ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Mechanics of root elongation and the effects of 3,5-diiodo-4-hydroxybenzoic acid (DIHB) (1987)
    Springer
    Plant and soil 99 (1987), S. 211-218 
    Details
    ISSN: 1573-5036
    Keywords: Aeration ; Barley ; 3,5-Diiodo-4-hydroxybenzoic acid ; Extensibility ; Mechanical impedance ; Osmotic potential ; Pea ; Root elongation ; Wheat ; Young's modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This paper reports the results of two series of experiments. In the first the effects of DIHB on the rate of root elongation were compared on unstressed roots and on roots stressed by mechanical impedance and by inadequate levels of aeration. Barley plants were grown in beds of small glass spheres through which nutrient solution was circulated. Mechanical impedance of 25 kPa was applied by subjecting the beds to a confining pressure. Inadequate aeration was obtained by reducing the oxygen concentration in the nutrient solution to 5%. The second series examined possible effects of DIHB on the elastic modulus of root tips of wheat and pea. Elastic modulus gives an indication of the behaviour of roots in structured soil where penetration of peds can be limited by the buckling of root tips. The elastic modulus was measured in experiments of the static cantilever type on roots previously immersed in solutions of polyethylene glycol of different osmotic potential. Elastic modulus measurements can also detect any changes in turgor pressure and wilting characteristics of roots and can therefore help to identify the mechanisms of action of DIHB. DIHB caused increases in root elongation relative to controls in all cases: 26±5.7% in unstressed roots, 14±6.4% in mechanically impeded roots and 54±9.8% in roots growing in 5% oxygen. DIHB had no effect on the elastic modulus, osmotic or turgor pressure of the roots. It is concluded that DIHB acts by modifying the cell wall extensibility factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370868
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    The behaviour of roots encountering cracks in soil (1984)
    Springer
    Plant and soil 79 (1984), S. 11-28 
    Details
    ISSN: 1573-5036
    Keywords: Beta distribution ; Buckling ; Cracks ; Crack width ; Lateral roots ; Pea ; Penetration ; Penetrometer ; Rape ; Remoulded soil ; Roots ; Safflower ; Seminal axes ; Soil strength ; Undisturbed soil ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary It is shown that probabilities of root penetration across cracks in soil can be calculated effectively using a mathematical model involving root stress and soil distributions and penetrometer/root stress ratios. Penetration criteria are developed, and it is found that the effective penetrometer/root stress ratios take values of about 4 for crack widths smaller than about 2 mm and about 8 for wider cracks. Root swelling does not appear to contribute significantly to the probability of root penetration through any effect on root buckling stress. Suggestions are made for further work on the effects of soil structure and strength on root behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02182140
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Model experiments on the behaviour of roots at the interface between a tilled seed-bed and a compacted sub-soil (1986)
    Springer
    Plant and soil 95 (1986), S. 123-133 
    Details
    ISSN: 1573-5036
    Keywords: Aggregate ; Compaction pan ; Penetrometer ; Root penetration ; Seed-bed ; Soil strength ; Triticum aestivum ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary When elongating seminal roots of developing plants reach the base of a tilled seedbed, they often encounter a layer of dense, strong untilled soil. At this interface, they may be deflected horizontally and instead of penetrating the sub-soil, they may form a horizontal mat of roots at the base of the seed-bed. If this occurs, the plants are unable to absorb the reserves of water in the sub-soil, and are very sensitive to short periods of drought. Model experiments were done with artificial sub-soil layers having a range of strengths and with artificial seed-beds having sieved soil aggregates in the 4–7.7, 2–4 and 1–2 mm size ranges. Roots of wheat were grown through the aggregate beds and the proportions of roots which penetrated into the sub-soil were investigated as functions of sub-soil strength and diameter of the aggregates in the seed-bed. The proportion penetrating was found to decrease exponentially with sub-soil strength. The rate of decrease was similar for the 2–4 and 1–2 mm aggregates but was greater for the 4–6.7 mm aggregates. It is concluded that, provided that the roots of different plant species behave similarly, the base of the seed-bed should be composed of fine aggregates and that the penetrometer strength of the underlying untilled sub-soil should not exceed 0.4 MPa for plants with a single seminal axis or 3 MPa for plants such as wheat with 4 seminal axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378858
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Model experiments on the behaviour of roots at the interface between a tilled seed-bed and a compacted sub-soil (1986)
    Springer
    Plant and soil 95 (1986), S. 149-161 
    Details
    ISSN: 1573-5036
    Keywords: Compaction pan Earthworms ; Pea ; Pisum sativum ; Root channels ; Root entry ; Trematotropism ; Triticum aestivum ; Tunnels ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Roots which grow down through a seed-bed and encounter a strong, untilled sub-soil beneath may be unable to penetrate the sub-soil and may be deflected horizontally. They will continue to grow horizontally along the top of the sub-soil either until the seed-bed dries out and the roots wilt and cease elongating, or until they find some path of low resistance down through the sub-soil. Such paths are often cylindrical biopores such as earthworm tunnels or channels left after the decay of previous root systems. Model experiments were done with artificial impenetrable sub-soils containing arrays of round holes of various diameters. Roots of pea and wheat were grown down through beds of aggregates to encounter the artificial sub-soils at random positions. The roots were deflected horizontally until they encountered the vertical holes. The proportions of roots which entered the holes were found to decrease with decreasing hole diameter. Computer simulation studies were done to investigate some aspects of roots encountering impenetrable sub-soils containing random arrays of round holes. The distances that randomly-deflected roots would have to travel before encountering holes were studied as functions of hole diameter and hole density. The experimental results were combined and compared with the results from the computer simulations. It was found that the numbers of roots encountering holes within certain distances in practice were not significantly different from those simulated on the basis of random chance. Therefore there was no evidence for the roots sensing and growing preferentially towards the holes (trematotropism) in the well-aerated system used in the experiments. However, limited evidence shows that the possibility of trematotropism cannot be ruled out for poorly-aerated systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378860
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The behaviour of roots encountering cracks in soil (1984)
    Springer
    Plant and soil 77 (1984), S. 141-149 
    Details
    ISSN: 1573-5036
    Keywords: Cracks ; Crack width ; Lateral roots ; Pea ; Penetration ; Penetrometer ; Rape ; Remoulded soil ; Roots ; Safflower ; Seminal axes ; Soil strength ; Undisturbed soil ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Experimental methods are described for observing the behaviour of roots encountering cracks in soil. The proportions of roots which enter a second soil block after crossing a crack of known width were measured. Soil strength was measured with a penetrometer. Results are presented for the proportions of seminal roots of wheat and primary lateral roots of pea which enter moulded soil of various strengths after crossing cracks. Results are also presented for the proportions of seminal roots of pea, rape and safflower which enter undisturbed soil after crossing cracks. It was found that, in all cases, the proportion of roots penetrating the second soil block decreased with increasing crack width and increasing soil strength. Also, a smaller proportion of thinner roots penetrated the second soil block than thicker roots under similar conditions. Root diameter in the cracks was influenced by both crack width and soil strength, and an empirical equation is presented to describe this effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02182918
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    facet.materialart.
    Unknown
    New materials drive high-performance aircraft (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: This report shows how advanced composite materials and new processing methods are enabling lighter, lower cost aircraft structures. High-temperature polymers research will focus on systems capable of 50,000 to 100,000 hours of operation in the 212-400 F temperature range. Prospective materials being evaluated include high-temperature epoxies, toughened bismaleimides, cyanates, thermoplastics, polyimides and other polymers.
    Keywords: COMPOSITE MATERIALS
    Type: Aerospace America (ISSN 0740-722X); 30; 9, Se
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 7
    facet.materialart.
    Unknown
    Characterization of multiaxial warp knit composites (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The objectives were to characterize the mechanical behavior and damage tolerance of two multiaxial warp knit fabrics to determine the acceptability of these fabrics for high performance composite applications. The tests performed included compression, tension, open hole compression, compression after impact and compression-compression fatigue. Tests were performed on as-fabricated fabrics and on multi-layer fabrics that were stitched together with either carbon or Kevlar stitching yarn. Results of processing studies for vacuum impregnation with Hercules 3501-6 epoxy resin and pressure impregnation with Dow Tactix 138/H41 epoxy resin and British Petroleum BP E905L epoxy resin are presented.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 589-619
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
    Unknown
    Resin transfer molding of textile preforms for aircraft structural applications (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA LaRC is conducting and supporting research to develop cost-effective fabrication methods that are applicable to primary composite aircraft structures. One of the most promising fabrication methods that has evolved is resin transfer molding (RTM) of dry textile material forms. RTM has been used for many years for secondary structures, but has received increased emphasis because it is an excellent method for applying resin to damage-tolerant textile preforms at low cost. Textile preforms based on processes such as weaving, braiding, knitting, stitching, and combinations of these have been shown to offer significant improvements in damage tolerance compared to laminated tape composites. The use of low-cost resins combined with textile preforms could provide a major breakthrough in achieving cost-effective composite aircraft structures. RTM uses resin in its lowest cost form, and storage and spoilage costs are minimal. Near net shape textile preforms are expected to be cost-effective because automated machines can be used to produce the preforms, post-cure operations such as machining and fastening are minimized, and material scrap rate may be reduced in comparison with traditional prepreg molding. The purpose of this paper is to discuss experimental and analytical techniques that are under development at NASA Langley to aid the engineer in developing RTM processes for airframe structural elements. Included are experimental techniques to characterize preform and resin behavior and analytical methods that were developed to predict resin flow and cure kinetics.
    Keywords: COMPOSITE MATERIALS
    Type: FAA, Ninth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Volume 3; p 1303-1315
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 9
    facet.materialart.
    Unknown
    RTM: Cost-effective processing of composite structures (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Resin transfer molding (RTM) is a promising method for cost effective fabrication of high strength, low weight composite structures from textile preforms. In this process, dry fibers are placed in a mold, resin is introduced either by vacuum infusion or pressure, and the part is cured. RTM has been used in many industries, including automotive, recreation, and aerospace. Each of the industries has different requirements of material strength, weight, reliability, environmental resistance, cost, and production rate. These requirements drive the selection of fibers and resins, fiber volume fractions, fiber orientations, mold design, and processing equipment. Research is made into applying RTM to primary aircraft structures which require high strength and stiffness at low density. The material requirements are discussed of various industries, along with methods of orienting and distributing fibers, mold configurations, and processing parameters. Processing and material parameters such as resin viscosity, perform compaction and permeability, and tool design concepts are discussed. Experimental methods to measure preform compaction and permeability are presented.
    Keywords: COMPOSITE MATERIALS
    Type: NASA, Washington, Technology 2001: The Second National Technology Transfer Conference and Exposition, Volume 2; p 12-21
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 10
    facet.materialart.
    Unknown
    Performance of resin transfer molded multiaxial warp knit composites (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Composite materials that are subjected to complex loads have traditionally been fabricated with multidirectionally oriented prepreg tape materials. Some of the problems associated with this type of construction include low delamination resistance, poor out-of-plane strength, and labor intensive fabrication processes. Textile reinforced composites with through-the-thickness reinforcement have the potential to solve some of these problems. Recently, a relatively new class of noncrimp fabrics designated as multiaxial warp knits have been developed to minimize some of the high cost and damage tolerance concerns. Multiple stacks of warp knit fabrics can be knitted or stitched together to reduce layup labor cost. The through-the-thickness reinforcement can provide significant improvements in damage tolerance and out-of-plane strength. Multilayer knitted/stitched preforms, in conjunction with resin transfer molding (RTM), offer potential for significant cost savings in fabrication of primary aircraft structures. The objectives of this investigation were to conduct RTM processing studies and to characterize the mechanical behavior of composites reinforced with three multiaxial warp knit fabrics. The three fabrics investigated were produced by Hexcel and Milliken in the United States, and Saerbeck in Germany. Two resin systems, British Petroleum E9O5L and 3M PR 500, were characterized for RTM processing. The performance of Hexcel and Milliken quasi-isotropic knitted fabrics are compared to conventional prepreg tape laminates. The performance of the Saerbeck fabric is compared to uniweave wing skin layups being investigated by Douglas Aircraft Company in the NASA Advanced Composites Technology (ACT) program. Tests conducted include tension, open hole tension, compression, open hole compression, and compression after impact. The effects of fabric defects, such as misaligned fibers and gaps between tows, on material performance are also discussed. Estimated material and labor cost savings are projected for the Saerbeck fabric as compared to uniweave fabric currently being used by Douglas in the NASA ACT wing development program.
    Keywords: COMPOSITE MATERIALS
    Type: Third NASA Advanced Composites Technology Conference, Volume 1, Part 1; p 231-261
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...