| 1. |
- Aguilar, J. A., et al.
(author)
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Triboelectric backgrounds to radio-based polar ultra-high energy neutrino (UHEN) experiments
- 2023
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In: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 145
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Journal article (peer-reviewed)abstract
- In the hopes of observing the highest-energy neutrinos (E> 1 EeV) populating the Universe, both past (RICE, AURA, ANITA) and current (RNO-G, ARIANNA, ARA and TAROGE-M) polar-sited experiments exploit the impulsive radio emission produced by neutrino interactions. In such experiments, rare single event candidates must be unambiguously identified above backgrounds. Background rejection strategies to date primarily target thermal noise fluctuations and also impulsive radio-frequency signals of anthropogenic origin. In this paper, we consider the possibility that 'fake' neutrino signals may also be generated naturally via the `triboelectric effect' This broadly describes any process in which force applied at a boundary layer results in displacement of surface charge, leading to the production of an electrostatic potential difference AV. Wind blowing over granular surfaces such as snow can induce such a potential difference, with subsequent coronal discharge. Discharges over timescales as short as nanoseconds can then lead to radio-frequency emissions at characteristic MHz-GHz frequencies. Using data from various past (RICE, AURA, SATRA, ANITA) and current (RNO G, ARIANNA and ARA) neutrino experiments, we find evidence for such backgrounds, which are generally characterized by: (a) a threshold wind velocity which likely depends on the experimental trigger criteria and layout; for the experiments considered herein, this value is typically O(10 m/s), (b) frequency spectra generally shifted to the low-end of the frequency regime to which current radio experiments are typically sensitive (100-200 MHz), (c) for the strongest background signals, an apparent preference for discharges from above-surface structures, although the presence of more isotropic, lower amplitude triboelectric discharges cannot be excluded.
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| 2. |
- Maltseva, Arina L., et al.
(author)
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Phylogeography of the closely related Littorina (Neritrema) species in the North-East Atlantic
- 2022
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In: Invertebrate Zoology. - : KMK Scientific Press. - 1812-9250 .- 1814-0815. ; 19:4, s. 404-424
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Journal article (peer-reviewed)abstract
- Phylogeographic studies of evolutionary young species co-existing over a vast geographic area can provide insights in the process of evolutionary divergence and its cohesiveness in different parts of the species ranges. The Littorina snails of the ‘saxatilis’ cryptic group diverged in near-glacial time, and tend to live in sympatry. L. saxatilis is widely distributed on both sides of the North Atlantic, while L. arcana and L. compressa are patchy distributed on the shores of Europe and Atlantic islands. The biogeographic history of the Littorina ‘saxatilis’ cryptic group is still obscure, with L. saxatilis studied much better than the other two species. We evaluated the population structure of the three ‘saxatilis’ species on the coasts of Wales, the Norwegian and the Barents seas using several genetic markers: the mitochondrial cytochrome b gene (cytb, partial, 26 haplotypes for 268 sequences), nuclear (5 microsatellite loci in 458 individuals) and whole-genome (2bRAD, 63 417 loci in 114 individuals) markers. Analyses based on the cytb and microsatellite markers showed a deep divergence between the British and the North European populations of all three species with a high genetic similarity between their sympatric populations from Wales. L. compressa had the highest differentiation from both L. arcana and L. saxatilis and demonstrated the clear population structure due to allele frequency. The degree of the genetic differentiation between sympatric L. arcana and L. saxatilis in some regions was lower than between the regions within a species. Moreover, analyses of all three types of used markers indicate that the continental populations of L. arcana include individuals with contrasting genomic profiles. Our results suggest that L. arcana and L. compressa separated from their common ancestor L. islandica after L. saxatilis. The three sibling species survived glaciation in a refugium (or refugia) on the British coasts, separated from the mainland refugium (or refugia). After the glaciation, L. compressa colonised the mainland, most likely from a single European refugium. Post-glacial continental repopulation by L. arcana could have occurred from at least two sources, with two differentiated lineages still recognisable. Further inclusion of Littorina populations from South Norway and France is needed to complete the reconstruction of biogeographic history in these three evolutionary young species of Littorina snails.
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| 3. |
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| 4. |
- Heissler, P., et al.
(author)
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Multi‑μJ harmonic emission energy from laser‑driven plasma
- 2015
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In: Applied physics. B, Lasers and optics (Print). - : Springer. - 0946-2171 .- 1432-0649. ; 118:2, s. 195-201
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Journal article (peer-reviewed)abstract
- We report on simultaneous efficiency and divergence measurements for harmonics from solid targets generated by the relativistic oscillating mirror mechanism. For a value of the normalized vector potential of aL≃1.5aL≃1.5, we demonstrate the generation of 30 μJ high-harmonic radiation in a 17±317±3 mrad divergence cone. This corresponds to a conversion efficiency of ≳≳ 10−4 in the 17–80 nm range into a well-confined beam. Presuming phase-locked harmonics, our results predict unprecedented levels of average power for a single attosecond pulse in the generated pulse train. Results of PIC simulations raise the prospect of attaining efficiencies of a few percent at higher laser intensities.
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| 5. |
- Mikhailov, V., et al.
(author)
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Measurements of electron and positron fluxes below the geomagnetic cutoff by the PAMELA magnetic spectrometer
- 2017
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In: Proceedings of Science. - : Sissa Medialab Srl.
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Conference paper (peer-reviewed)abstract
- We present a measurements of electron and positron fluxes below the geomagnetic cutoff rigidity in wide energy range from 50 MeV to several GeVs by the PAMELA magnetic spectrometer. The instrument was launched on June 15th 2006 on-board the Resurs-DK satellite on low orbit with 70 degrees inclination and altitude between 350 and 600 km. Features of spatial distributions of secondary electrons and positrons in the near Earth space, including the South Atlantic Anomaly, were investigated in terms of lifetime and geographical origin. The separation in stably trapped, long lifetime quasi-trapped, and short lifetime albedo components was performed on base of back tracing procedure in geomagnetic field. A significant difference in relative abundance of positrons with respect to electrons is seen for the stable trapped and the quasi-trapped populations what pointing out on differences in trapping mechanism of those populations.
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| 6. |
- Mikhailov, V. V., et al.
(author)
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Trapped Positrons and Electrons in the Inner Radiation Belt According to Data of the PAMELA Experiment
- 2018
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In: Physics of Atomic Nuclei. - : PLEIADES PUBLISHING INC. - 1063-7788 .- 1562-692X. ; 81:4, s. 515-519
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Journal article (peer-reviewed)abstract
- Measurements of secondary-electron and secondary-positron fluxes below the geomagnetic cutoff in near-Earth space were performed by means of the PAMELA magnetic spectrometer installed on board the Resurs-DK1 satellite launched on June 15, 2006, in an elliptical orbit of inclination 70A degrees and altitude 350 to 600 km. This spectrometer permits measuring the fluxes of electrons and positrons over a wide energy range, as well as determining their spatial distributions to a precision of about 2A degrees. A calculation of particle trajectories in the geomagnetic field makes it possible to separate electrons and positrons originating from cosmic-ray interactions in the Earth's magnetosphere. The spatial distributions of quasitrapped, trapped, and short-lived albedo positrons and electrons of energy above 70 MeV in the radiation belt were analyzed. The ratio of the electron-to-positron fluxes and the energy spectra of the electrons and positrons in question are indicative of different productionmechanisms for stably trapped and quasitrapped secondary particles.
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| 7. |
- Mikhailova, M., et al.
(author)
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Magnetic dilution of complex ferrates
- 2002
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In: Journal of Magnetism and Magnetic Materials. - 0304-8853 .- 1873-4766. ; 242, s. 741-743
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Journal article (peer-reviewed)abstract
- The magnetic and structural properties of La1+0.85yBa1-0.85yFeyAl1-yO4 (0.0056less than or equal toyless than or equal to0.088) solid solutions have been investigated to demonstrate the dependence of the valence state of iron atoms on the composition of sublattice. From the magnetic susceptibility measurements. the coexistence of Fe(II)-Fe(III) hetero valence states has been confirmed and the results showed the tendency of these atoms to form clusters.
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| 8. |
- Winkler, A., et al.
(author)
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Magnetism in Re-based ferrimagnetic double perovskites
- 2009
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 073047-
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Journal article (peer-reviewed)abstract
- We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A(2)FeReO(6) (A = Ba, Sr, Ca) by x-ray magnetic circular dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds, an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr(2)ScReO(6) proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.
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