Three Single Wheel Machines for Traction and Soil Compaction Research

Three single wheel machines for traction and soil compaction research have been developed in recent years at the USDA-ARS National Soil Dynamics Laboratory.  The Traction Research Vehicle has been used extensively for soil bin traction and soil compaction experiments.  The vehicle uses feedback computer control to control tire dynamic load, forward velocity, inflation pressure, and in a given run, either travel reduction or net traction.  The all-terrain vehicle (ATV) tire single wheel machine has been used in determining traction and motion resistance characteristics of ATV tires in soil bins.  The ATV tire machine uses the forward velocity feedback computer control of the Traction Research Vehicle and uses deadweight loading for dynamic load.  Tire angular velocity is manually controlled by the operator using a joystick.  A single wheel traction research machine designed for use in the field has been developed, but computer control has not been completed

Local starburst galaxies and their descendants

Despite strong interest in the starburst (hereafter SB) phenomenon, the concept remains ill-defined. We use a strict definition of SB to examine the statistical properties of local SB and post-starburst (hereafter PB) galaxies. We also seek relationships to active galaxies. Potential SB galaxies are selected from the SDSS DR7 and their stellar content is analysed. We apply an age dependent dust attenuation correction and derive star formation rates (SFR), ages and masses of the young and old populations. The photometric masses nicely agree with dynamical masses derived from the H-alpha emission line width. To select SB galaxies, we use the birthrate parameter b=SFR/, requiring b>=3. The PB sample is selected from the citerion EW(Hdelta_abs)>=6 A. Only 1% of star-forming galaxies are found to be SB galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median SB age is 70 Myr, roughly independent of mass. The b-parameter strongly depends on burst age. Values close to b=60 are found at ages ~10 Myr, while almost no SBs are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L* galaxies is 5%, decreasing slowly with mass. The median mass fraction of the recent burst in the PB sample is 5-10%. The age-mass distribution of the progenitors of the PBs is bimodal with a break at log(M)~10.6 above which the ages are doubled. The SB and PB luminosity functions (hereafter LFs) follow each other closely until M_r~-21, when AGNs begin to dominate. The PB LF continues to follow the AGN LF while SB loose significance. This suggests that the number of luminous SBs is underestimated by about one dex at high luminosities, due to large amounts of dust and/or AGN blending. It also indicates that the SB phase preceded the AGN phase. We also discuss the conditions for global gas outflow caused by stellar feedback.Comment: Accepted for publication in Astronomy and Astrophysics. This is an extended, substantially revised and corrected version with partly modified conclusion

Journal of African Christian Biography: v. 2, no. 3

A publication of the Dictionary of African Christian Biography with U.S. offices located at the Center for Global Christianity and Mission at Boston University. This issue focuses on: 1. Agnes Okoh. 2. Self-Sacrificial Christian Pioneers of Uganda. 3. Apolo Kivebulaya. 4. Njangalia. 5. Spetume Florence. 6. Luwum. 7. Janani Jakaliya. 8. Anglican Church in Uganda. 9. Lamin Sanneh

Discrete Element Modeling (DEM) of Cone Penetration Testing on Soil With Varying Relative Soil Density

Modeling soil-tool interaction is essential for equipment design and performance evaluation on soil behavior responses under loading. Computational tools based on particle-based mechanics such as Discrete Element Modeling (DEM) and Smoothed Particle Hydrodynamics (SPH) have potential in modeling large strain soil dynamic behaviors from soil-tool interaction. The objective of this study is to validate the accuracy and robustness of DEM calibration methodology as it relates to soil deformation during cone penetration on varying initial soil relative density. The influence of factors such as DEM material properties and cone to particle size ratio on DEM cone penetration simulation will be investigated. The paper presents a comparison of DEM predicted cone penetration resistance and laboratory measured penetration data on Norfolk sandy loam. Soil mechanical behavior was modeled with Hertz-Mindlin (HM) contact stiffness model and a new coupled frictional law for static and rolling resistance coefficients. The DEM material properties were calibrated using residual strength from direct shear test. DEM simulations were performed using LIGGGHTS, open source DEM code. Cone penetrometer experiments using anÂASABE standard cone with 12.53 mm cone base diameter and 30-degree cone tip were used to validate the calibrated DEM model. DEM prediction of cone penetration resistance trend and steady state values were in close agreement with the laboratory measured data for relative density range from 5 to 30%. At higher dense states (relative density of 90%), DEM calibration requires further improvement

A Theoretical Approach for Determining Irregularities of the Bottom of the Tillage Layer Caused by Horizontal Axis Rotary Tillers

Horizontal axis rotary tillers produce irregularities in the tillage depth when they are inappropriately operated and constructed. In such cases, mixing and breaking of soil throughout the tillage layer is not uniform and some untilled ridges will remain at the bottom determining the effect of design and operational characteristics on the height of the resultant ridges at the bottom of the tillage layer. In this study, a method based on the derived geometrical relationships between the rotary tiller operational parameters was developed to determine heights of ridges occurring at the bottom of the tillage layer. The ridge heights can be calculated for various combinations of blade peripheral speed, forward travel speed, rotor radius, and the number of blades on one side of a rotary tiller flange. This method allows for the investigation of effects of rotary tiller operational and constructional properties of horizontal axis rotary tillers on the ridge heights at the bottom of the tillage layers. The results obtained using this method show that the heights of ridges at the bottom of the tillage layer increase with increases in forward travel speed and decrease with increases in blade peripheral speed, rotor radius, and the number of blades on one side of a flange

Habitable Climate Scenarios for Proxima Centauri b With a Dynamic Ocean

The nearby exoplanet Proxima Centauri b will be a prime future target for characterization, despite questions about its retention of water. Climate models with static oceans suggest that an Earth-like Proxima b could harbor a small dayside region of surface liquid water at fairly warm temperatures despite its weak instellation. We present the first 3-dimensional climate simulations of Proxima b with a dynamic ocean. We find that an ocean-covered Proxima b could have a much broader area of surface liquid water but at much colder temperatures than previously suggested, due to ocean heat transport and depression of the freezing point by salinity. Elevated greenhouse gas concentrations do not necessarily produce more open ocean area because of possible dynamic regime transitions. For an evolutionary path leading to a highly saline present ocean, Proxima b could conceivably be an inhabited, mostly open ocean planet dominated by halophilic life. For an ocean planet in 3:2 spin-orbit resonance, a permanent tropical waterbelt exists for moderate eccentricity. Simulations of Proxima Centauri b may also be a model for the habitability of planets receiving similar instellation from slightly cooler or warmer stars, e.g., in the TRAPPIST-1, LHS 1140, GJ 273, and GJ 3293 systems.Comment: Submitted to Astrobiology; 38 pages, 12 figures, 5 table