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151.
Fatsiha Mendil Madjid Berkani Abdelmalek Zamouche Leszek Rycerz 《Comptes Rendus Chimie》2013,16(9):795-798
In the present work, we have synthesized praseodymium(III) chloride, PrCl3, from the praseodymium oxide, Pr6O11, by dry method in the presence of ammonium chloride, NH4Cl. This study includes the establishment of an assembly synthesis under inert gas. The thermal decomposing process of pure NH4Cl was investigated by TG–DTG. The results showed that NH4Cl begins to lose weight at 188 °C, large loss of weight ending at 302 °C when NH4Cl is heated at the rate of 10 °C/min under N2 atmosphere. For chlorination, NH4Cl participates directly in the reaction, and HCl decomposed from NH4Cl also contributes to the chlorination reaction. The influence of various synthesis parameters (temperature, contact time and chemical composition) on the reaction yield was studied, and the optimum conditions for synthesis were, thus, determined and discussed. 相似文献
152.
Morisaka T Karczmarski L Akamatsu T Sakai M Dawson S Thornton M 《The Journal of the Acoustical Society of America》2011,129(1):449-457
Field recordings of echolocation signals produced by Heaviside's dolphins (Cephalorhynchus heavisidii) were made off the coast of South Africa using a hydrophone array system. The system consisted of three hydrophones and an A-tag (miniature stereo acoustic data-logger). The mean centroid frequency was 125 kHz, with a -3 dB bandwidth of 15 kHz and -10 dB duration of 74 μs. The mean back-calculated apparent source level was 173 dB re 1 μPa(p.-p.). These characteristics are very similar to those found in other Cephalorhynchus species, and such narrow-band high-frequency echolocation clicks appear to be a defining characteristic of the Cephalorhynchus genus. Click bursts with very short inter-click intervals (up to 2 ms) were also recorded, which produced the "cry" sound reported in other Cephalorhynchus species. Since inter-click intervals correlated positively to click duration and negatively to bandwidth, Heaviside's dolphins may adjust their click duration and bandwidth based on detection range. The bimodal distribution of the peak frequency and stable bimodal peaks in spectra of individual click suggest a slight asymmetry in the click production mechanism. 相似文献
153.
Mourre method of commutators is used to get low energy resolvent bound for an abstract operatorin a Hilbert space and for a second order variable coefficient elliptic operator in Rd, d?3. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
154.
The title derivatives were synthesized containing two meso-tri-p-tolylpheneleneporphyrin units attached via amide bridges to 4, 7- and 4,4′ positions of the respective heteroaromatic spacers. 相似文献
155.
Zbigniew Turzyński Konrad Witkowski Leszek Woliński Jerzy Szafko 《Journal of Polymer Science.Polymer Physics》1990,28(4):467-479
This work is the continuation of the investigations of changes in the structure of polystyrene initiated by radiation of wavelengths λ ≥ 270 nm in oxygen-free solutions in CCl4 and CHCl3. Coupled integral and quasielastic light scattering techniques have been applied, enabling observations of changes in the molecular weight distribution function w(M). On the basis of the experimental data and application of Saito and Inokuti's theoretical results, it is shown that in the irradiated solutions polystyrene undergoes simultaneous chain scission and crosslinking. The average number of scissions and crosslinks per macromolecule as a function of irradiation time is calculated. The effect of macromolecular mobility on both photochemical processes is also discussed. 相似文献
156.
Leszek Marcinkowski 《Numerische Mathematik》2002,93(2):361-386
Summary. In this paper mortar element methods for the clamped plate problem are discussed. Locally, we use conforming Hsieh-Clough-Tocher
(HCT) and reduced HCT macro elements and a nonconforming Morley element. We establish error bounds for these methods.
Received December 1, 2000 / Revised version received December 3, 2001 / Published online April 17, 2002
This work was partially supported by Polish Scientific Grant 237/PO3/99/16 相似文献
157.
Orzeł L Fiedor L Wolak M Kania A van Eldik R Stochel G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(30):9419-9430
The mechanism of acetate-assisted transmetalation of tetrapyrroles was investigated in a model system consisting of chlorophyll a and copper(II) acetate in organic solvents by using a spectroscopic and kinetic approach. Surprisingly, acetate ions bind to the central Mg in chlorophyll much more strongly than do acetonitrile, methanol and even pyridine, one of the best ligands in chlorophyllic systems. This exceptionally strong non-symmetrical axial ligation of the central Mg by acetate causes its out-of-plane displacement and deformation of the tetrapyrrole ring, thus facilitating the interaction with an incoming CuII complex. This mechanism is controlled by a keto-enol tautomerism of the chlorophyll isocyclic ring. Additionally, depending on solvent, acetate activates the incoming metal ions. These new insights allow to suggest a mechanism for the acetate method of metal exchange in tetrapyrrolic macrocycles, which resembles biological insertion of metal ions into porphyrins. It also provides a guideline for the design of more efficient methods for the metalation of porphyrins and related macrocycles. 相似文献
158.
Leszek Pazderski Andrzej Surdykowski Magorzata Pazderska-Szabowicz Jerzy Sitkowski Lech Kozerski Bohdan Kamieski Edward Szyk 《Central European Journal of Chemistry》2008,6(1):55-64
trans-[Co(py)4Cl2]Cl·6H2O, mer-[Co(py)3Cl3] and mer-[Co(py)3(CO3)Cl] were studied by UV-Vis, far-IR and 1H, 13C, 15N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of 1H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands.
13C nuclei were deshielded upon Co(III) coordination, while 15N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). 13C and 15N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)4Cl2]Cl·6H2O and mer-[Co(py)3Cl3], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)4Cl2]Cl → mer-[Co(py)3Cl3] + py reaction was monitored by 1H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)3Cl3] preparation.
相似文献
159.
160.
We experimentally demonstrate an effective method of manipulating terahertz radiation using a metamaterial loaded with a liquid crystal. Active control of the terahertz beam was performed by in-plane electrical switching of the nematic liquid crystal in the metamaterial device. By changing the magnitude of the AC bias voltage from 0 to 100 V, a reversible transmittance shift of up to 10% was achieved for an incident beam with horizontal electric field polarisation and 27% for vertical polarisation with frequency at around 0.7 THz. Metamaterials with electrically tunable characteristics have potential applications in transmission, modulation and switching components and devices for controlling the intensity and phase of terahertz radiation. 相似文献