21/4 Staraya Basmannaya Ulitsa
Persistent motion of passive asymmetric bodies in non-equilibrium media has been experimentally observed in a variety of settings. However, fundamental constraints on the efficiency of such motion are not fully explored. Understanding such limits, and ways to circumvent them, is important for efficient utilization of energy stored in agitated surroundings for purposes of taxis and transport. Here, we examine such issues in the context of erratic movements of a passive asymmetric dumbbell driven by non-equilibrium noise. For uncorrelated (white) noise, we find a (non-Boltzmann) joint probability distribution for the velocity and orientation, which indicates that the dumbbell preferentially moves along its symmetry axis. The dumbbell thus behaves as an Ornstein–Uhlenbeck walker, a prototype of active matter. Exploring the efficiency of this active motion, we show that in the over-damped limit, the persistence length l of the dumbbell is bound from above by half its mean size, while the propulsion speed v∥ is proportional to its inverse size. The persistence length can be increased by exploiting inertial effects beyond the over-damped regime, but this improvement always comes at the price of smaller propulsion speeds. This limitation is explained by noting that the diffusivity of a dumbbell, related to the product v∥ l, is always less than that of its components, thus severely constraining the usefulness of passive dumbbells as active particles.
We present results from applying the SNAD anomaly detection pipeline to the third public data release of the Zwicky Transient Facility (ZTF DR3). The pipeline is composed of three stages: feature extraction, search of outliers with machine learning algorithms, and anomaly identification with followup by human experts. Our analysis concentrates in three ZTF fields, comprising more than 2.25 million objects. A set of four automatic learning algorithms was used to identify 277 outliers, which were subsequently scrutinized by an expert. From these, 188 (68 per cent) were found to be bogus light curves – including effects from the image subtraction pipeline as well as overlapping between a star and a known asteroid, 66 (24 per cent) were previously reported sources whereas 23 (8 per cent) correspond to non-catalogued objects, with the two latter cases of potential scientific interest (e.g. one spectroscopically confirmed RS Canum Venaticorum star, four supernovae candidates, one red dwarf flare). Moreover, using results from the expert analysis, we were able to identify a simple bi-dimensional relation that can be used to aid filtering potentially bogus light curves in future studies. We provide a complete list of objects with potential scientific application so they can be further scrutinised by the community. These results confirm the importance of combining automatic machine learning algorithms with domain knowledge in the construction of recommendation systems for astronomy. Our code is publicly available.
Fast radio bursts (FRBs) are bright, millisecond-scale radio flashes of unknown physical origin1. Young, highly magnetized, isolated neutron stars—magnetars—have been suggested as the most promising candidates for FRB progenitors owing to their energetics and high X-ray flaring activity2,3. Here we report the detection with Konus-Wind of a hard X-ray event of 28 April 2020 temporally coincident with a bright, two-peak radio burst4,5 in the direction of Galactic magnetar SGR 1935+2154, with properties remarkably similar to those of FRBs. We show that the two peaks of the double-peaked X-ray burst coincide in time with the radio peaks and infer a common source and the association of these phenomena. An unusual hardness of the X-ray spectrum strongly distinguishes the 28 April event among multiple ‘ordinary’ flares from SGR 1935+2154. A recent non-detection5,6,7 of radio emission from about 100 typical soft bursts from SGR 1935+2154 favours the idea that bright, FRB-like magnetar signals are associated with rare, hard-spectrum X-ray bursts. The implied rate of these hard X-ray bursts (~0.04 yr−1 magnetar−1) appears consistent with the rate estimate4 of SGR 1935+2154-like radio bursts (0.007–0.04 yr−1 magnetar−1).
We investigate the coherent vortex produced by two-dimensional turbulence excited in a finite box. We establish analytically the mean velocity
profile of the vortex for the case where the bottom friction is negligible and express its characteristics via the parameters of pumping. Our
theoretical predictions are verified and confirmed by direct numerical simulations in the framework of two-dimensional weakly compressible
hydrodynamics with zero boundary conditions.
Motivated by the recent experimental observations of the DNA loop extrusion by protein motors, in this paper, we investigate the statistical properties of the growing polymer loops within the ideal chain model. The loop conformation is characterized statistically by the mean gyration radius and the pairwise contact probabilities. It turns out that a single dimensionless parameter, which is given by the ratio of the loop relaxation time over the time elapsed since the start of extrusion, controls the crossover between near-equilibrium and highly non-equilibrium asymptotics in the statistics of the extruded loop, regardless of the specific time dependence of the extrusion velocity. In addition, we show that two-sided and one-sided loop extruding motors produce the loops with almost identical properties. Our predictions are based on two rigorous semi-analytical methods accompanied by asymptotic analysis of slow and fast extrusion limits.
Magnetic nanostructures reveal unique interface induced properties that differ from those of bulk materials, thus magnetization distributions in interface regions are of high interest. Meanwhile, direct measurement of magnetization distribution in layered nanostructures is a complicated task. Here we study magnetic field induced effects in optical second harmonic generation (SHG) in three-layer ferromagnetic / heavy metals nano films. For a certain experimental geometry, which excludes the appearance of magnetooptical effects for homogeneously magnetized structures, magnetization induced SHG intensity variation is observed. Symmetry analysis of the SHG intensity dependencies on external magnetic field shows that the nonlinear source terms proportional to the out-of-plane gradient component of magnetization govern the observed effect.
We explore correlations of eigenstates around the many-body localization (MBL) transition in their dependence on the energy difference (frequency) ω and disorder W. In addition to the genuine many-body problem, XXZ spin chain in random field, we consider localization on random regular graphs that serves as a toy model of the MBL transition. Both models show a very similar behavior. On the localized side of the transition, the eigenstate correlation function β(ω) shows a power-law enhancement of correlations with lowering ω; the corresponding exponent depends on W. The correlation between adjacent-in-energy eigenstates exhibits a maximum at the transition point W_c, visualizing the drift of W_c with increasing system size towards its thermodynamic-limit value. The correlation function β(ω) is related, via Fourier transformation, to the Hilbert-space return probability. We discuss measurement of such (and related) eigenstate correlation functionson state-of-the-art quantum computers and simulators.
The role of magnetic field decay in normal radio pulsars is still debated. In this paper, we present results which demonstrate that an episode of magnetic field decay in hot young neutron stars can explain anomalous values of braking indices recently measured for more than a dozen of sources. It is enough to have few tens of per cent of such hot neutron stars in the total population to explain observables. Relatively rapid decay operates at ages ≲ few ×100 kyrs with a characteristic timescale of a similar value. We speculate that this decay can be related to electron scattering off phonons in neutron star crusts. This type of decay saturates as a neutron star cools down. Later on, a much slower decay due to crustal impurities dominates. Finally, we demonstrate that this result is in agreement with our early studies.
Recent progress in observational astronomy and astrophysics has stimulated the intensive laboratory studies aimed at elucidation of the mechanisms of evolution of molecular matter in interstellar space and various space objects. One of the most intriguing and rapidly developing areas of these studies is the so-called "cold astrochemistry" devoted to the complex processes occurring in astrophysical ices. In this context, the matrix isolation technique (known for decades) is a very useful approach for both interpretings the results of astrophysical observations and verifying possible mechanisms of key astrochemical processes. This review outlines the most important results of recent studies using matrix isolation technique, which contribute to the solution of the problems of "cold astrochemistry" in two main aspects: (i) spectroscopy of astrochemical important molecules, ions and radicals stabilized in cryogenic matrices; (ii) experimental modeling of mechanisms of radiation-induced and "in dark" chemical reactions occurring in "cold" space environments (interstellar, cometary and planetary ices). In the first aspect, special attention is paid to new spectroscopic data obtained using various methods (electronic and vibrational absorption spectroscopy, electronic paramagnetic resonance spectroscopy). In the second aspect, we consider the chemical effects resulting from both direct excitation of isolated molecules and the transfer of energy initially absorbed by the medium. Special attention is paid to recent studies of spectroscopic characteristics and radiation-induced evolution of matrix-isolated weak intermolecular complexes, which can be considered as "building blocks" for the cold synthesis of complex molecules in the absence of diffusion mobility. In addition, we consider the use of matrix isolation for the studies of low-temperature chemical reactions "in dark" involving atoms and highly reactive intermediates, which can occur in cold space environments. In the final part, we briefly discuss the applicability of the results of matrix isolation experiments for interpretation of the mechanisms in molecular ices and highlight the prospects of this field. The review can also be useful for the specialists in various aspects of chemistry and chemical physics (radiation chemistry, photochemistry, molecular spectroscopy, low-temperature chemistry).
The bibliography includes 379 references.
We propose a novel type of photonic-crystal (PC) based nanostructures for efficient and tunable optically-induced spin current generation via the Spin Seebeck and inverse spin Hall effects. It is experimentally demonstrated that optical surface modes localized at the PC surface covered by ferromagnetic layer and materials with giant spin-orbit coupling (SOC) notably increase the efficiency of the optically-induced spin current generation and provides its tunability by modifying light wavelength or angle of incidence. Up to 100% of the incident light power can be transferred to heat within the SOC layer and, therefore, to spin current. Importantly, high efficiency becomes accessible even for ultra-thin SOC layers. Moreover, surface patterning of the PC-based spintronic nanostructure allows local generation of spin currents at the pattern scales rather than diameter of the laser beam.
We use a traditional surface science approach to create and study an atomically thin NiI2 film (a promising two-dimensional ferromagnetic material) formed on nickel substrate as a result of molecular iodine adsorption. The I/Ni(100) system was examined with scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and density functional theory calculations. We found out that the iodine adsorption on Ni(100) at 300 K leads to the formation of non-equilibrium phases, whereas the adsorption at elevated temperature (≥390 K) gives rise to the thermodynamically stable phases. In both cases, a simple p(2 × 2) structure is formed at 0.25 ML. As more iodine is adsorbed at 300 K, the p(2 × 2) phase is replaced by the small coexisting domains of c(3 × 2) and c(6 × 2) phases both corresponding to the coverage of 0.33 ML, while adsorption at elevated temperature results in the formation of only one c(3 × 2) phase. At further iodine adsorption the c(3 × 2) phase transforms into the c(5 × 2) one, while the c(6 × 2) phase – into the (√10×√10)R18°(√10×√10)R18° one both corresponding to the coverage of 0.40 ML. In addition to simple chemisorbed phases, a new shifted-row reconstruction of Ni(100) induced by iodine adsorption was discovered. At coverages exceeding 0.40 ML, we observed complex LEED patterns and superstructures in STM and assigned them to specific surface reconstructions. We also found that prolonged iodine dosing leads to the nucleation of nickel iodide islands and the growth of a 2D atomically thin iodide film partially exfoliated from the substrate.
A new method of surface plasmon waves excitation based on the photoluminescence of a nanostructured metal
surface is proposed. The method was demonstrated using a plasmonic crystal formed by an array of nanoholes
in 200 nm thick Ag film (supporting SPP resonances) covered by a 10 nm thin Au layer (for efficient excitation
of photo-induced luminescence). It was shown that using this method it is possible: (i) to excite SPP waves in
ultra-large spectral range, (ii) to measure plasmonic crystal optical properties, (iii) to measure optical characteristics
of the SPP waves.
We introduce a simple physical picture to explain the process of molecular sorting, whereby specific
proteins are concentrated and distilled into submicrometric lipid vesicles in eukaryotic cells. To this
purpose, we formulate a model based on the coupling of spontaneous molecular aggregation with vesicle
nucleation. Its implications are studied by means of a phenomenological theory describing the diffusion of
molecules toward multiple sorting centers that grow due to molecule absorption and are extracted when
they reach a sufficiently large size. The predictions of the theory are compared with numerical simulations
of a lattice-gas realization of the model and with experimental observations. The efficiency of the
distillation process is found to be optimal for intermediate aggregation rates, where the density of sorted
molecules is minimal and the process obeys simple scaling laws. Quantitative measures of endocytic
sorting performed in primary endothelial cells are compatible with the hypothesis that these optimal
conditions are realized in living cells.
The nitrogen containing molecules of general structure C3HxN are important astrochemical species, which occur in interstellar and other extraterrestrial media. In this work, we have first demonstrated the formation of a number of nitriles and isonitriles (C2H3CN, C2H3NC and C2H5NC) through a direct radiation-induced synthesis from the matrix isolated intermolecular complexes HCN…C2Hn (n = 2, 4, 6) at 6 K. The deposited matrices Ng/HCN/C2Hn (Ng = Ar, Kr or Xe) were irradiated with X-rays and the formation of products was monitored by FTIR spectroscopy. In addition to synthetic products (C3HxN molecules), irradiation results in dehydrogenation of the initial complexes and their isomerization to the corresponding HNC…C2Hn complexes. The formation of propionitrile (C2H5CN) also cannot be excluded, although this molecule was not detected experimentally, possibly due to its poor IR absorption coefficients. Cyanoacetylene (HC3N) is accumulated with an induction period and becomes predominating at high absorbed doses, which points to its formation from the radiation-induced decomposition of the primary products. The obtained results suggest new possible routes for formation of nitriles, isonitriles and cyanoacetylene in complex astrochemical ices.
The development of modulational instability involving dust acoustic perturbations in dusty ionospheric plasma and in dusty plasmas of meteor tails in Earth’s ionosphere was considered. The effect of collisions of electrons, ions, and dust grains with neutrals at different altitudes was estimated. It is shown that, in this case, the influence of collisions of electrons and ions with neutrals is usually less significant than the influence of collisions between dust grains and neutrals. It is demonstrated that the effect of the modulational instability on the propagation of electromagnetic waves in the dusty ionospheric plasma is the most significant at heights of 100-120 km. The values of the wave vectors of the electromagnetic pump wave at which inelastic collisions with neutrals are important for the development of modulational interaction are calculated. The modulational interaction in the dusty ionosphere is important for the explanation of different phenomena such as ground-based observations of low-frequency ionospheric radio noises with frequencies below 60 Hz. The absence of observations of low-frequency ionospheric radio noise during such phenomena as noctilucent clouds and polar mesosphere summer echoes caused by the presence of dusty plasmas at heights of 80-95 km is explained by suppression of the development of the modulational instability at these heights. The role of inelastic collisions with neutrals in meteor tails is also discussed. It is shown that for typical parameters of dusty plasmas of meteor tails such collisions do not influence the development of the modulation instability in meteor tails.
We investigate the prospects of the Spectrum-Roentgen-Gamma (SRG) mission in search for the keV-scale mass sterile neutrino dark matter radiatively decaying into active neutrinos and photons. The ongoing all-sky x-ray survey of the SRG space observatory with data acquired by the ART-XC and eROSITA telescopes can provide a possibility to fully explore the resonant production mechanism of the dark matter sterile neutrino, which exploits the lepton asymmetry in the primordial plasma consistent with cosmological limits from the big bang nucleosynthesis. In particular, it is shown that at the end of the four year all-sky survey, the sensitivity of the eROSITA telescope near the 3.5 keV line signal reported earlier can be comparable to that of the XMM-Newton with all collected data, which will allow one to carry out another independent study of the possible sterile neutrino decay signal in this area. In the energy range below ≈2.4 keV , the expected constraints on the model parameters can be significantly stronger than those obtained with the XMM-Newton. From the ART-XC data, in the energy range approximately from 5 to 20 keV, it can be possible to get more stringent constraints than those obtained with NuSTAR so far. We conclude that the SRG mission has a very high potential in testing the sterile neutrino dark matter hypothesis.
In the middle of the last century, it was demonstrated that with a decrease in the size of superconducting
structures, for example, the thickness of a thin film, its critical temperature Tc shifts by a certain amount.
It increases in aluminum, tin, and indium, and decreases in mercury, niobium and lead. However, there is
still no generally accepted theory explaining this effect. In the 70s, during the largest volume of research
on this topic, V.L. Ginzburg assumed that the transition temperature of a sufficiently pure, monoatomic
superconductor film will be exactly the same as in a bulk body. However, this assumption has not been
verified, and the question of the nature of this effect is still open. For the study, we chose aluminum, due
to the fact that the dependence of Tc of the film on its thickness is very predictable and increases with
decreasing size. Despite a number of works on the study of this dependence in aluminum, it is not always
possible to accurately establish a correspondence with the theory. This is because characteristics vary
from sample to sample, even made in the same batch. In our case, polycrystalline films were prepared, the
crystallite sizes in which are comparable to the film thickness, and epitaxial samples with an atomically
smooth surface. The films were fabricated by electron-beam deposition and molecular-beam epitaxy on
various substrates. Within the BCS model, the critical temperature of the superconducting transition
exponentially depends on the density of electronic states at the Fermi level N (EF) and the electron-
phonon interaction constant V: TC ~ exp (-1 / N (EF)) * V. It is shown in this work that, due to QSE in
thin superconducting films, both parameters N (EF) and V change nonmonotonically with the sample
thickness. This behavior is a consequence of form resonance theory. Presumably, the effect caused by the
disordering of crystallites, as well as by the surface or substrate, does not have a dominant role
specifically in our case, since the aluminum films are of high quality, and their thicknesses go far beyond
the limits of ultrathin objects, in which surface phenomena begin to play a decisive role. As a result of
this study, the experimental and theoretical dependences of TC on the thickness of films prepared by
different methods on different substrates were obtained.
We present a five-dimensional intermolecular potential energy surface (PES) of the NH3–N2 complex, bound state calculations, and new microwave (MW) measurements that provide information on the structure of this complex and a critical test of the potential. Ab initio calculations were carried out using the explicitly correlated coupled cluster [CCSD(T)-F12a] approach with the augmented correlation-consistent aug-cc-pVTZ basis set. The global minimum of the PES corresponds to a configuration in which the angle between the NH3 symmetry axis and the intermolecular axis is 58.7○ with the N atom of the NH3 unit closest to the N2 unit, which is nearly parallel to the NH3 symmetry axis.
The intermolecular distance is 7.01 a0, and the binding energy De is 250.6 cm–1. The bound rovibrational levels of the four nuclear spin isomers of the complex, which are formed when ortho/para (o/p)-NH3 combines with (o/p)-N2, were calculated on this intermolecular potential surface. The computed dissociation energies D0 are 144.91 cm−1, 146.50 cm−1, 152.29 cm−1, and 154.64 cm−1 for (o)-NH3–(o)-N2, (o)-NH3–(p)-N2, (p)-NH3–(o)-N2, and (p)-NH3–(p)-N2, respectively. Guided by these calculations, the pure rotational transitions of the NH3–N2 van der Waals complex were observed in the frequency range of 13–27 GHz using the chirped-pulse Fourier-transform MW technique. A complicated hyperfine structure due to three quadrupole 14N nuclei was partly resolved and examined for all four nuclear spin isomers of the complex. Newly obtained data definitively established the K values (the projection of the angular momentum J on the intermolecular axis) for the lowest states of the different NH3–N2 nuclear spin isomers.
We compute the absolute Poisson’s ratio and the bending rigidity exponent of a free-standing two-dimensional crystalline membrane embedded into a space of large dimensionality , . We demonstrate that, in the regime of anomalous Hooke’s law, the absolute Poisson’s ratio approaches material independent value determined solely by the spatial dimensionality : where . Also, we find the following expression for the exponent of the bending rigidity: . These results cannot be captured by self-consistent screening approximation.
Highly pure, organic, crystalline materials with nonlinear optical (NLO) properties are in great demand due to their potential to be utilized in miniaturized nanophotonic device applications. Perylene dye is one of the celebrated near‐direct bandgap NLO materials. It crystallizes in two distinctive polymorphic forms (square‐shaped, α, and rhombus‐shaped, β) emitting yellow and green fluorescence, respectively. However, selective access to any one of the polymorphic microcrystals possessing qualities such as smooth‐surface and mirror‐like light‐reflecting sharp edges is a challenging task. On the other hand, these qualities are indispensable for a microcrystal to operate as an optical cavity. Here, a cost‐effective and straightforward, yet promising sublimation technique to grow microscale perylene crystals with the above qualities in a polymorph‐selective manner at ambient pressure is presented. As a result, both polymorphic microcrystals act as whispering gallery mode (WGM) cavities in the linear and notably, NLO regime as well. In agreement with the experiments, finite difference time domain numerical calculations support the WGM‐cavity‐type and also reveal the intricate localization of electric‐field within these cavities. Further, the quadratic dependence of emission intensity as a function of laser power establishes the two‐photon absorption nature of the optical cavities pumped by infrared lasers.
Effect of cryogenic treatment on amorphous phase rejuvenation in Al-based alloys was studied by X-ray diffraction,
transmission and high-resolution electron microscopy. It was established that cryogenic cycling may
lead to amorphization of nanocrystalline regions and amorphous phase rejuvenation in partially crystalline
samples. The composition of nanocrystals in the investigated samples differed from that of amorphous phase,
therefore, the process of amorphization under cryogenic cycling was accompinied by mass transfer. A degree of
amorphization depends on the duration of cryogenic cycling and increases with an increase in its duration.
Amorphization of a partially crystalline structure under cryogenic cycling is observed for nanocrystals formed
under both heat treatment and deformation.