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排序方式: 共有73条查询结果,搜索用时 15 毫秒
1.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
2.
Chappell DJ Giani S Tanner G 《The Journal of the Acoustical Society of America》2011,130(3):1420-1429
Standard methods for describing the intensity distribution of mechanical and acoustic wave fields in the high frequency asymptotic limit are often based on flow transport equations. Common techniques are statistical energy analysis, employed mostly in the context of vibro-acoustics, and ray tracing, a popular tool in architectural acoustics. Dynamical energy analysis makes it possible to interpolate between standard statistical energy analysis and full ray tracing, containing both of these methods as limiting cases. In this work a version of dynamical energy analysis based on a Chebyshev basis expansion of the Perron-Frobenius operator governing the ray dynamics is introduced. It is shown that the technique can efficiently deal with multi-component systems overcoming typical geometrical limitations present in statistical energy analysis. Results are compared with state-of-the-art hp-adaptive discontinuous Galerkin finite element simulations. 相似文献
3.
Labiche M Orr NA Marqués FM Angélique JC Axelsson L Benoit B Bergmann UC Borge MJ Catford WN Chappell SP Clarke NM Costa G Curtis N D'Arrigo A de Góes Brennand E Dorvaux O Fazio G Freer M Fulton BR Giardina G Grévy S Guillemaud-Mueller D Hanappe F Heusch B Jones KL Jonson B Le Brun C Leenhardt S Lewitowicz M Lopez MJ Markenroth K Mueller AC Nilsson T Ninane A Nyman G de Oliveira F Piqueras I Riisager K Saint Laurent MG Sarazin F Singer SM Sorlin O Stuttgé L 《Physical review letters》2001,86(4):600-603
The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation. 相似文献
4.
Selective Reductive Elimination at Alkyl Palladium(IV) by Dissociative Ligand Ionization: Catalytic C(sp3)−H Amination to Azetidines 下载免费PDF全文
Manuel Nappi Chuan He William G. Whitehurst Ben G. N. Chappell Prof. Dr. Matthew J. Gaunt 《Angewandte Chemie (International ed. in English)》2018,57(12):3178-3182
A palladium(II)‐catalyzed γ‐C?H amination of cyclic alkyl amines to deliver highly substituted azetidines is reported. The use of a benziodoxole tosylate oxidant in combination with AgOAc was found to be crucial for controlling a selective reductive elimination pathway to the azetidines. The process is tolerant of a range of functional groups, including structural features derived from chiral α‐amino alcohols, and leads to the diastereoselective formation of enantiopure azetidines. 相似文献
5.
This study examines the difficulties college students experience when creating and interpreting graphs in which speed is one of the variables. Nineteen students, all preservice elementary or middle school teachers, completed an upper‐level course exploring algebraic concepts. Although all of these preservice teachers had previously completed several mathematics courses, including calculus, they demonstrated widespread misconceptions about the variable speed. This study identifies four cognitive obstacles held by the students, provides excerpts of their graphical constructions and verbal interpretations, and discusses potential causes for the confusion. In particular, misconceptions arose when students interpreted the behavior and nature of speed within a graphical context, as well as in situations where they were required to construct a graph involving speed as a variable. The study concludes by offering implications for the teaching and learning of speed and its interpretation within a graphical setting. 相似文献
6.
Epstein DM Chappell LL Khalili H Supkowski RM Horrocks WD Morrow JR 《Inorganic chemistry》2000,39(10):2130-2134
The interaction of three Eu(III) macrocyclic complexes Eu(THED)3+, Eu(ATHC)3+, and Eu(ATHC)3+, and Eu(S-THP)3+ with two 5'-cap model compounds, GpppG and m7GpppG is studied (THED = 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,-10-tetraazacyclododecane, ATHC = 1-(carbamoylmethyl)-4,7,10-tris(2-hydroxyethyl)-1,4,7,10- tetraazacyclododecane, S-THP = 1S,4S,7S,10S-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). Laser-induced excitation luminescence spectroscopy is used to study the binding of Eu(S-THP)3+ to GpppG (K = 5.9 x 10(4) M-1) and to characterize the Eu(S-THP)-GpppG complex. Both Eu(THED)3+ and Eu(S-THP)3+ bind to m7GpppG as monitored by use of fluorescence spectroscopy with binding constants of 5.9 x 10(3) and 4.4 x 10(4) M-1, respectively. The kinetics of cleavage of GpppG by two macrocyclic complexes is studied. Cleavage of GpppG by Eu(THED)3+ is accelerated by 15-fold in the presence of an equivalent of Zn(NO3)2 at pH 7.3, 37 degrees C, suggesting that two metal ions accelerate the cap cleavage reaction. Eu(ATHC)3+ promotes cleavage of GpppG with a pseudo-first-order rate constant of 2.6 x 10(-5) s-1 at pH 7.3, 37 degrees C, and 0.30 mM complex. 相似文献
7.
Ayora-Talavera T Chappell J Lozoya-Gloria E Loyola-Vargas VM 《Applied biochemistry and biotechnology》2002,97(2):135-145
Catharanthus roseus (L.) G. Don hairy roots harboring hamster 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) (EC 1.1.1.88) cDNA without membrane-binding
domain were evaluated by quantifying the levels of sterols and some indol-alkaloids. Clone 236, with the highest hybridization
signal, had the lowest soluble and microsomal HMGR activity and produced more ajmalicine and catharanthine than the control
but had reduced campesterol concentration. Clone 19, with low hybridization signal, had high soluble HMGR activity and produced
high levels of campesterol and five to seven times more serpentine than the control but a low level of ajmalicine and no accumulation
of catharanthine. These results suggest a possible role for HMGR in indole alkaloid biosynthesis and a possible cosuppression
of both the endogenous and foreign HMGR genes in clone 236. 相似文献
8.
The heterogeneous nucleation of gas bubbles from cavities in a surface in contact with a liquid is a widely recognized phenomenon. This process has previously been theoretically analyzed extensively for a conical crevice, although in practice a wide range of cavity geometries might be expected. The method of analysis originally presented by Atchley and Prosperetti [J. Acoust. Soc. Am. 86, 1065-1084 (1989)] for the unstable growth of a gas-liquid interface in a conical crevice is here extended to any axisymmetric cavity geometry and four such different geometries are analyzed. Although the method presented neglects gas transfer, and therefore is most directly suitable for acoustic cavitations, this method is still valuable in comparing the nucleation behavior of different cavity types. It is found that once the interface has emerged outside the cavity, its behavior is determined by the size of the cavity's opening. Given that the behavior of the interface once it is outside the cavity will also be determined by the local flow conditions, the threshold for unstable growth of the interface inside the cavity leading to its emergence is the important value and will determine differences between cavity geometries in practice, as shown in the examples presented. 相似文献
9.
(+)-Germacrene A, an important intermediate in sesquiterpene biosynthesis, was isolated in pure form from a genetically engineered yeast and was characterized by chromatographic properties (TLC, GC), MS, optical rotation, UV, IR, 1H NMR, and 13C NMR data. Variable-temperature 500 MHz 1H NMR spectra in CDCl3 showed that this flexible cyclodecadiene ring exists as three NMR-distinguishable conformational isomers in a ratio of about 5:3:2 at or below ordinary probe temperature (25 °C). The conformer structures were assigned by 1H NMR data comparisons, NOE experiments, and vicinal couplings as follows: 1a (52%, UU), 1b (29% UD), and 1c (19%, DU). 相似文献
10.
We present a new approach for modelling noise and vibration in complex mechanical structures in the mid-to-high frequency regime. It is based on a dynamical energy analysis (DEA) formulation which extends standard techniques such as statistical energy analysis (SEA) towards non-diffusive wave fields. DEA takes into account the full directionality of the wave field and makes sub-structuring obsolete. It can thus be implemented on mesh grids commonly used, for example, in the finite element method (FEM). The resulting mesh based formulation of DEA can be implemented very efficiently using discrete flow mapping (DFM) as detailed in Chappell et al. (2013) and described here for applications in vibro-acoustics. A mid-to-high frequency vibro-acoustic response can be obtained over the whole modelled structure. Abrupt changes of material parameter at interfaces are described in terms of reflection/transmission matrices obtained by solving the wave equation locally. Two benchmark model systems are considered: a double-hull structure used in the ship-building industry and a cast aluminium shock tower from a Range Rover. We demonstrate that DEA with DFM implementation can handle multi-mode wave propagation effectively, taking into account mode conversion between shear, pressure and bending waves at interfaces, and on curved surfaces. 相似文献