Efficient encapsulation of functionalized spherical nanoparticles by viral protein cages was found to occur even if the nanoparticle is larger than the inner cavity of the native capsid. This result raises the intriguing possibility of reprogramming the self-assembly of viral structural proteins. The iron oxide nanotemplates used in this work are superparamagnetic, with a blocking temperature of about 250 K, making these virus-like particles interesting for applications such as magnetic resonance imaging and biomagnetic materials. Another novel feature of the virus-like particle assembly described in this work is the use of an anionic lipid micelle coat instead of a molecular layer covalently bound to the inorganic nanotemplate. Differences between the two functionalization strategies are discussed.

The observation of neutrons turning into antineutrons would constitute a discovery of fundamental importance for particle physics and cosmology. Observing the n−n transition would show that baryon number (B) is violated by two units and that matter containing neutrons is unstable. It would provide a clue to how the matter in our universe might have evolved from the B = 0 early universe. If seen at rates observable in foreseeable next-generation experiments, it might well help us understand the observed baryon asymmetry of the universe. A demonstration of the violation of B − L by 2 units would have a profound impact on our understanding of phenomena beyond the Standard Model of particle physics.Slow neutrons have kinetic energies of a few meV. By exploiting new slow neutron sources and optics technology developed for materials research, an optimized search for oscillations using free neutrons from a slow neutron moderator could improve existing limits on the free oscillation probability by at least three orders of magnitude. Such an experiment would deliver a slow neutron beam through a magnetically-shielded vacuum chamber to a thin annihilation target surrounded by a low-background antineutron annihilation detector. Antineutron annihilation in a target downstream of a free neutron beam is such a spectacular experimental signature that an essentially background-free search is possible. An authentic positive signal can be extinguished by a very small change in the ambient magnetic field in such an experiment. It is also possible to improve the sensitivity of neutron oscillation searches in nuclei using large underground detectors built mainly to search for proton decay and detect neutrinos. This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron oscillations, and suggests avenues both for theoretical investigation and for future improvement in the experimental sensitivity.

No abstract

The mechanism of chemical vapor deposition of Cu, CU2O, CuO, and CU3N from Cu(hfacac)2-(H2O) was studied by XRD, MS, FTIR, XPS, SIMS, and NMR techniques. The molecular structure of the precursor was established by a single-crystal X-ray diffraction experiment.Crystallographic data (-165 °C): triclinic space group PI, a = 9.402(3) k,b = 11.068(3) A, c = 7.958(2) A, a = 105.71(2)°, 0 = 100.99(2)°, y = 76.27(2)°, V = 767.31 A* 123 45678, Z = 2, R = 0.0303, i?w = 0.0312. In the presence of excess water in the process gas stream, a facile release of free Hhfacac ligand from the copper complex is activated by a proton transfer from coordinated water. Ligand-mediated reduction of the metal from Cu2+ to Cu+ and from Cu+ to Cu°oxidation states occurs in the absence of an external reducing agent at temperatures of 280 and 400 °C, respectively. Evidence for this ligand-mediated reduction is seen in the presence of the two major ligand-oxidation products (CF3COOH and CFsC(OH)2-CH(OH)2) in the effluent from the deposition reaction. A labeling experiment using H2180 proved that oxygen in copper oxide films deposited from Cu(hfacac)2 onto insulating substrates is derived from water and not the hfacac ligand. As an example of benefits that can be derived from this mechanistic knowledge, we have also shown that replacing H2O with NH3 leads to the formation of CU3N.

Iron oxide nanoparticles with diameters of 20.1 and 8.5 nm coated with phospholipids containing poly-(ethylene glycol) (PEG) tails were studied using small-angle X-ray scattering (SAXS), transmission electron microscopy, dynamic light scattering, and magnetometry. Novel SAXS data analysis methods are applied to build three-dimensional structural models of the nanoparticles coated with PEGylated phospholipids in aqueous solution. The SAXS data demonstrate that the density inside iron oxide nanoparticles is not uniform and depends on the nanoparticle size, which in turn is dependent on the reaction conditions. This heterogeneity is attributed to the presence of two crystalline phases, spinel and wüstite, in the nanoparticles. Because of magnetic properties, the nanoparticles in solution associate in flexible dynamic clusters consisting on average of four individual cores. The magnetometry further supports the SAXS-based models.

We have measured the magnetoresistance in a series of Ga1−xMnxAs samples with 0.033≤ x ≤ 0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative (i.e. the sample resistance is higher when its magnetization is perpendicular to the measuring current than when the two are parallel) and has a magnitude on the order of 5% at temperatures near 10K and below. This stands in contrast to the results for most conventional magnetic materials where the SRA is considerably smaller in magnitude for those few cases in which a negative sign is observed. The magnitude of the SRA drops from its maximum at low temperatures to zero at TC in a manner that is consistent with mean field theory. These results should provide a significant test for emerging theories of transport in this new class of materials. PACS: 75.50.Pp, 72.20.My, 72.80.Ey, 73.50.Jt The recent discovery of ferromagnetism at temperatures as high as 110K in Ga 1−x Mn x As has greatly broadened the interest in diluted magnetic semiconductors over the past few years [1][2][3]. A large number of groups are now investigating these materials which could form the basis for a wide variety of new magneto-electronic devices that may be grown pseudo-morphically on GaAs. The utility of similar devices has already been established using nano-composite structures based on metallic magnetic materials (the so-called giant magnetoresistance and tunnel junction magnetoresistance [4,5]). The semiconducting materials open up new opportunities as they also introduce the prospects of optical or electronic control of the magnetic properties [6,7].These new materials present many interesting challenges as we embark on efforts to make use of their properties in real devices. These challenges come from both the fundamental point of view (trying to understand their properties and what factors control them) and from the desire to manufacture high quality materials in the face of severe constraints imposed by the possibility of nucleating unwanted phases during growth [2]. These two challenges are intimately connected since the density of carriers is expected to influence such material properties as the Curie temperature and magnetic anisotropy [8,9], but this density is strongly influenced by defects included in the structure as a result of the constraints on the growth conditions.In view of our limited understanding of these materials it is prudent to spend some effort exploring the transport properties of individual material layers in preparation for constructing multilayered structures to form devices. Toward that end, in this article we report on magnetotransport measurements in a series of Ga 1−x Mn x As films (x= 0.033 to 0.053). We concentrate on the dependence of the film resistivity on the orientation of an applied magnetic field in the hope that this dependence might be less sensitive to the details of the disorder in the films than is the resistivity itself.The Mn-alloyed films were...

Iron oxide nanoparticles (NPs) with diameters of 16.1, 20.5, and 20.8 nm prepared from iron oleate precursors were coated with poly(maleic acid-alt-1-octadecene) (PMAcOD). The coating procedure exploited hydrophobic interactions of octadecene and oleic acid tails while hydrolysis of maleic anhydride moieties allowed the NP hydrophilicity. The PMAcOD nanostructure in water and the PMAcOD-coated NPs were studied using transmission electron microscopy, ζ-potential measurements, small-angle X-ray scattering, and fluorescence measurements. The combination of several techniques suggests that independently of the iron oxide core and oleic acid shell structures, PMAcOD encapsulates NPs, forming stable hydrophilic shells which withstand absorption of hydrophobic molecules, such as pyrene, without shell disintegration. Moreover, the PMAcOD molecules are predominantly attached to a single NP instead of self-assembling into the PMAcOD disklike nanostructures or attachment to several NPs. This leads to highly monodisperse aqueous samples with only a small fraction of NPs forming large aggregates due to cross-linking by the copolymer macromolecules.

This article demonstrates the encapsulation of cubic iron oxide NPs by Brome mosaic virus capsid shells and the formation, for the first time, of virus-based nanoparticles (VNPs) with cubic cores. Cubic iron oxide nanoparticles (NPs) functionalized with phospholipids containing poly(ethylene glycol) tails and terminal carboxyl groups exhibited exceptional relaxivity in magnetic resonance imaging experiments, which opens the way for in vivo MRI studies of systemic virus movement in plants. Preliminary data on cell-to-cell and long-distance transit behavior of cubic iron oxide NPs and VNPs in N. benthamiana leaves indicate that VNPs have specific transit properties, i.e., penetration into tissue and long-distance transfer through the vasculature in N. Benthamiana plants, even at low temperature (6° C), while NPs devoid of virus protein coats exhibit limited transport by comparison. These particles potentially open new opportunities for the high contrast functional imaging in plants and for the delivery of therapeutic anti-microbial cores into plants.