114 research outputs found
Broken Symmetry as a Stabilizing Remnant
The Goldberger-Wise mechanism enables one to stabilize the length of the
warped extra dimension employed in Randall-Sundrum models. In this work we
generalize this mechanism to models with multiple warped throats sharing a
common ultraviolet brane. For independent throats this generalization is
straight forward. If the throats possess a discrete interchange symmetry like
Z_n the stabilizing dynamics may respect the symmetry, resulting in equal
throat lengths, or they may break it. In the latter case the ground state of an
initially symmetric configuration is a stabilized asymmetric configuration in
which the throat lengths differ. We focus on two- (three-) throat setups with a
Z_2 (Z_3) interchange symmetry and present stabilization dynamics suitable for
either breaking or maintaining the symmetry. Though admitting more general
application, our results are relevant for existing models in the literature,
including the two throat model with Kaluza-Klein parity and the three throat
model of flavor based on a broken Z_3 symmetry.Comment: 23 pages; v2 minor cosmetic chang
Incoherent vector vortex-mode solitons in self-focusing nonlinear media
We suggest a novel type of composite spatial optical soliton created by a
coherent vortex beam guiding a partially incoherent light beam in a
self-focusing nonlinear medium. We show that the incoherence of the guided mode
may enhance, rather than suppress, the vortex azimuthal instability, and also
demonstrate strong destabilization of dipole-mode solitons by partially
incoherent light
Inverse seesaw and dark matter in models with exotic lepton triplets
We show that models with exotic leptons transforming as E ~ (1,3,-1) under
the standard model gauge symmetry are well suited for generating neutrino mass
via a radiative inverse seesaw. This approach realizes natural neutrino masses
and allows multiple new states to appear at the TeV scale. The exotic leptons
are therefore good candidates for new physics that can be probed at the LHC.
Furthermore, remnant low-energy symmetries ensure a stable dark matter
candidate, providing a link between dark matter and the origins of neutrino
mass.Comment: 6 pages, 3 figures (revtex4.1, two-columns
Moderate- to high-intensity exercise does not modify cortical β-amyloid in Alzheimer's disease
Acute hypoxia increases the cerebral metabolic rate:a magnetic resonance imaging study
The aim of the present study was to examine changes in cerebral metabolism by magnetic resonance imaging of healthy subjects during inhalation of 10% O(2) hypoxic air. Hypoxic exposure elevates cerebral perfusion, but its effect on energy metabolism has been less investigated. Magnetic resonance imaging techniques were used to measure global cerebral blood flow and the venous oxygen saturation in the sagittal sinus. Global cerebral metabolic rate of oxygen was quantified from cerebral blood flow and arteriovenous oxygen saturation difference. Concentrations of lactate, glutamate, N-acetylaspartate, creatine and phosphocreatine were measured in the visual cortex by magnetic resonance spectroscopy. Twenty-three young healthy males were scanned for 60 min during normoxia, followed by 40 min of breathing hypoxic air. Inhalation of hypoxic air resulted in an increase in cerebral blood flow of 15.5% (p = 0.058), and an increase in cerebral metabolic rate of oxygen of 8.5% (p = 0.035). Cerebral lactate concentration increased by 180.3% ([Formula: see text]), glutamate increased by 4.7% ([Formula: see text]) and creatine and phosphocreatine decreased by 15.2% (p [Formula: see text]). The N-acetylaspartate concentration was unchanged (p = 0.36). In conclusion, acute hypoxia in healthy subjects increased perfusion and metabolic rate, which could represent an increase in neuronal activity. We conclude that marked changes in brain homeostasis occur in the healthy human brain during exposure to acute hypoxia
A visual rating scale for cingulate island sign on 18F-FDG-PET to differentiate dementia with Lewy bodies and Alzheimer's disease
Comparison of Global Cerebral Blood Flow Measured by Phase-Contrast Mapping MRI with O-15-H2O Positron Emission Tomography
PURPOSE: To compare mean global cerebral blood flow (CBF) measured by phase‐contrast mapping magnetic resonance imaging (PCM MRI) and by (15)O‐H(2)O positron emission tomography (PET) in healthy subjects. PCM MRI is increasingly being used to measure mean global CBF, but has not been validated in vivo against an accepted reference technique. MATERIALS AND METHODS: Same‐day measurements of CBF by (15)O‐H(2)O PET and subsequently by PCM MRI were performed on 22 healthy young male volunteers. Global CBF by PET was determined by applying a one‐tissue compartment model with measurement of the arterial input function. Flow was measured in the internal carotid and vertebral arteries by a noncardiac triggered PCM MRI sequence at 3T. The measured flow was normalized to total brain weight determined from a volume‐segmented 3D T (1)‐weighted anatomical MR‐scan. RESULTS: Mean CBF was 34.9 ± 3.4 mL/100 g/min measured by (15)O‐H(2)O PET and 57.0 ± 6.8 mL/100 g/min measured by PCM MRI. The measurements were highly correlated (P = 0.0008, R(2) = 0.44), although values obtained by PCM MRI were higher compared to (15)O‐H(2)O PET (absolute and relative differences were 22.0 ± 5.2 mL/100 g/min and 63.4 ± 14.8%, respectively). CONCLUSION: This study confirms the use of PCM MRI for quantification of global CBF, but also that PCM MRI systematically yields higher values relative to (15)O‐H(2)O PET, probably related to methodological bias. Level of Evidence: 3 J. Magn. Reson. Imaging 2017;45:692–699
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