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171.
J. J. LaBrecque Z. A. De Benzo E. Marcano C. A. Peña 《Journal of Radioanalytical and Nuclear Chemistry》1984,84(2):407-413
The comparison of an ambient temperature mercuric iodide spectrometer (HgI2) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI2 spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the NbK
peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela. 相似文献
172.
S. Jovanović F. De Corte A. Simonits L. Moens P. Vukotić J. Hoste 《Journal of Radioanalytical and Nuclear Chemistry》1987,113(1):177-185
In absolute or comparator standardization methods of (n, ) activation analysis with reactor neutrons, the epithermal neutron flux nonideality, if neglected, max lead to significant errors on the analytical result. The concept of the effective resonance energy
, introduced to correct for this effect, is reviewed. 相似文献
173.
A New Efficient Synthesis of p-Nitrocalix[4]arene 总被引:1,自引:0,他引:1
YongLI JiaSongWANG QiWANG DeShanLI 《中国化学快报》2004,15(4):400-403
A new efficient synthesis of p-nitrocalix[4]arene from calix[4]arene by using nitrogen dioxide is described.The compound is an useful intermediates for the introduction of other functional groups to obtain N containing substituted calix[4]arene.The reaction mechanism is briefly discussed. 相似文献
174.
V. Nastro D. Vuono M. Guzzo G. Niceforo I. Bruno P. De
Luca 《Journal of Thermal Analysis and Calorimetry》2006,84(1):181-184
The aim of this paper is to characterize some raw
materials used for ceramics material production. Five samples of clay have
been analyzed. It has been carried out a patterned sampling in a quarry in
Rosarno (South Italy).
Chemical-physical
properties on clay samples are determined. Test pieces have been prepared
and physical properties after firing are determined by DSC thermal analysis,
XRD analysis and X-ray fluorescence. It is important to note the high amount
of Fe2O3. The mixture principally
contains quartz, illite and oligoclase. It has been observed the colour and
the shape after firing: predominant colour is red. In this case the clay has
been used in mixtures covered with glazes. The colour of internal clay is
hidden by opaque of glazes. The analysed raw materials can be used in a slip
for single fired red tiles. The A2sp clay produces best ceramics at 1000°C. 相似文献
175.
176.
32P was separated from the irradiated silicon matrix as ammonium phosphomolybdate and the activity was measured with a GM tube
or on a plastic scintillator. The second-order interference was taken into consideration.
Research associate of the N.F.W.O. 相似文献
177.
178.
De Salvo G Gattuso G Notti A Parisi MF Pappalardo S 《The Journal of organic chemistry》2002,67(3):684-692
A series of tri-O-substituted 1,3-bridged calix[5]arene crown-6 ethers bearing alkyl, arylalkyl, alkoxyalkyl, and alkoxycarbonylmethyl residues at the lower rim and either (t)()Bu or H substituents at the upper rim have been synthesized. (1)H NMR studies have shown that p-tert-butylcalix[5]crowns, irrespective of the size and nature of their lower rim pendant groups, adopt preorganized conelike conformations, whereas p-H-calix[5]crowns with bulky substituents preferentially exist in solution as partial cone conformers (C(1) symmetry). Calix[5]crown derivatives behave as mono- or ditopic receptors for isomeric butylammonium ions, forming endo-cavity (inside the calixarene cup) and/or exo-cavity (at the crown ether moiety) 1:1 complexes according to the shape of the guest. These two binding modes can be clearly distinguished and monitored by (1)H NMR titration experiments. 相似文献
179.
180.
Wu T Froeyen M Kempeneers V Pannecouque C Wang J Busson R De Clercq E Herdewijn P 《Journal of the American Chemical Society》2005,127(14):5056-5065