Sebastian Buettrich

The growing demand for wireless data transmission imposes the search for alternatives to the current spectrum exploration schemes. In the long term, dynamic spectrum access seems to be the only viable solution,once the technical details for its implementation are solved. In the near term, the use of currently vacant spectrum allocated to TV broadcast is poised to alleviate the spectrum crunch while opening the path for dynamic spectrum access. We strongly believe that presenting some of the aspects involved in the exploitation of White Spaces (WS) by a group of international experts can be useful to practitioners and regulators interested in the topic. The present work is comprised of independent pieces in which each of the authors express their own viewpoint on the matter (and not necessarily that of the organisation to which they belong). Authors from Africa, Europe, North and South America, delve into both advocacy and regulatory issues, as well as in the technical details of som...

This paper is the result of a six-week research project on the topic of crowd computer interaction, which was conducted at ITU in October/November 2011 while the first author was resident as a visiting professor. The project led to a proposal for mesh mobs, a new type of smart crowd, in which physically collocated people interact via their WiFi-enabled mobile phones. The paper provides a brief background to crowd computer interaction, motivates the concept of mesh mob and presents some design and implementation issues pertaining to ...

ABSTRACT Resonancelike intensity variations of the impact radiation were observed at electric-field anticrossings of 1snl 1L and 3L Stark sublevels (n=5, 6, 7; l>=2), when investigating excitation of helilium atoms by 12.5 keV proton impact. The measured signal amplitudes provide strong evidence that the collision process excites the electron selectively to the (n1 , n2, m) hydrogenic Stark states (0, n-1, 0) and (0, n-2, +/-1), indicating that the electron is promoted along in-saddle sequences of H+2-like molecular orbitals during the final phase of the collision.

Collisional excitation of helium atoms by protons of intermediate energies 0953-4075/31/12/008/img10 is investigated experimentally. By measuring the intensities of various spectral lines as functions of an electric field applied parallel or antiparallel to the proton beam, we found that the excited He atoms are left after the collision in transient states with large electric dipole moments directed upstream. The experimental

ABSTRACT Using electric-field anticrossing techniques, we investigated the coherent excitation ofn=5–8 He I states with different orbital angular momenta by proton impact. These measurements give strong evidence that saddle dynamics of H 2 + -like systems are well suited for describing the final phase of 12.5 keV H+-He collisions. We conclude that, besides electron promotion via the 2p orbital, the collision system undergoes diabatic 1s–3d transitions during the close encounter and present an explanation of the electric dipole moments measured for excitation of H(n=2) states by H+-He and H-He collisions.