Effects of irrigated and dryland cultivation on soil carbon, nitrogen and phosphorus in northeastern Colorado

2001 Spring.Includes bibliographical references.I investigated the effects of irrigated and fertilized com agriculture on soil C, N and P in northeastern Colorado as they compare to dryland wheat-fallow fields and native rangelands in the semiarid shortgrass steppe of northeastern Colorado. Three replicates each of native rangeland, dry land wheat-fallow, and irrigated corn fields located in or adjacent to the Pawnee National Grasslands were selected for this study. I measured potentially mineralizable C and N from 0-15cm in the soil profile, particulate organic matter (POM) C and Nin the upper 30cm, total and NaHC03-P to a depth of 105cm, and total soil C and N to a depth of 195cm in the soil profile. Irrigated corn fields contained significantly lower mineralizable, POM, and total C and N than rangelands in the upper 5cm of soil. Com fields also had significantly greater NaHCOrP content than rangelands or wheat-fallow fields to a 1-meter depth in the soil. Wheat-fallow fields had significantly less potentially mineralizable and POM C and N than rangelands or corn fields in the upper 5cm of soil. Cumulative losses of total C and N in wheat-fallow fields extended to depths of 75cm or more. There were no significant differences in total P among land use types. Differences in C and N between corn and wheat-fallow fields are likely due to differences in the quantity of plant residue inputs. The distribution of C, N and NaHC03-P through the soil profile in corn fields also differed from rangelands. Soil C, N and NaHC03-P in the soil profile of rangelands decreased from the surf ace down, whereas in com fields C, N and NaHC03-P increased from the surf ace to 30cm and then decreased. Distribution of C, N and P in corn fields may be due to leaching of C or N or decomposition changes in the soil profile. In wheat-fallow fields, C, N and NaHC03-P showed a more uniform distribution in the upper 30cm of soil than rangelands, likely due to tillage practices that mix the upper soil layers in wheat-fallow fields. These results indicate that irrigated and fertilized corn crops in this region of the semiarid shortgrass steppe depletes pools of C and N at the soil surf ace but does not cause a change in C or N below the 5cm layer of soil. The differences in amount and distribution of C and N observed in this study among dryland wheat-fallow and irrigated corn fields indicate that the type of crop grown in this region should be an important consideration for regional studies that evaluate C and N changes due to cultivation

Generalized analysis of quasi-steady-state and transient decay open circuit voltage measurements

The current–voltage characteristics of solar cells and photodiodes can be determined by measuring the open-circuit voltage as a function of a slowly varying light intensity. This article presents a detailed theoretical analysis and interpretation of such quasi-steady-state Vocmeasurements(QssVoc). The ability of this analysis to accurately obtain the true steady-state device characteristics even in the case of high lifetime, high resistivitysilicon devices is demonstrated experimentally. The QssVoc technique can be used to determine the minority carrier lifetime, and the new generalized analysis is required to do this accurately. An important outcome is that solar cell and diode device characteristics can be obtained from measurements of either the photoconductance or the open-circuit voltage, even using transient techniques.This work has been funded by the Australian Research Council. The authors also thank S. Glunz and S. Rein from the Fraunhofer Institute of Solar Energy Systems, for the use of the solar cell used in Fig. 5

Metabolic control of gene transcription in non-alcoholic fatty liver disease: the role of the epigenome

Non-alcoholic fatty liver disease (NAFLD) is estimated to affect 24% of the global adult population. NAFLD is a major risk factor for the development of cirrhosis and hepatocellular carcinoma, as well as being strongly associated with type 2 diabetes and cardiovascular disease. It has been proposed that up to 88% of obese adults have NAFLD, and with global obesity rates increasing, this disease is set to become even more prevalent. Despite intense research in this field, the molecular processes underlying the pathology of NAFLD remain poorly understood. Hepatic intracellular lipid accumulation may lead to dysregulated tricarboxylic acid (TCA) cycle activity and associated alterations in metabolite levels. The TCA cycle metabolites alpha-ketoglutarate, succinate and fumarate are allosteric regulators of the alpha-ketoglutarate-dependent dioxygenase family of enzymes. The enzymes within this family have multiple targets, including DNA and chromatin, and thus may be capable of modulating gene transcription in response to intracellular lipid accumulation through alteration of the epigenome. In this review, we discuss what is currently understood in the field and suggest areas for future research which may lead to the development of novel preventative or therapeutic interventions for NAFLD

Morphology and segmentation of the western Galápagos Spreading Center, 90.5°–98°W : plume-ridge interaction at an intermediate spreading ridge

Author Posting. © American Geophysical Union 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 8515, doi:10.1029/2003GC000609.Complete multibeam bathymetric coverage of the western Galápagos Spreading Center (GSC) between 90.5°W and 98°W reveals the fine-scale morphology, segmentation and influence of the Galápagos hot spot on this intermediate spreading ridge. The western GSC comprises three morphologically defined provinces: A Western Province, located farthest from the Galápagos hot spot west of 95°30′W, is characterized by an axial deep, rift valley morphology with individual, overlapping, E-W striking segments separated by non-transform offsets; A Middle Province, between the propagating rift tips at 93°15′W and 95°30′W, with transitional axial morphology strikes ∼276°; An Eastern Province, closest to the Galápagos hot spot between the ∼90°50′W Galápagos Transform and 93°15′W, with an axial high morphology generally less than 1800 m deep, strikes ∼280°. At a finer scale, the axial region consists of 32 individual segments defined on the basis of smaller, mainly <2 km, offsets. These offsets mainly step left in the Western and Middle Provinces, and right in the Eastern Province. Glass compositions indicate that the GSC is segmented magmatically into 8 broad regions, with Mg # generally decreasing to the west within each region. Striking differences in bathymetric and lava fractionation patterns between the propagating rifts with tips at 93°15′W and 95°30′W reflect lower overall magma supply and larger offset distance at the latter. The structure of the Eastern Province is complicated by the intersection of a series of volcanic lineaments that appear to radiate away from a point located on the northern edge of the Galápagos platform, close to the southern limit of the Galápagos Fracture Zone. Where these lineaments intersect the GSC, the ridge axis is displaced to the south through a series of overlapping spreading centers (OSCs); abandoned OSC limbs lie even farther south. We propose that southward displacement of the axis is promoted during intermittent times of increased plume activity, when lithospheric zones of weakness become volcanically active. Following cessation of the increased plume activity, the axis straightens by decapitating southernmost OSC limbs during short-lived propagation events. This process contributes to the number of right stepping offsets in the Eastern Province.This work was supported by NSF grants OCE98- 18632 to the University of Hawai’i and OCE98-19117 to the Woods Hole Oceanographic Institution; support was provided to M. B. by a CIW/DTM Postdoctoral Fellowshi

Voltage gated inter-cation selective ion channels from graphene nanopores

With the ability to selectively control ionic flux, biological protein ion channels perform a fundamental role in many physiological processes. For practical applications that require the functionality of a biological ion channel, graphene provides a promising solid-state alternative, due to its atomic thinness and mechanical strength. Here, we demonstrate that nanopores introduced into graphene membranes, as large as 50 nm in diameter, exhibit inter-cation selectivity with a ~20x preference for K+ over divalent cations and can be modulated by an applied gate voltage. Liquid atomic force microscopy of the graphene devices reveals surface nanobubbles near the pore to be responsible for the observed selective behavior. Molecular dynamics simulations indicate that translocation of ions across the pore likely occurs via a thin water layer at the edge of the pore and the nanobubble. Our results demonstrate a significant improvement in the inter-cation selectivity displayed by a solid-state nanopore device and by utilizing the pores in a de-wetted state, offers an approach to fabricating selective graphene membranes that does not rely on the fabrication of sub-nm pores

A test for the search for life on extrasolar planets: Looking for the terrestrial vegetation signature in the Earthshine spectrum

We report spectroscopic observations (400 to 800nm, R = approx 100) of Earthshine in June, July and October 2001 from which normalised Earth albedo spectra have been derived. The resulting spectra clearly show the blue colour of the Earth due to Rayleigh diffusion in its atmosphere. They also show the signatures of oxygen, ozone and water vapour. We tried to extract from these spectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%) around 700nm has been measured in the Earth albedo. It is interpreted as being due to the vegetation red edge, expected to be between 2 to 10% of the Earth albedo at 700nm, depending on models. We discuss the primary goal of the present observations: their application to the detection of vegetation-like biosignatures on extrasolar planets.Comment: 7 pages, 7 figures. A&A, accepted 6 May 200

Recovering the state sequence of hidden Markov models using mean-field approximations

Inferring the sequence of states from observations is one of the most fundamental problems in Hidden Markov Models. In statistical physics language, this problem is equivalent to computing the marginals of a one-dimensional model with a random external field. While this task can be accomplished through transfer matrix methods, it becomes quickly intractable when the underlying state space is large. This paper develops several low-complexity approximate algorithms to address this inference problem when the state space becomes large. The new algorithms are based on various mean-field approximations of the transfer matrix. Their performances are studied in detail on a simple realistic model for DNA pyrosequencing.Comment: 43 pages, 41 figure

NMR imaging and hydrodynamic analysis of neutrally buoyant non-Newtonian slurry flows

The flow of solids loaded suspension in cylindrical pipes has been the object of intense experimental and theoretical investigations in recent years. These types of flows are of great interest in chemical engineering because of their important use in many industrial manufacturing processes. Such flows are for example encountered in the manufacture of solid-rocket propellants, advanced ceramics, reinforced polymer composites, in heterogenous catalytic reactors, and in the pipeline transport of liquid-solids suspensions. In most cases, the suspension microstructure and the degree of solids dispersion greatly affect the final performance of the manufactured product. For example, solid propellant pellets need to be extremely-well dispersed in gel matrices for use as rocket engine solid fuels. The homogeneity of pellet dispersion is critical to allow good uniformity of the burn rate, which in turn affects the final mechanical performance of the engine. Today`s manufacturing of such fuels uses continuous flow processes rather than batch processes. Unfortunately, the hydrodynamics of such flow processes is poorly understood and is difficult to assess because it requires the simultaneous measurements of liquid/solids phase velocities and volume fractions. Due to the recent development in pulsed Fourier Transform NMR imaging, NMR imaging is now becoming a powerful technique for the non intrusive investigation of multi-phase flows. This paper reports and exposes a state-of-the-art experimental and theoretical methodology that can be used to study such flows. The hydrodynamic model developed for this study is a two-phase flow shear thinning model with standard constitutive fluid/solids interphase drag and solids compaction stresses. this model shows good agreement with experimental data and the limitations of this model are discussed