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951.
D.Yu. Akimov H.M. Araújo E.J. Barnes V.A. Belov A. Bewick A.A. Burenkov R. Cashmore V. Chepel A. Currie D. Davidge J. Dawson T. Durkin B. Edwards C. Ghag A. Hollingsworth M. Horn A.S. Howard A.J. Hughes W.G. Jones G.E. Kalmus A.S. Kobyakin A.G. Kovalenko V.N. Lebedenko A. Lindote I. Liubarsky M.I. Lopes R. Lüscher K. Lyons P. Majewski A.StJ. Murphy F. Neves S.M. Paling J. Pinto da Cunha R. Preece J.J. Quenby L. Reichhart P.R. Scovell C. Silva V.N. Solovov N.J.T. Smith P.F. Smith V.N. Stekhanov T.J. Sumner C. Thorne L. de Viveiros R.J. Walker 《Physics letters. [Part B]》2010
952.
It is shown that a real novel shares many characteristic features with a null model in which the words are randomly distributed throughout the text. Such a common feature is a certain translational invariance of the text. Another is that the functional form of the word-frequency distribution of a novel depends on the length of the text in the same way as the null model. This means that an approximate power-law tail ascribed to the data will have an exponent which changes with the size of the text-section which is analyzed. A further consequence is that a novel cannot be described by text-evolution models such as the Simon model. The size-transformation of a novel is found to be well described by a specific Random Book Transformation. This size transformation in addition enables a more precise determination of the functional form of the word-frequency distribution. The implications of the results are discussed. 相似文献
953.
Maria G. da Fonseca Ramon K. S. Almeida Albaneide F. Wanderley Ulysses V. S. Ferreira Luiza N. H. Arakaki José A. Simoni Claudio Airoldi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):453-457
Polar n-alkylmonoamines of general formula H3C(CH2)
n
NH2 (n = 1, 3, 5) interacted with layered silicate vermiculite at the solid/liquid interface. The maximum amount of amine intercalated
(N
f
) inside the interlamellar space were 0.62, 0.46, and 0.38 mmol g−1, to give the following order of intercalation ethyl → butyl → hexylamines. The layered vermiculite solid was suspended in
deionized water and calorimetrically titrated with this series of amines, to give favorable thermodynamic data, such as exothermic
enthalpy, negative Gibbs free energy and positive entropy data. 相似文献
954.
Rosa M Rosa Infante M Miguel Mda G Lindman B 《Langmuir : the ACS journal of surfaces and colloids》2006,22(13):5588-5596
Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride (ALA) and N(alpha)-lauroyl-arginine-methyl ester hydrochloride (LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate (HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate (SOS) and sodium cetyl sulfate (SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure (cubosomes) and internal hexagonal structure (hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. (Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications. 相似文献
955.
Ferreira VF Jorqueira A Leal KZ Pimentel HR Seidl PR da Silva MN da Souza MC Pinto AV Wardell JL Wardell SM 《Magnetic resonance in chemistry : MRC》2006,44(4):481-490
The assignment of the diazo site in products of the reaction of p-toluenesulfonylhydrazine with beta-lapachone, 3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione, and other 1,2-naphthoquinones in methanol solution at room temperature has been accomplished using 1H,13C HMBC and 1H,15N HMBC NMR experiments. Only one diazo-naphthalenone product was isolated in yields ranging from 50-100% from each reaction. The site of diazo substitution of beta-lapachone and derivatives is the 1-position, in contrast to substitution at the 2-position in 4-MeO-1,2-naphthoquinone. Steric factors, rather than electronic factors, control the reaction site. Along with 2-diazo-1(2H)-naphthalenone, an additional product isolated from the reaction of p-toluenesulfonylhydrazide with 1,2-naphthoquinone was 2-diazo-4-hydroxy-1(2H)-naphthalenone. Confirmation of the formation of 6-diazo-2,2-dimethyl-2,3,4,6-tetrahydro-2H-benzo[h]cromen-5-one, obtained from beta-lapachone, was achieved using single crystal X-ray diffraction. 相似文献
956.
We present an ab initio procedure for accurately calculating aqueous-phase pKa values and apply it to study the acidity of nitrous acid (HNO2, or HONO). The aqueous-phase pK(a) of nitrous acid was obtained from calculated gas-phase acidities and solvation free energies via a thermodynamic cycle and the solvation model chemistry of Barone et al. (J. Chem. Phys. 1997, 107, 3210). Solvation free energies were calculated at the HF/6-31G(d) level using the dielectric-polarizable continuum and the integral equation formalism-polarizable continuum solvent models (D-PCM and IEF-PCM, respectively), with the D-PCM model yielding the most accurate pKa values. For HF free energies of solvation, significant improvements in accuracy could be made by moving to the larger 6-311++G(3df,3pd) and aug-cc-pVQZ basis sets. Solvation free energies were also calculated using the density functional theory (DFT) methods B3LYP, TPSS, PBE0, B1B95, VSXC, B98 and O3LYP, with the most accurate methods being TPSS and VSXC, which provided average errors of less than 0.11 pKa units. Solvation free energies calculated with the different DFT methods were relatively insensitive to the basis set used. Our theoretical calculations are compared with experimental results obtained using stopped flow spectrophotometry. The pKa of nitrous acid was measured as 3.16 at 25 degrees C, and the enthalpy and entropy of nitrous acid dissociation were calculated from measurements as 6.7 kJ mol(-1) and -38.4 J mol(-1) K(-1), respectively, between 25 and 45 degrees C. The UV/visible absorption spectra of the nitrite ion and nitrous acid were also examined, and molar extinction coefficients were obtained for each. 相似文献
957.
Heleno VC da Silva R Pedersoli S de Albuquerque S Bastos JK Silva ML Donate PM da Silva GV Lopes JL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(1):234-239
In this paper we present a complete 1H and 13C NMR spectral analysis of three lignan lactones (methylpluviatolide, dimethylmatairesinol and hinokinin) by the use of techniques such as COSY, HMQC, HMBC and J-resolved. Complete assignment and all homonuclear hydrogen coupling constant measurements were performed, providing enough data also to the confirmation of the relative stereochemistry. 相似文献
958.
Gaiao Eda N Martins VL Lyra Wda S de Almeida LF da Silva EC Araújo MC 《Analytica chimica acta》2006,570(2):283-290
The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H3PO4 in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H3PO4, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection. 相似文献
959.
Kirby AJ Davies JE Brandão TA da Silva PF Rocha WR Nome F 《Journal of the American Chemical Society》2006,128(38):12374-12375
Ammonia oxide is revealed as a stable molecule in a crystal structure and as a likely reactive species in many reactions of hydroxylamine. 相似文献
960.
McCarthy EL Egeler TJ Bickerstaff LE Pereira da Cunha M Millard PJ 《Analytical and bioanalytical chemistry》2006,386(7-8):1975-1984
Unique base sequences derived from RNA of both infectious hematopoietic necrosis virus (IHNV) and infectious salmon anemia
virus (ISAV) were detected and identified using a combination of surface-associated molecular padlock DNA probes (MPPs) and
rolling circle amplification (RCA) in microcapillary tubes. DNA oligonucleotides with base sequences identical to RNA obtained
from IHNV or ISAV were recognized by MPPs. Circularized MPPs were then captured on the inner surfaces of glass microcapillary
tubes by immobilized DNA oligonucleotide primers. Extension of the immobilized primers by isothermal RCA produced DNA concatamers,
which were labeled with fluorescent SYBR Green II nucleic acid stain, and measured by microfluorimetry. Molecular padlock
probes, combined with this method of surface-associated isothermal RCA, exhibited high selectivity without the need for thermal
cycling. This method is applicable to the design of low-power field sensors capable of multiplex detection of viral, bacterial,
and protozoan pathogens within localized regions of microcapillary tubes.
相似文献