École Polytechnique Fédérale de Lausanne

About: École Polytechnique Fédérale de Lausanne is a facility organization based out in Lausanne, Switzerland. It is known for research contribution in the topics: Population & Catalysis. The organization has 44041 authors who have published 98296 publications receiving 4372092 citations. The organization is also known as: EPFL & ETHL.

Single-layer MoS2 nanopores as nanopower generators

Abstract: Osmotic power generation is a promising renewable energy source. This study demonstrates the use of single-layer molybdenum disulfide (MoS2) nanopores as osmotic nanogenerators. The transport of water through a membrane scales inversely with membrane thickness, so atomically thin materials should provide the ideal medium to host the nanopores in an osmotic power generator. Aleksandra Radenovic and colleagues produced nanopores in two-dimensional MoS2 and, using a salt gradient across a single nanopore, generated a power output per area orders of magnitude greater than that previously reported for nanotubes. They also show that a chemical potential gradient across a single nanopore in MoS2 can generate enough power to operate a single-layer MoS2 transistor.

Aftershocks driven by a high-pressure CO2 source at depth.

Abstract: In northern Italy in 1997, two earthquakes of magnitudes 5.7 and 6 (separated by nine hours) marked the beginning of a sequence that lasted more than 30 days, with thousands of aftershocks including four additional events with magnitudes between 5 and 6. This normal-faulting sequence is not well explained with models of elastic stress transfer, particularly the persistence of hanging-wall seismicity that included two events with magnitudes greater than 5. Here we show that this sequence may have been driven by a fluid pressure pulse generated from the coseismic release of a known deep source of trapped high-pressure carbon dioxide (CO2). We find a strong correlation between the high-pressure front and the aftershock hypocentres over a two-week period, using precise hypocentre locations and a simple model of nonlinear diffusion. The triggering amplitude (10-20 MPa) of the pressure pulse overwhelms the typical (0.1-0.2 MPa) range from stress changes in the usual stress triggering models. We propose that aftershocks of large earthquakes in such geologic environments may be driven by the coseismic release of trapped, high-pressure fluids propagating through damaged zones created by the mainshock. This may provide a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow.

Mobile Ad Hoc Networking

Abstract: Contributors.Preface.1. Mobile Ad-Hoc networking with a View of 4G Wireless: Imperatives and Challenges (J. Liu & I. Chlamtac).2. Off-the-Shelf Enables of Ad Hoc Networks (G. Zaruba & S. Das).3. IEEE 802.11 in Ad Hoc Networks: Protocols, Performance and Open Issues (G. Anastasi, et al.).4. Scatternet Formation in Bluetooth Networks (S. Basagni, et al.).5. Antenna Beamforming and Power Control for Ad Hoc Networks (R. Ramanathan).6. Topology Control in Wireless Ad Hoc Networks (X. Li).7. Broadcasting and Activity Scheduling in Ad Hoc Networks (I. Stojmenovic & J. Wu).8. Location Discovery (A. Savvidesn & M. Srivastava).9. Mobile Ad Hoc Networks (MANETs): Routing Technology for Dynamic, Wireless Networking (J. Macker & M. Corson).10. Routing Approaches in Mobile Ad Hoc Networks (E. Belding-Royer).11. Energy-Efficient Communication in Ad Hoc Wireless Networks (L. Feeney).12. Ad Hoc Networks Security (P. Michiardi & R. Molva).13. Self-Organized and Cooperative Ad Hoc Networking (S. Giordano & A. Urpi).14. Simulation and Modeling of Wireless, Mobile, and Ad Hoc Networks (A. Boukerche & L. Bononi).15. Modeling Cross-Layering Interaction Using Inverse Optimization (V. Syrotiuk & A.Bikki).16. Algorithmic Challenges in Ad Hoc Networks (A. Farago).Index.About the Editors.

Single-nanowire solar cells beyond the Shockley-Queisser limit

Abstract: Light management is of great importance in photovoltaic cells, as it determines the fraction of incident light entering the device. An optimal p–n junction combined with optimal light absorption can lead to a solar cell efficiency above the Shockley–Queisser limit. Here, we show how this is possible by studying photocurrent generation for a single core–shell p–i–n junction GaAs nanowire solar cell grown on a silicon substrate. At 1 sun illumination, a short-circuit current of 180 mA cm –2 is obtained, which is more than one order of magnitude higher than that predicted from the Lambert–Beer law. The enhanced light absorption is shown to be due to a light-concentrating property of the standing nanowire, as shown by photocurrent maps of the device. The results imply new limits for the maximum efficiency obtainable with III–V based nanowire solar cells under 1 sun illumination.

Closing the Gap in the Capacity of Wireless Networks Via Percolation Theory

Abstract: An achievable bit rate per source-destination pair in a wireless network of n randomly located nodes is determined adopting the scaling limit approach of statistical physics It is shown that randomly scattered nodes can achieve, with high probability, the same 1/radicn transmission rate of arbitrarily located nodes This contrasts with previous results suggesting that a 1/radicnlogn reduced rate is the price to pay for the randomness due to the location of the nodes The network operation strategy to achieve the result corresponds to the transition region between order and disorder of an underlying percolation model If nodes are allowed to transmit over large distances, then paths of connected nodes that cross the entire network area can be easily found, but these generate excessive interference If nodes transmit over short distances, then such crossing paths do not exist Percolation theory ensures that crossing paths form in the transition region between these two extreme scenarios Nodes along these paths are used as a backbone, relaying data for other nodes, and can transport the total amount of information generated by all the sources A lower bound on the achievable bit rate is then obtained by performing pairwise coding and decoding at each hop along the paths, and using a time division multiple access scheme