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Urea

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Urea - Free Register to Access Experts & Abstracts

Caue Ribeiro - One of the best experts on this subject based on the ideXlab platform.

  • slow release fertilizers based on Urea Urea formaldehyde polymer nanocomposites
    Chemical Engineering Journal, 2016
    Co-Authors: Cintia F Yamamoto, Elaine I Pereira, Teruo Matsunaka, Luiz Henrique Capparelli Mattoso, Caue Ribeiro
    Abstract:

    Abstract A novel nanocomposite material based on the exfoliation of montmorillonite into a matrix of Urea/Urea–formaldehyde polymer was developed to be used as nitrogen-loaded slow release fertilizers. The nanocomposites were produced by cold plastic extrusion, a simple and high-productive method, using a formaldehyde precursor to accomplish polymerization in situ during extrusion processing. Characterizations showed that the extruded fertilizer nanocomposites presented good mechanical resistance, and that the Urea release was noticeably controlled by the extent of polymerization. Water immersion experiments demonstrated that the nanocomposite structure was responsible for the effective slow Urea release behavior. A dependence of the availability of other nitrogenous compounds (NH 4 + and NO 3 − ) on the polymerization degree was also demonstrated by soil incubation tests. The Urea/Urea–formaldehyde polymer nanocomposites were found to be versatile and smart materials capable of supplying the enormous demand for novel efficient nitrogen fertilizers.

Gerald J Beck - One of the best experts on this subject based on the ideXlab platform.

  • hemodialyzer mass transfer area coefficients for Urea increase at high dialysate flow rates
    Kidney International, 1997
    Co-Authors: John K. Leypoldt, Lawrence Y Agodoa, Prakash Keshaviah, John T. Daugirdas, Tom Greene, Alfred K Cheung, Gerald J Beck
    Abstract:

    Hemodialyzer mass transfer-area coefficients for Urea increase at high dialysate flow rates. The dialyzer mass transfer-area coefficient (K o A) for Urea is an important determinant of Urea removal during hemodialysis and is considered to be constant for a given dialyzer. We determined Urea clearance for 22 different models of commercial hollow fiber dialyzers ( N = ~5/model, total N=107) in vitro at 37°C for three countercurrent blood (Q b ) and dialysate (Q d ) flow rate combinations. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from Urea concentrations in the input and output flows on both the blood and dialysate sides. Urea K o A values, calculated from the mean of the blood and dialysate side clearances, varied between 520 and 1230ml/min depending on the dialyzer model, but the effect of blood and dialysate flow rate on Urea K o A was similar for each. Urea K o A did not change (690 ± 160 vs. 680 ± 140 ml/min, P = NS) when Q b increased from 306 ± 7 to 459 ± 10ml/min at a nominal Q d of 500ml/min. When Q d increased from 504 ± 6 to 819 ± 8ml/min at a nominal Q b of 450ml/min, however, Urea K o A increased ( P d from 500 to 800ml/min alters the mass transfer characteristics of hollow fiber hemodialyzers and results in a larger increase in Urea clearance than predicted assuming a constant K o A.

Cintia F Yamamoto - One of the best experts on this subject based on the ideXlab platform.

  • slow release fertilizers based on Urea Urea formaldehyde polymer nanocomposites
    Chemical Engineering Journal, 2016
    Co-Authors: Cintia F Yamamoto, Elaine I Pereira, Teruo Matsunaka, Luiz Henrique Capparelli Mattoso, Caue Ribeiro
    Abstract:

    Abstract A novel nanocomposite material based on the exfoliation of montmorillonite into a matrix of Urea/Urea–formaldehyde polymer was developed to be used as nitrogen-loaded slow release fertilizers. The nanocomposites were produced by cold plastic extrusion, a simple and high-productive method, using a formaldehyde precursor to accomplish polymerization in situ during extrusion processing. Characterizations showed that the extruded fertilizer nanocomposites presented good mechanical resistance, and that the Urea release was noticeably controlled by the extent of polymerization. Water immersion experiments demonstrated that the nanocomposite structure was responsible for the effective slow Urea release behavior. A dependence of the availability of other nitrogenous compounds (NH 4 + and NO 3 − ) on the polymerization degree was also demonstrated by soil incubation tests. The Urea/Urea–formaldehyde polymer nanocomposites were found to be versatile and smart materials capable of supplying the enormous demand for novel efficient nitrogen fertilizers.

John K. Leypoldt - One of the best experts on this subject based on the ideXlab platform.

  • effect of low dialysate flow rate on hemodialyzer mass transfer area coefficients for Urea and creatinine
    Home hemodialysis international. International Symposium on Home Hemodialysis, 1999
    Co-Authors: John K. Leypoldt, Alfred K Cheung
    Abstract:

    : Recent work has shown that the dialyzer mass transfer area coefficient (Ko A) for Urea increases when the dialysate flow rate is increased from 500 to 800 mL/min. In this study we determined Urea and creatinine clearances for two commercial dialyzers containing polysulfone hollow fibers in vitro at 37°C, a nominal blood flow rate of 300 mL/ min, and dialysate flow rates (Qd ) ranging from 100 to 800 mL/min. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from solute concentrations in the input and output flows on both the blood and dialysate sides. Urea and creatinine Ko A values, calculated from the mean of the blood and dialysate side clearances, increased (p < 0.01) with increasing Qd over the entire range studied. The increase in both Urea and creatinine Ko A with increasing Qd was proportional to the Ko A value. These data show that changes in Qd alter small solute clearances greater than predicted assuming a constant Ko A.

  • hemodialyzer mass transfer area coefficients for Urea increase at high dialysate flow rates
    Kidney International, 1997
    Co-Authors: John K. Leypoldt, Lawrence Y Agodoa, Prakash Keshaviah, John T. Daugirdas, Tom Greene, Alfred K Cheung, Gerald J Beck
    Abstract:

    Hemodialyzer mass transfer-area coefficients for Urea increase at high dialysate flow rates. The dialyzer mass transfer-area coefficient (K o A) for Urea is an important determinant of Urea removal during hemodialysis and is considered to be constant for a given dialyzer. We determined Urea clearance for 22 different models of commercial hollow fiber dialyzers ( N = ~5/model, total N=107) in vitro at 37°C for three countercurrent blood (Q b ) and dialysate (Q d ) flow rate combinations. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from Urea concentrations in the input and output flows on both the blood and dialysate sides. Urea K o A values, calculated from the mean of the blood and dialysate side clearances, varied between 520 and 1230ml/min depending on the dialyzer model, but the effect of blood and dialysate flow rate on Urea K o A was similar for each. Urea K o A did not change (690 ± 160 vs. 680 ± 140 ml/min, P = NS) when Q b increased from 306 ± 7 to 459 ± 10ml/min at a nominal Q d of 500ml/min. When Q d increased from 504 ± 6 to 819 ± 8ml/min at a nominal Q b of 450ml/min, however, Urea K o A increased ( P d from 500 to 800ml/min alters the mass transfer characteristics of hollow fiber hemodialyzers and results in a larger increase in Urea clearance than predicted assuming a constant K o A.

Alfred K Cheung - One of the best experts on this subject based on the ideXlab platform.

  • effect of low dialysate flow rate on hemodialyzer mass transfer area coefficients for Urea and creatinine
    Home hemodialysis international. International Symposium on Home Hemodialysis, 1999
    Co-Authors: John K. Leypoldt, Alfred K Cheung
    Abstract:

    : Recent work has shown that the dialyzer mass transfer area coefficient (Ko A) for Urea increases when the dialysate flow rate is increased from 500 to 800 mL/min. In this study we determined Urea and creatinine clearances for two commercial dialyzers containing polysulfone hollow fibers in vitro at 37°C, a nominal blood flow rate of 300 mL/ min, and dialysate flow rates (Qd ) ranging from 100 to 800 mL/min. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from solute concentrations in the input and output flows on both the blood and dialysate sides. Urea and creatinine Ko A values, calculated from the mean of the blood and dialysate side clearances, increased (p < 0.01) with increasing Qd over the entire range studied. The increase in both Urea and creatinine Ko A with increasing Qd was proportional to the Ko A value. These data show that changes in Qd alter small solute clearances greater than predicted assuming a constant Ko A.

  • hemodialyzer mass transfer area coefficients for Urea increase at high dialysate flow rates
    Kidney International, 1997
    Co-Authors: John K. Leypoldt, Lawrence Y Agodoa, Prakash Keshaviah, John T. Daugirdas, Tom Greene, Alfred K Cheung, Gerald J Beck
    Abstract:

    Hemodialyzer mass transfer-area coefficients for Urea increase at high dialysate flow rates. The dialyzer mass transfer-area coefficient (K o A) for Urea is an important determinant of Urea removal during hemodialysis and is considered to be constant for a given dialyzer. We determined Urea clearance for 22 different models of commercial hollow fiber dialyzers ( N = ~5/model, total N=107) in vitro at 37°C for three countercurrent blood (Q b ) and dialysate (Q d ) flow rate combinations. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from Urea concentrations in the input and output flows on both the blood and dialysate sides. Urea K o A values, calculated from the mean of the blood and dialysate side clearances, varied between 520 and 1230ml/min depending on the dialyzer model, but the effect of blood and dialysate flow rate on Urea K o A was similar for each. Urea K o A did not change (690 ± 160 vs. 680 ± 140 ml/min, P = NS) when Q b increased from 306 ± 7 to 459 ± 10ml/min at a nominal Q d of 500ml/min. When Q d increased from 504 ± 6 to 819 ± 8ml/min at a nominal Q b of 450ml/min, however, Urea K o A increased ( P d from 500 to 800ml/min alters the mass transfer characteristics of hollow fiber hemodialyzers and results in a larger increase in Urea clearance than predicted assuming a constant K o A.