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861.
By using the first-principles calculation, we study the structural, magnetic, and electronic properties of the SrFeAsF compound and its Co-doped counterpart SrFe1 − xCoxAsF (x=0.125). It is shown that the competition of the nearest and next-nearest neighbor exchange coupling J1 and J2 between Fe ions gives rise to a frustrated striped antiferromagnetic order in SrFeAsF and an accompanied lattice distortion, while for the Co-doped case, both J1 and J2 decrease significantly as well as the lattice distortion, and thus the antiferromagnetic order is suppressed greatly. This is further confirmed by the electronic structure calculation that the density of states at the Fermi level increases with Co doping as well as the itinerancy of Fe d electron. 相似文献
862.
Tim R. Dargaville Mathew Celina Jeffrey W. Martin Bruce A. Banks 《Journal of Polymer Science.Polymer Physics》2005,43(18):2503-2513
The effects of atomic oxygen (AO) and vacuum UV radiation simulating low Earth orbit conditions on two commercially available piezoelectric polymer films, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE), have been studied. Surface erosion and pattern development are significant for both polymers. Erosion yields were determined as 2.8 × 10?24 cm3/atom for PVDF and 2.5 × 10?24 cm3/atom for P(VDF‐TrFE). The piezoelectric properties of the residual material of both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF‐TrFE) was observed. A lightly cross‐linked network was formed in the copolymer presumably because of penetrating vacuum ultraviolet (VUV) radiation, while the homopolymer remained uncross‐linked. These differences were attributed to varying degrees of crystallinity and potentially greater absorption, and hence damage, of VUV radiation in P(VDF‐TrFE) compared with PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2503–2513, 2005 相似文献
863.
Josef Lechner Ivan Sekerka 《International journal of environmental analytical chemistry》2013,93(4):313-322
Abstract A simple, versatile, automated direct potentiometry is described. It offers a wide range of possible applications for all types of ion-selective electrodes, including the glass electrode. The apparatus consists of two Fisher turntable sample changers connected to an Orion automatic switch, Orion pH/mV meter, and Orion printer system via a control module. The optimum sampling rate is 20 samples per hour F? and NH+ in water samples were determined by using commercially available ion-selective electrodes. 相似文献
864.
The paper provides a state-of-the-art review of the current understanding regarding the long-term response of polymer-matrix composites subjected to cyclic loading conditions. Typically, under such conditions, the behavior of polymeric systems is characterized by much higher creep rates than those observed in the cases of static loading. In this paper, research accomplishments in the subject area are discussed. New experimental results are presented regarding the cyclic-creep response of a composite system consisting of a thin-film piezoelectric polymer polyvinylidene fluoride (PVDF) with thin metallic layers deposited on both surfaces of the polymer. This composite was tested under the conditions of tensile static stresses with superimposed sinusoidal oscillations. As a result, considerable acceleration of creep rates has been recorded as the mean stresses, vibration amplitudes, and frequencies of oscillations tended to increase. These effects were observed even within the linear viscoelastic deformation range at room temperature; however, the acceleration of cyclic-creep rates tended to decrease below the freezing temperature. In general, as indicated in the conclusion, the problem of cyclic creep in polymeric systems is far from being well understood and requires further studies. 相似文献
865.
Surface functionalization of a commercially available poly(vinylidene fluoride) (PVDF) filtration membrane (Millipore DVPP) was performed using organic synthesis at the solid–liquid interface. Hydroxyl groups present on this hydrophilic membrane were activated by reaction with several activating and coupling agents prior to the covalent grafting of lysine. Transamination was used as well as a grafting method. The apparent surface of the PVDF membrane was characterized using SEM and XPS techniques before and after the wet chemical treatments. On the other hand, chemical reactivity of the open surface was assayed by the coupling to tritiated lysine and liquid scintillation counting (LSC) of the radioactivity associated to the samples. 相似文献
866.
867.
Ammonium fluoride was found to be very efficient modifier for the elimination of MgCl2 interference on Pb determination. Ammonium fluoride probably converts strongly interfering volatile MgCl2 to less volatile MgF2 matrix that makes possible the release of Pb analyte at lower temperature, before the matrix starts to vaporize. It was observed likewise that NH4F removes the interferences mentioned, i.e. caused by MgCl2 presence, much more effectively as compared with some modifiers, before now recommended for this purpose. The application of this modifier to the determination of Pb in 2% (m/v) MgCl2 has ensured the characteristic mass and LOD value in the original sample of 12 pg and 60 ng g−1, respectively (10 μl aliquots of sample). Applying the modifier to standards and samples enables the use of matrix-free standard solutions for attaining accurate analysis as verified by recovery studies. 相似文献
868.
The comparative studies on the miscibility and phase behavior between the blends of linear and star‐shaped poly(2‐methyl‐2‐oxazoline) with poly(vinylidene fluoride) (PVDF) were carried out in this work. The linear poly(2‐methyl‐2‐oxazoline) was synthesized by the ring opening polymerization of 2‐methyl‐2‐oxazoline in the presence of methyl p‐toluenesulfonate (MeOTs) whereas the star‐shaped poly(2‐methyl‐2‐oxazoline) was synthesized with octa(3‐iodopropyl) polyhedral oligomeric silsesquioxane [(IC3H6)8Si8O12, OipPOSS] as an octafunctional initiator. The polymers with different topological structures were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the star‐shaped poly(2‐methyl‐2‐oxazoline) was miscible with poly(vinylidene fluoride) (PVDF), which was evidenced by single glass‐transition temperature behavior and the equilibrium melting‐point depression. Nonetheless, the blends of linear poly(2‐methyl‐2‐oxazoline) with PVDF were phase‐separated. The difference in miscibility was ascribed to the topological effect of PMOx macromolecules on the miscibility. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 942–952, 2006 相似文献
869.
A. P. Voitovich V. S. Kalinov G. Baldacchini R. M. Montereali M. Cremona 《Journal of Applied Spectroscopy》1998,65(5):778-795
Results of investigations of radiative F
3
+
-color centers in lithium fluoride obtained by the methods of one- and two-photon absorption, polarization spectroscopy, and
luminescence in singlet, triplet and triplet-singlet channels are reported. The scheme of energy levels of the F
3
+
-center is revised. The probabilities of singlet-triplet conversion and the rates of depletion of the lower triplet state
in the range of 80–350 K are presented. Recommendations are given on the technology of radiative LiF coloration that provide
an increase in the F
3
+
-center concentration and a decrease in the concentration of some other centers that prevent lasing on the LiF:F
3
+
active medium from being obtained. The phototransformations of color centers in LiF are analyzed. The parameters of lasers
with LiF:F
3
+
active media that provide generation of radiation tunable in the green region of the spectrum are considered. Based on spectroscopic
data the maximum attainable time characteristics of such lasers are discussed. The prospects for further investigations of
LiF:F
3
+
lasers are outlined in brief.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 745–760, September–October, 1998. 相似文献
870.
The development of the morphology in poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) (PVDF/PHB) blends upon isothermal and anisothermal crystallization is investigated by time‐resolved small‐ and wide‐angle X‐ray scattering. The components are completely miscible in the melt but crystallize separately; they crystallize stepwise at different temperatures or sequentially with isothermal or anisothermal conditions, respectively. The PVDF crystallizes undisturbed whereas PHB crystallizes in a confined space that is determined by the existing supermolecular structure of the PVDF. The investigations reveal that composition inhomogeneities may initially develop in the remaining melt or in the amorphous phases of the PVDF upon crystallization of that component. The subsequent crystallization of the PHB depends on these heterogeneities and the supermolecular structure of PVDF (dendritically or globularly spherulitic). PHB may form separate spherulites that start to grow from the melt, or it may develop “interlocking spherulites” that start to grow from inside a PVDF spherulite. Occasionally, a large number of PVDF spherulites may be incorporated into PHB interlocking spherulites. The separate PHB spherulites may intrude into the PVDF spherulites upon further growth, which results in “interpenetrating spherulites.” Interlocking and interpenetrating are realized by the growth of separate lamellar stacks (“fibrils”) of the blend components. There is no interlamellar growth. The growth direction of the PHB fibrils follows that of the existing PVDF fibrils. Depending on the distribution of the PHB molecules on the interlamellar and interfibrillar PVDF regions, the lamellar arrangement of the PVDF may contract or expand upon PHB crystallization and the adjacent fibrils of the two components are linked or clearly separated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 974–985, 2004 相似文献