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21.
On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve 总被引:7,自引:0,他引:7
In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use of the retention curve to indirectly determine hydraulic conductivities is analyzed as follows. The theoretical derivation of the relationK(h) – (h) is briefly discussed with regards to potential sources of inaccuracy. The sensitivity of the algorithm forK(h) calculation is studied as a response to possible inaccuracies in the retention curve determination. Conclusions about the usability of calculated hydraulic conductivities are drawn. 相似文献
22.
In the paper we prove two inequalities involving Gelfand numbers of operators with values in a Hilbert space. The first inequality is a Rademacher version of the main result in [Pa-To-1] which relates the Gelfand numbers of an operator from a Banach spaceX intol
2
n
with a certain Rademacher average for the dual operator. The second inequality states that the Gelfand numbers of an operatoru froml
1
N
into a Hilbert space satisfy the inequality
相似文献
23.
Strong, low-energy two-photon absorption in extended amine-terminated cyano-substituted phenylenevinylene oligomers 总被引:8,自引:0,他引:8
Chung SJ Rumi M Alain V Barlow S Perry JW Marder SR 《Journal of the American Chemical Society》2005,127(31):10844-10845
Three quadrupolar oligophenylenevinylenes with five rings in the conjugated backbone, terminal donor groups, and various acceptors and/or donors along the backbone were synthesized and their two-photon spectroscopic properties investigated. These chromophores exhibit large two-photon absorption cross sections over a wide wavelength range and two distinct peaks, the strongest of which (deltamax > 3600 GM) is observed at 960-970 nm, a wavelength close to twice the value of the linear absorption maximum (2lambda(1)max). The findings on these chromophores are compared with those for analogous molecules with shorter conjugation length, for which the main two-photon band is at significantly shorter wavelength than 2lambda(1)max. 相似文献
24.
Tran Quang Minh Léon Christiaens Pierre Grandclaudon Alain Lablache-Combier 《Tetrahedron》1977,33(17):2225-2229
Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 ) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans. 相似文献
25.
26.
Simultaneous separation of flavanone glycosides and polymethoxylated flavones in citrus juices using liquid chromatography 总被引:5,自引:0,他引:5
We present a simultaneous liquid chromatographic method for the separation of two flavonoid compound families, flavanone glycosides (FGs) and polymethoxylated flavones (PMFs), which are usually found in citrus fruit species and varieties. This technique permits the quantitation of six FGs (narirutin, naringin, hesperidin, neohesperidin, didymin, poncirin) and six PMFs (sinensetin, hexamethoxyflavone, nobiletin, scutellarein, heptamethoxyflavone and tangeretin). This technique, to be used to characterize a citrus juice by its polyphenolic profile, has been applied to the determination of flavonoid compounds in grapefruit- and orange juice. Differentiation of orange juice varieties and mixtures containing tangor juice using polyphenolic profiles and flavonoid content has been achieved. 相似文献
27.
photoelectron-photoion coincidence spectroscopy and density functional theory calculations have been used to investigate the dissociation kinetics of the benzene chromium tricarbonyl ion, BzCr(CO)3+ (Bz = C6H6). The dissociation of the BzCr(CO)3+ ion proceeds by the sequential loss of three CO and benzene ligands. The first and third CO and the benzene loss reactions were associated with metastable precursor ions (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and breakdown diagram, the 0 K appearance energies of the four product ions were determined to be 8.33 +/- 0.05, 8.93 +/- 0.05, 9.97 +/- 0.06, and 11.71 +/- 0.06 eV, respectively. Combined with the ionization energy of BzCr(CO)3, 7.30 +/- 0.05 eV, the three successive Cr-CO bond energies in the BzCr(CO)3+ were found to alternate, with values of 1.03 +/- 0.05, 0.60 +/- 0.05, and 1.04 +/- 0.05 eV, respectively, and the Bz-Cr bond energy in BzCr+ is 1.74 +/- 0.05 eV, a trend confirmed by the density functional theory (DFT) calculations. Using the heats of formation of the fully dissociated products, C6H6, Cr+, and CO, the 298 K heats of formation the ionic BzCr(CO)n+ (n = 03) species were determined. By scaling the DFT calculated bond energies for the neutral molecules, the heats of formation of the neutral BzCr(CO)n (n = 03) were also obtained. 相似文献
28.
Philip Wormald Kristina Wickholm Per Tomas Larsson Tommy Iversen 《Cellulose (London, England)》1996,3(1):141-152
An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by13C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the13C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions. 相似文献
29.
Jean M. J. Tronchet Bernard Gentile Alain P. Bonenfant Olivier R. Martin 《Helvetica chimica acta》1979,62(3):696-699
Further examples of O-isopropylidenaldehydosugars in the furanose series Formyl-bearing furanose derivatives 1–3 (α-D -xylo or α-D -erythro configurations) and 5–8 (configurations α-D -ribo, α-D -lyxo, β-L -threo and D -arabino) have been prepared by classical synthetic steps and their properties mainly spectroscopic, reported. The coupling constant between the formyl and the vicinal proton is always small. Like other members of the series, these new aldehydosugars constitute very useful and flexible synthetic intermediates. 相似文献
30.
Alain Pellegatti Et Andr Julg 《International journal of quantum chemistry》1976,10(1):113-121
The influence of various correlation functions, multiplying the monoelectronic space function, is studied and applied to the Helium atom and its isoelectronic series. We used Slater-type basis orbitals and the ground and first excited states have been studied, taking into account the virial and cusp conditions. In the ground state, a very good value for the correlation energy is obtained, using a function of the type For the excited states, this type of function overestimates the assumed value of the correlation energy. 相似文献
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