Identification of Icelandic tephras from the last two millennia in the White Sea region (Vodoprovodnoe peat bog,northwestern Russia)     

Polina Vakhrameeva  Maxim Portnyagin  Vera Ponomareva  Peter M. Abbott  Tatiana Repkina  Anna Novikova  Andreas Koutsodendris  Jörg Pross 《第四纪科学杂志》2020,35(4):493-504

The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.  相似文献   

Primordial black holes     

Maxim Yu. Khlopov 《天体物理学报》2010,(6):495-528

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Anthropogenic pollution stimulates oxidative stress in soft tissues of mussel <Emphasis Type="Italic">Crenomytilus grayanus</Emphasis> (Dunker1853)     

Nina N. Belcheva  Maxim V. Zakhartsev  Nadezhda V. Dovzhenko  Avianna F. Zhukovskaya  Victor Ya. Kavun  Victor P. Chelomin 《Ocean Science Journal》2011,46(2):85-94

The digestive gland and gills of the mussel Crenomytilus grayanus extracted from three locations — (i) sampled from a clean and (ii) polluted site and (iii) transplanted from the nonpolluted to polluted site - were analysed for antioxidant enzymes (superoxide dismutase, catalase, glutathione reductase), total oxyradical scavenging capacity and levels of lipid peroxidation products (malondialdehyde, conjugated dienes and lipofuscin). Perturbation of redox status was found in both digestive gland and gill tissues of mussels living in the polluted area. As the activities of superoxide dismutase and catalase were 1.2–3 times higher, the total oxyradical scavenging capacity was lower by 20–35% and the levels of lipid peroxidation products were 2–7 times higher compared to mussels from the reference site. In transplanted mussels, the lipid peroxidation process in both tissues was significantly stimulated (the level of conjugated dienes was increased 1.7–2.5-fold; malondialdehyde and lipofuscin contents were increased 3.5–5-fold) and the total oxyradical scavenging capacity fell by 50–70%. In addition, the transplantation generally resulted in transient and variable responses of antioxidant enzymes for both tissues. Complex response-behaviour of the antioxidant enzymes strongly points to the necessity of employing a combined approach that takes into account activities of antioxidant enzymes and the total oxyradical scavenging capacity, as well as measurement of oxidative damage (e.g., lipid peroxidation) to evaluate the physiological health of molluscs.  相似文献   

Self-interacting dark matter from the hidden heterotic-string sector     

Alon E. Faraggi  Maxim Pospelov 《Astroparticle Physics》2002,16(4):39-461

It has been suggested recently that self-interacting dark matter (SIDM) fits better the observational characteristics of galaxy dynamics. We propose that the SIDM is composed from the glueballs of the hidden sector non-Abelian gauge group, while the hidden matter states exist in vector-like representation and decouple from the light spectrum. It is shown that these glueballs are semi-stable with the lifetime larger than the present age of the Universe, if their mass is 1 GeV or less. The constraint on their abundance today suggests that the energy was stored in the hidden sector soon after inflation. This imposes an upper limit on the reheating temperature. We further study the naturalness of this scenario in the context of the free-fermionic string models and point out a class of such models where the SIDM from the hidden sector is indeed plausible.  相似文献   

Explosive reconnection in magnetars     

Maxim Lyutikov 《Monthly notices of the Royal Astronomical Society》2003,346(2):540-554

The X-ray activity of anomalous X-ray pulsars and soft γ-ray repeaters may result from the heating of their magnetic corona by direct currents dissipated by magnetic reconnection. We investigate the possibility that X-ray flares and bursts observed from anomalous X-ray pulsars and soft γ-ray repeaters result from magnetospheric reconnection events initiated by development of the tearing mode in magnetically dominated relativistic plasma. We formulate equations of resistive force-free electrodynamics, discuss the relation of the latter to ideal electrodynamics, and give examples of both ideal and resistive equilibria. Resistive force-free current layers are unstable towards the development of small-scale current sheets where resistive effects become important. Thin current sheets are found to be unstable due to the development of the resistive force-free tearing mode. The growth rate of the tearing mode is intermediate between the short Alfvén time-scale  τ_A  and a long resistive time-scale  τ_R: Γ∼ 1/(τ_Rτ_A)^1/2  , similar to the case of non-relativistic non-force-free plasma. We propose that growth of the tearing mode is related to the typical rise time of flares, ∼10 ms. Finally, we discuss how reconnection may explain other magnetar phenomena and ways to test the model.  相似文献   

Optical layouts of the WSO-UV spectrographs     

Vladimir Panchuk  Maxim Yushkin  Timur Fatkhullin  Mikhail Sachkov 《Astrophysics and Space Science》2014,353(1):163-168

Electron acoustic blow up solitary waves and periodic waves are studied in a classical unmagnetized plasma containing cold electron fluid, kappa distributed hot electrons and stationary ions. We obtain Korteweg-de Vries (KdV) equation for electron acoustic waves (EAWs) using the reductive perturbation technique (RPT). Applying bifurcation theory of planar dynamical systems to the obtained KdV equation, we prove the existence of electron acoustic blowup solitary and periodic wave solutions. Depending on different physical parameters, two types of exact explicit solutions of the mentioned waves are derived. Our model may be applied to explain blow up solitary and periodic wave features that may occur in the planetary magnetosphere and the plasma sheet boundary layer.  相似文献   

Magnetic acceleration of relativistic active galactic nucleus jets     

Serguei S. Komissarov  Maxim V. Barkov  Nektarios Vlahakis  Arieh Königl 《Monthly notices of the Royal Astronomical Society》2007,380(1):51-70

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Our distorted view of magnetars: application of the resonant cyclotron scattering model     

Nanda Rea  Silvia Zane  Maxim Lyutikov  Roberto Turolla 《Astrophysics and Space Science》2007,308(1-4):61-65

The X-ray spectra of the magnetar candidates are customarily fitted with an empirical, two component model: an absorbed blackbody and a power-law. However, the physical interpretation of these two spectral components is rarely discussed. It has been recently proposed that the presence of a hot plasma in the magnetosphere of highly magnetized neutron stars might distort, through efficient resonant cyclotron scattering, the thermal emission from the neutron star surface, resulting in production of non-thermal spectra. Here we discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC implementation, as well as preliminary results of its application to Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters. N.R. is supported by an NWO Post-Doctoral Fellowship. S.Z. thanks the Particle Physics and Astronomy Research Council, PPARC, for support through an Advanced Fellowship.  相似文献   

Magnetar-energized supernova explosions and gamma-ray burst jets     

Serguei S. Komissarov  Maxim V. Barkov 《Monthly notices of the Royal Astronomical Society》2007,382(3):1029-1040

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An X-ray absorption spectroscopy study of Cd binding onto bacterial consortia     

Bhoopesh Mishra  Maxim I. Boyanov  Shelly D. Kelly  Robert Nerenberg  Jeremy B. Fein 《Geochimica et cosmochimica acta》2009,73(15):4311-6719

In this study, we use extended X-ray absorption fine structure (EXAFS) spectroscopy measurements to examine the atomic environment of Cd bound onto two experimental bacterial consortia: one grown from river water, and one grown from a manufacturing gas plant site. The experiments were conducted as a function of pH and demonstrate that the complex mixtures of bacteria, containing both Gram-positive and Gram-negative species, yield relatively simple EXAFS spectra, a result which indicates that only a limited number of functional group types contribute to Cd binding for each bacterial consortium. The EXAFS spectra indicate that the average Cd binding environment in the river water consortium varies significantly with pH, but the manufacturing gas plant consortium exhibits a Cd binding environment that remains relatively constant over the pH range examined. The EXAFS data for the river water consortium were modeled using carboxyl, phosphoryl and sulfhydryl sites. However, only carboxyl and phosphoryl sites were required to model the manufacturing gas plant consortium data under similar experimental conditions. This is the first EXAFS study to identify and quantify the relative importance of metal binding sites in bacterial consortia. Although our results indicate differences in the binding environments of the two consortia, the data suggest that there are broad similarities in the binding environments present on a wide range of bacterial cell walls.  相似文献