Research and modeling of laser ablation by ultra-short laser pulses for metal targets

In this article an improved mathematical model for a laser metal ablation by ultra-short duration laser pulses is proposed. The model is based on two-temperature hydrodynamic model for electrons and ions and wide-range equation of state for metals. The results of the computer simulation for aluminum and copper are compared with experimental data at a different laser fluence and duration of pulses for ablation depth. A good agreement with them and the experimental data of ablation depth is received

In memory of Arkady Viktorovich Kryazhimskiy (1949-2014)

The article is devoted to the description of Academician Arkady Kryazhimskiy's life path. The facts of the scientific biography of Acad. Kryazhimskiy are presented with the emphasis on his outstanding contribution into the theory of dynamic inversion, the theory of differential games, and control theory. His personal talents in different spheres are also marked out

THE MACHINE FOR AUTOMATED PRODUCTION OF BLANKS MATERIAL MR

The article describes the design of the machine for automated production of blanks from material MR (metallic rubber). In the future, creation of this machine will allow researching the effect of blanks structure upon the properties offinished products from the material MR

Registration of high-intensity electron and x-ray fields with polycrystalline CVD diamond detectors

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Phase diagram of the Holstein polaron in one dimension

The behavior of the 1D Holstein polaron is described, with emphasis on lattice coarsening effects, by distinguishing between adiabatic and nonadiabatic contributions to the local correlations and dispersion properties. The original and unifying systematization of the crossovers between the different polaron behaviors, usually considered in the literature, is obtained in terms of quantum to classical, weak coupling to strong coupling, adiabatic to nonadiabatic, itinerant to self-trapped polarons and large to small polarons. It is argued that the relationship between various aspects of polaron states can be specified by five regimes: the weak-coupling regime, the regime of large adiabatic polarons, the regime of small adiabatic polarons, the regime of small nonadiabatic (Lang-Firsov) polarons, and the transitory regime of small pinned polarons for which the adiabatic and nonadiabatic contributions are inextricably mixed in the polaron dispersion properties. The crossovers between these five regimes are positioned in the parameter space of the Holstein Hamiltonian.Comment: 19 pages, 9 figure

Study of doubly strange systems using stored antiprotons

Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the P‾ANDA experiment at FAIR. For the first time, high resolution γ-spectroscopy of doubly strange ΛΛ-hypernuclei will be performed, thus complementing measurements of ground state decays of ΛΛ-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Ξ−-atoms will be feasible and even the production of Ω−-atoms will be within reach. The latter might open the door to the |S|=3 world in strangeness nuclear physics, by the study of the hadronic Ω−-nucleus interaction. For the first time it will be possible to study the behavior of Ξ‾+ in nuclear systems under well controlled conditions

Shift in the paradigm for GSSP boundary definition

© 2020 International Association for Gondwana Research For over 200 years the use of biotic events as the basis for the establishment of chronostratigraphic boundaries has been the only approach successfully utilized for international and national chronostratigraphy. The traditional biostratigraphic method provides relatively high resolution, averaging 1 Ma or sometimes less. This biochronological evolutionary approach to the Global Boundary Stratotype section and Point (GSSP) utilizes biotic Primary Markers (PM), with a few exceptions, encompasses the integrated PM and other non-PM markers as the general principles for defining GSSP boundaries and is a reasonably reliable mechanism for global correlation and a relatively stable International Geologic Time Scale (IGTS). The biotic PM's, however, possessed several serious restrictions: the nature of biological taxonomy, climatic, sedimentary, environmental - and directly applicable within the tropics-subtropics only. Biotic evolution and radiogenic isotopes are the only systems in geologic time that encompass the direction of time. The latter possessed less restrictions than the former. The recent tendency to define GSSP's utilizing magnetic chrons, climatic events and geochemistry may work in the Cenozoic, but is useless in the Mesozoic and older sediments because their cyclic nature (repeatedness) and the need for a second, directional in time index (biostratigraphic or radioisotopic) to place the PM in the right position within the scale. I propose here to utilize volcanic ash beds as the best Primary Marker in geologic chronostratigraphy. The U-Pb system is one of the most dependable of the geochronologic systems because it relies on a simple and non-interpretive radioisotopic decay constant. The ash-bed GSSP as a lithological horizon is universal for the GSSP definition and can be correlated as an age in any facies (marine, lagoon and continental), regardless of paleoclimatic zones, paleoceanographic, geochemical, and most other geological factors. Even moderate level metamorphism (>900 °С) does not affect the U-Pb dating of zircons. The GSSP at the base of a volcanic ash bed (Primary Marker) could be established in a short working time and these ash beds can be integrated with the existing as well as new biostratigraphic, geochemical, magnetostratigraphic and astronomical data (Secondary Markers) to create a robust, accurate and highly useable time scale. Several potential GSSP's that could be established with the volcanic ash beds close to the traditional and/or historical boundaries serve as examples for this approach and include Devonian-Carboniferous, Moscovian-Kasimovian, Kasimovian-Gzhelian, and Sakmarian-Artinskian boundaries

Tunguska сoals, Siberian sills and the Permian-Triassic extinction

The latest Permian-Triassic volcanism that created the Siberian traps, including the products of the explosion and interaction of the magmas with regional volcanic and sedimentary rocks, is now considered to be the main driving forces of the end-Permian mass extinction - the greatest global extinction in the Earth history. As proposed, the trap magmatism induced metamorphism of the sedimentary succession that released the sediment-derived CO2 from the thermogenic cracking of coal by intrusive heating. Although the coal-intrusion interaction plays a central role in this model, the coal geology in Tunguska Basin, i.e. spatial and temporal distribution of coals, coal metamorphism and specifics of the metamorphism at the contact of coals and intrusions, has never been assessed from this prospective. The overall goal of this study is to clarify the role and contribution CO2 of the Tunguska coals to the model. The study suggests that the thickness and distribution of the sills within the coal-bearing successions at most minimally influence the overall metamorphic grade of the coals in Tunguska Basin. The age of the explosion pipes that delivered CO2 into the atmosphere most probably is early Triassic to Jurassic-early Cretaceous. The low degree of metamorphism driven by the magmatism, questions estimates of the amount of sediment-derived CO2 generated that could have influenced or driven the PTB extinction. Furthermore, as a mechanism to deliver such gases to the atmosphere, the explosion pipes post-date the extinction

The Influence of the Permian-Triassic Magmatism in the Tunguska Basin, Siberia on the Regional Floristic Biota of the Permian-Triassic Transition in the Region

The end-Permian extinction event (EPEE) considered to have been caused by the eruption of the Siberian Large Igneous Province (SLIP), the age of which is critical for extinction-SLIP model evaluation. The Tunguska Basin flora during this time, in accordance with the EPEE model, supposed to have been killed by the massive injection into the atmosphere of poisonous substances such as methane, sulfates, mercury and massive combastion of coals. In addition, supposed numerous fires presumably devastated the regional flora. However, the diversity of the Tunguska Basin flora drasticly increased at the beginning of Induan or slightly earlier and become diverse at the species level in the Olenekian and Anisian, when the main phase of basalt eruption and associated intrusive activity occurred. The overall magmatic activity during the latest Permian and Early Triassic did not kill the flora, but rather stimulate their diversity. The geomagnetic secular variations from the intrusions revealed the similarity of paleomagnetic directions of the Norilsk group layered intrusions with those of the upper Olenekian and lower Anisian Mokulaev and Kharaelakh volcanic formations and intrusions of the Talnakh group with the Olenekian Moronga-Mokulaev formations. The U-Pb dates and the geomagnetic secular variations data expose the obvious discrepancy between these two datasets. The paleomagnetic data suggest that the Norilsk-1 intrusion is younger than the Talnakn and Kharaelakh intrusions, but the U-Pb dates indicate the opposite. The data from layered intrusions in Norilsk and the other regions suggest their prolonged duration and multi-stadial formation. The U-Pb dates from the intrusions of the Norilsk region roughly constrain the onset of the SLIP and generally postdate the end-Permian extinction