Showing 211 - 220 of 733 Items
Linear relations between N ≥ 4 supergravity and subleading-color SYM amplitudes
Date: 2012-02-27
Creator: Stephen G. Naculich, Horatiu Nastase, Howard J. Schnitzer
Access: Open access
- The IR divergences of supergravity amplitudes are less severe than those of planar SYM amplitudes, and are comparable to those subleading-color SYM amplitudes that are most subleading in the 1/N expansion, namely O(1/ε L) for L-loop amplitudes. We derive linear relations between one- and two-loop four-point amplitudes and one-loop five-point amplitudes of N ≥ 4, 5, and 6 supergravity and the most-subleading-color contributions of the analogous amplitudes of N = 0, 1, and 2 SYM theory, extending earlier results for N = 8 supergravity amplitudes. Our work relies on linear relations between N = 4 supergravity and planar SYM amplitudes that were recently derived using the double-copy property of gravity, and color-kinematic duality of gauge theories. © SISSA 2012.
An isochromosome confers drug resistance in vivo by amplification of two genes, ERG11 and TAC1
Date: 2008-05-01
Creator: Anna Selmecki, Maryam Gerami-Nejad, Carsten Paulson, Anja Forche, Judith, Berman
Access: Open access
- Acquired azole resistance is a serious clinical problem that is often associated with the appearance of aneuploidy and, in particular, with the formation of an isochromosome [i(5L)] in the fungal opportunist Candida albicans. Here we exploited a series of isolates from an individual patient during the rapid acquisition of fluconazole resistance (FluR). Comparative genome hybridization arrays revealed that the presence of two extra copies of Chr5L, on the isochromosome, conferred increased FluR and that partial truncation of Chr5L reduced FluR. In vitro analysis of the strains by telomere-mediated truncations and by gene deletion assessed the contribution of all Chr5L genes and of four specific genes. Importantly, ERG11 (encoding the drug target) and a hyperactive allele of TAC1 (encoding a transcriptional regulator of drug efflux pumps) made independent, additive contributions to FluR in a gene copy number-dependent manner that was not different from the contributions of the entire Chr5L arm. Thus, the major mechanism by which i(5L) formation causes increased azole resistance is by amplifying two genes: ERG11 and TAC1. © 2008 The Authors.
Clarifying (Opportunity) Costs
Date: 2015-05-01
Creator: Daniel F. Stone
Access: Open access
- Opportunity cost is widely considered to be a fundamental concept in economics. But the definition of the term continues to be both unclear and controversial. I describe how the term is widely used in two distinct ways, both in academic and non-academic contexts. I propose a practical way for educators to clarify the concept and related terminology.
Expert assessment of vulnerability of permafrost carbon to climate change
Date: 2013-07-01
Creator: E. A.G. Schuur, B. W. Abbott, W. B. Bowden, V. Brovkin, P., Camill, J. G. Canadell, J. P. Chanton, F. S. Chapin, T. R. Christensen, P. Ciais, B. T. Crosby, C. I. Czimczik, G. Grosse, J. Harden, D. J. Hayes, G. Hugelius
Access: Open access
- Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19-45 Pg C by 2040, 162-288 Pg C by 2100, and 381-616 Pg C by 2300 in CO equivalent using 100-year CH global warming potential (GWP). These values become 50 % larger using 20-year CH GWP, with a third to a half of expected climate forcing coming from CH even though CH was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing. © 2013 The Author(s). 2 4 4 4 4
Two databases derived from BGC-Argo float measurements for marine biogeochemical and bio-optical applications
Date: 2017-11-22
Creator: Emanuele Organelli, Marie Barbieux, Hervé Claustre, Catherine Schmechtig, Antoine, Poteau, Annick Bricaud, Emmanuel Boss, Nathan Briggs, Giorgio Dall'Olmo, Fabrizio D'Ortenzio, Edouard Leymarie, Antoine Mangin, Grigor Obolensky, Christophe Penkerc'H, Louis Prieur, Collin Roesler, Romain Serra, Julia Uitz, Xiaogang Xing
Access: Open access
- Since 2012, an array of 105 Biogeochemical-Argo (BGC-Argo) floats has been deployed across the world's oceans to assist in filling observational gaps that are required for characterizing open-ocean environments. Profiles of biogeochemical (chlorophyll and dissolved organic matter) and optical (single-wavelength particulate optical backscattering, downward irradiance at three wavelengths, and photosynthetically available radiation) variables are collected in the upper 1000 m every 1 to 10 days. The database of 9837 vertical profiles collected up to January 2016 is presented and its spatial and temporal coverage is discussed. Each variable is quality controlled with specifically developed procedures and its time series is quality-assessed to identify issues related to biofouling and/or instrument drift. A second database of 5748 profile-derived products within the first optical depth (i.e., the layer of interest for satellite remote sensing) is also presented and its spatiotemporal distribution discussed. This database, devoted to field and remote ocean color applications, includes diffuse attenuation coefficients for downward irradiance at three narrow wavebands and one broad waveband (photosynthetically available radiation), calibrated chlorophyll and fluorescent dissolved organic matter concentrations, and single-wavelength particulate optical backscattering. To demonstrate the applicability of these databases, data within the first optical depth are compared with previously established bio-optical models and used to validate remotely derived bio-optical products. The quality-controlled databases are publicly available from the SEANOE (SEA scieNtific Open data Edition) publisher at https://doi.org/10.17882/49388 and https://doi.org/10.17882/47142 for vertical profiles and products within the first optical depth, respectively.
Are melanized feather barbs stronger?
Date: 2004-01-01
Creator: Michael Butler, Amy S. Johnson
Access: Open access
- Melanin has been associated with increased resistance to abrasion, decreased wear and lowered barb breakage in feathers. But, this association was inferred without considering barb position along the rachis as a potentially confounding variable. We examined the cross-sectional area, breaking force, breaking stress, breaking strain and toughness of melanized and unmelanized barbs along the entire rachis of a primary feather from an osprey (Pandion haliaetus). Although breaking force was higher for melanized barbs, breaking stress (force divided by cross-sectional area) was greater for unmelanized barbs. But when position was considered, all mechanical differences between melanized and unmelanized barbs disappeared. Barb breaking stress, breaking strain and toughness decreased, and breaking stiffness increased, distally along the rachis. These proximal-distal material property changes are small and seem unlikely to affect flight performance of barbs. Our observations of barb bending, breaking and morphology, however, lead us to propose a design principle for barbs. We propose that, by being thicker-walled dorso-ventrally, the barb's flexural stiffness is increased during flight; but, by allowing for twisting when loaded with dangerously high forces, barbs firstly avoid failure by bending and secondly avoid complete failure by buckling rather than rupturing.
More loops and legs in Higgs-regulated N = 4 SYM amplitudes
Date: 2010-01-01
Creator: Johannes M. Henn, Stephen G. Naculich, Howard J. Schnitzer, Marcus Spradlin
Access: Open access
- We extend the analysis of Higgs-regulated planar amplitudes of N = 4 supersymmetric Yang-Mills theory to four loops for the four-gluon amplitude and to two loops for the five-gluon amplitude. Our calculations are consistent with a proposed all-loop ansatz for planar MHV n-gluon amplitudes that is the analog of the BDS ansatz in dimensional regularization. In all cases considered, we have verified that the IR-finite parts of the logarithm of the amplitudes have the same dependence on kinematic variables as the corresponding functions in dimensionally-regulated amplitudes (up to overall additive constants, which we determine). We also study various Regge limits of N = 4 SYM planar n-gluon amplitudes. Euclidean Regge limits of Higgs-regulated n ≥ 4 amplitudes yield results similar in form to those found using dimensional regularization, but with different expressions for the gluon trajectory and Regge vertices resulting from the different regulator scheme. We also show that the Regge limit of the four-gluon amplitude is dominated at next-to-leading-log order by vertical ladder diagrams together with the class of vertical ladder diagrams with a single H-shaped insertion. © 2010 SISSA, Trieste, Italy.
Where to put things? Spatial land management to sustain biodiversity and economic returns
Date: 2008-06-01
Creator: Stephen Polasky, Erik Nelson, Jeff Camm, Blair Csuti, Paul, Fackler, Eric Lonsdorf, Claire Montgomery, Denis White, Jeff Arthur
Access: Open access
- Expanding human population and economic growth have led to large-scale conversion of natural habitat to human-dominated landscapes with consequent large-scale declines in biodiversity. Conserving biodiversity, while at the same time meeting expanding human needs, is an issue of utmost importance. In this paper we develop a spatially explicit landscape-level model for analyzing the biological and economic consequences of alternative land-use patterns. The spatially explicit biological model incorporates habitat preferences, area requirements and dispersal ability between habitat patches for terrestrial vertebrate species to predict the likely number of species that will be sustained on the landscape. The spatially explicit economic model incorporates site characteristics and location to predict economic returns for a variety of potential land uses. We apply the model to search for efficient land-use patterns that maximize biodiversity conservation objectives for given levels of economic returns, and vice versa. We apply the model to the Willamette Basin, Oregon, USA. By thinking carefully about the arrangement of activities, we find land-use patterns that sustain high levels of biodiversity and economic returns. Compared to the 1990 land-use pattern, we show that both biodiversity conservation and the value of economic activity could be increased substantially. © 2008 Elsevier Ltd.
Nonlinear coherent structures in granular crystals
Date: 2017-09-06
Creator: C. Chong, Mason A. Porter, P. G. Kevrekidis, C. Daraio
Access: Open access
- The study of granular crystals, which are nonlinear metamaterials that consist of closely packed arrays of particles that interact elastically, is a vibrant area of research that combines ideas from disciplines such as materials science, nonlinear dynamics, and condensed-matter physics. Granular crystals exploit geometrical nonlinearities in their constitutive microstructure to produce properties (such as tunability and energy localization) that are not conventional to engineering materials and linear devices. In this topical review, we focus on recent experimental, computational, and theoretical results on nonlinear coherent structures in granular crystals. Such structures - which include traveling solitary waves, dispersive shock waves, and discrete breathers - have fascinating dynamics, including a diversity of both transient features and robust, long-lived patterns that emerge from broad classes of initial data. In our review, we primarily discuss phenomena in one-dimensional crystals, as most research to date has focused on such scenarios, but we also present some extensions to two-dimensional settings. Throughout the review, we highlight open problems and discuss a variety of potential engineering applications that arise from the rich dynamic response of granular crystals.
Framing ICT Usage in the Real Estate Industry
Date: 2013-04-12
Creator: Steven Jones
Access: Open access
- The real estate industry, like many, is one based on a competitive consumer culture in which professionals vie for the business and, ultimately, the loyalty of customers. In this case, those customers are purchasing what, for most, is a significant investment, requiring them to navigate various legal and regulatory processes that might be impossible without the assistance of a knowledgeable, seasoned agent. It is the presence of agency that renders real estate unique from retail and other industries where goods and services trade hands. Furthermore, the rise of various information and communication technologies (ICT) over the course of the past 25 years may have led to new challenges for real estate agents and allied professionals. Some scholars surmise that the increased prevalence of ICTs in various industries can become disruptive to those industries, causing individuals and organizations working within them to either adapt accordingly or become obsolete (Bower and Christensen 1995; Markus, et al. 2006).