Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

Compact Binary Merger Rates: Comparison with LIGO/Virgo Upper Limits

Abstract: Here, we compare evolutionary predictions of double compact object merger rate densities with initial and forthcoming LIGO/Virgo upper limits. We find that: (i) Due to the cosmological reach of advanced detectors, current conversion methods of population synthesis predictions into merger rate densities are insufficient. (ii) Our optimistic models are a factor of 18 below the initial LIGO/Virgo upper limits for BH–BH systems, indicating that a modest increase in observational sensitivity (by a factor of ~2.5) may bring the first detections or first gravitational wave constraints on binary evolution. (iii) Stellar-origin massive BH–BH mergers should dominate event rates in advanced LIGO/Virgo and can be detected out to redshift z sime 2 with templates including inspiral, merger, and ringdown. Normal stars ($$\lt 150\;{M}_{\odot }$$) can produce such mergers with total redshifted mass up to $${M}_{ {\rm{tot,z}}}\simeq 400\;{M}_{\odot }$$. (iv) High black hole (BH) natal kicks can severely limit the formation of massive BH–BH systems (both in isolated binary and in dynamical dense cluster evolution), and thus would eliminate detection of these systems even at full advanced LIGO/Virgo sensitivity. We find that low and high BH natal kicks are allowed by current observational electromagnetic constraints. (v) The majority of our models yield detections of all types of mergers (NS–NS, BH–NS, BH–BH) with advanced detectors. Numerous massive BH–BH merger detections will indicate small (if any) natal kicks for massive BHs.

Laser-driven shock acceleration of monoenergetic ion beams

Abstract: We show that monoenergetic ion beams can be accelerated by moderate Mach number collisionless, electrostatic shocks propagating in a long scale-length exponentially decaying plasma profile. Strong plasma heating and density steepening produced by an intense laser pulse near the critical density can launch such shocks that propagate in the extended plasma at high velocities. The generation of a monoenergetic ion beam is possible due to the small and constant sheath electric field associated with the slowly decreasing density profile. The conditions for the acceleration of high-quality, energetic ion beams are identified through theory and multidimensional particle-in-cell simulations. The scaling of the ion energy with laser intensity shows that it is possible to generate $\ensuremath{\sim}200\text{ }\text{ }\mathrm{MeV}$ proton beams with state-of-the-art 100 TW class laser systems.

Gravitational wave searches for ultralight bosons with LIGO and LISA

Abstract: Ultralight bosons can induce superradiant instabilities in spinning black holes, tapping their rotational energy to trigger the growth of a bosonic condensate. Possible observational imprints of these boson clouds include (i) direct detection of the nearly monochromatic (resolvable or stochastic) gravitational waves emitted by the condensate, and (ii) statistically significant evidence for the formation of ``holes'' at large spins in the spin versus mass plane (sometimes also referred to as ``Regge plane'') of astrophysical black holes. In this work, we focus on the prospects of LISA and LIGO detecting or constraining scalars with mass in the range ${m}_{s}\ensuremath{\in}[{10}^{\ensuremath{-}19},{10}^{\ensuremath{-}15}]\text{ }\text{ }\mathrm{eV}$ and ${m}_{s}\ensuremath{\in}[{10}^{\ensuremath{-}14},{10}^{\ensuremath{-}11}]\text{ }\text{ }\mathrm{eV}$, respectively. Using astrophysical models of black-hole populations calibrated to observations and black-hole perturbation theory calculations of the gravitational emission, we find that, in optimistic scenarios, LIGO could observe a stochastic background of gravitational radiation in the range ${m}_{s}\ensuremath{\in}[2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13},{10}^{\ensuremath{-}12}]\text{ }\text{ }\mathrm{eV}$, and up to $1{0}^{4}$ resolvable events in a 4-year search if ${m}_{s}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }\mathrm{eV}$. LISA could observe a stochastic background for boson masses in the range ${m}_{s}\ensuremath{\in}[5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19},5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}]$, and up to $\ensuremath{\sim}{10}^{3}$ resolvable events in a 4-year search if ${m}_{s}\ensuremath{\sim}{10}^{\ensuremath{-}17}\text{ }\text{ }\mathrm{eV}$. LISA could further measure spins for black-hole binaries with component masses in the range $[{10}^{3},{10}^{7}]{M}_{\ensuremath{\bigodot}}$, which is not probed by traditional spin-measurement techniques. A statistical analysis of the spin distribution of these binaries could either rule out scalar fields in the mass range $\ensuremath{\sim}[4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18},{10}^{\ensuremath{-}14}]\text{ }\text{ }\mathrm{eV}$, or measure ${m}_{s}$ with ten percent accuracy if light scalars in the mass range $\ensuremath{\sim}[{10}^{\ensuremath{-}17},{10}^{\ensuremath{-}13}]\text{ }\text{ }\mathrm{eV}$ exist.

Dynamic positioning and way-point tracking of underactuated AUVs in the presence of ocean currents

Abstract: This paper addresses the problem of dynamic positioning and way-point tracking of underactuated autonomous underwater vehicles (AUVs) in the presence of constant unknown ocean currents and parametric modelling uncertainty. A non-linear adaptive controller is proposed that steers an AUV along a sequence of way-points consisting of desired positions (x, y) in a inertial reference frame, followed by vehicle positioning at the final target point. The controller is first derived at the kinematic level assuming that the ocean current disturbance is known. An exponential observer for the current is then designed and convergence of the resulting closed-loop system trajectories is analysed. Finally, integrator backstepping and Lyapunov based techniques are used to extend the kinematic controller to the dynamic case and to deal with model parameter uncertainty. Simulation results with a dynamic model of an underactuated autonomous underwater shuttle for the transport of benthic labs are presented and discussed.

Algorithms for Projection-Pursuit Robust Principal Component Analysis

Abstract: Principal Component Analysis (PCA) is very sensitive in presence of outliers. One of the most appealing robust methods for principal component analysis uses the Projection-Pursuit principle. Here, one projects the data on a lower-dimensional space such that a robust measure of variance of the projected data will be maximized. The Projection-Pursuit based method for principal component analysis has recently been introduced in the field of chemometrics, where the number of variables is typically large. In this paper, it is shown that the currently available algorithm for robust Projection-Pursuit PCA performs poor in presence of many variables. A new algorithm is proposed that is more suitable for the analysis of chemical data. Its performance is studied by means of simulation experiments and illustrated on some real datasets.