9,766 research outputs found
Electron Interactions and Transport Between Coupled Quantum Hall Edges
We examine the effects of electron-electron interactions on transport between
edge states in a multilayer integer quantum Hall system. The edge states of
such a system, coupled by interlayer tunneling, form a two-dimensional, chiral
metal at the sample surface. We calculate the temperature-dependent
conductivity and the amplitude of conductance fluctuations in this chiral
metal, treating Coulomb interactions and disorder exactly in the weak-tunneling
limit. We find that the conductivity increases with increasing temperature, as
observed in recent experiments, and we show that the correlation length
characterising conductance fluctuations varies inversely with temperature.Comment: 4 pages, 2 figures, typos corrected, Ref. 17 added, minor changes
made for publicatio
Velocity weakening and possibility of aftershocks in nanofriction experiments
We study the frictional behavior of small contacts as those realized in the
atomic force microscope and other experimental setups, in the framework of
generalized Prandtl-Tomlinson models. Particular attention is paid to
mechanisms that generate velocity weakening, namely a decreasing average
friction force with the relative sliding velocity.The mechanisms studied model
the possibility of viscous relaxation, or aging effects in the contact. It is
found that, in addition to producing velocity weakening, these mechanisms can
also produce aftershocks at sufficiently low sliding velocities. This provides
a remarkable analogy at the microscale, of friction properties at the
macroscale, where aftershocks and velocity weakening are two fundamental
features of seismic phenomena.Comment: 8 pages, 7 figure
Assessing the sociology of sport: On sports mega-events and capitalist modernity
On the 50th anniversary of the ISSA and IRSS, one of the leading international scholars on sport and consumer culture, John Horne, considers the trajectory and challenges of research on sports mega-events and their place in capitalist modernity. In anchoring work on this topic in Roche’s definition of mega-events, Horne notes that sports mega-events are important symbolic, economic, and political elements in the orientation of nations to stake their place in global society. Fundamental issues about the concept of ‘mega-event’ pose challenges for scholars as questions remain over what qualifies as a sports mega-event and how ‘lived experience’ with such events transacts with media spectacularization and characterization. The essay closes by posing broader questions for further investigation about the economic, political, and social risks and benefits of sports mega-events and how these events may portend and relate to changing relations of economic and political power on a global scale
Dry Friction due to Adsorbed Molecules
Using an adiabatic approximation method, which searches for Tomlinson
model-like instabilities for a simple but still realistic model for two
crystalline surfaces in the extremely light contact limit, with mobile
molecules present at the interface, sliding relative to each other, we are able
to account for the virtually universal occurrence of "dry friction." The model
makes important predictions for the dependence of friction on the strength of
the interaction of each surface with the mobile molecules.Comment: four pages of latex, figure provide
Development of probabilistic models for quantitative pathway analysis of plant pest introduction for the EU territory
This report demonstrates a probabilistic quantitative pathway analysis model that can be used in risk assessment for plant pest introduction into EU territory on a range of edible commodities (apples, oranges, stone fruits and wheat). Two types of model were developed: a general commodity model that simulates distribution of an imported infested/infected commodity to and within the EU from source countries by month; and a consignment model that simulates the movement and distribution of individual consignments from source countries to destinations in the EU. The general pathway model has two modules. Module 1 is a trade pathway model, with a Eurostat database of five years of monthly trade volumes for each specific commodity into the EU28 from all source countries and territories. Infestation levels based on interception records, commercial quality standards or other information determine volume of infested commodity entering and transhipped within the EU. Module 2 allocates commodity volumes to processing, retail use and waste streams and overlays the distribution onto EU NUTS2 regions based on population densities and processing unit locations. Transfer potential to domestic host crops is a function of distribution of imported infested product and area of domestic production in NUTS2 regions, pest dispersal potential, and phenology of susceptibility in domestic crops. The consignment model covers the several routes on supply chains for processing and retail use. The output of the general pathway model is a distribution of estimated volumes of infested produce by NUTS2 region across the EU28, by month or annually; this is then related to the accessible susceptible domestic crop. Risk is expressed as a potential volume of infested fruit in potential contact with an area of susceptible domestic host crop. The output of the consignment model is a volume of infested produce retained at each stage along the specific consignment trade chain
Co-ordinated rabbit control using 1080
In the coming season it is proposed to poison with 1080 most of the rabbit-infested areas south of the East-West railway and comprising chiefly the South-West and Great Southern areas. The Agriculture Protection Board will be employing 14 Rabbit Control Units each consisting of two men, a Land Rover and caravan. These will be grouped in two main batches of six each, with the other two kept in reserve to do small isolated areas as required
Local spectroscopy and atomic imaging of tunneling current, forces and dissipation on graphite
Theory predicts that the currents in scanning tunneling microscopy (STM) and
the attractive forces measured in atomic force microscopy (AFM) are directly
related. Atomic images obtained in an attractive AFM mode should therefore be
redundant because they should be \emph{similar} to STM. Here, we show that
while the distance dependence of current and force is similar for graphite,
constant-height AFM- and STM images differ substantially depending on distance
and bias voltage. We perform spectroscopy of the tunneling current, the
frequency shift and the damping signal at high-symmetry lattice sites of the
graphite (0001) surface. The dissipation signal is about twice as sensitive to
distance as the frequency shift, explained by the Prandtl-Tomlinson model of
atomic friction.Comment: 4 pages, 4 figures, accepted at Physical Review Letter
Review and synthesis of problems and directions for large scale geographic information system development
Problems and directions for large scale geographic information system development were reviewed and the general problems associated with automated geographic information systems and spatial data handling were addressed
Contact and Friction of Nano-Asperities: Effects of Adsorbed Monolayers
Molecular dynamics simulations are used to study contact between a rigid,
nonadhesive, spherical tip with radius of order 30nm and a flat elastic
substrate covered with a fluid monolayer of adsorbed chain molecules. Previous
studies of bare surfaces showed that the atomic scale deviations from a sphere
that are present on any tip constructed from discrete atoms lead to significant
deviations from continuum theory and dramatic variability in friction forces.
Introducing an adsorbed monolayer leads to larger deviations from continuum
theory, but decreases the variations between tips with different atomic
structure. Although the film is fluid, it remains in the contact and behaves
qualitatively like a thin elastic coating except for certain tips at high
loads. Measures of the contact area based on the moments or outer limits of the
pressure distribution and on counting contacting atoms are compared. The number
of tip atoms making contact in a time interval grows as a power of the interval
when the film is present and logarithmically with the interval for bare
surfaces. Friction is measured by displacing the tip at a constant velocity or
pulling the tip with a spring. Both static and kinetic friction rise linearly
with load at small loads. Transitions in the state of the film lead to
nonlinear behavior at large loads. The friction is less clearly correlated with
contact area than load.Comment: RevTex4, 17 pages, 13 figure
- …