ВЗАИМОДЕЙСТВИЕ СТОЛБЧАТЫХ ФУНДАМЕНТОВ С МЁРЗЛЫМ ГРУНТОМ

The frozen soils’ stress-strain state varies with time due to the internal soil rheological processes. Those processes become active within the thawing period of the active soil layer causing increase in settlement of the engineering structures’ foundations. Hence, creep processes and thawing of frozen soils should be considered when designing the transportation facilities for regions of the Far North and Siberia.The objective of the research is to develop a procedure for evaluating the variation in time of the stress-strain state of the frozen soil under the post footing of a bridge pier’s foundation considering the frozen soil creep and thawing. The interaction of the bridge pier post foundations and frozen silt-loam soil is modelled and studied. The research is based on the example of an existing overpass over the M‑56 Lena motor road situated at Amga–Samyrdah stage of Tommot–Yakutsk section of the Berkakit–Tommot–Yakutsk railway line. This overpass has piers with post foundations. The above railway line is in the area of hard frozen soils.The study focuses on changes in principal normal compressive stresses with the course of time, as well as on the frozen soil movements under the post footing. The time allotted for the above system behavior study is limited to five months. There are two design cases: a) considering the frozen soil thawing up to a depth range of 1,5 to 4 m; b) without considering the frozen soil thawing.The research has shown that the thawing of the frozen soil up to a comparatively low depth as compared to natural level results in a significant increase (by 2÷2,5 times) in the values of post foundation settlement as compared with the design case without thawing. At the same time, it was found that small values of thawing have a subtle effect on the frozen soil’s stress state under the post footing. Besides, all reviewed design cases (with / without thawing revealed that stress of the frozen soil under the post footing decreases with time (stress relaxation).Известно, что напряжённо-деформированное состояние мёрзлых грунтов изменяется во времени вследствие протекающих в них реологических процессов [1; 2]. Указанные процессы активизируются в период оттаивания деятельного слоя грунта, что приводит к увеличению осадки фундаментов искусственных сооружений. Вследствие этого учёт процессов ползучести и оттаивания мёрзлых грунтов является важной задачей при проектировании транспортных конструкций в районах Крайнего Севера и Сибири.Целью исследования является развитие методики оценки изменения во времени напряжённо-деформированного состояния в мёрзлом грунте под подошвой столба фундамента мостовой опоры c учётом ползучести и оттаивания мёрзлого грунта.Моделируется и исследуется взаимодействие столбчатых фундаментов мостовых опор c пылеватым глинистым мёрзлым грунтом. Исследование проводится на примере реально существующего путепровода через автодорогу М‑56 «Лена», находящегося на перегоне Амга–Самырдах железнодорожного участка Томмот–Якутск железнодорожной линии Беркакит–Томмот–Якутск и имеющего опоры с фундаментами столбчатого типа. Указанная железнодорожная линия расположена в районе твердомёрзлых грунтов.Исследуется изменение с течением времени главных сжимающих нормальных напряжений, а также перемещений в мёрзлом грунте под подошвой столба. Отрезок времени, в течение которого исследуется поведение вышеописанной системы, ограничен пятью месяцами. Рассматриваются два расчётных варианта: а) с учётом оттаивания мёрзлого грунта на различные величины (от 1,5 м до 4 м); б) без учёта оттаиваниямёрзлого грунта.Показано, что оттаивание мёрзлого грунта даже на сравнительно небольшую величину от уровня природного рельефа приводит к существенному увеличению значений осадки столбчатого фундамента по сравнению с расчётным вариантом, когда оттаивание отсутствует (в 2÷2,5 раза). Вместе с тем установлено, что небольшие величины оттаивания оказывают малозаметное влияние на напряжённое состояние в мёрзлом грунте под подошвой столба. Кроме того, во всех рассмотренных расчётных вариантах (с учётом и без учёта оттаивания) зафиксировано снижение напряжений в мёрзлом грунте под подошвой столба с течением времени (релаксация напряжений).

Bioactive Calcium Phosphate Coatings on Metallic Implants

Biocomposites based on bioinert metals or alloys and bioactive calcium phosphate coatings are a promising tendency of the new-generation implants development. In recent years, the approach of regenerative medicine based on the use of biodegradable biomaterials has been priority direction. Such materials are capable of initiating the bone tissue regeneration and replaced by the newly formed bone. The microarc oxidation (MAO) method allows obtaining the bioactive coatings with a porous structure, special functional properties, and modified by the essential elements. During the last decade, the investigations in the field of the nanostructured biocomposites based on bioinert Ti, Zr, Nb and their alloys with a calcium phosphate coatings deposited by the MAO method have been studied in the Institute of Strength Physics and Materials Science SB RAS, Tomsk. In this article the possibility to produce the bioactive coatings with high antibacterial and osseoconductive properties due to the introduction in the coatings of Zn, Cu, Ag, La, Si elements and wollastonite CaSiO[3] was shown. The high hydrophilic and bioresorbed coatings stimulate the processes of osseointegration of the implant into the bone tissue. A promising direction in the field of the medical material science is a development of the metallic implants with good biomechanical compatibility to the bone, such as Ti-Nb alloys with a low elastic modulus that can be classified as biomaterials of the second generation. Zr and its alloys are promising materials for the dentistry and orthopedic surgery due to their high strength and corrosion resistance. Biodegradable Mg alloys are biomaterials of third generation. Such materials can dissolve with a certain speed in human body and excreted from the body thereby excluding the need for reoperation. This article presents the analysis of the study results of bioactive MAO coatings on Ti, Ti-Nb, Zr-Nb and Mg alloys and their promising medical application

Angle-dependent magnetoresistance in the weakly incoherent interlayer transport regime

We present comparative studies of the orientation effect of a strong magnetic field on the interlayer resistance of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ samples characterized by different crystal quality. We find striking differences in their behavior which is attributed to the breakdown of the coherent charge transport across the layers in the lower quality sample. In the latter case, the nonoscillating magnetoresistance background is essentially a function of only the out-of-plane field component, in contradiction to the existing theory.Comment: 4 pges, 3 figure

Low-energy electronic properties of clean CaRuO3_3: elusive Landau quasiparticles

We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a $T^2$ temperature dependence in the electrical resistivity only below 1.5 K, whose coefficient is substantially suppressed in large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with anomalously low coherence scale. Non-Fermi liquid (NFL) $T^{3/2}$ dependence is found between 2 and 25 K. The high sample quality allows access to the intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6 THz, the conductivity is Drude-like and can be modeled by FL concepts, while for higher frequencies non-Drude behavior, inconsistent with FL predictions, is found. This establishes CaRuO$_3$ as a prime example of optical NFL behavior in the THz range.Comment: 12 pages, 21 figures including supplemental materia

High-Field de Haas-van Alphen Effect in non-centrosymmetric CeCoGe3 and LaCoGe3

We report on de Haas-van Alphen effect measurements in the non-centrosymmetric systems CeCoGe3 and LaCoGe3 in magnetic field up to 28 Tesla. In both compounds, two new high frequencies were observed in high fields. The frequencies were not detected in previous lower field measurements. The frequencies do not originate from magnetic breakdown, and, therefore, are likely to be intrinsic features of the compounds. In CeCoGe3, the corresponding effective masses are strongly enhanced, being of the order of 30 bare electron masses.Comment: 3 pages, 4 figures, to be published in Proc. Int. Conf. Heavy Electrons (ICHE2010) J. Phys. Soc. Jpn. 80 (2011

Magnetic Breakdown in the electron-doped cuprate superconductor Nd2−x_{2-x}Cex_xCuO4_4: the reconstructed Fermi surface survives in the strongly overdoped regime

We report on semiclassical angle-dependent magnetoresistance oscillations (AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply-connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime. Our results suggest an intimate relation between translational symmetry breaking and the superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR

SYNTHESIS AND STRUCTURE-ACTIVITY RELATIONSHIPS OF THE NOVEL ISOTHIOBARBAMINE ANALOGUES WITH LOWERED BASICITY

This work was supported by the Russian Scientific Foundation, project № 19-13-00123

Neutron Irradiation of Mg11B2 : From the Enhancement to the Suppression of Superconducting Properties

In this letter we present the effect of neutron irradiation up to fluences of 3.9 1019 n/cm2 on the superconducting properties of MgB2. In order to obtain a disorder structure homogeneously distributed, the experiment was carried out on bulk samples prepared with the 11B isotope. Up to fluences of 1018 n/cm2 the critical temperature is slightly diminished (36 K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K. For larger neutron fluences the critical temperature is suppressed down to 12 K and the superconducting properties come out strongly degraded.Comment: 13 pages, 4 figures. Submitted to Appl.Phys.Let

Correlation between Fermi surface transformations and superconductivity in the electron-doped high-TcT_c superconductor Nd2−x_{2-x}Cex_xCuO4_4

Two critical points have been revealed in the normal-state phase diagram of the electron-doped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$ by exploring the Fermi surface properties of high quality single crystals by high-field magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas effect shows that the weak superlattice potential responsible for the Fermi surface reconstruction in the overdoped regime extrapolates to zero at the doping level $x_c = 0.175$ corresponding to the onset of superconductivity. Second, the high-field Hall coefficient exhibits a sharp drop right below optimal doping $x_{\mathrm{opt}} = 0.145$ where the superconducting transition temperature is maximum. This drop is most likely caused by the onset of long-range antiferromagnetic ordering. Thus, the superconducting dome appears to be pinned by two critical points to the normal state phase diagram.Comment: 9 pages; 7 figures; 1 tabl