7 research outputs found
Tuning a Circular p-n Junction in Graphene from Quantum Confinement to Optical Guiding
The motion of massless Dirac-electrons in graphene mimics the propagation of
photons. This makes it possible to control the charge-carriers with components
based on geometrical-optics and has led to proposals for an all-graphene
electron-optics platform. An open question arising from the possibility of
reducing the component-size to the nanometer-scale is how to access and
understand the transition from optical-transport to quantum-confinement. Here
we report on the realization of a circular p-n junction that can be
continuously tuned from the nanometer-scale, where quantum effects are
dominant, to the micrometer scale where optical-guiding takes over. We find
that in the nanometer-scale junction electrons are trapped in states that
resemble atomic-collapse at a supercritical charge. As the junction-size
increases, the transition to optical-guiding is signaled by the emergence of
whispering-gallery modes and Fabry-Perot interference. The creation of tunable
junctions that straddle the crossover between quantum-confinement and
optical-guiding, paves the way to novel design-architectures for controlling
electronic transport.Comment: 16 pages, 4 figure
Assessment of groundwater recharge influenced by floodwater spreading : an integrated approach with limited accessible data
To assess the response of groundwater to artificial recharge through floodwater spreading (FWS) a combination approach of water table fluctuations and water budget was used. In this process, water level data in six observation wells installed inside and around the site of the FWS systems together with the amount of rainfall and volume of floodwater diverted to the system were examined during the period 1993-2012. Specific yield was also determined based on measured soil hydraulic properties for three experimental wells hand drilled within the FWS systems. The observation wells located inside the FWS systems were less susceptible to drought and abstractions than the other wells in the area. The hydrograph of the wells inside the FWS showed a large disparity in rises (0.5-2.05m) after the two major floods in 2004 and 2005 due to systems closure in 2004. The water budget calculated based on water table fluctuations for 2010/11 showed that the contribution of FWS systems to total recharge in the study area was about 57-61%