A high-field 3He metastability exchange optical pumping polarizer operating in a 1.5T medical scanner for lung magnetic resonance imaging Erratum: "Theoretical signal-to-noise ratio and spatial resolution dependence on the magnetic field strength for hyperpolarized noble gas magnetic resonance imaging of human lungs" [Med. Phys.32, 221-229 (2005)] Med. Phys. 33, 1525 (2006); 10.1118/1.2189711Theoretical signal-to-noise ratio and spatial resolution dependence on the magnetic field strength for hyperpolarized noble gas magnetic resonance imaging of human lungs Med.Hyperpolarized noble gas ͑HNG͒ magnetic resonance ͑MR͒ imaging is a very promising noninvasive tool for the investigation of animal models of lung disease, particularly to follow longitudinal changes in lung function and anatomy without the accumulated radiation dose associated with x rays. The two most common noble gases for this purpose are 3 He ͑helium 3͒ and 129 Xe ͑xenon 129͒, the latter providing a cost-effective approach for clinical applications. Hyperpolarization is typically achieved using spin-exchange optical pumping techniques resulting in ϳ10 000-fold improvement in available magnetization compared to conventional Boltzmann polarizations. This substantial increase in polarization allows high spatial resolution ͑Ͻ1 mm͒ single-slice images of the lung to be obtained with excellent temporal resolution ͑Ͻ1 s͒. Complete three-dimensional images of the lungs with 1 mm slice thickness can be obtained within reasonable breath-hold intervals ͑Ͻ20 s͒. This article provides an overview of the current methods used in HNG MR imaging with an emphasis on ventilation studies in animals. Special MR hardware and software considerations are described in order to use the strong but nonrecoverable magnetization as efficiently as possible and avoid depolarization primarily by molecular oxygen. Several applications of HNG MR imaging are presented, including measurement of gross lung anatomy ͑e.g., airway diameters͒, microscopic anatomy ͑e.g., apparent diffusion coefficient͒, and a variety of functional parameters including dynamic ventilation, alveolar oxygen partial pressure, and xenon diffusing capacity.

We construct a two-dimensional action that is an extension of spherically symmetric Einstein-Lanczos-Lovelock gravity. The action contains arbitrary functions of the areal radius and the norm squared of its gradient, but the field equations are second order and obey Birkhoff's theorem. In complete analogy with spherically symmetric Einstein-Lanczos-Lovelock gravity, the field equations admit the generalized Misner-Sharp mass as the first integral that determines the form of the vacuum solution. The arbitrary functions in the action allow for vacuum solutions that describe a larger class of interesting nonsingular black-hole spacetimes than previously available.

Time-dependent analytic solutions of the Einstein-Skyrme system -gravitating Skyrmions-, with topological charge one are analyzed in detail. In particular, the question of whether these Skyrmions reach a spherically symmetric configuration for t → +∞ is discussed. It is shown that there is a static, spherically symmetric solution described by the Ermakov-Pinney system, which is fully integrable by algebraic methods. For Λ > 0 this spherically symmetric solution is found to be in a "neutral equilibrium" under small deformations, in the sense that under a small squashing it would neither blow up nor dissapear after a long time, but it would remain finite forever (plastic deformation). Thus, in a sense, the coupling with Einstein gravity spontaneously breaks the spherical symmetry of the solution. However, in spite of the lack of isotropy, for t → ∞ (and Λ > 0) the space time is locally flat and the anisotropy of the Skyrmion only reflects the squashing of spacetime.

Einstein-Gauss-Bonnet gravity (EGB) provides a natural higher dimensional and higher order curvature generalization of Einstein gravity. It contains a new, presumably microscopic, length scale that should affect short distance properties of the dynamics, such as Choptuik scaling. We present the results of a numerical analysis in generalized flat slice co-ordinates of self-gravitating massless scalar spherical collapse in five and six dimensional EGB gravity near the threshold of black hole formation. Remarkably, the behaviour is universal (i.e. independent of initial data) but qualitatively different in five and six dimensions. In five dimensions there is a minimum horizon radius, suggestive of a first order transition between black hole and dispersive initial data. In six dimensions no radius gap is evident. Instead, below the GB scale there is a change in the critical exponent and echoing period.arXiv:1208.5250v3 [gr-qc]