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1

Electronic Resource

Equilibrium behavior of symmetric ABA triblock copolymer melts (1999)

Matsen, M. W. ; Thompson, R. B.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 111 (1999), S. 7139-7146

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Melts of ABA triblock copolymer molecules with identical end blocks are examined using self-consistent field theory (SCFT). Phase diagrams are calculated and compared with those of homologous AB diblock copolymers formed by snipping the triblocks in half. This creates additional end segments which decreases the degree of segregation. Consequently, triblock melts remain ordered to higher temperatures than their diblock counterparts. We also find that middle-block domains are easier to stretch than end-block domains. As a result, domain spacings are slightly larger, the complex phase regions are shifted towards smaller A-segment compositions, and the perforated-lamellar phase becomes more metastable in triblock melts as compared to diblock melts. Although triblock and diblock melts exhibit very similar phase behavior, their mechanical properties can differ substantially due to triblock copolymers that bridge between otherwise disconnected A domains. We evaluate the bridging fraction for lamellar, cylindrical, and spherical morphologies to be about 40%–45%, 60%–65%, and 75%–80%, respectively. These fractions only depend weakly on the degree of segregation and the copolymer composition. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.480006

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2

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Laboratory nondestructive evaluation technology for materials characterization (1996)

Thompson, R. B.

Springer

Journal of nondestructive evaluation 15 (1996), S. 163-176

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ISSN: 1573-4862

Keywords: Ultrasonic techniques ; magnetic techniques ; dislocations ; grain size ; creep ; fatigue ; hydrogen attack

Source: Springer Online Journal Archives 1860-2000

Topics: Electrical Engineering, Measurement and Control Technology , Mathematics

Notes: Abstract This paper summarizes advances in ultrasonic and magnetic technologies for materials characterization that have recently occurred in the research laboratory and appear to have the potential to impact technology gaps of concern to the energy production industry. Included are discussions of the possibilities that one can characterize structure, such as grain size and dislocations, properties, such as fracture toughness, degradation mechanisms, such as creep, fatigue, and hydrogen attack, as well as the stresses which drive many of the degradation mechanisms. Throughout the discussions, careful attention is given to differentiating those quantities which are fundamentally related to the nondestructive evaluation response, and those which are related by empirical correlations. Included is a discussion of future work needed to further develop these technologies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00732043

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3

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Production and water use in lettuces under variable water supply (1996)

Gallardo, M. ; Jackson, L. E. ; Schulbach, K. ; [et al.]

Springer

Irrigation science 16 (1996), S. 125-137

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ISSN: 1432-1319

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m−2 mm−1 and for fresh weight of 48 g m−2 mm−1 . For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02215620

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4

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Production and water use in lettuces under variable water supply (1996)

Gallardo, M. ; Jackson, L. E. ; Schulbach, K. ; [et al.]

Springer

Irrigation science 16 (1996), S. 125-137

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ISSN: 1432-1319

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m–2 mm–1 and for fresh weight of 48 g m–2 mm–1. For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002710050011

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5

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Performance evaluation of the Golay code pulse compression technique (1996)

Jeong, P. ; Thompson, R. B. ; Kim, Y. H.

Springer

Research in nondestructive evaluation 8 (1996), S. 125-147

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ISSN: 1432-2110

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The Center for NDE, Iowa State University, has developed a laboratory prototype Golay code pulse compression system and tested it on a variety of materials. The performance of the system was evaluated in terms of signal-to-noise ratio enhancement (SNRE), resolution, and computation speed. The system's error sources also were discussed. The Golay code pulse compression was simulated on a computer and demonstrated the effective noise suppression. In addition, an equivalent pulse of the Golay code (delta-like pulse) was derived theoretically using a simple ultrasonic inspection model, which demonstrated its equivalence on the output correlated signal. Overall, the pulse compression technique extended the detection range for a given peak power and considerably reduced the system'swhite noise, hence providing enhanced signal-to-noise ratios (SNRs). An average of 30 dB improvement in SNR was obtained from highly energy-absorbent materials such as rubber, plastics, corks (insulation materials), and thick composites using the Golay codes of up to 512 bits. However, the technique did not effectively reduce coherent scattering noises from the coarse grain boundaries in cast stainless steels, Inconel weld metal, and material lay-ups in thin composites. Furthermore, it was found that, depending upon the system's hardware capabilities, the overall performance could be degraded considerably.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02433945

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6

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Pulse-labelling a cover crop with 13C to follow its decomposition in soil under field conditions (1996)

Thompson, R. B.

Springer

Plant and soil 180 (1996), S. 49-55

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ISSN: 1573-5036

Keywords: cover crop ; 13C ; carbon labelling ; decomposition ; residue

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract A preliminary study was conducted using the stable isotope 13C to pulse label the cover crop phacelia (Phacelia tanacetifolia) to examine its decomposition in soil, under field conditions. Plants were grown, in pots, in the greenhouse and after four weeks of growth were labelled with 13CO2 six times, at 1–2 week intervals. A single chamber was placed over the pots, and 13CO2 was generated, inside the chamber, by injecting lactic acid into sodium carbonate (99 atom % 13C). For calculating the quantity of Na2CO3 required, a target enrichment of 5 atom% 13C within the shoots of plants, assuming no respiration losses, was used. When harvested, at flowering, the mean enrichment of the shoot material was 3.0466 atom% 13C, or 1.9654 atom% excess 13C. To assess uniformity of labelling within plants, the shoot of a single plant was divided into leaves and stem from three sections of equal length. Ninety-three percent of this plant's dry matter had a 13C enrichment within 20 % of the weighted mean. At a field site with sandy soil, 13C labelled shoot and root material were combined and mixed with soil (0–15 cm). The soil was sampled 16 and 179 days later to determine the recovery of the added excess 13C in soil total C. The recoveries in soil (0–30 cm) were, respectively, 78 and 40 % at 16 and 179 days; there was appreciable variation associated with the recovery data from day 16, much less so at day 179. Methodological procedures for (i) enhancing the uniformity of labelling with 13C within plants, and (ii) minimising variability in the recovery of 13C from soil are suggested. ei]R Merckx

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00015410

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7

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Using calcium carbide with the acetylene inhibition technique to measure denitrification from a sprinkler irrigated vegetable crop (1996)

Thompson, R. B.

Springer

Plant and soil 179 (1996), S. 9-16

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ISSN: 1573-5036

Keywords: acetylene inhibition ; calcium carbide ; denitrification ; nitrogen ; vegetable production

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The use of calcium carbide (CaC2) pellets as a source of acetylene (C2H2) for the C2H2 inhibition technique to measure denitrification in the field was examined in a sandy loam soil cropped to lettuce. CaC2 was used in combination with vented closed chambers. Three grams of 2–4 mm CaC2 pellets were inserted at 7 and 20 cm for raised beds, and 6 and 15 cm for furrows, in four holes located at right angles, 2.5 cm outside a 20 cm dia. chamber pushed 4 cm into the soil. Acetylene concentrations were determined in the centre of the chamber 1.0 and 4.0 hours after applying CaC2, in beds (two dates) and furrows (one date) at different depths to 20 and 15 cm, respectively, for beds and furrows. At soil matric potentials of ca. 0.01 and ca. 0.06 MPa, soil C2H2 concentrations were 〉1.0% (v/v) for all determinations. Weekly measurements of denitrification were made from a sprinkler irrigated lettuce crop for 8 weeks. Measurements were made 24 hours after irrigation and on one occasion 48 hours after. Measured mean rates of denitrification were generally 〈100 g N ha−1 d−1, much less than published data following furrow irrigation of vegetable crops in a nearby region. In another sandy loam soil at ca. 0.08 MPa, soil C2H2 concentrations were ≥2.0 % at 5 and 15 cm, 1.0 and 6.0 hours after adding CaC2. Using CaC2 to generate C2H2 in soil is a convenient approach for field measurements where the C2H2 inhibition technique is used with chambers to determine the nitrous oxide flux. In comparison with C2H2 supply via probe systems, CaC2 overcomes the requirements for cylinders of pressurised C2H2 gas and complex on-site plumbing.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00011637

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