Showing 111 - 120 of 5709 Items
Sign changes of Fourier coefficients of Hilbert modular forms
Date: 2014-01-01
Creator: Jaban Meher, Naomi Tanabe
Access: Open access
- Sign changes of Fourier coefficients of various modular forms have been studied. In this paper, we analyze some sign change properties of Fourier coefficients of Hilbert modular forms, under the assumption that all the coefficients are real. The quantitative results on the number of sign changes in short intervals are also discussed. © 2014 Elsevier Inc.
Simple-current symmetries, rank-level duality, and linear skein relations for Chern-Simons graphs
Date: 1993-04-12
Creator: Stephen G. Naculich, Harold A. Riggs, Howard J. Schnitzer
Access: Open access
- A previously proposed two-step algorithm for calculating the expectation values of arbitrary Chern-Simons graphs fails to determine certain crucial signs. The step which involves calculating tetrahedra by solving certain non-linear equations is repaired by introducing additional linear equations. The step which involves reducing arbitrary graphs to sums of products of tetrahedra remains seriously disabled, apart from a few exceptional cases. As a first step towards a new algorithm for general graphs we find useful linear equations for those special graphs which support knots and links. Using the improved set of equations for tetrahedra we examine the symmetries between tetrahedra generated by arbitrary simple currents. Along the way we describe the simple, classical origin of simple-current charges. The improved skein relations also lead to exact identities between planar tetrahedra in level K G(N) and level N G(K) Chern-Simons theories, where G(N) denotes a classical group. These results are recast as WZW braid-matrix identities and as identities between quantum 6-jsymbols at appropriate roots of unity. We also obtain the transformation properties of arbitrary graphs, knots, and links under simple-current symmetries and rank-level duality. For links with knotted components this requires precise control of the braid eigenvalue permutation signs, which we obtain from plethysm and an explicit expression for the (multiplicity-free) signs, valid for all compact gauge groups and all fusion products. © 1993.
A hydrophobic, carboxy-proximal region of a light-harvesting chlorophyll a/b protein is necessary for stable integration into thylakoid membranes.
Date: 1989-01-01
Creator: B. D. Kohorn, E. M. Tobin
Access: Open access
- Proteins synthesized as soluble precursors in the cytoplasm of eukaryotic cells often cross organellar membrane barriers and then insert into lipid bilayers. One such polypeptide, the light-harvesting chlorophyll a/b-binding protein (LHCP), must also associate with pigment molecules and be assembled into the photosystem II light-harvesting complex in the chloroplast thylakoid membrane. A study of the import of mutant LHCPs into isolated chloroplasts has shown that a putative alpha-helical membrane-spanning domain near the carboxy terminus (helix 3) is essential for the stable insertion of LHCP in the thylakoid. Protease digestion experiments are consistent with the carboxy terminus of the protein being in the lumen. This report also shows that helix 3, when fused to a soluble protein, can target it to the thylakoids of isolated, intact chloroplasts. Although helix 3 is required for the insertion of LHCP and mutant derivatives into the thylakoid, the full insertion of helix 3 itself requires additionally the presence of other regions of LHCP. Thus, LHCP targeting and integration into thylakoid membranes requires a complex interaction involving a number of different domains of the LHCP polypeptide.
A genome-wide screen identifies genes that affect somatic homolog pairing in drosophila
Date: 2012-07-01
Creator: Jack R. Bateman, Erica Larschan, Ryan D'Souza, Lauren S. Marshall, Kyle E., Dempsey, Justine E. Johnson, Barbara G. Mellone, Mitzi I. Kuroda
Access: Open access
- In Drosophila and other Dipterans, homologous chromosomes are in close contact in virtually all nuclei, a phenomenon known as somatic homolog pairing. Although homolog pairing has been recognized for over a century, relatively little is known about its regulation. We performed a genome-wide RNAibased screen that monitored the X-specific localization of the male-specific lethal (MSL) complex, and we identified 59 candidate genes whose knockdown via RNAi causes a change in the pattern of MSL staining that is consistent with a disruption of X-chromosomal homolog pairing. Using DNA fluorescent in situ hybridization (FISH), we confirmed that knockdown of 17 of these genes has a dramatic effect on pairing of the 359 bp repeat at the base of the X. Furthermore, dsRNAs targeting Pr-set7, which encodes an H4K20 methyltransferase, cause a modest disruption in somatic homolog pairing. Consistent with our results in cultured cells, a classical mutation in one of the strongest candidate genes, pebble (pbl), causes a decrease in somatic homolog pairing in developing embryos. Interestingly, many of the genes identified by our screen have known roles in diverse cell-cycle events, suggesting an important link between somatic homolog pairing and the choreography of chromosomes during the cell cycle. © 2012 Bowers et al.
Inelastic channels in WW scattering
Date: 1993-01-01
Creator: S. G. Naculich, C. P. Yuan
Access: Open access
- If the electroweak symmetry-breaking sector becomes strongly interacting at high energies, it can be probed through longitudinal W scattering. We present a model with many inelastic channels in the WLWL scattering process, corresponding to the production of heavy fermion pairs. These heavy fermions affect the elastic scattering of WL's by propagating in loops, greatly reducing the amplitudes in some charge channels. We conclude that the symmetry-breaking sector cannot be fully explored by using, for example, the WL±WL± mode alone, even when no resonance is present; all WLWL→WLWL scattering modes must be measured. © 1993 The American Physical Society.
Nonlinear excitations in magnetic lattices with long-range interactions
Date: 2019-06-24
Creator: Miguel Molerón, C. Chong, Alejandro J. Martínez, Mason A. Porter, P. G., Kevrekidis, Chiara Daraio
Access: Open access
- We study - experimentally, theoretically, and numerically - nonlinear excitations in lattices of magnets with long-range interactions. We examine breather solutions, which are spatially localized and periodic in time, in a chain with algebraically-decaying interactions. It was established two decades ago (Flach 1998 Phys. Rev. E 58 R4116) that lattices with long-range interactions can have breather solutions in which the spatial decay of the tails has a crossover from exponential to algebraic decay. In this article, we revisit this problem in the setting of a chain of repelling magnets with a mass defect and verify, both numerically and experimentally, the existence of breathers with such a crossover.
Dendrites of Cardiac Ganglion Regulate Heartbeat of American Lobster, Homarus americanus, Through Stretch Feedback
Date: 2014-05-01
Creator: Mara R Chin-Purcell
Access: Open access
- Central pattern generators are neuronal networks that produce reliable rhythmic motor output. A simple pattern generator, known as the cardiac ganglion (CG), controls the heart of the American lobster, Homarus americanus. Previous studies have suggested that stretch feedback relays information to the cardiac ganglion about the degree of filling in the heart, and that this feedback is mediated by stretch-sensitive dendrites extending from CG neurons. I sought to determine the mechanisms behind this stretch feedback pathway. One hundred second extension pyramids were applied to each heart while amplitude and frequency of contractions were recorded; 87% of hearts responded to stretch with a significant increase in frequency of contractions. To ascertain the role of dendrites in this feedback pathway, the accessible branches along the trunk of the CG were severed, de-afferenting the CG. In de-afferented hearts, stretch sensitivity was significantly less than in intact hearts, suggesting that the dendrites extending from the CG are essential for carrying stretch feedback information. To separate the effects of active and passive forces of heart contraction on stretch sensitivity, the CG was de-efferented by severing the motor nerves that induce muscle contraction. Hearts with only anterolateral nerves cut or with all four efferents cut were significantly less stretch sensitive than controls. These results indicate that the CG is sensitive to active stretch of each contraction. Hearts with reduced stretch feedback had more irregular frequency of contractions, indicating that a role of stretch feedback in the cardiac system may be to maintain a regular heart rate.
Thompson's group F is not almost convex
Date: 2003-12-01
Creator: Sean Cleary, Jennifer Taback
Access: Open access
- We show that Thompson's group F does not satisfy Cannon's almost convexity condition AC(n) for any positive integer n with respect to the standard generating set with two elements. To accomplish this, we construct a family of pairs of elements at distance n from the identity and distance 2 from each other, which are not connected by a path lying inside the n-ball of length less than k for increasingly large k. Our techniques rely upon Fordham's method for calculating the length of a word in F and upon an analysis of the generators' geometric actions on the tree pair diagrams representing elements of F. © 2003 Elsevier Inc. All rights reserved.