On the interaction between two Kerr black holes

The double-Kerr solution is generated using both a Backlund transformation and the Belinskii-Zakharov inverse-scattering technique. We build a dictionary between the parametrisations naturally obtained in the two methods and show their equivalence. We then focus on the asymptotically flat double-Kerr system obeying the axis condition which is Z_2^\phi invariant; for this system there is an exact formula for the force between the two black holes, in terms of their physical quantities and the coordinate distance. We then show that 1) the angular velocity of the two black holes decreases from the usual Kerr value at infinite distance to zero in the touching limit; 2) the extremal limit of the two black holes is given by |J|=cM^2, where c depends on the distance and varies from one to infinity as the distance decreases; 3) for sufficiently large angular momentum the temperature of the black holes attains a maximum at a certain finite coordinate distance. All of these results are interpreted in terms of the dragging effects of the system.Comment: 19 pages, 4 figures. v2: changed statement about thermodynamical equilibrium in section 3; minor changes; added references. v3: added references to previous relevant work; removed one equation (see note added); other minor corrections; final version to be published in JHE

Thermodynamical description of stationary, asymptotically flat solutions with conical singularities

We examine the thermodynamical properties of a number of asymptotically flat, stationary (but not static) solutions having conical singularities, with both connected and non-connected event horizons, using the thermodynamical description recently proposed in arXiv:0912.3386 [gr-qc]. The examples considered are the double-Kerr solution, the black ring rotating in either S^2 or S^1 and the black Saturn, where the balance condition is not imposed for the latter two solutions. We show that not only the Bekenstein-Hawking area law is recovered from the thermodynamical description but also the thermodynamical angular momentum is the ADM angular momentum. We also analyse the thermodynamical stability and show that, for all these solutions, either the isothermal moment of inertia or the specific heat at constant angular momentum is negative, at any point in parameter space. Therefore, all these solutions are thermodynamically unstable in the grand canonical ensemble.Comment: 19 pages, 12 figure

On the backreaction of frame dragging

The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin j^2>1, which is related to the behaviour of the ring angular velocity. Using the `gravitomagnetic clock effect', for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in both phases, when the central black hole mass increases, for fixed ring mass and angular momentum. A close parallelism between the results for the fat phase and those obtained recently for the double Kerr solution is drawn, considering also a regular black Saturn system with J^{BH}\neq 0.Comment: 18 pages, 8 figure

A Double Myers-Perry Black Hole in Five Dimensions

Using the inverse scattering method we construct a six-parameter family of exact, stationary, asymptotically flat solutions of the 4+1 dimensional vacuum Einstein equations, with U(1)^2 rotational symmetry. It describes the superposition of two Myers-Perry black holes, each with a single angular momentum parameter, both in the same plane. The black holes live in a background geometry which is the Euclidean C-metric with an extra flat time direction. This background possesses conical singularities in two adjacent compact regions, each corresponding to a set of fixed points of one of the U(1) actions in the Cartan sub-algebra of SO(4). We discuss several aspects of the black holes geometry, including the conical singularities arising from force imbalance, and the torsion singularity arising from torque imbalance. The double Myers-Perry solution presented herein is considerably simpler than the four dimensional double Kerr solution and might be of interest in studying spin-spin interactions in five dimensional general relativity.Comment: 23 pages, 7 figures, LaTeX. v2: minor changes, references added; version published in JHE

dMyc-dependent upregulation of CD98 amino acid transporters is required for Drosophila brain tumor growth

Funding Information: We would like to thank Tiago Baptista and Hugo Silva for experimental help. We thank Florence Janody and Rita Teodoro for critical reading of the manuscript. We thank Juergen Knoblich for the Miranda antibody. We thank the cytometry and fly facilities at NOVA Medical School for technical support and CONGENTO: consortium for genetically tractable organisms (LISBOA-01-0145-FEDER-022170); Bloomington Drosophila Stock Center (NIH P40OD018537) and Vienna Drosophila Resource Center (VDRC) [52 ], for the stocks used in this study; the Developmental Studies Hybridoma Bank, created by the NICHD of the NIH and maintained at The University of Iowa, Department of Biology, Iowa City, IA 52242. Funding Information: Open access funding provided by FCT|FCCN (b-on). This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (H2020-ERC-2017-STG-GA 759853-StemCellHabitat); by Wellcome Trust and Howard Hughes Medical Institute (HHMI-208581/Z/17/Z-Metabolic Reg SC fate); EMBO Installation grant (H2020-EMBO-3311/2017/G2017) and by Fundação para a Ciência e Tecnologia (IF/01265/2014/CP1252/CT0004, EXPL/BIA-BID/1394/2021 and 2020.05639.BD to A.R.R). This work was supported by iNOVA4Health—UIDB/04462/2020 and UIDP/04462/2020, and by the Associated Laboratory LS4FUTURE (LA/P/0087/2020), two programs financially supported by Fundação para a Ciência e Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior. Publisher Copyright: © 2023, The Author(s).Tumor cells have an increased demand for nutrients to sustain their growth, but how these increased metabolic needs are ensured or how this influences tumor formation and progression remains unclear. To unravel tumor metabolic dependencies, particularly from extracellular metabolites, we have analyzed the role of plasma membrane metabolic transporters in Drosophila brain tumors. Using a well-established neural stem cell-derived tumor model, caused by brat knockdown, we have found that 13 plasma membrane metabolic transporters, including amino acid, carbohydrate and monocarboxylate transporters, are upregulated in tumors and are required for tumor growth. We identified CD98hc and several of the light chains with which it can form heterodimeric amino acid transporters, as crucial players in brat RNAi (bratIR) tumor progression. Knockdown of these components of CD98 heterodimers caused a dramatic reduction in tumor growth. Our data also reveal that the oncogene dMyc is required and sufficient for the upregulation of CD98 transporter subunits in these tumors. Furthermore, tumor-upregulated dmyc and CD98 transporters orchestrate the overactivation of the growth-promoting signaling pathway TOR, forming a core growth regulatory network to support brat IR tumor progression. Our findings highlight the important link between oncogenes, metabolism, and signaling pathways in the regulation of tumor growth and allow for a better understanding of the mechanisms necessary for tumor progression.publishersversionpublishe

Does customer-based reputation add to social and mass media reputation in judging social responsibility of banks?

Purpose: Reputation is a critical asset for finance and banking organizations where the mere suspicion of a problem suffices to trigger media turmoil with high risk of market share losses. Investing in media to build reputation has been therefore a priority for banks. However, another source of reputation may stem from direct front-office contact and it is yet unknown to which extent it plays a role when confronted with the widespread social and mass media reach. This study aims at testing the extent of the importance of customer-based reputation, as against media-based reputation, in explaining customer outcomes.info:eu-repo/semantics/publishedVersio

Pediatric Sinogenic Subdural Empyema: Case Report and Operative Technique

Intracranial complications of sinusitis in the pediatric age are rare but potentially life threatening. They usually occur with nonspecific symptoms such as headache, fever, nausea and vomiting rather than a classic neurological presentation, but they may evolve in few hours, leading to significant morbidity with permanent brain damage and sometimes to death. For this reason, early diagnosis and prompt treatment are essential. Our case demonstrates a sinogenic subdural empyema in an immunocompetent young boy who reached our Emergency Department due to a continuous right-sided headache, unresponsive to pain relievers. The clinical history and the diagnostic process are described: at first, laboratory exams, neurologic and otolaryngological assessment were performed, together with a cranial CT scan showing an inflammatory involvement of the right frontal, ethmoidal and maxillary sinuses. Intravenous antibiotic therapy was initiated. After a few hours the patient showed a sudden worsening of his clinical conditions: he was drowsy with left lower extremity hyposthenia and ipsilateral deep tendon reflexes absence. Considering the patient’s aggravated clinical presentation an emergent MRI with contrast enhancement was conducted, showing left midline shift, a widening of the liquor space on the right frontal and parietal convexity and noticeable meningeal enhancement after contrast injection. After a Neurosurgical and ENT evaluation the patient was taken to the operating room for a combined craniotomy and trans-nasal endoscopic drainage of the empyema. We present the surgical procedure with a pictorial step-by-step description. After the surgical procedure the patient’s condition gradually improved. He regained full neurological function, was accompanied by a rehabilitation team on recovering full force on the left extremities. At discharge the patient had no apparent neurological deficits. Subdural empyema is a rare but severe complication of pediatric sinusitis. Early diagnosis with combined medical and surgical therapies play a key role to reduce morbidity and mortality