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31.
Iron oxide nanoparticles made from the thermal decomposition method are highly uniform in all respects (size, shape, composition and crystallography), making them ideal candidates for many bioapplications. The surfactant coating on the as-synthesized nanoparticles renders the nanoparticles insoluble in aqueous solutions. For biological applications nanoparticles must be water soluble. Here we demonstrate the phase transfer of our nanoparticles with the biocompatible copolymer Pluronic F127. Transmission electron microscopy, Fourier transform infrared spectroscopy and dynamic light scattering indicate that the nanoparticles are coated discretely. Magnetic measurements show that the nanoparticles remain superparamagnetic with saturation magnetization ∼96% of the maximum theoretical value. 相似文献
32.
《Solid State Ionics》2006,177(26-32):2467-2471
AgI nanoparticles were prepared by solution-based routes using water-soluble anionic or cationic polyelectrolytes as capping agents. Depending on the polyelectrolytes, AgI nanoparticles with well-defined morphology, size, and phase compositions were obtained: the use of poly(sodium 4-styrenesulfonate) (PSS) resulted in AgI nano-rods of β-AgI in wurtzite structure (2H); with poly(acrylic acid sodium salt) (PAS) truncated-tetrahedron shaped γ-AgI nanoparticles (nanotetrahedra) in zinc-blende structure (3C) were obtained; by employing poly(diallyldimethylammonium chloride) (PDADMAC) plate-like AgI nanoparticles (nano-plates) consisting of unusual polytype phases of AgI (7H and 9R) were formed. Macroscopically unstable γ-AgI and 7H and 9R phases could be stabilized in the form of nanocrystalline powders. They transform reversibly into the high temperature α-AgI phase and exhibit unusually high ionic conductivity and substantially smaller transformation enthalpy values compared to the macroscopic β-AgI. 相似文献
33.
《Physica A》2006,371(2):157-170
We study the effects of an external periodic perturbation on a Poisson rate process, with special attention to the perturbation-induced sojourn-time patterns. We show that these patterns correspond to turning a memory-less sequence into a sequence with memory. The memory effects are stronger the slower the perturbation. The adoption of a de-trending technique, applied with no caution, might generate the impression that no fluctuation–periodicity correlation exists. We find that this is due to the fact that the perturbation-induced memory is a global property and that the result of a local in time analysis would not find any memory effect, insofar as the process under study is locally a Poisson process. We find that an efficient way to detect this memory effect is to analyze the moduli of the de-trended sequence. We turn the sequence to analyze into a diffusion process, and we evaluate the Shannon entropy of the resulting diffusion process. We find that both the original sequence and the suitably processed de-trended sequence yield the same dependence of entropy on time, namely, an initial scaling larger than ordinary scaling, and a sequel of weak oscillations, which are a clear signature of the external perturbation, in both cases. This is a clear indication of the fluctuation–periodicity correlation. 相似文献
34.
35.
The issues involved in teaching English language learners mathematics while they are learning English pose many challenges for mathematics teachers and highlight the need to focus on language-processing issues related to teaching mathematical content. Two realistic-type problems from high-stakes tests are used to illustrate the complex interactions between culture, language, and mathematical learning. The analyses focus on aspects of the problems that potentially increase cognitive demands for second-language learners. An analytical framework is presented that is designed to enable mathematics teachers to identify critical elements in problems and the learning environment that contribute to increased cognitive demands for students of English as a second language. The framework is proposed as a cycle of teacher reflection that would extend a constructivist model of teaching to include broader linguistic, cultural, and cognitive processing issues of mathematics teaching, as well as enable teachers to develop more accurate mental models of student learning. 相似文献
36.
Alp E. E. Sturhahn W. Toellner T. S. Zhao J. Hu M. Brown D. E. 《Hyperfine Interactions》2002,144(1-4):3-20
Nuclear resonant inelastic X-ray scattering of synchrotron radiation is being applied to ever widening areas ranging from
geophysics to biophysics and materials science. Since its first demonstration in 1995 using the 57Fe resonance, the technique has now been applied to materials containing 83Kr, 151Eu, 119Sn, and 161Dy isotopes. The energy resolution has been reduced to under a millielectronvolt. This, in turn, has enabled new types of
measurements like Debye velocity of sound, as well as the study of origins of non-Debye behavior in presence of other low-energy
excitations. The effect of atomic disorder on phonon density of states has been studied in detail. The flux increase due to
the improved X-ray sources, crystal monochromators, and time-resolved detectors has been exploited for reducing sample sizes
to nano-gram levels, or using samples with dilute resonant nuclei like myoglobin, or even monolayers. Incorporation of micro-focusing
optics to the existing experimental setup enables experiments under high pressure using diamond-anvil cells. In this article,
we will review these developments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
《Applied and Computational Harmonic Analysis》2006,20(2):250-260
Beurling–Landau-type results are known for a rather small class of functions limited to the Paley–Wiener space and certain spline spaces. Here, we show that the sampling and reconstruction problem in shift-invariant spaces is robust with respect to two classes of probing measures as well as to the underlying shift-invariant space. As an application we enlarge the class of functions for which Beurling–Landau-type results hold. 相似文献
38.
《Journal of Geometry and Physics》2006,56(8):1326-1356
This paper introduces the notion of “relative gerbes” for smooth maps of manifolds, and discusses their differential geometry. The equivalence classes of relative gerbes are further classified by the relative integral cohomology in degree 3. 相似文献
39.
《Polyhedron》2007,26(9-11):1849-1858
Three compounds composed of phenazine and copper chloride have been prepared and studied by infrared spectroscopy, X-ray diffraction, and variable temperature magnetization. The compounds synthesized and studied are: Cu(phenazine)Cl2 (1), (phenazinium)2CuCl4 · H2O (2), and [Cu(phenazine)Cl2 · H2O]2 (3). Compounds 1 and 2 are described as antiferromagnetic Heisenberg chains with exchange constants ∣J∣/kB = 33.8 K and 8.6 K, respectively. 相似文献
40.