scholarly journals EFFECTS OF LINEAR AND EXPONENTIAL FITTING ON THE INITIAL RATE OF CHANGE IN CO2 CONCENTRATION ACROSS THE SOIL SURFACE

2007 ◽  
Vol 31 (3) ◽  
pp. 380-385
Author(s):  
WEN Xue-Fa ◽  
◽  
SUN Xiao-Min ◽  
LIU Yun-Fen ◽  
LI Xiao-Bo
Keyword(s):  
Initial Rate ◽  
Soil Surface ◽  
Rate Of Change ◽  
Exponential Fitting

Weed Seedbank Response to Tillage, Herbicides, and Crop Rotation Sequence

Weed Science ◽  
1992 ◽  
Vol 40 (4) ◽  
pp. 654-659 ◽  
Author(s):  
Daniel A. Ball
Keyword(s):  
Weed Control ◽  
Crop Production ◽  
Soil Surface ◽  
Rate Of Change ◽  
Dominant Factor ◽  
Weed Seed ◽  
Weed Species ◽  
Cropping Sequence ◽  
Primary Tillage ◽  
Pinto Beans

Changes in the weed seedbank due to crop production practices are an important determinant of subsequent weed problems. Research was conducted to evaluate effects of primary tillage (moldboard plowing and chisel plowing), secondary tillage (row cultivation), and herbicides on weed species changes in the soil seedbank in three irrigated row crop rotational sequences over a 3-yr period. The cropping sequences consisted of continuous corn for 3 yr, continuous pinto beans for 3 yr, or sugarbeets for 2 yr followed by corn in the third year. Cropping sequence was the most dominant factor influencing species composition in the seedbank. This was partly due to herbicide use in each cropping sequence producing a shift in the weed seedbank in favor of species less susceptible to applied herbicides. A comparison between moldboard and chisel plowing indicated that weed seed of predominant species were more prevalent near the soil surface after chisel plowing. The number of predominant annual weed seed over the 3-yr period increased more rapidly in the seedbank after chisel plowing compared to moldboard plowing unless effective weed control could be maintained to produce a decline in seedbank number. In this case, seedbank decline was generally more rapid after moldboard plowing. Row cultivation generally reduced seedbanks of most species compared to uncultivated plots in the pinto bean and sugarbeet sequences. A simple model was developed to validate the observation that rate of change in the weed seedbank is influenced by type of tillage and weed control effectiveness.

An assessment of the depletion technique for comparative measurement of phosphorus uptake in plants

1987 ◽  
Vol 38 (2) ◽  
pp. 263 ◽  
Author(s):  
KD McLachlan ◽  
YH Kuang ◽  
WJ Muller
Keyword(s):  
Kinetic Parameters ◽  
Initial Rate ◽  
Phase 1 ◽  
Phosphorus Uptake ◽  
Subterranean Clover ◽  
Solution Concentration ◽  
Rate Of Change ◽  
Plant Performance ◽  
Depletion Curve ◽  
Kinetics Of

This paper examines the depletion of a standard 32P solution by 221 plants, either cereals or clovers, as a means of determining the recognized parameters, Vmax, Km and Cmin, in the kinetics of phosphorus uptake, and attempts to relate them to comparative phosphorus uptake by the plants, with a view to recognizing the more efficient ones.No single depletion curve was found. The data were grouped into six distinct curve types, based on the change in solution concentration (C) with time (t) and the rate of change in concentration (dC/dt) with concentration. The six types were part of one general curve which could be separated into 3 phases.In Phase 1, solution concentration was non-limiting, and plant performance was the principal determinant in depleting the solution. In the second and third phases, plant performance became progressively less dominant and the solution concentration more dominant in determining the concentration of the remaining solution.For comparative phosphorus uptake purposes, it is suggested that only the initial rate of uptake (Phase 1) is worth measuring and that this has attendant difficulties; the issue whether these kinetic parameters are real, or measurements of the model selected, is raised and discussed.No relation was found between these kinetic parameters and the efficiency of phosphorus use by subterranean clover plants grown in soil. Despite these practical shortcomings, variability in uptake capability between individual plants, even of the same line, was demonstrated. This plant variability offers a new area of plant nutrition for exploitation.

scholarly journals Ramdas layer and thermal wave during winter period

MAUSAM ◽  
2022 ◽  
Vol 52 (4) ◽  
pp. 697-702
Author(s):  
S. ABRAHAM THAMBI RAJA ◽  
G. RENUKA ◽  
K. RETNAKUMARI
Keyword(s):  
Mathematical Model ◽  
Heat Flux ◽  
Energy Balance ◽  
Thermal Wave ◽  
Soil Surface ◽  
Soil Heat Flux ◽  
Rate Of Change ◽  
Winter Period ◽  
Maximum Height ◽  
Lower Height

Earlier works on Ramdas Layer were about its certainty, its existence, energy balance on the layer and a matching mathematical model. We, first identified it in Thiruvananthapuram, Kerala, for eight days during a fortnight study on soil heat flux. A lifted minimum in temperature could have implications in agriculture and horticulture and so with a view to finding out a range of height through which Ramdas layer occurs, Ramdas-max, Ramdas-min are identified. On 24 January 1994, Ramdas layer occurred at a maximum height of 0.8m from the surface and the day is labeled as Ramdas-max. On 1 February 1994, it occurred at a lower height of 0.4m from the surface and the day is labeled as Ramdas-min.   The thermal wave at the ground and at 0.05m depth, the range of thermal wave, its relationship with Ramdas layer, the temperature profile, the rate of change of heat in that layer with that at the surface and the subsoil heat flux at the sub-soil surface stratum(surface-0.05m) during R~mdas-max and Ramdas-min are duly compared and discussed.

Persistence of Three Dinitroaniline Herbicides on the Soil Surface

Weed Science ◽  
1980 ◽  
Vol 28 (1) ◽  
pp. 105-110 ◽  
Author(s):  
K. E. Savage ◽  
T. N. Jordan
Keyword(s):  
Initial Rate ◽  
Soil Surface ◽  
Sampling Period ◽  
Silt Loam ◽  
Field Sampling ◽  
Direct Sunlight ◽  
Sampling Studies ◽  
Nylon Mesh ◽  
Life Values ◽  
Dinitroaniline Herbicides

Rates of loss of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] from soil surfaces were evaluated in a series of field sampling studies. Herbicides were sprayed onto soil enclosed in rings with nylon mesh bottoms, exposed to field conditions, and analyzed periodically by gas chromatography. The herbicides were lost rapidly in the first 3 to 5 days from Bosket silt loam and Sharkey clay, although the initial rate of loss was less rapid in the clay. Trifluralin and fluchloralin were lost more rapidly than pendimethalin. Half-life values for the first 3 to 5 days for trifluralin, fluchloralin, and pendimethalin, respectively, were 2, 1.5, and 4 days on silt loam and 2, 4, and 6 days on clay. Rates of loss were much lower for the remainder of the 7- or 12-day sampling periods. Rainfall on the first day of the sampling period resulted in increased initial loss of all herbicides. Shading from direct sunlight greatly reduced the loss of fluchloralin and pendimethalin as compared to exposure to full sunlight, although trifluralin loss remained fairly rapid under shaded conditions. Simulated rainfall on the first day resulted in significantly increased dissipation of fluchloralin and pendimethalin.

Thermal Stability of Zinc and Selenium Implanted GaAs

1989 ◽  
Vol 146 ◽  
Author(s):  
A C T Tang ◽  
B J Sealy ◽  
A A Rezazadeh
Keyword(s):  
Activation Energy ◽  
Thermal Stability ◽  
Carrier Concentration ◽  
Initial Rate ◽  
Heat Treatments ◽  
Rate Of Change ◽  
First Time ◽  
Thermal Stability Of

ABSTRACTWe have observed for the first time reversible changes in the sheet carrier concentration of the rapid thermally annealed Se and Zn implanted GaAs samples during subsequent heat treatments. The electrical profiles of the implanted samples have also been modified during the annealing processes. By observing the initial rate of change in the carrier concentration, an activation energy of about 2 eV is obtained which is thought to correspond to the diffusion of gallium atoms/vacancies.

Thermal diffusion in solutions of electrolytes

1960 ◽  
Vol 255 (1282) ◽  
pp. 307-330 ◽  
Keyword(s):  
Steady State ◽  
Initial Rate ◽  
Wheatstone Bridge ◽  
Rate Of Change ◽  
Soret Coefficient ◽  
Free System ◽  
Platinized Platinum ◽  
Solutions Of Electrolytes ◽  
Concentration Changes ◽  
The Mean

A conductimetric method for following the small concentration changes that occur when a temperature gradient is maintained in an aqueous electrolyte is described. The solution is contained in a Perspex cell between silver end-plates which are faced with platinized platinum and kept at temperatures differing by about 10°C. A further connexion to the cell (a ‘centretap’) is made through a small lateral hole equidistant from the ends. The cell is incorporated in an audio-frequency Wheatstone bridge and movement of solute from one half of the cell to the other is followed by measuring the ratio of their resistances. For a convection-free system, the Soret coefficient (σ) may be derived either from the initial rate of change of the ratio or from its value in the steady state. It is found experimentally that there are discrepancies between the two estimates of σ, and also related anomalies in the rate of change of concentration, which can be ascribed to convection. It can be shown that the initial rate observations should be free from convection errors, and the effect of convection on the steady state can be analysed by dimensional methods. The observed discrepancies are correlated with the relevant properties of the solutions in the manner suggested by this analysis. The Soret coefficients of eighteen 1:1 salts in 0⋅01 m aqueous solution and at mean temperature 25⋅0°C have been determined by this method. Some additional measurements have been made at 34⋅7°C and at other concentrations in the range 0⋅002 to 0⋅02m. Three salts of other valency types (potassium, thallous and cadmium sulphates) have also been studied. The molar heats of transport of the salts ( Q *) have been calculated from the Soret coefficients. The results show that Q * (i) is an additive function of contributions characteristic of the constituent ions in dilute (0⋅01 M) solutions of 1:1 electrolytes, (ii) increases markedly on raising the mean temperatures from 25⋅0 to 34⋅7°C, in agreement with the results of Alexander (1954) and Longsworth (1957) (iii) increases appreciably on dilution below 0⋅01 M, indicating that heats of transport are influenced by long-range inter-ionic forces.

A Numerical Study of the Impact of Tunnel Depth on Surface Displacement in Shield Tunnel Construction

2013 ◽  
Vol 423-426 ◽  
pp. 1248-1252
Author(s):  
Hui Ting Zhan ◽  
Hong Yuan ◽  
Jia Yu Wu ◽  
Yu Sen Yuan
Keyword(s):  
Numerical Study ◽  
Surface Displacement ◽  
Soil Surface ◽  
Rate Of Change ◽  
Shield Tunnel ◽  
Tunnel Construction ◽  
Displacement Curve ◽  
3D Finite Element Method ◽  
Tunnel Depth ◽  
The Impact

Using 3d finite element method can simulate the process of shield tunnel construction. The paper studies the impact of different tunnel depth on the deformation of soil, when considering different excavation steps in the process of tunnel construction. The results show that the shallower the tunnel depth, and the greater the amount of the surface displacement during the tunnel construction. In the process of the tunnel excavation, the soil surface displacement in front of the shield machine is the result of superposition of the uplift and subsidence. When the tunnel depth increases, the surface displacement curve becomes smoother, and the rate of change becomes slower.

Carbonic anhydrase and cardiac pH regulation

1996 ◽  
Vol 271 (6) ◽  
pp. C1838-C1846 ◽  
Author(s):  
J. I. Vandenberg ◽  
N. D. Carter ◽  
H. W. Bethell ◽  
A. Nogradi ◽  
Y. Ridderstrale ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Cardiac Tissue ◽  
Initial Rate ◽  
Contractile Function ◽  
Ph Regulation ◽  
Rate Of Change ◽  
Ischemic Myocardium ◽  
Resonance Spectroscopy ◽  
Co2 Efflux ◽  
Perfused Heart

Membrane-bound carbonic anhydrase (CA) has recently been identified in mammalian cardiac tissue. In this study, we have investigated the histochemical location and functional role of CA in the ferret heart. Heart sections stained by a modified Hansson's technique showed CA to be located on capillary endothelial membranes as well as on sarcolemmal membranes. In the Langendorff-perfused heart, washout of CO2 brought about by switching perfusion between 25 mM HCO3(-)-5% CO2-buffered solution and nominally HCO3(-)-CO2-free solution caused a transient rise in intracellular pH (pHi) measured by the chemical shift of 2-deoxy-D-glucose 6-phosphate with 31P nuclear magnetic resonance spectroscopy. The initial rate of change of pHi, measured over the first 60-75 s of CO2 efflux, was significantly reduced from 0.41 +/- 0.03 pH units/min (n = 9) in control hearts to 0.28 +/- 0.02 pH units/min (n = 5) in the presence of the membrane-permeable CA inhibitor 6-ethoxzolamide (P < 0.05 compared with control) and to 0.22 +/- 0.04 pH units/min (n = 5) in the presence of the membrane-impermeable CA inhibitor CL-11,366 (P < 0.01 compared with control). After reperfusion of the ischemic myocardium, both CA inhibitors caused a significant slowing of initial rate of change in pH (and initial rate of recovery of contractile function) compared with control hearts. These results suggest that CA, by facilitating the hydration-dehydration of CO2-H2CO3, alters the relative concentrations of CO2 inside and outside the cells, thus enhancing the rate of CO2 transfer from the intracellular to extracellular compartments, which contributes significantly to pHi recovery after reperfusion of the ischemic myocardium.

Effect of extracellular Po 2 on the fall in intracellular Po 2 in contracting single myocytes

2003 ◽  
Vol 94 (5) ◽  
pp. 1964-1970 ◽  
Author(s):  
Casey A. Kindig ◽  
Richard A. Howlett ◽  
Michael C. Hogan
Keyword(s):  
Skeletal Muscle ◽  
Time Delay ◽  
Time Constant ◽  
Initial Rate ◽  
Metabolic Response ◽  
Rate Of Change ◽  
Phosphorescence Quenching ◽  
Mean Response Time ◽  
The Mean ◽  
Lumbrical Muscles

The purpose of this investigation was to study the effects of altered extracellular Po 2 (Pe O2 ) on the intracellular Po 2(Pi O2 ) response to contractions in single skeletal muscle cells. Single myocytes ( n = 12) were dissected from lumbrical muscles of adult female Xenopus laevis and injected with 0.5 mM Pd- meso-tetra(4-carboxyphenyl)porphine for assessment of Pi O2 via phosphorescence quenching. At a Pe O2 of ∼20 (low), ∼40 (moderate), and ∼60 (high) Torr, tetanic contractions were induced at a frequency of 0.67 Hz for ∼2 min with a 5-min recovery between bouts (blocked order design). The Pi O2 response to contractions was characterized by a time delay followed by a monoexponential decline to steady-state (SS) values. The fall in Pi O2 to SS values was significantly greater at each progressively greater Pe O2 (all P < 0.05). The mean response time (time delay + time constant) was significantly faster in the low (35.2 ± 5.1 s; P < 0.05 vs. high) and moderate (43.3 ± 6.4 s; P < 0.05 vs. high) compared with high Pe O2 (61.8 ± 9.4 s) and was correlated positively ( r = 0.965) with the net fall in Pi O2 . However, the initial rate of change of Pi O2 (calculated as net fall in Pi O2 /time constant) was not different ( P > 0.05) among Pe O2 trials. These latter data suggest that, over the range of 20–60 Torr, Pe O2 does not play a deterministic role in setting the initial metabolic response to contractions in isolated frog myocytes. Additionally, these results suggest that oxidative phosphorylation in these myoglobin-free myocytes may be compromised by Pe O2 at values nearing 60 Torr.

scholarly journals Kinetic Spectrophotometric Determination of Certain Cephalosporins in Pharmaceutical Formulations

2009 ◽  
Vol 2009 ◽  
pp. 1-12 ◽  
Author(s):  
Mahmoud A. Omar ◽  
Osama H. Abdelmageed ◽  
Tamer Z. Attia
Keyword(s):  
Initial Rate ◽  
Pharmaceutical Formulations ◽  
Fixed Time ◽  
Rate Of Change ◽  
Ceftriaxone Sodium ◽  
Accuracy And Precision ◽  
Significant Difference ◽  
Cephalosporin Antibiotics ◽  
Kinetic Spectrophotometric

A simple, reliable, and sensitive kinetic spectrophotometric method was developed for determination of eight cephalosporin antibiotics, namely, Cefotaxime sodium, Cephapirin sodium, Cephradine dihydrate, Cephalexin monohydrate, Ceftazidime pentahydrate, Cefazoline sodium, Ceftriaxone sodium, and Cefuroxime sodium. The method depends on oxidation of each of studied drugs with alkaline potassium permanganate. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 610 nm. The initial rate and fixed time (at 3 minutes) methods are utilized for construction of calibration graphs to determine the concentration of the studied drugs. The calibration graphs are linear in the concentration ranges 5–15 g  and 5–25 g  using the initial rate and fixed time methods, respectively. The results are validated statistically and checked through recovery studies. The method has been successfully applied for the determination of the studied cephalosporins in commercial dosage forms. Statistical comparisons of the results with the reference methods show the excellent agreement and indicate no significant difference in accuracy and precision.

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