• Korean Journal of Soil Science and Fertilizer
• /
• v.21 no.1
• /
• pp.73-78
• /
• 1988

A laboratory experiments were carried out to study the urea transformation and kinetics of soil urease in paddy soils with different properties. Urea transformation in paddy soils followed first-order kinetics, the rate of urea hydrolysis and the first-order constant was higher in the soil with high total urease activity (TUA) and accumulated urease activity (AUA) than those with low TUA and AUA. The values of Km and Vmax indicated that the Km values of accumulated urease in the soils were different in each soils and lower than that of microbial urease. However, the Km values of microbial urease were nearly same each other.

• 대한핵의학회:학술대회논문집
• /
• 1976.06a
• /
• pp.72.2-73
• /
• 1976

• Asian-Australasian Journal of Animal Sciences
• /
• v.18 no.6
• /
• pp.795-801
• /
• 2005

Eighteen Suffolk wether lambs (BW = 24 kg) were chronically exposed to temperatures of cold (2$^{\circ}C$) or warm (22$^{\circ}C$). The experimental design consisted of a 2${\times}$3 factorial with a single crossover of environment treatment. The sheep were closely shorn and were housed in individual metabolic crates in controlled environment rooms. Sheep consumed pelleted diets ad libitum, which consisted of mainly barley grain and brome grass, and diets contained 7, 11 or 14% crude protein (CP). Animals were catheterized via one jugular vein with a PVC catheter and received a single injection of 60-65 Ci of $^{14}$C]urea. Plasma urea-N (PUN), urinary urea (UU), and carbon specific radioactivity were measured. Urea metabolism was not affected by environment. Percent urea recycling and urea space clearance were highest (p<0.05) on the low nitrogen diet. Urea pool was increased (p<0.10) for the 14% CP diet. Both UU and PUN concentration were positively related (p<0.01) with diet CP content. Therefore, dietary CP content significantly influenced urea metabolism, however, cold exposure did not alter those parameters.

• Elastomers and Composites
• /
• v.50 no.2
• /
• pp.92-97
• /
• 2015

A study on reaction kinetics for a PTMG/TDI prepolymer with 2,2'-dichloro-4,4'-methylenedianiline (MOCA), of which formulations may be generally used for fabricating high performance polyurethane elastomers, was peformed using non-isothermal differential scanning calorimetry (DSC). A number of thermograms were obtained at several constant heating rates, and analysed using Flynn-Wall-Ozawa (FWO) isoconversional method for activation energy, $E_a$ and extended-Avrami equation for reaction order, n. Urea formation reaction of the present system was observed to occur through the simple exothermic reaction process in the temperature range of $100{\sim}130^{\circ}C$ for the heating rate of $3{\sim}7^{\circ}C/min$. and could be well-fitted with generalized sigmoid function. Though activation energy was nearly constant as $53.0{\pm}0.5kJ/mol$, it tended to increase a little at initial stage, but it decreases at later stage by the transformation into diffusion-controlled reaction due to the increased viscosity. Reaction order was evaluated as about 2.8, which was somewhat higher than the generally well-known $2^{nd}$ order values for the various urea reactions. Both the reaction order and reaction rate explicitly increased with temperature, which was considered as the indication of occurring the side reactions such as allophanate or biuret formation.

• 한국해양학회지
• /
• v.28 no.4
• /
• pp.323-331
• /
• 1993

The concentration-dependence of and the effect of light on urea decomposition, and the suppression of urea decomposition by ammonium were studied to understand adaptations in phytoplankton to utilization of urea in the estuarine system of the Mankyung and Dongjin rivers and a hypertrophied pond. Results of size-fractionation showed that bacterial fraction played a minor role (14%) in urea decomposition in the estuary. However, the role of bacteria in urea decomposition seemed to increase in a hypertrophic pond. Natural phytoplankton communities exhibited a monophonic or biphasic kinetics of urea decomposition over a wide range of concentration (upto 7.7 mM). the addition of high concentration of ammonium and incubation of the euphotic samples in the dark caused reductions in the urea decomposition rates. It is suggested that understanding of adaptations in phytoplankton to urea decomposition would help to study the temporal and spatial variabilities of urea decomposition rates in the field and the significance of urea in nitrogen cycle.

• Asian-Australasian Journal of Animal Sciences
• /
• v.24 no.6
• /
• pp.774-780
• /
• 2011

Inadequate supply of glucose or glucogenic substrates to the body tissues can affect metabolism of absorbed acetogenic metabolites from the gut and therefore, influence feed intake in ruminants. This study investigated the effect of energy supplementation on rumen kinetics in the gut, and the acetate clearance rate in the body tissues of sheep fed low quality basal roughage. A basal diet consisting of urea-treated mixture of wheaten chaff and barley straw (3:1 DM) containing 22.2 g N/kg DM was used. Four Merino cross wethers weighing $45{\pm}4.38\;kg$ fitted with permanent rumen and abomasal cannulae were allocated to four treatments in a $4{\times}4$ LSD. The treatments were basal diet ($E_0$), or basal diet supplemented with sucrose (112.5 g/d) administered intraruminally ($E_R$), abomasally ($E_A$), or via both routes (50:50) ($E_{RA}$). There was no difference (p>0.05) in the rumen liquid kinetics parameters between the four dietary treatments. However, there was a trend of animals supplemented with sucrose wholly or partly through the abomasum having lower faecal DM and therefore poor pellet formation, and low pH. Although the glucogenic potential of the fermentation products absorbed from the rumen was increased (p<0.001) by intra-ruminal supplementation with sucrose ($E_R$ and $E_{RA}$), there was no significant difference (p<0.05) in acetate clearance rate between the four dietary treatments.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1655-1659
• /
• 2008

Using numerical models, we investigated the efficiency of toxin removal using pulsatile flow in blood purification systems that use semipermeable membranes. The model consisted of a three-compartmental mass transfer model for the inside body and a solute kinetics model for the dialyzer. The model predicted the toxin concentration inside the body during blood purification therapy, and the toxin removal efficiencies at different flow configurations were compared quantitatively. According to the simulation results, the clearances of urea and ${\beta}_2$ microglobulin (B2M) using a pulsatile pump were improved by up to 30.9% for hemofiltration, with a 2.0% higher urea clearance and 4.6% higher B2M clearance for high flux dialysis, and a 3.9% higher urea clearance and 8.2% higher B2M clearance for hemodiafiltration. These results suggest that using a pulsatile blood pump in blood purification systems with a semipermeable membrane improves the efficacy of toxin removal, especially for large molecules and hemofiltration treatment.

• Asian-Australasian Journal of Animal Sciences
• /
• v.16 no.3
• /
• pp.368-373
• /
• 2003

This experiment was conducted to examine the effects on the composition and rumen degradation in sacco of rice straw treated with animal urine (1 l of 2.9 g N/kg DM straw) and urea plus calcium hydroxide (2% urea plus 0.5% $Ca(OH)_2$/kg DM straw) as a cheap and relatively safe alternative for ammonia (3% ammonia solution/kg DM straw). Mold occurred in urine treated straw, but other treatments were apparently mold-free. All treatments significantly (p<0.05) increased CP content in the straw compared with untreated one. Ammonia-treated straw contained CP at about twice that in urine or urea-calcium hydroxide treated straw. NDF and hemicellulose contents decreased significantly (p<0.05) in all treatments, while ADF and cellulose showed no differences compared with untreated straw. The degradable fraction of DM, CP, NDF, hemicellulose and cellulose was significantly (p<0.05) increased for ammonia and urea-calcium hydroxide treatments than for urine treated or untreated straw except for CP of urine treated straw. Chemical treatment of rice straw increased the readily degradable fraction of CP, while it decreased the slowly degradable fraction for urine or urea-calcium hydroxide treated rice straw. The degradation rate of hemicellulose was significantly (p<0.05) increased for ammonia and urea-calcium hydroxide treatments compared to urine treated or untreated straw. However, no effect on cellulose degradation rate was found by any of the treatments. There was no improvement in the degradation kinetics caused by the urine treatment despite the improvement of the chemical composition. Although the improvement in rumen degradability was less in the urea-calcium hydroxide treatment than in the ammonia treatment, its use may be more desirable because it is less expensive to obtain, less hazardous nature, and readily available. For further improvement it is necessary to investigate the supplementation of slowly degradable nitrogen to ureacalcium hydroxide treated rice straw diet.

• Korean Journal of Materials Research
• /
• v.11 no.9
• /
• pp.727-732
• /
• 2001

The cure kinetics of diglycidyl ether of bisphenol A (DGEBA)/4,4'- methylene dianiline (MDA) system with synthesized phenyl glycidyl ether-dimethylurea (PGE-DMU) was studied by Kissinger and Ozawa equations with DSC analysis in the temperature range of $20~300^{\circ}C$ To investigate the reaction mechanism between epoxy group of PGE and urea group of DMU, FT-lR spectroscopy analysis was used. The epoxide group of PGE reacted with the urea group of DMU and formed a hydroxyl group which acted as a catalyst on the cure reaction of other epoxide and amine groups. The activation energy of DGEBA/MDA system without PGE-DMU was 46.5 kJ/mol and those of the system with 5 and 10 phr of PGE- DMU were 43.4 and 37.0 kJ/mol, respectively. Ozawa method also showed the same tendency.

• Journal of Applied Biological Chemistry
• /
• v.60 no.2
• /
• pp.173-178
• /
• 2017

This study was conducted to investigate the effect of pyroligneous acids on urea hydrolysis for the purpose of inhibiting ammonia volatilization during urea fertilizer application. Different types of synthetic urease inhibitors have been searched and developed, but their use is limited due to varying inhibition effects on soil urease, and environmental problems. In this study, the effect of pyroligneous acids, a natural substance, on urea hydrolysis in soil was evaluated by analyzing inhibition of urease activity. Pyroligneous acids inhibited plant urease and microbial urease activity, as well as soil urease with various urease complex. In addition, pyroligneous acids exhibited non-competitive urease inhibition effect through urease kinetics and inhibited urea hydrolysis in the soil. This study showed that pyroligneous acids treatment with urea fertilizer decreases the loss of urea fertilizer, improves the efficiency of nitrogen application on plant and reduces the amount of nitrogen fertilizers applied in soil.