Dendrimer-Encapsulated Nanoparticles: New Synthetic and Characterization Methods and Catalytic Applications

In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized using a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently reduced chemically to yield nearly size-monodisperse particles having diameters in the 1-2 nm range. Monometallic, bimetallic (alloy and core@shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica, but also as a stabilizer for the nanoparticle. In this perspective, we report on progress in the synthesis, characterization, and applications of these materials since our last review in 2005. Significant advances in the synthesis of core@shell DENs, characterization, and applications to homogeneous and heterogeneous catalysis (including electrocatalysis) are emphasized.U.S. Department of Energy, Office of Basic Energy Sciences DE-FG02-09ER16090U.S. National Science Foundation 0847957Robert A. Welch Foundation F-0032Chemistr

Gaussianity revisited: Exploring the Kibble-Zurek mechanism with superconducting rings

In this paper we use spontaneous flux production in annular superconductors to shed light on the Kibble-Zurek scenario. In particular, we examine the effects of finite size and external fields, neither of which is directly amenable to the KZ analysis. Supported by 1D and 3D simulations, the properties of a superconducting ring are seen to be well represented by analytic Gaussian approximations which encode the KZ scales indirectly. Experimental results for annuli in the presence of external fields corroborate these findings.Comment: 20 pages, 10 figures; submitted to J. Phys: Condens. Matter for the special issue 'Condensed Matter Analogues of Cosmology'; v2: considerably reduced length, incorporation of experimental details into main text, discussion improved, references added, version accepted for publicatio

Phase Transition in Strongly Degenerate Hydrogen Plasma

Direct fermionic path-integral Monte-Carlo simulations of strongly coupled hydrogen are presented. Our results show evidence for the hypothetical plasma phase transition. Its most remarkable manifestation is the appearance of metallic droplets which are predicted to be crucial for the electrical conductivity allowing to explain the rapid increase observed in recent shock compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript submitted to JETP Letter

Photometric validation of a model independent procedure to extract galaxy clusters

By means of CCD photometry in three bands (Gunn g, r, i) we investigate the existence of 12 candidate clusters extracted via a model independent peak finding algorithm (\cite{memsait}) from DPOSS data. The derived color-magnitude diagrams allow us to confirm the physical nature of 9 of the cluster candidates, and to estimate their photometric redshifts. Of the other candidates, one is a fortuitous detection of a true cluster at z~0.4, one is a false detection and the last is undecidable on the basis of the available data. The accuracy of the photometric redshifts is tested on an additional sample of 8 clusters with known spectroscopic redshifts. Photometric redshifts turn out to be accurate within z~0.01 (interquartile range).Comment: A&A in pres

Moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits

Boulders moving in flash floods cause considerable damage and casualties. More and bigger boulders move in flash floods than predicted from published theory. The interpretation of flow conditions from the size of large particles within flash flood deposits has, until now, generally assumed that the velocity (or discharge) is unchanging in time (i.e. flow is steady), or changes instantaneously between periods of constant conditions. Standard practice is to apply theories developed for steady flow conditions to flash floods, which are however inherently very unsteady flows. This is likely to lead to overestimates of peak flow velocity (or discharge). Flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean-flow drag. These transient forces, generated by rapid velocity changes, are generally ignored in published theories, but they are briefly so large that they could initiate the motion of boulders. This paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow, and discusses the implications. Keywords

Refinement of the Reflective Function Questionnaire for Youth (RFQY) Scale B using item response theory

We conducted item response theory (IRT) analyses to refine the Reflective Function Questionnaire for Youth (RFQY) Scale B. Data from a non-clinical sample of young people (n = 737; ages 18-25) was used to derive a shortened version of the RFQY. Results were replicated in a clinical sample of inpatient adolescents (n = 467; ages 12-17), resulting in a five-item measure, thereafter named the RFQY-5. The RFQY-5 item set was then scrutinized for construct validity against the original 23-item RFQY item set in a randomly selected sample of 100 inpatient adolescents not included in the IRT replication, and 186 healthy adolescents drawn from the community. Results showed that the RFQY-5 performed similarly as the long version in terms of associations with criterion variables, and outperformed the longer version in discriminating between inpatient and community-dwelling adolescents who differed in their levels of borderline traits. The study provides evidence in support of the use of the RFQY-5 in research and clinical settings

Sorghum, 1965

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