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81.
Coronado E Giménez-López MC Korzeniak T Levchenko G Romero FM Segura A García-Baonza V Cezar JC de Groot FM Milner A Paz-Pasternak M 《Journal of the American Chemical Society》2008,130(46):15519-15532
The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process. 相似文献
82.
Yoon KY Kotsmar C Ingram DR Huh C Bryant SL Milner TE Johnston KP 《Langmuir : the ACS journal of surfaces and colloids》2011,27(17):10962-10969
Iron oxide nanoparticles, in the form of sub-100-nm clusters, were synthesized in the presence of poly(acrylic acid) (PAA) or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) to provide electrosteric stabilization. The superparamagnetic nanoclusters were characterized using a superconducting quantum interference device (SQUID), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and zeta potential measurements. To anchor the polymer shell on the nanoparticle surface, the polymer was cross-linked for a range of cross-linking densities. For nanoclusters with only 12% (w/w) PSS-alt-MA, electrosteric stabilization was sufficient even in 8 wt % NaCl. For PAA, the cross-linked polymer shell was essentially permanent and did not desorb even upon dilution of the nanoparticles for iron oxide concentrations down to 0.014 wt %. Without cross-linking, over half of the polymer desorbed from the particle surfaces. This general approach of the adsorption of polymer stabilizers onto nanoparticles followed by cross-linking may be utilized for a wide variety of cross-linkable polymers without the need to form covalent bonds between the nanoparticles and polymer stabilizer. Thus, this cross-linking approach is an efficient and inexpensive method of stabilizing nanoparticles for large-scale applications, including the electromagnetic imaging of subsurface reservoirs, even at high salinity. 相似文献
83.
We discuss the transport of a tracer particle through the Bose?CEinstein condensate of a Bose gas. The particle interacts with the atoms in the Bose gas through two-body interactions. In the limiting regime where the particle is very heavy and the Bose gas is very dense, but very weakly interacting (??mean-field limit??), the dynamics of this system corresponds to classical Hamiltonian dynamics. We show that, in this limit, the particle is decelerated by emission of gapless modes into the condensate (Cerenkov radiation). For an ideal gas, the particle eventually comes to rest. In an interacting Bose gas, the particle is decelerated until its speed equals the propagation speed of the Goldstone modes of the condensate. This is a model of ??Hamiltonian friction??. It is also of interest in connection with the phenomenon of ??decoherence?? in quantum mechanics. This note is based on work we have carried out in collaboration with D Egli, I M Sigal and A Soffer. 相似文献
84.
We introduce a novel contrast mechanism for imaging blood flow by use of magnetomotive optical Doppler tomography (MM-ODT), which combines an externally applied temporally oscillating high-strength magnetic field with ODT to detect erythrocytes moving according to the field gradient. Hemoglobin contrast was demonstrated in a capillary tube filled with moving blood by imaging the Doppler frequency shift, which was observed independently of blood flow rate and direction. Results suggest that MM-ODT may be a promising technique with which to image blood flow. 相似文献
85.
We report a crossover in optical propagation in random layered media from localization towards diffusion as the interaction of the wave with the sample is transformed from one to three dimensional due to nonuniformity in the layer thickness. The crossover occurs at the point that the lateral spread of the wave equals the transverse coherence length in the transmitted speckle pattern. 相似文献
86.
DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements
have been reported for the Co1.1−x
Zn
x
Ge0.1Fe1.2O1 spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic
ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained
under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important
role of magnetic anisotropy (due to the presence of Co2+ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed. 相似文献
87.
Scott T. Milner 《Journal of Polymer Science.Polymer Physics》1994,32(16):2743-2755
Polymer “brushes” are formed when long-chain molecules are somehow attached by one end at an interface with a relatively small area per chain. Such adsorbed brushes in the presence of solvent may be used to modify surface properties, stabilize colloidal particles, etc. Strongly segregated block copolymer phases, or interfacial layers of such “polymeric surfactants” may also be modeled in terms of “melt brushes,” (i.e., brushes without solvent). In both cases, when chain attachments are crowded on the interface, the chains stretch out to avoid neighboring chains. The resulting physical state has properties markedly different from polymer solutions, gels, or weakly adsorbed polymer layers. When the chains are strongly stretched, their statistical mechanics become simpler, as fluctuations around the set of most probable conformations are suppressed. This makes possible many pencil-and-paper calculations of brush properties, including bending and compressional moduli, and detailed knowledge of the chain conformations. As a recent example, I will describe calculations of phase diagrams of strongly segregated block copolymers including bicontinuous double-diamond phases. © 1994 John Wiley & Sons, Inc. 相似文献
88.
Kamal K. Seth D. Barlow A. Saha R. Soundranayagam S. Iversen M. Kaletka M. Basko D. Smith G.W. Hoffmann M.L. Barlett R. Fergerson J. McGill E.C. Milner 《Physics letters. [Part B]》1985,158(1):23-27
Differential cross sections and analyzing powers for inelastic scattering of 500 MeV polarized protons to several low-lying states in 40Ca and 48Ca are presented. Phenomenological optical potentials (including density squared terms) have been determined and the data have been analyzed to obtain mass deformation parameters. It is expected that these data will be useful in further testing the recently developed relativistic impulse approximation formalisms and in studying the need for medium modification of the interaction. 相似文献
89.
Mineral acid supporting electrolytes, both in the presence and absence of tartrate ions, have been examined for use in the determination of small amounts of uranium by square wave polarography. A perchloric acid-tartrate supporting electrolyte is most suitable for analytical work and has been used for the determination of uranium in mineral samples. 相似文献
90.
Stuart Farquharson David Milner M.A. Tadayyoni Michael J. Weaver 《Journal of Electroanalytical Chemistry》1984,178(1):143-152
An application of surface-enhanced Raman spectroscopy (SERS) to evaluating the kinetics of electrochemical reactions is outlined. This involves monitoring the potential-dependent SERS intensities of the adsorbed reactant at a rotating disk electrode in a potential region where the kinetics are under mixed mass transfer-heterogeneous electron transfer control. Comparisons are made between the kinetic behavior extracted from the SERS intensity-potential dependence and that obtained from the faradaic current flow. For Co(NH3)63+ reduction at silver, where the reactant is electrostatically attracted but not bound to the surface, the SERS and electrochemical rate behavior is closely compatible. However, for Cr(NH3)5Br2+ and Cr(NH3)5NCS2+ reduction, where the reactants bind directly to the surface prior to electron transfer, the reactivities at the SERS-active sites are substantially higher than for the prevalent adsorbate as obtained electrochemically. These findings suggest that surface sites displaying efficient Raman scattering may also provide centers of catalytic activity. 相似文献