Identification of photons in double beta-decay experiments using segmented germanium detectors - studies with a GERDA Phase II prototype detector

The sensitivity of experiments searching for neutrinoless double beta-decay of germanium was so far limited by the background induced by external gamma-radiation. Segmented germanium detectors can be used to identify photons and thus reduce this background component. The GERmanium Detector Array, GERDA, will use highly segmented germanium detectors in its second phase. The identification of photonic events is investigated using a prototype detector. The results are compared with Monte Carlo data.Comment: 20 pages, 7 figures, to be submitted to NIM-

A Generalised Sidelobe Canceller Architecture Based on Oversampled Subband Decompositions

Adaptive broadband beamforming can be performed in oversampled subband signals, whereby an independent beamformer is operated in each frequency band. This has been shown to result in a considerably reduced computational complexity. In this paper, we primarily investigate the convergence behaviour of the generalised sidelobe canceller (GSC) based on normalised least mean squares algorithm (NLMS) when operated in subbands. The minimum mean squared error can be limited, amongst other factors, by the aliasing present in the subbands. With regard to convergence speed, there is strong indication that the subband-GSC converges faster than a fullband counterpart of similar modelling capabilities. Simulations are presented

Comparison of gluon flux-tube distributions for quark-diquark and quark-antiquark hadrons

The distribution of gluon fields in hadrons is of fundamental interest in QCD. Using lattice QCD we have observed the formation of gluon flux tubes within 3 quark (baryon) and quark plus antiquark (meson) systems for a wide variety of spatial distributions of the color sources. In particular we have investigated three quark configurations where two of the quarks are close together and the third quark is some distance away, which approximates a quark plus diquark string. We find that the string tension of the quark-diquark string is the same as that of the quark-antiquark string on the same lattice. We also compare the longitudinal and transverse profiles of the gluon flux tubes for both sets of strings, and find them to be of similar radii and to have similar vacuum suppression.Comment: 6 pages, 9 figures and 1 tabl

First principles theoretical studies of half-metallic ferromagnetism in CrTe

Using full-potential linear augmented plane wave method (FP-LAPW) and the density functional theory, we have carried out a systematic investigation of the electronic, magnetic, and cohesive properties of the chalcogenide CrTe in three competing structures: rock-salt (RS), zinc blende (ZB) and the NiAs-type (NA) hexagonal. Although the ground state is of NA structure, RS and ZB are interesting in that these fcc-based structures, which can possibly be grown on many semiconductor substrates, exhibit half-metallic phases above some critical values of the lattice parameter. We find that the NA structure is not half-metallic at its equilibrium volume, while both ZB and RS structures are. The RS structure is more stable than the ZB, with an energy that is lower by 0.25 eV/atom. While confirming previous results on the half-metallic phase in ZB structure, we provide hitherto unreported results on the half-metallic RS phase, with a gap in the minority channel and a magnetic moment of 4.0 $\mu_{B}$ per formula unit. A comparison of total energies for the ferromagnetic (FM), non-magnetic (NM), and antiferromagnetic (AFM) configurations shows the lowest energy configuration to be FM for CrTe in all the three structures. The FP-LAPW calculations are supplemented by linear muffin-tin orbital (LMTO) calculations using both local density approximation (LDA) and LDA+U method. The exchange interactions and the Curie temperatures calculated via the linear response method in ZB and RS CrTe are compared over a wide range of the lattice parameter. The calculated Curie temperatures for the RS phase are consistently higher than those for the ZB phase.Comment: 11 pages, 14 figure

Anharmonic effect on lattice distortion, orbital ordering and magnetic properties in Cs2AgF4

We develop the cluster self-consistent field method incorporating both electronic and lattice degrees of freedom to study the origin of ferromagnetism in Cs$_{2}$AgF$_{4}$. After self-consistently determining the harmonic and anharmonic Jahn-Teller distortions, we show that the anharmonic distortion stabilizes the staggered x$^{2}$-z$^{2}$/y$^{2}$-z$^{2}$ orbital and ferromagnetic ground state, rather than the antiferromagnetic one. The amplitudes of lattice distortions, Q$_{2}$ and Q$_{3}$, the magnetic coupling strengthes, J$_{x,y}$, and the magnetic moment, are in good agreement with the experimental observation.Comment: 13 pages, 5 figure

Subtropical middle atmosphere dynamics observed by the Chung Li radar

The Chung Li Radar (24.91 N; 121.24 E) has been operating since 1986. A five beam observational configuration was used on a regular basis to study the various dynamics processes in the atmosphere-lower stratosphere height region. Due to its geographical location, the annual Typhoon and Mei-Yu seasons provide good opportunities to study the various interesting dynamic processes such as instabilities, generation of gravity waves, wave mean field interaction, etc. Three dimensional air motions due to these fronts are presented. Special cases of gravity wave generation, propagation and their effects on the turbulent layers are discussed

Ultrafast Enhancement of Ferromagnetism via Photoexcited Holes in GaMnAs

We report on the observation of ultrafast photo-enhanced ferromagnetism in GaMnAs. It is manifested as a transient magnetization increase on a 100-ps time scale, after an initial sub-ps demagnetization. The dynamic magnetization enhancement exhibits a maximum below the Curie temperature Tc and dominates the demagnetization component when approaching Tc. We attribute the observed ultrafast collective ordering to the p-d exchange interaction between photoexcited holes and Mn spins, leading to a correlation-induced peak around 20K and a transient increase in Tc.Comment: 4 page

Stability of BTZ black strings

We study the dynamical stability of the BTZ black string against fermonic and gravitational perturbations. The BTZ black string is not always stable against these perturbations. There exist threshold values for $m^2$ related to the compactification of the extra dimension for fermonic perturbation, scalar part of the gravitational perturbation and the tensor perturbation, respectively. Above the threshold values, perturbations are stable; while below these thresholds, perturbations can be unstable. We find that this non-trivial stability behavior qualitatively agrees with that predicted by a thermodynamical argument, showing that the BTZ black string phase is not the privileged stable phase.Comment: 9 pages, revised version to appear in Phys. Rev.