Showing 451 - 460 of 2039 Items
The N = 2 U(N) gauge theory prepotential and periods from a perturbative matrix model calculation
Date: 2003-02-24
Creator: Stephen G. Naculich
Howard J. Schnitzer
Niclas Wyllard
Access: Open access
- We perform a completely perturbative matrix model calculation of the physical low-energy quantities of the N = 2 U(N) gauge theory. Within the matrix model framework we propose a perturbative definition of the periods a i in terms of certain tadpole diagrams, and check our conjecture up to first order in the gauge theory instanton expansion. The prescription does not require knowledge of the Seiberg-0Witten differential or curve.We also compute the N = 2 prepotential F(a) perturbatively up to the first-instanton level, finding agreement with the known result. 2002 Elsevier Science B.V. All rights reserved.
Vacuum states of N =1* mass deformations of N =4 and N =2 conformal gauge theories and their brane interpretations
Date: 2001-08-27
Creator: Stephen G. Naculich
Howard J. Schnitzer
Niclas Wyllard
Access: Open access
- We find the classical supersymmetric vacuum states of a class of N =1* field theories obtained by mass deforming superconformal models with simple gauge groups and N =4 or N =2 supersymmetry. In particular, new classical vacuum states for mass-deformed N =4 models with Sp(2N) and SO(N) gauge symmetry are found. We also derive the classical vacua for various mass-deformed N =2 models with Sp(2N) and SU(N) gauge groups and antisymmetric (and symmetric) hypermultiplets. We suggest interpretations of the mass-deformed vacua in terms of three-branes expanded into five-brane configurations. © 2001 Elsevier Science B.V.
Probing quantum Hall state homogeneity with surface waves
Date: 2013-01-01
Creator: M. E. Msall
W. Dietsche
S. Schmult
K. Von Klitzing
Access: Open access
- We study single quantum wells and matched density bilayer samples. Simultaneous measurements of the Hall voltages using low frequency lock-in techniques and of the changes in the 232 MHz (12.6 μm) SAW propagation measured with a vector network-analyzer allow comparison of the complex bulk and edge conductivities. The vtotal 1 bilayer state is seen directly in the SAW measurement only when the conductivity is below ∼ 6 × 10 -7 Siemens and is destroyed at moderate SAW powers by localized heating. The simultaneous reduction of the conductivity minima extracted from Hall data and from SAW data conclusively demonstrates that the vtotal 1 state disappears simultaneously throughout the bulk and not by the formation of competing domains or conducting filaments. © Published under licence by IOP Publishing Ltd.
Arginine methylation of yeast mRNA-binding protein Npl3 directly affects its function, nuclear export, and intranuclear protein interactions
Date: 2005-09-02
Creator: Anne E. McBride
Jeffrey T. Cook
Elizabeth A. Stemmler
Kate L. Rutledge
Kelly A., McGrath
Jeffrey A. Rubens
Access: Open access
- Arginine methylation can affect both nucleocytoplasmic transport and protein-protein interactions of RNA-binding proteins. These effects are seen in cells that lack the yeast hnRNP methyltransferase (HMT1), raising the question of whether effects on specific proteins are direct or indirect. The presence of multiple arginines in individual methylated proteins also raises the question of whether overall methylation or methylation of a subset of arginines affects protein function. We have used the yeast mRNA-binding protein Npl3 to address these questions in vivo. Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry was used to identify 17 methylated arginines in Npl3 purified from yeast: whereas 10 Arg-Gly-Gly (RGG) tripeptides were exclusively dimethylated, variable levels off methylation were found for 5 RGG and 2 RG motif arginines. We constructed a set of Npl3 proteins in which subsets of the RGG arginines were mutated to lysine. Expression of these mutant proteins as the sole form of Npl3 specifically affected growth of a strain that requires Hmtl. Although decreased growth generally correlated with increased numbers of Arg-to-Lys mutations, lysine substitutions in the N terminus of the RGG domain showed more severe effects. Npl3 with all 15 RGG arginines mutated to lysine exited the nucleus independent of Hmtl, indicating a direct effect of methylation on Npl3 transport. These mutations also resulted in a decreased, methylation-independent interaction of Npl3 with transcription elongation factor Tho2 and inhibited Npl3 self-association. These results support a model in which arginine methylation facilitates Npl3 export directly by weakening contacts with nuclear proteins. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.
From local to global behavior in competitive Lotka-Volterra systems
Date: 2003-01-01
Creator: E. C. Zeeman
M. L. Zeeman
Access: Open access
- In this paper we exploit the linear, quadratic, monotone and geometric structures of competitive Lotka-Volterra systems of arbitrary dimension to give geometric, algebraic and computational hypotheses for ruling out nontrivial recurrence. We thus deduce the global dynamics of a system from its local dynamics. The geometric hypotheses rely on the introduction of a split Liapunov function. We show that if a system has a fixed point p ∈ int R+n and the carrying simplex of the system lies to one side of its tangent hyperplane at p, then there is no nontrivial recurrence, and the global dynamics are known. We translate the geometric hypotheses into algebraic hypotheses in terms of the definiteness of a certain quadratic function on the tangent hyperplane. Finally, we derive a computational algorithm for checking the algebraic hypotheses, and we compare this algorithm with the classical Volterra-Liapunov stability theorem for Lotka-Volterra systems.
Can the electroweak symmetry-breaking sector be hidden?
Date: 1992-10-29
Creator: S. G. Naculich
C. P. Yuan
Access: Open access
- In a recent paper, Chivukula and Golden claimed that the electroweak symmetry-breaking sector could be hidden if there were many inelastic channels in the longitudinal WW scattering process. They presented a model in which the W's couple to pseudo-Goldstone bosons, which may be difficult to detect experimentally. Because of these inelastic channels, thw WW interactions do not become strong in the TeV region. We demonstrate that, despite the reduced WW elastic amplitudes in this model, the total event rate (∼ 5000 extra longitudinal W+W- pairs produced in one standard SSC year) does not decrease with an increasing number of inelastic channels, and is roughly the same as in a model with a broad high-energy resonance and no inelastic channels. © 1992.
Carbon cycle studies based on the distribution of O2 in air
Date: 1999-01-01
Creator: Michael L. Bender
Mark O. Battle
Access: Open access
Statement by Allen Sockabasin collected by Rachel George on January 20, 2015
Date: 2015-01-20
Creator: Allen Sockabasin
Access: Open access
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.