A Computational Study of Cluster Dynamics in Structural Lubricity: Role of Cluster Rotation

We present a computational study of sliding between gold clusters and a highly oriented pyrolytic graphite substrate, a material system that exhibits ultra-low friction due to structural lubricity. By means of molecular dynamics, it is found that clusters may undergo spontaneous rotations during manipulation as a result of elastic instability, leading to attenuated friction due to enhanced interfacial incommensurability. In the case of a free cluster, shear stresses exhibit a non-monotonic dependency on the strength of the tip-cluster interaction, whereby rigid clusters experience nearly constant shear stresses. Finally, it is shown that the suppression of the translational degrees of freedom of a cluster's outermost-layer can partially annihilate out-of-plane phonon vibrations, which leads to a reduction of energy dissipation that is in compliance with Stokesian damping. It is projected that the physical insight attained by the study presented here will result in enhanced control and interpretation of manipulation experiments at structurally lubric contacts

Molecular-Dynamics Simulations of Some BaXF4 Compounds

We have carried out molecular-dynamics simulations on BaXF4 compounds, where X is Mg, Mn, or Zn. Ab initio potentials, with no adjustable parameters, were used to obtain short-range interactions between ion pairs. We found a polar ground-state structure which is in agreement with the A21am space group reported experimentally. We were able to reverse polarization in BaMgF4 at high temperatures, using large fields, but were unable to reverse polarization in the other compounds. The second-order phase transition in the Mn compound at 250 K was reproduced. We believe this to be the first extension of molecular dynamics to materials consisting of chains of F octahedra

Evaluating The Effects of Signal Control Applications on Roundabout’s LOS Performance Using VISSIM Microsimulation Model

The existence of unbalanced and high traffic flows at roundabout have resulted in poor performance and safety concerns. Past research has shown that applications of signal control at problematic roundabouts had significantly improved its Level of Service (LOS) performance. This study investigates the effects of different signal phasing plans on the roundabout’s LOS performance using VISSIM microsimulation model. The findings revealed that both Approach-Signal-Control Roundabout ACSR and Two-Stop-Line Control Signalized Roundabout TSLSR signal phasing methods did not significantly improve the roundabout’s entry capacities. Partial signal control applications, however, have resulted in a significant reduction in vehicle delays and higher entry capacities. The results of this study provide a good overview to local traffic practitioners on how to evaluate and implement the signal control strategy at problematic roundabouts. &nbsp

Evaluating The Effects of Signal Control Applications on Roundabout’s LOS Performance Using VISSIM Microsimulation Model

The existence of unbalanced and high traffic flows at roundabout have resulted in poor performance and safety concerns. Past research has shown that applications of signal control at problematic roundabouts had significantly improved its Level of Service (LOS) performance. This study investigates the effects of different signal phasing plans on the roundabout’s LOS performance using VISSIM microsimulation model. The findings revealed that both Approach-Signal-Control Roundabout ACSR and Two-Stop-Line Control Signalized Roundabout TSLSR signal phasing methods did not significantly improve the roundabout’s entry capacities. Partial signal control applications, however, have resulted in a significant reduction in vehicle delays and higher entry capacities. The results of this study provide a good overview to local traffic practitioners on how to evaluate and implement the signal control strategy at problematic roundabouts. &nbsp

Effect of Interlayer Coupling on Ultrafast Charge Transfer from Semiconducting Molecules to Mono- and Bilayer Graphene

Graphene is used as flexible electrodes in various optoelectronic devices. In these applications, ultrafast charge transfer from semiconducting light absorbers to graphene can impact the overall device performance. Here, we propose a mechanism in which the charge-transfer rate can be controlled by varying the number of graphene layers and their stacking. Using an organic semiconducting molecule as a light absorber, the charge-transfer rate to graphene is measured by using time-resolved photoemission spectroscopy. Compared to graphite, the charge transfer to monolayer graphene is about 2 times slower. Surprisingly, the charge transfer to A−B–stacked bilayer graphene is slower than that to both monolayer graphene and graphite. This anomalous behavior disappears when the two graphene layers are randomly stacked. The observation is explained by a charge-transfer model that accounts for the band-structure difference in mono- and bilayer graphene, which predicts that the charge-transfer rate depends nonintuitively on both the layer number and stacking of graphene

The Influence of Adjacent Segment on the Reliability of Cu Dual Damascene Interconnects

Three terminal âdotted-I’ interconnect structures, with vias at both ends and an additional via in the middle, were tested under various test conditions. Mortalities (failures) were found in right segments with jL value as low as 1250 A/cm, and the mortality of a dotted-I segment is dependent on the direction and magnitude of the current in the adjacent segment. Some mortalities were also found in the right segments under a test condition where no failure was expected. Cu extrusion along the delaminated Cu/Si₃N₄ interface near the central via region was believed to cause the unexpected failures. From the time-to-failure (TTF), it is possible to quantify the Cu/Si₃N₄ interfacial strength and bonding energy. Hence, the demonstrated test methodology can be used to investigate the integrity of the Cu dual damascene processes. As conventionally determined critical jL values in two-terminal via-terminated lines cannot be directly applied to interconnects with branched segments, this also serves as a good methodology to identify the critical effective jL values for immortality.Singapore-MIT Alliance (SMA

Understanding and promoting oral health of Indonesian domestic helpers in Hong Kong

Includes bibliographical references (p. 44).published_or_final_versio

Optimization of torrefaction conditions for high energy density solid biofuel from oil palm biomass and fast growing species available in Malaysia

Without appropriate treatment, lignocellulosic biomass is not suitable to be fed into existing combustion systems because of its high moisture content, low bulk energy density and difficulties in transport, handling and storage. The aim of this study was to investigate the effects of torrefaction treatment on the weight loss and energy properties of fast growing species in Malaysia (Acacia spp., and Macaranga spp.) as well as oil palm biomass (oil palm trunk and empty fruit bunch). The lignocellulosic biomass was torrefied at three different temperatures 200, 250 and 300 °C for 15, 30 and 45 min. Response surface methodology was used for optimization of torrefaction conditions, so that biofuel of high energy density, maximized energy properties and minimum weight loss could be manufactured. The analyses showed that increase in heating values was affected by treatment severity (cumulated effect of temperature and time). Our results clearly demonstrated an increased degradation of the material due to the combined effects of temperature and treatment time. While the reaction time had less impact on the energy density of torrefied biomass, the effect of reaction temperature was considerably stronger under the torrefaction conditions used in this study. It was demonstrated that each biomass type had its own unique set of operating conditions to achieve the same product quality. The optimized torrefaction conditions were verified empirically and applicability of the model was confirmed. The torrefied biomass occurred more suitable than raw biomass in terms of calorific value, physical and chemical properties. The results of this study could be used as a guide for the production of high energy density solid biofuel from lignocellulosic biomass available in Malaysia