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101.
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
102.
J Christiansen 《Journal of chromatography. A》1976,123(1):57-63
A micro-method based on in situ thin-layer chromatography has been developed for the determination of quinidine and salicylic acid in 10-mu 1 samples of serum or plasma. The sample is applied directly to the silica gel layer without extraction, the proteins being precipitated on the chromatogram origin by means of ethanol. The chromatogram can be evaluated quantitatively by fluorescence scanning. Different pre-coated plates were investigated. 相似文献
103.
Numerical studies of the dynamics of sine-Gordon solitons in two spatial dimensions are presented. New results like 4π-break up, “soliton-on-soliton effect”, and scattering at a circular inhomogeneity for line solitons on large-area Josephson junctions are reported. For elliptic ring solitons we find oscillating eccentricity between the major axes in the pulson phase. Colliding non-concentric ring solitons are shown to form larger oval ring solitons or to repel each other. This new effect is qualitatively explained in terms of the 4π-break up for line solitons. 相似文献
104.
Johnsen M Paterson MJ Arnbjerg J Christiansen O Nielsen CB Jørgensen M Ogilby PR 《Physical chemistry chemical physics : PCCP》2008,10(8):1177-1191
Two-photon excitation spectra have been recorded over the large spectral range of 540-1000 nm for five phenylene-vinylene oligomers that differ in the length of the conjugated pi system. The significant changes observed in the two-photon excitation spectra and absorption cross sections as a function of this systematic change in the chromophore are discussed in light of (1) the corresponding one-photon absorption spectra and (2) high-level density functional response theory calculations performed on analogues of these systems. The results obtained illustrate one way to exploit parameters that influence nonlinear optical properties in large organic molecules. Specifically, data are provided to indicate that when the frequency of the laser used in the two-photon experiment is nearly-resonant with an allowed one-photon transition, significant increases in the two-photon absorption cross section can be realized. This phenomenon of the so-called resonance enhancement allows for greater control in obtaining an optimal response when using existing two-photon chromophores, and provides a much-needed guide for the systematic development and efficient use of two-photon singlet oxygen sensitizers. 相似文献
105.
Biosynthesis and structure of aeruginoside 126A and 126B, cyanobacterial peptide glycosides bearing a 2-carboxy-6-hydroxyoctahydroindole moiety 总被引:1,自引:0,他引:1
Ishida K Christiansen G Yoshida WY Kurmayer R Welker M Valls N Bonjoch J Hertweck C Börner T Hemscheidt T Dittmann E 《Chemistry & biology》2007,14(5):565-576
Aeruginosins represent a group of peptide metabolites isolated from various cyanobacterial genera and from marine sponges that potently inhibit different types of serine proteases. Members of this family are characterized by the presence of a 2-carboxy-6-hydroxyoctahydroindole (Choi) moiety. We have identified and fully sequenced a NRPS gene cluster in the genome of the cyanobacterium Planktothrix agardhii CYA126/8. Insertional mutagenesis of a NRPS component led to the discovery and structural elucidation of two glycopeptides that were designated aeruginoside 126A and aeruginoside 126B. One variant of the aglycone contains a 1-amino-2-(N-amidino-Delta(3)-pyrrolinyl)ethyl moiety at the C terminus, the other bears an agmatine residue. In silico analyses of the aeruginoside biosynthetic genes aerA-aerI as well as additional mutagenesis and feeding studies allowed the prediction of enzymatic steps leading to the formation of aeruginosides and the unusual Choi moiety. 相似文献
106.
Arnbjerg J Paterson MJ Nielsen CB Jørgensen M Christiansen O Ogilby PR 《The journal of physical chemistry. A》2007,111(26):5756-5767
Singlet molecular oxygen, O2(a1Deltag), can be efficiently produced in a photosensitized process using either one- or two-photon irradiation. The aromatic ketone 1-phenalenone (PN) is an established one-photon singlet oxygen sensitizer with many desirable attributes for use as a standard. In the present work, photophysical properties of two other aromatic ketones, pyrene-1,6-dione (PD) and benzo[cd]pyren-5-one (BP), are reported and compared to those of PN. Both PD and BP sensitize the production of singlet oxygen with near unit quantum efficiency in a nonpolar (toluene) and a polar (acetonitrile) solvent. With their more extensive pi networks, the one-photon absorption spectra for PD and BP extend out to longer wavelengths than that for PN, thus providing increased flexibility for sensitizer excitation over the range approximately 300-520 nm. Moreover, PD and BP have much larger two-photon absorption cross sections than PN over the range 655-840 nm which, in turn, results in amounts of singlet oxygen that are readily detected in optical experiments. One- and two-photon absorption spectra of PD and BP obtained using high-level calculations model the salient features of the experimental data well. In particular, the ramifications of molecular symmetry are clearly reflected in both the experimental and calculated spectra. The use of PD and BP as standards for both the one- and two-photon photosensitized production of singlet oxygen is expected to facilitate the development of new sensitizers for application in singlet-oxygen-based imaging experiments. 相似文献
107.
108.
Experimental data are reported on isotactic polypropylene in uniaxial cyclic tensile tests with various maximum strains at room temperature. It is demonstrated that polypropylene reveals all characteristic features (hysteresis of energy, damage accumulation, and strain-hardening) of the Mullins effect. Constitutive equations are derived for the viscoplastic behavior of semicrystalline polymers at three-dimensional deformations with small strains. Adjustable parameters in the stress?Cstrain relations are found by fitting the observations. Numerical simulation shows that the model adequately predicts the viscoplastic response of polypropylene in uniaxial and biaxial cyclic tests. 相似文献
109.
Anders Rønne Rassmusen Mads Peter Sørensen Yuri Borisovich Gaididei Peter Leth Christiansen 《Acta Appl Math》2011,115(1):43-61
A wave equation including nonlinear terms up to the second order for a thermoviscous Newtonian fluid is proposed. In the lossless
case this equation results from an expansion to third order of the Lagrangian for the fundamental non-dissipative fluid dynamical
equations. Thus it preserves the Hamiltonian structure, in contrast to the Kuznetsov equation, a model often used in nonlinear
acoustics. An exact traveling wave front solution is derived from a generalized traveling wave assumption for the velocity
potential. Numerical studies of the evolution of a number of arbitrary initial conditions as well as head-on colliding and
confluent wave fronts exhibit several nonlinear interaction phenomena. These include wave fronts of changed velocity and amplitude
along with the emergence of rarefaction waves. An analysis using the continuity of the solutions as well as the boundary conditions
is proposed. The dynamics of the rarefaction wave is approximated by a collective coordinate approach in the energy balance
equation. 相似文献
110.
MY Bashouti K Sardashti J Ristein SH Christiansen 《Physical chemistry chemical physics : PCCP》2012,14(34):11877-11881
Silicon nanowires (Si NWs) terminated with hydrogen atoms exhibit higher activation energy under ambient conditions than equivalent planar Si(100). The kinetics of sub-oxide formation in hydrogen-terminated Si NWs derived from the complementary XPS surface analysis attribute this difference to the Si-Si backbond and Si-H bond propagation which controls the process at lower temperatures (T < 200 °C). At high temperatures (T≥ 200 °C), the activation energy was similar due to self-retarded oxidation. This finding offers the understanding of early-stage oxide growth that affects the conductance of the near-gap channels leading towards more efficient Si NW electronic devices. 相似文献