Blanuša double

A snark is a non-trivial cubic graph admitting no Tait coloring. We examine the structure of the two known snarks on 18 vertices, the Blanuša graph and the Blanuša double. By showing that one is of genus 1, the other of genus 2, we obtain maps on the torus and double torus which are not 4-colorable. The Blanuša graphs appear also to be a counter example for the conjecture that the orientable genus of a dot product of n Petersen graphs is n-1 (Tinsley and Watkins, 1985). We also prove that the 6 known snarks of order 20 are all of genus 2

Quantum oscillations of the magnetic torque in the nodal-line Dirac semimetal ZrSiS

We report a study of quantum oscillations (QO) in the magnetic torque of the nodal-line Dirac semimetal ZrSiS in the magnetic fields up to 35 T and the temperature range from 40 K down to 2 K, enabling high resolution mapping of the Fermi surface (FS) topology in the $k_z=\pi$ (Z-R-A) plane of the first Brillouin zone (FBZ). It is found that the oscillatory part of the measured magnetic torque signal consists of low frequency (LF) contributions (frequencies up to 1000 T) and high frequency (HF) contributions (several clusters of frequencies from 7-22 kT). Increased resolution and angle-resolved measurements allow us to show that the high oscillation frequencies originate from magnetic breakdown (MB) orbits involving clusters of individual $\alpha$ hole and $\beta$ electron pockets from the diamond shaped FS in the Z-R-A plane. Analyzing the HF oscillations we have unequivocally shown that the QO frequency from the dog-bone shaped Fermi pocket ($\beta$ pocket) amounts $\beta=591(15)$ T. Our findings suggest that most of the frequencies in the LF part of QO can also be explained by MB orbits when intraband tunneling in the dog-bone shaped $\beta$ electron pocket is taken into account. Our results give a new understanding of the novel properties of the FS of the nodal-line Dirac semimetal ZrSiS and sister compounds

Multiband Photometry Evolution in the First Weeks of SN 2023ixf, a possible II-L Subtype Supernova

Multiband photometric observations and their evaluation to instrumental magnitudes were performed using standard Johnson-Cousins filters (B, V, Rc) as well r and g Sloan filters, and not standard ones (R, G, B, and Clear filters). These were recorded from 9 observatories and from the MicroObservatory Robotic Telescope Network. The results describe the rapid ascent towards the maximum (2.5 magnitudes about in five days in the B filter) and the slow decrease after the maximum (0.0425 +/- 0.02 magnitudes/day in the B filter). The results highlight the strong variation of the B-V colour indices during the first 50 days (from -0.20 +/- 0.02 to +0.85 +/- 0.02) and V-R (from 0 +/- 0.01 to +0.50 +/- 0.01) after the explosion, presumably corresponding to the cooling of the stellar photosphere. At 50 days after the explosion the magnitude decrease from the maximum was observed to continue where it faded by 2.5 magnitudes (B filter), thus we propose SN 2023ixf is a Type II, subtype L, supernova (SNe)

European Red List of Habitats Part 1. Marine habitats

The European Red List of Habitats provides an overview of the risk of collapse (degree of endangerment) of marine, terrestrial and freshwater habitats in the European Union (EU28) and adjacent regions (EU28+), based on a consistent set of categories and criteria, and detailed data and expert knowledge from involved countries1. A total of 257 benthic marine habitat types were assessed. In total, 19% (EU28) and 18% (EU28+) of the evaluated habitats were assessed as threatened in categories Critically Endangered, Endangered and Vulnerable. An additional 12% were Near Threatened in the EU28 and 11% in the EU28+. These figures are approximately doubled if Data Deficient habitats are excluded. The percentage of threatened habitat types differs across the regional seas. The highest proportion of threatened habitats in the EU28 was found in the Mediterranean Sea (32%), followed by the North-East Atlantic (23%), the Black Sea (13%) and then the Baltic Sea (8%). There was a similar pattern in the EU28+. The most frequently cited pressures and threats were similar across the four regional seas: pollution (eutrophication), biological resource use other than agriculture or forestry (mainly fishing but also aquaculture), natural system modifications (e.g. dredging and sea defence works), urbanisation and climate change. Even for habitats where the assessment outcome was Data Deficient, the Red List assessment process has resulted in the compilation of a substantial body of useful information to support the conservation of marine habitats