Inhibition by Proton Buffers of Photosynthetic Utilization of Bicarbonate in Chara corallina

1985 ◽  
Vol 12 (3) ◽  
pp. 257 ◽  
Author(s):  
G.D Price ◽  
M.R Badger
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Inorganic Carbon ◽  
Chara Corallina ◽  
Bulk Phase ◽  
Initial Slope ◽  
Photosynthetic Response ◽  
Acidic Compartment ◽  
Rate Limiting

A simple model was developed to explain the mechanism by which buffers inhibit HCO*3� utilization in Chara corallina. The chief assumption was that an acidic compartment exists in the peiiplasmic space and that exogenous buffer species must cross the apoplast to dissipate this H+ gradient (�pH). Assuming that HCO*3� utilization depends on H+ extrusion, buffer-induced H+ dissipation should result in a reduction in inorganic carbon (C*i) limited photosynthesis. The model predicts that buffers with a pKa midway between the bulk phase pH (pHo) and an assumed periplasmic pH will be most effective in dissipating the periplasmic �pH. Experiments conducted at pHo = 9.3 and with 5 mM concentrations of various buffers show that buffers in the range pKa 7.5-9.0 are most inhibitory to HCO*3� utilization. The initial slope of the photosynthetic response to C*i (i.e. where C*i availability is rate limiting) is more sensitive to buffers than rates at high C*i levels. Buffer inhibition was reversible. Experimental data correspond well with the model and indicate that HCO*3� utilization sites in the periplast are considerably more acidic than the bulk phase during photosynthetic HCO*3� utilization. Results suggest that during buffer inhibition experiments �pH is around 2 or more units when the bulk phase pH is 9.3.

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

1985 ◽  
Vol 248 (5) ◽  
pp. C498-C509 ◽  
Author(s):  
D. Restrepo ◽  
G. A. Kimmich
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Sugar Transport ◽  
Enzyme Kinetic ◽  
Steady State Distribution ◽  
State Distribution ◽  
Least Squares Fit ◽  
Coupling Stoichiometry ◽  
Rate Limiting ◽  
Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

Modulation of photosynthesis and inorganic carbon acquisition in a marine microalga by nitrogen, iron, and light availability

2005 ◽  
Vol 83 (7) ◽  
pp. 917-928 ◽  
Author(s):  
Erica B Young ◽  
John Beardall
Keyword(s):  
Inorganic Carbon ◽  
Dunaliella Tertiolecta ◽  
Initial Slope ◽  
Carbon Concentrating Mechanism ◽  
High Affinity ◽  
N Limitation ◽  
Marine Microalga ◽  
Concentrating Mechanism ◽  
Energy Limitation ◽  
Use Efficiency

The marine microalga Dunaliella tertiolecta Butcher expresses a high affinity for dissolved inorganic carbon (DIC) through a carbon-concentrating mechanism (CCM), known to be influenced by CO2 availability and instantaneous light supply. However, the regulation by light and nutrient supply during growth is less understood, although N and Fe limitation impose an energy limitation by compromising the photosynthetic apparatus. Dunaliella tertiolecta was grown under steady-state conditions of limited light, N, and Fe availability, and the affinity for DIC was measured under saturating light. High affinity DIC uptake capacity was maintained by D. tertiolecta under all growth-limiting conditions, but was modulated in response to the limiting resource. Affinity of photosynthesis for DIC(k0.5) was significantly reduced in cells grown under low light, both in turbidostats and in batch culture (p ≤ 0.03), although cell-normalized Pmax was not significantly affected. In contrast, N and Fe limitation resulted in a significant reduction in cell chlorophyll, Pmax, and maximum photosystem II quantum yield (Fv/Fm), but the affinity for DIC was enhanced with increasing N or Fe stress. While the affinity for DIC improved with increasing N stress (k0.5 < 17.8 µM at µ = 0.27 d–1 versus k0.5 > 26 µM at µ ≥ 0.77 d–1), light use efficiency (α) was impaired under N limitation, suggesting a trade-off between light harvesting capacity and active DIC uptake. Stable C isotope analysis of Fe-limited cells confirmed a lower fractionation by the most Fe-limited cells, consistent with the k0.5 data and more active DIC acquisition (δ13C = –19.56 at µ = 0.27 d–1 cf. δ13C = –26.28 at µ = 0.77 d–1). Assessment of affinity for DIC using k0.5 was supported by the close fit of P versus DIC curves to Michaelis–Menten kinetics; with the high DIC affinity of D. tertiolecta, there was poor resolution in the initial slope of the P versus DIC curve as a parameter of affinity for DIC. Enhanced DIC uptake efficiency under Fe and N limitation may relate to improved resource-use efficiency conferred by CCM activity.Key words: algae, carbon-concentrating mechanism, iron, light, nitrogen, nutrient limitation, photosynthesis.

The Tensile Property of the SPF/Cotton Blended Yarn

2011 ◽  
Vol 321 ◽  
pp. 192-195
Author(s):  
Qing Bin Yang ◽  
Xiao Yang
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Tensile Property ◽  
Cotton Fibers ◽  
Blended Yarn ◽  
The Difference ◽  
The Relationship

In order to analysis the relationship between the strength and elongation and the blended ratio of SPF/Cotton blended yarn, the strength and elongation of SPF /cotton blended yarn with different blended ratio were measured and compared with the simple model. The results indicated that For the SPF/cotton blended yarn, the difference between the experimental data and the model value is remarkable because of the high cohesion of the cotton fibers.

scholarly journals Flow fields associated with in situ mineral leaching

1994 ◽  
Vol 36 (2) ◽  
pp. 133-151 ◽  
Author(s):  
Lawrence K. Forbes ◽  
Anthony M. Watts ◽  
Graeme A. Chandler
Keyword(s):  
Simple Model ◽  
Free Boundary ◽  
Numerical Method ◽  
Flow Rate ◽  
Recovery Rate ◽  
Flow Fields ◽  
Vertical Line ◽  
Rate Limiting ◽  
Mineral Leaching

AbstractA simple model for underground mineral leaching is considered, in which liquor is injected into the rock at one point and retrieved from the rock by being pumped out at another point. In its passage through the rock, the liquor dissolves some of the ore of interest, and this is therefore recovered in solution. When the injection and recovery points lie on a vertical line, the region of wetted rock forms an axi-symmetric plume, the surface of which is a free boundary. We present an accurate numerical method for the solution of the problem, and obtain estimates for the maximum possible recovery rate of the liquor, as a fraction of the injected flow rate. Limiting cases are discussed, and other geometries for fluid recovery are considered.

scholarly journals Isotopic fractionation during grain coarsening of wet snow

1993 ◽  
Vol 18 ◽  
pp. 129-134 ◽  
Author(s):  
Masayoshi Nakawo ◽  
Shigeru Chiba ◽  
Hiroshi Satake ◽  
Shigeru Kinouchi
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Rapid Change ◽  
Isotopic Fractionation ◽  
Water Interface ◽  
Grain Coarsening ◽  
Isotope Concentration ◽  
Large Particles ◽  
Wet Snow ◽  
Ice Water

Isotopic composition of solid and liquid portions of wet snow was investigated experimentally. The compositions changed with time, δ values of ice becoming heavier than those for water. A simple model was proposed to explain their temporal variation. It predicted, however, a more rapid change of δ values than the trend obtained in the experiments. This suggests the presence of a “diffusion layer” adjacent to growing snow particles, where isotope concentration has dropped at the ice-water interface because of the fractionation during grain coarsening. The slope in δD–δ18O diagram estimated by the model is compatible with the experimental data. It is considered, therefore, that the freezing fraction, the part of the liquid which refreezes to relatively large particles during grain coarsening, could be estimated by measuring the isotope concentration.

A SIMPLE MODEL FOR ORIENTATIONAL ORDERING OF A SILVER MONOLAYER ELECTRODEPOSITED ON A C(0001) SURFACE

1995 ◽  
Vol 02 (04) ◽  
pp. 489-494 ◽  
Author(s):  
E.E. MOLA ◽  
A.G. APPIGNANESSI ◽  
J.L. VICENTE ◽  
L. VAZQUEZ ◽  
R.C. SALVAREZZA ◽  
...  
Keyword(s):  
Experimental Data ◽  
Fourier Series ◽  
Simple Model ◽  
Series Expansion ◽  
Unit Cell ◽  
Fourier Series Expansion ◽  
Crystal Formation ◽  
Substrate Potential ◽  
Weber Type ◽  
Orientational Ordering

The model for the angular orientational energy (AOE) has been extended to hexagonal submonolayer domains of Ag electrodeposited at a constant overpotential on a C(0001) surface. These domains which are characterized by an epitaxy angle θ=15±5° and an Ag−Ag distance d Ag−Ag =0.330± 0.016 nm, can be considered as precursors of 3D Ag crystal formation, according to a Volmer-Weber type mechanism. Calculations are based upon a simple Hamiltonian evaluated by introducing the concept of the commensurable unit cell. A Fourier series expansion for the substrate potential was used. Results from the model predict the existence of a commensurable cell in agreement with the experimental data derived from STM imaging.

scholarly journals Estimate of Glacier Ablation under a Debris Layer from Surface Temperature and Meteorological Variables

1982 ◽  
Vol 28 (98) ◽  
pp. 29-34 ◽  
Author(s):  
M. Nakawo ◽  
G.J. Young
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Surface Temperature ◽  
Temperature Data ◽  
Meteorological Variables ◽  
Glacier Ablation ◽  
Surface Temperature Data ◽  
Good Agreement

AbstractA simple model suggests that the ablation under a debris layer could be estimated from meteorological variables if the surface temperature data of the layer are available. This method was tested by analyzing the data obtained from experiments with artificial debris layers. Fairly good agreement was obtained between the estimated and the experimental data.

PHOTOEMISSION CALCULATION WITH A SIMPLE MODEL FOR THE PHOTON FIELD: APPLICATION TO ALUMINIUM

1991 ◽  
Vol 05 (01) ◽  
pp. 65-72 ◽  
Author(s):  
P. DAS ◽  
R.K. THAPA ◽  
N. KAR
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Fermi Level ◽  
Dielectric Function ◽  
Cross Sections ◽  
Free Electron ◽  
Surface Region ◽  
Field Application ◽  
Frequency Dependent ◽  
Photon Field

Photoemission cross-sections are calculated, using a simple “local” dielectric function for computing the photon field in the surface region and free electron wavefunctions. Comparisons are made with the experimental data for the frequency-dependent normal photoemission from the Fermi level of aluminium, and the importance of the variation of the photon field in the surface region is pointed out.

Some Observations on X-Ray Emission as a Function of Accelerating Voltage in the Microprobe

1964 ◽  
Vol 8 ◽  
pp. 384-399
Author(s):  
D. L. Burk
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Atomic Number ◽  
X Ray ◽  
Absorption Wavelength

AbstractData are presented from several systems for which the emitted X-ray intensity goes through a maximum as accelerating voltage is increased. An attempt is made to systematize the data in terms of absorption, wavelength, and atomic number. A very simple model, analyzed graphically, is capable of displaying many of the features of the experimental data.

Optimizing sulfurisation conditions in the fabrication of Cu2ZnSnS4absorber layers from electroplated precursors

2009 ◽  
Vol 1210 ◽  
Author(s):  
Jonathan James Scragg ◽  
Daniel Wolverson ◽  
Guillaume Zoppi ◽  
Laurence M Peter
Keyword(s):  
Simple Model ◽  
Grain Growth ◽  
Phase Formation ◽  
Bulk Material ◽  
Limiting Factor ◽  
Processing Conditions ◽  
Surface Phases ◽  
Rate Limiting ◽  
Temperature Time ◽  
Photoelectrochemical Measurement

AbstractUsing direct photoelectrochemical measurement of the photocurrent obtained from Cu2ZnSnS4(CZTS) absorber layers made by a two-stage electroplating-sulfurisation process, the influence of processing conditions (temperature, time, and pressure) on material quality was investigated with a view to understanding the long sulfurisation times usually found in the literature. The improvement in photocurrent due to KCN etching was also studied, and seems to be due both to removal of surface phases and also slower etching of the bulk material. The optimum sulfurisation time was found to be around 50 minutes, despite evidence that sulfur incorporation and phase formation are complete within 5 minutes. Slow grain growth was suggested as a rate-limiting factor, and a rate constant was derived based on a simple model.

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