Critical Dynamics of a Two-dimensional Superfluid near a Non-Thermal Fixed Point

Critical dynamics of an ultracold Bose gas far from equilibrium is studied in two spatial dimensions. Superfluid turbulence is created by quenching the equilibrium state close to zero temperature. Instead of immediately re-thermalizing, the system approaches a meta-stable transient state, characterized as a non-thermal fixed point. A focus is set on the vortex density and vortex-antivortex correlations which characterize the evolution towards the non-thermal fixed point and the departure to final (quasi-)condensation. Two distinct power-law regimes in the vortex-density decay are found and discussed in terms of a vortex binding-unbinding transition and a kinetic description of vortex scattering. A possible relation to decaying turbulence in classical fluids is pointed out. By comparing the results to equilibrium studies of a two-dimensional Bose gas, an intuitive understanding of the location of the non-thermal fixed point in a reduced phase space is developed.Comment: 11 pages, 13 figures; PRA versio

Specific features of state regulation of operations with cryptocurrencies in the conditions of digitalization

Purpose: The article investigates specific features of state regulation of operations with cryptocurrencies in the conditions of the world economy digitalization. Design/Methodology/Approach: In order to form the state regulation of operations with cryptocurrencies, which create additional risks for the national currencies functioning in international financial and credit relations, it is necessary to consider this phenomenon first, from the position of a complete ban on the use of cryptocurrencies as a means of payment, second, in combination of a ban on the use of cryptocurrencies as means of payment, third, from the possibility of expanding the range of cryptocurrency users by including legal entities into it and fourth, the full legalization of the cryptocurrency. Findings: The authors developed and proposed a set of measures aimed at the formation of common standards and norms of state regulation of operations with cryptocurrencies in international financial relations. Practical Implications: The results of the study can be applied in the development of legal regulation of virtual currencies not only at the national level, but also at the international level. Originality/Value: The main contribution of the study is to identify possible risks in the sphere of state regulation of cryptocurrencies based on the experience of some countries: from formal permission (including recommendations on possible risks) or the application of general principles of regulation in the field of payments to the complete ban of such activities.peer-reviewe

X-ray diffraction measurements of the c-axis Debye-Waller factors of YBa2Cu3O7 and HgBa2CaCu2O6

We report the first application of x-rays to the measurement of the temperature dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of (0,0,l) peaks of YBa2Cu3O7 and HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high Tc superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through T$_c$. This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at Tc. This method in combination with measurements by other techniques will give more details concerning dynamics of the lattice.Comment: 4 pages, 2 figures. To be published in Physical Review B (Brief Report

Використання наночасток гідроксилапатиту стронцію для профілактики та лікування підвищеної стертості зубів (лабораторні дослідження)

Summary. The paper describes a method for strontium hydroxyapatite nanoparticles for the prevention and treatment of high abrasion of teeth with minimum size of the primary particles with a high degree of aggregation and the penetration of nanoparticles into the crystal lattice of the tooth enamel, which is provided by increasing the density of the enamel layer the effectiveness of treatment and prevention of high abrasion of teeth.The aim of the study – development of several derivatives of strontium salts having different structure of nanoparticles for the purpose of their further integration into the enamel layer to increase the enamel strength.Materials and Methods. On the basis of the proposed method we designed research protocol samples of teeth with increased abrasion to assess the penetration and fixation of nanoparticles on the surface of the tooth enamel. The use of the proposed method in a dental practice would improve the effectiveness of treatment and prevention of high abrasion of teeth due to inclusion in the complex treatment in the form of applications, ointments and gels.Results and Discussion. We obtained nanoparticles synthesized from strontium nitrate in the form of prisms measuring from 30 nm to 34 nm in size obtained by precipitation from strontium chloride.Conclusions. As a result of experimental research, strontium hydroxylapatite nanostructures from anion derivatives (chloride, nitrate, acetate) were discovered. Microscopic investigation showed that they consisted of plates, needles and equiaxed particles with dimensions from 19.4 to 35 nm, which is confirmed by X-ray, trace studies and microscopic studies.Резюме. В статье описан метод наночастиц гидроксилапатита стронция для предотвращения и лечения абразии зубов с минимальным размером первичных частиц высокой степени агрегации и проникновением наночастиц в кристаллическую решетку зубной эмали, которая обеспечивается увеличивая плотность эмалевого слоя, эффективность лечения и предотвращение высокой абразии зубов.Цель исследования – разработать несколько производных солей стронция, имеющих различную структуру наночастиц с целью дальнейшей интеграции их в эмалевый слой для повышения прочности эмали.Материалы и методы. На основе предложенного метода разработаны исследовательские протокольные образцы зубов с повышенной абразией для оценки проникновения и фиксации наночастиц на поверхности зубной эмали. Использование предложенного метода в стоматологической практике повысило бы эффективность лечения и профилактики высокой абразии зубов из-за включения в комплексное лечение мазей и гелей в виде приложений.Результаты исследований и их обсуждение. Мы исследовали наночастицы, синтезированные из нитрата стронция в виде призм размером от 30 нм до 34 нм, полученных осаждением из хлорида стронция. Морфология образцов изменяется в зависимости от природы производных анионов. Пластинки, иглы и равноосные частицы можна объяснить различными видами взаимодействия анионов исходных солей с гидроксилапатитом.Выводы. В результате экспериментальных исследований были обнаружены наноструктуры гидроксилапатита стронция из анионных производных (хлорид, нитрат, ацетат). Результаты микроскопических исследований показали, что они состоят из пластин, игл и равноосных частиц размером от 19,4 до 35 нм, что подтверждается рентгеновскими, следовыми и микроскопическими исследованиями.Резюме. У статті описано спосіб застосування наночастинок гідроксилапатиту стронцію для профілактики та лікування абразії зубів із мінімальним розміром первинних часток високого ступеня агрегації та проникнення наночастинок у кристалічну решітку зубної емалі, збільшуючи щільність емалевого шару, ефективність обробки та запобігання швидкій абразії зубів.Мета дослідження – розробити кілька похідних солей стронцію, що мають різну структуру наночастинок з метою подальшої інтеграції їх в емалевий шар для підвищення міцності емалі.Матеріали і методи. На основі запропонованого методу розроблено дослідницькі протоколи зразків зубів із підвищеною абразією для оцінки проникнення та фіксації наночастинок на поверхні зубної емалі. Використання запропонованого методу в стоматологічній практиці дозволить підвищити ефективність лікування і профілактики високої абразії зубів завдяки включенню в комплексне лікування мазей і гелів у вигляді аплікацій, мазей і гелів.Результати досліджень та їх обговорення. Ми дослідили наночастинки, синтезовані з нітрату стронцію у вигляді призм розміром від 30 нм до 34 нм, які отримали при осадженні хлориду стронцію. Морфологія зразків змінюється залежно від природи похідних аніонів. Пластинки, голки і рівновісні частинки можна пояснити різними видами взаємодії аніонів вихідних солей з гідроксилапатитом.Висновки. В результаті експериментальних досліджень були виявлені наноструктури стронцію гідроксилапатиту з похідних аніонів (хлорид, нітрат, ацетат). Мікроскопічні дослідження показали, що вони складаються з пластин, голок і рівноосних частинок з розмірами від 19,4 до 35 нм, що підтверджується рентгенівськими дослідженнями, дослідженнями мікроскопії та мікроскопічними дослідженнями

Thermal and Mechanical Characteristics of Polymer Composites Based on Epoxy Resin, Aluminium Nanopowders and Boric Acid

The epoxy polymers are characterized by low thermal stability and high flammability. Nanoparticles are considered to be effective fillers of polymer composites for improving their thermal and functional properties. In this work, the epoxy composites were prepared using epoxy resin ED-20, polyethylene polyamine as a hardener, aluminum nanopowder and boric acid fine powder as flame-retardant filler. The thermal characteristics of the obtained samples were studied using thermogravimetric analysis and differential scanning calorimetry. The mechanical characteristics of epoxy composites were also studied. It was found that an addition of all fillers enhances the thermal stability and mechanical characteristics of the epoxy composites. The best thermal stability showed the epoxy composite filled with boric acid. The highest flexural properties showed the epoxy composite based on the combination of boric acid and aluminum nanopowder

Neutron Resonance Spectroscopy of 117Sn from1 eV to 1.5 keV

Parity violation has been studied recently for neutron resonances in 117Sn. The neutron resonance spectroscopy is essential for the analysis of the parity violation data. We have measured neutron resonances in 117Sn for neutron energies from 1 to 1500 eV using the time-of-flight method and the (n,γ) reaction. The sample was enriched to 87.6% 117Sn. Neutron scattering and radiative widths were determined, and orbital angular momentum assignments were made with a Bayesian analysis. The s-wave and p-wave strength functions and average level spacings were determined

Parity Violation in Neutron Resonances of 117 Sn

Parity nonconservation (PNC) has been studied in neutron p-wave resonances of 117Sn. The longitudinal asymmetries were measured for 29 p-wave resonances in the neutron energy range 0.8 eV to 1100 eV. Statistically significant PNC effects were observed for four resonances. A statistical analysis determined the rms weak mixing matrix element and the weak spreading width. A weak spreading width of Γw=(0.28-0.15+0.56)×10-7 eV was obtained for117Sn

Density-induced BCS to Bose-Einstein crossover

We investigate the zero-temperature BCS to Bose-Einstein crossover at the mean-field level, by driving it with the attractive potential and the particle density.We emphasize specifically the role played by the particle density in this crossover.Three different interparticle potentials are considered for the continuum model in three spatial dimensions, while both s- and d-wave solutions are analyzed for the attractive (extended) Hubbard model on a two-dimensional square lattice. For this model the peculiar behavior of the crossover for the d-wave solution is discussed.In particular, in the strong-coupling limit when approaching half filling we evidence the occurrence of strong correlations among antiparallel-spin fermions belonging to different composite bosons, which give rise to a quasi-long-range antiferromagnetic order in this limit.Comment: 10 pages, 5 enclosed figure

Stripes in Doped Antiferromagnets: Single-Particle Spectral Weight

Recent photoemission (ARPES) experiments on cuprate superconductors provide important guidelines for a theory of electronic excitations in the stripe phase. Using a cluster perturbation theory, where short-distance effects are accounted for by exact cluster diagonalization and long-distance effects by perturbation (in the hopping), we calculate the single-particle Green's function for a striped t-J model. The data obtained quantitatively reproduce salient (ARPES-) features and may serve to rule out "bond-centered" in favor of "site-centered" stripes.Comment: final version as appeared in PRL; (c) 2000 The American Physical Society; 4 pages, 4 figure

Hole pairing and phonon dynamics in generalized 2D t−J−t-J-Holstein models

The formation of hole pairs in the planar t-J model is studied in the presence of independent {\it dynamic} vibrations of the in-plane oxygen atoms. In-plane (breathing modes) and out-of-plane (buckling modes) displacements are considered. We find strong evidences in favor of a stabilization of the two hole bound pair by out-of-plane vibrations of the in-plane oxygens. On the contrary, the breathing modes weaken the binding energy of the hole pair. These results are discussed in the context of the superconducting cuprates.Comment: 4 pages LaTeX and 6 PostScript figures in uuencoded for