Linearity of charge measurement in laser filaments

We evaluate the linearity of three electric measurement techniques of the initial electron density in laser filaments by comparing their results for a pair of filaments and for the sum of each individual filament. The conductivity measured between two plane electrodes in a longitudinal configuration is linear within 2% provided the electric field is kept below 100 kV/m. Furthermore, simulations show that the signal behaves like the amount of generated free electrons. The slow ionic current measured with plane electrodes in a parallel configuration is representative of the ionic charge available in the filament, after several $\mu$s, when the free electrons have recombined. It is linear within 2% with the amount of ions and is insensitive to misalignment. Finally, the fast polarization signal in the same configuration deviates from linearity by up to 80% and can only be considered as a semi-qualitative indication of the presence of charges, e.g., to characterize the filament length.Comment: 17 pages, 7 figure

García Lorca, Federico (2018). Juego y teoría del duende. Estudio y edición crítica anotada de José Javier León. Prólogo de Andrés Soria Olmedo. Sevilla: Athenaica, 290 pp.

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Quasinormal resonances of near-extremal Kerr-Newman black holes

We study analytically the fundamental resonances of near-extremal, slowly rotating Kerr-Newman black holes. We find a simple analytic expression for these black-hole quasinormal frequencies in terms of the black-hole physical parameters: omega=m Omega-2i pi T(l+1+n), where T and Omega are the temperature and angular velocity of the black hole. The mode parameters l and m are the spheroidal harmonic index and the azimuthal harmonic index of a co-rotating mode, respectively. This analytical formula is valid in the regime Im omega << Re omega <<1/M, where M is the black-hole mass.Comment: 4 page

A biodiversity hypothesis

Biodiversity hypothesis states that contact with natural environments enriches the human microbiome, promotes immune balance and protects from allergy and inflammatory disorders. We are protected by two nested layers of biodiversity, microbiota of the outer layer (soil, natural waters, plants, animals) and inner layer (gut, skin, airways). The latter inhabits our body and is colonized from the outer layer. Explosion of human populations along with cultural evolution is profoundly changing our environment and lifestyle. Adaptive immunoregulatory circuits and dynamic homeostasis are at stake in the newly emerged urban surroundings. In allergy, and chronic inflammatory disorders in general, exploring the determinants of immunotolerance is the key for prevention and more effective treatment. Loss of immunoprotective factors, derived from nature, is a new kind of health risk poorly acknowledged until recently. The paradigm change has been implemented in the Finnish allergy programme (2008-2018), which emphasized tolerance instead of avoidance. The first results are promising, as allergy burden has started to reduce. The rapidly urbanizing world is facing serious biodiversity loss with global warming, which are interconnected. Biodiversity hypothesis of health and disease has societal impact, for example, on city planning, food and energy production and nature conservation. It has also a message for individuals for health and well-being: take nature close, to touch, eat, breathe, experience and enjoy. Biodiverse natural environments are dependent on planetary health, which should be a priority also among health professionals.Peer reviewe

Are multiple-choice questions a good tool for the assessment of clinical competence in Internal Medicine?

There are many feasible tools for the assessment of clinical practice, but there is a wide consensus on the fact that the simultaneous use of several different methods could be strategic for a comprehensive overall judgment of clinical competence. Multiple-choice questions (MCQs) are a well-established reliable method of assessing knowledge. Constructing effective MCQ tests and items requires scrupulous care in the design, review and validation stages. Creating high-quality multiple-choice questions requires a very deep experience, knowledge and large amount of time. Hereby, after reviewing their construction, strengths and limitations, we debate their completeness for the assessment of professional competence

Stability analysis of f(R)-AdS black holes

We study the stability of f(R)-AdS (Schwarzschild-AdS) black hole obtained from f(R) gravity. In order to resolve the difficulty of solving fourth order linearized equations, we transform f(R) gravity into the scalar-tensor theory by introducing two auxiliary scalars. In this case, the linearized curvature scalar becomes a dynamical scalaron, showing that all linearized equations are second order. Using the positivity of gravitational potentials and S-deformed technique allows us to guarantee the stability of f(R)-AdS black hole if the scalaron mass squared satisfies the Breitenlohner-Freedman bound. This is confirmed by computing quasinormal frequencies of the scalaron for large f(R)-AdS black hole.Comment: 17 pages, 1 figure, version to appear in EPJ

Cosmological Evolution of Supermassive Black Holes. II. Evidence for Downsizing of Spin Evolution

The spin is an important but poorly constrained parameter for describing supermassive black holes (SMBHs). Using the continuity equation of SMBH number density, we explicitly obtain the mass-dependent cosmological evolution of the radiative efficiency for accretion, which serves as a proxy for SMBH spin. Our calculations make use of the SMBH mass function of active and inactive galaxies (derived in the first paper of this series), the bolometric luminosity function of active galactic nuclei (AGNs), corrected for the contribution from Compton-thick sources, and the observed Eddington ratio distribution. We find that the radiative efficiency generally increases with increasing black hole mass at high redshifts (z>~1), roughly as \eta \propto M_bh^0.5, while the trend reverses at lower redshifts, such that the highest efficiencies are attained by the lowest mass black holes. Black holes with M_bh>~10^8.5M_sun maintain radiative efficiencies as high as \eta~0.3-0.4 at high redshifts, near the maximum for rapidly spinning systems, but their efficiencies drop dramatically (by an order of magnitude) by z~0. The pattern for lower mass holes is somewhat more complicated but qualitatively similar. Assuming that the standard accretion disk model applies, we suggest that the accretion history of SMBHs and their accompanying spins evolve in two distinct regimes: an early phase of prolonged accretion, plausibly driven by major mergers, during which the black hole spins up, then switching to a period of random, episodic accretion, governed by minor mergers and internal secular processes, during which the hole spins down. The transition epoch depends on mass, mirroring other evidence for "cosmic downsizing" in the AGN population; it occurs at z~2 for high-mass black holes, and somewhat later, at z~1, for lower-mass systems.Comment: To appear in the ApJ, 11 pages and 9 figure

An XMM-Newton view of the `bare' nucleus of Fairall 9

We present the spectral results from a 130 ks observation, obtained from the X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves, reveals a `softer-when-brighter' behaviour which is typical for radio-quiet type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data of the reflection grating spectrometer and we did not find any significant evidence supporting the presence of warm-absorber in the low X-ray energy part of the source's spectrum. This means that the central nucleus of Fairall 9 is `clean' and thus its X-ray spectral properties probe directly the physical conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV energy-range, derived from the EPIC data, can be modelled by a relativistically blurred disc-reflection model. This spectral model yields for Fairall 9 an intermediate black-hole best-fit spin parameter of $\alpha=0.39^{+0.48}_{-0.30}$.Comment: Accepted for publication in MNRAS. The paper contains 11 figures and 1 tabl

Spectral Photon-Counting Computed Tomography: Technical Principles and Applications in the Assessment of Cardiovascular Diseases

Spectral Photon-Counting Computed Tomography (SPCCT) represents a groundbreaking advancement in X-ray imaging technology. The core innovation of SPCCT lies in its photon-counting detectors, which can count the exact number of incoming x-ray photons and individually measure their energy. The first part of this review summarizes the key elements of SPCCT technology, such as energy binning, energy weighting, and material decomposition. Its energy-discriminating ability represents the key to the increase in the contrast between different tissues, the elimination of the electronic noise, and the correction of beam-hardening artifacts. Material decomposition provides valuable insights into specific elements’ composition, concentration, and distribution. The capability of SPCCT to operate in three or more energy regimes allows for the differentiation of several contrast agents, facilitating quantitative assessments of elements with specific energy thresholds within the diagnostic energy range. The second part of this review provides a brief overview of the applications of SPCCT in the assessment of various cardiovascular disease processes. SPCCT can support the study of myocardial blood perfusion and enable enhanced tissue characterization and the identification of contrast agents, in a manner that was previously unattainable