The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Luis Pena A Ardila - One of the best experts on this subject based on the ideXlab platform.
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measuring the single Particle Density matrix for fermions and hard core bosons in an optical lattice
Physical Review Letters, 2018Co-Authors: Luis Pena A Ardila, Markus Heyl, Andre EckardtAbstract:Ultracold atoms in optical lattices provide clean, tunable, and well-isolated realizations of paradigmatic quantum lattice models. With the recent advent of quantum-gas microscopes, they now also offer the possibility to measure the occupations of individual lattice sites. What, however, has not yet been achieved is to measure those elements of the single-Particle Density matrix, which are off- diagonal in the occupation basis. Here, we propose a scheme to access these basic quantities both for fermions as well as hard-core bosons and investigate its accuracy and feasibility. The scheme relies on the engineering of a large effective tunnel coupling between distant lattice sites and a protocol that is based on measuring site occupations after two subsequent quenches.
Jan Graefe - One of the best experts on this subject based on the ideXlab platform.
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a new approach to calculate the Particle Density of soils considering properties of the soil organic matter and the mineral matrix
Geoderma, 2006Co-Authors: Jorg Ruhlmann, Martin Korschens, Jan GraefeAbstract:Abstract The Particle Density of soil ( ρ S ) represents one of the soil's basic physical properties and it depends on the composition of both the mineral and the organic soil components. It therefore varies for different soils, e.g. within the group of mineral soils, and ranges from 2.4–2.9 g cm −3 . Hence, awareness of this variability is important for properties estimated by a calculation involving Particle Density. Because ρ S depends on both the soil's solid mineral Particles and soil organic matter composition, we derived a function based on the mixture ratio of these two soil components. This approach represents a further development of earlier investigations dealing with the influence of organic carbon ( C org ) on ρ S . To parameterise this function, two data sets were used: (1) data from soils with C org contents between 0% and 54.88% and corresponding values of ρ S between 1.49 and 2.72 g cm −3 ; and (2) data from soils of 17 German long-term experiments contrasting in soil texture and in soil mineral inventory. Data set 1 was used to quantify the influence of soil organic matter on ρ S , and data set 2 was used to calculate the influence of mineral matrix on ρ S . The soil organic matter has two major influences on ρ S : (1) via a mass effect (expressed as a mixture ratio between organic and mineral soil components); and (2) via a quality effect (expressed as calculated changes in Particle Density of organic soil components). Here, we calculated that with increasing content of soil organic matter (0–100%), the Particle Density of organic soil components rose from about 1.10 to 1.50 g cm −3 , and present possible reasons for this phenomenon. Additionally, we demonstrate that the mineral matrix of the soil affects ρ S especially via variations in the mineral inventory, but conclude that differences in Particle size distribution of soils were to a lesser extent suitable for describing the influence of the mineral matrix on ρ S . Overall, using our approach should generate more realistic values of ρ S , and consequently of all calculated parameters which are sensitive to ρ S .
Richard D Bowden - One of the best experts on this subject based on the ideXlab platform.
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organic c and n stabilization in a forest soil evidence from sequential Density fractionation
Soil Biology & Biochemistry, 2006Co-Authors: Phillip Sollins, Christopher W Swanston, Markus Kleber, Timothy R Filley, Marc G Kramer, Susan E Crow, Bruce A Caldwell, Kate Lajtha, Richard D BowdenAbstract:Abstract In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size Particles. When fractionated according to Particle Density, C and N concentration (per g fraction) and C/N of these soil organo-mineral Particles decrease with increasing Particle Density across soils of widely divergent texture, mineralogy, location, and management. The variation in Particle Density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these Particles, and (2) variations in Density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing Particle Density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model). To explore mechanisms underlying this trend in C concentration and C/N with Particle Density, we sequentially Density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm −3 and analyzed the six fractions for measures of organic matter and mineral phase properties. All measures of OM composition showed either: (1) a monotonic change with Density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing Density, and 14 C mean residence time (MRT) increased with Particle Density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, 13 C and 15 N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral Particle Density, and also with an “onion” layering model. X-ray diffraction before and after separation of magnetic materials showed that the sequential Density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in Density of the organo-mineral Particles in this soil. Thus, our data are consistent with the hypothesis that variation in Particle Density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.
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organic c and n stabilization in a forest soil evidence from sequential Density fractionation
Journal Name: Soil Biology and Biochemistry vol. 38 N A October 1 2006 pp. 3313?3324, 2006Co-Authors: Phillip Sollins, Christopher W Swanston, Markus Kleber, Timothy R Filley, Marc G Kramer, Susan E Crow, Bruce A Caldwell, Kate Lajtha, Richard D BowdenAbstract:In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size Particles. When fractionated according to Particle Density, C and N concentration (per g fraction) and C/N of these soil organo-mineral Particles decrease with increasing Particle Density across soils of widely divergent texture, mineralogy, location, and management. The variation in Particle Density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these Particles, and (2) variations in Density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing Particle Density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (‘‘onion’’ layering model). To explore mechanisms underlying this trend in C concentration and C/N with Particle Density, we sequentially Density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm � 3 and analyzed the six fractions for measures of organic matter and mineral phase properties. All measures of OM composition showed either: (1) a monotonic change with Density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing Density, and 14 C mean residence time (MRT) increased with Particle Density from ca. 150 years to 4980 years in the four organo-mineral fractions. In contrast, C/N, 13 Ca nd 15 N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral Particle Density, and also with an ‘‘onion’’ layering model. X-ray diffraction before and after separation of magnetic materials showed that the sequential Density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in Density of the organomineral Particles in this soil. Thus, our data are consistent with the hypothesis that variation in Particle Density reflects variation in thickness of the organic accumulations and with an ‘‘onion’’ layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or ‘‘onion’’ layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors. Published by Elsevier Ltd.
Andre Eckardt - One of the best experts on this subject based on the ideXlab platform.
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measuring the single Particle Density matrix for fermions and hard core bosons in an optical lattice
Physical Review Letters, 2018Co-Authors: Luis Pena A Ardila, Markus Heyl, Andre EckardtAbstract:Ultracold atoms in optical lattices provide clean, tunable, and well-isolated realizations of paradigmatic quantum lattice models. With the recent advent of quantum-gas microscopes, they now also offer the possibility to measure the occupations of individual lattice sites. What, however, has not yet been achieved is to measure those elements of the single-Particle Density matrix, which are off- diagonal in the occupation basis. Here, we propose a scheme to access these basic quantities both for fermions as well as hard-core bosons and investigate its accuracy and feasibility. The scheme relies on the engineering of a large effective tunnel coupling between distant lattice sites and a protocol that is based on measuring site occupations after two subsequent quenches.
Peter Bilson Obour - One of the best experts on this subject based on the ideXlab platform.
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predicting soil Particle Density from clay and soil organic matter contents
Geoderma, 2017Co-Authors: Per Schjonning, R A Mcbride, Thomas Keller, Peter Bilson ObourAbstract:Abstract Soil Particle Density (Dp) is an important soil property for calculating soil porosity expressions. However, many studies assume a constant value, typically 2.65 Mg m − 3 for arable, mineral soils. Few models exist for the prediction of Dp from soil organic matter (SOM) content. We hypothesized that better predictions may be obtained by including the soil clay content in least squares prediction equations. A calibration data set with 79 soil samples from 16 locations in Denmark, comprising both topsoil and subsoil horizons, was selected from the literature. Simple linear regression indicated that Dp of clay Particles was approximately 2.86 Mg m − 3 , while that of sand + silt Particles could be estimated to ~ 2.65 Mg m − 3 . Multiple linear regression showed that a combination of clay and SOM contents could explain nearly 92% of the variation in measured Dp. The clay and SOM prediction equation was validated against a combined data set with 227 soil samples representing A, B, and C horizons from temperate North America and Europe. The new prediction equation performed better than two SOM-based models from the literature. Validation of the new clay and SOM model using the 227 soil samples gave a root mean square error and mean error of 0.041 and + 0.013 Mg m − 3 , respectively. Predictions were accurate for all levels of SOM content in the validation data set. The model gave very precise predictions for soils with clay contents lower than 0.3 kg kg − 1 , while a moderate over-prediction was observed for soils very high in clay. Finally, we developed a texture-enhanced curvilinear model that will be useful for predicting Dp of soils with high contents of clay and in particular SOM.
