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We present a theoretical study of the exchange interaction in a system of spatially disordered magnetic moments. A typical example of such a system is an impurity semiconductor, whose magnetic properties are associated with the exchange interaction of the impurity atoms. In this study, we consider the case of antiferromagnetic exchange interaction, which we describe by the Heisenberg Hamiltonian. To calculate the magnetic properties of the disordered system, we employ the density of states method. Our calculations demonstrate a good quantitative agreement with the dependence of the Si:P magnetic susceptibility on temperature in a wide range of impurity concentrations and temperatures.

The kinetic stability of collisionless, sloshing beam-ion (45{\deg} pitch angle) plasma is studied in a 3D simple magnetic mirror, mimicking the Wisconsin High-temperature superconductor Axisymmetric Mirror (WHAM) experiment. The collisional Fokker-Planck code CQL3D-m provides a slowing-down beam-ion distribution to initialize the kinetic-ion/fluid-electron code Hybrid-VPIC, which then simulates free plasma decay without external heating or fueling. Over 1-10 $\mu$s, drift-cyclotron loss-cone (DCLC) modes grow and saturate in amplitude. DCLC scatters ions to a marginally-stable distribution with gas-dynamic rather than classical-mirror confinement. Sloshing ions can trap cool (low-energy) ions in an electrostatic potential well to stabilize DCLC, but DCLC itself does not scatter sloshing beam-ions into said well. Instead, cool ions must come from external sources such as charge-exchange collisions with a low-density neutral population. Manually adding cool ~1 keV ions improves beam-ion confinement ~2-5x in Hybrid-VPIC simulations, which qualitatively corroborates measurements from real mirror devices with sloshing ions., Comment: Submitted; 35 pages, 14 figures

This paper presents the Hammir tandem mirror design based on Realta Fusion's first-of-a-kind model for axisymmetric magnetic mirror fusion performance. This model uses an integrated end plug simulation model including, heating, equilibrium, and transport combined with a new formulation of the plasma operation contours (POPCONs) technique for the tandem mirror central cell. Using this model, it is shown that an end plug utilizing high temperature superconducting magnets and modern neutral beams enables a classical tandem mirror pilot plant producing a fusion gain Q > 5. The approach here represents an important advance in tandem mirror design. The high fidelity end plug model enables calculations of heating and transport in the highly non-Maxwellian end plug to be made more accurately and the central cell POPCON technique allows consideration of a wide range of parameters in the relatively simple near-Maxwellian central cell, facilitating the selection of more optimal central cell plasmas. These advances make it possible to find more conservative classical tandem mirror fusion pilot plant operating points with lower $\beta$, temperatures, neutral beam energies, and end plug performance than designs in the literature. Despite being more conservative, it is shown that these operating points can still form the basis of a viable fusion pilot plant.

The best way to check the validity of our theories (models) is by direct comparison with the experiment (observations). In this study, we address the numerical inaccuracies intrinsic to the process of comparing theory and observations. To achieve this goal, we built 4D spectra grids for Wolf-Rayet stars (WC and WN spectral classes) and Blue Supergiants (BSGs) characterized by low metallicity similar to that of the Small Magellanic Cloud (SMC). Through rigorous testing on designated `test' models, we demonstrated that the numerical precision of derived stellar parameters (effective temperature, mass-loss rate, luminosity, and wind velocity) is not exceeding 0.05 dex. Moreover, the mean absolute deviation of the numerically derived stellar parameters is consistently below this threshold for objects with both weak (SMC grid) and strong winds (WC and WN grids), even in the presence of Gaussian noise. Furthermore, we explored the influence of unaccounted factors, including variations in the metal abundances, wind acceleration laws, and clumping, on the precision of the derived parameters. We found that the first two factors have the strongest influence on the numerical accuracy of the derived stellar parameters. Variations in abundances predominantly influenced the mass-loss rate for weak-wind scenarios, while effective temperature and luminosity remained robust. We found that the wind acceleration law influence the numerical uncertainty of the derived wind parameters mostly for models with weak winds. Interestingly, different degrees of clumping demonstrated good precision for spectra with strong winds, contrasting with a decrease in the precision for weak-wind cases. We found also that the accuracy of our approach depends on spectral range and the inclusion of ultraviolet spectral range improves the precision of derived parameters, especially for object with weak winds., Comment: 28 pages, 14 figures, 4 tables

Sub-picosecond optical laser processing of metals is actively utilized for modification of a heated surface layer. But for deeper modification of different materials a laser in the hard x-ray range is required. Here, we demonstrate that a single 9-keV x-ray pulse from a free-electron laser can form a um-diameter cylindrical cavity with length of ~1 mm in LiF surrounded by shock-transformed material. The plasma-generated shock wave with TPa-level pressure results in damage, melting and polymorphic transformations of any material, including transparent and non-transparent to conventional optical lasers. Moreover, cylindrical shocks can be utilized to obtain a considerable amount of exotic high-pressure polymorphs. Pressure wave propagation in LiF, radial material flow, formation of cracks and voids are analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final structure with the long cavity. Similar results can be produced with semiconductors and ceramics, which opens a new pathway for development of laser material processing with hard x-ray pulses.

Transformer-based recommender systems, such as BERT4Rec or SASRec, achieve state-of-the-art results in sequential recommendation. However, it is challenging to use these models in production environments with catalogues of millions of items: scaling Transformers beyond a few thousand items is problematic for several reasons, including high model memory consumption and slow inference. In this respect, RecJPQ is a state-of-the-art method of reducing the models' memory consumption; RecJPQ compresses item catalogues by decomposing item IDs into a small number of shared sub-item IDs. Despite reporting the reduction of memory consumption by a factor of up to 50x, the original RecJPQ paper did not report inference efficiency improvements over the baseline Transformer-based models. Upon analysing RecJPQ's scoring algorithm, we find that its efficiency is limited by its use of score accumulators for each item, which prevents parallelisation. In contrast, LightRec (a non-sequential method that uses a similar idea of sub-ids) reported large inference efficiency improvements using an algorithm we call PQTopK. We show that it is also possible to improve RecJPQ-based models' inference efficiency using the PQTopK algorithm. In particular, we speed up RecJPQ-enhanced SASRec by a factor of 4.5 x compared to the original SASRec's inference method and by a factor of 1.56 x compared to the method implemented in RecJPQ code on a large-scale Gowalla dataset with more than a million items. Further, using simulated data, we show that PQTopK remains efficient with catalogues of up to tens of millions of items, removing one of the last obstacles to using Transformer-based models in production environments with large catalogues., Comment: Accepted by RecSys 2024

Transformer-based Cross-Encoders achieve state-of-the-art effectiveness in text retrieval. However, Cross-Encoders based on large transformer models (such as BERT or T5) are computationally expensive and allow for scoring only a small number of documents within a reasonably small latency window. However, keeping search latencies low is important for user satisfaction and energy usage. In this paper, we show that weaker shallow transformer models (i.e., transformers with a limited number of layers) actually perform better than full-scale models when constrained to these practical low-latency settings since they can estimate the relevance of more documents in the same time budget. We further show that shallow transformers may benefit from the generalized Binary Cross-Entropy (gBCE) training scheme, which has recently demonstrated success for recommendation tasks. Our experiments with TREC Deep Learning passage ranking query sets demonstrate significant improvements in shallow and full-scale models in low-latency scenarios. For example, when the latency limit is 25ms per query, MonoBERT-Large (a cross-encoder based on a full-scale BERT model) is only able to achieve NDCG@10 of 0.431 on TREC DL 2019, while TinyBERT-gBCE (a cross-encoder based on TinyBERT trained with gBCE) reaches NDCG@10 of 0.652, a +51% gain over MonoBERT-Large. We also show that shallow Cross-Encoders are effective even when used without a GPU (e.g., with CPU inference, NDCG@10 decreases only by 3% compared to GPU inference with 50ms latency), which makes Cross-Encoders practical to run even without specialized hardware acceleration., Comment: Accepted by ECIR2024

Sequential Recommendation is a popular recommendation task that uses the order of user-item interaction to model evolving users' interests and sequential patterns in their behaviour. Current state-of-the-art Transformer-based models for sequential recommendation, such as BERT4Rec and SASRec, generate sequence embeddings and compute scores for catalogue items, but the increasing catalogue size makes training these models costly. The Joint Product Quantisation (JPQ) method, originally proposed for passage retrieval, markedly reduces the size of the retrieval index with minimal effect on model effectiveness, by replacing passage embeddings with a limited number of shared sub-embeddings. This paper introduces RecJPQ, a novel adaptation of JPQ for sequential recommendations, which takes the place of item embeddings tensor and replaces item embeddings with a concatenation of a limited number of shared sub-embeddings and, therefore, limits the number of learnable model parameters. The main idea of RecJPQ is to split items into sub-item entities before training the main recommendation model, which is inspired by splitting words into tokens and training tokenisers in language models. We apply RecJPQ to SASRec, BERT4Rec, and GRU4rec models on three large-scale sequential datasets. Our results showed that RecJPQ could notably reduce the model size (e.g., 48% reduction for the Gowalla dataset with no effectiveness degradation). RecJPQ can also improve model performance through a regularisation effect (e.g. +0.96% NDCG@10 improvement on the Booking.com dataset). Overall, RecJPQ allows the training of state-of-the-art transformer recommenders in industrial applications, where datasets with millions of items are common., Comment: Accepted by ACM WSDM 2024

We study the theoretical model of a ferromagnetic semiconductor as a system of randomly distributed Ising spins with a long-range exchange interaction. Using the density-of-states approach, we analytically obtain the magnetic susceptibility and heat capacity over a wide range of temperatures and magnetic fields. It is shown that the finite system of spins in magnetic field less than a certain critical field is in a superparamagnetic state due to thermodynamic fluctuations. The complex phase structure of a ferromagnetic semiconductor is discussed.

Sequential recommendation is an important recommendation task that aims to predict the next item in a sequence. Recently, adaptations of language models, particularly Transformer-based models such as SASRec and BERT4Rec, have achieved state-of-the-art results in sequential recommendation. In these models, item ids replace tokens in the original language models. However, this approach has limitations. First, the vocabulary of item ids may be many times larger than in language models. Second, the classical Top-K recommendation approach used by these models may not be optimal for complex recommendation objectives, including auxiliary objectives such as diversity, coverage or coherence. Recent progress in generative language models inspires us to revisit generative approaches to address these challenges. This paper presents the GPTRec sequential recommendation model, which is based on the GPT-2 architecture. GPTRec can address large vocabulary issues by splitting item ids into sub-id tokens using a novel SVD Tokenisation algorithm based on quantised item embeddings from an SVD decomposition of the user-item interaction matrix. The paper also presents a novel Next-K recommendation strategy, which generates recommendations item-by-item, considering already recommended items. The Next-K strategy can be used for producing complex interdependent recommendation lists. We experiment with GPTRec on the MovieLens-1M dataset and show that using sub-item tokenisation GPTRec can match the quality of SASRec while reducing the embedding table by 40%. We also show that the recommendations generated by GPTRec on MovieLens-1M using the Next-K recommendation strategy match the quality of SASRec in terms of NDCG@10, meaning that the model can serve as a strong starting point for future research., Comment: Accepted at Gen-IR@SIGIR2023 workshop

This paper classifies all modular data of integral modular fusion categories up to rank 13. Furthermore, it also classifies all integral half-Frobenius fusion rings up to rank 12. We find that each perfect integral modular fusion category up to rank 13, as well as every perfect integral half-Frobenius fusion ring up to rank 12, is trivial. We have also refined the non-pointed odd-dimensional modular data at ranks below 25 to three items, all of rank 17, FPdim 225, and type [[1,3],[3,8],[5,6]], filling gaps in the literature. For rank 25, we have narrowed down the perfect case to 3 types. Our initial key insight is that the Egyptian fractions, which are typically employed to list possible types, can be chosen with squared denominators. We then develop several type criteria as initial filters. In particular, we establish that the number of distinct basic FPdims in a non-trivial perfect fusion ring must be at least 4. To obtain the fusion rings, we solve the dimension and associativity equations using new features on Normaliz created specifically for this purpose. The S-matrices (if they exist) are obtained by self-transposing the character table, while the T-matrices are derived by solving the Anderson-Moore-Vafa equations. Finally, we verify the extended axioms of modular data. From rank 13 onward, the types were further restricted by additional properties unique to the modular case, which involved the universal grading, congruence representations of the modular group and Galois action, leading to critical arithmetic constraints. In particular, we get that, up to rank 21, a prime divisor of the global FPdim does not exceed the rank, and more strongly up to rank 15 in the non-pointed case, does not exceed half the rank. Ultimately, we narrowed down the classification at rank 14 to 35 possible types, 8 of which are non-perfect., Comment: 34 pages. New results involving stronger arithmetic constraints, motivated by new results on the rank of Z(Rep(G)); reduction of the rank 14 case to 35 types; reduction of perfect odd-dim rank 25 to 3 types; the computational proofs are now well documented; new features on Normaliz involving modular grading; new SageMath functions available for classifying constrained types. Comments are welcome!

High-power femtosecond laser radiation propagates nonlinearly in air exhibiting pulse self-focusing and strong multiphoton medium ionization, which leads to the spatial fragmentation of laser pulse into highly-localized light channels usually called the filaments. The filaments are characterized by high optical intensity, reduced (even zero) angular spreading and can contain laser plasma or be plasmaless (postfilaments). The presence of optical turbulence on the propagation path dramatically changes pulse filamentation dynamics and in some cases causes pulse fragmentation enhancement and collapse arrest. For the first time to our knowledge, we experimentally and theoretically investigate the transverse profile of Ti:sapphire femtosecond laser radiation nonlinearly propagating a 65 m air path to the region of postfilament evolution after passing through an artificial localized air turbulence. We show that when a turbulent layer is placed before the filamentation region, the average number of high-intensive local fluence maxima ("hot points") in pulse profile as well as their sizes grow as the turbulence strength increases, and then saturates at some levels. On the contrary, the deposition of a turbulent screen within the filamentation region has almost no effect on both the number and the average diameter of the postfilaments.

The effectiveness of multiple electron cyclotron resonance (ECR) harmonics has been thoroughly investigated in context of high current drive efficiency, generally observed in fully non-inductive operation of the low aspect ratio EXL-50 spherical tokamak (ST) powered by electron cyclotron (EC) waves. The Fokker-Plank equation is numerically solved to obtain electron distribution function, under steady state of the relativistic nonlinear Coulomb collision and quasi-linear diffusion operators, for calculating plasma current driven by the injected EC wave. For the extra-ordinary EC wave, simulation results unfold a mechanism by which electrons moving around the cold second harmonic ECR layer strongly resonate with higher harmonics via the relativistic Doppler shifted resonance condition. This feature is in fact evident above a certain value of input EC wave power in simulation, indicating it to be a non-linear phenomenon. Similar to the experimental observation, high efficiency in current drive (over 1 A/W) has indeed been found in simulation for a typical low density ($\sim 1\times10^{18}~m^{-3}$), low temperature ($\lesssim 100$ eV) plasma of EXL-50 by taking into account multi-pass absorptions in our simulation model. However, such characteristic is not found in the ordinary EC-wave study for both single-pass and multi-pass simulations, suggesting it as inefficient in driving current on our ST device., Comment: 22 pages, 15 figures. Submitted to the Nuclear Fusion journal

Small cations such as guanidinium and cesium can act as templating cations to form low dimensional phases (2D, 1D, 0D) in the case of excess of organic halides. However, such phases with the widely used formamidinium (FA+) cation have not been reported so far. In this study, we discovered two novel low dimensional phases with a composition of FA2PbBr4 and investigated the prerequisites of their formation upon crystallization of FABr-excessive solutions of FAPbBr3. We found that both phases have the structure of (110) layered perovskite but are represented by two different polymorphs with eclipsed and staggered arrangement of adjacent layers. It was shown that FA2PbBr4 phases usually exist in a labile equilibrium with FAPbBr3 3D perovskite and can form composites with it. The optical properties of both polymorphs were comprehensively studied by means of absorption spectroscopy, diffuse reflection spectroscopy and photoluminescence spectroscopy. DFT calculations were applied to investigate the band structure of the FA2PbBr4 and to corroborate the conclusions on their optoelectronic properties. As a result, we found that FA2PbBr4 phases irradiated by UV can exhibit effective green photoluminescence due to a transfer of excitation energy to defective states or 3D perovskite inclusions., Comment: 24 pages, 19 figures

The paper deals with the edge diffraction of the single charged Laguerre-Gaussian beam outside the waist. Based on the Kirchhoff-Fresnel integral, the behavior of the optical vortex (OV) migration during sequential beam blocking by the straight edge of the screen is performed analytically. Universal combination of the diffracting-beam parameters determining the shape for the OV spiral trajectories is revealed. Parametric equations describing the OV dislocation dependent on the beam screening degree are derived. In addition, the spiral trajectory, which describes the OV positions in the case of the screen-edge translatory motion across the incident beam under conditions of the weak diffraction perturbation, is obtained. As a result, the equation for a wider region of diffraction perturbation is selected as a best matching function for a certain variation interval of the beam parameters. The work has prepared the basis for solving the inverse diffraction problem: determining parameters of the beam diffractive interaction with obstacles from the migration trajectory of the optical vortex., Comment: 15 pages, 6 figures, submitted to Optics and Lasers in Engineering

This paper presents the results of a comprehensive study on the optimization of the optical system for independent amplitude and phase wavefront manipulation, which is based on a digital micromirror device implementation. The parameters of generated binary fringe patterns to reach the optimal quality of target complex-valued wavefront have been found for several examples, and a general algorithm for DMD pattern optimization is described. It was shown that a trade-off between spatial resolution and quantization of the target amplitude and phase distribution should be achieved. The increase of carrier frequency results in higher spatial resolution of the modulated complex wave but decreases its quantization. The dependence of the best DMD-pattern generation parameters on the type of target complex wavefront is discussed in terms of spatial resolution and quantization degree., Comment: 14 pages, 8 figures

We describe a first open-access database of experimentally investigated hybrid organic-inorganic materials with two-dimensional (2D) perovskite-like crystal structure. The database includes 515 compounds, containing 180 different organic cations, 10 metals (Pb, Sn, Bi, Cd, Cu, Fe, Ge, Mn, Pd, Sb) and 3 halogens (I, Br, Cl) known so far and will be regularly updated. The database contains a geometrical and crystal chemical analysis of the structures, which are useful to reveal quantitative structure-property relationships for this class of compounds. We show that the penetration depth of spacer organic cation into the inorganic layer and M-X-M bond angles increase in the number of inorganic layers (n). The machine learning model is developed and trained on the database, for the prediction of a band gap with accuracy within 0.1 eV. Another machine learning model is trained for the prediction of atomic partial charges with accuracy within 0.01 e. We show that the predicted values of band gaps decrease with an increase of the n and with an increase of M-X-M angles for single-layered perovskites. In general, the proposed database and machine learning models are shown to be useful tools for the rational design of new 2D hybrid perovskite materials.

We present results from a global view on the colliding-wind binary WR 147. We analysed new optical spectra of WR 147 obtained with Gran Telescopio CANARIAS and archive spectra from the Hubble Space Telescope by making use of modern atmosphere models accounting for optically thin clumping. We adopted a grid-modelling approach to derive some basic physical characteristics of both stellar components in WR 147. For the currently accepted distance of 630 pc to WR 147, the values of mass-loss rate derived from modelling its optical spectra are in acceptable correspondence with that from modelling its X-ray emission. However, they give a lower radio flux than observed. A plausible solution for this problem could be if the volume filling factor at large distances from the star (radio-formation region) is smaller than close to the star (optical-formation region). Adopting this, the model can match well both optical and thermal radio emission from WR 147. The global view on the colliding-wind binary WR 147 thus shows that its observational properties in different spectral domains can be explained in a self-consistent physical picture., Comment: Accepted for publication in MNRAS; 15 pages, 11 figures, 2 tables

Let $(\mathcal{P},\leqslant)$ be a finite poset. Define the numbers $a_1,a_2,\ldots$ (respectively, $c_1,c_2,\ldots$) so that $a_1+\ldots+a_k$ (respectively, $c_1+\ldots+c_k$) is the maximal number of elements of $\mathcal{P}$ which may be covered by $k$ antichains (respectively, $k$ chains.) Then the number $e(\mathcal{P})$ of linear extensions of poset $\mathcal{P}$ is not less than $\prod a_i!$ and not more than $n!/\prod c_i!$. A corollary: if $\mathcal{P}$ is partitioned onto disjoint antichains of size $b_1,b_2, \ldots$, then $e(\mathcal{P})\geqslant \prod b_i!$.

Laser ablation through liquid is an important process that have to be studied for applications which use laser ablation in liquid (LAL) and laser shock peening (LSP). LAL is employed for production of suspensions of nanoparticles, while LSP is applied to increase hardness and fatique/corrosion resistance properties of a surface layer. A bubble appears in liquid around the laser spot focused at a target surface after strong enough laser pulse. In the paper we connect the early quasi-plane heated layer created by a pulse in liquid and the bubble forming at much later stages. In the previous works these early stage from one side and the late stage from another side existed mainly as independent entities. At least, quantitative links between them were unknown. We consider how the quasi-plane heated layer of liquid forms thank to thermal conduction, how gradually conduction becomes weaker, and how the heated layer of liquid nearly adiabatically expands to few orders of magnitude in volume during the drop of pressure. Our molecular dynamics simulations show that the heated layer is filled by the diffusive atomic metal-liquid mixture. Metal atoms began to condense into nanoparticles (NP) when they meet cold liquid outside the edge of a mixing zone. This process limits diffusive expansion of metal atoms, because diffusive ability of NP is less than this ability for individual atoms. Thus the mixture expands together with hot liquid, and the NPs approximately homogeneously fill an interior of a bubble., Comment: 13 pages, 19 figures - paper was reported on FLAMN-2019 https://flamn.ifmo.ru/ and submitted to "Optical and Quantum Electronics"

Fundamental parameters are determined for three bright, nearby K-giants, {\beta} Gem (K0 III), {\mu} Leo (K2 III), and {\alpha} Tau (K5 III). It is notable that around all three stars the giant planets have been found. Our results are compared with published high-precision data for benchmark stars included in the Gaia project. Very good agreement was obtained for all three giants with these data for the basic parameters Teff, logg, and M. Special attention was devoted to analysis of the Fe I lines which are the basis of a simultaneous determination of the metallicity index [Fe/H] and microturbulent parameter Vt. The equivalent widths W of the Fe I lines are automatically measured from published spectra for the benchmark stars. An analysis of Fe I lines from the list of "golden lines" selected in a study of benchmark stars led to the conclusion that the excitation potential El of the low level of the lines plays an substantial role in determining [Fe/H] and Vt. It is shown that in the case of the early K-giants {\beta} Gem and {\mu} Leo for lines in the range of W from 100 to 300 m{\AA} there is a dependence of the [Fe/H] and Vt values on El. It is shown that a correct accounting for it leads an ambiguity in the determination of [Fe/H] and Vt for {\beta} Gem and {\mu} Leo. In the case of the coolest K-giant {\alpha} Tau (Aldebaran) with a temperature Teff = 3920K, this effect seems to be less pronounced. Recommendations are given for the Fe I lines selection for [Fe/H] and Vt determination. It is sonfirmed for the example of the three stars studied here that the non-LTE effects in the Fe I lines for the K-giants with normal metallicity are very minor, so they cannot be the reason of the revealed ambiguity in [Fe/H] and Vt values. The low ratios of the carbon 12C/13C and oxygen 16O/17O isotopes confirm that all three giants passed the phase of deep convective mixing., Comment: 22 pages, 6 figures, 6 tables

Microstructured optical waveguides (MOW) are of great interest for chemical and biological sensing. Due to the high overlap between a guiding light mode and an analyte filling of one or several fiber capillaries, such systems are able to provide strong sensitivity with respect to variations in the refractive index and the thickness of filling materials. Here, we introduce a novel type of functionalized MOWs whose capillaries are coated by a layer-by-layer (LBL) approach, enabling the alternate deposition of silica particles (SiO2) at different diameters - 300 nm, 420 nm, and 900 nm - and layers of poly(diallyldimethylammonium chloride) (PDDA). We demonstrate up to three covering bilayers consisting of 300-nm silica particles. Modifications in the MOW transmission spectrum induced by coating are measured and analyzed. The proposed technique of MOW functionalization allows one to reach novel sensing capabilities, including an increase in the effective sensing area and the provision of a convenient scaffold for the attachment of long molecules such as proteins., Comment: 16 pages, 14 figures

Periodical spatial modulation of the excitonic resonance in a quantum well could lead to the formation of a new highly directional and resonant coherent optical response -- resonant diffraction. Such excitonic diffraction gratings were demonstrated in epitaxially grown quantum wells patterned by the low-dose ion beam irradiation before or after the growth. In this paper we present a theoretical model of the resonant diffraction formation based on the step-by-step approximation of the Maxwell equation solution. The resulting theory allows us to reliably describe experimental data, as well as to predict the way to increase the diffraction efficiency., Comment: Shortened version

We present a theoretical investigation of the lateral shift of an infrared light beam reflected from a magnetic film deposited on a non-magnetic dielectric substrate, taking into account the linear magneto-electric interaction in the magnetic film. We use the stationary phase method to evaluate the lateral shift. It is shown that the magneto-electric coupling leads to a six-fold enhancement of the lateral shift amplitude of a p-(s-) polarized incident beam reflected into a s-(p-) polarized beam. A reversal of the magnetization in the film leads to a nonreciprocal sign change of the lateral shift., Comment: 6 pages, 3 figyres

The ecologically best way to produce nanoparticles (NP) is based on laser ablation in liquid (LAL). In the considered here case the LAL means that a gold target is irradiated through transparent water. During and after irradiation the heated material from surface of a target forms a plume which expands into liquid. In this paper we study a reach set of physical processes mixed with complicated hydrodynamic phenomena which all accompany LAL. These theoretical and simulation investigations are very important for practical applications. Laser pulses with different durations $\tau_L$ covering 5-th orders of magnitudes range from 0.1 ps to 0.5 ns and large absorbed fluences $F_{abs}$ near optical breakdown of liquid are compared. It is shown that the trajectory of the contact boundary with liquid at the middle and late stages after passing of the instant of maximum intensity of the longest pulse are rather similar for very different pulse durations (of course at comparable energies $F_{abs});$ we consider the pulses with a Gaussian temporal shape $I\propto \exp(-t^2/\tau_L^2).$ We follow how hot (few eV range) dense gold plasma expands, cools down, intersects a saturation curve, and condenses into NPs. These NPs appear first inside the water-gold diffusively mixed intermediate layer where gold vapor has the lowest temperature. Later in time pressure around the gold-water contact drops down below critical pressure for water. Thus NPs find themselves in gaseous water bubble where density of water gradually decreases to $10^{-4}-10^{-5}$ g/cm$\!^3$ at the instant of maximum expansion of a bubble., Comment: 21 pages, 11 figures