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1.
In this paper we study some mappings of skew ruled surfaces in simply isotropic space which preserve the generators. We study isometries, conformal mappings and mappings which preserve the area. Furthermore, we study mappings of surfaces in I
3
1 which preserve the asymptotic lines.Received December 18, 2001; in revised form July 12, 2002
Published online April 4, 2003 相似文献
2.
Ma?a?Raji?? Linari? Zora?Popovi?Email author ?eljka?Soldin 《Journal of Thermal Analysis and Calorimetry》2007,88(2):489-493
This work presents preparation and thermal characterization of three
novel organomercurials: Hg2(CF3COCHCOCF3)2-μ2-(CF3COCCOCF3)μ2(CF3C(OH)2CH2C(OH)2CF3)
(I), Hg2(CF3COCHCOCF3)2-μ2-(CF3COCCOCF3)
(II) and Hg2(CH3COCHCOCF3)2-μ2-(CH3COCCOCF3)
(III) which means that they contain at least
one direct mercury-to-carbon bond among the carbonyl groups of β-diketone
molecules which are capable for chelating of metal ions. IR-spectra support
the conclusion that mercury is most probably bound to the γ-carbon of
fluorinated derivatives of acetylacetone and is not chelated through oxygen
in any of the isolated compounds.
The thermal decomposition of
mercurated hexafluoro- and trifluoroacetylacetone in nitrogen occurs in a
few steps. Each step was identified and studied by simultaneous DTA/TG analyzer.
On the basis of dynamic heating experiments by TG applying Flynn-Wall method
the activation energy for each of them was determined. 相似文献
3.
eljka Fiket Marija Petrovi Gordana Meduni Tatjana Ivoevi Tomislav Fiket Lizzy Zhang Xu Yan Wang Shiming Ding 《Molecules (Basel, Switzerland)》2021,26(21)
Assessing the environmental quality of coastal systems is important not only for the management and protection of such areas, but also for improving the quality of water resources. Since sediment itself can often be a source of certain toxic elements, in addition to information on the distribution of metals in the water column and in the sediment itself, it is useful to determine the bioavailable forms of individual elements, particularly toxic ones. In this study, water and sediment geochemical data were supplemented with oxyanion mobility in sediments estimated by diffusion gradients in thin film (DGTs). The data obtained indicate that the chemical composition of the water in the Raša River estuary primarily reflects the high input of suspended sediment from the catchment, the mixing of freshwater and seawater, and to a lesser extent the effects of anthropogenic activities. Although sediment composition is primarily determined by geological and hydrodynamic conditions in the catchment, it also indicates moderate enrichment in Co, Cr, Mo and Ni. In contrast, the distribution of oxyanions in sediment pore water indicates the influence of sediment as a source of some elements in the bottom water; e.g., sediment contributes to 40% of the arsenic bottom water budget. The obtained depth profiles of the oxyanion distribution in the sediment pore water indicate an early onset of suboxic to anoxic conditions in Raša Bay, which is prone to rapid sedimentation. All this demonstrates the need to consider the bioavailable forms of elements when assessing environmental quality, as the lack of such information can lead to an incomplete assessment, especially in dynamic coastal systems such as estuaries. 相似文献
4.
5.
Surface State‐Induced Anomalous Negative Thermal Quenching of Multiferroic BiFeO3 Nanowires
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Kovur Prashanthi Željka Antić Garima Thakur Miroslav D. Dramićanin Thomas Thundat 《固体物理学:研究快报》2018,12(1)
Wide‐bandgap semiconductor nanowires with surface defect emission centers have the potential to be used as sensitive thermometers and optical probes. Here, we show that the green luminescence of multiferroic BiFeO3 (BFO) nanowires shows an anomalous negative thermal quenching (NTQ) with increasing temperatures. The release of trapped carriers from localized surface defect states is suggested as the possible mechanism for the increased green luminescence which was experimentally observed at elevated temperatures. A reasonable interpretation of the photoluminescence (PL) processes in BFO nanowires is achieved, and the activation energies of the PL quenching and thermal hopping are deduced. Negative thermal quenching of BFO nanowires provides a new strategy for optical thermometry at higher temperatures. 相似文献
6.
Gordana Pavlovi Zora Popovi
eljka Soldin Dubravka Matkovi‐alogovi 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):801-803
The reaction of 1‐methyl‐1,3‐imidazole‐2‐thione (meimtH) with mercury(II) iodide in methanol in a 2:1 molar ratio resulted in the formation of single crystals of the title compound, [HgI2(C4H6N2S)2]. The Hg atom is coordinated by two I [2.7809 (9) and 2.7999 (8) Å] and two thione S atoms [2.520 (3) and 2.576 (3) Å] with irregular tetrahedral coordination geometry. The NH groups of the imidazole ring take part in intra‐ and intermolecular hydrogen bonds with I atoms [N?I 3.596 (8) and 3.611 (9) Å, respectively] joining molecules into infinite chains parallel to the z axis. 相似文献
7.
Zora Popović Gordana Pavlović Željka Soldin Jasminka Popović Dubravka Matković-Čalogović Maša Rajić 《Structural chemistry》2002,13(5-6):415-424
The series of compounds of the general formulae HgX2(tzdtH) and HgX2(tzdtH)2 (X = Cl, Br, I; tzdtH = 1,3-thiazolidine-2-thione) have been prepared, as well as Hg(tzdt)2. IR, 1H, and 13C NMR spectral data of the complexes indicate thione donation, which is confirmed by the crystal structure analyses of [HgBr2(tzdtH)]2, [HgI2(tzdtH)]2, and HgI2(tzdtH)2. The structures of [HgBr2(tzdtH)]2 and [HgI2(tzdtH)]2 consist of centrosymmetric doubly bridged dimers, but they are not isostructural. The asymmetry in the HgX2Hg bridge is more pronounced in the bromo than in the iodo derivative [S–Hg–X(terminal) is 138.19(9)° for X = Br and 123.49(10)° for X = I], which is accompanied by the stronger Hg–S covalent bond in the bromo than in the iodo complex [2.435(4) vs. 2.510(3) Å]. The Hg–X(bridging) (X = Br, I) bond distances are shorter than the sum of van der Waals radii for mercury and X. Dimeric centrosymmetric complex units are held together only by van der Waals forces in [HgI2(tzdtH)]2, while in [HgBr2(tzdtH)]2 there is an intramolecular hydrogen bond of N–H Br type (3.34(1) Å). HgI2(tzdtH)2 exists as a mononuclear tetrahedral complex with two long Hg–S [2.672(1) Å] and two short Hg–I bond distances [2.688(1) Å] related by a twofold axis. The molecules of HgI2(tzdtH)2 are linked into infinite chains along the c axis by intermolecular N–H S [3.38(1) Å] hydrogen bonds. 相似文献
8.
Zora Popović Draginja Mrvoš-Sermek Željka Soldin Vesna Tralić-Kulenović 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(1):20-21
The reaction of 2-methyl-1,3-benzothiazole (mebta) with mercury(II) chloride in methanol in a 1:1 molar ratio resulted in the formation of single crystals of the title compound, [HgCl2(C8H7NS)]n. The molecules exist as continuous chlorine-bridged chains in which Hg atoms lie in distorted trigonal bipyramidal environments. The equatorial positions are occupied by an N atom from the ligand [2.236 (8) Å] and two Cl atoms [2.428 (3) and 2.459 (3) Å]. The two axial Hg—Cl contacts to two neighbouring molecules [2.874 (3) and 2.964 (3) Å] are significantly shorter than the sum of the respective van der Waals radii, and form close to linear Cl—Hg—Cl sequences [177.80 (7)°]. 相似文献
9.
Catalin Schiopu Corina Flangea Florina Capitan Alina Serb Željka Vukelić Svjetlana Kalanj-Bognar Eugen Sisu Michael Przybylski Alina D. Zamfir 《Analytical and bioanalytical chemistry》2009,395(8):2465-2477
We report here on a preliminary investigation of ganglioside composition and structure in human hemangioma, a benign tumor
in the frontal cortex (HFC) in comparison to normal frontal cortex (NFC) tissue using for the first time advanced mass spectrometric
methods based on fully automated chip-nanoelectrospray (nanoESI) high-capacity ion trap (HCT) and collision-induced dissociation
(CID). The high ionization efficiency, sensitivity and reproducibility provided by the chip-nanoESI approach allowed for a
reliable MS-based ganglioside comparative assay. Unlike NFC, ganglioside mixture extracted from HFC was found dominated by
species of short glycan chains exhibiting lower overall sialic acid content. In HFC, only GT1 (d18:1/20:0), and GT3 (d18:1/25:1)
polysialylated species were detected. Interestingly, none of these trisialylated forms was detected in NFC, suggesting that
such components might selectively be associated with HFC. Unlike the case of previously investigated high malignancy gliosarcoma,
in HFC one modified O-Ac-GD2 and one modified O-Ac-GM4 gangliosides were observed. This aspect suggests that these O-acetylated structures could be associated with cerebral tumors having reduced malignancy grade. Fragmentation analysis by
CID in MS2 mode using as precursors the ions corresponding to GT1 (d18:1/20:0) and GD1 (d18:1/20:0) provided data corroborating for
the first time the presence of the common GT1a and GT1b isomers and the incidence of unusual GT1c and GT1d glycoforms in brain
hemangioma tumor.
相似文献
10.
Zora Popovi
eljka Soldin Gordana Pavlovi 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(7):m272-m274
The title compound, [Hg(C6H4NO2)I(C6H5NO2)], has twofold symmetry along the Hg—I bond. The HgII ion coordinates one I atom [at 2.6045 (4) Å], two N and two O atoms [at 2.298 (3) and 2.481 (2) Å] from one picolinate ion, and one picolinic acid molecule in a very irregular trigonal–bipyramidal coordination. The single hydroxy H atom required for chemical neutrality is both statistically (by crystal symmetry) and structurally disordered, and is involved in an intermolecular O—H⋯O hydrogen bond [O⋯O = 2.455 (4) Å], connecting the molecules into one‐dimensional infinite chains along the [101] direction. 相似文献