Microscopic theory of spin-orbit torques and skyrmion dynamics

We formulate a general microscopic approach to spin-orbit torques in thin ferromagnet/heavy-metal bilayers in linear response to electric current or electric field. The microscopic theory we develop avoids the notion of spin currents and spin-Hall effect. Instead, the torques are directly related to a local spin polarization of conduction electrons, which is computed from generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one correspondence between polarization susceptibility tensor components and different torque terms in the Landau-Lifshitz-Gilbert equation for magnetization dynamics. The spin-orbit torques arising from Rashba or Dresselhaus type of spin-orbit interaction are shown to have different symmetries. We analyze these spin-orbit torques microscopically for a generic electron model in the presence of an arbitrary smooth magnetic texture. For a model with spin-independent disorder we find a major cancelation of the torques. In this case the only remaining torque corresponds to the magnetization-independent Edelstein effect. Furthermore, our results are applied to analyze the dynamics of a Skyrmion under the action of electric current.Comment: 13 pages, 4 figure

Beyond skyrmions: Review and perspectives of alternative magnetic quasiparticles

Magnetic skyrmions have attracted enormous research interest since their discovery a decade ago. The non-trivial real-space topology of these nano-whirls leads to fundamentally interesting and technologically relevant consequences — the skyrmion Hall effect of the texture and the topological Hall effect of the electrons. Furthermore, it grants skyrmions in a ferromagnetic surrounding great stability even at small sizes, making skyrmions aspirants to become the carriers of information in the future. Still, the utilization of skyrmions in spintronic devices has not been achieved yet, among other reasons, due to shortcomings in their current-driven motion. In this review, we present recent trends in the field of topological spin textures that go beyond skyrmions. The majority of these objects can be considered a combination of multiple subparticles, such as the bimeron, or the skyrmion analogues in different magnetic surroundings, such as antiferromagnetic skyrmions, as well as three-dimensional generalizations, such as hopfions. We classify the alternative magnetic quasiparticles – some of them observed experimentally, others theoretical predictions – and present the most relevant and auspicious advantages of this emerging field

River Discharge

In 2014, combined discharge from the eight largest Arctic rivers (2,487 km3) was 10% greater than average discharge for the period 1980-1989. Values for 2013 (2,282 km3) and 2012 (2,240 km3) were 1% greater than and 1% less than the 1980-1989 average, respectively. For the first seven months of 2015, the combined discharge for the six largest Eurasian Arctic rivers shows that peak discharge was 10% greater and five days earlier than the 1980-1989 average for those months

Laser Conoscopy Study of Optical Anomalies in Uniaxial Crystals

New experimental possibilities of detecting fine optical anomalies in uniaxial crystals are demonstrated on a level with numerical estimation of refractive index and mechanical stress variations that cause distortions of the optical indicatrix. New possibilities are due to the use of an exact equation for isochromes derived for uniaxial crystals without mathematical simplifications commonly used by other authors. It allows one to calculate and graphically reproduce the theoretical form of isochromes of any orders in the conoscopic picture of an ideal crystal with known principal refractive indices, the thickness and orientation of the crystal surfaces, and also the wavelength of the radiation and the parameters of the optical circuit. A computer comparison of the theoretical image with an experimental conoscopic picture of a real crystal, fixed by a color digital camera on a semitransparent screen, is performed. The data on the variations of refractive indices and mechanical stresses in the crystal are retrieved from the mathematical processing of differences in the conoscopic images. The applications of the proposed method for the analysis of optical homogeneity of paratellurite and lithium niobate single crystals are presented. Keywords: method of conoscopy, isochromes, piezo-optic effec

Identification of a herbicide-resistant biotype of Echinochloa crus-galli in Ukraine

Ukraine is one of the world’s guarantors of food security and has the potential to further increase agricultural production. However, the vast majority of herbicides used on crops are acetolactate synthase (ALS) inhibitors, which poses a threat of herbicide-resistant weed species. The emergence and spread of herbicide-resistant weed biotypes can significantly increase the cost of growing crops to the point of loss of profitability. Herbicide resistance in barnyardgrass (Echinochloa crus-galli var. crus-galli) has been studied in long-term field and greenhouse experiments. Resistance of E. crus-galli to the ALS herbicide triazolopyrimidine derivative ‒ penoxsulam was identified. Expressed resistance was observed in weed plants grown from seeds collected under production conditions in Kherson region in 2015–2016 and 2020–2021. Cross resistance was observed for imidazolinone and sulfonylurea derivatives. It should be noted that the level of cross resistance to ALS herbicides was slightly higher for plants derived from weed seeds harvested in 2020–2021 compared to those harvested in 2015–2016. The introduction of a herbicidal composition of a herbicide mixture ‒ an inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD) (an enzyme in plants in the chain of carotenoid synthesis) ‒ mesotrione with an ALS-inhibitor (nicosulfuron) allowed effective control of the weed, which indicates the absence of multiple resistance to herbicides ‒ inhibitors of carotenoid synthesis. The high efficiency of E. crus-galli control was established by the application of herbicides ‒ inhibitors of fatty acid synthesis (graminicides). The highest level of efficiency in the experiments was observed with the application of fluazifop-butyl and somewhat less ‒ with pinoxaden. A tendency to reduce phytotoxicity to barnyardgrass from the south of Ukraine was observed with the introduction of tepraloxydim and quizalofop-ethyl. A lower level of phytotoxicity of fenoxaprop-p-ethyl on E. crus-galli should be noted compared to the effect of pinoxaden. No multiple resistance was observed with glyphosate (5-enolpyruvylshikimate-3-phosphate synthase inhibitor) and reglone (photosystem I inhibitor), allowing control of vegetative weeds at the beginning and end of the growing season. It has been established that monocot weed species have significantly increased their presence and harmfulness in agrophytocenoses in Ukraine and in the world since the 1950s with the widespread introduction of selective dicotyledonous species control with aryloxyphenoxyacetic, propionic and benzoic acid derivatives. This trend has been maintained until recently ‒ barnyardgrass is one of the dominant weed species in modern agrophytocenoses of Ukraine. Therefore, the identification of the ALS-resistant biotype of barnyardgrass complicates weed control in the following crops in rotations in the southern regions of the country: in maize crops with cross resistance to nicosulfuron, in sunflower ‒ to imidazolinones (imazamox, imazapyr), and also makes it impossible to use penoxsulam in rice production. Traditionally, the use of synthetic auxins, phenoxyacetic acid derivatives, etc. is used to control ALS-resistance. However, in Kherson region of Ukraine, already in the third year of application of rinskor (florpyrauxifen-benzyl), some weed plants were found on rice fields affected by ALS-resistant barnyardgrass, which recovered after the use of synthetic auxin. Therefore, the control of ALS-resistance (penoxsulam, etc.) in E. crus-galli with the application florpyrauxifen-benzyl in the Kherson region of Ukraine is already limited. An obvious and economically feasible preventive measure against the emergence of resistant weed biotypes is the implementation of GAP (Good Agricultural Practice, FAO) approaches: in particular, the use of high quality seeds without weed impurities, increasing the proportion of agrotechnical weed control measures, restoring and expanding crop rotations with mandatory rotation of herbicides with different modes of action, introducing dicotyledonous/leguminous crops into rotations, and using herbicides with different modes of action in crops separately or in mixtures. At the same time, agrotechnical measures and the preservation of biodiversity in agrophytocenoses should be the main factor in controlling resistance in weeds. The use of herbicides and their mixtures with different modes of action is of secondary importance. The identification of highly damaging ALS-resistant E. crus-galli in southern Ukraine indicates the insufficient effectiveness of weed control exclusively with herbicides with a single mechanism of action and requires a significant revision of the principles of crop rotation and ways of weed control in the country to maintain high levels of profitability and productivity of agrophytocenoses. Solving this problem is urgent for the preservation of Ukraine's potential as one of the guarantors of global food security

Assessment of the impact of the educational process on motor activity and health level of cadets of educational institutions of the ministry of internal affairs of Russia

The important components of the physical training of internal affairs officers, as well as other specialists, are the level of physical activity and quality health indicators. These components will determine the physical fitness of law enforcement specialists, not to mention the effectiveness of their duties. Graduates of general educational institution entering the educational organizations of the Ministry of Internal Affairs of Russia make the first step towards the development of the identity of a law enforcement officer. Therefore, the level of future professional knowledge, skills, and abilities, as well as competencies during their study at a higher education institution will determine the ability of a police officer to cope with his/her official dutie

Geometric Random Inner Products: A New Family of Tests for Random Number Generators

We present a new computational scheme, GRIP (Geometric Random Inner Products), for testing the quality of random number generators. The GRIP formalism utilizes geometric probability techniques to calculate the average scalar products of random vectors generated in geometric objects, such as circles and spheres. We show that these average scalar products define a family of geometric constants which can be used to evaluate the quality of random number generators. We explicitly apply the GRIP tests to several random number generators frequently used in Monte Carlo simulations, and demonstrate a new statistical property for good random number generators

Chirality inversion and radius blow-up of a N\'eel-type skyrmion by a Pearl vortex

We develop a theory for the coaxial configuration of a N\'eel-type skyrmion and a Pearl vortex in thin superconductor-chiral ferromagnetic heterostructures. Using direct numerical solution of the Euler-Lagrange equation and micromagnetic simulations we demonstrate that the inhomogeneous magnetic field of the Pearl vortex significantly modifies the skyrmion profile with respect to the one in the absence of the vortex. We discover drastic enlargement of the skyrmion's radius and inversion of the skyrmion's chirality. To unravel physics behind these effects we invent novel two-parameter ansatz for the magnetization profile of the skyrmion in the presence of the vortex. Chirality inversion and radius blow-up are controlled not only by the material parameters of the heterostructure but also by the thickness of the superconductor. Our findings can have implications for Majorana modes localized at skyrmion-vortex pairs.Comment: 6 pages, 2 figures; 1 video file and its description (as ancillary files