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排序方式: 共有128条查询结果,搜索用时 178 毫秒
41.
Alicia Dickenstein Laura Felicia Matusevich Timur Sadykov 《Advances in Mathematics》2005,196(1):78-123
We undertake the study of bivariate Horn systems for generic parameters. We prove that these hypergeometric systems are holonomic, and we provide an explicit formula for their holonomic rank as well as bases of their spaces of complex holomorphic solutions. We also obtain analogous results for the generalized hypergeometric systems arising from lattices of any rank. 相似文献
42.
We report a method for obtaining highly reproducible surface-enhanced Raman spectroscopy (SERS) of single and double-stranded thiolated DNA oligomers. Following a protocol that relaxes the DNA into an extended conformation, SERS spectra of DNA oligonucleotides are found to be extremely similar, strongly dominated by the Stokes modes of adenine. A spectral correlation function analysis useful for assessing reproducibility and for quantifying the highly complex changes corresponding to modifications in molecular conformation of the adsorbate molecules is introduced. This approach is used to monitor the interaction of DNA with cisplatin, a chemotherapy agent in widespread use. 相似文献
43.
Borodi G Bratu I Dragan F Peschar R Helmholdt RB Hernanz A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(5):1041-1048
Inclusion complexes of atenolol with beta-cyclodextrin (beta-CD) in aqueous solution have been investigated with (1)H NMR and UV-vis spectroscopy. The stoichiometry of this inclusion complex was established to be equimolar (1:1) and its stability constant was determined by UV-vis spectroscopy. The crystal structure of the beta-CD-atenolol (1:1) inclusion compound has been solved from synchrotron powder diffraction data using direct-space search techniques. The crystal structure model and (1)H NMR data are in good agreement and, with support of Hyperchem MM+ molecular dynamics results, suggest which protons are likely to be involved in the inclusion process that leads to the supramolecular architecture of this guest-host complex. 相似文献
44.
Ricci C Nyadong L Yang F Fernandez FM Brown CD Newton PN Kazarian SG 《Analytica chimica acta》2008,623(2):178-186
Pharmaceutical counterfeiting has become a significant public health problem worldwide and new, rapid, user-friendly, reliable and inexpensive methods for drug quality screening are needed. This work illustrates the chemical characterization of genuine and fake artesunate antimalarial tablets by portable Raman spectroscopy and validation by FT-Raman spectroscopy and ambient mass spectrometry. The applicability of a compact and robust portable Raman spectrometer (TruScan™) for the in situ chemical identification of counterfeit tablets is reported. 相似文献
45.
Vagner Irina Varlam Carmen Faurescu Ionut Faurescu Denisa Bucura Felicia 《Journal of Radioanalytical and Nuclear Chemistry》2017,314(2):709-713
Natural essential oil sample obtained from basil (Ocinum basilicum), and ethanol sample obtained from wine were measured to determine 14C specific activity, using two different sample preparation methods, and liquid scintillation counting method. The paper describes the use of two preparation methods, direct measurement method and CO2 absorption method, and the results obtained for this comparative study. Depending on carbon content of the sample and bubbling time, different correction factors of carbon mass trapped in liquid scintillation cocktail were established for CO2 absorption method.
相似文献46.
We investigate the solution space of hypergeometric systemsof differential equations in the sense of Gelfand, Graev,Kapranov and Zelevinski. For any integer d 2, we constructa matrix A(d) d x 2d and a parameter vector ß(d)such that the holonomic rank of the A-hypergeometric systemHA(d)(ß(d)) exceeds the simplicial volume vol(A(d))by at least d 1. The largest previously known gap betweenrank and volume was 2. Our construction gives evidence to the general observation thatrank jumps seem to go hand in hand with the existence of multipleLaurent (or Puiseux) polynomial solutions. 相似文献
47.
Yang Hsia Eric Gnesa Simon Tang Felicia Jeffery Paul Geurts Liang Zhao Andreas Franz Craig Vierra 《Applied Physics A: Materials Science & Processing》2011,105(2):301-309
The diversity in function and mechanical behavior of spider silks, and the ability to produce these silks recombinantly, have
tremendous potential in creating a new class of biomimetic materials. Here we investigate the structural and mechanical properties
of pyriform silks from the golden orb-weaver, Nephila clavipes. Nanoscale indentation measurements using atomic force microscopy on natural pyriform silk suggests that this biomaterial
has high toughness that may be suitable for dissipating high amounts of mechanical energy. We also observed the occurrence
of highly organized nanocrystals within the pyriform silk fibers that may contribute to the remarkable energy dissipation
capability of these silks. It has been demonstrated that poly-(Gly–Ala) and poly-Ala stretches within the internal block repeat
modules of dragline silk fibroins form nanocrystals, and these nanocrystalline structures may be responsible for the high
extensibility of the dragline silks. In contrast, amino acid sequence analysis shows that PySp2 does not contain the same
motifs. In the absence of poly-(Gly–Ala) and poly-Ala repeats, we hypothesized that PySp2 contains new protein motifs sufficient
to polymerize into functional structures. To investigate the functional contributions of these novel motifs during pyriform
fiber formation, we expressed different recombinant PySp2 fibroins with various segments spanning its block repeat units.
We demonstrate that PySp2 recombinant proteins with the Pro-rich sub-block domain (PXP motifs, where X= sub-set of the amino acids A, L, or R) and/or the Ser + Gln + Ala-rich sub-block domain (QQSSVAQS motifs) are sufficient
for artificial fiber formation. Moreover, we show that recombinant PySp2 proteins that contain a single block repeat unit
can self-assemble into foam-like nanostructures. Collectively, our findings support the use of PySp2 recombinant proteins
for a wide range of biomimetic materials with morphologies ranging from fibers to porous structures. 相似文献
48.
Felicia Phei Lin Lim Giuseppe Luna Khai Ching Tan Edward R.T. Tiekink Anton V. Dolzhenko 《Tetrahedron》2019,75(15):2322-2329
3-Amino-substituted 5-aminopyrazoles were found to be suitable substrates for the synthesis of new 4-aminopyrazolo[1,5-a][1,3,5]triazines (5-aza-9-deaza-adenines) when used in the one-pot, three-component reaction with cyanamide and triethyl orthoformate under microwave irradiation. The reaction proceeded selectively and its scope was demonstrated by the preparation of a library of 4-aminopyrazolo[1,5-a][1,3,5]triazines. Some structural aspects of the prepared compounds were investigated using dynamic NMR spectroscopy and X-ray crystallography. The operational simplicity, short reaction time, and good reproducibility are attractive features of the developed robust and practical approach for the synthesis of 7-amino-substituted 4-aminopyrazolo[1,5-a][1,3,5]triazines. 相似文献
49.
Mihaela Valeanu G. Filoti V. Kuncser Felicia Tolea B. Popescu A. Galatanu G. Schinteie A.D. Jianu I. Mitelea D. Schinle C.M. Craciunescu 《Journal of magnetism and magnetic materials》2008,320(14):e164-e167
Four Fe–Mn–Si alloys, Fe62Mn32Si6, Fe62Mn20Si5Cr8Ni5, Fe62Mn16Si5Cr12Ni5 and Fe65Mn9Si7Cr10Ni9, were obtained by the melt-spinning method. The samples were structurally, magnetic and shape memory effect (SME) investigated, both “as quenched” and thermally treated. The Mn-rich compositions show different phase, magnetic behavior and SME in comparison with Mn-poor compositions. The thermal treatments generate transformation between the two existing majority phases ( and γ), related magnetization and SME behavior. The features are derived from the corroboration of structural, magnetic interaction and magnitude of SME data. 相似文献
50.
Ma José Negro Ignacio Ballesteros Paloma Manzanares José Miguel Oliva Felicia Sáez Mercedes Ballesteros 《Applied biochemistry and biotechnology》2006,132(1-3):922-932
The use of stalks instead of tubers as a source of carbohydrates for ethanol production has been investigated. The inulin
present in the stalks of Jerusalem artichoke was extracted with water and the effect of solid-liquid ratio, temperature, and
acid addition was studied and optimized in order to attain a high-fructose fermentable extract. The maximum extraction efficiency
(corresponding to 35 g/L) of soluble sugars was obtained at 1/6 solidliquid ratio.
Fermentations of hydrolyzed extracts by baker's yeast and direct fermentation by an inulinease activity yeast were also performed
and the potential to use this feedstock for bioethanol production assessed. The results show that the carbohydrates derived
from Jerusalem artichoke stalks can be converted efficiently to ethanol by acidic hydrolysis followed by fermentation with
Saccharomyces cerevisiae or by direct fermentation of inulin using Kluyveromyces marxianus strains. In this last case about 30 h to complete fermentation was required in comparison with 8–9 h obtained in experiments
with S. cerevisiae growth on acid extracted juices. 相似文献