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排序方式: 共有321条查询结果,搜索用时 31 毫秒
81.
JosÉ Humberto De Queiroz Jean-Louis Uribelarrea Alain Pareilleux 《Applied biochemistry and biotechnology》1991,30(3):285-295
Cultivation of the fission yeastSchizosaccharomyces pombe in a cellrecycle fermentor with cross-flow filtration using mineral membranes to recycle the biomass is described. Total
cell retention resulted in high cell density cultures with high productivities.
The dependence of both the growth kinetics and metabolic status on the operating conditions was identified and quantified.
Growth was controlled by the inhibitory effect of ethanol so long as glucose was in excess as might be expected for fermentative
metabolism. Under oxygen excess conditions, a partly oxidative catabolism of glucose occurred due to growth limitation by
the glucose feed flow. The cells displayed a purely oxidative metabolism when ethanol was not present in the broth but a respiro-fermentative
metabolism when ethanol was present as was the case when oxygen supply to the culture was limiting. 相似文献
82.
Dias AR Martins AM Ascenso JR Ferreira H Duarte MT Henriques RT 《Inorganic chemistry》2003,42(8):2675-2682
The preparations of 1,4,7-(NHPhSiMe(2))(3)-1,4,7-triazacyclononane (H(3)N(3)-tacn) and its lithium and sodium derivatives are described. The X-ray structure of the THF adduct of the lithium derivative, Li(3)N(3)-tacn(THF)(2), shows that one of the macrocycle pendant arms is bent to allow the coordination of the its lithium ion to two tacn amines. In solution, a fluxional process makes all the pending arms magnetically equivalent. The reactions of Li(3)N(3)-tacn or Na(3)N(3)-tacn with either TiCl(4) and TiCl(3)(THF)(3) led to the formation of [Ti(N(3)-tacn)], 5. The oxidation of 5 with various oxidizing reagents gave cationic complexes [Ti(N(3)-tacn)]X, 6 (X = I, Cl, SCN, PF(6), BPh(4)), that exist as a pair of enantiomers, lambda(lambdalambdalambda)/delta(deltadeltadelta), which interconvert in solution. The molecular structures of 5 and 6 (X = I, BPh(4)) show the coordination of the six nitrogen donor set to the titanium. Due to the short length of the tacn pendant arms, the hexadentate bonding mode of the ligand is mainly achieved through the sharpening of the N-Si-N angles. The reaction of [Ti(N(3)-tacn)]I, 6a, with W(CO)(6) led to the synthesis of [Ti(N(3)-tacn)][W(CO)(5)I], 7. 相似文献
83.
Humberto Terrones 《Journal of mathematical chemistry》1994,15(1):143-156
Mathematical transformations for graphite with positive, negative and zero Gaussian curvatures are presented. When the Gaussian curvatureK is zero, we analyse a bending transformation from a planar sheet into a cone. The Bonnet, the Goursat and a mixed transformation are studied for graphitic structures with the same topologies as triply periodic minimal surfaces (K < 0). We have found that using the Kenmotsu equations for surfaces of constant mean curvature it is possible to invert spherical and cylindrical graphite. A bending transformation for surfaces of revolution is also studied; during this transformation the helical arrangement of cylinders changes. All these transformations can give an insight into kinematic processes of curved graphite and into new shapes. 相似文献
84.
The method of flexible constraints was implemented in a Monte Carlo code to perform numerical simulations of liquid water and ice Ih in the constant number of molecules, volume, and temperature and constant pressure, instead of volume ensembles, using the polarizable and flexible mobile charge densities in harmonic oscillators (MCDHO) model. The structural and energetic results for the liquid at T=298 K and rho=997 kg m(-3) were in good agreement with those obtained from molecular dynamics. The density obtained at P=1 atm with flexible constraints, rho=1008 kg m(-3), was slightly lower than with the classical sampling of the intramolecular vibrations, rho=1010 kg m(-3). The comparison of the structures and energies found for water hexamers and for ice Ih with six standard empirical models to those obtained with MCDHO, show this latter to perform better in describing water far from ambient conditions: the MCDHO minimum lattice energy, density, and lattice constants were in good agreement with experiment. The average angle HOH of the water molecule in ice was predicted to be slightly larger than in the liquid, yet 1.2% smaller than the experimental value. 相似文献
85.
86.
Humberto Carrillo Calvet 《Applicable analysis》2013,92(3-4):191-208
The theorems that are presented in this paper, are a contribution to the foundations of the averaging method for ordinary differential equations. They involve the study of the persistent features of vector fields, under non autonomous perturbations of mean value zero. The problem of obtain ing qualitative information from the study of the averaged equation is considered and theorems that give new conditions to guarantee the uniform validitv of the approximation over the time interval [ 0.∞), are proved. A general icsult on the persistence of attractors is presented. The analysis uses in a fundamental way, a generalization of the notion of a solution stable under persistent disturbances. The proofs do not require special behavior of the linearized system and the results obtained are not only local, but give relevant information about the persistence of domains of attraction. 相似文献
87.
88.
Alfonso Oliva Aurora Molinari Jean Angulo Ricardo Schrebler Humberto Gómez Ricardo Córdova 《合成通讯》2013,43(23):4353-4360
The electrooxidation of 1-phenyl-3-methyl-4-butyldithiocarboxylate-5-pyrazolone 1 has been studied in ethanol/water solution, using a glassy carbon electrode surface. The electrochemical and spectroscopic data are in agreement with a bis-ketenedithioacetal disulphide compound 2 as the only product of the reaction. 相似文献
89.
Rodrigo Brito Santos Railmara Pereira da Silva Felipe Akihiro Melo Otsuka Danielle de Jesus Trindade Aline Costa Santos Humberto Reis Matos 《Biomedical chromatography : BMC》2019,33(4)
Hexokinases play a critical role in the cellular uptake and utilization of glucose. As such, they are of fundamental importance to all cells. By catalyzing glucose to produce glucose‐6‐phosphate, hexokinases control the first irreversible step of glucose metabolism and initiate all major pathways of glucose consumption. Our objective was to develop and validate highly sensitive and selective high‐performance liquid chromatography with photodiode array detector (HPLC‐PDA) assays allowing the determination of adenosine diphosphate, which was used for the determination of hexokinase activity. Samples were analyzed by HPLC‐PDA using a C18 analytical column (250 × 4.6 mm) for chromatographic separation. Optimal detection was achieved based on isocratic elution with a mobile phase consisting of a mixture of sodium phosphate monobasic buffer and methanol. This method met all of the requirements of specificity, sensitivity, linearity, precision, accuracy and stability generally accepted in bioanalytical chemistry and was successfully applied to a study of hexokinase activity in an alloxan‐induced diabetic rat model. Determination of hexokinase activity will permit characterization of cellular metabolic state in many diseases, such as cancer and diabetes. 相似文献
90.
Humberto Ramos Quoirin 《Mathematische Nachrichten》2015,288(14-15):1727-1740
We investigate a perturbed semilinear indefinite elliptic equation and show that the results known for the unperturbed equation still hold if the perturbation is sufficiently small. To this end, we use a continuity argument that allows us to establish the existence of two positive solutions even in the case where the strong maximum principle does not apply. 相似文献