10 research outputs found
Effective models of two-flavor QCD: from small towards large
We study effective models of chiral fields and Polyakov loop expected to
describe the dynamics responsible for the phase structure of two-flavor QCD. We
consider chiral sector described either using linear sigma model or
Nambu-Jona-Lasinio model and study how these models, on the mean-field level
when coupled with the Polyakov loop, behave as a function of increasing bare
quark (or pion) mass. We find qualitatively similar behaviors for the cases of
linear sigma model and Nambu-Jona-Lasinio model and, relating to existing
lattice data, show that one cannot conclusively decide which or the two
approximate symmetries drives the phase transitions near the physical point
Deconfinement vs. chiral symmetry and higher representation matter
The interplay of deconfinement and chiral symmetry restoration are considered
in terms of effective theories. We generalize the earlier model studies by
considering fermions in higher representations, and study the finite
temperature phase diagrams of SU(2) and SU(3) gauge theories with two fermion
flavors in fundamental, adjoint or two-index symmetric representations. We
discuss our results in relation to recent lattice simulations on these theories
and outline possible applications in the context of dynamical electroweak
symmetry breaking.Comment: 13 pages, 6 figure
Defining the anterior nucleus of the thalamus (ANT) as a deep brain stimulation target in refractory epilepsy: Delineation using 3Â T MRI and intraoperative microelectrode recording
AbstractBackgroundDeep brain stimulation (DBS) is a minimally invasive and reversible method to treat an increasing number of neurological and psychiatric disorders, including epilepsy. Targeting poorly defined deep structures is based in large degree on stereotactic atlas information, which may be a major source of inconsistent treatment effects.Aim of the studyIn the present study, we aimed to study whether a recently approved target for epilepsy (anterior nucleus of thalamus, ANT) is visualized in clinically established 3Â T MRI and whether ANT is delineated using intraoperative microelectrode recording (MER). We have especially focused on individual variation in the location of ANT in stereotactic space. We also aimed to demonstrate the role of individual variation in interpretation of MER data by projecting samples onto ACâPC (anterior and posterior commissure) and ANT-normalized coordinate systems.MethodsDetailed analysis of ANT delineations in 3Â T MRI short tau inversion recovery (STIR) images from eight patients undergoing DBS for refractory epilepsy was performed. Coronal and sagittal cross-sectional models of ANT were plotted in the ACâPC coordinate system to study individual variation. A total of 186 MER samples collected from 10 DBS trajectories and 5 patients were analyzed, and the location of each sample was calculated and corrected accordingly to the location of the final DBS electrode and projected to the ACâPC or coordinate system normalized to ANT.ResultsMost of the key structures in the anatomic atlas around ANT (mammillothalamic tract and external medullary lamina) were identified in STIR images allowing visual delineation of ANT. We observed a high degree of anatomical variation in the location of ANT, and the cross-sectional areas overlapped by study patients decreased in a linear fashion with an increasing number of patients. MER information from 10 individual trajectories correlated with STIR signal characteristics by demonstrating a spike-negative zone, presumably white matter layer, at the lateral aspect of ANT in ANT-normalized coordinate system as predicted by STIR images. However, MER information projected to the ACâPC coordinate system was not able to delineate ANT.ConclusionsANT is delineated in 3Â T MRI by visualization of a thin white matter lamina between ANT and other nuclear groups that lack spiking activity. Direct targeting in the anterior thalamic area is superior to indirect targeting due to extensive individual variation in the location of ANT. Without detailed imaging information, however, a single trajectory MER has little localizing value