41 research outputs found
Geroch group for Einstein spaces and holographic integrability
We review how Geroch's reduction method is extended from Ricci-flat to
Einstein spacetimes. The Ehlers-Geroch SL(2,R) group is still present in the
three-dimensional sigma-model that captures the dynamics, but only a subgroup
of it is solution-generating. Holography provides an alternative
three-dimensional perspective to integrability properties of Einstein's
equations in asymptotically anti-de Sitter spacetimes. These properties emerge
as conditions on the boundary data (metric and energy-momentum tensor) ensuring
that the hydrodynamic derivative expansion be resummed into an exact
four-dimensional Einstein geometry. The conditions at hand are invariant under
a set of transformations dubbed holographic U-duality group. The latter fills
the gap left by the Ehlers-Geroch group in Einstein spaces, and allows for
solution-generating maps mixing e.g. the mass and the nut charge.Comment: v1: 1+24 pages, Latex, imbrication with arXiv:1403.6511 in sections 2
and 3. arXiv admin note: text overlap with arXiv:1510.0645
Thermal Flow Measurements by a Flexible Sensor, Implemented on the External Surface of the Flow Channel
AbstractA thermal gas flow sensor was developed and evaluated. The presented implementation requires only low-cost manufacturing techniques and readily available components, while maintaining a high level of detection range and sensitivity. Heater and sensing elements were integrated on a flexible substrate and the device was formed by bending the substrate so that the active elements were placed on the external surface of the formed channel, therefore zero flow interference is achieved and a wide variety of fluids can be measured without compromising the sensor integrity. Evaluation was made using air flow rates in the range of 0-65SLPM utilizing electrical measurements and IR imaging techniques simultaneously
Holographic perfect fluidity, Cotton energy-momentum duality and transport properties
We investigate background metrics for 2+1-dimensional holographic theories
where the equilibrium solution behaves as a perfect fluid, and admits thus a
thermodynamic description. We introduce stationary perfect-Cotton geometries,
where the Cotton--York tensor takes the form of the energy--momentum tensor of
a perfect fluid, i.e. they are of Petrov type D_t. Fluids in equilibrium in
such boundary geometries have non-trivial vorticity. The corresponding bulk can
be exactly reconstructed to obtain 3+1-dimensional stationary black-hole
solutions with no naked singularities for appropriate values of the black-hole
mass. It follows that an infinite number of transport coefficients vanish for
holographic fluids. Our results imply an intimate relationship between
black-hole uniqueness and holographic perfect equilibrium. They also point
towards a Cotton/energy--momentum tensor duality constraining the fluid
vorticity, as an intriguing boundary manifestation of the bulk mass/nut
duality.Comment: V3: 1+39 pages, JHEP versio
A Deep Learning Approach for Dynamic Balance Sheet Stress Testing
In the aftermath of the financial crisis, supervisory authorities have
considerably improved their approaches in performing financial stress testing.
However, they have received significant criticism by the market participants
due to the methodological assumptions and simplifications employed, which are
considered as not accurately reflecting real conditions. First and foremost,
current stress testing methodologies attempt to simulate the risks underlying a
financial institution's balance sheet by using several satellite models, making
their integration a really challenging task with significant estimation errors.
Secondly, they still suffer from not employing advanced statistical techniques,
like machine learning, which capture better the nonlinear nature of adverse
shocks. Finally, the static balance sheet assumption, that is often employed,
implies that the management of a bank passively monitors the realization of the
adverse scenario, but does nothing to mitigate its impact. To address the above
mentioned criticism, we introduce in this study a novel approach utilizing deep
learning approach for dynamic balance sheet stress testing. Experimental
results give strong evidence that deep learning applied in big
financial/supervisory datasets create a state of the art paradigm, which is
capable of simulating real world scenarios in a more efficient way.Comment: Preprint submitted to Journal of Forecastin
Arteriovenous Malformation of the Pancreas
Pancreatic arteriovenous malformation (PAVM) is a very rare and mostly congenital lesion, with less than 80 cases described in the English-published literature. It is defined as a tumorous vascular abnormality that is constructed between an anomalous bypass anastomosis of the arterial and venous networks within the pancreas. It represents about 5% of all arteriovenous malformations found in the gastrointestinal tract. Herein, we present a 64-year-old patient with symptomatic PAVM involving the body and tail of the organ, which was successfully treated by transcatheter arterial embolization. The disease spectrum and review of the literature are also presented
Massive Uterine Leiomyoma in a Patient with Friedreich's Ataxia: Is There a Possible Association?
A possible association between Friedreich's ataxia (FA) and neoplastic development has been recognized. FA patients have low frataxin levels and insufficient response to oxidative stress. In these patients fibroblasts are characterized by a high rate of mutations. Herein, a case of a 39-year-old woman with FA tetraplegia, who was admitted in our department with intestinal obstruction due to a huge uterine tumor, is described. An abdominal CT revealed a huge intra-abdominal mass originating from the right cornu of the uterus. Tumor excision and adhesionlysis were performed. The histological examination of the tumor revealed a leiomyoma. FA patients seem to present with a variety of neoplasms uncommon for their young age. This is the first report of a leiomyoma originating from the genital system in a female patient with FA tetraplegia. Therefore it is important to identify neoplasms at an early stage in patients with FA and start immediate therapy