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排序方式: 共有84条查询结果,搜索用时 15 毫秒
1.
Dragoslav Herceg 《Numerische Mathematik》1989,56(7):675-693
Summary The numerical solution of a nonlinear singularly perturbed two-point boundary value problem is studied. The developed method is based on Hermitian approximation of the second derivative on special discretization mesh. Numerical examples which demonstrate the effectiveness of the method are presented.This research was partly supported by NSF and SIZ for Science of SAP Vojvodina through funds made available to the U.S.-Yugoslav Joint Board on Scientific and Technological Cooperation (grants JF 544, JF 799) 相似文献
2.
D. Djikanović A. Kalauzi K. Radotić C. Lapierre M. Jeremić 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(9):1425-1428
In this work, we deconvoluted the fluorescence spectra of lignin and a lignin model compound using a combination of one symmetric
(Gaussian) and the most appropriate number of asymmetric (Log-normal) models. We aimed to obtain new data on the structural
characteristics of lignin as a complex molecule using fluorescence spectroscopy in combination with FTIR spectra. We analyzed
the emission spectra of the lignin model compound, DHP, and isolated lignins from a deciduous tree, poplar, and a coniferous
tree, spruce. The number of applied asymmetric components was varied for each sample until the component positions obtained
from deconvolution of a series of spectra became constant. The lignin model compound contains fewer components in the emission
spectrum. The same components in the spectra of all three samples show that they contain the same fluorophores. The small
shift of the peak position can be attributed to the influence of different environments. The FTIR spectra of the three polymers
show a small difference between their structures. The main difference among the IR spectra of the three samples is in the
intensity of some peaks.
The text was submitted by the authors in English. 相似文献
3.
Mund G Vidovic D Batchelor RJ Britten JF Sharma RD Jones CH Leznoff DB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(19):4757-4763
Several iron(III) complexes incorporating diamidoether ligands are described. The reaction between [Li(2)[RN(SiMe(2))](2)O] and FeX(3) (X=Cl or Br; R=2,4,6-Me(3)Ph or 2,6-iPr(2)Ph) form unusual ate complexes, [FeX(2)Li[RN(SiMe(2))](2)O](2) (2, X=Cl, R=2,4,6-Me(3)Ph; 3, X=Br, R=2,4,6-Me(3)Ph; 4, X=Cl, R=2,6-iPr(2)Ph) which are stabilized by Li-pi interactions. These dimeric iron(III)-diamido complexes exhibit magnetic behaviour characteristic of uncoupled high spin (S= 5/2 ) iron(III) centres. They also undergo halide metathesis resulting in reduced iron(II) species. Thus, reaction of 2 with alkyllithium reagents leads to the formation of iron(II) dimer [Fe[Me(3)PhN(SiMe(2))](2)O](2) (6). Similarly, the previously reported iron(III)-diamido complex [FeCl[tBuN(SiMe(2))](2)O](2) (1) reacts with LiPPh(2) to yield the iron(II) dimer [Fe[tBuN(SiMe(2))](2)O](2) but reaction with LiNPh(2) gives the iron(II) product [Fe(2)(NPh(2))(2)[tBuN(SiMe(2))](2)O] (5). Some redox chemistry is also observed as side reactions in the syntheses of 2-4, yielding THF adducts of FeX(2): the one-dimensional chain [FeBr(2)(THF)(2)](n) (7) and the cluster [Fe(4)Cl(8)(THF)(6)]. The X-ray crystal structures of 3, 5 and 7 are described. 相似文献
4.
Brankica Jovanović Dragoslav Nikezić 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):939-944
Biological effects of radiation in terms of their effect on living cells are considered in this work. In dosimetry of the
human lung exist the need to include the influence of the biological effects. The aim of this work is to calculate the probability
of biological effects (transformation cell and production of lesion) per hit induced by alpha particle radiation on sensitive
cells of human lung. Probability was calculated by applying the analytical model cylinder bifurcation (Nikezić et al., Int
J Radiat Biol 79(3):175–180, 2003; Nikezić and Yu, Radiat Environ Biophys 42:49–53, 2003) which was created to simulate the geometry of human lung with the geometric distribution of cell nuclei in the airway wall
of the tracheobronchial tree. This analytical model of the human traheobronchial tree represent the exstension of the ICRP66
model, and follows it as much as possible. Reported probabilities are calculated for various targets and alpha particle energies
in order to show dependence of the probability of biological effects (transformation cell and production of lesion) per hit
from alpha particle energies and the geometry of tracheobronchial tree for the human lung. 相似文献
5.
The reaction between 3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridinecarboxaldehyde semicarbazone (pyridoxal-semicarbazone or PLSC) and appropriate chloride, sulfate, nitrate or thiocyanate Cu(II) salts in water/alcohol mixtures resulted in the formation of new copper(II) complexes: [Cu(PLSC)Cl2] (1), [Cu(PLSC)(H2O)(SO4)]2·3H2O (2), [Cu2(PLSC)2(NCS)2](NCS)2 (3), [Cu(PLSC)(NO3)2(CH3OH)] (4) and [Cu(PLSC-2H]NH3·H2O (5). The complexes were characterized by elemental analysis, conductometric measurements and IR spectroscopy, while complexes 1, 2, 3 and 4 were further characterized by single crystal X-ray diffraction. 相似文献
6.
Mansaray HB Kelly M Vidovic D Aldridge S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(19):5381-5386
The ability of substituted carbazol‐9‐yl systems to ligate in σ fashion through the amido N‐donor, or to adopt alternative coordination modes through the π system of the central five‐membered ring, can be tuned by systematic variation in the steric demands of substituents in the 1‐ and 8‐positions. The differing affinities of the two modes of coordination for hard and soft metal centres can be shown to influence not only cation selectivity, but also the redox properties of the metal centre. Thus, the highly sterically sterically demanding 1,3,6,8‐tetra‐tert‐butylcarbazolyl ligand can be used to generate the structurally characterised amido‐indium(I) complex, [{(tBu4carb)In}n], (together with its isostructural thallium counterpart) in which the metal centre interacts with the central pyrrolyl ring in η3 fashion [d(In? N)=2.679(3) Å; d(In? C)=2.819(3), 2.899(3) Å]. By contrast, the smaller 3,6‐di‐tert‐butylcarbazolyl system is less able to restrict the metal centre from binding at the anionic nitrogen donor in the plane of the carbazolyl ligand (i.e. in σ fashion). Analogous chemistry with InI precursors therefore leads to disproportionation to the much harder InII [and In0], and the formation of the mixed‐valence product, [In2{In2(tBu2carb)6}], a homoleptic molecular [In4(NR2)6] system. This chemistry reveals a flexibility of ligation for carbazolyl systems that contrasts markedly with that of the similarly sterically encumbered terphenyl ligand family. 相似文献
7.
Raman spectra of the species Hg(SCN)2, [Hg(SCN)3], and [Hg(SCN)4]2- in solution of ten aprotic donor solvents have been investigated in the region of the Hg-S vibration. Observed frequency values of measured band of Hg(SCN)2 and [Hg(SCN)3] in different solutions correlate well with donor strength of the solvents. There is a linearity between Hg-S frequency decreasing and increasing of the interaction of the solvent molecules with the mercury (II) ion in the thiocyanate complexes. No significant frequency changes have be found for [Hg(SCN)4]2-. Evidence based on the frequency shifts and depolarization ratios in various solvents supports the view that the Hg(SCN)2 in solution undergos departure from linearity as a result of increasing solvent coordination to the mercury (II) ion. Almost constant frequencies of Hg-S vibration of [Hg(SCN)4]2- in all investigated solvents suggest a regular tetrahedral structure of the ion in solution having much larger radius than corresponding HgX4 (X=Cl,Br,I) ions. 相似文献
8.
Dragoslav Jeremić Slobodan Macura Slobodan Milosavljević Vlatka Vajs 《Tetrahedron》1985,41(2):357-364
Identification of a novel trioxygenated Δ8(9),15_ pimaric acid methyl ester from plant species Lycopus europaeus by means of two-dimensional 1H NMR spectroscopy (COSY and NOESY) is reported. 相似文献
9.
The identification of two novel isomeric trioxygenated caryophyllenes from the plant species is reported. 相似文献