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Evangelos Matsinos

Publications and source records attributed to Evangelos Matsinos.

At least 19 recordsLinked to original sources
arXiv2024

Extreme-value Statistics: Rudiments and applications

This study provides a summary of the theory which enables the analysis of extreme values, i.e., of measurements acquired from the observation of extraordinary/rare physical phenomena. The formalism is developed in a transparent way, tailored to the application to real-world problems. Three examples of the application of the theory are detailed: first, an old problem, relating to the return period of floods caused by the Rh{ô}ne river, is revisited; second, the frequency of occurrence and the severity of meteorite impacts on the Earth are examined; the data, which are analysed in the third example, relate to the longevity of supercentenarians.

physics.data-an↗
arXiv2024

Modelling of the monthly global average temperature anomalies after the year 1900

Two ways of parameterising the temporal dependence of the global average temperature anomalies after 1900 are put forth in this technical note. The models are fitted to the data of the Berkeley Earth Group (up to the end of 2023), after the application of corrections which translate the input so that its average value over the last five decades of the $19$-th century vanishes; as the corrections are evaluated separately for each month of the year, the seasonal effects are removed from the data. The results are given in a convenient form for use.

physics.geo-ph↗
arXiv2023

Analysis of four sets of global average temperature anomalies

Four sets of global average temperature anomalies, altered so that they refer to pre-industrial temperature levels (baseline), as recommended by the Intergovernmental Panel on Climate Change, are analysed in this study. Expectation values of the time, at which the crossing of the $1.5^\circ$C threshold above the baseline will occur, are extracted from the two datasets which are accompanied by meaningful uncertainties; the two estimates are in the 2030s and differ by about four years: mid-2032 and mid-2036.

physics.ao-ph↗
arXiv2023

A discussion on two celebrated examples of application of linear regression

This work aims at providing some (further) perspective into the analysis of two well-known datasets in terms of the methods of linear regression. The first set has been taken from Hubble's 1929 investigation of the relation between the distances of galaxies and their recessional velocities. The second set relates to Galton's family data on human stature, collected for the purposes of his 1889 book on natural inheritance.

physics.hist-ph↗
arXiv2022

ZRH22: An improved analysis of the pion-nucleon measurements at low energy

Carried out in this study is an improved analysis of the measurements of the three pion-nucleon ($πN$) reactions, which can be subjected to experimental investigation at low energy (pion laboratory kinetic energy $T \leq 100$ MeV), i.e., of the two elastic-scattering (ES) processes $π^\pm p \to π^\pm p$ and of the $π^- p$ charge-exchange (CX) reaction $π^- p \to π^0 n$. After the application of the four steps of the first phase of the new analysis procedure, $52$ entries - of the $1150$ degrees of freedom of the new initial database (DB) of this project - were identified as outliers and were removed from the input. In this manner, three `clean' (devoid of outliers) DBs were obtained, which were submitted to further analysis using the ETH model. The phase-shift analysis (PSA) of the ES measurements comprises the results of one hundred joint fits to the data, each fit being carried out at one value (randomly generated, in normal distribution, according to a recent result) of the model parameter $m_σ$, which is associated with the effective range of the scalar-isoscalar part of the $πN$ interaction. The result of the PSA of the ES data for the (square of the) charged-pion coupling constant $f_c$ is: $f_c^2=0.0764(15)$. An exclusive fit of the ETH model to the low-energy $π^- p$ CX DB was also performed, for the first time in the recent years, after suppressing the contributions to the partial-wave amplitudes of the ETH model which originate from the scalar-isoscalar $t$-channel Feynman diagram. The predictions, obtained from these two types of fits (PSA of the ES data and exclusive fit of the ETH model to the $π^- p$ CX DB) for the (popular) symmetrised relative difference $R_2$ were compared in the entire low-energy region, separately for the $s$ wave, as well as for the no-spin-flip and spin-flip $p$-wave parts of the $πN$ scattering amplitude.

nucl-th↗
arXiv2022

Low-energy parameterisations of the pion-nucleon phase shifts

Compared in this work are a few sets of results, obtained from the pion-nucleon ($πN$) data at low energy (pion laboratory kinetic energy up to $100$ MeV) on the basis of the modelling of the $s$- and $p$-wave $K$-matrix elements (or of their reciprocal) via simple polynomials. The fitted values and uncertainties of the model parameters, as well as the corresponding Hessian (covariance) matrices, for three of these parameterisations are given in tabular form for two types of joint fits: to the measurements of the two elastic-scattering processes $π^\pm p \to π^\pm p$, and to those of the $π^+ p$ reaction and of the $π^- p$ charge-exchange reaction $π^- p \to π^0 n$. From these results, reliable and (largely) data-driven (hence model-independent) predictions, accompanied by uncertainties which reflect the statistical and systematic fluctuation of the input data, can be obtained for the low-energy constants of the $πN$ interaction (scattering lengths/volumes and range parameters), for the phase shifts, for the $K$-matrix elements, and for the partial-wave amplitudes in the (dominant at low energy) $s$ and $p$ waves. After the addition of the $d$- and $f$-wave contributions, and the inclusion of the electromagnetic effects, corresponding predictions can be obtained for the usual low-energy $πN$ observables, i.e., for the differential cross section and for the analysing power.

nucl-th↗
arXiv2022

What has been learnt from the analysis of the low-energy pion-nucleon data during the past three decades?

Over twenty-five years ago, two analyses of the pion-nucleon ($πN$) data at low energy (i.e., for pion laboratory kinetic energy $T \leq 100$ MeV) reported on the departure of the extracted scattering amplitudes, corresponding to the two elastic-scattering reactions $π^\pm p \to π^\pm p$ and to the $π^- p$ charge-exchange reaction $π^- p \to π^0 n$, from the triangle identity, which these amplitudes fulfil if the isospin invariance holds in the hadronic part of the $πN$ interaction. This discrepancy indicates that \emph{at least one} of the following assumptions is not valid: first, that the absolute normalisation of the bulk of the low-energy $πN$ datasets is correct; second, that any residual contributions to the corrections, which aim at the removal of the effects of electromagnetic (EM) origin from the measurements, are not significant; and third, that the isospin invariance holds in the hadronic part of the $πN$ interaction. In view of the incompatibility of the results of the various schemes of removal of the so-called trivial EM effects at the $πN$ threshold ($T = 0$ MeV), the likelihood of residual effects of EM origin in the extracted $πN$ scattering amplitudes (from the data in the scattering region, i.e., above the $πN$ threshold) must be reassessed. This work emphasises the importance of the development of a unified scheme for the determination of reliable EM corrections, \emph{applicable at the $πN$ threshold and in the scattering region}, in providing a resolution to the established discrepancy at low energy.

nucl-th↗
arXiv2022

Comment on "A phenomenological $π^- p$ scattering length from pionic hydrogen''

This short technical note addresses a number of issues regarding the estimates of the 2004 paper by Ericson, Loiseau, and Wycech for the corrections $δ_ε$ and $δ_Γ$, which aim at the removal of the effects of electromagnetic origin from the measurements of the strong-interaction shift $ε_{1s}$ and of the total decay width $Γ_{1s}$ of the ground state in pionic hydrogen.

hep-ph↗
arXiv2021

COVID-19: The extraction of the effective reproduction number from the time series of new cases

Addressed in this work is the performance of five popular algorithms, which aim at assessing the dissemination dynamics of the COVID-19 disease on the basis of the time series of new confirmed cases. The tests are based on simulated data, generated by means of a deterministic compartmental epidemiological model \cite{Matsinos2020a}, adapted herein to also include the possibility of the loss of immunity by the group of the recovered (or vaccinated) subjects. Assuming a simple temporal dependence of the effective reproduction number (the exact details are of no relevance as far as the conclusions of this work are concerned), time series of new cases were generated in a time domain of nearly one year for the five top-ranking countries in the cumulative number of infections by January 1, 2021. These countries are (in descending order of infections): the United States of America, India, Brazil, Russia, and the United Kingdom. The processing of each simulated time series led to the establishment of relations between the input (actual) and the reconstructed values of the effective reproduction number for each country and algorithm, separately; this work argues that all five algorithms underestimate the effective reproduction number when the latter exceeds the critical value of $1$. The five algorithms were subsequently applied to the real-life time series of new cases for the aforementioned five countries, which also span a temporal interval of nearly one year; corrected values of the effective reproduction number are obtained for these countries in 2020.

q-bio.PE↗
arXiv2020

COVID-19: On the quarantine duration after short visits to high-risk regions

A simple Monte-Carlo method will be put forward herein, to enable the extraction of an estimate for the quarantine duration, applicable to visitors to high-risk regions. Results will be obtained on the basis of an analysis of the upper tail of the cumulative distribution function of the time span between the departure of the travellers from the place where the infection occurs and the time instant when COVID-19 infections may currently be detected. As expected, the quarantine duration is a decreasing function of the fraction of the infected travellers, which one is prepared to identify as `acceptable risk'. The analysis suggests that a maximal $5~\%$ risk (of new infections originating from subjects who become infective after their quarantine is lifted) may be associated with a minimal quarantine duration of about eight days, $1~\%$ with about twelve, and $0.1~\%$ with about sixteen. Unless the distribution of the duration of short (typically, up to three weeks) travels departs significantly from the shape assumed in this study, the results of the present analysis do not provide support for the plans to shorten the quarantine duration of about ten days to two weeks, which currently applies to travellers entering most European countries from regions with a high risk of infection.

physics.soc-ph↗
arXiv2020

Comparison of results for the electromagnetic form factors of the proton at low $Q^2$

The goal in this work is the comparison of five parameterisations of the Sachs form factors of the proton $G^p_E$ (electric) and $G^p_M$ (magnetic) at low $4$-momentum transfer $Q^2$. It will be shown that a simple model, based on two dipoles which admit as parameters the rms electric charge radius $r_{E;p}$ and the rms magnetic radius $r_{M;p}$ of the proton, suffices for the purposes of the phase-shift analyses (PSAs) of the low-energy pion-nucleon ($πN$) data. The replacement of the electromagnetic form factors, currently used in the ETH model of the $πN$ interaction, by the parameterisation of this work will enable the removal from the PSAs of this research programme of the largest part of the dependence on extraneous sources.

hep-ph↗
arXiv2020

Determination of the masses and decay widths of the well-established $s$ and $p$ baryon resonances below $2$ GeV

This study appertains to the extraction of estimates for the masses and for the partial decay widths to pion-nucleon final states of the well-established (four-star) $s$ and $p$ baryon resonances below $2$ GeV. These estimates are exclusively obtained from the data contained in the recent compilation by the Particle Data Group. Only the $N$ ($S=0,I=1/2$) and the $Δ$ ($S=0,I=3/2$) states are considered, where $S$ and $I$ denote strangeness and total isospin, respectively.

hep-ph↗
arXiv2020

Proposals for the test of the isospin invariance in the pion-nucleon interaction at low energy

This work elaborates on former remarks of ours regarding two sets of predictions for the observables of the charge-exchange reaction $π^- p \to π^0 n$ at low energy (pion laboratory kinetic energy $T \leq 100$ MeV). The first prediction is obtained via the triangle identity from the results of fits to low-energy $π^\pm p$ elastic-scattering data, whereas the second is based on the same analysis of the combined low-energy $π^+ p$ and charge-exchange databases. Assuming the integrity of the data used in our fits (i.e., the absence of significant systematic effects in the determination of the absolute normalisation of the datasets) and the insignificance of residual effects in the electromagnetic corrections, a significant difference between these two sets of predictions may be interpreted as departure from the isospin invariance in the low-energy $πN$ interaction. We examine the sensitivity of the standard low-energy observables to the effect, and identify the kinematical regions which are promising for experimental survey. Accurate experiments under the suggested conditions will differentiate between the predictions, and thus provide an independent test of the isospin invariance in the low-energy $πN$ interaction.

nucl-th↗
arXiv2019

A brief history of the pion-nucleon coupling constant

This work provides a brief history of determinations of the pion-nucleon ($πN$) coupling constant from $πN$ and $N N$ data. From robust analyses of twenty reported values of the charged-pion coupling constant, exhibiting sizeable fluctuation, the result $f_c^2 = 762.9^{+6.5}_{-6.2} \cdot 10^{-4}$ is obtained. Similar values are extracted for the other two $πN$ coupling constants, $f_0^2$ and $f_p^2$, from fewer data. The average values of the various $πN$ coupling constants, extracted in this work, suggest no splitting, in agreement with the thesis of the Nijmegen group. Additional analysis of the $f_c^2$ and $f_0^2$ values, both reported in four studies, turned to be inconclusive: one of these studies suggests that $f_0 f_c$; no significant splitting effects are observed in the other two studies. The analysis of the low-energy $πN$ data with the ETH model indicates significant splitting and, under certain conditions, it implies that $f_0>f_c$. Also discussed in the paper are the electromagnetic corrections, which need to be applied to the strong shift and to the total decay width of the ground state of pionic hydrogen in order that estimates for the hadronic $s$-wave $πN$ scattering lengths be obtained; this is a relevant subject as $f_c^2$ may be extracted from the isovector scattering length by use of the Goldberger-Miyazawa-Oehme sum rule. Regarding the removal of the electromagnetic effects in the $πN$ system at threshold, my opinion is that Theory must find a way to provide reliable and accurate corrections, matching the level of accuracy of the experimental results.

nucl-th↗
arXiv2018

Analysis of luminosity measurements of the pre-white dwarf PG 1159-035: an approach featuring a dynamical database

In a previous work, those of the luminosity measurements of the pre-white dwarf PG 1159-035 which are available online yielded estimates for the optimal embedding dimension, for the dimensionality of the phase space reconstructed from these observations, and for the maximal Lyapunov exponent $λ$: the result $λ= (9.2 \pm 1.0 ({\rm stat.}) \pm 2.7 ({\rm syst.})) \cdot 10^{-2}~Δτ^{-1}$ ($Δτ=10$ s is the sampling interval in the measurements) was obtained, suggesting that the physical processes, underlying the variation of the luminosity of PG 1159-035, are chaotic. An improved approach is employed in the present work in relation to the database of embedding vectors: instead of assigning each of the input time-series arrays either to the training or to the test set, the new approach features the creation of a dynamical database, i.e., of one which depends on the choice of the input test file. Although the size of the database is thus increased by a factor of about $2$ (compared to the previous study), the impact of this change on the important results is found to be insignificant. The estimate of this work for the maximal Lyapunov exponent ($λ= (8.9 \pm 0.7 ({\rm stat.}) \pm 1.9 ({\rm syst.})) \cdot 10^{-2}~Δτ^{-1}$) is in very good agreement with the result of the earlier study.

astro-ph.IM↗
arXiv2018

Analysis of luminosity measurements of the pre-white dwarf PG 1159-035

The study of the luminosity measurements of the pre-white dwarf PG 1159-035 has established the properties of the rich power spectrum of the detected radiation and, derived thereof, the physical properties of this celestial body. Those of the measurements which are available online are analysed in this work from a different perspective. After the measurements were band-passed, they were split into two parts (of comparable sizes), one yielding the training (learning) set (i.e., the database of embedding vectors and associated predictions), the other the test set. The optimal embedding dimension $m_0=10$ was obtained using Cao's method; this result was confirmed by an analysis of the correlation dimension. Subsequently, the extraction of the maximal Lyapunov exponent $λ$ was pursued for embedding dimensions $m$ between $3$ and $12$; results were obtained after removing the prominent undulations of the out-of-sample prediction-error arrays $S (k)$ by fitting a monotonic function to the data. The grand mean of the values, obtained for sufficient embedding dimensions ($10 \leq m \leq 12$), was: $λ= (9.2 \pm 1.0 ({\rm stat.}) \pm 2.7 ({\rm syst.})) \cdot 10^{-2}~Δτ^{-1}$, where $Δτ=10$ s is the sampling interval in the measurements. On the basis of this significantly non-zero result, it may be concluded that the physical processes, underlying the variation of the luminosity of PG 1159-035, are non-linear. The aforementioned result for $λ$ was obtained using the $L^\infty$-norm distance; a larger, yet not incompatible, result was extracted with the Euclidean ($L^2$-norm) distance.

astro-ph.IM↗