arXiv subjects

Dmitry Karpov

Publications and source records attributed to Dmitry Karpov.

11 recordsLinked to original sources

arXiv2026

Understanding ultrafast x-ray 'echoes' diffracted from single crystals

Multiple x-ray beams generated by interference processes in perfect crystals were imaged with a resolution of about 100nm using tele-ptychography in the diffraction direction. These multiple wave-fields, also known as x-ray diffraction echoes, are related to the process known as the Pendelloesung effect and are described by dynamical diffraction theory. The echoes are produced by the constructive interference of diffracted x-rays at the exit surface of the crystal sample. In the imaged diffraction peak, we observed 10 echoes maxima with a total signal length of 78 um. Which translates into a total temporal delay in the signal of less than 108 fs.This makes the echoes of high importance for x-ray optics at x-ray Free Electron Laser sources, as the effect could be used for future ultrafast x-ray beam splitters. In addition to this application, echoes can be exploited to follow ultrafast processes in single crystal micro-structures such as melting or strain propagation.

cond-mat.mtrl-sci↗

arXiv2026

No One-Size-Fits-All: Building Systems For Translation to Bashkir, Kazakh, Kyrgyz, Tatar and Chuvash Using Synthetic And Original Data

We explore machine translation for five Turkic language pairs: Russian-Bashkir, Russian-Kazakh, Russian-Kyrgyz, English-Tatar, English-Chuvash. Fine-tuning nllb-200-distilled-600M with LoRA on synthetic data achieved chrF++ 49.71 for Kazakh and 46.94 for Bashkir. Prompting DeepSeek-V3.2 with retrieved similar examples achieved chrF++ 39.47 for Chuvash. For Tatar, zero-shot or retrieval-based approaches achieved chrF++ 41.6, while for Kyrgyz the zero-shot approach reached 45.6. We release the dataset and the obtained weights.

cs.CL↗

arXiv2025

Noise2Ghost: Self-supervised deep convolutional reconstruction for ghost imaging

We present a new self-supervised deep-learning-based Ghost Imaging (GI) reconstruction method, which provides unparalleled reconstruction quality for noisy acquisitions among unsupervised methods. We present the supporting mathematical framework and results from theoretical and real data use cases. Self-supervision removes the need for clean reference data while offering strong noise reduction. This provides the necessary tools for addressing signal-to-noise ratio concerns for GI acquisitions in emerging and cutting-edge low-light GI scenarios. Notable examples include micro- and nano-scale x-ray emission imaging, e.g., x-ray fluorescence imaging of dose-sensitive samples. Their applications include in-vivo and in-operando case studies for biological samples and batteries.

cs.CV↗

arXiv2025

Dead, Slow and Overworked Graphite: Operando X-ray Microdiffraction Mapping of Aged Electrodes

Aging limits lithium-ion battery lifetime and must be understood to improve durability and performance, requiring a detailed understanding of how aging alters the availability of cyclable lithium and the integrity of active particles. In this work, (de)lithiation mechanisms are examined and spatially-resolved at the microscale in aged graphite electrodes dismounted from a large format graphite/LiFePO4-Li(NiCoAl)O2 cell at 70% remaining capacity. A multi-technique workflow is employed, combining electrochemical methods with post-mortem structural and morphological analyses, and introducing synchrotron microX-ray 2D diffraction imaging as a technique to probe aged graphite, applied at C-rates from C/5 to C. In-plane and through-plane heterogeneities in graphite dynamics are evidenced, showing the presence of inactive regions localized in two dimensions. In these areas, particles are either disconnected (irreversibly lost) or kinetically limited (reactivated at a slow C-rate), with dead or slow particles exhibiting a wide range of compositions, from x = 0 to x = 1 in LixC6. These inactivated graphite particles are found to be heterogeneously distributed throughout the depth of the aged negative electrode. In particular, the most inactivated region localizes at the negative electrode-separator interface, correlating to overworking graphite near the separator.

cond-mat.mtrl-sci↗

arXiv2023

Monolingual and Cross-Lingual Knowledge Transfer for Topic Classification

This article investigates the knowledge transfer from the RuQTopics dataset. This Russian topical dataset combines a large sample number (361,560 single-label, 170,930 multi-label) with extensive class coverage (76 classes). We have prepared this dataset from the "Yandex Que" raw data. By evaluating the RuQTopics - trained models on the six matching classes of the Russian MASSIVE subset, we have proved that the RuQTopics dataset is suitable for real-world conversational tasks, as the Russian-only models trained on this dataset consistently yield an accuracy around 85\% on this subset. We also have figured out that for the multilingual BERT, trained on the RuQTopics and evaluated on the same six classes of MASSIVE (for all MASSIVE languages), the language-wise accuracy closely correlates (Spearman correlation 0.773 with p-value 2.997e-11) with the approximate size of the pretraining BERT's data for the corresponding language. At the same time, the correlation of the language-wise accuracy with the linguistical distance from Russian is not statistically significant.

cs.CL↗

arXiv2023

Enhanced piezoelectric response at nanoscale vortex structures in ferroelectrics

The piezoelectric response is a measure of the sensitivity of a material's polarization to stress or its strain to an applied field. Using in-operando x-ray Bragg coherent diffraction imaging, we observe that topological vortices are the source of a five-fold enhancement of the piezoelectric response near the vortex core. The vortices form where several low symmetry ferroelectric phases and phase boundaries coalesce. Unlike bulk ferroelectric solid solutions in which a large piezoelectric response is associated with coexisting phases in the proximity of the triple point, the largest responses for pure BaTiO3 at the nanoscale are in spatial regions of extremely small spontaneous polarization at vortex cores. The response decays inversely with polarization away from the vortex, analogous to the behavior in bulk ceramics as the cation compositions are varied away from the triple point. We use first-principles-based molecular dynamics to augment our observations, and our results suggest that nanoscale piezoelectric materials with large piezoelectric response can be designed within a parameter space governed by vortex cores. Our findings have implications for the development of next-generation nanoscale piezoelectric materials.

cond-mat.mtrl-sci↗

arXiv2023

X-ray nanotomography reveals formation of single diamonds by block copolymer self-assembly

Block copolymers are recognised as a valuable platform for creating nanostructured materials with unique properties. Morphologies formed by block copolymer self-assembly can be transferred into a wide range of inorganic materials, enabling applications including energy storage and metamaterials. However, imaging of the underlying, often complex, nanostructures in large volumes has remained a challenge, limiting progress in materials development. Taking advantage of recent advances in X-ray nanotomography, we non-invasively imaged exceptionally large volumes of nanostructured soft materials at high resolution, revealing a single diamond morphology in a triblock terpolymer composite network. This morphology, which is ubiquitous in nature, has so far remained elusive in block copolymers, despite its potential to create materials with large photonic bandgaps. The discovery was made possible by the precise analysis of distortions in a large volume of the self-assembled diamond network, which are difficult to unambiguously assess using traditional characterisation tools. We anticipate that high-resolution X-ray nanotomography, which allows imaging of much larger sample volumes than electron-based tomography, will become a powerful tool for the quantitative analysis of complex nanostructures and that structures such as the triblock terpolymer-directed single diamond will enable the generation of advanced multicomponent composites with hitherto unknown property profiles.

cond-mat.soft↗

arXiv2023

High-resolution three-dimensional imaging of topological textures in single-diamond networks

Highly periodic structures are often said to convey the beauty of nature. However, most material properties are strongly influenced by the defects they contain. On the mesoscopic scale, molecular self-assembly exemplifies this interplay; thermodynamic principles determine short-range order, but long-range order is mainly impeded by the kinetic history of the material and by thermal fluctuations. For the development of self-assembly technologies, it is imperative to characterise and understand the interplay between self-assembled order and defect-induced disorder. Here we used synchrotron-based hard X-ray nanotomography to reveal a pair of extended topological defects within a self-assembled single-diamond network morphology. These defects are morphologically similar to the comet and trefoil patterns of equal and opposite half-integer topological charges observed in liquid crystals and appear to maintain a constant separation across the thickness of the sample, resembling pairs of full vortices in superconductors and other hard condensed matter systems. These results are expected to open new windows to study defect formation in soft condensed matter, particularly in biological systems where most structures are formed by self-assembly.

cond-mat.soft↗

arXiv2022

Hard X-ray helical dichroism of disordered molecular media

Chirality is a structural property of molecules lacking mirror symmetry that has strong implications in diverse fields, ranging from life to materials sciences. Established spectroscopic methods that are sensitive to chirality, such as circular dichroism (CD), exhibit weak signal contributions on an achiral background. Helical dichroism (HD), which is based on the orbital angular momentum (OAM) of light, offers a new approach to probe molecular chirality, but it has never been demonstrated on disordered samples. Furthermore, in the optical domain the challenge lies in the need to transfer the OAM of the photon to an electron that is localized on an Å-size orbital. Here, we overcome this challenge using hard X-rays with spiral Fresnel zone, which can induce an OAM. We present the first HD spectra of a disordered powder sample of enantiopure molecular complexes of [Fe(4,4'-diMebpy)3]2+ at the iron K-edge (7.1 keV) with OAM-carrying beams. The HD spectra exhibit the expected inversions of signs switching from a left to a right helical wave front or from an enantiomer to the other. The asymmetry ratios for the HD spectra are within one to five percent for OAM beams with topological charges of one and three. These results open a new window into the studies of molecular chirality and its interaction with the orbital angular momentum of light.

physics.chem-ph↗

arXiv2020

X-ray ptychographic topography, a new tool for strain imaging

Strain and defects in crystalline materials are responsible for the distinct mechanical, electric and magnetic properties of a desired material, making their study an essential task in material characterization, fabrication and design. Existing techniques for the visualization of strain fields, such as transmission electron microscopy and diffraction, are destructive and limited to thin slices of the materials. On the other hand, non-destructive X-ray imaging methods either have a reduced resolution or are not robust enough for a broad range of applications. Here we present X-ray ptychographic topography, a new method for strain imaging, and demonstrate its use on an InSb micro-pillar after micro-compression, where the strained region is visualized with a spatial resolution of 30 nm. Thereby, X-ray ptychographic topography proves itself as a robust non-destructive approach for the imaging of strain fields within bulk crystalline specimens with a spatial resolution of a few tens of nanometers.

cond-mat.mtrl-sci↗

arXiv2018

A Shack-Hartmann sensor for single-shot multi-contrast imaging with hard X-rays

An array of compound refractive X-ray lenses (CRL) with 20x20 lenslets, a focal distance of 20 cm and a visibility of 0.93 is presented. It can be used as a Shack-Hartmann sensor for hard X-rays (SHARX) for wavefront sensing and permits for true single-shot multi-contrast imaging the dynamics of materials with a spatial resolution in the micrometer range, sensitivity on nanosized structures and temporal resolution on the microsecond scale. The object's absorption and its induced wavefront shift can be assessed simultaneously together with information from diffraction channels. This enables the imaging of hierarchical materials. In contrast to the established Hartmann sensors the SHARX has an increased flux efficiency through focusing of the beam rather than blocking parts of it. We investigated the spatiotemporal behavior of a cavitation bubble induced by laser pulses. Furthermore, we validated the SHARX by measuring refraction angles of a single diamond CRL, where we obtained an angular resolution better than 4 microrad.

physics.app-ph↗