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61.
Determination of aromatics in diesel fuels by HPLC is covered by European Standard EN 12916 (April 2000). The Standard is based on former standards IP 391/90 and IP 391/95. The method used for measurements is NP HPLC and separation is performed on silica or modified silica columns with RI detection. The precision of the method was checked by determining the repeatability and reproducibility. The content of aromatics was measured in a number of commercial samples. The measurements have been performed in three different laboratories and under different working and instrumental conditions. Satisfactory agreement was established for repeatability and was slightly poorer for reproducibility. The content of polyaromatics is within the tolerance range (IP 590/99) and the content of tricyclic and higher aromatics (tri+) is close to the limit of quantitition in some samples. Clear differences in the content of polycyclic aromatics in domestic diesel and eurodiesel fuels were observed. The results have confirmed the ruggedness and robustness of the measuring method. 相似文献
62.
J. M. Filipovic D. M. Petrovic-Dakov Lj. P. Vrhovac J. S. Velickovic 《Journal of Thermal Analysis and Calorimetry》1992,38(4):709-713
The course and kinetics of free radical polymerization in bulk ofp-alkylphenyl methacrylates with AIBN initiator were studied by DSC, in the temperature range 348–373 K. The enthalpy of polymerization, the residual monomer content, as well as the overall reaction rate constants and the activation energies were determined. The similar values of the overall rate constants indicate that the relatively small alkyl substituents inp-position of the phenyl ring affect the polymerization rate to a very small, if any, extent.
Zusammenfassung Mittels DSC wurden im Temperaturbereich 348–373 K Reaktionsweg und Kinetik der radikalischen Raumpolymerisation vonp-Alkylphenylmethacrylaten mit AIBN Initiator untersucht. Dabei wurden die Polymerisationsenthalpie, der Monomerrest-gehalt als auch die Geschwindigkeitskonstanten und die Aktivierungsenergien der Gesamt-reaktion bestimmt. Ähnliche Werte für die Gesamtgeschwindigkeitskonstanten weisen darauf hin, daß die relativ kleinen Alkylsubstituenten inp-Stellung des Phenylringes die Polymerisationsgeschwindigkeit nur in sehr kleinem Maße — wenn überhaupt — beeinflussen.相似文献
63.
Qiuhao Qu Hiroki Morizono Dashuang Shi Mendel Tuchman Ljubica Caldovic 《BMC biochemistry》2007,8(1):4
Background
In microorganisms and plants, the first two reactions of arginine biosynthesis are catalyzed by N-acetylglutamate synthase (NAGS) and N-acetylglutamate kinase (NAGK). In mammals, NAGS produces an essential activator of carbamylphosphate synthetase I, the first enzyme of the urea cycle, and no functional NAGK homolog has been found. Unlike the other urea cycle enzymes, whose bacterial counterparts could be readily identified by their sequence conservation with arginine biosynthetic enzymes, mammalian NAGS gene was very divergent, making it the last urea cycle gene to be discovered. Limited sequence similarity between E. coli NAGS and fungal NAGK suggests that bacterial and eukaryotic NAGS, and fungal NAGK arose from the fusion of genes encoding an ancestral NAGK (argB) and an acetyltransferase. However, mammalian NAGS no longer retains any NAGK catalytic activity. 相似文献64.
Bojan B. Radak Ljubica T. Petkovska epan S. Miljani Raymond T. Bailey Francis R. Cruickshank David Pugh 《Journal of Chemical Sciences》1991,103(3):409-412
Spectra of coincidence of CH3C1 IR absorption with CO2-laser emission were recorded by a photoacoustic detection method in the whole range of CO2-laser emission. The samples were neat gas and mixtures with argon, at several pressures (10 to 600Torr) so that pressure
effects could be observed. The results show that argon affects absorption of CO2-laser emission quite differently from neat chloromethane, both regarding the most prominent coincidences and background absorption. 相似文献
65.
Wei Xu Richard J. Puddephatt Ljubica Manojlovic-Muir Kenneth W. Muir Christopher S. Frampton 《Journal of inclusion phenomena and macrocyclic chemistry》1994,19(1-4):277-290
The hostt-butylcalix[4]arene,1a, forms a 11 inclusion compound with acetonitrile as guest. The inclusion compound has been isolated and characterised by X-ray analysis of a twinned crystal at 123 K. The acetonitrile guest lies on a crystallographic four-fold symmetry axis passing through the centre of the bowl of1a which adopts a regular cone conformation. A known tetradentate and a new tridentate phosphinitocalix[4]arene derivative,2a and2c respectively, have been synthesized from1a and Ph2Cl. Both2a and2c show a strong ability to coordinate with late transition metals and new complexes of gold(I), palladium(II) and platinum(II) are reported.
Supplementary Data relating to this paper have been deposited with the British Library as Supplementary Publication No. SUP 92171 (5 pp.)This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes. 相似文献
66.
Mario Komar Maja Molnar Marijana Jukić Ljubica Glavaš-Obrovac 《Green Chemistry Letters and Reviews》2020,13(2):93-101
ABSTRACT A synthesis of two series of 3-substituted quinazolinones was performed utilizing a green chemistry approach, deep eutectic solvents and microwaves, namely. 2-Methyl-3-substituted-quinazolin-4(3H)-one derivatives were synthesized in a two-step reaction, using choline chloride:urea deep eutectic solvent (DES). 3-Substituted-quinazolin-4(3H)-ones were synthesized in one-pot one-step reaction of anthranilic acid, amines and orthoester in a microwave reactor. For the synthesis of 2-methyl-3-substituted-quinazolin-4(3H)-ones, first conventional synthesis of benzoxazinone, as an intermediate, was performed. Further, benzoxazinone in reaction with corresponding amines, in choline choline:urea deep eutectic solvent, furnished desired compounds. These procedures are based on green principles with the aim of developing synthetic routes for the potential antitumor agents. All compounds were characterized by LC/MS, 1H NMR and 13C NMR spectral techniques. Compound 1 bearing trifluoromethoxyphenyl group showed promising activity against HuT-78 cell line with IC50 of 51.4?±?5.1?µM. 相似文献
67.
Mediterranean Journal of Mathematics - We derive some interesting properties of generalized almost Hermitian spaces. Additionally, we study basic equations of holomorphically projective mappings... 相似文献
68.
Ljubica T. Petkovska Bojan B. Radak epan S. Miljani Raymond T. Bailey Francis R. Cruickshank David Pugh 《Journal of Chemical Sciences》1991,103(3):401-404
Spectra of coincidence of SO2 IR absorption with CO2-laser emission at pressure of 50,100 and 450 Torr were recorded by the use of a photoacoustic detection method in the whole
range of CO2-laser emission. The spectra show that SO2 absorbs many CO2-laser lines in the range 1084–1071 cm−1 with the strongest absorption at 1082.29cm−1, laser line R(26). The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative
intensity with respect to one another. In addition, the fine structure of line spectra, characteristic of lower pressure samples,
disappear as pressure is increased. 相似文献
69.
Zorica M. Jakšić Milica Cvetković Julija R. Šćepanović Ivana Lončarević Ljuba Budinski-Petković Slobodan B. Vrhovac 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(6):108
We report on measurements of the electrical conductivity on a two-dimensional packing of metallic disks when a stable current of ~1 mA flows through the system. At low applied currents, the conductance σ is found to increase by a pattern σ(t) = σ ∞ ? Δσ E α [ ? (t/τ) α ], where E α denotes the Mittag-Leffler function of order α ∈ (0,1). By changing the inclination angle θ of the granular bed from horizontal, we have studied the impact of the effective gravitational acceleration g eff = gsinθ on the relaxation features of the conductance σ(t). The characteristic timescale τ is found to grow when effective gravity g eff decreases. By changing both the distance between the electrodes and the number of grains in the packing, we have shown that the long term resistance decay observed in the experiment is related to local micro-contacts rearrangements at each disk. By focusing on the electro-mechanical processes that allow both creation and breakdown of micro-contacts between two disks, we present an approach to granular conduction based on subordination of stochastic processes. In order to imitate, in a very simplified way, the conduction dynamics of granular material at low currents, we impose that the micro-contacts at the interface switch stochastically between two possible states, “on” and “off”, characterizing the conductivity of the micro-contact. We assume that the time intervals between the consecutive changes of state are governed by a certain waiting-time distribution. It is demonstrated how the microscopic random dynamics regarding the micro-contacts leads to the macroscopic observation of slow conductance growth, described by an exact fractional kinetic equations. 相似文献
70.