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排序方式: 共有157条查询结果,搜索用时 15 毫秒
131.
Aloisio Pessoa de Araujo 《Journal of multivariate analysis》1978,8(4):598-613
It is shown, with the use of a concentration inequality of LeCam, that associated with an infinitely divisible random variable with values in a separable Banach space there is a Lévy-Khintchine formula. A partial converse of this fact is also proved. Relations between the continuity of the compound Poisson and the Gaussian variables associated with a Lévy measure are studied. A central limit theorem is obtained and examples are given. 相似文献
132.
J.A. Squella M. Huerta S. Bollo H. Pessoa L.J. Núez-Vergara 《Journal of Electroanalytical Chemistry》1997,420(1-2)
The electrochemical reduction of three nitrotetralone derivatives by tast and differential pulse polarography and cyclic voltammetry in a wide pH range was studied. In aqueous media, the reduction of mono- and dinitrotetralone follows the general pattern of reduction of aromatic nitro compounds: the nitro group is reduced in a four-electron step to a hydroxylamine group. However, in mixed media this reduction differs from that of other nitrobenzenes, due to the fact that the formation of the nitroradical anion was not observed. The reduction of the acetoxy derivative was studied only at alkaline pH, because it suffered acid hydrolysis. The ionization pK of the protonatable groups were polarographically obtained. 相似文献
133.
dos Santos PA Amarante MF Pereira AM Bertoni B França SC Pessoa C de Moraes MO Costa-Lotufo LV Pereira MR Lopes NP 《Chemical & pharmaceutical bulletin》2004,52(12):1433-1435
This work reports for the first time the production a furanoheliangolide (goyazensolide) by plant cell culture. Monitoring of the goyazensolide metabolism revealed that the maximum production occurred during the lag phase of the Lychnophora ericoides callus culture. The antiproliferative activity of obtained goyazensolide was evaluated against seven cancer cell lines using MTT assay. The results revealed a potent cytotoxic activity for the furaheliangolide with IC50 values in the range of 0.06 microg/ml for CEM leukemia cells to 0.75 microg/ml for B16 melanome cells. 相似文献
134.
Teresa M.V.D. Pinho e Melo Ana L. CardosoAntónio M.d'A. Rocha Gonsalves Richard C. StorrJoão Costa Pessoa José A. PaixãoAna M. Beja Manuela Ramos Silva 《Tetrahedron letters》2003,44(34):6409-6412
A phosphorus ylide bearing a 10-phenylsulfonylisoborneol unit reacted with ketenes, generated in situ from acid chlorides and triethylamine, to give allenic compounds. The reaction with methylketene led to asymmetric induction with the selective synthesis of an allene with axial chirality corresponding to an S configuration. The structure of the chiral allene 10-phenylsulfonylisobornyl penta-2,3-dienoate was determined by X-ray crystallography. Chirooptical studies of the chiral allene derivatives were done. 相似文献
135.
Castro SL Neto OD Santos SR Medeiros EP Lima RA Martins VL Araújo MC Josué CC Korn M 《Journal of AOAC International》2005,88(4):1064-1068
A flow-injection biamperometric method for determination of pantoprazole (PTZ) in pharmaceutical tablets is reported for the first time. The reversible redox couples Fe3+/Fe2+, Fe(CN)6(3-)/Fe(CN)6(4-), Ce4+/Ce3+, VO3(-)NO2+, and I2/I- were tested as indicating redox systems for biamperometric determination of PTZ in a flow-injection assembly with optimized flow parameters. The best results were obtained using V03(-)NO2+, which showed to be a selective and sensitive biamperometric indicating system for PTZ even in the presence of excipients and antioxidants that typically are found in drugs. The analytical graph was linear (r = 0.99945) in the range from 10 to 100 mg/L using 25 mmol/L VO3(-) as the reagent and water as the carrier stream and applying 100 mV between the 2 platinum wire electrodes. The limits of detection and quantitation were 200 and 667 microg/L, respectively, with a sensibility of calibration of 22.6 mV/mg/L. The proposed method was successfully applied to determine PTZ in commercial pharmaceutical tablets with a mean relative error of 1.60% (n = 5) and mean relative standard deviation of 3.10%. Recoveries close to 100% showed good agreement between the expected amount of PTZ in tablets (40 mg) and the results found by the application of the proposed method and demonstrated that the formulations used in the tablet compositions do not interfere in the PTZ analysis. The system had good stability, with a relative standard deviation of 3.80% for 9 sequential injections of a 60 mg/L PTZ solution. A sampling rate of about 100 samples/h was obtained. 相似文献
136.
Yan Xu Michele Vitolo Cristina Northfleet de Albuquerque Adalberto Pessoa Jr. 《Applied biochemistry and biotechnology》2003,108(1-3):853-865
To improve the selectivity of glucose-6-phosphate dehydrogenase (G6PDH) extraction by an aqueous two-phase system, a simple
and inexpensive affinity aqueous two-phase system using unbound reactive triazine dyes as ligands was introduced. In a polyethylene
glycol (PEG)/hydroxypropyl starch (PES) system, the unbound free triazine dyes, Cibacron Blue F3GA and Procion Red HE3B, partitioned
unevenly in the top PEG-rich phase and thus showed an affinity effect on G6PDH, but no influence on hexokinase. The various
parameters investigated were pH of the system, buffers, molecular weight of PEG, and ligand type and concentration. A two-step
affinity extraction process was established for the purification of G6PDH from baker’s yeast. The total yield of G6PDH was
66.9% and purification factor was 2.35. 相似文献
137.
Jakusch T Marcão S Rodrigues L Correia I Pessoa JC Kiss T 《Dalton transactions (Cambridge, England : 2003)》2005,(18):3072-3078
The dipeptide and tripeptide analogues salicyl-L-aspartic acid (Sal-L-Asp) and salicylglycyl-L-aspartic acid (SalGly-L-Asp) were synthesized and their protonation and complex formation with V(IV)O2+ were studied in aqueous solution through the use of pH-potentiometry and spectroscopic (UV-Vis, CD and EPR) techniques. The phenolate terminus proved to be a good anchoring site to promote (i) the metal ion-induced deprotonation and subsequent coordination of the peptide amide group(s) in the pH range 4-5 for the dipeptide analogue, (ii) and in the pH range 5-6 in a very cooperative way for the tripeptide analogue. The results suggest that the presence of good anchoring donors on both sides of the amide groups is responsible for the cooperative deprotonation of the two amide-NH groups. 相似文献
138.
Thereza Christina Vessoni Penna Marina Ishii Adalberto Pessoa Junior Olivia Cholewa 《Applied biochemistry and biotechnology》2004,114(1-3):469-483
The thermal stability of the recombinant green fluorescent protein (GFPuv) expressed by Escherichia coli cells and isolated by three-phase partitioning extraction with hydrophobic interaction chromatography was studied. The GFPuv
(3.5–9.0 μg of GFPuv/mL) was exposed to various pH conditions (4.91–9.03) and temperatures (75–95°C) in the 10 mM buffers: acetate (pH 5.0–7.0), phosphate (pH 5.5–8.0), and Tris-HCl (pH 7.0–9.0). The extent of protein denaturation (loss
of fluorescence intensity) was expressed in decimal reduction time (D-value), the time exposure required to reduce 90% of the initial fluorescence intensity of GFPuv. For pH 7.0 to 8.0, the thermostability
of GFPuv was slightly greater in phosphate buffer than in Tris-HCl. At 85°C, the D-values (pH 7.1–7.5) ranged from 7.24 (Tris-HCl) to 13.88 min (phosphate) The stability of GFPuv in Tris-HCl (pH>8.0) was
constant at 90 and 95°C, and the D-values were 7.93 (pH 8.38–8.92) and 6.0 min (pH 8.05–8.97), respectively. The thermostability of GFPuv provides the basis
for its potential utility as a fluorescent biologic indicator to assay the efficacy of moist-heat treatments at temperatures
lower than 100°C. 相似文献
139.
We classify all centers of a planar weight-homogeneous polynomial vector field of weight degree 1, 2, 3 and 4. 相似文献
140.
R. S. Pessoa J. C. Sagás B. V. M. Rodrigues N. K. A. M. Galvão M. A. Fraga G. Petraconi H.S. Maciel 《Brazilian Journal of Physics》2018,48(4):411-420
Hollow cathode discharge (HCD) is widely used in material processing and plasma emission spectroscopy due to several advantages over other plasma sources. Basically, the HCD consists of a cathode with a hollow structure (cavity, hole, or parallel faces) and an anode of arbitrary shape. In this investigation, experimental studies on low-pressure plane-parallel HCD operated at different process conditions are reported. Herein, we investigate the dependence of the discharge current on the product of the gas pressure and inter-cathode distance (pD). In addition, the electron temperature and density were inferred from the current-voltage characteristics of a single cylindrical Langmuir probe positioned between the cathodes, on the discharge axis. The measurements were carried out at different gas pressures, magnetic field intensities, working gases, inter-cathode distances, cathode materials, and discharge voltages. The results showed that, at different gas pressures, the maximum discharge current (Id,max) is not only a function of the product pD, but also of the pressure itself. Application of a uniform longitudinal magnetic field improved plasma confinement between cathodes, leading to a substantial increase in Id,max in most of the situations considered in this study. However, for oxygen discharge, a strong discharge current reduction after the application of the magnetic field was observed. In relation to the Langmuir probe studies, it was observed that the uniform longitudinal magnetic field reduced the electron temperature, but this behavior depends strictly on pD. The typical values of electron density and electron temperature in the case of the nitrogen discharge were ne?=?1017 m?3 and Te?=?2.5 eV, respectively. Finally, our experiments showed that the pD range for hollow cathode effects was between 0.2–5 Pa m. 相似文献