176 research outputs found
Pressure Induced Charge Disproportionation in LaMnO
We present a total energy study as a function of volume in the cubic phase of
LaMnO. A charge disproportionated state into planes of
MnO/MnO was found. It is argued that the pressure
driven localisation/delocalisation transition might go smoothly through a
region of Mn and Mn coexistence.Comment: 3 pages, 1 figure, Conference Proceedings: Nanospintronics: Design
and Realization (Kyoto, Japan 24-28 May, 2004
Free-Flight Trajectory Simulation of the ADEPT Sounding Rocket Test Using CFD
A computational study of the Adaptive Deployable Entry and Placement Technology (ADEPT) Sounding Rocket (SR-1) Test is presented using the US3D flow solver. ADEPT SR-1 is intended, in part, to assess the dynamic stability of this entry vehicle architecture. Given that no dynamic stability data exists for the ADEPT geometry, a limited ballistic range campaign has been performed to characterize the vehicle's stability characteristics pre-flight for Mach numbers between 1.21 and 2.5. Here, this data is used to assess the accuracy of US3D's free-flight CFD capability. Computed trajectories from US3D and experimental data show that the flow solver compares well in vehicle oscillation frequency, downrange distance, and oscillatory amplitude during high Mach number flight (Mavg = 2.36). For Mach numbers below 1.5, the solver under predicts total angle-of-attack by an average of 16%, but compares well in oscillatory frequency and downrange distance. Additionally, a capability for simulating the trajectory of the flight article through the atmosphere using CFD is presented. This capability couples US3D's free-flight capability to an atmosphere model that accounts for changes in free-stream density and temperature as the vehicle descends. Two simulations for the purpose of demonstrating the capability and viability of this approach are applied to SR-1 flight article, and some unique challenges are discussed
High-Yielding Corn Response to Applied Phosphorus, Potassium, and Sulfur in Nebraska
Nutrient management recommendations may change as yield levels and efficiency of crop production increase. Recommendations for P, K, and S were evaluated using results from 34 irrigated corn (Zea mays L.) trials conducted in diverse situations across Nebraska. The mean yield was 14.7 Mg ha-1 with adequate fertilizer applied. Th e median harvest index values were 0.52, 0.89, 0.15, and 0.56 for biomass, P, K, and S, respectively. Median grain yields were 372, 49, and 613 kg kg-1 of above-ground plant uptake of P, K, and S, respectively. The estimated critical Bray-1 P level for corn response to 20 kg P ha-1 was 20 mg kg-1 when the previous crop was corn compared with 10 mg kg-1 when corn followed soybean [Glycine max (L.) Merr.]. Soil test K was generally high with only three site-years kg-1. Over all trials, application of 40 kg K ha-1 resulted in a 0.2 Mg ha-1 mean grain yield decrease. Application of 22 kg S ha-1 did not result in significant yield increase in any trial. Soil test results accounted for twice as much variation in nutrient uptake when soil organic matter (SOM) and pH were considered in addition to the soil test nutrient values. The results indicate a need to revise the current recommendation for P, to maintain the current K and S recommendations, and to use SOM and pH in addition to soil test nutrient values in estimating applied nutrient requirements for irrigated high yield corn production
Cover Crop Effect on Subsequent Wheat Yield in the Central Great Plains
Crop production systems in the water-limited environment
of the semiarid central Great Plains may not have potential to
profitably use cover crops because of lowered subsequent wheat
(Triticum asestivum L.) yields following the cover crop. Mixtures
have reportedly shown less yield-reducing effects on subsequent
crops than single-species plantings. This study was conducted
to determine winter wheat yields following both mixtures
and single-species plantings of spring-planted cover crops. The
study was conducted at Akron, CO, and Sidney, NE, during
the 2012–2013 and 2013–2014 wheat growing seasons under
both rainfed and irrigated conditions. Precipitation storage
efficiency before wheat planting, wheat water use, biomass, and
yield were measured and water use efficiency and harvest index
were calculated for wheat following four single-species cover
crops (flax [Linum usitatissimum L.], oat [Avena sativa L.], pea
[Pisum sativum ssp. arvense L. Poir], rapeseed [Brassica napus
L.]), a 10-species mixture, and a fallow treatment with proso
millet (Panicum miliaceum L.) residue. There was an average 10%
reduction in wheat yield following a cover crop compared with
following fallow, regardless of whether the cover crop was grown
in a mixture or in a single-species planting. Yield reductions
were greater under drier conditions. The slope of the wheat
water use–yield relationship was not significantly different for
wheat following the mixture (11.80 kg ha–1 mm–1) than for wheat
following single-species plantings (12.32–13.57 kg ha–1 mm–1).
The greater expense associated with a cover crop mixture
compared with a single species is not justified
Study of the Negative Magneto-Resistance of Single Proton-Implanted Lithium-Doped ZnO Microwires
The magneto-transport properties of single proton-implanted ZnO and of
Li(7\%)-doped ZnO microwires have been studied. The as-grown microwires were
highly insulating and not magnetic. After proton implantation the Li(7\%) doped
ZnO microwires showed a non monotonous behavior of the negative
magneto-resistance (MR) at temperature above 150 K. This is in contrast to the
monotonous NMR observed below 50 K for proton-implanted ZnO. The observed
difference in the transport properties of the wires is related to the amount of
stable Zn vacancies created at the near surface region by the proton
implantation and Li doping. The magnetic field dependence of the resistance
might be explained by the formation of a magnetic/non magnetic heterostructure
in the wire after proton implantation.Comment: 6 pages with 5 figure
Exchange interaction and its tuning in magnetic binary chalcogenides
Using a first-principles Green's function approach we study magnetic
properties of the magnetic binary chalcogenides Bi2Te3, Bi2Se3, and Sb2Te3. The
magnetic coupling between transition-metal impurities is long-range, extends
beyond a quintuple layer, and decreases with increasing number of d electrons
per 3d atom. We find two main mechanisms for the magnetic interaction in these
materials: the indirect exchange interaction mediated by free carriers and the
indirect interaction between magnetic moments via chalcogen atoms. The
calculated Curie temperatures of these systems are in good agreement with
available experimental data. Our results provide deep insight into magnetic
interactions in magnetic binary chalcogenides and open a way to design new
materials for promising applications
High-Yielding Corn Response to Applied Phosphorus, Potassium, and Sulfur in Nebraska
Nutrient management recommendations may change as yield levels and efficiency of crop production increase. Recommendations for P, K, and S were evaluated using results from 34 irrigated corn (Zea mays L.) trials conducted in diverse situations across Nebraska. The mean yield was 14.7 Mg ha-1 with adequate fertilizer applied. Th e median harvest index values were 0.52, 0.89, 0.15, and 0.56 for biomass, P, K, and S, respectively. Median grain yields were 372, 49, and 613 kg kg-1 of above-ground plant uptake of P, K, and S, respectively. The estimated critical Bray-1 P level for corn response to 20 kg P ha-1 was 20 mg kg-1 when the previous crop was corn compared with 10 mg kg-1 when corn followed soybean [Glycine max (L.) Merr.]. Soil test K was generally high with only three site-years kg-1. Over all trials, application of 40 kg K ha-1 resulted in a 0.2 Mg ha-1 mean grain yield decrease. Application of 22 kg S ha-1 did not result in significant yield increase in any trial. Soil test results accounted for twice as much variation in nutrient uptake when soil organic matter (SOM) and pH were considered in addition to the soil test nutrient values. The results indicate a need to revise the current recommendation for P, to maintain the current K and S recommendations, and to use SOM and pH in addition to soil test nutrient values in estimating applied nutrient requirements for irrigated high yield corn production
Isospin properties of electric dipole excitations in 48Ca
Two different experimental approaches were combined to study the electric
dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold.
Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and
nearly mono-energetic linearly polarized photons with energies between 6.6 and
9.51 MeV provided strength distribution and parities, and an
(\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for
an isoscalar probe. The unexpected difference observed in the dipole response
is compared to calculations using the first-order random-phase approximation
and points to an energy-dependent isospin character. A strong isoscalar state
at 7.6 MeV was identified for the first time supporting a recent theoretical
prediction.Comment: 6 pages, 5 figures, as accepted in Phys. Lett.
Agronomic Potential of Using Precipitated Calcium Carbonate on Early Plant Growth and Soil Quality in the Intermountain West - Greenhouse Studies
Storage and management of large piles of precipitated calcium carbonate (PCC) from sugarbeet processing are a challenge in the western US. Potential uses of this product on surrounding agricultural lands in western NE, eastern WY and northeast CO requires an evaluation of chemical and agronomic impacts of PCC on soils and crop growth. A preliminary greenhouse study was conducted in Scottsbluff, NE using 10 soils from the 3 states. Soils were mixed with 11, 22, 33 and 44 Mg ha-1 rates of PCC to test the early plant growth of sugarbeet, corn, and dry bean in addition to determining soil chemical characteristics. Chemical analysis of PCC from the three processing factories indicates that PCC provides some nitrogen and phosphorus, in addition to some iron, depending on rate. Application of four rates of PCC to neutral to slightly alkali soils neither improved nor negatively impacted the soil chemical characteristics. Dry matter of the three crops after 7 weeks showed no significant effects of PCC. Future utilization of PCC in this region will require further research based on longterm investigations of possible effects of PCC on soil chemical characteristics and plant growth under field conditions
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