Considering light-matter interactions in Friedmann equations

The Friedmann equations valid for the transparent universe are modified for the universe with opacity caused by absorption of light by ambient cosmic dust in intergalactic space. The modified equations lead to a cosmological model, in which cosmic opacity produces radiation pressure that counterbalances gravitational forces. The proposed model predicts a cyclic expansion/contraction evolution of the Universe within a limited range of scale factors with no initial singularity. The maximum redshift, at which the contraction of the Universe stops, is ~14-15. The model avoids dark energy and removes some other tensions of the standard cosmological model.Comment: 10 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:1902.1052

Fault plane picking from focal mechanisms in reverse faulting stress: Application to the Mw6.9 Boumerdes (Algeria) earthquake sequence

Identification of the fault plane from two nodal planes of the focal mechanism is, in general, ambiguous. This problem is commonly solved using other constraints provided by tectonic, geological or seismic studies. In this paper, we evaluate the probability of identifying the fault plane using knowledge of stress field. We employ two alternative methods: (1) the slip angle method (SA), and (2) the highest instability method (IS). First, the efficiency of the methods was tested on synthetic data consisting of focal mechanisms compatible with a reverse stress regime. The tests revealed that the fraction of faults correctly picked by the IS method is higher than that of the SA method, particularly for large noise values. Second, the methods were applied to the aftershocks of the Boumerdes (Algeria) earthquake of May 21, 2003. This application showed that when taking into account the focal solutions for which the fault planes are determined using the IS method with a high probability, we observe consistency between the selected faults and the tectonics of the study area.The research was partially supported by Czech Science Foundation, grant no 22-10747S

Frequency‐Dependent Moment Tensors of Induced Microearthquakes

Analysis of 984 induced microearthquakes from The Geysers geothermal reservoir in California reveals that the retrieved moment tensors depend on the frequency band of the inverted waveforms. The observed dependence is more significant for the percentages of the double‐couple, compensated linear vector dipole, and isotropic (ISO) components than for the focal mechanisms. The average root‐mean‐square of the moment tensors obtained in different frequency bands is correlated with spectra of ambient noise. The percentages of double‐couple and ISO components tend to decrease and increase with the upper cutoff frequency (fu), respectively. This suggests that shear rupture radiates energy preferentially in a lower frequency band and tensile rupture in a higher frequency band. Events displaying a strong increase of the ISO with fu are confined within the same depth interval as the injection points. This might be related to the strong thermoelastic effects in the vicinity of injection points that promote opening of small cracks adjacent to the main fractures

Focal mechanisms produced by shear faulting in weakly transversely isotropic crustal rocks

ABSTRACT Shear faulting in anisotropic rocks produces non-doublecouple ͑non-DC͒ mechanisms. The non-DC mechanisms can comprise the isotropic ͑ISO͒ and compensated linear vector dipole ͑CLVD͒ components. The formulas for percentages of the ISO and CLVD are simplified under the assumption of weak transverse isotropy and can be expressed advantageously in terms of Thomsen's anisotropy parameters. Shear faulting in crustal rocks with anisotropy strength of 10% can produce an ISO of up to 10% and a CLVD of up to 30%. Such values are significant and detectable in carefully determined focal mechanisms

Fair ranking of researchers and research teams.

The main drawback of ranking of researchers by the number of papers, citations or by the Hirsch index is ignoring the problem of distributing authorship among authors in multi-author publications. So far, the single-author or multi-author publications contribute to the publication record of a researcher equally. This full counting scheme is apparently unfair and causes unjust disproportions, in particular, if ranked researchers have distinctly different collaboration profiles. These disproportions are removed by less common fractional or authorship-weighted counting schemes, which can distribute the authorship credit more properly and suppress a tendency to unjustified inflation of co-authors. The urgent need of widely adopting a fair ranking scheme in practise is exemplified by analysing citation profiles of several highly-cited astronomers and astrophysicists. While the full counting scheme often leads to completely incorrect and misleading ranking, the fractional or authorship-weighted schemes are more accurate and applicable to ranking of researchers as well as research teams. In addition, they suppress differences in ranking among scientific disciplines. These more appropriate schemes should urgently be adopted by scientific publication databases as the Web of Science (Thomson Reuters) or the Scopus (Elsevier)

Considering light-matter interactions in Friedmann equations based on the conformal FLRW metric

Introduction: Recent observations indicate that the Universe is not transparent but partially opaque due to absorption of light by ambient cosmic dust. This implies that the current cosmological model valid for the transparent universe must be modified for the opaque universe. Objectives: The paper studies a scenario of the evolution of the Universe when the cosmic opacity steeply rises with redshift, because the volume of the Universe was smaller and the cosmic dust density was higher in the previous epochs. In this case, the light-matter interactions become important, because cosmic opacity produces radiation pressure that counterbalances gravitational forces. Methods: The radiation pressure due to cosmic opacity is evaluated and incorporated into the Friedmann equations, which describe cosmic dynamics. The equations are based on the conformal FLRW metric and are consistent with observations of the cosmological redshift as well as time dilation. Using astronomical observations of basic cosmological parameters, the solution of the modified Friedmann equations is numerically modelled. Results: The presented model predicts a cyclic expansion/contraction evolution of the Universe within a limited range of scale factors with no Big Bang. The redshift of the Universe with the minimum volume is about 15–17. The model avoids dark energy and removes several fundamental tensions of the standard cosmological model. In agreement with observations, the modified Friedmann equations predict the existence of very old mature galaxies at high redshifts and they do not limit the age of stars in the Universe. The new model is consistent with theory of cosmic microwave background as thermal radiation of cosmic dust. Conclusion: The paper demonstrates that considering light-matter interactions in cosmic dynamics is crucial and can lead to new cosmological models essentially different from the currently accepted ΛCDM model

The nuclear accent instantiation in English texts read by Czech speakers

The thesis is concerned with Czech accent in English in the intonation domain, specifically the differences between nuclear melodic patterns in read speech of Czech speakers with a heavy accent and native British speakers. It is aiming to contribute to the study of "Czech" English with a later possibility of using the results in language teaching. The first part focuses on foreign accent in general together with its connection to comprehensibility and the influence of the first language. We then go through some theoretical concepts in studying intonation and their application in Czech and English intonology. In the experimental part we compare the melodic patterns of Czech and British speakers using cluster analysis. The main differences are evident in non-final utterances, where Czech speakers use mostly rising contours while British speakers more often use falling contours

A comparison of the standard <i>h</i>-index and the fractional and authorship-weighted indices for selected highly-cited astronomers and astrophysicists.

<p>Upper panel: the standard <i>h</i>-index (grey colour) and the authorship-weighted <i>h</i>_<i>W</i>-index (red colour). Lower panel: differences between the standard <i>h</i>-index and the authorship-weighted <i>h</i>_<i>W</i>-index (grey colour) and between the fractional <i>h</i>_<i>m</i>-index and the authorship-weighted <i>h</i>_<i>W</i> -index (red colour). Absolute values of the differences are shown. The lower panel indicates a good consistency between <i>h</i>_<i>m</i> and <i>h</i>_<i>W</i>.</p