Showing 1511 - 1520 of 2545 Items
Study of the decay Λc+→λl+νl
Date: 1994-03-10
Creator: T. Bergfeld
B. I. Eisenstein
G. Gollin
B. Ong
M., Palmer
M. Selen
J. J. Thaler
A. J. Sadoff
R. Ammar
S. Ball
P. Baringer
A. Bean
D. Besson
D. Coppage
N. Copty
R. Davis
N. Hancock
M. Kelly
N. Kwak
H. Lam
Y. Kubota
M. Lattery
J. K. Nelson
D. Patton
D. Perticone
R. Poling
V. Savinov
S. Schrenk
R. Wang
M. S. Alam
I. J. Kim
Access: Open access
- Using the CLEO II detector at CESR we observe 500 Λl+ pairs consistent with the semileptonic decay Λc+ → λ+ν We measure σ(e+e- → Λ+cX) · B(Λ+c → Λl+νl) = 4.77±0.25±0.66 pb. Combining with the charm semileptonic width and the lifetime of the Λc we also obtain B(Λ+c → pK-π+). We find no evidence for Λl+νl final states in which there are additional Λ+c decay products. We measure the decay asymmetry parameter of Λ+c → Λe+νe to be αΛc = -0.89+0.17+0.09-0.11-0.05. © 1994.
Matrix-model description of N = 2 gauge theories with non-hyperelliptic Seiberg-Witten curves
Date: 2003-12-08
Creator: Stephen G. Naculich
Howard J. Schnitzer
Niclas Wyllard
Access: Open access
- Using matrix-model methods we study three different N=2 models: U(N)×U(N) with matter in the bifundamental representation, U(N) with matter in the symmetric representation, and U(N) with matter in the antisymmetric representation. We find that the (singular) cubic Seiberg-Witten curves (and associated Seiberg-Witten differentials) implied by the matrix models, although of a different form from the ones previously proposed using M-theory, can be transformed into the latter and are thus physically equivalent. We also calculate the one-instanton corrections to the gauge-coupling matrix using the perturbative expansion of the matrix model. For the U(N) theories with symmetric or antisymmetric matter we use the modified matrix-model prescription for the gauge-coupling matrix discussed in our paper: Cubic curves from matrix models and generalized Konishi anomalies (hep-th/0303268). Moreover, in the matrix model for the U(N) theory with antisymmetric matter, one is required to expand around a different vacuum than one would naively have anticipated. With these modifications of the matrix-model prescription, the results of this paper are in complete agreement with those of Seiberg-Witten theory obtained using M-theory methods. © 2003 Elsevier B.V. All rights reserved.
Tame combing and almost convexity conditions
Date: 2011-12-01
Creator: Sean Cleary
Susan Hermiller
Melanie Stein
Jennifer Taback
Access: Open access
- We give the first examples of groups which admit a tame combing with linear radial tameness function with respect to any choice of finite presentation, but which are not minimally almost convex on a standard generating set. Namely, we explicitly construct such combings for Thompson's group F and the Baumslag-Solitar groups BS(1, p) with p ≥ 3. In order to make this construction for Thompson's group F, we significantly expand the understanding of the Cayley complex of this group with respect to the standard finite presentation. In particular we describe a quasigeodesic set of normal forms and combinatorially classify the arrangements of 2-cells adjacent to edges that do not lie on normal form paths. © 2010 Springer-Verlag.
An improved comparison of atmospheric Ar/N2 time series and paired ocean-atmosphere model predictions
Date: 2008-11-16
Creator: Nicolas Cassar
Galen A. McKinley
Michael L. Bender
Robert Mika
Mark, Battle
Access: Open access
- Ar/N2 variations in the atmosphere reflect ocean heat fluxes, air-sea gas exchange, and atmospheric dynamics. Here atmospheric Ar/N2 time series are compared to paired ocean-atmosphere model predictions. Agreement between Ar/N2 observations and simulations has improved in comparison to a previous study because of longer time series and the introduction of automated samplers at several of the atmospheric stations, as well as the refinement of the paired ocean-atmosphere models by inclusion of Ar and N2 as active tracers in the ocean component. Although analytical uncertainties and collection artifacts are likely to be mainly responsible for observed Ar/N2 outliers, air parcel back-trajectory analysis suggests that some of the variability in Ar/N2 measurements could be due to the low-altitude history of the air mass collected and, by extension, the local oceanic Ar/N2 signal. Although the simulated climatological seasonal cycle can currently be evaluated with Ar/N2 observations, longer time series and additional improvements in the signal-to-noise ratio will be required to test other model predictions such as interannual variability, latitudinal gradients, and the secular increase in atmospheric Ar/N2 expected to result from ocean warming. Copyright 2008 by the American Geophysical Union.
A cascading N = 1 Sp(2N + 2M) × Sp(2N) gauge theory
Date: 2002-08-26
Creator: Stephen G. Naculich
Howard J. Schnitzer
Niclas Wyllard
Access: Open access
- We study the N=1 Sp(2N + 2M) × Sp(2N) cascading gauge theory on a stack of N physical and M fractional (half) D3-branes at the singularity of an orientifolded conifold. In addition to the D3-branes and an O7-plane, the background contains eight D7-branes, which give rise to matter in the fundamental representation of the gauge group. The moduli space of the gauge theory is analyzed and its structure is related to the brane configurations in the dual type IIB theory and in type IIA/M-theory. © 2002 Elsevier Science B.V. All rights reserved.
Mutations in a signal sequence for the thylakoid membrane identify multiple protein transport pathways and nuclear suppressors
Date: 1994-07-01
Creator: Tracy A. Smith
Bruce D. Kohorn
Access: Open access
- The apparatus that permits protein translocation across the internal thylakoid membranes of chloroplasts is completely unknown, even though these membranes have been the subject of extensive biochemical analysis. We have used a genetic approach to characterize the translocation of Chlamydomonas cytochrome f, a chloroplast-encoded protein that spans the thylakoid once. Mutations in the hydrophobic core of the cytochrome f signal sequence inhibit the accumulation of cytochrome f, lead to an accumulation of precursor, and impair the ability of Chlamydomonas cells to grow photosynthetically. One hydrophobic core mutant also reduces the accumulation of other thylakoid membrane proteins, but not those that translocate completely across the membrane. These results suggest that the signal sequence of cytochrome f is required and is involved in one of multiple insertion pathways. Suppressors of two signal peptide mutations describe at least two nuclear genes whose products likely describe the translocation apparatus, and selected second- site chloroplast suppressors further define regions of the cytochrome f signal peptide.
Direct selection for sequences encoding proteases of known specificity
Date: 1991-06-15
Creator: Tracy A. Smith
Bruce D. Kohorn
Access: Open access
- We have developed a simple genetic selection that could be used to isolate eukaryotic cDNAs encoding proteases that cleave within a defined amino acid sequence. The selection was developed by using the transcription factor GAL4 from Saccharomyces cerevisiae as a selectable marker, a cloned protease from tobacco etch virus (TEV), and an 18-amino acid TEV protease target sequence. In yeast, TEV protease cleaves its target even when the target is fused to internal regions of the GAL4 protein. This cleavage separates the DNA binding domain from the transcription activation domain of GAL4, rendering it transcriptionally inactive. The proteolytic cleavage can be detected phenotypically by the inability of cells to metabolize galactose. Cells expressing the TEV protease can also be selected on the suicide substrate 2-deoxygalactose. DNA binding studies show that the TEV protease decreases the activity of the GAL4/target fusion protein. Because another protease target sequence of 55 amino acids can be inserted into GAL4 without any loss of transcriptional activity, this assay offers the opportunity to use high-efficiency cDNA cloning and expression vectors to select coding sequences of other proteases from various species. The assay could also be used to help define both target specificities and functional domains of proteases.
Two antisymmetric hypermultiplets in N = 2 SU(N) gauge theory: Seiberg-Witten curve and M-theory interpretation
Date: 1999-10-04
Creator: Isabel P. Ennes
Stephen G. Naculich
Henric Rhedin
Howard J. Schnitzer
Access: Open access
- The one-instanton contribution to the prepotential for N = 2 supersymmetric gauge theories with classical groups exhibits a universality of form. We extrapolate the observed regularity to SU (N) gauge theory with two antisymmetric hypermultiplets and Nf ≤ 3 hypermultiplets in the defining representation. Using methods developed for the instanton expansion of non-hyperelliptic curves, we construct an effective quartic Seiberg-Witten curve that generates this one-instanton prepotential. We then interpret this curve in terms of an M-theoretic picture involving NS 5-branes, D4-branes, D6-branes, and orientifold sixplanes, and show that for consistency, an infinite chain of 5-branes and orientifold sixplanes is required, corresponding to a curve of infinite order. © 1999 Elsevier Science B.V. All rights reserved.
Comparing enhancer action in cis and in trans
Date: 2012-08-01
Creator: Jack R. Bateman
Justine E. Johnson
Melissa N. Locke
Access: Open access
- Studies from diverse systems have shown that distinct interchromosomal interactions are a central component of nuclear organization. In some cases, these interactions allow an enhancer to act in trans, modulating the expression of a gene encoded on a separate chromosome held in close proximity. Despite recent advances in uncovering such phenomena, our understanding of how a regulatory element acts on another chromosome remains incomplete. Here, we describe a transgenic approach to better understand enhancer action in trans in Drosophila melanogaster. Using phiC31-based recombinase-mediated cassette exchange (RMCE), we placed transgenes carrying combinations of the simple enhancer GMR, a minimal promoter, and different fluorescent reporters at equivalent positions on homologous chromosomes so that they would pair via the endogenous somatic pairing machinery of Drosophila. Our data demonstrate that the enhancer GMR is capable of activating a promoter in trans and does so in a variegated pattern, suggesting stochastic interactions between the enhancer and the promoter when they are carried on separate chromosomes. Furthermore, we quantitatively assessed the impact of two concurrent promoter targets in cis and in trans to GMR, demonstrating that each promoter is capable of competing for the enhancer's activity, with the presence of one negatively affecting expression from the other. Finally, the single-cell resolution afforded by our approach allowed us to show that promoters in cis and in trans to GMR can both be activated in the same nucleus, implying that a single enhancer can share its activity between multiple promoter targets carried on separate chromosomes. © 2012 by the Genetics Society of America.
One-instanton predictions of Seiberg-Witten curves for product groups
Date: 1999-01-01
Creator: Isabel P. Ennes
Stephen G. Naculich
Henric Rhedin
Howard J. Schnitzer
Access: Open access
- One-instanton predictions for the prepotential are obtained from the Seiberg-Witten curve for the Coulomb branch of script N sign = 2 supersymmetric gauge theory for the product group IIn=1m SU(Nn) with a massless matter hypermultiplet in the bifundamental representation (Nn,N̄n+1) of SU(Nn) × SU(Nn+1) for n = 1 to m - 1, together with N0 and Nm+1 matter hypermultiplets in the fundamental representations of SU(N1) and SU(Nm) respectively. The derivation uses a generalization of the systematic perturbation expansion about a hyperelliptic curve developed by us in earlier work. © 1999 Published by Elsevier Science B.V. All rights reserved.