Americans from a variety of generations. It pulls from theories of diaspora and race, emphasizing the importance of context and migration trajectories when understanding Lebanese American identities. My findings demonstrate wide-ranging diversity in how Christian Lebanese-Americans understand and articulate identity due to three major factors: divergent migrant pathways in multiple countries, generational difference given changing racial politics in the U.S., and generational difference given the impacts of U.S. foreign policy in the Middle East upon young Lebanese-Americans.
A Machine Learning Approach to Sector Based Market Efficiency
Date: 2023-01-01
Creator: Angus Zuklie
Access: Open access
- In economic circles, there is an idea that the increasing prevalence of algorithmic trading is improving the information efficiency of electronic stock markets. This project sought to test the above theory computationally. If an algorithm can accurately forecast near-term equity prices using historical data, there must be predictive information present in the data. Changes in the predictive accuracy of such algorithms should correlate with increasing or decreasing market efficiency. By using advanced machine learning approaches, including dense neural networks, LSTM, and CNN models, I modified intra day predictive precision to act as a proxy for market efficiency. Allowing for the basic comparisons of the weak form efficiency of four sectors over the same time period: utilities, healthcare, technology and energy. Finally, Within these sectors, I was able to detect inefficiencies in the stock market up to four years closer to modern day than previous studies.
Host and symbiont-specific patterns of gene expression in response to cold stress in the temperate coral Astrangia poculata
Date: 2023-01-01
Creator: Kellie Navarro
Access: Open access
- The coral Astrangia poculata inhabits hard-bottom environments from the Gulf of Mexico to Massachusetts and withstands large seasonal variation in temperature (–2 to 26 °C). This thermal range and its ability to live in a facultative symbiosis makes this species an ideal model system for investigating stress responses to ocean temperature variation. Although it has been shown that aposymbiotic A. poculata upregulates more genes in response to cold stress than heat stress, the transcriptomic response of the holobiont (coral host and symbiotic algae) to stress is unknown. In this study, we characterize changes in gene expression in both the host and symbionts under cold stress (6ºC) and ambient (12ºC) seawater temperatures. We use RNAseq to visualize how patterns of global gene expression change in response to these temperatures within the transcriptomes of replicate corals (n=10, each temperature) and their symbiont partners. By filtering the holobiont assembly for known coral host and symbiont genes, we contrasted patterns of differential expression (DE) for each partner and the functional processes for each set of DE genes. Differential gene expression analyses revealed that the cnidarian coral host responds strongly to cold stress, while algal symbionts did not have a significant stress response. In the coral host, we found up-regulation of biological processes associated with DNA repair, immunity, and maintaining cellular homeostasis as well as downregulation of mechanisms associated with DNA repair and RNA splicing, indicating inhibition of necessary cellular processes due to environmental stress.
Neurophysiological Effects of Temperature on the Mammalian Spinal Central Pattern Generator (CPG) Network for Locomotion Access to this record is restricted to members of the Bowdoin community. Log in here to view.
- Restriction End Date: 2026-06-01
Date: 2023-01-01
Creator: Eliza M. Rhee
Access: Access restricted to the Bowdoin Community
The combinatorial effects of temperature and salinity on the nervous system of the American lobster, Homarus americanus
Date: 2024-01-01
Creator: Katrina Carrier
Access: Open access
- The ability of nervous systems to maintain function when exposed to global perturbations in temperature and salinity is a non-trivial task. The nervous system of the American lobster (H. americanus), a marine osmoconformer and poikilotherm, must be robust to these stressors, as they frequently experience fluctuations in both. I characterized the effects of temperature on the output of the pyloric circuit, a central pattern generator in the stomatogastric nervous system (STNS) that controls food filtration and established the maximum temperature that neurons in this circuit can withstand without “crashing” (ceasing to function but recovering when returned to normal conditions). I established a range of saline concentrations that did not cause the system to crash, and then determined whether combinatorial changes in temperature and salinity concentrations alter the maximum temperature the system tolerated. Even as burst frequency increased as temperature increased, phase constancy was observed. Interestingly, the system crashed at higher temperatures upon exposure to lower saline concentrations and lower temperatures in higher saline concentrations. I also established the range of saline concentrations that the lobster’s whole heart and cardiac ganglion (CG), the nervous system that controls the lobster’s heartbeat, can withstand. Then, I examined whether exposure to altered salinity and elevated temperature alters the crash temperature of the whole heart and CG. The CG crashed at higher temperatures than the whole heart in each saline concentration. Like the STNS, the whole heart and CG both crashed at higher temperatures in lower saline concentrations and higher temperatures in lower saline concentrations.
The Body Negotiating Unprecedented Movement
Date: 2024-01-01
Creator: Mei Bock
Access: Open access
- A collection of poems exploring threads including the Lower East Side, immigration, stray animals, art, and Chinese-American identity.
ELMO, A Possible Pectin Biosynthesis Scaffold Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2023-01-01
Creator: Nuoya (Laura) Yang
Access: Access restricted to the Bowdoin Community
An Analysis of Tidal Mixing Front Dynamics and Frontal Biophysical Interaction in the Harpswell Sound Shelf Sea
Date: 2023-01-01
Creator: Lemona Yingzhuo Niu
Access: Open access
- Tidal Mixing Fronts (TMFs) are prominent hydrographic features of tidally energetic shallow shelf seas, representing the transition from mixed to stratified waters. These frontal boundaries often host enhanced phytoplankton primary productivity, as complete vertical mixing exhumes nutrients from depth to the light-lit surface. Existing observational programs for locating TMFs include infra-red satellite imagery of sea surface temperature (SST) and vertical profiling of temperature and density. However, challenges in observationally distinguishing mixed from mixing using only conservatively mixed hydrographic properties persist. A novel approach based on phytoplankton in-situ oxygen production response to light is proposed in this paper to distinguish stable mixed from actively mixing regimes, and thus to identify remnant versus active TMFs. This project focuses on Harpswell Sound, a shallow (< 40m) coastal reverse estuary, as a case study of TMF dynamics. Our data unambiguously reveal the cross-shelf structure of active, mixed, and stratified regimes. Competition between wind mixing and buoyancy due to solar heating and river plumes were found to be the primary drivers of the active and remnant front locations, while tidal currents were a secondary driver. Such dynamism explains both the temporally variable and spatially patchy phytoplankton blooms observed in the shallow shelf sea environment of Harpswell Sound.
Peripheral modulation of cardiac contractions in the American lobster, Homarus americanus, by the peptide myosuppressin is mediated by effects on the cardiac muscle itself
Date: 2023-01-01
Creator: Isabel Stella Petropoulos
Access: Open access
- A substantial factor for behavioral flexibility is modulation — largely via neuropeptides — which occurs at multiple sites including neurons, muscles, and the neuromuscular junction (NMJ). Complex modulation distributed across multiple sites provides an interesting question: does modulation at multiple locations lead to greater dynamics than one receptor site alone? The cardiac neuromuscular system of the American lobster (Homarus americanus), driven by a central pattern generator called the cardiac ganglion (CG), is a model system for peptide modulation. The peptide myosuppressin (pQDLDHVFLRFamide) has been shown in the whole heart to decrease contraction frequency, largely due to its effects on the CG, as well as increase contraction amplitude by acting on periphery of the neuromuscular system, either at the cardiac muscle, the NMJ, or both. This set of experiments addresses the location(s) at which myosuppressin exerts its effects at the periphery. To elucidate myosuppressin’s effects on the cardiac muscle, the CG was removed, and muscle contractions were stimulated with L-glutamate while superfusing myosuppressin. Myosuppressin increased glutamate-evoked contraction amplitude in the isolated muscle, suggesting that myosuppressin exerts its peripheral effects directly on the cardiac muscle. To examine effects on the NMJ, excitatory junction potentials were evoked by stimulating of the motor nerve and intracellularly recording a single muscle fiber both in control saline and in the presence of myosuppressin. Myosuppressin did not modulate the amplitude of EJPs suggesting myosuppressin acts at the muscle and not at the NMJ, to cause an increase in contraction amplitude.
Beyond Religion: Reframing Liberal Democracy’s Treatment of Exemptions Within the Public-Private Separation This record is embargoed.
- Embargo End Date: 2027-05-16
Date: 2024-01-01
Creator: Julianna Brown
Access: Embargoed
Modeling UV Light Through N95 Filters
Date: 2023-01-01
Creator: Lorenzo Hess
Access: Open access
- Reuse of N95 FFRs helps mitigate the effects of shortages. UV-C exposure is an ideal method for the decontamination necessary for FFR reuse. Recent research quantifies the transmittance of UV-C through the 3M1870+ and 3M9210+ FFRs [1]. Other research measures the reduction in viral load in relation to UV-C exposure time [11]. We design and program a ray tracing simulator in MATLAB to characterize the distribution of scattered photons in N95 FFRs. We implement an object-oriented FFR with configurable physical characteristics. We use the simulator to record the number of photons available for decontamination in each sub-layer of the filtering layers of the 3M1870+ and 3M9210+ for a given number of photons incident to the layers. We make assumptions about the photon absorption and viral deactivation in each sub-layer to derive a relation between the number of incident photons and the number of viruses remaining. The transmittance computed by our simulator matches the experimentally measured transmittance. The diameter of the simulated scattered beam also matches the experimentally measured scattered beam diameters. Our data, combined with our assumptions about absorption and deactivation, however, fail to account for the dropoff in viral load observed at about 25 seconds of exposure time in the 3M1870+.
Exploring sex-specific and developmental outcomes of early life adversity on DNA methylation in parvalbumin-containing interneurons Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2023-01-01
Creator: Emma Straw Noel
Access: Access restricted to the Bowdoin Community
Power Play: The President's Role in Shaping Renewable Energy Regulation and Policy
Date: 2023-01-01
Creator: Luke Bartol
Access: Open access
- With the impacts of climate change becoming more and more apparent every day, finding means of effective action to mitigate its effects become increasingly critical. While localized work can play an important role, federal action is necessary to have the most widespread and effective impact, especially on interconnected issues such as clean energy. Congressional action is the avenue of change at this level, however in an increasingly partisan and divided environment, progress on this front is far short of what is needed. Looking to the president is logical here, both as a single actor more insulated from partisan fights, but also as head of the branch in charge of implementing the nation’s laws. This paper looks to explore what means of influence the president has on the action taken by federal agencies and how such methods can be made more effective. Through a principal-agent framework, the role of regulatory and appointment powers are examined with a variety of historical and contemporary case studies. While only a subset of the powers afforded to a president, the areas explored offer wide latitude for action, in areas that are particularly important for energy development. The paper concludes with some reflections for the future, suggesting how these considerations can be practically applied.
"You get a lot besides just affordable housing; you get a support network”: Community Engagement in Sustainable Affordable Housing Development This record is embargoed.
- Embargo End Date: 2029-05-16
Date: 2024-01-01
Creator: Katie Draeger
Access: Embargoed
Focusing Surface-Acoustic-Wave Microcavities on GaAs
Date: 2020-01-22
Creator: Madeleine E. Msall, Paulo V. Santos
Access: Open access
- Focusing microcavities for surface acoustic waves (SAWs) produce highly localized strain and piezoelectric fields that can dynamically control excitations in nanostructures. Focusing transducers (FIDTs) that generate SAW beams that match nanostructure dimensions require pattern correction due to diffraction and wave-velocity anisotropy. The anisotropy correction is normally implemented by adding a quadratic term to the dependence of the wave velocity on the propagation angle. We show that a SAW focusing to a diffraction-limited size in GaAs requires corrections that more closely follow the group-velocity wave front, which is not a quadratic function. Optical interferometric mapping of the resultant SAW displacement field reveals tightly focused SAW beams on GaAs with a minimal beam waist. An additional set of Gouy-phase-corrected passive fingers creates an acoustic microcavity in the focal region with a small volume and a high quality factor. Our λSAW=5.6μm FIDTs are expected to scale well to the approximately 500-nm wavelength regime needed to study strong coupling between vibrations and electrons in electrostatic GaAs quantum dots.
A simple family of analytical trumpet slices of the Schwarzschild spacetime
Date: 2014-06-07
Creator: Kenneth A. Dennison, Thomas W. Baumgarte
Access: Open access
- We describe a simple family of analytical coordinate systems for the Schwarzschild spacetime. The coordinates penetrate the horizon smoothly and are spatially isotropic. Spatial slices of constant coordinate time t feature a trumpet geometry with an asymptotically cylindrical end inside the horizon at a prescribed areal radius R0 (with 0 < R0 M) that serves as the free parameter for the family. The slices also have an asymptotically flat end at spatial infinity. In the limit R0 = 0 the spatial slices lose their trumpet geometry and become flat - in this limit, our coordinates reduce to Painlevé- Gullstrand coordinates. © 2014 IOP Publishing Ltd.
Collapse of a rotating supermassive star to a supermassive black hole: Post-Newtonian simulations
Date: 2002-01-01
Creator: M. Saijo, T.W. Baumgarte, S.L. Shapiro, M. Shibata
Access: Open access
The moment of inertia of the binary pulsar J0737-3039A: Constraining the nuclear equation of state
Date: 2004-01-01
Creator: I.A. Morrison, T.W. Baumgarte, S.L. Shapiro, V.R. Pandharipande
Access: Open access
Inclusive (2P) production in (3S) decay
Date: 1991-01-01
Creator: R. Morrison, D. Schmidt, M. Procario, D. R. Johnson, K., Lingel, P. Rankin, J. G. Smith, J. Alexander, M. Artuso, C. Bebek, K. Berkelman, D. Besson, T. E. Browder, D. G. Cassel, E. Cheu, D. M. Coffman, P. S. Drell, R. Ehrlich, R. S. Galik, M. Garcia-Sciveres, B. Geiser, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, K. Honscheid, J. Kandaswamy, N. Katayama, D. L. Kreinick, J. D. Lewis, G. S. Ludwig
Access: Open access
- Using the CsI calorimeter of the CLEO II detector, the spin triplet b(2P) states are observed in (3S) radiative decays with much higher statistics than seen in previous experiments. The observed mass splittings are not described well by theoretical models, while the relative branching ratios agree with predictions that include relativistic corrections to the radiative transition rates. © 1991 The American Physical Society.
Study of continuum D*+ spin alignment
Date: 1991-01-01
Creator: Y. Kubota, J. K. Nelson, D. Perticone, R. Poling, S., Schrenk, G. Crawford, R. Fulton, T. Jensen, D. R. Johnson, H. Kagan, R. Kass, R. Malchow, F. Morrow, J. Whitmore, P. Wilson, D. Bortoletto, D. Brown, J. Dominick, R. L. McIlwain, D. H. Miller, M. Modesitt, C. R. Ng, S. F. Schaffner, E. I. Shibata, I. P.J. Shipsey, M. Battle, H. Kroha, K. Sparks, E. H. Thorndike, C. H. Wang, M. S. Alam
Access: Open access
- The spin alignment of D*+ mesons produced in e+e- annihilation at s=10.5 GeV is obtained from a study of the angular distribution of the decay D*+D0+. The alignment is studied as a function of momentum and compared to theoretical predictions. We find an average value of the spin alignment parameter of =0.040.020.01. We obtain a model-dependent measurement of the probability of producing a vector particle PV=0.770.020.01 for D mesons. © 1991 The American Physical Society.
Measurement of the ratio B(D0'e)B(D0K-e+e)
Date: 1991-01-01
Creator: G. Crawford, R. Fulton, K. K. Gan, T. Jensen, D. R., Johnson, H. Kagan, R. Kass, R. Malchow, F. Morrow, J. Whitmore, P. Wilson, D. Bortoletto, D. Brown, J. Dominick, R. L. McIlwain, D. H. Miller, M. Modesitt, C. R. Ng, S. F. Schaffner, E. I. Shibata, I. P.J. Shipsey, M. Battle, P. Kim, H. Kroha, K. Sparks, E. H. Thorndike, C. H. Wang, M. S. Alam, I. J. Kim, B. Nemati, V. Romero
Access: Open access
- Using the CLEO detector at the Cornell Electron Storage Ring, we have performed a direct measurement of the ratio of D0 semileptonic branching fractions into vector and pseudoscalar final states. We find B(D0K*-e+e)B(D0K-e+e)=0.510.180.06, in agreement with the ratio derived by the E691 experiment which compares D+ and D0 final states. We also set an upper limit on the ratio B(D0*0-e+e)B(D0K*-e+e)<0.64 at 90% confidence level. © 1991 The American Physical Society.
Study of D0 decays into final states with a 0 or
Date: 1991-01-01
Creator: K. Kinoshita, F. M. Pipkin, M. Procario, Richard Wilson, J., Wolinski, D. Xiao, Y. Zhu, R. Ammar, P. Baringer, D. Coppage, R. Davis, P. Haas, M. Kelly, N. Kwak, Ha Lam, S. Ro, Y. Kubota, J. K. Nelson, D. Perticone, R. Poling, S. Schrenk, G. Crawford, R. Fulton, T. Jensen, D. R. Johnson, H. Kagan, R. Kass, R. Malchow, F. Morrow, J. Whitmore, P. Wilson
Access: Open access
- We have made measurements of decay modes of neutral D mesons into exclusive final states containing photons using data collected with the CLEO detector at the Cornell Electron Storage Ring. We report observation of D0'K-+-+0 (charge conjugates are implicit), and present new measurements of the branching ratios for D0'K-+0, D0'K0+0-, D0'K00, K*0, and D0'K0. Where possible, results are compared with theoretical predictions for two-body D0 decays. © 1991 The American Physical Society.
Measurements of semileptonic branching fractions of B mesons at the '(4S) resonance
Date: 1992-01-01
Creator: S. Henderson, K. Kinoshita, F. Pipkin, M. Procario, M., Saulnier, R. Wilson, J. Wolinski, D. Xiao, R. Ammar, P. Baringer, D. Coppage, R. Davis, P. Haas, M. Kelly, N. Kwak, Ha Lam, S. Ro, Y. Kubota, J. K. Nelson, D. Perticone, R. Poling, S. Schrenk, G. Crawford, R. Fulton, T. Jensen, D. R. Johnson, H. Kagan, R. Kass, R. Malchow, F. Morrow, J. Whitmore
Access: Open access
- We report new measurements of semileptonic branching fractions of B mesons produced at the '(4S) resonance determined by fitting the inclusive electron and muon momentum spectra to different theoretical models. Using B(B»'X"-») to denote the average of the semileptonic branching fractions for B decay to electrons and muons, we obtain B(B»'X"-»)= (10.5±0.2±0.4)% using the refined free-quark model of Altarelli et al., and B(B»'X"-»)=(11.2±0.3±0.4)% using a modified version of the form-factor model of Isgur et al., in which the D**"-» contribution is allowed to float in the fit. The average of these two results is B(B»'X"-»)=(10.8±0. 2±0.4±0.4)%, where the errors are statistical, systematic uncertainties in the measurement, and systematic uncertainties associated with the theoretical models, respectively. Semileptonic branching fractions as low as this are difficult to accommodate in theoretical models where hadronic B-meson decays arise only from spectator diagrams. We use dilepton yields to limit the uncertainty in the semileptonic branching fraction due to the possible existence of non-BB» decays of the '(4S). In addition, we tag neutral B mesons using the decays B»0'D*+- and B»0'D*+"-» to obtain the first direct measurement of semileptonic branching fractions for neutral B mesons; the average of the electron and muon results for neutral B mesons is B(B»0'X"-»)=(9.9±3.0±0.9)%. © 1992 The American Physical Society.
Atmospheric O2/N2 changes, 1993-2002: Implications for the partitioning of fossil fuel CO2 sequestration
Date: 2005-12-01
Creator: Michael L. Bender, David T. Ho, Melissa B. Hendricks, Robert Mika, Mark O., Battle, Pieter P. Tans, Thomas J. Conway, Blake Sturtevant, Nicolas Cassar
Access: Open access
- Improvements made to an established mass spectrometric method for measuring changes in atmospheric O2/N2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3-4 per meg, corresponding to 0.6-0.8 ppm O2 in air. Records of changes in O2/N2 from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements Of CO2 from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994-2002, We find the average CO2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC yr -1 respectively; these numbers include a correction of 0.3 Gt C yr-l due to secular outgassing of ocean O2. Interannual variability calculated from these data shows a strong land carbon source associated with the 1997-1998 El Niño event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Niño events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O2. The origin of these fluxes is not yet understood. Copyright 2005 by the American Geophysical Union.
Mercury in the snow and firn at Summit Station, Central Greenland, and implications for the study of past atmospheric mercury levels
Date: 2008-06-30
Creator: X. Faïn, C. P. Ferrari, A. Dommergue, M. Albert, M., Battle, L. Arnaud, J. M. Barnola, W. Cairns, C. Barbante, C. Boutron
Access: Open access
- Gaseous Elemental Mercury (Hg° or GEM) was investigated at Summit Station, Greenland, in the interstitial air extracted from the perennial snowpack (firn) at depths ranging from the surface to 30 m, during summer 2005 and spring 2006. Photolytic production and destruction of Hg° were observed close to the snow surface during summer 2005 and spring 2006, and we observed dark oxidation of GEM up to 270 cm depth in June 2006. Photochemical transformation of gaseous elemental mercury resulted in diel variations in the concentrations of this gas in the near-surface interstitial air, but destruction of Hg° was predominant in June, and production was the main process in July. This seasonal evolution of the chemical mechanisms involving gaseous elemental mercury produces a signal that propagates downward through the firn air, but is unobservably small below 15 m in depth. As a consequence, multi-annual averaged records of GEM concentration should be well preserved in deep firn air at depths below 15 m, and available for the reconstruction of the past atmospheric history of GEM over the last decades.
Quantum lifetime of two-dimensional holes
Date: 2007-08-01
Creator: J. P. Eisenstein, D. Syphers, L. N. Pfeiffer, K. W. West
Access: Open access
- The quantum lifetime of two-dimensional holes in a GaAs/AlGaAs double quantum well is determined via tunneling spectroscopy. At low temperatures the lifetime is limited by impurity scattering but at higher temperatures hole-hole Coulomb scattering dominates. Our results are consistent with the Fermi liquid theory, at least up to rs = 11. At the highest temperatures the measured width of the hole spectral function becomes comparable to the Fermi energy. A new, tunneling-spectroscopic method for determining the in-plane effective mass of the holes is also demonstrated. © 2007 Elsevier Ltd. All rights reserved.
Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s
Date: 2009-09-22
Creator: Xavier Faïn, Christophe P. Ferrari, Aurélien Dommergue, Mary R. Albert, Mark, Battle, Jeff Severinghaus, Laurent Arnaud, Jean Marc Barnola, Warren Cairns, Carlo Barbante, Claude Boutron
Access: Open access
- Mercury (Hg) is an extremely toxic pollutant, and its biogeochemical cycle has been perturbed by anthropogenic emissions during recent centuries. In the atmosphere, gaseous elemental mercury (GEM; Hg°) is the predominant form of mercury (up to 95%). Here we report the evolution of atmospheric levels of GEM in mid- to high-northern latitudes inferred from the interstitial air of firn (perennial snowpack) at Summit, Greenland. GEM concentrations increased rapidly after World War II from ≈1.5 ng m-3 reaching a maximum of ≈3 ng m-3 around 1970 and decreased until stabilizing at ≈1.7 ng m -3 around 1995. This reconstruction reproduces real-time measurements available from the Arctic since 1995 and exhibits the same general trend observed in Europe since 1990. Anthropogenic emissions caused a two-fold rise in boreal atmospheric GEM concentrations before the 1970s, which likely contributed to higher deposition of mercury in both industrialized and remotes areas. Once deposited, this toxin becomes available for methylation and, subsequently, the contamination of ecosystems. Implementation of air pollution regulations, however, enabled a large-scale decline in atmospheric mercury levels during the 1980s. The results shown here suggest that potential increases in emissions in the coming decades could have a similar large-scale impact on atmospheric Hg levels.
Elliptic models, type IIB orientifolds, and the AdS/CFT correspondence
Date: 2000-12-18
Creator: Isabel P. Ennes, Carlos Lozano, Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- We analyze the large N supergravity descriptions of the class of type IIB models T-dual to elliptic type IIA brane configurations containing two orientifold 6-planes and up to two NS 5-branes. The T-dual IIB configurations contain N D3-branes in the background of an orientifold 7-plane and, in some models, a Z2 orbifold and/or D7-branes, which give rise to four-dimensional N=2 (or N=4) gauge theories with at most two factors. We identify the chiral primary states of the supergravity theories, and match them to gauge invariant operators of the corresponding superconformal theories using Maldacena's duality. © 2000 Elsevier Science B.V.
A record of atmospheric halocarbons during the twentieth century from polar firn air
Date: 1999-06-24
Creator: James H. Butler, Mark Battle, Michael L. Bender, Stephen A. Montzka, Andrew D., Clarke, Eric S. Saltzman, Cara M. Sucher, Jeffrey P. Severinghaus, James W. Elkins
Access: Open access
- Measurements of trace gases in air trapped in polar firn (unconsolidated snow) demonstrate that natural sources of chlorofluorocarbons, halons, persistent chlorocarbon solvents and sulphur hexafluoride to the atmosphere are minimal or non-existent. Atmospheric concentrations of these gases, reconstructed back to the late nineteenth century, are consistent with atmospheric histories derived from anthropogenic emission rates and known atmospheric lifetimes. The measurements confirm the predominance of human activity in the atmospheric budget of organic chlorine, and allow the estimation of atmospheric histories of halogenated gases of combined anthropogenic and natural origin. The pre-twentieth-century burden of methyl chloride was close to that at present, while the burden of methyl bromide was probably over half of today's value.
Partitioning of the global fossil CO2 sink using a 19-year trend in atmospheric O2
Date: 1999-07-01
Creator: R. L. Langenfelds, R. J. Francey, L. P. Steele, M. Battle, R. F., Keeling, W. F. Budd
Access: Open access
- O2/N2 is measured in the Cape Grim Air Archive (CGAA), a suite of tanks filled with background air at Cape Grim, Tasmania (40.7°S, 144.8°E) between April 1978 and January 1997. Derived trends are compared with published O2/N2 records and assessed against limits on interannual variability of net terrestrial exchanges imposed by trends of δ13C in CO2. Two old samples from 1978 and 1987 and eight from 1996/97 survive critical selection criteria and give a mean 19-year trend in δ(O2/N2) of -16.7 ± 0.5 per meg yr-1, implying net storage of +2.3 ± 0.7 GtC (1015 g carbon) yr-1 of fossil fuel CO2 in the oceans and +0.2 ± 0.9 GtC yr-1 in the terrestrial biosphere. The uptake terms are consistent for both O2/N2 and δ13C tracers if the mean 13C isotopic disequilibrium flux, combining terrestrial and oceanic contributions, is 93 ± 15 GtC ‰ yr-1. Copyright 1999 by the American Geophysical Union.