Efficient Notification of Meeting Points for Moving Groups via Independent Safe Regions

published_or_final_versio

Experimental investigations of synchrotron radiation at the onset of the quantum regime

The classical description of synchrotron radiation fails at large Lorentz factors, $\gamma$, for relativistic electrons crossing strong transverse magnetic fields $B$. In the rest frame of the electron this field is comparable to the so-called critical field $B_0 = 4.414\cdot10^9$ T. For $\chi = \gamma B/B_0 \simeq 1$ quantum corrections are essential for the description of synchrotron radiation to conserve energy. With electrons of energies 10-150 GeV penetrating a germanium single crystal along the $$ axis, we have experimentally investigated the transition from the regime where classical synchrotron radiation is an adequate description, to the regime where the emission drastically changes character; not only in magnitude, but also in spectral shape. The spectrum can only be described by quantum synchrotron radiation formulas. Apart from being a test of strong-field quantum electrodynamics, the experimental results are also relevant for the design of future linear colliders where beamstrahlung - a closely related process - may limit the achievable luminosity.Comment: 11 pages, 18 figures, submitted to PR

The Baum-Connes Conjecture via Localisation of Categories

We redefine the Baum-Connes assembly map using simplicial approximation in the equivariant Kasparov category. This new interpretation is ideal for studying functorial properties and gives analogues of the assembly maps for all equivariant homology theories, not just for the K-theory of the crossed product. We extend many of the known techniques for proving the Baum-Connes conjecture to this more general setting

HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw

We present HST/STIS observations of ESO 184-G82, the host galaxy of the gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous galaxy. We detect an object consistent with being a point source within the astrometric uncertainty of 0.018 arcseconds of the position of the supernova. The object is located inside a star-forming region and is at least one magnitude brighter than expected for the supernova based on a simple radioactive decay model. This implies either a significant flattening of the light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ Letter

Phonon `notches' in a-b -plane optical conductivity of high-Tc superconductors

It is shown that a correlation between the positions of the $c$-axis longitudinal optic ($LO_c$) phonons and ``notch''-like structures in the $a$-$b$ plane conductivity of high-$T_c$ superconductors results from phonon-mediated interaction between electrons in different layers. It is found that the relative size of the notches depends on $\lambda_{ph}(\Omega_{ph}/\gamma_{ph})$, where $\lambda_{ph}$, $\Omega_{ph}$ and $\gamma_{ph}$ are the effective coupling strength, the frequency and the width of the optical phonon which is responsible for the notch. Even for $\lambda_{ph}\approx 0.01$ the effect can be large if the phonon is very sharp.Comment: 5 pages, REVTeX, 4 uuencoded figure