Showing papers by "Instituto Superior Técnico published in 2017"

Pesticides, environment, and food safety

Abstract: Agrochemicals have enabled to more than duplicate food production during the last century, and the current need to increase food production to feed a rapid growing human population maintains pressure on the intensive use of pesticides and fertilizers. However, worldwide surveys have documented the contamination and impact of agrochemical residues in soils, and terrestrial and aquatic ecosystems including coastal marine systems, and their toxic effects on humans and nonhuman biota. Although persistent organic chemicals have been phased out and replaced by more biodegradable chemicals, contamination by legacy residues and recent residues still impacts on the quality of human food, water, and environment. Current and future increase in food production must go along with production of food with better quality and with less toxic contaminants. Alternative paths to the intensive use of crop protection chemicals are open, such as genetically engineered organisms, organic farming, change of dietary habits, and development of food technologies. Agro industries need to further develop advanced practices to protect public health, which requires more cautious use of agrochemicals through prior testing, careful risk assessment, and licensing, but also through education of farmers and users in general, measures for better protection of ecosystems, and good practices for sustainable development of agriculture, fisheries, and aquaculture. Enhanced scientific research for new developments in food production and food safety, as well as for environmental protection, is a necessary part of this endeavor. Furthermore, worldwide agreement on good agriculture practices, including development of genetically modified organisms (GMOs) and their release for international agriculture, may be urgent to ensure the success of safe food production.

A kilonova as the electromagnetic counterpart to a gravitational-wave source

Abstract: Gravitational waves were discovered with the detection of binary black-hole mergers and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of -1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

Science with the space-based interferometer LISA. V. Extreme mass-ratio inspirals

Abstract: The space-based Laser Interferometer Space Antenna (LISA) will be able to observe the gravitational-wave signals from systems comprised of a massive black hole and a stellar-mass compact object. These systems are known as extreme-mass-ratio inspirals (EMRIs) and are expected to complete ∼104–105 cycles in band, thus allowing exquisite measurements of their parameters. In this work, we attempt to quantify the astrophysical uncertainties affecting the predictions for the number of EMRIs detectable by LISA, and find that competing astrophysical assumptions produce a variance of about three orders of magnitude in the expected intrinsic EMRI rate. However, we find that irrespective of the astrophysical model, at least a few EMRIs per year should be detectable by the LISA mission, with up to a few thousands per year under the most optimistic astrophysical assumptions. We also investigate the precision with which LISA will be able to extract the parameters of these sources. We find that typical fractional statistical errors with which the intrinsic parameters (redshifted masses, massive black hole spin and orbital eccentricity) can be recovered are ∼10-6–10-4. Luminosity distance (which is required to infer true masses) is inferred to about 10% precision and sky position is localized to a few square degrees, while tests of the multipolar structure of the Kerr metric can be performed to percent-level precision or better.

An overview of Demand Response: Key-elements and international experience

Abstract: The increasing penetration of renewable energy sources (RES) in power systems intensifies the need of enhancing the flexibility in grid operations in order to accommodate the uncertain power output of the leading RES such as wind and solar generation. Utilities have been recently showing increasing interest in developing Demand Response (DR) programs in order to match generation and demand in a more efficient way. Incentive- and price-based DR programs aim at enabling the demand side in order to achieve a range of operational and economic advantages, towards developing a more sustainable power system structure. The contribution of the presented study is twofold. First, a complete and up-to-date overview of DR enabling technologies, programs and consumer response types is presented. Furthermore, the benefits and the drivers that have motivated the adoption of DR programs, as well as the barriers that may hinder their further development, are thoroughly discussed. Second, the international DR status quo is identified by extensively reviewing existing programs in different regions.

Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 1018 eV

Abstract: Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature Clues to their origin come from studying the distribution of their arrival directions Using 3 × 10 4 cosmic rays with energies above 8 × 10 18 electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 km 2 sr year, we determined the existence of anisotropy in arrival directions The anisotropy, detected at more than a 52σ level of significance, can be described by a dipole with an amplitude of 65 − 09 + 13 percent toward right ascension α d = 100 ± 10 degrees and declination δ d = − 24 − 13 + 12 degrees That direction indicates an extragalactic origin for these ultrahigh-energy particles

Alignment-free sequence comparison: benefits, applications, and tools

Abstract: Alignment-free sequence analyses have been applied to problems ranging from whole-genome phylogeny to the classification of protein families, identification of horizontally transferred genes, and detection of recombined sequences. The strength of these methods makes them particularly useful for next-generation sequencing data processing and analysis. However, many researchers are unclear about how these methods work, how they compare to alignment-based methods, and what their potential is for use for their research. We address these questions and provide a guide to the currently available alignment-free sequence analysis tools.

Chalcogen bonding in synthesis, catalysis and design of materials

Abstract: Chalcogen bonding is a type of noncovalent interaction in which a covalently bonded chalcogen atom (O, S, Se or Te) acts as an electrophilic species towards a nucleophilic (negative) region(s) in another or in the same molecule. In general, this interaction is strengthened by the presence of an electron-withdrawing group on the electron-acceptor chalcogen atom and upon moving down in the periodic table of elements, from O to Te. Following a short discussion of the phenomenon of chalcogen bonding, this Perspective presents some demonstrative experimental observations in which this bonding is crucial for synthetic transformations, crystal engineering, catalysis and design of materials as synthons/tectons.

PHYLOViZ 2.0: providing scalable data integration and visualization for multiple phylogenetic inference methods

Abstract: Summary: High Throughput Sequencing provides a cost effective means of generating high resolution data for hundreds or even thousands of strains, and is rapidly superseding methodologies based on a few genomic loci. The wealth of genomic data deposited on public databases such as Sequence Read Archive/European Nucleotide Archive provides a powerful resource for evolutionary analysis and epidemiological surveillance. However, many of the analysis tools currently available do not scale well to these large datasets, nor provide the means to fully integrate ancillary data. Here we present PHYLOViZ 2.0, an extension of PHYLOViZ tool, a platform independent Java tool that allows phylogenetic inference and data visualization for large datasets of sequence based typing methods, including Single Nucleotide Polymorphism (SNP) and whole genome/core genome Multilocus Sequence Typing (wg/cgMLST) analysis. PHYLOViZ 2.0 incorporates new data analysis algorithms and new visualization modules, as well as the capability of saving projects for subsequent work or for dissemination of results. Availability and Implementation: http://www.phyloviz.net/ (licensed under GPLv3). Contact: cvaz@inesc-id.pt Supplementary information: Supplementary data are available at Bioinformatics online.

Are merging black holes born from stellar collapse or previous mergers

Abstract: 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.

Tests for the existence of black holes through gravitational wave echoes

Abstract: The existence of black holes and spacetime singularities is a fundamental issue in science. Despite this, observations supporting their existence are scarce, and their interpretation is unclear. In this Perspective we outline the case for black holes that has been made over the past few decades, and provide an overview of how well observations adjust to this paradigm. Unsurprisingly, we conclude that observational proof for black holes is, by definition, impossible to obtain. However, just like Popper’s black swan, alternatives can be ruled out or confirmed to exist with a single observation. These observations are within reach. In the coming years and decades, we will enter an era of precision gravitational-wave physics with more sensitive detectors. Just as accelerators have required larger and larger energies to probe smaller and smaller scales, more sensitive gravitational-wave detectors will probe regions closer and closer to the horizon, potentially reaching Planck scales and beyond. What may be there, lurking? Black holes and spacetime singularities are fundamental in science. While observational proof for black holes is hard to come by, alternatives can be ruled out or confirmed to exist through precision gravitational wave observations.

Mining industry and sustainable development: time for change

Abstract: Mining industries provide most of the materials we rely on to build infrastructures and instruments of daily use, to obtain large amounts of energy, and to supply agriculture with fertilizers that enable most of foods produced. At the same time, mining is the human activity that has been more disturbing to environment and is linked to large social impacts and inequalities. Notwithstanding, our future is deeply depending on mining. Several mining sectors, from phosphate to uranium, are reviewed and their current impacts and challenges are discussed. The mining legacy and environmental remediation, the present mining and challenges, and the future mining and society are discussed in relationship with environmental health and sustainable development. It is concluded that current mining practices need to change and contribute to community development with more equity, and to protect better natural resources and ecosystems in order to be environmentally acceptable and compliant with sustainable development objectives.

Testing strong-field gravity with tidal Love numbers

Abstract: The authors calculate the tidal Love numbers (TLN), which encode the effect of rapidly changing gravitational fields on deformable, self-gravitating objects, for various exotic compact objects. They have found a universal logarithmic dependence of the TLNs close to black holes and use this to propose future gravitational wave measurements of TLNs, which would provide a test for general relativity in the strong field regime.

Light-Ring Stability for Ultracompact Objects.

Abstract: We prove the following theorem: axisymmetric, stationary solutions of the Einstein field equations formed from classical gravitational collapse of matter obeying the null energy condition, that are everywhere smooth and ultracompact (i.e., they have a light ring) must have at least two light rings, and one of them is stable. It has been argued that stable light rings generally lead to nonlinear spacetime instabilities. Our result implies that smooth, physically and dynamically reasonable ultracompact objects are not viable as observational alternatives to black holes whenever these instabilities occur on astrophysically short time scales. The proof of the theorem has two parts: (i) We show that light rings always come in pairs, one being a saddle point and the other a local extremum of an effective potential. This result follows from a topological argument based on the Brouwer degree of a continuous map, with no assumptions on the spacetime dynamics, and, hence, it is applicable to any metric gravity theory where photons follow null geodesics. (ii) Assuming Einstein's equations, we show that the extremum is a local minimum of the potential (i.e., a stable light ring) if the energy-momentum tensor satisfies the null energy condition.

3-D Target Localization in Wireless Sensor Networks Using RSS and AoA Measurements

Abstract: This paper addresses target localization problems in both noncooperative and cooperative 3-D wireless sensor networks (WSNs), for both cases of known and unknown sensor transmit power, i.e., $P_{T}$ . We employ a hybrid system that fuses distance and angle measurements, extracted from the received signal strength and angle-of-arrival information, respectively. Based on range and angle measurement models, we derive a novel nonconvex estimator based on the least squares criterion. The derived nonconvex estimator tightly approximates the maximum-likelihood estimator for small noise. We then show that the developed estimator can be transformed into a generalized trust region subproblem framework, by following the squared range approach, for noncooperative WSNs. For cooperative WSNs, we show that the estimator can be transformed into a convex problem by applying appropriate semidefinite programming relaxation techniques. Moreover, we show that the generalization of the proposed estimators for known $P_{T}$ is straightforward to the case where $P_{T}$ is not known. Our simulation results show that the new estimators have excellent performance and are robust to not knowing $P_{T}$ . The new estimators for noncooperative localization significantly outperform the existing estimators, and our estimators for cooperative localization show exceptional performance in all considered settings.

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.

Empathy in Virtual Agents and Robots: A Survey

Abstract: This article surveys the area of computational empathy, analysing different ways by which artificial agents can simulate and trigger empathy in their interactions with humans. Empathic agents can be seen as agents that have the capacity to place themselves into the position of a user’s or another agent’s emotional situation and respond appropriately. We also survey artificial agents that, by their design and behaviour, can lead users to respond emotionally as if they were experiencing the agent’s situation. In the course of this survey, we present the research conducted to date on empathic agents in light of the principles and mechanisms of empathy found in humans. We end by discussing some of the main challenges that this exciting area will be facing in the future.

High-performance ternary organic solar cells with thick active layer exceeding 11% efficiency

Abstract: We present a novel ternary organic solar cell with an uncommonly thick active layer (∼300 nm), featuring thickness invariant charge carrier recombination and delivering 11% power conversion efficiency (PCE). A ternary blend was used to demonstrate photovoltaic modules of high technological relevance both on glass and flexible substrates, yielding 8.2% and 6.8% PCE, respectively.

Stochastic and Resolvable Gravitational Waves from Ultralight Bosons

Abstract: Ultralight scalar fields around spinning black holes can trigger superradiant instabilities, forming a long-lived bosonic condensate outside the horizon. We use numerical solutions of the perturbed field equations and astrophysical models of massive and stellar-mass black hole populations to compute, for the first time, the stochastic gravitational-wave background from these sources. In optimistic scenarios the background is observable by Advanced LIGO and LISA for field masses m_{s} in the range ∼[2×10^{-13},10^{-12}] and ∼5×[10^{-19},10^{-16}] eV, respectively, and it can affect the detectability of resolvable sources. Our estimates suggest that an analysis of the stochastic background limits from LIGO O1 might already be used to marginally exclude axions with mass ∼10^{-12.5} eV. Semicoherent searches with Advanced LIGO (LISA) should detect ∼15(5) to 200(40) resolvable sources for scalar field masses 3×10^{-13} (10^{-17}) eV. LISA measurements of massive BH spins could either rule out bosons in the range ∼[10^{-18},2×10^{-13}] eV, or measure m_{s} with 10% accuracy in the range ∼[10^{-17},10^{-13}] eV.