The triangular lattice antiferromagnet RbFe(MoO$_4$)$_2$ orders antiferromagnetically in a planar 120$^\circ$-structure below $T_\textrm{N}\approx 4$ K. A striking feature of RbFe(MoO$_4$)$_2$ magnetic phase diagram is the presence of collinear ``1/3-plateau'' magnetic phase, which is stabilized by thermal and quantum fluctuations at magnetization $M\approx \frac{1}{3} M_\textrm{sat}$. Static disorder caused by impurities is predicted to act against the effect of fluctuations and to suppress collinear plateau phase (Maryasin and Zhitomirsky, PRL 111, 247201 (2013)). Balance between ``dynamic'' thermal and quantum fluctuations and ``static'' impurity-induced disorder is temperature-sensitive, which allows thermal fluctuations to take over the effect of static disorder and leads to the revival of the fluctuation-stabilized ``1/3-plateau'' phase on heating. Here we present experimental results directly confirming this prediction and demonstrating re-establishment of the plateau-like phase in the diluted Rb$_{(1-x)}$K$_{x}$Fe(MoO$_4$)$_2$ sample at moderate dilution level $x=15$\% on heating as the effect of thermal fluctuations increases.
Convection, differential rotation, and meridional circulation of solar plasma are studied based on helioseismic data covering the period from May 2010 to August 2024, significantly prolonged compared to that previously considered. Depth variation in the spatial spectrum of convective motions indicates a superposition of differently scaled flows. The giant-cell-scale component of the velocity field demonstrates a tendency to form meridionally elongated (possibly bananashaped) structures. The integrated spectral power of the flows is anticorrelated with the solar-activity level in the near-surface layers and positively correlates with it in deeper layers. An extended 22-year cycle of zonal flows ("torsional oscillations" of the Sun) and variations of the meridional flows are traced. A secondary meridional flow observed at the epoch of the maximum of Solar Cycle 24 to be directed equatorward in the subsurface layers is clearly manifest in Cycle 25.
The linear (proportional to local vacancy concentration) term in specific resistance of the material does not directly contribute to the change of memristor's total resistance when the vacancies are redistributed inside while keeping their total number constant. But it still changes kinetics of the vacancy drift under the influence of a passing electric current. These changes are especially significant in the presence of metal-insulator phase transition in the memristor's material. In this paper, kinetic equation for local vacancy concentration is obtained, and exact solutions for its steady states are analyzed. It is shown that not only in the weakly nonlinear case (when the dependence of the specific resistance on the vacancy concentration can be neglected), but also in a strongly non-linear memristor with phase transition, its kinetics can be reduced to the classical exactly solvable Burgers equation.
Electron-electron scattering processes in a quantum well in a quantizing magnetic field are considered. A matrix of electron-electron scattering rates containing all types of transitions between Landau levels within a single subband is calculated. This matrix is analyzed, and the relative magnitude of transition rates of different types is determined.
A new method for determining the accelerating potential above the polar caps of radio pulsars with an arbitrary inclination angle of the magnetic axis to the rotation axis has been proposed. The approach has been based on the concept of a vacuum gap, the height and shape of the upper boundary of which are found self-consistently together with the solution of the corresponding Poisson equation. In turn, information about the accelerating potential has made it possible to determine the transverse profiles of the secondary plasma density. It has also been shown that the effect of inverse Compton scattering on the considered processes is insignificant.
We established exact in order estimates an approximation of the Sobolev classes $W^{\boldsymbol{r}}_{p,\boldsymbolα}(\mathbb{T}^d)$ of periodic functions of many variables with a bounded dominating mixed derivative. The approximation is made using trigonometric polynomials with the spectrum in step-hyperbolic crosses, and the error is estimated in the metric of the space $B_{q,1}(\mathbb{T}^d)$, $1 \leqslant p, q < \infty$.
The latest results of the most detailed analysis of multi-epoch polarization-sensitive observations of active galactic nuclei (AGN) jets at parsecs scales by very long baseline interferometry (VLBI) reveal several characteristic patterns of linear polarization distribution and its variability (Pushkarev et al., 2023; Zobnina et al., 2023). Some of the observed profiles can be reproduced by a simple model of a jet threaded by a helical magnetic field. However, none of the models presented to date can explain the observed polarization profiles with an increase in its degree towards the edges of the jet, and accompanied by a 'fountain' type electric vector pattern and its high temporal variability in the center. Based on simulations of the VLBI observations of relativistic jets, we show here that the observed transverse linear polarization profiles, atypical for the simple magnetic field models can be naturally produced assuming the finite resolution of VLBI arrays and precession of a jet on ten-years scales, observational indications of which are found in an increasing number of AGN. In our simulations, we qualitatively reproduce the distribution of the electric vector and its variab
By critically examining the traditional theory of homogeneous nucleation of precipitates in solid solutions, it is revealed that the theory's assertion regarding an increase in the nucleation free energy due to elastic strain associated with the difference in atomic volumes between the two phases is applicable to coherent precipitates, but becomes incorrect when applied to incoherent precipitates. This conclusion is obtained by accounting for thermal point defects in the matrix, which can be absorbed at the interface between an incoherent particle and the matrix during nucleation, thereby relieving elastic stresses. Accordingly, a new kinetic model based on the Reiss theory for binary nucleation is proposed for predicting the nucleation rate of incoherent precipitates by agglomeration of solute atoms and point defects, with a further extension to account for excess vacancies formed under non-equilibrium conditions of quenching experiments.
The fundamental quantum Coulomb problem in the momentum space is considered. A differential equation with SO(4) simmetry has been obtained in the momentum space instead of the integral Fock equation. The corresponding equation in the coordinate space is the sum of the squares of the angular momentum and the Runge-Lenz operators.This approach is unknown in the momentum space where the Runge-Lenz operator is not applied in the existing theory. The Runge-Lenz operator obtained in the momentum space is simplier than that in the coordinate space and allows one to effectively consider the Coulomb problem in the momentum space. A relation of new operator to the infinitesimal rotation operator of the three-dimensional the Fock sphere has been determined.
A Sidon set is a set of integers containing no nontrivial solutions to the equation $a+b=c+d$. We improve on the lower bound on the diameter of a Sidon set with $k$ elements: if $k$ is sufficiently large and ${\cal A}$ is a Sidon set with $k$ elements, then $diam({\cal A})\ge k^2-1.99405 k^{3/2}$. Alternatively, if $n$ is sufficiently large, then the largest subset of $\{1,2,\dots,n\}$ that is a Sidon set has cardinality at most $n^{1/2}+0.99703 n^{1/4}$. While these are only slight numerical improvements on Balogh-Füredi-Roy (arXiv:2103:15850v2), we use a method that is logically simpler.
Filyokov and Karpov [Inzhenerno-Fizicheskii Zhurnal 13, 624 (1967)] have proposed a theory of non-equilibrium steady states in direct analogy with the theory of equilibrium states : the principle is to maximize the Shannon entropy associated to the probability distribution of dynamical trajectories in the presence of constraints, including the macroscopic current of interest, via the method of Lagrange multipliers. This maximization leads directly to generalized Gibbs distribution for the probability distribution of dynamical trajectories, and to some fluctuation relation of the integrated current. The simplest stochastic dynamics where these ideas can be applied are discrete-time Markov chains, defined by transition probabilities $W_{i \to j}$ between configurations $i$ and $j$ : instead of choosing the dynamical rules $W_{i \to j} $ a priori, one determines the transition probabilities and the associate stationary state that maximize the entropy of dynamical trajectories with the other physical constraints that one wishes to impose. We give a self-contained and unified presentation of this type of approach, both for discrete-time Markov Chains and for continuous-time Master Equat
English translation of a Russian article from 1928. Translator's abstract: The article presents general considerations on the validity of the superposition principle for light in vacuo from out a quantum theoretic point of view. It contains a report on an optical experiment designed to detect the phenomenon of photon-photon scattering. To understand the negative result of the performed experiment, a consideration of the solar corona is undertaken in order to derive an empirical upper limit on the photon-photon scattering rate. Source details: S. I. Vavilov: Zamechaniya ob empiricheskoi tochnosti opticheskogo printsipa superpozitsii. Zhurnal Russkogo Fiziko-Khimicheskogo Obshchestva pri Leningradskom Universitete, Chast' Fizicheskaya [Journal of the Russian Physico-Chemical Society at Leningrad University, Physical Part], Vol. LX (1928) No. 6, pp. 555-563.
A general Kneser hypergraph ${\rm KG}^r(\mathcal{H})$ is an $r$-uniform hypergraph that somehow encodes the edge intersections of a ground hypergraph $\mathcal{H}$. The colorability defect of $\mathcal{H}$ is a combinatorial parameter providing a lower bound for the chromatic number of ${\rm KG}^r(\mathcal{H})$ which is addressed in a series of works by Dol'nikov [Sibirskii Matematicheskii Zhurnal, 1988}], Kříž [Transaction of the American Mathematical Society, 1992], and Ziegler~[Inventiones Mathematicae, 2002]. In this paper, we define a new combinatorial parameter, the equitable colorability defect of hypergraphs, which provides some common improvements of these works. Roughly speaking, we propose a new lower bound for the chromatic number of general Kneser hypergraphs which substantially improves Ziegler's lower bound. It is always as good as Ziegler's lower bound and we provide several families of hypergraphs for which the difference between these two lower bounds is arbitrary large. This specializes to a substantial improvement of the Dol'nikov-Kříž lower bound for the chromatic number of general Kneser hypergraphs as well. Furthermore, we prove a result ensuring the existenc
NASA has chosen 41 commercial technology projects that could solve critical challenges for future missions to the Moon and Mars。 From powering lunar outposts to protecting spacecraft from Moon dust, the innovations are designed to push both space exploration and the commercial space economy forward
A catastrophic asteroid breakup may have triggered a huge wave of impacts across the inner solar system about 800 million years ago。 The debris was launched from near a gravitational gateway controlled by Jupiter, sending fragments toward Earth, the Moon, and Mars。 The bombardment may explain ancient lunar craters and could have contributed to majo
Four nearby white dwarf stars have been discovered hiding in plain sight beside brighter red dwarf companions。 Hubble's ultraviolet observations finally revealed the long-hidden stellar remnants, including one just 25 light-years away that took nearly three decades to confirm。 The findings match long-standing predictions and suggest our corner of t
A giant planet had been hiding inside one of astronomy’s most closely studied planetary systems, concealed by a bright disk of cosmic dust。 Webb revealed Beta Pictoris d through atmospheric traces of carbon monoxide, water vapor, and methane, showcasing a promising new method for finding elusive exoplanets
Researchers have recreated the physics of extracting energy from a spinning black hole using a stationary device that produces synthetic ultrafast rotation。 The achievement transforms a long-standing theoretical idea into a practical experiment and could inspire new advances in optics, wireless communications, and quantum science