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244 results on '"Tkacz, M."'

1. Superconductivity at 250 K in lanthanum hydride under high pressures

Author

Drozdov, A. P., Kong, P. P., Minkov, V. S., Besedin, S. P., Kuzovnikov, M. A., Mozaffari, S., Balicas, L., Balakirev, F., Graf, D., Prakapenka, V. B., Greenberg, E., Knyazev, D. A., Tkacz, M., and Eremets, M. I.

Subjects
Condensed Matter - Superconductivity
Abstract

The discovery of superconductivity at 203 K in H3S brought attention back to conventional superconductors whose properties can be described by the Bardeen-Cooper-Schrieffer (BCS) and the Migdal-Eliashberg theories. These theories predict that high, and even room temperature superconductivity (RTSC) is possible in metals possessing certain favorable parameters such as lattice vibrations at high frequencies. However, these general theories do not suffice to predict real superconductors. New superconducting materials can be predicted now with the aid of first principles calculations based on Density Functional Theory (DFT). In particular, the calculations suggested a new family of hydrides possessing a clathrate structure, where the host atom (Ca, Y, La) is at the center of the cage formed by hydrogen atoms. For LaH10 and YH10 superconductivity, with critical temperatures Tc ranging between 240 and 320 K is predicted at megabar pressures. Here, we report superconductivity with a record Tc ~ 250 K within the Fm-3m structure of LaH10 at a pressure P ~ 170 GPa. We proved the existence of superconductivity at 250 K through the observation of zero-resistance, isotope effect, and the decrease of Tc under an external magnetic field, which suggests an upper critical magnetic field of 120 T at zero-temperature. The pressure dependence of the transition temperatures Tc (P) has a maximum of 250-252 K at the pressure of about 170 GPa. This leap, by ~ 50 K, from the previous Tc record of 203 K indicates the real possibility of achieving RTSC (that is at 273 K) in the near future at high pressures and the perspective of conventional superconductivity at ambient pressure.

Published
2018
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10. High-Pressure Sorption of Hydrogen in Urea

Author

Tkacz M, Andrzej Katrusiak, and Fatemeh Safari

Subjects
Materials science, Hydrogen, Analytical chemistry, chemistry.chemical_element, 02 engineering and technology, 010402 general chemistry, complex mixtures, 01 natural sciences, Article, chemistry.chemical_compound, symbols.namesake, Phase (matter), Molecule, Physical and Theoretical Chemistry, Sorption, 021001 nanoscience & nanotechnology, 0104 chemical sciences, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, General Energy, chemistry, Urea, symbols, Nanodot, 0210 nano-technology, Raman spectroscopy, Stoichiometry
Abstract

Hydrogen sorption in urea C(NH2)2O has been probed by direct measurements in Sievert’s apparatus at 7.23 and 11.12 MPa as well as by Raman spectroscopy for the sample compressed and heated in a high-pressure gas-loaded diamond-anvil cell up to 14 GPa. Both these methods consistently indicate the occurrence of small nonstoichiometric sorption of hydrogen in urea phase I. The compression of urea in hydrogen affects the Raman shifts of the C–N bending mode δ and the stretching mode υs. The sorption affects the H2 vibron position too. The sorption of 1.3 × 10–2 at 11.12 MPa corresponds to a stochastic distribution of H2 molecules in channel pores of urea. The mechanism leading to this stochastic sorption involves strong correlations between the swollen nanodot regions around the pores accommodating H2 molecules and the squeezed neighboring pores too narrow to act as possible sorption sites. This study on the hydrogen-bonded framework (HOF) of urea marks the smallest pores capable of absorbing hydrogen documented so far. This observation also reveals a new class of compounds, which is located between those that absorb large stoichiometric amounts of certain guest molecules and those that do not absorb them at all, namely, the group of compounds that absorb the guests in a stochastic manner.

Published
2021
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21. HYDRATES OF METHANE AND HYDROGEN

Author

Antonov, V.E., Efimchenko, V.S., Klyamkin, S.N., Kuzovnikov, M.A., and Tkacz, M.

Subjects
Condensed Matter::Quantum Gases, Astrophysics::Earth and Planetary Astrophysics, Physics::Chemical Physics, Physics::Atmospheric and Oceanic Physics
Abstract

Gas hydrates are icelike solids composed of guest molecules or atoms of gases trapped inside the cages formed within a crystalline host framework (clathrate) of hydrogenbonded water molecules. The report will mainly be devoted to various aspects of the formation and decomposition of methane hydrates, large deposits of which are found in permafrost and under the ocean floor on the continental shelf, as well as hydrogen hydrates, the transformations of which should play a significant role in the evolution of ice satellites of giant planets.

Published
2019
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36. Trichostatin A Inhibits Rhabdomyosarcoma Proliferation and Induces Differentiation through MyomiR Reactivation.

Author

TARNOWSKI, M., TKACZ, M., KOPYTKO, P., BUJAK, J., PIOTROWSKA, K., and PAWLIK, A.

Subjects
RHABDOMYOSARCOMA, TRICHOSTATIN A, SOFT tissue tumors, GENETIC mutation, CELL proliferation
Abstract

Rhabdomyosarcoma (RMS) is a malignant tumour of soft tissues, occurring mainly in children and young adults. RMS cells derive from muscle cells, which due to mutations and epigenetic modifications have lost their ability to differentiate. Epigenetic modifications regulate expression of genes responsible for cell proliferation, maturation, differentiation and apoptosis. HDAC inhibitors suppress histone acetylation; therefore, they are a promising tool used in cancer therapy. Trichostatin A (TsA) is a pan-inhibitor of HDAC. In our study, we investigated the effect of TsA on RMS cell biology. Our findings strongly suggest that TsA inhibits RMS cell proliferation, induces cell apoptosis, and reactivates tumour cell differentiation. TsA up-regulates miR-27b expression, which is involved in the process of myogenesis. Moreover, TsA increases susceptibility of RMS cells to routinely used chemotherapeutics. In conclusion, TsA exhibits anti-cancer properties, triggers differentiation, and thereby can complement an existing spectrum of chemotherapeutics used in RMS therapy. [ABSTRACT FROM AUTHOR]

Published
2019
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37. High pressure study of changes in energy and intensity of excitations in crystalline metal glyoximes.

Author

Tkacz, M. and Drickamer, H. G.

Subjects
*ELECTRONIC excitation, *LIGANDS (Chemistry)
Abstract

The effect of high pressure has been measured on the energy and integrated intensity of electronic excitations of several layered crystals of glyoximes containing Ni, Pd, or Pt. Large changes in both energy and intensity were observed, both of which were completely reversible. The shifts in energy with pressure, are explained in terms of the relative spatial extent of the outer d and p orbitals of Ni, Pd, and Pt. The effects of back donation from the ligands and intensity borrowing from the higher energy charge transfer excitations are considered as possible causes of the observed intensity changes. It was concluded that intensity borrowing was the major cause of the observed changes. [ABSTRACT FROM AUTHOR]

Published
1986
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38. The effect of pressure on electronic excitations in TCNQ and its complexes.

Author

Tkacz, M., Jurgensen, C. W., and Drickamer, H. G.

Subjects
*SPECTRUM analysis, *ELECTRONIC structure
Abstract

The electronic spectra of TCNQ and TCNQ complexes has been investigated at high pressure up to 150 kbar. The observed pressure shifts are discussed in terms of intermolecular interactions. The results are also compared with available theoretical calculations. [ABSTRACT FROM AUTHOR]

Published
1986
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40. T–P–XPhase Diagram of the Water–Hydrogen System at Pressures up to 10 kbar

Author

Kuzovnikov, M. A. and Tkacz, M.

Abstract

The stability field of the C0hydrogen hydrate in the pressure–temperature phase diagram of the water–hydrogen system is studied by volumetry under hydrogen excess. This stability field is confined by the sII hydrate stability field at the low-pressure side; by the liquid stability field at the high-temperature side; and by the C1hydrate stability field at the high-pressure side. The pressure of the C0↔ C1phase equilibrium is temperature-independent in the studied temperature range from −20 to +18 °C. The corresponding equilibrium line in the phase diagram terminates at the nonvariant quadruple point “C0hydrate + C1hydrate + liquid H2O + H2gas” (or Q3) at 7.7(3) kbar and +22(2) °C. The volume change accompanying the C0→ C1phase transition, and the dTdPH2slopes of the melting lines of the C0and C1hydrates are measured by volumetry. Thermodynamic considerations are used to estimate the hydrogen content H2/H2O ≈ 0.53(5) and 0.23(5) of the C0and C1hydrates, respectively, near the Q3point.

Published
2019
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43. The influence of hydrogenation on superconducting properties of MgB₂

Author

Zaleski, A.J., Iwasieczko, W., Kaczorowski, D., Drulis, H., Tkacz, M., Klamut, J., and Zogal, O.J.

Subjects
Статьи, посвященные столетию со дня рождения Л. В. Шубникова
Abstract

In the paper we present the results of the ac susceptibility measurements of two newly discovered superconducting diboride - MgB₂.

Published
2001

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