Size-dependent transformation from triangular to rectangular fluxon lattice in Bi-2212 mesa structures

We present a systematic study of the field and size dependencies of the static fluxon lattice configuration in Bi-2212 intrinsic Josephson junctions and investigate conditions needed for the formation of a rectangular fluxon lattice required for a high power flux-flow oscillator. We fabricate junctions of different sizes from Bi2Sr2CaCu2O8+x and Bi1.75Pb0.25Sr2CaCu2O8+x single crystals using the mesa technique and study the Fraunhofer-like modulation of the critical current with magnetic field. The modulation can be divided into three regions depending on the formed fluxon lattice. At low field, no periodic modulation and no ordered fluxon lattice is found. At intermediate fields, modulation with half-flux quantum periodicity due to a triangular lattice is seen. At high fields, the rectangular lattice gives integer flux quantum periodicity. We present these fields in dependence on the sample size and conclude that the transitions between the regions depend only on lambdaJ(Jc) and occur at about 0.4 and 1.3 fluxons per lambdaJ, respectively. These numbers are universal for the measured samples and are consistent with performed numerical simulations.Comment: Conference paper LT2

Persistent electrical doping of Bi2Sr2CaCu2O8+x mesa structures

Application of a significantly large bias voltage to small Bi2Sr2CaCu2O8+x mesa structures leads to persistent doping of the mesas. Here we employ this effect for analysis of the doping dependence of the electronic spectra of Bi-2212 single crystals by means of intrinsic tunneling spectroscopy. We are able to controllably and reversibly change the doping state of the same single crystal from underdoped to overdoped state, without changing its chemical composition. It is observed that such physical doping is affecting superconductivity in Bi-2212 similar to chemical doping by oxygen impurities: with overdoping the critical temperature and the superconducting gap decrease, with underdoping the c-axis critical current rapidly decreases due to progressively more incoherent interlayer tunneling and the pseudogap rapidly increases, indicative for the presence of the critical doping point. We distinguish two main mechanisms of persistent electric doping: (i) even in voltage contribution, attributed to a charge transfer effect, and (ii) odd in voltage contribution, attributed to reordering of oxygen impurities

Word and bit line operation of a 1x1 {\mu}m2 superconducting vortex-based memory

The lack of dense random access memory is one of the main bottlenecks for the creation of a digital superconducting computer. In this work we study experimentally vortex-based superconducting memory cells. Three main results are obtained. First, we test scalability and demonstrate that the cells can be straightforwardly miniaturized to submicron sizes. Second, we emphasize the importance of conscious geometrical engineering. In the studied devices we introduce an asymmetric easy track for vortex motion and show that it enables a controllable manipulation of vortex states. Finally, we perform a detailed analysis of word and bit line operation of a 1x1 {\mu}m2 cell. High-endurance, nonvolatile operation at zero magnetic field is reported. Remarkably, we observe that the combined word and bit line threshold current is significantly reduced compared to the bare word-line operation. This could greatly improve the selectivity of individual cell addressing in a multibit RAM. The achieved one square micron area is an important milestone and a significant step forward towards creation of a dense cryogenic memory.Comment: 9 pages, 6 figure

Analysis of changes in the genome of Vibrio cholerae O1 El Tor genovariants during the current period of the cholera pandemic

Introduction. The genome variability of genetic variants of El Tor cholera agent has led to the emergence of strains carrying mutations in various genes associated with epidemically important pathogen properties. This situation requires an assessment of the trends in these changes in order to predict the pathogenic potential of previously unknown variants and promptly develop new tools for their diagnostics and prevention. The purpose of this work was to analyze the dynamic changes in pathogenicity and drug resistance genes of V. cholerae El Tor genetic variants from endemic countries and Russia. Materials and methods. We analyzed complete genome nucleotide sequences of 104 V. cholerae El Tor strains from the NCBI Gen Bank and European Nucleotide Archive databases, as well as those obtained by us. The nucleotide sequences were analyzed using the UGEN v. 45.1 software. The dendrogram was constructed using maximum parsimony algorithm in BioNumerics v.7.6 software package based on the multiple alignment generated using the Snippy 4.6.0 program. Results. Genomic sequences of 103 strain genovariants isolated on the territory of nine endemic countries of Asia and Africa, as well as in Russia in 1991-2022, have been compared. It is shown that the process of genovariant genome changing was multistage and occurred due to the continuous accumulation of point mutations in key (ctxB and tcpA) and additional (rtxA) genes of pathogenicity and core genes of antibiotic resistance (gyrA, parC and carR), as well as a deletion in SXT element. The most important was the change in the ctxB gene and the emergence of new genovariants with the ctxB7 allele, which replaced the previously prevalent strains. Analysis of altered genome regions of 83 strains from endemic regions has revealed eight genotypes, while the strains (21 isolates) imported to Russia belonged to only five of them including highly virulent strains with the ctxB7 allele and lost PolR biovar-specific feature due to carR gene mutation. The established close phylogenetic relatedness of genovariants from Russia with strains from endemic Asian countries confirms their importation from this region. Conclusion. The sequential occurrence and accumulation of mutations in the pathogenicity and drug resistance genes in the genome of genovariants in endemic regions have been shown, which leads to a change in their epidemically important features. The importation of new highly virulent genovariants into Russia has been established, which indicates the need for an ongoing assessment of changes in the genome of this pathogen for the timely development of adequate means of gene diagnostics and prevention

Hemozoin "knobs" in Opisthorchis felineus infected liver

Background Hemozoin is the pigment produced by some blood-feeding parasites. It demonstrates high diagnostic and therapeutic potential. In this work the formation of co-called hemozoin “knobs” – the bile duct ectasia filled up by hemozoin pigment - in Opisthorhis felineus infected hamster liver has been observed. Methods The O. felineus infected liver was examined by histological analysis and magnetic resonance imaging (MRI). The pigment hemozoin was identified by Fourier transform infrared spectroscopy and high resolution electrospray ionization mass spectrometry analysis. Hemozoin crystals were characterised by high resolution transmission electron microscopy. Results Hemozoin crystals produced by O. felineus have average length 403 nm and the length-to-width ratio equals 2.0. The regurgitation of hemozoin from parasitic fluke during infection leads to formation of bile duct ectasia. The active release of hemozoin from O. felineus during in vitro incubation has also been evidenced. It has been shown that the hemozoin knobs can be detected by magnetic resonance imaging. Conclusions In the paper for the first time the characterisation of hemozoin pigment extracted from liver fluke O. felineus has been conducted. The role of hemozoin in the modification of immune response by opisthorchiasis is assumed

How to write a contemporary scientific article

Today scientists are drowned in information and have no time for reading all publications even in a specific area. The information is sifted and only a small fraction of articles is being read. Under circumstances, scientific articles have to be properly adjusted to pass through the superficial sifting. Here I present written down instructions that I used to give to my students with almost serious advises on how to write (and how not to write) a contemporary scientific article. I argue that it should tell a story and should answer on the three main questions: Why, What and So what?Comment: Almost serious advices to PhD students: 3 pages, 1 Fi