219 research outputs found
Identification of Electron Donor States in N-doped Carbon Nanotubes
Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and
characterized by Scanning Tunneling Spectroscopy and transmission electron
microscopy. The doped nanotubes are all metallic and exhibit strong electron
donor states near the Fermi level. Using tight-binding and ab initio
calculations, we observe that pyridine-like N structures are responsible for
the metallic behavior and the prominent features near the Fermi level. These
electron rich structures are the first example of n-type nanotubes, which could
pave the way to real molecular hetero-junction devices.Comment: 5 pages, 4 figures, revtex, submitted to PR
Grain Size Control of Tetragonal Zirconia Polycrystals Using the Space Charge Concept
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65680/1/j.1151-2916.1990.tb06449.x.pd
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Results of a self-triggered prototype system for radio-detection of extensive air showers at the Pierre Auger Observatory
We describe the experimental setup and the results of RAuger, a small radio-antenna array, consisting of three fully autonomous and self-triggered radio-detection stations, installed close to the center of the Surface Detector (SD) of the Pierre Auger Observatory in Argentina. The setup has been designed for the detection of the electric field strength of air showers initiated by ultra-high energy cosmic rays, without using an auxiliary trigger from another detection system. Installed in December 2006, RAuger was terminated in May 2010 after 65 registered coincidences with the SD. The sky map in local angular coordinates (i.e., zenith and azimuth angles) of these events reveals a strong azimuthal asymmetry which is in agreement with a mechanism dominated by a geomagnetic emission process. The correlation between the electric field and the energy of the primary cosmic ray is presented for the first time, in an energy range covering two orders of magnitude between 0.1 EeV and 10 EeV. It is demonstrated that this setup is relatively more sensitive to inclined showers, with respect to the SD. In addition to these results, which underline the potential of the radio-detection technique, important information about the general behavior of self-triggering radio-detection systems has been obtained. In particular, we will discuss radio self-triggering under varying local electric-field conditions
- âŠ