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41.
Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
42.
CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
43.
G A Buck S Longacre A Raibaud U Hibner C Giroud T Baltz D Baltz H Eisen 《Nature》1984,307(5951):563-566
African trypanosomes evade clearance in immune-competent hosts by periodically replacing their major surface glycoprotein with an antigenically different glycoprotein. Expression of many of these variant surface glycoproteins (VSGs) is associated with the duplication and transposition of silent basic copy genes (BCs) into unlinked genomic expression sites. The new expression-linked VSG gene copies (ELCs) are oriented with their 3' ends proximal to chromosome telomeres. Other VSG genes are activated without the production of an ELC. The 3' ends of these VSG genes are near chromosome telomeres both when they are active and when they are inactive. Recently, we have shown that activation of the VSG-1 gene in the BoTaR (Bordeaux trypanozoon antigen repertoire) serodeme of Trypanosoma equiperdum involves the duplication and transposition of a telomeric BC gene into one of at least three unlinked telomeric sites. Here we show that the VSG-1 ELC is inactivated but not eliminated in some antigenic variants derived from a VSG-1 expressor. In addition, a subsequent variant that again expresses VSG-1 has not reactivated the residual VSG-1 ELC (R-ELC), but instead contains a new, active VSG-1 ELC in an unlinked telomeric site. These results show that the simple presence of an ELC in a potential expression site is not sufficient for its expression. 相似文献
44.
A semi-micro method for determining the boiling temperature of a liquid mixture using a thermistor is described. Boiling temperatures of the binary mixtures n-heptane—toluene, toluene—n-octane and 1-n-octene—n-octane were determined as functions of the composition. The isobaric T—x values were used to compute equilibrium vapour composition by numerical integration of the Duhem—Margules equation. The T—x—y values are presented at 101325, 79993 (or 85326), 53329 and 26664 Pa. 相似文献
45.
Evidence for lateral gene transfer between Archaea and bacteria from genome sequence of Thermotoga maritima. 总被引:27,自引:0,他引:27
K E Nelson R A Clayton S R Gill M L Gwinn R J Dodson D H Haft E K Hickey J D Peterson W C Nelson K A Ketchum L McDonald T R Utterback J A Malek K D Linher M M Garrett A M Stewart M D Cotton M S Pratt C A Phillips D Richardson J Heidelberg G G Sutton R D Fleischmann J A Eisen O White S L Salzberg H O Smith J C Venter C M Fraser 《Nature》1999,399(6734):323-329
The 1,860,725-base-pair genome of Thermotoga maritima MSB8 contains 1,877 predicted coding regions, 1,014 (54%) of which have functional assignments and 863 (46%) of which are of unknown function. Genome analysis reveals numerous pathways involved in degradation of sugars and plant polysaccharides, and 108 genes that have orthologues only in the genomes of other thermophilic Eubacteria and Archaea. Of the Eubacteria sequenced to date, T. maritima has the highest percentage (24%) of genes that are most similar to archaeal genes. Eighty-one archaeal-like genes are clustered in 15 regions of the T. maritima genome that range in size from 4 to 20 kilobases. Conservation of gene order between T. maritima and Archaea in many of the clustered regions suggests that lateral gene transfer may have occurred between thermophilic Eubacteria and Archaea. 相似文献
46.
47.
M. Samuel U. Smilansky B.A. Watson Y. Eisen A.M. Kleinfeld D. Werdecker 《Nuclear Physics A》1977,279(2):210-222
Cross sections for the elastic scattering of 4He by 122, 124, 126, 128Te and 3He by 128Te and for inelastic transitions to the lowest 2+ states of Te isotopes were measured for several scattering angles at bombarding energies in the vicinity of the Coulomb barrier. The data were analyzed in the framework of the optical model and the DWBA from which optical potential and deformation parameters were extracted. A detailed study of the fit procedure is presented with emphasis on the significance of the extracted parameters and the correlations among them. 相似文献
48.
49.
Summary The retention indices (I) and their structural increments (l/°C, H, l) of C6–C14 n-alkenes on polyphenyl ether (PFE) and C12–C14 n-alkenes on polyethylene glycol 4000 (PEG) at 20–160 °C have been determined and correlated with the molecular structure of the isomers. A number of common regularities in gas chromatographic behaviour on these liquid phases and squalane (SQ) [1–3] have been found. On PFE the elution order of isomeric n-alkenes is similar to that on SQ (except C8–C10 1-alkenes and cis-4-tetradecene), for pairs with cis- and trans-configuration it depends on the column temperature, position of double bond and the number of carbon atoms (n) in the molecule. On PEG the cis- are always retained longer than the corresponding trans-alkenes. The linear relationships between 1 and n on PFE and PEG are given in equation form. 相似文献
50.
W. J. Michkelson A. A. Elwelt Dr. L. S. Kudrjawzewa O. G. Eisen 《Monatshefte für Chemie / Chemical Monthly》1974,105(6):1379-1386
The boiling points of unbranched C8?C10 alkenes were determined by an ebulliometric method at the following pressures: 200, 300, 400 and 600 torr and at atmospheric pressure. The equipment used is described and the results obtained presented in tabular form. The constants of theAntoine equation and the normal boiling points were calculated. 相似文献