Showing 281 - 290 of 733 Items
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.
Clonal growth: Invasion or stability? A comparative study of clonal architecture and diversity in native and introduced lineages of Phragmites australis (Poaceae)
Date: 2014-09-01
Creator: Vladimir Douhovnikoff, Eric L.G. Hazelton
Access: Open access
- Premise of the study: The characteristics of clonal growth that are advantageous in invasive plants can also result in native plants’ ability to resist invasion. In Maine, we compared the clonal architecture and diversity of an invasive lineage (introduced Phragmites) and a noninvasive lineage (native Phragmites) present in much of North America. This study is the fi rst on standscale diversity using a sample size and systematic spatial-sampling scheme adequate for characterizing clonal structure in Phragmites. Our questions included: (1) Does the structure and extent of clonal growth suggest that the potential for clonal growth contributes to the invasiveness of the introduced lineage? (2) Is clonal growth common in the native lineage, acting as a possible source of ecological resistance and resilience?
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders, John A. Broadwater, Paula A. Bekeny, Johanna E. Salmon, Ann S., Lee, Aimee M. Eldridge, Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a “structural” arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribulose‐1,5‐bisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the “mantle” (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehyde‐3‐phosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIV‐1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying α‐helix to α‐helix, βturn to β‐turn, and subunit to subunit. Copyright © 1994 The Protein Society
Clonal diversity in an expanding community of Arctic Salix spp. and a model for recruitment modes of arctic plants
Date: 2010-11-01
Creator: Vladimir Douhovnikoff, Gregory R. Goldsmith, Ken D. Tape, Cherrie Huang, Nadine, Sur, M. Syndonia Bret-Harte
Access: Open access
- Rapid climate change in arctic environments is leading to a widespread expansion in woody deciduous shrub populations. However, little is known about the reproductive, dispersal, and establishment mechanisms associated with shrub expansion. It is assumed that harsh environmental conditions impose limitations on plant sexual reproduction in the Arctic, such that population survival and expansion is predominately a function of clonal recruitment. We present contrary evidence from microsatellite genetic data suggesting the prevalence of recruitment by seed. Further, we present a conceptual model describing modes of recruitment in relation to the abiotic environment. Climate change may be alleviating abiotic stress so that resources are available for more frequent recruitment by seed. Such changes have widespread implications for ecosystem structure and functioning, including species composition, wildlife habitat, biogeochemical cycling, and surface energy balance. © 2010 Regents of the University of Colorado.
Two-photon production of charged pion and kaon pairs
Date: 1994-01-01
Creator: J. Dominick, M. Lambrecht, S. Sanghera, V. Shelkov, T., Skwarnicki, R. Stroynowski, I. Volobouev, G. Wei, P. Zadorozhny, M. Artuso, M. Goldberg, D. He, N. Horwitz, R. Kennett, R. Mountain, G. C. Moneti, F. Muheim, Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, K. Kinoshita, K. W. Edwards, M. Ogg
Access: Open access
- A measurement of the cross section for the combined two-photon production of charged pion and kaon pairs is performed using 1.2 fb-1 of data collected by the CLEO II detector at the Cornell Electron Storage Ring. The cross section is measured at invariant masses of the two-photon system between 1.5 and 5.0 GeV/c2, and at scattering angles more than 53° away from the γγ collision axis in the γγ center-of-mass frame. The large background of leptonic events is suppressed by utilizing the CsI calorimeter in conjunction with the muon chamber system. The reported cross section is compared with leading order QCD models as well as previous experiments. Although the functional dependence of the measured cross section disagrees with leading order QCD at small values of the two-photon invaraint mass, the data show qualitatively a transition to perturbative behavior at an invariant mass of approximately 2.5 GeV/c2. © 1994 The American Physical Society.
Production and decay of D1 (2420)0 and D2* (2460)0
Date: 1994-06-30
Creator: P. Avery, A. Freyberger, J. Rodriguez, R. Stephens, S., Yang, J. Yelton, D. Cinabro, S. Henderson, T. Liu, M. Saulnier, R. Wilson, H. Yamamoto, T. Bergfeld, B. I. Eisenstein, G. Gollin, B. Ong, M. Palmer, M. Selen, J. J. Thaler, K. W. Edwards, M. Ogg, B. Spaan, A. Bellerive, D. I. Britton, E. R.F. Hyatt, D. B. MacFarlane, P. M. Patel, A. J. Sadoff, R. Ammar, S. Ball, P. Baringer
Access: Open access
- We have investigated D+ π- and D*+ π- final states and observed the two established L = 1 charmed mesons, the D1 (2420)0 with mass 2421-2-2+1+2 MeV/c2 and width 20-5-3+6+3 MeV/c2 and the D2* (2460)0 with mass 2465 ± 3 ± 3 MeV/c2 and width 28-7-6+8+6 MeV/c2. Properties of these final states, including their decay angular distributions and spin-parity assignments, have been studied. We identify these two mesons as the jlight = 3 2 doublet predicted by HQET. We also obtain constraints on Γs/ (Γs + ΓD) as a function of the cosine of the relative phase of the two amplitudes in the D1 (2420)0 decay. © 1994.
Measurement of the branching fraction scrB(τ-→h- →π0ντ)
Date: 1994-01-01
Creator: M. Artuso, M. Goldberg, D. He, N. Horwitz, R., Kennett, R. Mountain, G. C. Moneti, F. Muheim, Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, X. Xing, G. Zhu, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, K. Kinoshita, B. Barish, M. Chadha, S. Chan, D. F. Cowen, G. Eigen, J. S. Miller, C. O'Grady, J. Urheim, A. J. Weinstein, D. Acosta
Access: Open access
- Using data from the CLEO II detector at the Cornell Electron Storage Ring, we measure scrB(τ-→h-π0ντ) where h- refers to either π- or K-. We use three different methods to measure this branching fraction. The combined result is scrB(τ-→h-π0ντ)=0.2587±0. 0012±0.0042, in good agreement with standard model predictions. © 1994 The American Physical Society.
“Magali García Ramis: La historia que uno se inventa”. A Body of One’s Own: Conversations with Caribbean Women Writers
Date: 2007-01-01
Creator: Nadia V. Celis Salgado, Magali García Ramis
Access: Open access
Targeted identification of glycosylated proteins in the gastric pathogen helicobacter pylori (Hp)
Date: 2013-09-01
Creator: Kanokwan Champasa, Scott A. Longwell, Aimee M. Eldridge, Elizabeth A. Stemmler, Danielle H., Dube
Access: Open access
- Virulence of the gastric pathogen Helicobacter pylori (Hp) is directly linked to the pathogen's ability to glycosylate proteins; for example, Hp flagellin proteins are heavily glycosylated with the unusual nine-carbon sugar pseudaminic acid, and this modification is absolutely essential for Hp to synthesize functional flagella and colonize the host's stomach. Although Hp's glycans are linked to pathogenesis, Hp's glycome remains poorly understood; only the two flagellin glycoproteins have been firmly characterized in Hp. Evidence from our laboratory suggests that Hp synthesizes a large number of as-yet unidentified glycoproteins. Here we set out to discover Hp's glycoproteins by coupling glycan metabolic labeling with mass spectrometry analysis. An assessment of the subcellular distribution of azide-labeled proteins by Western blot analysis indicated that glycoproteins are present throughout Hp and may therefore serve diverse functions. To identify these species, Hp's azide-labeled glycoproteins were tagged via Staudinger ligation, enriched by tandem affinity chromatography, and analyzed by multidimensional protein identification technology. Direct comparison of enriched azide-labeled glycoproteins with a mock-enriched control by both SDS-PAGE and mass spectrometry-based analyses confirmed the selective enrichment of azide-labeled glycoproteins. We identified 125 candidate glycoproteins with diverse biological functions, including those linked with pathogenesis. Mass spectrometry analyses of enriched azide-labeled glycoproteins before and after cleavage of O-linked glycans revealed the presence of Staudinger ligation-glycan adducts in samples only after beta-elimination, confirming the synthesis of O-linked glycoproteins in Hp. Finally, the secreted colonization factors urease alpha and urease beta were biochemically validated as glycosylated proteins via Western blot analysis as well as by mass spectrometry analysis of cleaved glycan products. These data set the stage for the development of glycosylation-based therapeutic strategies, such as new vaccines based on natively glycosylated Hp proteins, to eradicate Hp infection. Broadly, this report validates metabolic labeling as an effective and efficient approach for the identification of bacterial glycoproteins. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.
Monteverde: Ecology and Conservation of a Tropical Cloud Forest
Date: 2000-01-01
Creator: Nalini M. Nadkarni, Nathaniel T. Wheelwright
Access: Open access
- The Monteverde Cloud Forest Reserve has captured the worldwide attention of biologists, conservationists, and ecologists and has been the setting for extensive investigation over the past 40 years. Roughly 40,000 ecotourists visit the Cloud Forest each year, and it is often considered the archetypal high-altitude rain forest. Featuring synthetic chapters and specific accounts written by more than 100 biologists and local residents, the 573-page book documents in a single volume everything known about the biological diversity of Monteverde, Costa Rica, and how to protect it. New short chapters which update and expand the research presented in the 2000 Oxford publication were written in 2014 and are now available.