Showing 1961 - 1970 of 4695 Items
Approximate initial data for binary black holes
Date: 2006-09-21
Creator: Kenneth A. Dennison
Thomas W. Baumgarte
Harald P. Pfeiffer
Access: Open access
- We construct approximate analytical solutions to the constraint equations of general relativity for binary black holes of arbitrary mass ratio in quasicircular orbit. We adopt the puncture method to solve the constraint equations in the transverse-traceless decomposition and consider perturbations of Schwarzschild black holes caused by boosts and the presence of a binary companion. A superposition of these two perturbations then yields approximate, but fully analytic binary black hole initial data that are accurate to first order in the inverse of the binary separation and the square of the black holes' momenta. © 2006 The American Physical Society.
Animal-to-animal variability in the phasing of the crustacean cardiac motor pattern: An experimental and computational analysis
Date: 2013-01-01
Creator: Alex H. Williams
Molly A. Kwiatkowski
Adam L. Mortimer
Eve Marder
Mary Lou, Zeeman
Patsy S. Dickinson
Access: Open access
- The cardiac ganglion (CG) of Homarus americanus is a central pattern generator that consists of two oscillatory groups of neurons: "small cells" (SCs) and "large cells" (LCs). We have shown that SCs and LCs begin their bursts nearly simultaneously but end their bursts at variable phases. This variability contrasts with many other central pattern generator systems in which phase is well maintained. To determine both the consequences of this variability and how CG phasing is controlled, we modeled the CG as a pair of Morris-Lecar oscillators coupled by electrical and excitatory synapses and constructed a database of 15,000 simulated networks using random parameter sets. These simulations, like our experimental results, displayed variable phase relationships, with the bursts beginning together but ending at variable phases. The model suggests that the variable phasing of the pattern has important implications for the functional role of the excitatory synapses. In networks in which the two oscillators had similar duty cycles, the excitatory coupling functioned to increase cycle frequency. In networks with disparate duty cycles, it functioned to decrease network frequency. Overall, we suggest that the phasing of the CG may vary without compromising appropriate motor output and that this variability may critically determine how the network behaves in response to manipulations. © 2013 the American Physiological Society.
Quantum kinks: Solitons at strong coupling
Date: 1992-01-01
Creator: Stephen G. Naculich
Access: Open access
- We examine solitons in theories with heavy fermions. These "quantum" solitons differ dramatically from semiclassical (perturbative) solitons because fermion loop effects are important when the Yukawa coupling is strong. We focus on kinks in a (1 + 1)-dimensional 4 theory coupled to fermions; a large-N expansion is employed to treat the Yukawa coupling g nonperturbatively. A local expression for the fermion vacuum energy is derived using the WKB approximation for the Dirac eigenvalues. We find that fermion loop corrections increase the energy of the kink and (for large g) decrease its size. For large g, the energy of the quantum kink is proportional to g, and its size scales as 1g, unlike the classical kink; we argue that these features are generic to quantum solitons in theories with strong Yukawa couplings. We also discuss the possible instability of fermions to solitons. © 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.
Phononic rogue waves
Date: 2018-09-13
Creator: E. G. Charalampidis
J. Lee
P. G. Kevrekidis
C. Chong
Access: Open access
- We present a theoretical study of extreme events occurring in phononic lattices. In particular, we focus on the formation of rogue or freak waves, which are characterized by their localization in both spatial and temporal domains. We consider two examples. The first one is the prototypical nonlinear mass-spring system in the form of a homogeneous Fermi-Pasta-Ulam-Tsingou (FPUT) lattice with a polynomial potential. By deriving an approximation based on the nonlinear Schrödinger (NLS) equation, we are able to initialize the FPUT model using a suitably transformed Peregrine soliton solution of the NLS equation, obtaining dynamics that resembles a rogue wave on the FPUT lattice. We also show that Gaussian initial data can lead to dynamics featuring a rogue wave for sufficiently wide Gaussians. The second example is a diatomic granular crystal exhibiting rogue-wave-like dynamics, which we also obtain through an NLS reduction and numerical simulations. The granular crystal (a chain of particles that interact elastically) is a widely studied system that lends itself to experimental studies. This study serves to illustrate the potential of such dynamical lattices towards the experimental observation of acoustic rogue waves.
A genomewide survey argues that every zygotic gene product is dispensable for the initiation of somatic homolog pairing in Drosophila
Date: 2008-11-01
Creator: Jack R. Bateman
C. Ting Wu
Access: Open access
- Studies from diverse organisms show that distinct interchromosomal interactions are associated with many developmental events. Despite recent advances in uncovering such phenomena, our understanding of how interchromosomal interactions are initiated and regulated is incomplete. During the maternal-to-zygotic transition (MZT) of Drosophila embryogenesis, stable interchromosomal contacts form between maternal and paternal homologous chromosomes, a phenomenon known as somatic homolog pairing. To better understand the events that initiate pairing, we performed a genomewide assessment of the zygotic contribution to this process. Specifically, we took advantage of the segregational properties of compound chromosomes to generate embryos lacking entire chromosome arms and, thus, all zygotic gene products derived from those arms. Using DNA fluorescence in situ hybridization (FISH) to assess the initiation of pairing at five separate loci, this approach allowed us to survey the entire zygotic genome using just a handful of crosses. Remarkably, we found no defect in pairing in embryos lacking any chromosome arm, indicating that no zygotic gene product is essential for pairing to initiate. From these data, we conclude that the initiation of pairing can occur independently of zygotic control and may therefore be part of the developmental program encoded by the maternal genome. Copyright © 2008 by the Genetics Society of America.
Site-specific transformation of Drosophila via φC31 integrase-mediated cassette exchange
Date: 2006-06-30
Creator: Jack R. Bateman
Anne M. Lee
C. Ting Wu
Access: Open access
- Position effects can complicate transgene analyses. This is especially true when comparing transgenes that have inserted randomly into different genomic positions and are therefore subject to varying position effects. Here, we introduce a method for the precise targeting of transgenic constructs to predetermined genomic sites in Drosophila using the φC31 integrase system in conjunction with recombinase-mediated cassette exchange (RMCE). We demonstrate the feasibility of this system using two donor cassettes, one carrying the yellow gene and the other carrying GFP. At all four genomic sites tested, we observed exchange of donor cassettes with an integrated target cassette carrying the mini-white gene. Furthermore, because RMCE-mediated integration of the donor cassette is necessarily accompanied by loss of the target cassette, we were able to identify integrants simply by the loss of mini-white eye color. Importantly, this feature of the technology will permit integration of unmarked constructs into Drosophila, even those lacking functional genes. Thus, φC31 integrase-mediated RMCE should greatly facilitate transgene analysis as well as permit new experimental designs. Copyright © 2006 by the Genetics Society of America.
Υ(1S)→γ+noninteracting particles
Date: 1995-01-01
Creator: R. Balest
K. Cho
T. Ford
D. R. Johnson
K., Lingel
M. Lohner
P. Rankin
J. G. Smith
J. P. Alexander
C. Bebek
K. Berkelman
K. Bloom
T. E. Browder
D. G. Cassel
H. A. Cho
D. M. Coffman
D. S. Crowcroft
P. S. Drell
D. Dumas
R. Ehrlich
P. Gaidarev
R. S. Galik
M. Garcia-Sciveres
B. Geiser
B. Gittelman
S. W. Gray
D. L. Hartill
B. K. Heltsley
S. Henderson
C. D. Jones
S. L. Jones
Access: Open access
- We consider the decay of Υ(1S) particles produced at CESR into a photon which is observed by the CLEO detector plus particles which are not seen. These could be real particles which fall outside of our acceptance, or particles which are noninteracting. We report the results of our search fo the process Υ(1S)→γ+''unseen'' for photon energies >1 GeV, obtaining limits for the case where ''unseen'' is either a single particle or a particle-antiparticle pair. Our upper limits represent the highest sensitivity measurements for such decays to date. © 1995 The American Physical Society.
The role of adjuvant in mediating antigen structure and stability
Date: 2012-01-01
Creator: Latoya Jones Braun
Aimee M. Eldridge
Jessica Cummiskey
Kelly K. Arthur
Deborah S., Wuttke
Access: Open access
- The purpose of this study was to probe the fate of a model antigen, a cysteine-free mutant of bacteriophage T4 lysozyme, to the level of fine structural detail, as a consequence of its interaction with an aluminum (Al)-containing adjuvant. Fluorescence spectroscopy and differential scanning calorimetry were used to compare the thermal stability of the protein in solution versus adsorbed onto an Al-containing adjuvant. Differences in accessible hydrophobic surface areas were investigated using an extrinsic fluorescence probe, 8-Anilino-1-naphthalenesulfonic acid (ANS). As has been observed with other model antigens, the apparent thermal stability of the protein decreased following adsorption onto the adjuvant. ANS spectra suggested that adsorption onto the adjuvant caused an increase in exposure of hydrophobic regions of the protein. Electrostatic interactions drove the adsorption, and disruption of these interactions with high ionic strength buffers facilitated the collection of two-dimensional 15N heteronuclear single quantum coherence nuclear magnetic resonance data of protein released from the adjuvant. Although the altered stability of the adsorbed protein suggested changes to the protein's structure, the fine structure of the desorbed protein was nearly identical to the protein's structure in the adjuvant-free formulation. Thus, the adjuvant-induced changes to the protein that were responsible for the reduced thermal stability were not observed upon desorption. © 2011 Wiley Periodicals, Inc.
Measurement of the branching fraction for γ (1S) → τ+τ-
Date: 1994-12-01
Creator: D. Cinabro
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
A. Bellerive
D. I. Britton
E. R.F. Hyatt
D. B. MacFarlane
P. M. Patel
B. Spaan
A. J. Sadoff
R. Ammar
P. Baringer
A. Bean
D. Besson
D. Coppage
N. Copty
R. Davis
N. Hancock
M. Kelly
S. Kotov
Access: Open access
- We have studied the leptonic decay of the γ (1S) resonance into tau pairs using the CLEO II detector. A clean sample of tau pair events is identified via events containing two charged particles where exactly one of the particles is an identified electron. We find B(γ(1S) → τ+τ-) = (2.61±0.12-0.13+0.09)%. The result is consistent with expectations from lepton universality. © 1994.