University of Arizona

About: University of Arizona is a education organization based out in Tucson, Arizona, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 63805 authors who have published 155998 publications receiving 6854915 citations. The organization is also known as: UA & U of A.

Geminivirus strain demarcation and nomenclature

Abstract: Geminivirus taxonomy and nomenclature is growing in complexity with the number of genomic sequences deposited in sequence databases Taxonomic and nomenclatural updates are published at regular intervals (Fauquet et al in Arch Virol 145:1743–1761, 2000, Arch Virol 148:405–421, 2003) A system to standardize virus names, and corresponding guidelines, has been proposed (Fauquet et al in Arch Virol 145:1743–1761, 2000) This system is now followed by a large number of geminivirologists in the world, making geminivirus nomenclature more transparent and useful In 2003, due to difficulties inherent in species identification, the ICTV Geminiviridae Study Group proposed new species demarcation criteria, the most important of which being an 89% nucleotide (nt) identity threshold between full-length DNA-A component nucleotide sequences for begomovirus species This threshold has been utilised since with general satisfaction More recently, an article has been published to clarify the terminology used to describe virus entities below the species level [5] The present publication is proposing demarcation criteria and guidelines to classify and name geminiviruses below the species level Using the Clustal V algorithm (DNAStar MegAlign software), the distribution of pairwise sequence comparisons, for pairs of sequences below the species taxonomic level, identified two peaks: one at 85–94% nt identity that is proposed to correspond to “strain” comparisons and one at 92–100% identity that corresponds to “variant” comparisons Guidelines for descriptors for each of these levels are proposed to standardize nomenclature under the species level In this publication we review the status of geminivirus species and strain demarcation as well as providing updated isolate descriptors for a total of 672 begomovirus isolates As a consequence, we have revised the status of some virus isolates to classify them as “strains”, whereas several others previously classified as “strains” have been upgraded to “species” In all other respects, the classification system has remained robust, and we therefore propose to continue using it An updated list of all geminivirus isolates and a phylogenetic tree with one representative isolate per species are provided

Uncertainty in hydrologic modeling: Toward an integrated data assimilation framework

Abstract: [1] Despite significant recent developments in computational power and distributed hydrologic modeling, the issue of how to adequately address the uncertainty associated with hydrological predictions remains a critical and challenging one. This issue needs to be properly addressed for hydrological modeling to realize its maximum practical potential in environmental decision-making processes. Arguably, the key to properly addressing hydrologic uncertainty is to understand, quantify, and reduce uncertainty involved in hydrologic modeling in a cohesive, systematic manner. Although general principles and techniques on addressing hydrologic uncertainty are emerging in the literature, there exist no well-accepted guidelines about how to actually implement these principles and techniques in various hydrologic settings in an integrated manner. This paper reviews, in relevant detail, the common data assimilation methods that have been used in hydrologic modeling to address problems of state estimation, parameter estimation, and system identification. In particular, the paper discusses concepts, methods, and issues involved in hydrologic data assimilation from a systems perspective. An integrated hierarchical framework is proposed for pursuing hydrologic data assimilation in several progressive steps to maximally reduce uncertainty in hydrologic predictions.

On the nature of core-collapse supernova explosions

Abstract: We investigate in this paper the core-collapse supernova explosion mechanism in both one and two dimensions. With a radiation/hydrodynamic code based upon the PPM algorithm, we verify the usefulness of neutrino-driven overturn (\convection") between the shock and the neutrinosphere in igniting the supernova explosion. The 2-D simulation of the core of a 15M star that we present here indicates that the breaking of spherical symmetry may be central to the explosion itself and that a multitude of bent and broken ngers is a common feature of the ejecta. As in one-dimension, the explosion seems to be a mathematically critical phenomenon, evolving from a steady-state to explosion after a critical mass accretion rate through the stalled shock has been reached. In the 2-D simulation we show here, the pre-explosion convective phase lasted 30 overturns ( 100 milliseconds) before exploding. The pre-explosion steady-state in 2-D is similar to that achieved in 1-D, but, in 2-D, due to the higher dwell time of matter in the overturning region, the average entropy achieved behind the stalled shock is larger. In addition, the entropy gradient in the convecting region is atter. These e ects, together with the dynamical pressure of the buoyant plumes, serve to increase the steady-state shock radius (Rs) over its value in 1-D by 30%{100%. A large Rs enlarges the volume of the gain region, puts shocked matter lower in the gravitational potential well, and lowers the accretion ram pressure at the shock for a given _ M. The critical condition for explosion is thereby relaxed. Since the \escape" temperature (Tesc) decreases with radius faster than the actual matter temperature (T ) behind the shock, a larger Rs puts a larger fraction of the shocked material above its local escape temperature. T > Tesc is the condition for a thermally-driven corona to lift o of a star. In one, two, or three dimensions, since supernovae are driven by

Pennies from eBay: the Determinants of Price in Online Auctions

Abstract: This paper presents an exploratory analysis of the determinants of prices in online auctions for collectible United States one-cent coins at the eBay Web site. Starting with an initial data set of 20,000 auctions, we perform regression analysis on a restricted sample of 461 coins for which we obtained estimates of book value. We have three major findings. First, a seller’s feedback ratings, reported by other eBay users, have a measurable effect on her auction prices. Negative feedback ratings have a much greater effect than positive feedback ratings do. Second, minimum bids and reserve prices have positive effects on the final auction price. In particular, minimum bids appear only to have a significant effect when they are binding on a single bidder, as predicted by theory. Third, when a seller chooses to have her auction last for a longer period of days, this significantly increases the auction price on average.

The mass assembly history of field galaxies: detection of an evolving mass limit for star forming galaxies

Abstract: We characterize the mass-dependent evolution of more than 8000 galaxies using spectroscopic redshifts from the DEEP2 Galaxy Redshift Survey in the range 0.4 < z < 1.4 and stellar masses calculated from K-band photometry obtained at Palomar Observatory. This sample spans more than 1.5 deg^2 in four independent fields. Using rest-frame U - B color and [O II] equivalent widths, we distinguish star-forming from passive populations in order to explore the nature of "downsizing"—a pattern in which the sites of active star formation shift from high-mass galaxies at early times to lower mass systems at later epochs. We identify a mass limit, M_Q, above which star formation appears to be quenched and show that the physical mechanisms responsible for downsizing can thus be empirically quantified by charting the evolution in this threshold mass. We find that M_Q decreases with time by a factor of ~3 across our redshift range according to M_Q α (1 + z)^(3.5). To further constrain possible quenching mechanisms, we investigate how downsizing depends on local galaxy environment using the projected third-nearest-neighbor statistic D_(p,3). For the majority of galaxies near the median density, there is no significant correlation between downsizing and environment. However, a trend is observed in the comparison between environments that are more than 3 times overdense or underdense relative to the median. Here, downsizing appears accelerated in overdense regions that host higher numbers of massive, early-type galaxies as compared to the underdense regions. Our results significantly constrain recent suggestions for the origin of downsizing and indicate that the process for quenching star formation must, primarily, be internally driven