Hydrodynamical moving-mesh simulations of the tidal disruption of stars by supermassive black holes

When a star approaches a black hole closely, it may be pulled apart by gravitational forces in a tidal disruption event (TDE). The flares produced by TDEs are unique tracers of otherwise quiescent supermassive black holes (SMBHs) located at the centre of most galaxies. In particular, the appearance of such flares and the subsequent decay of the light curve are both sensitive to whether the star is partially or totally destroyed by the tidal field. However, the physics of the disruption and the fall-back of the debris are still poorly understood. We are here modelling the hydrodynamical evolution of realistic stars as they approach a SMBH on parabolic orbits, using for the first time the moving-mesh code AREPO, which is particularly well adapted to the problem through its combination of quasi-Lagrangian behaviour, low advection errors, and high accuracy typical of mesh-based techniques. We examine a suite of simulations with different impact parameters, allowing us to determine the critical distance at which the star is totally disrupted, the energy distribution and the fallback rate of the debris, as well as the hydrodynamical evolution of the stellar remnant in the case of a partial disruption. Interestingly, we find that the internal evolution of the remnant's core is strongly influenced by persistent vortices excited in the tidal interaction. These should be sites of strong magnetic field amplification, and the associated mixing may profoundly alter the subsequent evolution of the tidally pruned star.Comment: 13 pages, 9 figures. Accepted for publication by MNRA

Electron microscopy analysis of femtosecond laser-assisted capsulotomy before and after lens fragmentation

Studying anterior lens capsule cutting edge profiles from femtosecond laser-assisted capsulotomy procedures performed before and after lens fragmentation. Twenty eyes (10 patients) with age-related cataract underwent femtosecond laser-assisted surgery (FLACS) using the Ziemer Z8 platform. First step of laser surgery was either capsulotomy (group first) or fragmentation (group second). One eye of each patient was assigned randomly, the second eye treated with the different sequence of procedures. After anterior capsule removal, tissue was fixed in cacodylate-buffered solution and cutting-edge profiles were analysed using scanning electron microscopy (SEM). All cases had cataract grade 2 and 3 based on LOCS III grading. SEM analysis showed more smooth edges in the first group, especially in cases with pseudoexfoliation (P = 0.037); more tags and bridges and a significant number of staggered cutting patterns (7 out of 10 cases) in the second group. All cases evolved the same microgroves with \textquotedblvalleys and mountains \textquotedbl as signs of the photodisruption process. Femtosecond laser capsulotomy should be performed before lens fragmentation minimizing the rate of cutting errors. Especially in eyes with advanced cataract, as intracapsular pressure may increase due to lens fragmentation without anterior capsular opening

The P2Y12 receptor induces platelet aggregation through weak activation of the αIIbβ3 integrin – a phosphoinositide 3-kinase-dependent mechanism

AbstractHigh concentrations of adenosine-5′-diphosphate ADP are able to induce partial aggregation without shape change of P2Y1 receptor-deficient mouse platelets through activation of the P2Y12 receptor. In the present work we studied the transduction pathways selectively involved in this phenomenon. Flow cytometric analyses using R-phycoerythrin-conjugated JON/A antibody (JON/A-PE), an antibody which recognizes activated mouse αIIbβ3 integrin, revealed a low level activation of αIIbβ3 in P2Y1 receptor-deficient platelets in response to 100 μM ADP or 1 μM 2MeS-ADP. Adrenaline induced no such activation but strongly potentiated the effect of ADP in a dose-dependent manner. Global phosphorylation of 32P-labeled platelets showed that P2Y12-mediated aggregation was not accompanied by an increase in the phosphorylation of myosin light chain (P20) or pleckstrin (P47) and was not affected by the protein kinase C (PKC) inhibitor staurosporine. On the other hand, two unrelated phosphoinositide 3-kinase inhibitors, wortmannin and LY294002, inhibited this aggregation. Our results indicate that (i) the P2Y12 receptor is able to trigger a P2Y1 receptor-independent inside-out signal leading to αIIbβ3 integrin activation and platelet aggregation, (ii) ADP and adrenaline use different signaling pathways which synergize to activate the αIIbβ3 integrin, and (iii) the transduction pathway triggered by the P2Y12 receptor is independent of PKC but dependent on phosphoinositide 3-kinase

Ex vivo excimer laser ablation of cornea guttata and ROCK inhibitor‐aided endothelial recolonization of ablated central cornea

Purpose To determine whether excimer laser ablation of guttae is a viable strategy for removal of diseased tissue in Fuchs' endothelial corneal dystrophy (FECD) on excised human Descemet membranes and whether an excimer laser‐created wound on healthy human corneas ex vivo is recolonized with corneal endothelial cells. Methods Descemet membranes of FECD patients and corneal endothelium of normal human corneas were ablated ex vivo using an excimer laser licensed for glaucoma surgery. Specimens were kept in cell culture medium supplemented with 10 μm of rho‐kinase inhibitor ripasudil. Corneal endothelial cell regeneration was observed using light and electron scanning microscopy. Furthermore, the whole corneal samples were evaluated by haematoxylin/eosin staining and immunohistochemical analysis using antibodies against Na+/K+‐ATPase. Results Guttae and corneal endothelium could be ablated with an excimer laser without total ultrastructural damage to the Descemet membrane or stroma. Nearly complete endothelial wound closure was accomplished after 26–38 days in treated corneas. Light and electron scanning microscopy suggested the establishment of a layer of flat endothelial cells. Additionally, Na+/K+‐ATPase expression could only be observed on the inner side of the Descemet membrane. Conclusion Our proof of concept study demonstrated that excimer lasers can be used to ablate diseased tissue from excised FECD Descemet membranes ex vivo. Additionally, corneal endothelial cells recolonize a previously ablated endothelial area in healthy human corneas ex vivo under treatment with ripasudil. Thus, our results are the first experimental basis to further investigate the feasibility of an excimer laser ablation as a graftless FECD treatment option

Self-consistent MHD simulation of jet launching in a neutron star - white dwarf merger

The merger of a white dwarf (WD) and a neutron star (NS) is a relatively common event that will produce an observable electromagnetic signal. Furthermore, the compactness of these stellar objects makes them an interesting candidate for gravitational wave (GW) astronomy, potentially being in the frequency range of LISA and other missions. To date, three-dimensional simulations of these mergers have not fully modelled the WD disruption, or have used lower resolutions and have not included magnetic fields even though they potentially shape the evolution of the merger remnant. In this work, we simulate the merger of a 1.4$M_\odot$ NS with a 1$M_\odot$ carbon oxygen WD in the magnetohydrodynamic moving mesh code \AREPO. We find that the disruption of the WD forms an accretion disk around the NS, and the subsequent accretion by the NS powers the launch of strongly magnetized, mildly relativistic jets perpendicular to the orbital plane. Although the exact properties of the jets could be altered by unresolved physics around the NS, the event could result in a transient with a larger luminosity than kilonovae. We discuss possible connections to fast blue optical transients (FBOTs) and long-duration gamma-ray bursts. We find that the frequency of GWs released during the merger is too high to be detectable by the LISA mission, but suitable for deci-hertz observatories such as LGWA, BBO or DECIGO.Comment: Accepted for publication in A&A. 13 pages, 11 figure

Quantification of recombinant and platelet P2Y1 receptors utilizing a [125I]-labeled high-affinity antagonist 2-iodo-N6-methyl-(N)-methanocarba-2′-deoxyadenosine-3′,5′-bisphosphate ([125I]MRS2500)

The ADP-activated P2Y1 receptor is broadly expressed and plays a crucial role in ADP-promoted platelet aggregation. We previously synthesized 2-iodo-N6-methyl–(N)-methanocarba-2′-deoxyadenosine 3′,5′-bisphosphate (MRS2500), as a selective, high affinity, competitive antagonist of this receptor. Here we report utilization of a trimethylstannyl precursor molecule for the multistep radiochemical synthesis of a [125I]-labeled form of MRS2500. [125I]MRS2500 bound selectively to Sf9 insect cell membranes expressing the human P2Y1 receptor but did not specifically bind to membranes isolated from empty vector-infected cells. Binding of [125I]MRS2500 to P2Y1 receptors was saturable with a Kd of 1.2 nM. Known agonists and antagonists of the P2Y1 receptor inhibited [125I]MRS2500 binding to P2Y1 receptor-expressing membranes with potencies in agreement with those previously observed in functional assays of this receptor. A high-affinity binding site for [125I]MRS2500 also was observed on intact human platelets (Kd = 0.61 nM) and mouse platelets (Kd = 1.20 nM) that exhibited the pharmacological selectivity of the P2Y1 receptor. The densities of sites observed were 151 sites/platelet and 229 sites/platelet in human and mouse platelets, respectively. In contrast, specific binding was not observed in platelets isolated from P2Y1 receptor (−/−) mice. Taken together, these data illustrate the synthesis and characterization of a novel P2Y1 receptor radioligand and its utility for examining P2Y1 receptors natively expressed on human and mouse platelets

Navigating the integration of biotic interactions in biogeography

Biotic interactions are widely recognised as the backbone of ecological communities, but how best to study them is a subject of intense debate, especially at macro-ecological scales. While some researchers claim that biotic interactions need to be observed directly, others use proxies and statistical approaches to infer them. Despite this ambiguity, studying and predicting the influence of biotic interactions on biogeographic patterns is a thriving area of research with crucial implications for conservation. Three distinct approaches are currently being explored. The first approach involves empirical observation and measurement of biotic interactions' effects on species demography in laboratory or field settings. While these findings contribute to theory and to understanding species' demographies, they can be challenging to generalise on a larger scale. The second approach centers on inferring biotic associations from observed co-occurrences in space and time. The goal is to distinguish the environmental and biotic effects on species distributions. The third approach constructs extensive potential interaction networks, known as metanetworks, by leveraging existing knowledge about species ecology and interactions. This approach analyses local realisations of these networks using occurrence data and allows understanding large distributions of multi-taxa assemblages. In this piece, we appraise these three approaches, highlighting their respective strengths and limitations. Instead of seeing them as conflicting, we advocate for their integration to enhance our understanding and expand applications in the emerging field of interaction biogeography. This integration shows promise for ecosystem understanding and management in the Anthropocene era

Red wine polyphenols prevent metabolic and cardiovascular alterations associated with obesity in Zucker fatty rats (Fa/Fa)

Peer reviewedPublisher PD