Showing 51 - 60 of 733 Items
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.
Elliptic models, type IIB orientifolds, and the AdS/CFT correspondence
Date: 2000-12-18
Creator: Isabel P. Ennes, Carlos Lozano, Stephen G. Naculich, Howard J. Schnitzer
Access: Open access
- We analyze the large N supergravity descriptions of the class of type IIB models T-dual to elliptic type IIA brane configurations containing two orientifold 6-planes and up to two NS 5-branes. The T-dual IIB configurations contain N D3-branes in the background of an orientifold 7-plane and, in some models, a Z2 orbifold and/or D7-branes, which give rise to four-dimensional N=2 (or N=4) gauge theories with at most two factors. We identify the chiral primary states of the supergravity theories, and match them to gauge invariant operators of the corresponding superconformal theories using Maldacena's duality. © 2000 Elsevier Science B.V.
Religion and science in the Eastern mediterranean
Date: 2016-09-01
Creator: Robert Morrison
Access: Open access
- “Science and Orthodox Christianity: An Overview” is an ambitious survey that reminds scholars of science in Islamic societies that the conversation between Islam and science is really a conversation between Islam and science in different contexts and that conversations between Islam and science can be found with less renowned scientific developments such as prophetic medicine. This response points out parallels in how Greek Orthodox and Ottoman Muslim scholars mediated new developments in Western European science and in how both Greek Orthodox and some Ottoman Muslim scholars propounded a mathematical humanism. Finally, it argues that the account of post-1453 scientific exchange is more complex than “Science and Orthodox Christianity” intimates. At the least, if there was no scholarly exchange between Greek Orthodox Christians, on the one hand, and, on the other hand, Muslims and Jews—who, in turn, enjoyed scholarly exchange with the West well after 1453—there are clearly two different Easts.
With age comes immaturity: Do countries with older populations issue shorter maturity debt?
Date: 2021-12-01
Creator: Gonca Senel, Mark L.J. Wright
Access: Open access
- Recent work has found that countries with older populations face steeper yield curves and issue shorter maturity debt than do younger countries. We reexamine these findings using a new database of public debt maturity and yields for OECD countries. We first show that the behavior of eurozone countries in the pre-euro period drives these results. Next, including more recent data from the post-euro period, we show that the relationship between population age, maturity, and yield curve slopes disappears. This finding is robust to excluding high-credit-risk countries. Last, we show that these patterns reemerge after the European debt crisis, suggesting that eurozone capital markets have resegmented.
Homozygosity at the MTL locus in clinical strains of Candida albicans: Karyotypic rearrangments and tetraploid formation
Date: 2004-06-01
Creator: Melanie Legrand, Paul Lephart, Anja Forche, Frank Michael C. Mueller, T., Walsh, P. T. Magee, Beatrice B. Magee
Access: Open access
- One hundred and twenty Candida albicans clinical isolates from the late 1980s and early 1990s were examined for homosygosity at the MTL locus. Of these, 108 were heterozygous (MTLa/MTLα), whereas seven were MTLa and five were MTLα. Five of the homozygous isolates were able to switch to the opaque cell morphology, while opaque cells were not detectable among the remaining seven. Nevertheless, all but one of the isolates homozygous at the MTL locus were shown to mate and to yield cells containing markers from both parents; the non-mater was found to have a frameshift in the MTLα1 gene. In contrast to Saccharomyces cerevisiae, C. albicans homozygotes with no active MTL allele failed to mate rather than mating as a cells. There was no correlation between homoxygosity and fluconazole resistance, mating and fluconazole resistance or switching and fluconazole resistance, in part because most of the strains were isolated before the widespread use of this antifungal agent, and only three were in fact drug resistant Ten of the 12 homozygotes had rearranged karyotypes involving one or more homologue of chromosomes 4, 5, 6 and 7. We suggest that karyotypic rearrangement, drug resistance and homozygosity come about as the result of induction of hyperrecombination during the infection process; hence, they tend to occur together, but each is the independent result of the same event. Furthermore, as clinical strains can mate and form tetraploids, mating and marker exchange are likely to be a significant part of the life cycle of C. albicans in vivo.
Partisan selective engagement: Evidence from Facebook
Date: 2020-09-01
Creator: Marcel Garz, Jil Sörensen, Daniel F. Stone
Access: Open access
- This study investigates the effects of variation in “congeniality” of news on Facebook user engagement (likes, shares, and comments). We compile an original data set of Facebook posts by 84 German news outlets on politicians that were investigated for criminal offenses from January 2012 to June 2017. We also construct an index of each outlet's media slant by comparing the language of the outlet with that of the main political parties, which allows us to measure the congeniality of the posts. We find that user engagement with congenial posts is higher than with uncongenial ones, especially in terms of likes. The within-outlet, within-topic design allows us to infer that the greater engagement with congenial news is likely driven by psychological and social factors, rather than a desire for accurate or otherwise instrumental information.
Aneuploid chromosomes are highly unstable during DNA transformation of candida albicans∇
Date: 2009-10-01
Creator: Kelly Bouchonville, Anja Forche, Karen E.S. Tang, Anna Selmecki, Judith, Berman
Access: Open access
- Candida albicans strains tolerate aneuploidy, historically detected as karyotype alterations by pulsed-fleld gel electrophoresis and more recently revealed by array comparative genome hybridization, which provides a comprehensive and detailed description of gene copy number. Here, we first retrospectively analyzed 411 expression array experiments to predict the frequency of aneuploidy in different strains. As expected, significant levels of aneuploidy were seen in strains exposed to stress conditions, including UV light and/or sorbose treatment, as well as in strains that are resistant to antifungal drugs. More surprisingly, strains that underwent transformation with DNA displayed the highest frequency of chromosome copy number changes, with strains that were initially aneuploid exhibiting ∼3-fold more copy number changes than strains that were initially diploid. We then prospectively analyzed the effect of lithium acetate (LiOAc) transformation protocols on the stability of trisomie chromosomes. Consistent with the retrospective analysis, the proportion of karyotype changes was highly elevated in strains carrying aneuploid chromosomes. We then tested the hypothesis that stresses conferred by heat and/or LiOAc exposure promote chromosome number changes during DNA transformation procedures. Indeed, a short pulse of very high temperature caused frequent gains and losses of multiple chromosomes or chromosome segments. Furthermore, milder heat exposure over longer periods caused increased levels of loss of heterozygosity. Nonetheless, aneuploid chromosomes were also unstable when strains were transformed by electroporation, which does not include a heat shock step. Thus, aneuploid strains are particularly prone to undergo changes in chromosome number during the stresses of DNA transformation protocols. Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Civil Society under the Law ‘On Foreign Agents’: NGO Strategies and Network Transformation
Date: 2018-04-21
Creator: Maria Tysiachniouk, Svetlana Tulaeva, Laura A. Henry
Access: Open access
- This essay analyses how the ‘foreign agent’ law has been interpreted and implemented by the Russian authorities and examines diverse NGO survival strategies in response to the ‘foreign agent’ label. The foreign agent law has disrupted and transformed resource mobilisation strategies and transnational NGO networks. Based on qualitative research on environmental NGOs, we offer a typology of NGO responses to the foreign agent law, providing examples to show how the organisations attempt to ensure their survival.
Two modes of transvection at the eyes absent gene of Drosophila demonstrate plasticity in transcriptional regulatory interactions in cis and in trans
Date: 2019-01-01
Creator: Katherine Tian, Rachel E. Henderson, Reyna Parker, Alexia Brown, Justine E., Johnson, Jack R. Bateman
Access: Open access
- For many genes, proper gene expression requires coordinated and dynamic interactions between multiple regulatory elements, each of which can either promote or silence transcription. In Drosophila, the complexity of the regulatory landscape is further complicated by the tight physical pairing of homologous chromosomes, which can permit regulatory elements to interact in trans, a phenomenon known as transvection. To better understand how gene expression can be programmed through cis- and trans-regulatory interactions, we analyzed transvection effects for a collection of alleles of the eyes absent (eya) gene. We find that trans-activation of a promoter by the eya eye-specific enhancers is broadly supported in many allelic backgrounds, and that the availability of an enhancer to act in trans can be predicted based on the molecular lesion of an eya allele. Furthermore, by manipulating promoter availability in cis and in trans, we demonstrate that the eye-specific enhancers of eya show plasticity in their promoter preference between two different transcriptional start sites, which depends on promoter competition between the two potential targets. Finally, we show that certain alleles of eya demonstrate pairing-sensitive silencing resulting from trans-interactions between Polycomb Response Elements (PREs), and genetic and genomic data support a general role for PcG proteins in mediating transcriptional silencing at eya. Overall, our data highlight how eya gene regulation relies upon a complex but plastic interplay between multiple enhancers, promoters, and PREs.
Economic-based projections of future land use in the conterminous United States under alternative policy scenarios
Date: 2012-04-01
Creator: V. C. Radeloff, E. Nelson, A. J. Plantinga, D. J. Lewis, D., Helmers, J. J. Lawler, J. C. Withey, F. Beaudry, S. Martinuzzi
Access: Open access
- Land-use change significantly contributes to biodiversity loss, invasive species spread, changes in biogeochemical cycles, and the loss of ecosystem services. Planning for a sustainable future requires a thorough understanding of expected land use at the fine spatial scales relevant for modeling many ecological processes and at dimensions appropriate for regional or national-level policy making. Our goal was to construct and parameterize an econometric model of land-use change to project future land use to the year 2051 at a fine spatial scale across the conterminous United States under several alternative land-use policy scenarios. We parameterized the econometric model of land-use change with the National Resource Inventory (NRI) 1992 and 1997 land-use data for 844 000 sample points. Land-use transitions were estimated for five land-use classes (cropland, pasture, range, forest, and urban). We predicted land-use change under four scenarios: business-as-usual, afforestation, removal of agricultural subsidies, and increased urban rents. Our results for the business-as-usual scenario showed widespread changes in land use, affecting 36% of the land area of the conterminous United States, with large increases in urban land (79%) and forest (7%), and declines in cropland (\-16%) and pasture (\-13%). Areas with particularly high rates of land-use change included the larger Chicago area, parts of the Pacific Northwest, and the Central Valley of California. However, while land-use change was substantial, differences in results among the four scenarios were relatively minor. The only scenario that was markedly different was the afforestation scenario, which resulted in an increase of forest area that was twice as high as the business-as-usual scenario. Land-use policies can affect trends, but only so much. The basic economic and demographic factors shaping land-use changes in the United States are powerful, and even fairly dramatic policy changes, showed only moderate deviations from the business-as-usual scenario. Given the magnitude of predicted land-use change, any attempts to identify a sustainable future or to predict the effects of climate change will have to take likely land-use changes into account. Econometric models that can simulate land-use change for broad areas with fine resolution are necessary to predict trends in ecosystem service provision and biodiversity persistence. © 2012 by the Ecological Society of America.