7 research outputs found
Multipacting
Multipacting (MP) is a resonant electron discharge, often plaguing
radiofrequency structures, produced by the synchronization of emitted electrons
with the RF fields and by the electron multiplication at the impact point with
the surface of the structure. The current of re-emitted electrons grows via
true secondary re-emission when the secondary yield for the primary electron
impact energy is greater than one. A simple example (MP in short-gap
accelerating axial-symmetric cavities) allows an analytical solution of the
equation of motion, giving both the synchronization (kinematics) and
multiplication (impact energy) conditions as a function of the gap voltage (or
accelerating field). Starting from this example a thorough discussion of MP
discharges in axial-symmetric accelerating structures will be given and some
poor man's rules are given to estimate the critical cavity field levels to meet
the kinematic condition for resonance. The results of these poor man's rules
are compared with computer simulations of MP discharges obtained by a
statistical analysis of the re-emission yield for impinging electrons versus RF
field level in the accelerating structure.Comment: presented at the CERN Accelerator School CAS 2010: RF for
accelerators, Ebeltoft, 8-17 June 201
Patterns of subregional cerebellar atrophy across epilepsy syndromes: An ENIGMAâEpilepsy study
Objective: The intricate neuroanatomical structure of the cerebellum is of longstanding interest in epilepsy, but has been poorly characterized within the current corticocentric models of this disease. We quantified crossâsectional regional cerebellar lobule volumes using structural magnetic resonance imaging in 1602 adults with epilepsy and 1022 healthy controls across 22 sites from the global ENIGMAâEpilepsy working group. Methods: A stateâofâtheâart deep learningâbased approach was employed that parcellates the cerebellum into 28 neuroanatomical subregions. Linear mixed models compared total and regional cerebellar volume in (1) all epilepsies, (2) temporal lobe epilepsy with hippocampal sclerosis (TLEâHS), (3) nonlesional temporal lobe epilepsy, (4) genetic generalized epilepsy, and (5) extratemporal focal epilepsy (ETLE). Relationships were examined for cerebellar volume versus age at seizure onset, duration of epilepsy, phenytoin treatment, and cerebral cortical thickness. Results: Across all epilepsies, reduced total cerebellar volume was observed (d = .42). Maximum volume loss was observed in the corpus medullare (dmax = .49) and posterior lobe gray matter regions, including bilateral lobules VIIB (dmax = .47), crus I/II (dmax = .39), VIIIA (dmax = .45), and VIIIB (dmax = .40). Earlier age at seizure onset ( η Ï max 2 = .05) and longer epilepsy duration ( η Ï max 2 = .06) correlated with reduced volume in these regions. Findings were most pronounced in TLEâHS and ETLE, with distinct neuroanatomical profiles observed in the posterior lobe. Phenytoin treatment was associated with reduced posterior lobe volume. Cerebellum volume correlated with cerebral cortical thinning more strongly in the epilepsy cohort than in controls. Significance: We provide robust evidence of deep cerebellar and posterior lobe subregional gray matter volume loss in patients with chronic epilepsy. Volume loss was maximal for posterior subregions implicated in nonmotor functions, relative to motor regions of both the anterior and posterior lobe. Associations between cerebral and cerebellar changes, and variability of neuroanatomical profiles across epilepsy syndromes argue for more precise incorporation of cerebellar subregional damage into neurobiological models of epilepsy
Thermal activation of NH4 precursor of acidic omega zeolite: A neutron and in-situ synchrotron powder diffraction combined study
For the first time, the real-time thermal activation of the NH4-omega zeolite (NH4-omega) was investigated through in situ synchrotron X-ray powder diffraction combined with neutron diffraction. The experimental approach allowed to study the precursor thermal behaviour upon heating, continuously monitoring the evolution of its structural features determined by NH4 ions and TMA calcination and dehydration processes. The activation of the precursor (H-omega sample) is fully reached at â600 °C, when all the NH4 content has been released, dehydration mostly occurred and TMA degradation completed. From a structural point of view, Rietveld structural refinements highlighted relevant structural changes. In particular variations in intertetrahedral angles allowed to make hypothesis about the possible distribution of BrĂžnsted acid sites on the framework oxygen atoms. The hypothesis was corroborated through the neutron Rietveld refinement of the deuterated and calcined omega (D-omega sample) that revealed the presence of two acid sites: D1 and D2 located on O5 and O2 framework oxygen atoms, respectively. Besides, neutron data confirmed the strong relation among framework and BrĂžnsted acid sites geometry and short- and/or long-range interactions. In summary, non-conventional sources were successfully used to probe both activation and formation of acidic sites in omega precursor as well as determine the number and location of BrĂžnsted sites in the deuterated omega
Patterns of subregional cerebellar atrophy across epilepsy syndromes: An ENIGMA-Epilepsy study.
OBJECTIVE: The intricate neuroanatomical structure of the cerebellum is of longstanding interest in epilepsy, but has been poorly characterized within the current cortico-centric models of this disease. We quantified cross-sectional regional cerebellar lobule volumes using structural MRI in 1,602 adults with epilepsy and 1,022 healthy controls across twenty-two sites from the global ENIGMA-Epilepsy working group. METHODS: A state-of-the-art deep learning-based approach was employed that parcellates the cerebellum into 28 neuroanatomical subregions. Linear mixed models compared total and regional cerebellar volume in i) all epilepsies; ii) temporal lobe epilepsy with hippocampal sclerosis (TLE-HS); iii) non-lesional temporal lobe epilepsy (TLE-NL); iv) genetic generalised epilepsy; and (v) extra-temporal focal epilepsy (ETLE). Relationships were examined for cerebellar volume versus age at seizure onset, duration of epilepsy, phenytoin treatment, and cerebral cortical thickness. RESULTS: Across all epilepsies, reduced total cerebellar volume was observed (d=0.42). Maximum volume loss was observed in the corpus medullare (dmax=0.49) and posterior lobe grey matter regions, including bilateral lobules VIIB (dmax= 0.47), Crus I/II (dmax= 0.39), VIIIA (dmax=0.45) and VIIIB (dmax=0.40). Earlier age at seizure onset (ηÏ2max=0.05) and longer epilepsy duration (ηÏ2max=0.06) correlated with reduced volume in these regions. Findings were most pronounced in TLE-HS and ETLE with distinct neuroanatomical profiles observed in the posterior lobe. Phenytoin treatment was associated with reduced posterior lobe volume. Cerebellum volume correlated with cerebral cortical thinning more strongly in the epilepsy cohort than in controls. SIGNIFICANCE: We provide robust evidence of deep cerebellar and posterior lobe subregional grey matter volume loss in patients with chronic epilepsy. Volume loss was maximal for posterior subregions implicated in non-motor functions, relative to motor regions of both the anterior and posterior lobe. Associations between cerebral and cerebellar changes, and variability of neuroanatomical profiles across epilepsy syndromes argue for more precise incorporation of cerebellum subregions into neurobiological models of epilepsy
Technical Design Report for PANDA Electromagnetic Calorimeter (EMC)
This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment, which is being developed for the Facility for Antiproton and Ion Research (FAIR) at Darmstadt, Germany. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface