69 research outputs found
AdS Black Holes from Duality in Gauged Supergravity
We study and utilize duality transformations in a particular STU-model of
four dimensional gauged supergravity. This model is a truncation of the de
Wit-Nicolai N=8 theory and as such has a lift to eleven-dimensional
supergravity on the seven-sphere. Our duality group is and while it
can be applied to any solution of this theory, we consider the known
asymptotically AdS, supersymmetric black holes and focus on duality
transformations which preserve supersymmetry. For static black holes we
generalize the supersymmetric solutions of Cacciatori and Klemm from three
magnetic charges to include two additional electric charges and argue that this
is co-dimension one in the full space of supersymmetric static black holes in
the STU-model. These new static black holes have nontrivial profiles for
axions. For rotating black holes, we generalize the known two-parameter
supersymmetric solution to include an additional parameter which represents
scalar hair. When lifted to M-theory, these black holes correspond to the near
horizon geometry of a stack of BPS rotating M2-branes, spinning on an
which is fibered non-trivially over a Riemann surface.Comment: 21 page
Dressing the Electron Star in a Holographic Superconductor
We construct new asymptotically AdS_4 solutions dual to 2+1 CFTs at finite
density and zero temperature by combining the ingredients of the electron star
and the holographic superconductor. The solutions, which we call "compact
electron stars", contain both a fermionic fluid and charged scalar hair in the
bulk. We show that the new solutions are thermodynamically favoured in the
region of parameter space where they exist. Along the boundary of this region,
we find evidence for a continuous phase transition between the holographic
superconductor and the compact star solution.Comment: 31 pages, 10 figures; added reference
Polarized solutions and Fermi surfaces in holographic Bose-Fermi systems
We use holography to study the ground state of a system with interacting
bosonic and fermionic degrees of freedom at finite density. The gravitational
model consists of Einstein-Maxwell gravity coupled to a perfect fluid of
charged fermions and to a charged scalar field which interact through a
current-current interaction. When the scalar field is non-trivial, in addition
to compact electron stars, the screening of the fermion electric charge by the
scalar condensate allows the formation of solutions where the fermion fluid is
made of antiparticles, as well as solutions with coexisting, separated regions
of particle-like and antiparticle-like fermion fluids. We show that, when the
latter solutions exist, they are thermodynamically favored. By computing the
two-point Green function of the boundary fermionic operator we show that, in
addition to the charged scalar condensate, the dual field theory state exhibits
electron-like and/or hole-like Fermi surfaces. Compared to fluid-only
solutions, the presence of the scalar condensate destroys the Fermi surfaces
with lowest Fermi momenta. We interpret this as a signal of the onset of
superconductivity.Comment: 46 pages, 17 figure
Mediastinal lymph nodes segmentation using 3D convolutional neural network ensembles and anatomical priors guiding
As lung cancer evolves, the presence of potentially malignant lymph nodes must be assessed to properly estimate disease progression and select the best treatment strategy. A method for accurate and automatic segmentation is hence decisive for quantitatively describing lymph nodes. In this study, the use of 3D convolutional neural networks, either through slab-wise schemes or the leveraging of downsampled entire volumes, is investigated. As lymph nodes have similar attenuation values to nearby anatomical structures, we use the knowledge of other organs as prior information to guide the segmentation. To assess the performances, a 5-fold cross-validation strategy was followed over a dataset of 120 contrast-enhanced CT volumes. For the 1178 lymph nodes with a short-axis diameter ≥10 mm, our best-performing approach reached a patient-wise recall of 92%, a false positive per patient ratio of 5 and a segmentation overlap of 80.5%. Fusing a slab-wise and a full volume approach within an ensemble scheme generated the best performances. The anatomical priors guiding strategy is promising, yet a larger set than four organs appears needed to generate an optimal benefit. A larger dataset is also mandatory given the wide range of expressions a lymph node can exhibit (i.e. shape, location and attenuation).publishedVersio
MR imaging of therapy-induced changes of bone marrow
MR imaging of bone marrow infiltration by hematologic malignancies provides non-invasive assays of bone marrow cellularity and vascularity to supplement the information provided by bone marrow biopsies. This article will review the MR imaging findings of bone marrow infiltration by hematologic malignancies with special focus on treatment effects. MR imaging findings of the bone marrow after radiation therapy and chemotherapy will be described. In addition, changes in bone marrow microcirculation and metabolism after anti-angiogenesis treatment will be reviewed. Finally, new specific imaging techniques for the depiction of regulatory events that control blood vessel growth and cell proliferation will be discussed. Future developments are directed to yield comprehensive information about bone marrow structure, function and microenvironment
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