Transformations of gold nanoparticles investigated using variable temperature high-resolution transmission electron microscopy.

Recently designed advanced in-situ specimen holders for transmission electron microscopy (TEM) have been used in studies of gold nanoparticles. We report results of variable temperature TEM experiments in which structural transformations have been correlated with specimen temperature, allowing general trends to be identified. Transformation to a decahedral morphology for particles in the size range 5-12nm was observed for the majority of particles regardless of their initial structure. Following in-situ annealing, decahedra were found to be stable at room temperature, confirming this as the equilibrium morphology, in agreement with recently calculated phase diagrams. Other transitions at low temperature in addition to surface roughening have also been observed and correlated with the same nanoscale phase diagram. Investigations of gold particles at high temperature have revealed evidence for co-existing solid and liquid phases. Overall, these results are important in a more precise understanding of the structure and action of catalytic gold nanoparticles and in the experimental verification of theoretical calculations.

Weighing supported nanoparticles: size-selected clusters as mass standards in nanometrology.

We present a new approach to quantify the mass and 3D shape of nanoparticles on supports, using size-selected nanoclusters as mass standards in scanning transmission electron microscope. Through quantitative image intensity analysis, we show that the integrated high angle annular dark field intensities of size-selected gold clusters soft-landed on graphite display a monotonic dependence on the cluster size as far as approximately 6500 atoms. We applied this mass standard to study gold nanoparticles prepared by thermal vapor deposition and by colloidal wet chemistry, and from which we deduced the shapes of these two types of nanoparticles as expected.

Three-dimensional atomic-scale structure of size-selected gold nanoclusters.

An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 3096 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems.

Monitoring Alfvén cascades with interferometry on the JET Tokamak.

A microwave interferometry technique is applied for the first time for detecting a discrete spectrum of Alfvén cascade (AC) eigenmodes excited with fast ions in reversed magnetic shear plasmas of the Joint European Torus. The interferometry measurements of plasma density perturbations associated with ACs show an unprecedented frequency and time resolution superior to that obtained with external magnetic coils. The measurements of ACs are used for monitoring the evolution of the safety factor and density of rational magnetic surfaces in the region of maximum plasma current.

A case-specific approach to the treatment of alcoholism: the application of control mastery theory to alcoholics anonymous and professional practice.

Effective treatment of alcoholism requires adopting a psychodynamically informed case-specific approach. Control mastery theory provides a powerful way to understand and treat the alcoholic patient. The theory posits that individuals hold unconscious pathogenic beliefs that contribute to the development and maintenance of alcoholism. The primary therapeutic goal is to create a safe atmosphere that enables patients to disabuse themselves of their maladaptive beliefs and their attendant guilt. In this way, patients become freer to more accurately test reality and thus more effectively pursue normal developmental goals. The treatment of the alcoholic patient progresses through phases, each of which poses different therapeutic challenges. The salient therapeutic tasks addressed in this article are denial, containing affect, relapse prevention, and Alcoholics Anonymous involvement. By understanding the individual's unique pathogenic belief system, the therapist is better equipped to help the patient through the generic phases and tasks of the recovery process.

Influence of viral envelope on Newcastle disease virus infection.

The adsorption characteristics of Newcastle disease virus (NDV) propagated in chicken cells (NDV-C) and in human cells (NDV-H) were examined. Adsorption experiments performed at different temperatures indicated that virus propagated in a particular cell infected that cell type more readily than did virus propagated in a different host. For example, NDV-C was more efficient in initiating infection of chicken cells at 22 C than was NDV-H; the reverse was true when human cells were employed. The results indicate that infection of susceptible cells by NDV is influenced by the host cell in which the virus was propagated. The data also suggest that NDV may be useful in studies on homologous and heterologous membrane-membrane interactions.