Colorado State University

About: Colorado State University is a education organization based out in Fort Collins, Colorado, United States. It is known for research contribution in the topics: Population & Radar. The organization has 31430 authors who have published 69040 publications receiving 2724463 citations. The organization is also known as: CSU & Colorado Agricultural College.

Sensitivity to Basis Mismatch in Compressed Sensing

Abstract: The theory of compressed sensing suggests that successful inversion of an image of the physical world (broadly defined to include speech signals, radar/sonar returns, vibration records, sensor array snapshot vectors, 2-D images, and so on) for its source modes and amplitudes can be achieved at measurement dimensions far lower than what might be expected from the classical theories of spectrum or modal analysis, provided that the image is sparse in an apriori known basis. For imaging problems in spectrum analysis, and passive and active radar/sonar, this basis is usually taken to be a DFT basis. However, in reality no physical field is sparse in the DFT basis or in any apriori known basis. No matter how finely we grid the parameter space the sources may not lie in the center of the grid cells and consequently there is mismatch between the assumed and the actual bases for sparsity. In this paper, we study the sensitivity of compressed sensing to mismatch between the assumed and the actual sparsity bases. We start by analyzing the effect of basis mismatch on the best k-term approximation error, which is central to providing exact sparse recovery guarantees. We establish achievable bounds for the l1 error of the best k -term approximation and show that these bounds grow linearly with the image (or grid) dimension and the mismatch level between the assumed and actual bases for sparsity. We then derive bounds, with similar growth behavior, for the basis pursuit l1 recovery error, indicating that the sparse recovery may suffer large errors in the presence of basis mismatch. Although, we present our results in the context of basis pursuit, our analysis applies to any sparse recovery principle that relies on the accuracy of best k-term approximations for its performance guarantees. We particularly highlight the problematic nature of basis mismatch in Fourier imaging, where spillage from off-grid DFT components turns a sparse representation into an incompressible one. We substantiate our mathematical analysis by numerical examples that demonstrate a considerable performance degradation for image inversion from compressed sensing measurements in the presence of basis mismatch, for problem sizes common to radar and sonar.

Rapid and highly variable warming of lake surface waters around the globe

Abstract: In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade−1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors—from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade−1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decade−1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.

Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change

Abstract: Roughly 90% of atmospheric ozone is found in the lower stratosphere in the ozone layer Since about the 1970s, anthropogenic emissions of ozone-depleting gases have led to depletion of ~3–4% of the total overhead ozone averaged over the globe 1 The strongest depletion is found over Antarctica during spring, when photochemical processes combine with a unique set of meteorological conditions to greatly increase the effectiveness of ozone-depleting gases, and more than half of the total overhead ozone is destroyed Characteristics of the resulting Antarctic ozone hole are reviewed in refs 1 and 2, and the identification and attribution of the phenomenon was recently celebrated in a special edition of Nature (http://wwwnaturecom/nature/focus/ ozonehole/) The Antarctic ozone hole is evident in ozone observations taken every spring since about the early 1980s 1 Its annual onset coincides with the return of sunlight to the cold polar stratosphere during September/October, and its decay with the collapse of the stratospheric vortex during November/December 1,2 The most obvious surface impact is an increase in ultraviolet radiation reaching the surface 1 Over the past decade, however, it has become clear that the ozone hole is also associated with widespread changes in the Southern Hemisphere tropospheric circulation and surface climate Our purpose here is to review the evidence that suggests that the Antarctic ozone hole has had a demonstrable effect on the surface climate of the Southern Hemisphere The ozone hole and Southern Hemisphere circulation Ozone absorbs incoming solar radiation Hence the depletion of ozone over Antarctica leads to cooling of the polar stratosphere 2,3

A Single P450 Allele Associated with Insecticide Resistance in Drosophila

Abstract: Insecticide resistance is one of the most widespread genetic changes caused by human activity, but we still understand little about the origins and spread of resistant alleles in global populations of insects. Here, via microarray analysis of all P450s in Drosophila melanogaster, we show that DDT-R, a gene conferring resistance to DDT, is associated with overtranscription of a single cytochrome P450 gene, Cyp6g1. Transgenic analysis of Cyp6g1 shows that overtranscription of this gene alone is both necessary and sufficient for resistance. Resistance and up-regulation in Drosophila populations are associated with a single Cyp6g1 allele that has spread globally. This allele is characterized by the insertion of an Accord transposable element into the 5' end of the Cyp6g1 gene.

Carbon and Nitrogen Distribution in Aggregates from Cultivated and Native Grassland Soils

Abstract: Long-term cultivation of grassland soils reduces soil organic C and N content and has been associated with a deterioration in the aggregate structure of the soil. This study examined the effects of bare fallow (moldboard plow), stubble mulch fallow (subtill), and no-till fallow management on aggregate size distribution and aggregate organic C and N contents compared with a native (virgin) grassland soil. Aggregate size fractions were separated by wet sieving and the proportion of soil was quantified for each aggregate size class. Mineralassociated (silt and clay) organic matter was isolated by dispersing aggregates in sodium hexametaphosphate and removing the sand and particulate organic matter (POM) by passing the dispersed aggregates through a 53-/un sieve. The POM fraction is composed primarily of partially decomposed root fragments and has an average C/N ratio of about 16. A large proportion of the total soil dry weight (50-60%) was isolated in the small macroaggregate (250-2000 fan) size class. The native grassland soil was more stable than the cultivated soils when slaked, and the no-till soil was more stable than the stubble mulch and bare fallow soil when slaked. Reduced tillage management is effective at increasing the proportion of macroaggregates and results in the accumulation of wheat (Triticum aestivum L.) derived POM within the aggregate structure compared with bare fallow soil. It has previously been shown that the POM fraction accounts for the majority of the soil organic matter (SOM) initially lost as a result of cultivation of grassland soils. The data reported in this study relates the loss of structural stability from cultivation to losses of organic C and N from the POM fraction. N GRASSLAND SOILS are generally highly structured and rich in SOM. Cultivation reduces SOM content (Jenny, 1941; Haas et al., 1957) and results in a deterioration of the aggregate structure (Chancy and Swift, 1984). The POM fraction, which is composed primarily of partially decomposed root fragments, accounts for the majority of the SOM initially lost as a result of cultivation of grassland soils (Cambardella and Elliott, 1992). Reductions in aggregate stability after cultivation are most pronounced in soil macroaggregates, while the stability of soil microaggregates remains unchanged (Tisdall and Oades, 1982; Oades, 1984). As macroaggregates disintegrate with tillage, the proportion of microaggregates increases, since microaggregates are not destroyed by cultivation (Tisdall and Oades, 1980; Elliott, 1986). Microaggregates have a lower organic matter concentration than macroaggregates (Dormaar, 1983) and this organic matter is less labile than that associated with macroaggregates (Elliott, 1986; Gupta and Germida, 1988). The disintegration of macroaggregates with cultivation into nutrient-poor microaggregates and the subsequent release of plant-available nutrients may be one explanation for the observed pattern of lower orC.A. Cambardella, USDA-ARS, National Soil Tilth Lab., 2150 Pammel Drive, Ames, IA 50011; and E.T. Elliott, Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO 80523. Received 30 June 1992. \"Corresponding author. Published in Soil Sci. Soc. Am. J. 57:1071-1076 (1993). ganic matter contents and reduced nutrient-supplying efficiencies in cultivated soils when compared with grassland soils (Elliott, 1986). Sustainable production has become a key issue in the management of cropping systems. Reduced tillage and no-till management have been initiated to mitigate some of the detrimental effects of intensive cultivation, such as reduction of soil organic matter and the concomitant increase in erosion and decrease in soil fertility (Fenster and Peterson, 1979). Little information exists in the literature on the effect of reduced tillage or no-till management on the nutrient contents of soil aggregates and their associated organic matter. This study examined the effects of bare fallow (moldboard plow), stubble mulch fallow (subtill), and notill management on aggregate size distributions and aggregate organic C and N contents compared with native grassland. MATERIALS AND METHODS