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).

Using the de Haas-van Alphen effect to map out the closed three-dimensional Fermi surface of natural graphite

The Fermi surface of graphite has been mapped out using de Haas van Alphen (dHvA) measurements at low temperature with in-situ rotation. For tilt angles $\theta>60^{\circ}$ between the magnetic field and the c-axis, the majority electron and hole dHvA periods no longer follow the $\cos(\theta)$ behavior demonstrating that graphite has a 3 dimensional closed Fermi surface. The Fermi surface of graphite is accurately described by highly elongated ellipsoids. A comparison with the calculated Fermi surface suggests that the SWM trigonal warping parameter $\gamma_3$ is significantly larger than previously thought

Evidence for a new magnetic field scale in CeCoIn5

The Nernst coefficient of CeCoIn5 displays a distinct anomaly at H_K ~ 23 T. This feature is reminiscent of what is observed at 7.8 T in CeRu2Si2, a well-established case of metamagnetic transition. New frequencies are observed in de Haas-van Alphen oscillations when the field exceeds 23 T, which may indicate a modification of the Fermi surface at this field.Comment: submitted to Physical Review Letter

Quasi-two-dimensional Fermi surfaces of the heavy-fermion superconductor Ce2_2PdIn8_8

We report low-temperature de Haas-van Alphen (dHvA) effect measurements in magnetic fields up to 35 T of the heavy-fermion superconductor Ce$_2$PdIn$_8$. The comparison of the experimental results with band-structure calculations implies that the 4$f$ electrons are itinerant rather than localized. The cyclotron masses estimated at high field are only moderately enhanced, 8 and 14 $m_0$, but are substantially larger than the corresponding band masses. The observed angular dependence of the dHvA frequencies suggests quasi-two-dimensional Fermi surfaces in agreement with band-structure calculations. However, the deviation from ideal two dimensionality is larger than in CeCoIn$_5$, with which Ce$_2$PdIn$_8$ bears a lot of similarities. This subtle distinction accounts for the different superconducting critical temperatures of the two compounds.Comment: accepted to Phys. Rev.

Hall plateaus at magic angles in bismuth beyond the quantum limit

We present a study of the angular dependence of the resistivity tensor up to 35 T in elemental bismuth complemented by torque magnetometry measurements in a similar configuration. For at least two particular field orientations a few degrees off the trigonal axis, the Hall resistivity was found to become field-independent within experimental resolution in a finite field window corresponding to a field which is roughly three times the frequency of quantum oscillations. The Hall plateaus rapidly vanish as the field is tilted off theses magic angles. We identify two distinct particularities of these specific orientations, which may play a role in the emergence of the Hall plateaus.Comment: 5 pages, 5 figure

Reply to the Comment by S.E. Sebastian and N. Harrison

no abstract for comment

Quantum Phase Interference and Neel-Vector Tunneling in Antiferromagnetic Molecular Wheels

The antiferromagnetic molecular wheel Fe18 of eighteen exchange-coupled Fe(III) ions has been studied by measurements of the magnetic torque, the magnetization, and the inelastic neutron scattering spectra. The combined data show that the low-temperature magnetism of Fe18 is very accurately described by the Neel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory. In addition, the magnetic torque as a function of applied field exhibits oscillations that reflect the oscillations in the NVT tunnel splitting with field due to quantum phase interference.Comment: 5 pages, 4 figures, REVTEX4, to appear in PR

Anderson lattice with explicit Kondo coupling: general features and the field-induced suppression of heavy-fermion state in ferromagnetic phase

We apply the extended (statistically-consistent, SGA) Gutzwiller-type approach to the periodic Anderson model (PAM) in an applied magnetic field and in the strong correlation limit. The finite-U corrections are included systematically by transforming PAM into the form with Kondo-type interaction and residual hybridization, appearing both at the same time. This effective Hamiltonian represents the essence of \textit{Anderson-Kondo lattice model}. We show that in ferromagnetic phases the low-energy single-particle states are strongly affected by the presence of the applied magnetic field. We also find that for large values of hybridization strength the system enters the so-called \textit{locked heavy fermion state}. In this state the chemical potential lies in the majority-spin hybridization gap and as a consequence, the system evolution is insensitive to further increase of the applied field. However, for a sufficiently strong magnetic field, the system transforms from the locked state to the fully spin-polarized phase. This is accompanied by a metamagnetic transition, as well as by drastic reduction of the effective mass of quasiparticles. In particular, we observe a reduction of effective mass enhancement in the majority-spin subband by as much as 20% in the fully polarized state. The findings are consistent with experimental results for Ce$_x$La$_{1-x}$B$_6$ compounds. The mass enhancement for the spin-minority electrons may also diminish with the increasing field, unlike for the quasiparticles states in a single narrow band in the same limit of strong correlations

Uniform and staggered magnetizations induced by Dzyaloshinskii-Moriya interactions in isolated and coupled spin 1/2 dimers in a magnetic field

We investigate the interplay of Dzyaloshinskii-Moriya interactions and an external field in spin 1/2 dimers. For isolated dimers and at low field, we derive simple expressions for the staggered and uniform magnetizations which show that the orientation of the uniform magnetization can deviate significantly from that of the external field. In fact, in the limit where the ${\bf D}$ vector of the Dzyaloshinskii-Moriya interaction is parallel to the external field, the uniform magnetization actually becomes {\it perpendicular} to the field. For larger fields, we show that the staggered magnetization of an isolated dimer has a maximum close to one-half the polarization, with a large maximal value of $0.35 g\mu_B$ in the limit of very small Dzyaloshinskii-Moriya interaction. We investigate the effect of inter-dimer coupling in the context of ladders with Density Matrix Renormalization Group (DMRG) calculations and show that, as long as the values of the Dzyaloshinskii-Moriya and of the exchange interaction are compatible with respect to the development of a staggered magnetization, the simple picture that emerges for isolated dimers is also valid for weakly coupled dimers with minor modifications. The results are compared with torque measurements on Cu$_{2}$(C$_{5}$H$_{12}$N$_{2}$)$_{2}$Cl$_{4}$.Comment: 8 pages, 9 figure