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The total cross section for the reaction pp-*ppn Q was measured at nine center-of-mass energies from 1.5 to 23 MeV above threshold. The experiment was carried out with the Indiana Cooler, a recently constructed storage ring. The experimental advantages of an electron-cooled proton beam were utilized. The data cover an energy range where only the lowest possible angular momentum state contributes in the exit channel. The measured energy dependence of the total cross section is not compatible with that predicted by models of s-wave pion production and rescattering. PACS numbers: 25.10,+s, 13.75.Cs, 21.30.+y, 29.25.Fb Meson-exchange models of the nucleon-nucleon (AW) interaction above the pion threshold rely on detailed information about the strongly coupled inelastic channels which must be treated coherently with the elastic interaction. Information on pion production in the NN system is also required in models of pion production or absorption in nuclei. Customarily, the partial waves in the exit channel of NN-* NNK reactions are labeled by Ll, where L is the angular momentum of the nucleon pair and / is the angular momentum of the pion with respect to the nucleon pair. l Within 100 MeV of threshold, because of the short range of the interaction, only Ss, Sp, Ps, and Pp final states contribute significantly; within 25 MeV the Ss configuration should dominate. In addition, the Sp final state is forbidden in the pp-* ppn° reaction.In the pp-^ppK° reaction, the normally dominant pion production via an intermediate A7V system is suppressed, since the N and the A cannot be in a relative S state. The rescattering contribution is also small because the dominant isovector part of low-energy nN scattering cannot contribute. Thus, near threshold, the pp-*ppn° reaction is dominated by the direct-production Born term. 2 The energy dependence of the cross section is customarily expressed in terms of n, the largest possible center-of-mass pion momentum (with nucleons at rest relative to each other) divided by the pion mass. Based on phase-space arguments, the assumption of r/ o)-This should greatly simplify the theoretical interpretation of the data. The experiment described here is the first to cover this energy range. Previous experiments were hampered by the fact that the cross section (due to the suppressed resonant production) is small and competes with background caused by nuclei other than hydrogen in the path of the beam. Because of the properties of the novel experimental environment described below, it becomes feasible to measure the four-momenta of both outgoing protons, making it possible to comple...

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Background: Early life assaultive violence exposure is a potent risk factor for PTSD and other mood and anxiety disorders. Neurocircuitry models posit that increased risk is mediated by heightened emotion processing in a salience network including dorsal anterior cingulate cortex, anterior insula, and amygdala. However, the processes of reinforcement learning (RL) also engage the salience network and are implicated in responses to early life trauma and PTSD. To define their relative roles in response to early life trauma and PTSD symptoms, the current study compared engagement of the salience network during emotion processing and reinforcement learning as a function of early life assault exposure.Methods: Adolescent girls (n=30 physically or sexually assaulted; n = 30 healthy comparison) aged 11-17 completed two tasks during fMRI: a facial emotion processing task and RL tasks using either social or non-social stimuli. Independent component analysis was used to identify a salience network and characterize its engagement in response to emotion processing and prediction error (PE) encoding during the RL tasks.Results: Assault was related to greater reactivity of the salience network during emotion processing. By contrast, we found that assaulted girls demonstrated lesser encoding of negative PEs in the salience network, particularly during the social RL tasks. The dysfunction of salience network activity during emotion processing and PE encoding was not associated with PTSD symptoms. Conclusions:These results suggest that hyper-vs hypo-activity of the salience network among trauma-exposed youth depends on the cognitive-affective domain.

Background: Prior studies of pediatric posttraumatic stress disorder (PTSD) have reported cross-sectional and age-related structural and functional brain abnormalities in networks associated with cognitive, affective, and self-referential processing. However, no reported studies have comprehensively examined longitudinal gray matter development and its intrinsic functional correlates in pediatric PTSD.Methods: Twenty-seven youth with PTSD and twenty-one non-traumatized typically developing (TD) youth were assessed at baseline and one-year follow-up. At each visit, youth completed structural MRI and resting-state functional MRI. Regions with volumetric abnormalities in the whole-brain structural analyses were identified and used as seeds in exploratory intrinsic connectivity analyses.Results: Youth with PTSD exhibited sustained reductions in grey matter volume (GMV) in right ventromedial prefrontal cortex (vmPFC) and bilateral ventrolateral prefrontal cortex (vlPFC). Group by time analyses revealed aberrant longitudinal development in dorsolateral prefrontal cortex (dlPFC) where TD youth exhibited normative decreases in GMV between baseline and follow-up while youth with PTSD showed increases in GMV. Using these regions as seeds, PTSD patients exhibited atypical longitudinal decreases in intrinsic prefrontal-amygdala andhippocampus connectivity, in contrast to increases in TD youth. Specifically, youth with PTSD showed decreasing vmPFC-amygdala connectivity as well as decreasing vlPFC-hippocampus connectivity over time. Notably, volumetric abnormalities in the vmPFC and vlPFC were predictive of symptom severity.