叶冠尺度野鸭湖湿地植物群落含水量的高光谱估算模型

利用高光谱遥感技术定量估测野鸭湖湿地植被含水量,对于监测和诊断野鸭湖湿地植被的生理状况及生长趋势具有重要意义,也能够为高光谱遥感影像在野鸭湖湿地植被含水量诊断中的实际应用提供理论依据和技术支持.采用Field Spec 3野外高光谱辐射仪,获取了野鸭湖典型湿地植被冠层和叶片的光谱,并测定了对应的含水量.以上述实测数据为基础,首先以芦苇为例初步探明了不同含水量水平下典型湿地植被冠层和叶片光谱反射率的响应模式,然后采用相关性及单变量线性与非线性拟合分析技术,从冠层和叶片两种层次,对不同尺度下的含水量与“三边”参数及高光谱植被指数进行了分析拟合,并采用交叉检验中的3K-CV方法对估算模型进行了测试和检验,确立了不同尺度下野鸭湖湿地植被含水量的定量监测模型.结果表明:(1)随着含水量水平的增加,芦苇冠层与叶片光谱在可见光波段(350-760 nm)和红外波段(760-2500 nm)的反射率均呈逐渐降低趋势.(2)不同尺度含水量与选取的光谱特征参数整体上相关性较强,与“三边”参数基本上都呈极显著相关,相关系数最大达到0.906;与高光谱指数全部呈极显著相关,相关系数最小为0.455,最大达到0.919,并通过选取不同尺度上相关性最佳的光谱特征参数,分别基于“三边”参数和高光谱植被指数构建了不同尺度下的含水量估算模型.其中,冠层尺度下,黄边面积(SDy)与SRWI( Simple Ratio Water Index)的估算效果最好,估算模型分别为y=-9.462x2 -2.671x+0.608和y=0.219e1.010x;叶片尺度下,红边面积(SDr)与WI( Water Index)的估算效果最好,估算模型分别为y=0.562x+0.376和y=2.028x2 -0.476x-1.009.通过3K-CV的交叉验证,不同尺度下的含水量估算模型均取得了较为理想的预测精度,预测精度的最小值为94.92％,最大值为97.06％,表明估测模型具有较高的可靠性与普适性.(3)高光谱植被指数与含水量拟合方程的拟合度相对高于“三边”参数与之建立方程的拟合度,说明多波段组合的光谱特征参数更适合含水量的判别.     

Chemical intermediates in α-methylnoradrenaline oxidation by tyrosinase—I. Spectral properties and stoichiometry

• 1.1. A pathway for a-methylnoradrenaline oxidation to α-methylnoradrenochrome, by tyrosinase, is proposed. Characterization of intermediates in this oxidative reaction and stoichiometry determination have both been performed.
• 2.2. It has been possible to detect spectrophotometrically o-quinone-H⁺ as the first intermediate in this pathway after oxidizing α-methylnoradrenaline with mushroom tyrosinase or sodium periodate in a pH range from 5 to 6.
• 3.3. The steps for α-methylnoradrenaline transformation into its aminochrome could be: α-methylnoradrenaline → o -α-methylnoradrenaline — H⁺ → o — α -methylnoradrenalinequinone → leuko — α — methylnora — drenochrome→α-methylnoradrenochrome.
• 4.4. No participation of oxygen was detected in the conversion of leuko-α-mehtylnoradrenochrome into α -methylnoradrenochrome.
• 5.5. Matrix analysis of the spectra obtained with a rapid scan spetrophotometer verified that o-quinone-H⁺ was transformed into aminochrome in a constant ratio.
• 6.6. The stoichiometry for this conversion followed the equation: 2 α-methylnoradrenalinequinone-H⁺ → α-methylnoradrenaline + α-methylnoradrenochrome.

     

Binding of copper(II) to thyrotropin-releasing hormone (TRH) and its analogs

Spectroscopy (UV-Vis, ¹H NMR, ESR) and electrochemistry revealed details of the structure of the Cu(II)-TRH (pyroglutamyl-histidyl-prolyl amide) complex. The ¹H NMR spectrum of TRH has been assigned. NMR spectra of TRH in the presence of Cu(II) showed that Cu(II) initially binds TRH through the imidazole. TRH analogs, pGlu-His-Pro-OH, pGlu-(1-Me)His-Pro-amide, pGlu-His-(3,4-dehydro)Pro-amide, pGlu-His-OH, pGlu-Glu-Pro-amide, and pGlu-Phe-Pro-amide provided comparison data. The stoichiometry of the major Cu(II)-TRH complex at pH 7.45 and greater is 1:1. The conditional formation constant (in pH 9.84 borate with 12.0 mM tartrate) for the formation of the complex is above 10⁵ M⁻¹. The coordination starts from the 1-N of the histidyl imidazole, and then proceeds along the backbone involving the deprotonated pGlu-His amide and the lactam nitrogen of the pGlu residue. The fourth equatorial donor is an oxygen donor from water. Hydroxide begins to replace the water before the pH reaches 11. Minority species with stoichiometry of Cu-(TRH)_x (x = 2-4) probably exist at pH lower than 8.0. In non-buffered aqueous solutions, TRH acts as a monodentate ligand and forms a Cu(II)-(TRH)₄ complex through imidazole nitrogens. All the His-containing analogs behave like TRH in terms of the above properties.     

The copper-molybdenum antagonism in ruminants. III. Reaction of copper(II) with tetrathiomolybdate(VI)

The stoichiometry of the reaction between Cu(II) and MoS₄²⁻ in neutral aqueous solution was observed to proceed with a 1.5:1 Cu:Mo ratio. The reaction results in the reduction of Cu(II) and the quantitative formation of an insoluble solid. The results contrast with an earlier report of a 1:1 stoichiometric ratio, this latter ratio was, however, observed with Cu^II(albumin) as reactant, in this case no precipitate was observed. The insoluble products were examined by a number of spectroscopic techniques and by X-ray power diffraction and elemental analysis. Two products were identified. Solid A is isostructural with the known (NH₄)Cu^IMoV^VIS₄, i.e. has the composition M^ICuMoS₄, M^I= NH₄⁺, Na⁺ or Et₄N⁺. Solid B has the approximate composition CuMoS₄O_x, x=2−3 and contains Cu(I) and Mo(V) centres. Formation of compound B therefore involves an unusual internal two-electron redox process. The reaction and products are of particular biological significance.     

Tailoring the Field Distribution of ZnO by Polyaniline for SPR-Based Fiber Optic Detection of Hardness of the Drinking Water

Due to the industrial development, drinking water is getting polluted by disposing several waste products of the industries. Hardness is one of the prominent impurities in drinking water which is mainly due to the presence of carbonate and bicarbonate ions (CO₃ ^2? and HCO₃ ^?) in it. Here, we present the synthesis of the zinc oxide (ZnO) and polyaniline (PANI) nanocomposite for the detection and estimation of hardness of the drinking water. The chemical formula of such a nanocomposite is defined in terms of the fraction of polyaniline nanoparticles reinforced in ZnO matrix and is derived as ZnO_(1???x)PANI _x (0?≤?x?≤?0.9); x is the composition ratio. Silver and ZnO_(1???x)PANI _x layers are coated over the unclad core of the optical fiber so as to create the four layer system as that of Kretschmann configuration SPR structure. The working principle involves the change in dielectric constant of (ZnO_(1???x)PANI _x ) by CO₃ ^2? or HCO₃ ^? ions in aqueous atmosphere. Due to the strong interaction of the sensing surface to the CO₃ ^2? and HCO₃ ^? ions, a red shift in the SPR spectrum is observed in the concentration range 0–200 μg/l. The sensitivity of the sensor depends on the composition ratio of the nanocomposite and has been found to be maximum for the composition ratio lying in the range 0.45–0.60. This has been further confirmed in terms of the enhancement of the electric field density and found to be in agreement with the experimental value. The sensitivity of the sensor with optimum value of the composition ratio is 0.094 and 0.065 nm/(μg/l) for CO₃ ^2? and HCO₃ ^?, respectively. The sensor is highly selective to CO₃ ^2? and HCO₃ ^?. The sensor has advantages of online monitoring and remote sensing of water quality because the probe is fabricated over an optical fiber.     

Further Study on the Statistical Test to Detect Spatial Pattern

In the study of spatial patterns, the statistic I' = (n — 1)s²/x was commonly used. In this paper, we found that x — s² has an approximated normal distribution with zero mean if the x_i's (i = 1 to n) are independent identically distributed Poisson variables. Based on this conclusion, the hypothesis that a point pattern is completely random can be tested directly. And a method for the test of spatial patterns was proposed which can be sued as an alternative to the Chi-square based dispersion index test.     

Mammalian Complex I Pumps 4 Protons per 2 Electrons at High and Physiological Proton Motive Force in Living Cells

Mitochondrial complex I couples electron transfer between matrix NADH and inner-membrane ubiquinone to the pumping of protons against a proton motive force. The accepted proton pumping stoichiometry was 4 protons per 2 electrons transferred (4H⁺/2e⁻) but it has been suggested that stoichiometry may be 3H⁺/2e⁻ based on the identification of only 3 proton pumping units in the crystal structure and a revision of the previous experimental data. Measurement of proton pumping stoichiometry is challenging because, even in isolated mitochondria, it is difficult to measure the proton motive force while simultaneously measuring the redox potentials of the NADH/NAD⁺ and ubiquinol/ubiquinone pools. Here we employ a new method to quantify the proton motive force in living cells from the redox poise of the bc₁ complex measured using multiwavelength cell spectroscopy and show that the correct stoichiometry for complex I is 4H⁺/2e⁻ in mouse and human cells at high and physiological proton motive force.     

A generalization of Pielou's index of non-randomness.

Pielou's index of non-randomness a measuring the distribution of point spatial patterns on a plane generalizes to an index in n-dimensional Euclidean space Eⁿ. This defines an index of non-randomness measuring the extent of regularity, randomness, or aggregation in distributions of point spatial patterns in Eⁿ.     

Water quality indicators: Comparison of a probabilistic index and a general quality index. The case of the Confederación Hidrográfica del Júcar (Spain)

The main objective of this work is to measure water quality using a stochastic index built with tools of Probability Theory. Its great advantage is that it accounts for the underlying uncertainty in quality classification that results from variations in the data for individual physical and chemical characteristics, considering them as random variables.We compare the results obtained by measuring water quality with this index (the probabilistic index, PI) and a classical deterministic index (the general quality index, GQI). Also we do a comparison with other usual indices in order to validate the PI index.To demonstrate the application of PI and GQI indices, we used information from the Confederación Hidrográfica del Júcar (Spain) for the period between 1990 and 2005. Our analyses showed that GQI was positively correlated with PI throughout the study period. Because of its high potential, the PI index can be used to analyze possible temporal changes in water quality, as well as to determine the individual influence of each variable in water quality. The results suggested an improvement in water quality over time and that omitting individually, one at a time, five of the nine water quality variables from the PI calculation significantly improved the calculated water quality.Novelty of this paper is the design of an index that takes into account the uncertainty inherent to data, and its application for measuring water quality from a general perspective.     

The causes of reduced proton-pumping efficiency in type B and C respiratory heme-copper oxidases,and in some mutated variants of type A

The heme-copper oxidases may be divided into three categories, A, B, and C, which include cytochrome c and quinol-oxidising enzymes. All three types are known to be proton pumps and are found in prokaryotes, whereas eukaryotes only contain A-type cytochrome c oxidase in their inner mitochondrial membrane. However, the bacterial B- and C-type enzymes have often been reported to pump protons with an H⁺/e^- ratio of only one half of the unit stoichiometry in the A-type enzyme. We will show here that these observations are likely to be the result of difficulties with the measuring technique together with a higher sensitivity of the B- and C-type enzymes to the protonmotive force that opposes pumping. We find that under optimal conditions the H⁺/e^- ratio is close to unity in all the three heme-copper oxidase subfamilies. A higher tendency for proton leak in the B- and C-type enzymes may result from less efficient gating of a proton pump mechanism that we suggest evolved before the so-called D-channel of proton transfer. There is also a discrepancy between results using whole bacterial cells vs. phospholipid vesicles inlaid with oxidase with respect to the observed proton pumping after modification of the D-channel residue asparagine-139 (Rhodobacter sphaeroides numbering) to aspartate in A-type cytochrome c oxidase. This discrepancy might also be explained by a higher sensitivity of proton pumping to protonmotive force in the mutated variant. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

RuBP carboxylase determination by enzymic estimation of D-3-PGA formed

RuBPcarboxylase activity was measured in extracts of barley (Hordeum Vulgare L., cv. HOP) seedlings both with the standard radiometric method and by measuring D-3-phosphoglyceric acid formed enzymically in a two stage assay. In the different conditions used, characterized by different NaHCO₃ concentrations, different pH and the presence and absence of oxygen, essentially the same ratio of D-3-PGA formed per ¹⁴CO₂ fixed was obtained. This ratio respected the known stoichiometry of two molecules of D-3-PGA formed per CO₂ fixed. It is suggested that measurement of D-3-PGA enzymically in a two stage assay can be routinely used for the determination of RuBP case activity instead of the radiometric method. The advantages and the validity of the method are discussed.     

Phosphorylation of skeletal muscle myosin light chain kinase by the catalytic subunit of cAMP-dependent protein kinase

Phosphatidylethanolamine (PE) was isolated from membranes of Bacillus megaterium. The organism was grown at 20°C and 55°C. The phase equilibria in PE/water systems were studied by ²H and ³¹P nuclear magnetic resonance, and by polarized light microscopy. PE isolated from B. megaterium grown at 20°C forms a lamellar liquid crystalline phase at the growth temperature, and at low water contents a cubic liquid crystalline phase at 58°C. The ratio iso/ante-iso acyl chains was 0.3 in this lipid. PE isolated from this organism grown at 55°C forms only a lamellar liquid crystalline phase up to at least 65°C. In this lipid the ratio iso/ante-iso acyl chains was 3.2.     

Determination of H/ATP Stoichiometry for the Plasma Membrane H-ATPase from Red Beet (Beta vulgaris L.) Storage Tissue

The H⁺/ATP stoichiometry was determined for the plasma membrane H⁺-ATPase from red beet (Beta vulgaris L., var Detroit Dark Red) storage tissue associated with native vesicles. The determination of H⁺/ATP stoichiometry utilized a kinetic approach where rates of H⁺ influx, estimated by three different methods, were compared to rates of ATP hydrolysis measured by the coupled enzyme assay under identical conditions. These methods for estimating H⁺ influx were based upon either determining the initial rate of alkalinization of the external medium from pH 6.13, measuring the rate of vesicle H⁺ leakage from a steadystate pH gradient after stopping the H⁺-ATPase or utilizing a mathematical model which describes the net transport of H⁺ at any given point in time. When the rate of H⁺ influx estimated by each of these methods was compared to the rate of ATP hydrolysis, a H⁺/ATP stoichiometry of about 1 was observed. In consideration of the maximum free energy available from ATP hydrolysis (ΔG_atp), this value for H⁺/ATP stoichiometry is sufficient to account for the magnitude of the proton electrochemical gradient observed across the plasma membrane in vivo.     

Vibrational raman spectra of lipid systems containing amphotericin B

Resonance-enhanced and normal vibrational Raman spectra were observed for both multilamellar and single-wall vesicle assemblies of dimyristoyl phosphatidylcholine containing amphotericin B, a channel-forming polyene antibiotic, and cholesterol. The decrease in the frequency of the polyene antibiotic C  C stretching mode at 1556 cm^?1 and the increase in intensity of the CCH in-plane deformation mode at 1002 cm^?1 indicate that amphotericin B is ordered in a lipid-cholesterol medium similarly to the solid, but is surrounded by a slightly more polar environment. The intensity of the C  C stretching mode I₁₅₅₆ decreases 4-fold during the broadened gel to liquid crystalline phase transition (16–32°C) of dimyristoyl lecithin-cholesterol (4 : 1) multilayers. Other resonance-enhanced vibrations of amphotericin B exhibit similar behavior. For amphotericin B in pure dimyristoyl lecithin multilayer or vesicle systems, however, the vibrational intensity associated with the C  C stretching mode remains constant during the melting of lipid hydrocarbon chains. In addition, a third effect occurs in liquid crystalline egg lecithin-cholesterol (4 : 1, mol ratio) multilayers in which I₁₅₅₆ first increases by 25% between 3 and 25°C, in parallel with the loss of active channels, and then remains constant as the temperature increases from 25 to 42°C. This latter intensity pattern is masked in the dimyristoyl lecithin-cholesterol system by the overwhelming effect upon the C  C mode from changes in the lipid chain packing characteristics which occur during the phase transition.The broadened phase transition in 4 : 1 dimyristoyl lecithin-cholesterol multilayers (16–32°C), as followed by the ratio of intensities at 2880 and 2850 cm^?1 (asymmetric and symmetric methylene C-H stretching modes, respectively) is slightly narrowed by the addition of amphotericin B, and effect from which a binding stoichiometry at 24° of 1 : 1 amphotericin B : cholesterol is estimated. This stoichiometry was confirmed by differential calorimetric scans, which also show the presence of a peak proportional to cholesterol content.Raman I_2880/2850 peak height ratios in pure dimyristoyl lecithin bilayers were increased over the 14–38°C range by amphotericin B, a spectral effect which suggests an ordering of the lipid matrix perhaps as a consequence of the polyene binding to the bilayer surface. For bilayers containing cholesterol, the ratios of intensities of the 2935 cm^?1 feature, composed mainly of acyl chain terminal methyl and underlying methylene C-H stretching modes, to the 2850 cm^?1 feature are significantly increased by amphotericin B. This effect indicates that the antibiotic penetrates the bilayer in the lipid-sterol system.     

Application of polyelectrolyte limiting laws to virial and asymptotic expansions for the Donnan equilibrium

We have applied a general polyelectrolyte theory to an analysis of the Donnan equilibrium. The polyelectrolyte concentration is measured by a dimensionless parameter x, equal to the ratio of the equivalent polyelectrolyte concentration to the concentration of salt in the external compartment. For small x, virial series - expansions in powers of x - are developed for the Donnan salt-exclusion, osmotic pressure, and electromotive force. For large x, asymptotic expansions for these effects are presented. Polyion-polyion interactions are explicitly neglected, so that the physical significance of the virial series differs from its meaning in neutral polymer chemistry. Numerical results illustrate large deviations from ideal Donnan behavior as well as satisfactory agreement with published data on the salt-exclusion and emf effects. However, results for the Donnan osmotic pressure disagree with the data, except in the case of zero salt concentration in the external compartment, for which agreement is almost exact.     

Hydroperoxide and carboxyl groups preferential location in oxidized biomembranes experimentally determined by small angle X-ray scattering: Implications in membrane structure

We report small angle X-ray scattering (SAXS) data from large unilamellar vesicles as model membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocoline (POPC) and two oxidized species, namely its hydroperoxidized form POPC-OOH and 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) lipid that has a carboxyl group at the end of its truncated sn-2 chain. The replacement of POPC by either POPC-OOH (POPC-OOH_xPOPC_1−x) or PazePC (PazePC_xPOPC_1−x), with oxidized lipid molar ratio x varying from 0.00 up to 1.00, permits to experimentally inspect changes in the membrane structural properties due to oxidation. The volume fraction distribution of each lipid chemical group along the bilayer is determined. The results quantify that 95% of the hydroperoxide group lies in the membrane polar moiety, near the carbonyl and phosphate groups, whereas just 5% of OOH group experiences the polar/apolar interface, for all values of x studied. In the case of PazePC up to x = 0.33, a bimodal distribution of the carboxyl group in the interior and polar regions of the lipid membrane is obtained, probably due to a dynamic movement of the shortened alkyl chain towards the water interface. The mean molecular area A gradually increases from 65.4 ± 0.4 Ų for POPC bilayers to 78 ± 2 Ų for pure POPC-OOH bilayers, whereas POPC-OOH membrane thickness resulted to be 20% thinner than the non-oxidized POPC membrane. For PazePC up to x = 0.33, A increases to 67 ± 2 Ų with 10% of membrane thinning. The SAXS results thus demonstrate how the lipid oxidation progress affects the membrane structural features, thus paving the way to better understand membrane damage under oxidative stress.     

E2P-like states of plasma membrane Ca2+‑ATPase characterization of vanadate and fluoride-stabilized phosphoenzyme analogues

The plasma membrane Ca²⁺?ATPase (PMCA) belongs to the family of P-type ATPases, which share the formation of an acid-stable phosphorylated intermediate as part of their reaction cycle. The crystal structure of PMCA is currently lacking. Its abundance is approximately 0.1% of the total protein in the membrane, hampering efforts to produce suitable crystals for X-ray structure analysis. In this work we characterized the effect of beryllium fluoride (BeF_x), aluminium fluoride (AlF_x) and magnesium fluoride (MgF_x) on PMCA. These compounds are known inhibitors of P-type ATPases that stabilize E2P ground, E2·P phosphoryl transition and E2·P_i product states. Our results show that the phosphate analogues BeF_x, AlF_x and MgF_x inhibit PMCA Ca²⁺?ATPase activity, phosphatase activity and phosphorylation with high apparent affinity. Ca²⁺?ATPase inhibition by AlF_x and BeF_x depended on Mg²⁺ concentration indicating that this ion stabilizes the complex between these inhibitors and the enzyme. Low pH increases AlF_x and BeF_x but not MgF_x apparent affinity. Eosin fluorescent probe binds with high affinity to the nucleotide binding site of PMCA. The fluorescence of eosin decreases when fluoride complexes bind to PMCA indicating that the environment of the nucleotide binding site is less hydrophobic in E2P-like states. Finally, measuring the time course of E?→?E2P-like conformational change, we proposed a kinetic model for the binding of fluoride complexes and vanadate to PMCA.In summary, our results show that these fluoride complexes reveal different states of phosphorylated intermediates belonging to the mechanism of hydrolysis of ATP by the PMCA.     

H-ATPase Activity from Storage Tissue of Beta vulgaris: II. H/ATP Stoichiometry of an Anion-Sensitive H-ATPase

The H⁺/ATP stoichiometry was determined for an anion-sensitive H⁺-ATPase in membrane vesicles believed to be derived from tonoplast. Initial rates of proton influx were measured by monitoring the alkalinization of a weakly buffered medium (pH 6.13) following the addition of ATP to a suspension of membrane vesicles of Beta vulgaris L. Initial rates of ATP hydrolysis were measured in an assay where ATP hydrolysis is coupled to NADH oxidation and monitored spectrophotometrically (A₃₄₀) or by monitoring the release of ³²P from [γ-³²P]ATP. Inasmuch as this anion-sensitive H⁺-ATPase is strongly inhibited by NO₃⁻, initial rates of H⁺ influx and ATP hydrolysis were measured in the absence and presence of NO₃⁻ to account for ATPase activity not involved in H⁺ transport. The NO₃⁻-sensitive activities were calculated and used to estimate the ratio of H⁺ transported to ATP hydrolyzed. These measurements resulted in an estimate of the H⁺/ATP stoichiometry of 1.96 ± 0.14 suggesting that the actual stoichiometry is 2 H⁺ transported per ATP hydrolyzed. When compared with the reported values of the electrochemical potential gradient for H⁺ across the tonoplast measured in vivo, our result suggests that the H⁺-ATPase does not operate near equilibrium but is regulated by cellular factors other than energy supply.     

The statistical detection of threshold signals in the retina

1. Photographic records of impulses from single ganglion cells in the cat's retina were made while the retina was stimulated by flashes occurring once a second. Ten flashes at each of several intensities near threshold were used. 2. For the purpose of statistical analysis, the number of impulses (x) falling within a critical period following each flash was used as an index of the response. Histograms of x were plotted and used to calculate rates of transfer of information by the ganglion cell for the case of an ideal experiment, the yes-no choice, in which flashes of intensity I and blanks are to be distinguished. 3. The information rate increased (a) with increasing stimulus intensity and (b) with the number of identical flashes or blanks presented successively in a block. The intensity chosen as threshold by the experimenter, who observed the impulses visually and aurally, corresponded to an average information rate for single flashes of 0.7 bit/flash, compared to the maximum possible rate of 1 bit/flash. A threshold intensity giving 0.4 or more bit/flash, if presented in blocks of six identical flashes, corresponded to 0.95 or more bit/block, or near certainty. Thus the calculation of information rates using the index x provides an estimate of threshold at least as sensitive as those obtained during an experiment, which were made only after observing the responses to five to ten flashes of the same intensity. 4. The index x has statistical properties similar to those of the "index of neural activity" used by Tanner and Swets (1954) in their statistical model of human vision, and represents a possible physical interpretation of their index. However, x gave values (0.5 to 1.5) of the parameter called the slope which were consistently smaller than their values (2.1 to 3.1).     

Concentric-tube airlift bioreactors

Gas holdup investigations were performed in three concentric-tube airlift reactors of different scales of operation (RIMP: 0.070 m³; RIS-1: 2.5 m³; RIS-2: 5.2 m³; nominal volumes). The influences of the top and bottom clearances and the flow resistances at the downcomer entrance were studied using tap water as liquid phase and air as gaseous phase, at atmospheric pressure. It was found that the gas holdup in the individual zone of the reactor: riser, downcomer and gas-separator, as well as that in the overall reactor is affected by the analyzed geometrical parameters in different ways, depending on their effects on liquid circulation velocity. Gas holdup was satisfactorily correlated with Fr, Ga, bottom spatial ratio (B), top spatial ratio (T), gas separation ratio (Y) and downcomer flow resistance ratio (A _d /A _R ). Correlations are presented for gas holdup in riser, downcomer, gas separator and for the total gas holdup in the reactor. All the above stressed the importance of the geometry in dynamic behaviour of airlift reactors.