Superlattices have attracted great interest because their use may make it possible to modify the spectra of two-dimensional electron systems and, ultimately, create materials with tailored electronic ...properties. In previous studies (see, for example, refs 1-8), it proved difficult to realize superlattices with short periodicities and weak disorder, and most of their observed features could be explained in terms of cyclotron orbits commensurate with the superlattice. Evidence for the formation of superlattice minibands (forming a fractal spectrum known as Hofstadter's butterfly) has been limited to the observation of new low-field oscillations and an internal structure within Landau levels. Here we report transport properties of graphene placed on a boron nitride substrate and accurately aligned along its crystallographic directions. The substrate's moiré potential acts as a superlattice and leads to profound changes in the graphene's electronic spectrum. Second-generation Dirac points appear as pronounced peaks in resistivity, accompanied by reversal of the Hall effect. The latter indicates that the effective sign of the charge carriers changes within graphene's conduction and valence bands. Strong magnetic fields lead to Zak-type cloning of the third generation of Dirac points, which are observed as numerous neutrality points in fields where a unit fraction of the flux quantum pierces the superlattice unit cell. Graphene superlattices such as this one provide a way of studying the rich physics expected in incommensurable quantum systems and illustrate the possibility of controllably modifying the electronic spectra of two-dimensional atomic crystals by varying their crystallographic alignment within van der Waals heterostuctures.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Interspecific gene comparisons are the keystones for many areas of biological research and are especially important for the translation of knowledge from model organisms to economically important ...species. Currently they are hampered by the low resolution of methods based on sequence analysis and by the complex evolutionary history of eukaryotic genes. This is especially critical for plants, whose genomes are shaped by multiple whole genome duplications and subsequent gene loss. This requires the development of new methods for comparing the functions of genes in different species. Here, we report ISEEML (Interspecific Similarity of Expression Evaluated using Machine Learning)-a novel machine learning-based algorithm for interspecific gene classification. In contrast to previous studies focused on sequence similarity, our algorithm focuses on functional similarity inferred from the comparison of gene expression profiles. We propose novel metrics for expression pattern similarity-expression score (ES)-that is suitable for species with differing morphologies. As a proof of concept, we compare detailed transcriptome maps of Arabidopsis thaliana, the model species, Zea mays (maize) and Fagopyrum esculentum (common buckwheat), which are species that represent distant clades within flowering plants. The classifier resulted in an AUC of 0.91; under the ES threshold of 0.5, the specificity was 94%, and sensitivity was 72%.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Introduction. Relevance and dating: one of the widely known stereotypes of the interaction between the Forest and the Steppe, considered as economic and social structures, is their innate rivalry and ...struggle.
Materials and methods. An analysis of the data available to historical science suggests that following the stereotypes described above, when considering specific events and consequences of the interaction between the Vyatichi ethno-potestar association and its nomadic neighbors (near and distant) in the 9th-11th centuries, leads to obviously erroneous conclusions.
Results. Source base: the sources here are, first of all, the results of archaeological research, which indicate numerous and clear signs of cultural, economic, administrative-military interaction. Applied methods: comparative-historical, diachronic-analytical using an interdisciplinary approach. In medieval Slavic history, one can find examples of different types of interaction between Slavic societies and their steppe neighbors: permanent struggle, principled war, neutral coexistence, as well as cooperation and interaction. One of the specific examples of this kind of interaction is the history of the emergence and development of the Upper Oka Vyatichi ethno-political association, which refutes most of the stereotypes stated above.
Conclusion. The period considered in this report indicates, rather, the likely symbiotic reciprocity of the interaction of the Vyatichi community with representatives of the nomadic culture, which over time was destroyed by the military and political activity of the Kievan Rurikovich. The first centuries of the existence of this community demonstrate the enviable productivity and effectiveness of the interaction of the Vyatichi with their nomadic neighbors in various aspects of interaction, ranging from economic, political and cultural enrichment to possible cooperation in the field of animal husbandry.
Devices made from graphene encapsulated in hexagonal boron-nitride exhibit pronounced negative bend resistance and an anomalous Hall effect, which are a direct consequence of room-temperature ...ballistic transport at a micrometer scale for a wide range of carrier concentrations. The encapsulation makes graphene practically insusceptible to the ambient atmosphere and, simultaneously, allows the use of boron nitride as an ultrathin top gate dielectric.
Background. At present, there are no special studies that generally consider the details of the work of the Main Army Supply Committee (Zemgor) with the national minor-ities who worked in its ...engineering and construction squads. The purpose of this study is to identify a number of specific features of the interaction of Zemgor, as a public organization, with a non-Russian and belonging to a different cultural and religious tradition, the contin-gent of the lower level of these construction teams in the process of their recruitment and functioning to solve national tasks, which, against the background of the coming general crisis, seems very relevant. Materials and methods. This study is based on archival materi-als, organization reports, memoirs and the results of a number of contemporary works. This made it possible to consider aspects of this issue that had not previously attracted the atten-tion of researchers. The article is based on the principles of historicism, objectivity, and complexity. As a methodological basis, general scientific methods of collecting, analyzing and synthesizing historical data, comparative historical and historical genetic methods were used. Results. The features of Zemgor’s work with national minorities are described and considered. Conclusions. The work of the Main Army Supply Committee of the All-Russian Zemstvo and city unions (Zemgor) took place as part of solving an acute nation-wide problem to overcome the shortage of workers. The preparation of the procedure and the subsequent involvement by Zemgor of national minorities in the work was carried out taking into account a wide range of issues necessary for their effective application.
Graphene's linear dispersion relation makes its charge carriers behave as if they were massless. However, near the Dirac point where graphene's valence and conduction bands meet, electron-electron ...interactions cause this relation to diverge, such that it becomes strongly nonlinear and the effective carrier velocity doubles. A study reports measurements of the cyclotron mass in suspended graphene for carrier concentrations n varying over three orders of magnitude.
We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the ...barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.
Capacitance measurements provide a powerful means of probing the density of states. The technique has proved particularly successful in studying 2D electron systems, revealing a number of interesting ...many-body effects. Here, we use large-area high-quality graphene capacitors to study behavior of the density of states in this material in zero and high magnetic fields. Clear renormalization of the linear spectrum due to electron–electron interactions is observed in zero field. Quantizing fields lead to splitting of the spin- and valley-degenerate Landau levels into quartets separated by interaction-enhanced energy gaps. These many-body states exhibit negative compressibility but the compressibility returns to positive in ultrahigh B. The reentrant behavior is attributed to a competition between field-enhanced interactions and nascent fractional states.
The above question is frequently asked by theorists who are interested in graphene as a model system, especially in context of relativistic quantum physics. We offer an experimental answer by ...describing electron transport in suspended devices with carrier mobilities of several 106 cm2 V–1 s–1 and with the onset of Landau quantization occurring in fields below 5 mT. The observed charge inhomogeneity is as low as ≈108 cm–2, allowing a neutral state with a few charge carriers per entire micrometer-scale device. Above liquid helium temperatures, the electronic properties of such devices are intrinsic, being governed by thermal excitations only. This yields that the Dirac point can be approached within 1 meV, a limit currently set by the remaining charge inhomogeneity. No sign of an insulating state is observed down to 1 K, which establishes the upper limit on a possible bandgap.
This article considers the extension of the multilayer hydrostatic CABARET-MFSH model to the case of three spatial variables. The model describes the dynamics of a fluid with a variable density and a ...free surface. The hyperbolic decomposition algorithm gives a representation of the matrix of the system as a product of 4 × 4 matrices, the eigenvalues of each of which are always real. An explicit CABARET scheme is used to solve the system of hyperbolic equations in each layer. To validate the model, the problem of a three-dimensional fluid flow with variable density is used. The numerical calculations are in satisfactory agreement with the experimental data.
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