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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 135 (1991), S. 31-41 
    ISSN: 1573-5036
    Keywords: penetrometer resistance ; plant species ; root diameter ; root elongation ; seedling roots ; soil strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The abilities of seedling roots of twenty-two plant species to penetrate a strong growth medium were compared under controlled conditions. Seedlings were grown for 10 days in compression chambers filled with siliceous sandy soil at 0.2 kg kg−1 water content and mean penetrometer resistance of 4.2 MPa. Root elongation and thickening were measured after growth. The results show that soil strength reduced the elongation of roots of all plant species by over 90% and caused the diameters of the roots to increase compared with control plants grown in vermiculite (0 MPa resistance). Differences in both root elongation and root diameter were observed among plant species. Generally, the roots of dicotyledons (with large diameters) penetrated the strong medium more than graminaceous monocotyledons (with smaller diameters). There was a significant positive correlation (r=0.78, p〈0.05) between root diameter and elongation over all the species in the stressed plants. The species were ranked according to the relative root elongation and relative root thickening. Based on this ranking, lupin (Lupinus angustifolius), medic (Medicago scutelata) and faba bean (Vicia faba) were the species with the greatest thickening and elongation while wheat (Triticum aestivum), rhodesgrass (Chloris gayana) and barley (Hordeum vulgare) had the least. The weight of the seeds did not seem to influence either the thickening or elongation of the roots.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5036
    Keywords: plant species ; polyethylene glycol (PEG) ; osmotic potential ; osmotic stress ; root elongation ; root diameter ; seedling roots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seedling roots of ten plant species were grown in siliceous sand wetted with solutions of polyethylene glycol (PEG) of MW=20,000 with osmotic potentials of 0.0, − 0.25, − 0.5 and − 1.0 MPa. After 48 h growth under controlled lighting, root elongation and root diameter were measured. Root elongation of all species was reduced by increasing levels of external osmotic stress. Dicotyledonous species were affected more than monocotyledons at potentials of − 0.25 and − 0.5 MPa but less at − 1.0 MPa. Root diameters of all the species were thicker than those of the unstressed at potentials of − 0.25 and − 0.5 MPa. At a potential of − 1.0 MPa the dicotyledons were still thicker, though not by as much as they were at − 0.25 and − 0.5 MPa. The monocotyledons, in contrast, were thinner at − 1.0 MPa. There was a significant positive correlation (r=0.81, p 〈0.01) between root diameter and root elongation at − 1.0 MPa potential. Species were ranked according to the relative root elongation (RRE) and relative root thickness (RRT) at the highest level of stress (− 1.0 MPa). In both rankings dicotyledonous species were in the top ranks and monocotyledous species were in lower positions. The results are compared with those for the elongation and thickening of roots growing against external mechanical stress obtained in a previous study. There were good correlations between the responses observed for the two types of external stress. The implications of these findings are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5036
    Keywords: penetration resistance ; plant species ; root diameter ; soil compaction ; soil strength ; tillage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to evaluate the influence of root diameter on the ability of roots of eight plant species to penetrate a compacted subsoil below a tilled layer. The soil was a fine sandy loam red-brown earth with a soil strength of about 3.0 MPa (at water content of 0.13 kg kg-1, corresponding to 0.81 plastic limit) at the base of a tilled layer. Relative root diameter (RRD), which was calculated as the ratio of the mean diameters of roots of plants grown in compacted soil to the mean diameters of those from uncompacted soil, was used to compare the sensitivity of roots to thicken under mechanical stress. Diameters of root tips of plants grown in soil with a compacted layer were consistently larger than those from uncompacted soil. Tap-rooted species generally had bigger diameters and RRDs than fibrous-rooted species. A higher proportion of thicker roots penetrated the strong layer at the interface than thinner roots. There were differences between plant species in the extent to which root diameter increased in response to the compaction. The roots which had larger RRD also tended to have higher penetration percentage. The results suggest that the size of a root has a significant influence on its ability to penetrate strong soil layers. It is suggested that this could be related to the effects which root diameter may have on root growth pressure and on the mode of soil deformation during penetration.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 157 (1993), S. 313-318 
    ISSN: 1573-5036
    Keywords: maximum growth pressure ; lupins ; Lupinus albus ; root diameter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The maximum axial growth pressure of roots of Lupinus albus cv Lublanc and Lupinus albus cv Lunoble (spring and autumn-sown cultivars respectively) were measured. The mean values were not significantly different with an overall mean value of 645 kPa. This value is not unusually large for plant roots and is surprising because lupins are known for their ability to penetrate strong soils. The autumn cultivar had a significantly greater maximum elongation rate under zero mechanical impedance than the spring cultivar. The impeded diameters were also larger in the autumn cultivars.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2018-06-28
    Description: A summary of recent composite structures and materials research at NASA Langley Research Center is presented. Fabrication research to develop low-cost automated robotic fabrication procedures for thermosetting and thermoplastic composite materials, and low-cost liquid molding processes for preformed textile materials is described. Robotic fabrication procedures discussed include ply-by-ply, cure-on-the-fly heated placement head and out-of-autoclave electron-beam cure methods for tow and tape thermosetting and thermoplastic materials. Liquid molding fabrication processes described include Resin Film Infusion (RFI), Resin Transfer Molding (RTM) and Vacuum-Assisted Resin Transfer Molding (VARTM). Results for a full-scale composite wing box are summarized to identify the performance of materials and structures fabricated with these low-cost fabrication methods.
    Keywords: Mechanical Engineering
    Type: Low Cost Composite Structures and Cost Effective Application of Titanium Alloys in Military Platforms; 17-1 - 17-11; RTO-MP-069(II)
    Format: text
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  • 6
    Publication Date: 2018-06-05
    Description: Gas turbine engines are currently being designed to have increased performance, lower weight and manufacturing costs, and higher reliability. Consequently, turbomachinery components, such as turbine and compressor blades, have designs that are susceptible to new vibration problems and eventual in-service failure due to high-cycle fatigue. To address this problem, researchers at the NASA Glenn Research Center are developing and testing innovative active blade vibration control concepts. Preliminary results of using an active blade vibration control system, involving a rotor supported by an active magnetic bearing in Glenn's Dynamic Spin Rig, indicate promising results (see the photograph). Active blade vibration control was achieved using feedback of blade strain gauge signals within the magnetic bearing control loop. The vibration amplitude was reduced substantially (see the graphs). Also, vibration amplitude amplification was demonstrated; this could be used to enhance structural mode identification, if desired. These results were for a nonrotating two-bladed disk. Tests for rotating blades are planned. Current and future active blade vibration control research is planned to use a fully magnetically suspended rotor and smart materials. For the fully magnetically suspended rotor work, three magnetic bearings (two radial and one axial) will be used as actuators instead of one magnetic bearing. This will allow additional degrees of freedom to be used for control. For the smart materials work, control effectors located on and off the blade will be considered. Piezoelectric materials will be considered for on-the-blade actuation, and actuator placement on a stator vane, or other nearby structure, will be investigated for off-the-blade actuation. Initial work will focus on determining the feasibility of these methods by performing basic analysis and simple experiments involving feedback control.
    Keywords: Mechanical Engineering
    Type: Research and Technology 2002; NASA/TM-2003-211990
    Format: application/pdf
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  • 7
    Publication Date: 2019-07-13
    Description: NASA Glenn Research Center (GRC) has developed a fully suspended magnetic bearing system for the Dynamic Spin Rig (DSR) that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust bearing and the associated control system were integrated into the DSR to provide noncontact magnetic suspension and mechanical excitation of the 35 lb vertical rotor with blades to induce turbomachinery blade vibration. A simple proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked very well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, and energy savings for the system. The test results of a variety of controllers we demonstrated up to the rig's maximum allowable speed of 10,000 rpm are shown.
    Keywords: Mechanical Engineering
    Type: ISMB-8-Paper-0160 , 8th International Symposium on Magnetic Bearings; Aug 26, 2002 - Aug 28, 2002; Mito; Japan
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-13
    Description: Most magnetic bearing control schemes use a bias current with a superimposed control current to linearize the relationship between the control current and the force it delivers. With the existence of the bias current, even in no load conditions, there is always some power consumption. In aerospace applications, power consumption becomes an important concern. In response to this concern, an alternative magnetic bearing control method, called Adaptive Variable Bias Control (AVBC), has been developed and its performance examined. The AVBC operates primarily as a proportional-derivative controller with a relatively slow, bias current dependent, time-varying gain. The AVBC is shown to reduce electrical power loss, be nominally stable, and provide control performance similar to conventional bias control. Analytical, computer simulation, and experimental results are presented in this paper.
    Keywords: Mechanical Engineering
    Type: NASA/TM-1998-206975 , NAS 1.15:206975 , E-11127 , 1998 American Controls Conference; Jun 24, 1998 - Jun 26, 1998; Philadelphia, PA; United States
    Format: application/pdf
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