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Search Results: 1 - 10 of 139334 matches for " K Schumacher "
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Fluid therapy in cardiac surgery patients
J. Schumacher,K.-F. Klotz
Applied Cardiopulmonary Pathophysiology , 2009,
Abstract:
Comparison of Prairie and Eroded Agricultural Lands on Soil Organic Carbon Retention (South Dakota)  [PDF]
K. R. Olson, A. N. Gennadiyev, R. G. Kovach, T. E. Schumacher
Open Journal of Soil Science (OJSS) , 2014, DOI: 10.4236/ojss.2014.44017
Abstract:


The primary objective of this research was to predict changes in soil organic carbon (SOC) and total soil nitrogen (TSN) stocks as a result of land use change from prairie to agricultural land if the mesic-frigid temperature line moved north in the US and the former frigid soils were cultivated. The conversion of prairie to agricultural use, as a result of climate shift, would release SOC to atmosphere and enhance greenhouse gas emissions. The SOC and TSN differences between the prairie site and agricultural land were compared in South Dakota. The agricultural land had 18% less SOC and 16% less TSN or only half of the expected loss from prairie levels. An attempt was made to document the land use history of the prairie site to understand why SOC and TSN losses were less than anticipated. The fly ash concentration levels on prairie side slopes suggested that the prairie was historically disturbed and eroded. Intensive grazing and burning contributed to the disturbance. The SOC and TSN stock losses appear to represent the minimal change that would occur in the next 100-year time period if a prairie was shifted to agricultural use as a result of climate shift and the mesic-frigid temperature line in US was to move north.


A Cell-Level Mechanism of Contrast Gain Control
Linus J. Schumacher,Geoff K. Nicholls
Quantitative Biology , 2013,
Abstract: The gain of neurons' responses in the auditory cortex is sensitive to contrast changes in the stimulus within a spectrotemporal range similar to their receptive fields, which can be interpreted to represent the tuning of the input to a neuron. This indicates a local mechanism of contrast gain control, which we explore with a minimal mechanistic model here. Gain control through noisy input has been observed in vitro and in a range of computational models. We investigate the behaviour of the simplest of such models to showcase gain control, a stochastic leaky integrate-and-fire (sLIF) neuron, which exhibits gain control through divisive normalisation of the input both with and without accompanying subtractive shift of the input-response curve, depending on whether input noise is proportional to or independent of its mean. To get a more direct understanding of how the input statistics change the response, we construct an analytic approximation to the firing rate of a sLIF neuron constituted of the expression for the deterministic case and a weighted average over the derived approximate steady-state distribution of conductance due to poissonian synaptic inputs. This analytic approximation qualitatively produces the same behaviour as simulations and could be extended by spectrotemporally tuned inputs to give a simple, physiological and local mechanism of contrast gain control in auditory sensing, building on recent experimental work that has hitherto only been described by phenomenological models. By comparing our weighted average firing rate curve with the commonly used sigmoidal input-response function, we demonstrate a nearly linear relationship between both the horizontal shift (or stimulus inflection point) and the inverse gain of the sigmoid and statistics derived from the sLIF model parameters, thus providing a structural constraint on the sigmoid parameter choice.
Out of Plane Thermal Conductivity of Carbon Fiber Reinforced Composite Filled with Diamond Powder  [PDF]
M. Srinivasan, P. Maettig, K. W. Glitza, B. Sanny, A. Schumacher, M. Duhovic, J. Schuster
Open Journal of Composite Materials (OJCM) , 2016, DOI: 10.4236/ojcm.2016.62005
Abstract: Highly conductive fillers have a strong influence on improving the poor out of plane thermal conductivity of carbon fiber reinforced composites. The objective of this study has been to investigate the role of the diamond powder (DP) in enhancing the out-of-plane thermal conductivity of the woven composites. Samples of the standard modulus T300 carbon fiber composite with 44% and 55% fiber volume fraction and the high modulus YS90A carbon fiber composite with 50% volume fraction were fabricated with their matrices comprising of neat epoxy and different loading of diamond powder within epoxy resin. Steady state thermal conductivity measurements were carried out and it was found from the measurements that the out of plane thermal conductivity of the standard modulus composite increased by a factor of 2.3 with 14% volume fraction of diamond powder in the composite while the out of plane thermal conductivity of the high modulus composite increased by a factor of 2.8 with 12% volume fraction of diamond powder in the composite. Finite Element Modeling (FEM) with the incorporation of microstructural characteristics is presented and good consistency between the measurements and FEM results were observed.
Validation of Numerical Modeling for the Prediction of Elastic and Failure Behavior of Diamond Powder Filled Woven Composites  [PDF]
M. Srinivasan, P. Maettig, K. W. Glitza, B. Sanny, A. Schumacher, M. Duhovic
Open Journal of Composite Materials (OJCM) , 2017, DOI: 10.4236/ojcm.2017.72004
Abstract: A numerical investigation was carried out to examine the role of micro-sized diamond powder filler on the on-axis tensile stiffness properties of the standard modulus T300 and the high modulus YS90A woven fabric composite plates by progressive damage modeling. Finite element modeling (FEM) results for the T300 composite with and without diamond powder predicted a specific case of fiber failure in all the plies showing the characteristics of brittle failure. Static tensile tests were carried out on the YS90A composite coupons containing no diamond powder (DP) and filled with 6% and 12% volume fractions of DP. A higher content of diamond powder in the coupons led to agglomeration. This induced stress concentrations and subsequently reduced the mechanical properties. FEM was carried out considering specimens with and without an induced stress concentration geometry in the YS90A coupons filled with DP. The results of the on-axis tensile tests indicated a delamination type of failure in both cases with additional fiber fracture in the Open Hole Tensile (OHT) coupons.
Schmidt number dependence of derivative moments for quasistatic straining motion
J. Schumacher,K. R. Sreenivasan,P. K. Yeung
Physics , 2003, DOI: 10.1017/S0022112003003756
Abstract: Bounds on high-order derivative moments of a passive scalar are obtained for large values of the Schmidt number, $Sc$. The procedure is based on the approach pioneered by Batchelor for the viscous-convective range. The upper bounds for derivative moments of order $n$ are shown to grow as $Sc^{n/2}$ for very large Schmidt numbers. The results are consistent with direct numerical simulations of a passive scalar, whose $Sc$ varies between 1/4 and 64, mixed by homogeneous isotropic turbulence. Although the analysis does not provide proper bounds for normalized moments, the combination of analysis and numerical data suggests that they decay with $Sc$, at least for odd orders. This paper has been withdrawn by the authors due to copyright. It appears in Journal of Fluid Mechanics (2003). http://jfm-www.damtp.cam.ac.uk/
Derivative moments in turbulent shear flows
J. Schumacher,K. R. Sreenivasan,P. K. Yeung
Physics , 2002, DOI: 10.1063/1.1524627
Abstract: We propose a generalized perspective on the behavior of high-order derivative moments in turbulent shear flows by taking account of the roles of small-scale intermittency and mean shear, in addition to the Reynolds number. Two asymptotic regimes are discussed with respect to shear effects. By these means, some existing disagreements on the Reynolds number dependence of derivative moments can be explained. That odd-order moments of transverse velocity derivatives tend not vanish as expected from elementary scaling considerations does not necessarily imply that small-scale anisotropy persists at all Reynolds numbers.
How accurately can soil organic carbon stocks and stock changes be quantified by soil inventories?
M. Schrumpf, E. D. Schulze, K. Kaiser,J. Schumacher
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: Precise determination of changes in organic carbon (OC) stocks is prerequisite to understand the role of soils in the global cycling of carbon and to verify changes in stocks due to management. A large dataset was collected to form base to repeated soil inventories at 12 CarboEurope sites under different climate and land-use, and with different soil types. Concentration of OC, bulk density (BD), and fine earth fraction were determined to 60 cm depth at 100 sampling points per site. We investigated (1) time needed to detect changes in soil OC, assuming future re-sampling of 100 cores; (2) the contribution of different sources of uncertainties to OC stocks; (3) the effect of OC stock calculation on mass rather than volume base for change detection; and (4) the potential use of pedotransfer functions (PTF) for estimating BD in repeated inventories. The period of time needed for soil OC stocks to change strongly enough to be detectable depends on the spatial variability of soil properties, the depth increment considered, and the rate of change. Cropland sites, having small spatial variability, had lower minimum detectable differences (MDD) with 100 sampling points (105 ± 28 gC m 2 for the upper 10 cm of the soil) than grassland and forest sites (206 ± 64 and 246 ± 64 gC m 2 for 0–10 cm, respectively). Expected general trends in soil OC indicate that changes could be detectable after 2–15 yr with 100 samples if changes occurred in the upper 10 cm of stone-poor soils. Error propagation analyses showed that in undisturbed soils with low stone contents, OC concentrations contributed most to OC stock variability while BD and fine earth fraction were more important in upper soil layers of croplands and in stone rich soils. Though the calculation of OC stocks based on equivalent soil masses slightly decreases the chance to detect changes with time at most sites except for the croplands, it is still recommended to account for changing bulk densities with time. Application of PTF for the estimation of bulk densities caused considerable underestimation of total variances of OC stocks if the error associated with the PTF was not accounted for, which rarely is done in soil inventories. Direct measurement of all relevant parameters approximately every 10 yr is recommended for repeated soil OC inventories.
How accurately can soil organic carbon stocks and stock changes be quantified by soil inventories?
M. Schrumpf,E. D. Schulze,K. Kaiser,J. Schumacher
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-723-2011
Abstract: Precise determination of changes in organic carbon (OC) stocks is prerequisite to understand the role of soils in the global cycling of carbon and to verify changes in stocks due to management. A large dataset was collected to form base to repeated soil inventories at 12 CarboEurope sites under different climate and land-use, and with different soil types. Concentration of OC, bulk density (BD), and fine earth fraction were determined to 60 cm depth at 100 sampling points per site. We investigated (1) time needed to detect changes in soil OC, assuming future re-sampling of 100 cores; (2) the contribution of different sources of uncertainties to OC stocks; (3) the effect of OC stock calculation on mass rather than volume base for change detection; and (4) the potential use of pedotransfer functions (PTF) for estimating BD in repeated inventories. The period of time needed for soil OC stocks to change strongly enough to be detectable depends on the spatial variability of soil properties, the depth increment considered, and the rate of change. Cropland sites, having small spatial variability, had lower minimum detectable differences (MDD) with 100 sampling points (105 ± 28 kg C m 2 for the upper 10 cm of the soil) than the grassland (206 ± 64 kg C m 2) and forest (246 ± 64 kg C m 2) sites. Expected general trends in soil OC indicate that changes could be detectable after 2–15 years with 100 samples if changes occurred in the upper 10 cm of stone-poor soils. Error propagation analyses showed that in undisturbed soils with low stone contents, OC concentrations contributed most to OC stock variability while BD and fine earth fraction were more important in upper soil layers of croplands and in stone rich soils. Though the calculation of OC stocks based on equivalent soil masses slightly decreases the chance to detect changes with time at most sites except for the croplands, it is still recommended to account for changing bulk densities with time. Application of PTF for the estimation of bulk densities caused considerable underestimation of total variances of OC stocks if the error associated with the PTF was not accounted for, which rarely is done in soil inventories. Direct measurement of all relevant parameters approximately every 10 years is recommended for repeated soil OC inventories.
Development of environmentally friendly cast alloys and composites. High zinc Al-base cast alloys
W.K. Krajewski,J. Buras,H. Haberl,P. Schumacher
Archives of Foundry Engineering , 2010,
Abstract: This work is devoted to grain refinement of the foundry Al-20 wt% Zn (AlZn20) alloy, aiming at improving ductility of the sand-cast alloy The melted alloy was inoculated using traditional AlTi5B1 (TiBAl) and AlTi3C0.15 (TiCAl) master alloys and newly introduced (Zn,Al)-Ti3 one. The performed structural examinations showed out significant increasing of the grain population of the inoculated alloy and plas-ticity increase represented by elongation. The high damping properties of the initial alloy, measured using an ultrasonic Olympus Epoch XT device, are basicly preserved after inoculation. Also tensile strength preserves its good values, while elongation shows an increase – which are beneficials of the employed grain-refining process.
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