Verification of Beam Models for Ionic Polymer-Metal Composite Actuator

Ionic Polymer-Metal Composite (IPMC) can work as an actuator by applying a few voltages.A thick IPMC actuator,whereNafion-117 membrane was synthesized with polypyrrole/alumina composite filler,was analyzed to verify the equivalent beamand equivalent bimorph beam models.The blocking force and tip displacement of the IPMC actuator were measured with a DCpower supply and Young’s modulus of the IPMC strip was measured by bending and tensile tests respectively.The calculatedmaximum tip displacement and the Young’s modulus by the equivalent beam model were almost identical to the correspondingmeasured data.Finite element analysis with thermal analogy technique was utilized in the equivalent bimorph beam model tonumerically reproduce the force-displacement relationship of the IPMC actuator.The results by the equivalent bimorph beammodel agreed well with the force-displacement relationship acquired by the measured data.It is confirmed that the equivalentbeam and equivalent bimorph beam models are practically and effectively suitable for predicting the tip displacement,blockingforce and Young’s modulus of IPMC actuators with different thickness and different composite of ionic polymer membrane.     

含离子液体体系中固定化细胞转化甘草酸生成单葡萄糖醛酸基甘草次酸

研究疏水性离子液体1-丁基-3-甲基咪唑六氟磷酸盐([BMIM]PF6)与醋酸-醋酸钠缓冲液两相体系中,固定化产紫青霉Penicillium purpurogenum Li-3细胞转化甘草酸(GL)生成单葡萄糖醛酸基甘草次酸(GAMG)的反应,并与缓冲液单相体系作为对照.确定了在[BMIM]PF6/缓冲液两相体系中,最适离子液体加入比例、缓冲液pH、反应温度、底物浓度分别为10%、5.8、35℃和6.0mmol/L,在此条件下反应58h,甘草酸转化率为87.03%,比缓冲液单相体系提高了15.02%.离子液体循环使用8次后,回收利用率维持在85.28%.主产物GAMG和副产物甘草次酸(GA)在两相体系中得到有效分离,为后续产物分离带来便利.     

Computation of pH evolution versus ionic products concentration in a fermentation broth

An algorithm developed for pH computation has been tested to calculate the theoretical pH changes in a culture medium during the course of a fermentation. A divergence between the computed pH value and the value measured with the electrode allows us to highlight the presence of undetected ionic products. The calculation with the algorithm by means of a computer requires only the knowledge of the ionic properties of the substrates and detected products and existing thermodynamic constants. (c) 1993 Wiley & Sons, Inc.     

生物法合成β-丙氨酸的分离纯化工艺研究

依据天冬氨酸和β-丙氨酸等电点的差异,采用静态吸附和动态吸附法,筛选适于分离β-丙氨酸的最佳树脂,并研究最佳树脂的吸附动力学和料液pH值、上样液流速,洗脱剂浓度等对β-丙氨酸分离的影响。结果表明:β-丙氨酸吸附的最佳树脂为HZ014,HZ014的静态吸附70 min达到动态平衡,吸附容量为72.92 g.kg-1,吸附率高于90%,最佳料液流速是2 ml.min-1,料液最佳pH为5.0,洗脱剂氨水浓度为4%。     

Eco-physiological responses of linseed (Linum usitatissimum) to salt and alkali stresses

AimsEffects of salt and alkali stresses (NaCl-Na₂SO₄ and NaHCO₃-Na₂CO₃) were compared on growth, photosynthesis characters, ionic balance and osmotic adjustment of linseed (Linum usitatissimum), to elucidate the mechanisms of salt and alkali stress (high pH value) damage to plants, and their physiological adaptive mechanisms to the stresses. MethodsThe experiment was carried out in an artificial greenhouse. Plants grew at approximately 700 mmol·m^-2·s^-1 photosynthetic photon flux density (PPFD) in greenhouse under photoperiod of 15 h in light and 9 h in dark. In each plastic pot (17 cm diameter) which contained 2.5 kg of washed sand, 20 linseed seeds were sown. The seedlings were exposed to stresses lasting 14 days after 2 months.Important findingsThe inhibitory effects of alkali stress on linseed growth were more remarkable than those of salt stress, indicating that alkali and salt represent two distinct forms of stress. The alkali stress increased the Na⁺ content in shoots, damaged the photosynthetic system, and highly reduced the net photosynthetic rate and C assimilation capacity. Under salinity stress, the Na⁺ content increased, the K⁺ content decreased with increasing stress. Greater changes were observed under alkali than under salt stress. Alkali stress caused the massive influx of Na⁺, which probably explained that the harmful of alkali stress on plants was stronger than that of salt stress. Under alkali stress, Ca²⁺ and Mg²⁺ decreased in roots, showing that high pH value around roots hindered the absorption of them. Fe²⁺ and Zn²⁺ had little effects on the osmotic adjustment, mainly because of they had a low ion content. Under salt stress, anion increased in order to balance the sharp increase of Na⁺. However, alkali stress made severe deficit of negative charge, broke the intracellular ionic balance and pH homeostasis, and caused a series of strain response. Our results showed that linseed enhanced the synthesis of soluble sugars to balance massive influx of Na⁺ under salt stress, but linseed enhanced the synthesis of organic acids to compensate for the shortage of inorganic anions, which might be a key pathway for the pH adjustment. In conclusion, the alkali stress (high pH value) clearly inhibited the growth, element absorption, ion homeostasis reconstruction of plants. Organic acid concentration is possibly a key adaptive factor for linseed to maintain intracellular ion balance and regulate high pH value under alkali stress.     

Experimental Measurement of Monovalent Cation Adsorption onto Bacillus subtilis Cells

Typically, the effects of ionic strength on metal adsorption to geosorbents are accounted for by models of the surface electric field, assuming a planar surface. However, bacterial cell walls are not two-dimensional surfaces. Furthermore, electric field model parameters for complex systems are difficult to determine and apply. We propose an alternative approach to electric field models of ionic strength effects by explicitly accounting for monovalent cation adsorption onto specific bacterial binding sites. We calculate stability constants for monovalent metal-bacterial surface complexes, and use them to determine the magnitude of correction needed for a previously determined stability constant for a Cd-bacterial surface complex.     

Quantifying post-fire regrowth of remotely sensed mediterranean vegetation with percolation-based methods

ABSTRACT

Mediterranean landscapes are characterized by high stability to fire since regeneration of pre-existing spatial relationships among distinctive vegetation patches is quite rapid. The aim of this paper is to introduce a method based on percolation theory to quantitatively estimate structural variations in remotely sensed biomass data linked to post-fire dynamics of Mediterranean vegetation. The ability of the proposed method to estimate fire-induced variations in Mediterranean vegetation patterns made it appropriate to the monitoring of post five vegetation regrowth in Mediterranean landscapes at the Landsat TM scale.     

Magnesium cation initiates nucleoside triphosphate to monophosphate conversion by a radical mechanism: Quantum molecular dynamics simulation

A DFT:B3LYP (6-311G** basis set) quantum molecular dynamics simulation was used to study the mechanism of Mg²⁺-induced conversion of guanosine triphosphate (GTP) to guanosine monophosphate (GMP). The computations were performed at 310 K in a bath of 178 water molecules surrounding the Mg(H₂O)₂-GTP complex and mimicking the hydration shells. Dissociation of the Mg²⁺-GTP complex (process duration, 5 ps) produces two phosphate anions (P_i), a hydrated Mg²⁺ cation, atomic oxygen, and a highly reactive GMP radical. This radical appears as a result of the action of Mg²⁺, which initiates the radical mechanism of GTP cleavage. At the initial stage of the interaction with GTP, Mg²⁺ is reduced to Mg⁺, producing an ion-radical pair ⁺Mg^·-^·GTP^3?. In the absence of Mg²⁺, an inert GMP molecule forms instead of the GMP radical as a result of hydrolytic cleavage of GTP via an ionic mechanism. Presumably, formation of the GMP radical and analogous radicals with adenosine, cytidine, thymidine, and uridine is a key point in the syntheses of deoxyribonucleic and ribonucleic acids.     

Aerolysin,a hemolysin fromAeromonas hydrophila,forms voltage-gated channels in planar lipid bilayers

Summary The cytolytic toxin aerolysin was found to form ion channels which displayed slight anion selectivity in planar lipid bilayers. In voltage-clamp experiments the ion current flowing through the channels was homogeneous indicating a defined conformation and a uniform size. The channels remained open between –70 to +70 mV, but outside this range they underwent voltage-dependent inactivation which was observed as open-closed fluctuations at the single-channel level. Zinc ions not only prevented the formation of channels by inhibiting oligomerization of monomeric aerolysin but they also induced a closure of preformed channels in a voltage-dependent fashion. The results of a Hill plot indicated that 2–3 zinc ions bound to a site within the channel lumen. Proaerolysin, and a mutant of aerolysin in which histidine 132 was replaced by an asparagine, were both unable to oligomerize and neither could form channels. This is evidence that oligomerization is a necessary step in channel formation.     

The effect of ionic stress on photosynthesis in Dunaliella tertiolecta

A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the Kautsky effect) in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3,4-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3,4-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FCCP carbonylcyanide p-trifluoromethoxyphenylhydrazone - PSI, II photosystem I, II