Guided Tissue Regeneration in Heart Valve Replacement: From Preclinical Research to First-in-Human Trials

Heart valve tissue-guided regeneration aims to offer a functional and viable alternative to current prosthetic replacements. Not requiring previous cell seeding and conditioning in bioreactors, such exceptional tissue engineering approach is a very fascinating translational regenerative strategy. After in vivo implantation, decellularized heart valve scaffolds drive their same repopulation by recipient’s cells for a prospective autologous-like tissue reconstruction, remodeling, and adaptation to the somatic growth of the patient. With such a viability, tissue-guided regenerated conduits can be delivered as off-the-shelf biodevices and possess all the potentialities for a long-lasting resolution of the dramatic inconvenience of heart valve diseases, both in children and in the elderly. A review on preclinical and clinical investigations of this therapeutic concept is provided with evaluation of the issues still to be well deliberated for an effective and safe in-human application

Missing black holes in brightest cluster galaxies as evidence for the occurrence of superkicks in nature

We investigate the consequences of superkicks on the population of supermassive black holes (SMBHs) in the Universe residing in brightest cluster galaxies (BCGs). There is strong observational evidence that BCGs grew prominently at late times (up to a factor 2-4 in mass from z=1), mainly through mergers with satellite galaxies from the cluster, and they are known to host the most massive SMBHs ever observed. Those SMBHs are also expected to grow hierarchically, experiencing a series of mergers with other SMBHs brought in by merging satellites. Because of the net linear momentum taken away from the asymmetric gravitational wave emission, the remnant SMBH experiences a kick in the opposite direction. Kicks may be as large as ~5000 Km/s ("superkicks"), pushing the SMBHs out in the cluster outskirts for a time comparable to galaxy-evolution timescales. We predict, under a number of plausible assumptions, that superkicks can efficiently eject SMBHs from BCGs, bringing their occupation fraction down to a likely range 0.9<f<0.99 in the local Universe. Future thirty-meter-class telescopes like ELT and TMT will be capable of measuring SMBHs in hundreds of BCGs up to z=0.2, testing the occurrence of superkicks in nature and the strong-gravity regime of SMBH mergers.Comment: 19 pages, 11 figures, accepted for publication in MNRA

Are merging black holes born from stellar collapse or previous mergers?

Advanced LIGO detectors at Hanford and Livingston made two confirmed and one marginal detection of binary black holes during their first observing run. The first event, GW150914, was from the merger of two black holes much heavier that those whose masses have been estimated so far, indicating a formation scenario that might differ from "ordinary" stellar evolution. One possibility is that these heavy black holes resulted from a previous merger. When the progenitors of a black hole binary merger result from previous mergers, they should (on average) merge later, be more massive, and have spin magnitudes clustered around a dimensionless spin ~0.7. Here we ask the following question: can gravitational-wave observations determine whether merging black holes were born from the collapse of massive stars ("first generation"), rather than being the end product of earlier mergers ("second generation")? We construct simple, observationally motivated populations of black hole binaries, and we use Bayesian model selection to show that measurements of the masses, luminosity distance (or redshift), and "effective spin" of black hole binaries can indeed distinguish between these different formation scenarios.Comment: 18 pages, 7 figures, 3 tables. Accepted for publication in PRD. Selected as PRD Editors' Suggestio

Black hole mergers: do gas discs lead to spin alignment?

In this Letter we revisit arguments suggesting that the Bardeen-Petterson effect can coalign the spins of a central supermassive black hole binary accreting from a circumbinary (or circumnuclear) gas disc. We improve on previous estimates by adding the dependence on system parameters, and noting that the nonlinear nature of warp propagation in a thin viscous disc affects alignment. This reduces the disc's ability to communicate the warp, and can severely reduce the effectiveness of disc-assisted spin alignment. We test our predictions with a Monte Carlo realization of random misalignments and accretion rates and we find that the outcome depends strongly on the spin magnitude. We estimate a generous upper limit to the probability of alignment by making assumptions which favour it throughout. Even with these assumptions, about 40% of black holes with $a \gtrsim 0.5$ do not have time to align with the disc. If the residual misalignment is not small and it is maintained down to the final coalescence phase this can give a powerful recoil velocity to the merged hole. Highly spinning black holes are thus more likely of being subject to strong recoils, the occurrence of which is currently debated.Comment: 6 pages, 2 figures, accepted in MNRA

Multiple light scattering and near-field effects in a fractal tree-like ensamble of dielectric nanoparticles

We numerically study light scattering and absorption in self-similar aggregates of dielectric nanoparticles, as generated by simulated ballistic deposition upon a surface starting from a single seed particle. The resulting structure exhibits a complex tree-like shape, intended to mimic the morphologic properties of building blocks of real nanostructured thin films produced by means of fine controlled physical deposition processes employed in nanotechnology. The relationship of scattering and absorption cross sections to morphology is investigated within a computational scheme which thoroughly takes into account both multiple scattering and near-field effects. Numerical results are compared with a pre-existing single scattering limited analytical treatment of light scattering in fractal aggregates of small dielectric particles.Comment: 10 pages, 9 figures. Accepted for publication in Physical Review

Astrophysical implications of GW190412 as a remnant of a previous black-hole merger

Two of the dominant channels to produce merging stellar-mass black-hole binaries are believed to be the isolated evolution of binary stars in the field and dynamical formation in star clusters. The first reported black-hole binary event from the third LIGO/Virgo observing run (GW190412) is unusual in that it has unequal masses, nonzero effective spin, and nonzero primary spin at 90\% confidence interval. We show that this event should be exceedingly rare in the context of both the field and cluster formation scenarios. Interpreting GW190412 as a remnant of a previous black-hole merger provides a promising route to explain its features. If GW190412 indeed formed hierarchically, we show that the region of the parameter space that is best motivated from an astrophysical standpoint (low natal spins and light clusters) cannot accommodate the observation. We analyze public GW190412 LIGO/Virgo data with a Bayesian prior where the more massive black hole resulted from a previous merger, and find that this interpretation is equally supported by the data. If the heavier component of GW190412 is indeed a merger remnant, then its spin magnitude is $\chi_1=0.56_{-0.21}^{+0.19}$, which is higher than the value previously reported by the LIGO/Virgo collaboration.Comment: 7 pages, 3 figures, 1 table. Published in PR

Symmetric Synchronous Collaborative Navigation

Synchronous collaborative navigation is a form of social navigation where users virtually share a web browser. In this paper, we present a symmetric, proxy-based architecture where each user can take the lead and guide others in visiting web sites, without the need for a special browser or other software. We show how we have applied this scheme to a problem-solving-oriented e-learning system

Nutational resonances, transitional precession, and precession-averaged evolution in binary black-hole systems

In the post-Newtonian (PN) regime, the timescale on which the spins of binary black holes precess is much shorter than the radiation-reaction timescale on which the black holes inspiral to smaller separations. On the precession timescale, the angle between the total and orbital angular momenta oscillates with nutation period $\tau$, during which the orbital angular momentum precesses about the total angular momentum by an angle $\alpha$. This defines two distinct frequencies that vary on the radiation-reaction timescale: the nutation frequency $\omega \equiv 2\pi/\tau$ and the precession frequency $\Omega \equiv \alpha/\tau$. We use analytic solutions for generic spin precession at 2PN order to derive Fourier series for the total and orbital angular momenta in which each term is a sinusoid with frequency $\Omega - n\omega$ for integer $n$. As black holes inspiral, they can pass through nutational resonances ($\Omega = n\omega$) at which the total angular momentum tilts. We derive an approximate expression for this tilt angle and show that it is usually less than $10^{-3}$ radians for nutational resonances at binary separations $r > 10M$. The large tilts occurring during transitional precession (near zero total angular momentum) are a consequence of such states being approximate $n=0$ nutational resonances. Our new Fourier series for the total and orbital angular momenta converge rapidly with $n$ providing an intuitive and computationally efficient approach to understanding generic precession that may facilitate future calculations of gravitational waveforms in the PN regime.Comment: 18 pages, 9 figures, version published in PR