• Journal of Bio-Environment Control
• /
• v.18 no.4
• /
• pp.309-315
• /
• 2009

Maintenance of adequate soil water content during the period of crop growth is necessary to support optimum plant growth and yields. A better understanding of soil water movement for precision irrigation would allow efficient supply of water to crops, thereby resulting in minimization of water drainage and contamination of ground water. This research reports on the characterization of spatial and temporal variations in water contents through three different textured soils, such as loam, sandy loam, and loamy sand, when water is applied on the soil surface using an one-line drip irrigation system and the soils are dried after the irrigation stops, respectively. Water contents through each soil profile were continuously monitored using three Sentek probes, each consisting of three capacitance sensors at 10, 20, and 30cm depths. Spatial variability in water content for each soil type was strongly influenced by soil textural class. There were big differences in wetting pattern and the rate of downward movement between loam and sandy loam soils, showing that the loam soil had a wider wetting pattern and a slower rate of downward movement than did the sandy loam soil. The wetting pattern in loamy sand soil was not apparent due to a low variability in water content (< 10%) by a lower-water holding capacity as compared to those measured in the loam and sandy loam soils, implying that the rate of water drainage below a depth of 30cm was high. When soils were dried, there were highly exponential relationships between water content and time elapsed after irrigation stops ($r^2$${\geq}$0.98). It was estimated that equilibrium moisture contents for loam, sandy loam, and loamy sand soils would be 17.6%, 6.2%, and 4.2%, respectively.

• Journal of the Korean Electrochemical Society
• /
• v.5 no.3
• /
• pp.131-142
• /
• 2002

The Langmuir adsorption isotherms of the under-potentially deposited hydrogen (UPD H) and the over-potentially deposited hydrogen (OPD H) at the poly-Pt/0.5M $H_2SO_4$ and 0.5 M LiOH aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift $(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1{\geq}{\theta}{\geq}0)$ at the interfaces. The phase-shift method, i.e., the phase-shift profile $({-\phi}\;vs.\;E)$ for the optimum intermediate frequency, can be used as a new electrochemical method to determine the Langmuir adsorption isotherms $({\theta}\;vs.\;E)$ of the UPD H and the OPD H for the cathodic $H_2$ evolution reactions at the interfaces. At the poly-Pt/0.5M $H_2SO_4$ aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the OPD H are $2.1\times10^{-4}$ and 21.0kJ/mol, respectively. At the poly-Pt/0.5M LiOH aqueous electrolyte interface, K transits from 2.7(UPD H) to $6.2\times10^{-6}$ (OPD H) depending on the cathode potential (E) and vice versa. Similarly, ${\Delta}G_{ads}$ transits from -2.5kJ/mol (UPD H) to 29.7kJ/mol (OPD H) depending on I and vice versa. The transition of K and ${\Delta}G_{ads}$ is attributed to the two distinct adsorption sites of the UPD H and the OPD H on the poly-Pt surface. The UPD H and the OPD H on the poly-Pt surface are the independent processes depending on the H adsorption sites themselves rather than the sequential processes for the cathodic $H_2$ evolution reactions. The criterion of the UPD H and the OPD H is the H adsorption sites and processes rather than the $H_2$ evolution reactions and potentials. The poly-Pt wire electrode is more efficient and useful than the Pt(100) disc electrode for the cathodic $H_2$ evolution reactions in the aqueous electrolytes. The phase-shift method is well complementary to the thermodynamic method rather than conflicting.

• Journal of Radiation Protection and Research
• /
• v.24 no.4
• /
• pp.195-203
• /
• 1999

It is difficult to determine dosimetric characteristics for small field photon beams since such small fields do not achieve complete lateral electronic equilibrium and have steep dose gradients. Dosimetric characteristics of small field 4, 6, and 10 MeV photon beams have been measured in water with a diamond detector and compared to measurements using small volume cylindrical and plane parallel ionization chambers. Percent depth dose (PDD) and beam profiles for 6 and 10 MeV photon beams were measured with diamond detector and cylindrical ion chamber for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. Total scatter factors($S_{c,p}$) for 4, 6, and 10 MeV photon beams were measured with diamond detector, cylindrical and plane parallel ion chambers for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. The $S_{c,p}$ factors obtained with three detectors for 4, 6, and 10 MeV photon beams agreed well ($\pm1.2%$) for field sizes greater than $2{\times}2,\;2.5{\times}2.5,\;and\;3{\times}3\;cm^2$, respectively. For smaller field sizes, the cylindrical and plane parallel ionization chambers measure a smaller $S_{c,p}$ factor, as a result of the steep dose gradients across their sensitive volumes. The PDD values obtained with diamond detector and cylindrical ionization chamber for 6 and 10MeV photon beams agreed well ($\pm1.5%$) for field sizes greater than $4{\times}4\;cm^2$. For smaller field sizes, diamond detector produced a depth-dose curve which had a significantly shallower falloff than that obtained from the measurements of relative depth-dose with a cylindrical ionization chamber. For the measurements of beam profiles, a distortion in terms of broadened penumbra was observed with a cylindrical ionization chamber since diamond detector exhibited higher spatial resolution. The diamond detector with small sensitive volume, near water equivalent, and high spatial resolution is suitable detector compared to ionization chambers for the measurements of small field photon beams.