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991.
Glassy carbon electrodes modified with coatings of poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium], poly-MPP, were employed for preconcentrating and detecting the anionic complex HgCl4(2-), which is the prevailing inorganic Hg(II) species in salt waters such as the pore-waters of sediments here examined. The application of ion-exchange voltammetry at poly-MPP coated electrodes in combination with an in situ pore-water sampler allowed the measurement of concentration vs. depth profiles for mercury dissolved in the pore-waters of a salt-marsh and of a mud-flat located in a polluted area of the Venice Lagoon. The trends of the mercury profiles are discussed in comparison with the trends measured from the same location for other trace metals (Zn, Cd, Cu and Pb) and reduced species such as S(-II) and Fe(II). 相似文献
992.
E. Fenyvesi M. Vikmon J. Szeman E. Redenti M. Delcanale P. Ventura J. Szejtli 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(3):339-344
The solubility of -cyclodextrin (-CD) was studied in aqueous solutions of various organic acids. The hydroxy acids, especially citric and tartaric acid were found to increase the solubility of -CD, while some other carboxylic acids reduced it. From solubility data the apparent complex association constants were calculated. 相似文献
993.
Molecular absorption spectra of CS are observed during the vaporization of crude and fuel oils in an electrothermal atomizer. The CS absorbance at 257.6 nm is used to determine the sulphur content of the oil, based on measurements in a conventional electrothermal atomic absorption spectrometer. The results for various fuel oils generally agree with those obtained by x-ray fluorescence spectrometry (ASTM D2622). The detection limit referred to the undiluted oil is 50 mg kg?1, and the repeatability is 3% at the 250 mg kg?1 level. Some oils exhibit uneven vaporization of sulphur species. 相似文献
994.
Giancarlo Verardo Angelo G. Giumanini Fausto Gorassini Paolo Strazzolini Franco Benetollo Gabriella Bombieri 《Journal of heterocyclic chemistry》1995,32(3):995-1001
1,3,5-Triscubstituted hexahydro-1,3,5-trazin-2-ones 3 are easily obtained by the reaction of 1,3,5-trisub-stituted hexahydro-1,3,5-triazines 1 with organic isocyanates 2 . The reaction is believed to occur by the sequential addition to 2 of two molecules of the monomeric N-methyleneamines in thermal equilibrium with 1. Substituent scrambling at the operating temperature (120°) was negligible. The crystal structure of 1,3,5-triphenylhexahydro-1,3,5-triazin-2-one (3a) has been determined by X-ray diffraction methods. 相似文献
995.
996.
Paolo Venzi 《Rendiconti del Circolo Matematico di Palermo》1981,30(3):421-434
In questa nota sono studiati gli spazi proiettivamenteq-ricorrenti, definiti dalla relazione % ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb \(W_{ijk, m_1 m_2 \ldots m_q }^p = a_{m_1 m_2 \ldots m_q } W_{ijk}^p \) ; doveW ijk p sono le componenti del tensore proiettivo di Weyl. Nei teoremi 4 e 7 è data una forma canonica del tensore di curvatura di questi spazi. È quindi dimostrato che uno spazio di questo tipo non può essere uno spazio di Einstein. Sono pure studiati gli spazi proiettivamenteq-ricorrenti che nello stesso tempo sono conformemente Euclidei e il casoq=2. 相似文献
997.
Paolo Cubiotti 《Set-Valued Analysis》1993,1(1):81-87
In this paper, we deal with the following generalized quasi-variational inequality problem: given a closed convex subsetX
n
, a multifunction :X 2
n
and a multifunction :X 2
X
, find a point (
) X ×
n
such that
We prove an existence theorem in which, in particular, the multifunction is not supposed to be upper semicontinuous. 相似文献
998.
A theoretical interpretation of the observed periodicity of large-scale (128 Mpc) correlations of galaxies is proposed as due to eigenvibrations of the closed expanding universe. Eigensolutions of the equations of motion for a scalar field in an inflationary model allow one to compute the energy density, interpreted as matter density. Isotropic eigensolution give rise to a matter density distribution having a periodic structure centered at the north pole of the closed Robertson-Walker universe represented by S3/Z2. It is able to reproduce well the striking periodicity of the observational data, in the galactic north-south directions. The dipole and quadrupole eigensolutions and the location of the co-moving observer in a point of S3/Z2 different from the center of the vibrational structure would imply, in a theoretically well predictable way, a decrease of the observed periodicity in some other directions.Partially supported by the State Committee for Scientific Research, Grant No. 2-0206-91-01. 相似文献
999.
Leopoldo Ceraulo Paolo De Maria Antonella Fontana Sara Frascari Domenico Spinelli 《Journal of heterocyclic chemistry》1992,29(6):1657-1662
The study of the electron ionization mass spectra of 5-nitro-3-thiophenecarboxanilides 1-24 has shown peculiar effects induced by the 5-nitro group on the fragmentation of molecular ions M and the thenoyl cation a (Scheme 1). A comparison of the abundances of the important fragment ions for 5-nitro-3-thiophene-carboxanilides with those of the corresponding 3-thiophenecarboxanilides shows that the extent of C-N amide bond cleavage decreases in the former series as a consequence of the increased bond strength. The produced ion a does not eliminate carbon monoxide as 2- and 3-thenoyl cations usually do. Again this behaviour depends on the electronic effects of the nitro group which strongly destabilizes the 5-nitro-3-thienyl cation and consequently strengthens the carbon-3 carbonyl carbon bond. Recalling the behavior of the previously studied 2- and 3-thiophenecarboxanilides most of the 2′-substituted 5-nitro-3-thiophenecarboxanilides give loss of the ‘ortho’ substituent of the phenyl ring furnishing the cyclic ion g(Scheme 2). In the instance of 2′-alkyl substituted derivatives the formation of abundant ions h' by loss of 5-nitrothenoyl radical from M (Scheme 3) was observed, thus confirming the occurrence of a cryptic ‘ortho’ effect. The results are also discussed in relation to those obtained on some related benzoylanilides. 相似文献
1000.
Paolo Ganis Donatella Furlani Daniele Marton Giuseppe Tagliavini Giovanni Valle 《Journal of organometallic chemistry》1985,293(2):207-212
The crystal structure of (C6H5)3SnCH2CHCH2 has been determined. The asymmetric unit consists of two molecules of triphenylallyltin having virtually the same conformation. Their geometrical parameters exclude pπ-dπ bonding between the metal and the allyl double bond, and seem to be in a better agreement with a σ-π conjugation effect. 相似文献