Positron annihilation spectra reveal isolated zinc vacancy (V(Zn)) creation in single-crystal ZnO exposed to 193-nm radiation at 100 mJ/cm(2) fluence. The appearance of a photoluminescence excitation peak at 3.18 eV in irradiated ZnO is attributed to an electronic transition from the V(Zn) acceptor level at ~100 meV to the conduction band. The observed V(Zn) density profile and hyperthermal Zn(...

At the SLC, a train consisting of one positron bunch fo l lowed by two electron bunches is accelerated in the linac, each separated by about 60 ns. Long-range transverse wakef ields from the leading bunch were found to cause up to a factor o f three increase in beam jitter for the trailing bunches. Incoming jitter is efficiently damped by BNS damping, but excitations in the middle of the linac ...

Stimulus-evoked neural activity increases both local oxygen metabolism and blood flow in active regions of the brain. However, multiple imaging modalities including functional magnetic resonance imaging and positron emission tomography have demonstrated that the degree of coupling between metabolism and blood flow is highly non-linear. Specifically oxygen metabolism appears to peak and decline ...

Long (σz ∼ 500 μm) SLAC electron and positron bunches sent into dense plasmas (ne = 0.6 − 2.3 × 10 cm−3) are subject to a transverse two-stream instability called the self-modulation instability or SMI. We use numerical simulations to show that when the SMI saturates, the wakefield excitation reaches the nonlinear regime of the plasma wakefield accelerator (PWFA). We show that defocused particl...

We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm ...

New results are presented for Ps(1s) scattering by H(1s), He(1S) and Li(2s). Calculations have been performed in a coupled state framework, usually employing pseudostates, and allowing for excitation of both the Ps and the atom. In the Ps(1s)H(1s) calculations the H− formation channel has also been included using a highly accurate H− wave function. Resonances resulting from unstable states in w...

The polarized cross-section ratio σLT′/σ0 from hard exclusive π−Δ++ electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV/10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. study, which provides first observation of this channel in deep-inelastic regime, focuses very forward-pion kinematics v...