Representation matrices for U(4)

We propose an algorithm for the numerical calculation of matrix elements of general U(4) group elements, applicable to large totally symmetric representations of U(4). A possible generalization to the U(6) case is pointed out

K X-ray multiplicities for rare earth atoms produced in (H.I., xn) nuclear reactions

K X-ray multiplicities are determined for a number of nuclear reaction products in the rare earth region. It is shown that if certain conditions are fulfilled the values of these multiplicities can be considered as characteristic for the reaction residues independently of the reaction used. They can thus be used for the quantitative determination of cross sections

Angular momentum dependence of incomplete fusion reactions

γ-ray multiplicities associated with various reaction channels have been measured for the 14N + 197Au system at Elab = 115 and 168 MeV. Channel selection accomplished via charged ejectile-KX-ray coincidence measurements permitted distinction between reactions with two or more charged fragments in the final state. For the former type of reactions the angular momentum dependence expected for (binary) incomplete fusion reactions is obserbed. For the latter, the same angular momentum dependence is found if sequential decay of the primary light fragment is assumed

Cross section balance in the 14N + 159Tb reaction and the origin of fast alpha particles

Exclusive cross sections have been obtained from particle-K X-ray coincidence data measured at 236 MeV for ejectiles ranging from 4 He to 15 N. Production cross sections for primary fragments and alpha particle multiplicities associated with different channels have been deduced. The major fraction of the alpha particles appears to originate from inelastic (damped) processes in which only light particles with Z < 2 are emitted

Methylphenidate Attenuates Limbic Brain Inhibition after Cocaine-Cues Exposure in Cocaine Abusers

Dopamine (phasic release) is implicated in conditioned responses. Imaging studies in cocaine abusers show decreases in striatal dopamine levels, which we hypothesize may enhance conditioned responses since tonic dopamine levels modulate phasic dopamine release. To test this we assessed the effects of increasing tonic dopamine levels (using oral methylphenidate) on brain activation induced by cocaine-cues in cocaine abusers. Brain metabolism (marker of brain function) was measured with PET and 18FDG in 24 active cocaine abusers tested four times; twice watching a Neutral video (nature scenes) and twice watching a Cocaine-cues video; each video was preceded once by placebo and once by methylphenidate (20 mg). The Cocaine-cues video increased craving to the same extent with placebo (68%) and with methylphenidate (64%). In contrast, SPM analysis of metabolic images revealed that differences between Neutral versus Cocaine-cues conditions were greater with placebo than methylphenidate; whereas with placebo the Cocaine-cues decreased metabolism (p<0.005) in left limbic regions (insula, orbitofrontal, accumbens) and right parahippocampus, with methylphenidate it only decreased in auditory and visual regions, which also occurred with placebo. Decreases in metabolism in these regions were not associated with craving; in contrast the voxel-wise SPM analysis identified significant correlations with craving in anterior orbitofrontal cortex (p<0.005), amygdala, striatum and middle insula (p<0.05). This suggests that methylphenidate's attenuation of brain reactivity to Cocaine-cues is distinct from that involved in craving. Cocaine-cues decreased metabolism in limbic regions (reflects activity over 30 minutes), which contrasts with activations reported by fMRI studies (reflects activity over 2–5 minutes) that may reflect long-lasting limbic inhibition following activation. Studies to evaluate the clinical significance of methylphenidate's blunting of cue-induced limbic inhibition may help identify potential benefits of this medication in cocaine addiction

Probabilities for sequential decay of projectile-like fragments in reactions with light heavy ions

Probabilities for sequential decay of various projectile-like fragments from 14N induced reactions on 159Tb have been determined via projectile-like fragment-K X-ray coincidence measurements at energies of 115 and 168 MeV. A close correspondence with results from particle-particle correlation studies was obtained