Communication: Diverse nanoscale cluster dynamics: Diffusion of 2D epitaxial clusters

The dynamics of nanoscale clusters can be distinct from macroscale behavior described by continuum formalisms. For diffusion of 2D clusters of N atoms in homoepitaxial systems mediated by edge atom hopping, macroscale theory predicts simple monotonic size scaling of the diffusion coefficient, DN ∼ N−β, with β = 3/2. However, modeling for nanoclusters on metal(100) surfaces reveals that slow nucleation-mediated diffusion displaying weak size scaling β \u3c 1 occurs for “perfect” sizes Np = L2 and L(L+1) for integer L = 3,4,… (with unique square or near-square ground state shapes), and also for Np+3, Np+4,…. In contrast, fast facile nucleation-free diffusion displaying strong size scaling β ≈ 2.5 occurs for sizes Np+1 and Np+2. DN versus N oscillates strongly between the slowest branch (for Np+3) and the fastest branch (for Np+1). All branches merge for N = O(102), but macroscale behavior is only achieved for much larger N = O(103). This analysis reveals the unprecedented diversity of behavior on the nanoscale

Osmotic blistering in enamel bonded with one-step self-etch adhesives

One-step self-etch adhesives behave as permeable membranes after polymerization, permitting water to move through the cured adhesives. We hypothesize that osmotic blistering occurs in bonded enamel when these adhesives are used without composite coupling. Tooth surfaces from extracted human premolars were bonded with 5 one-step self-etch adhesives. They were immersed in distilled water or 4.8 M CaCl2, and examined by stereomicroscopy, field-emission/environmental SEM, and TEM. Water blisters were observed in bonded enamel but not in bonded dentin when specimens were immersed in water. They collapsed when water was subsequently replaced with CaCl2. Blisters were absent from enamel in specimens that were immersed in CaCl 2 only. Water trees were identified from adhesive-enamel interfaces. Osmotic blistering in enamel is probably caused by the low water permeability of enamel. This creates an osmotic gradient between the bonded enamel and the external environment, causing water sorption into the interface.published_or_final_versio

Airways hyperresponsiveness to different inhaled combination therapies in adolescent asthmatics

Local electrical characterization has wide spectrum of applications in various areas. However, there are a number of difficulties that hinder the precise measurement of local electrical properties of samples, particularly those within nano-scale spatial resolution. Inspired by these challenges, we developed a nano-robot enabled electrical characterization system that can be utilized to pinpoint the local electrical properties of materials, devices, and bioentities with high spatial and electrical resolution. This system consists of an electrical characterization unit and a nano-robot with an augment reality system, which was developed from a traditional atomic force microscopy (AFM). The augment reality system provides real-time visual feedback. The real-time visual display integrated with the real-time force feedback from the nano-robot allows a precise control of the position and force of the AFM tips towards samples, which are significant for the sensitivity of local electrical measurement. The system design and implementation are presented in the paper. Experiments were carried out to study the local conductance of a multi-wall carbon nanotube (MWCNT), demonstrating the effectiveness of this system. © 2012 IEEE.Link_to_subscribed_fulltex

Non-equilibrium growth of metal clusters on a layered material: Cu on MoS2

We use a variety of experimental techniques to characterize Cu clusters on bulk MoS2 formed via physical vapor deposition of Cu in ultrahigh vacuum, at temperatures ranging from 300 K to 900 K. We find that large facetted clusters grow at elevated temperatures, using high Cu exposures. The cluster size distribution is bimodal, and under some conditions, large clusters are surrounded by a denuded zone. We propose that defect-mediated nucleation, and coarsening during deposition, are both operative in this system. At 780 K, a surprising type of facetted cluster emerges, and at 900 K this type predominates: pyramidal clusters with a triangular base, exposing (311) planes as side facets. This is a growth shape, rather than an equilibrium shape

Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong.

BACKGROUND: Health authorities worldwide, especially in the Asia Pacific region, are seeking effective public-health interventions in the continuing epidemic of severe acute respiratory syndrome (SARS). We assessed the epidemiology of SARS in Hong Kong. METHODS: We included 1425 cases reported up to April 28, 2003. An integrated database was constructed from several sources containing information on epidemiological, demographic, and clinical variables. We estimated the key epidemiological distributions: infection to onset, onset to admission, admission to death, and admission to discharge. We measured associations between the estimated case fatality rate and patients' age and the time from onset to admission. FINDINGS: After the initial phase of exponential growth, the rate of confirmed cases fell to less than 20 per day by April 28. Public-health interventions included encouragement to report to hospital rapidly after the onset of clinical symptoms, contact tracing for confirmed and suspected cases, and quarantining, monitoring, and restricting the travel of contacts. The mean incubation period of the disease is estimated to be 6.4 days (95% CI 5.2-7.7). The mean time from onset of clinical symptoms to admission to hospital varied between 3 and 5 days, with longer times earlier in the epidemic. The estimated case fatality rate was 13.2% (9.8-16.8) for patients younger than 60 years and 43.3% (35.2-52.4) for patients aged 60 years or older assuming a parametric gamma distribution. A non-parametric method yielded estimates of 6.8% (4.0-9.6) and 55.0% (45.3-64.7), respectively. Case clusters have played an important part in the course of the epidemic. INTERPRETATION: Patients' age was strongly associated with outcome. The time between onset of symptoms and admission to hospital did not alter outcome, but shorter intervals will be important to the wider population by restricting the infectious period before patients are placed in quarantine

Non-contact batch micro-assembly by centrifugal force

ABSTRACT * Due to the minute scale of MEMS, inertia forces are often neglected. However, we have proven that these forces can be significant even if a microstructure's mass is <1µg (a 250µmx100µm mass with MUMPs poly1, poly2, and Au layers). We have demonstrated that at this scale, mass inertia force can overcome surface forces and be used for non-contact self-assembly of MEMS structures. Centrifugal force was applied to hinged MUMPs#31 structures, causing these structures to self-assemble by rotating themselves 90 o out of substrate plane and automatically locked themselves to designed latches. This batch-assembly technique is very fast, low-cost, non-contact, and non-destructive. Moreover, we have successfully characterized the centrifugal forces needed to assemble these microstructures by integrating sensors on the same MUMPs chips to provide wireless signal that relate to the dynamic behavior of the microstructures. This is a very important result in terms of making feasible quantitative analyses of surface forces acting on surface micromachined MEMS devices