Electronic transport in polycrystalline graphene

Most materials in available macroscopic quantities are polycrystalline. Graphene, a recently discovered two-dimensional form of carbon with strong potential for replacing silicon in future electronics, is no exception. There is growing evidence of the polycrystalline nature of graphene samples obtained using various techniques. Grain boundaries, intrinsic topological defects of polycrystalline materials, are expected to dramatically alter the electronic transport in graphene. Here, we develop a theory of charge carrier transmission through grain boundaries composed of a periodic array of dislocations in graphene based on the momentum conservation principle. Depending on the grain boundary structure we find two distinct transport behaviours - either high transparency, or perfect reflection of charge carriers over remarkably large energy ranges. First-principles quantum transport calculations are used to verify and further investigate this striking behaviour. Our study sheds light on the transport properties of large-area graphene samples. Furthermore, purposeful engineering of periodic grain boundaries with tunable transport gaps would allow for controlling charge currents without the need of introducing bulk band gaps in otherwise semimetallic graphene. The proposed approach can be regarded as a means towards building practical graphene electronics.Comment: accepted in Nature Material

The exchangeability of shape

<p>Abstract</p> <p>Background</p> <p>Landmark based geometric morphometrics (GM) allows the quantitative comparison of organismal shapes. When applied to systematics, it is able to score shape changes which often are undetectable by traditional morphological studies and even by classical morphometric approaches. It has thus become a fast and low cost candidate to identify cryptic species. Due to inherent mathematical properties, shape variables derived from one set of coordinates cannot be compared with shape variables derived from another set. Raw coordinates which produce these shape variables could be used for data exchange, however they contain measurement error. The latter may represent a significant obstacle when the objective is to distinguish very similar species.</p> <p>Results</p> <p>We show here that a single user derived dataset produces much less classification error than a multiple one. The question then becomes how to circumvent the lack of exchangeability of shape variables while preserving a single user dataset. A solution to this question could lead to the creation of a relatively fast and inexpensive systematic tool adapted for the recognition of cryptic species.</p> <p>Conclusions</p> <p>To preserve both exchangeability of shape and a single user derived dataset, our suggestion is to create a free access bank of reference images from which one can produce raw coordinates and use them for comparison with external specimens. Thus, we propose an alternative geometric descriptive system that separates 2-D data gathering and analyzes.</p

Creation of multiple nanodots by single ions

In the challenging search for tools that are able to modify surfaces on the nanometer scale, heavy ions with energies of several 10 MeV are becoming more and more attractive. In contrast to slow ions where nuclear stopping is important and the energy is dissipated into a large volume in the crystal, in the high energy regime the stopping is due to electronic excitations only. Because of the extremely local (< 1 nm) energy deposition with densities of up to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence. Usually, each nanodot is due to the impact of a single ion and the dots are randomly distributed. We demonstrate that multiple periodically spaced dots separated by a few 10 nanometers can be created by a single ion if the sample is irradiated under grazing angles of incidence. By varying this angle the number of dots can be controlled.Comment: 12 pages, 6 figure

Outline of a Genome Navigation System Based on the Properties of GA-Sequences and Their Flanks

Introducing a new method to visualize large stretches of genomic DNA (see Appendix S1) the article reports that most GA-sequences [1] shared chains of tetra-GA-motifs and contained upstream poly(A)-segments. Although not integral parts of them, Alu-elements were found immediately upstream of all human and chimpanzee GA-sequences with an upstream poly(A)-segment. The article hypothesizes that genome navigation uses these properties of GA-sequences in the following way. (1) Poly(A) binding proteins interact with the upstream poly(A)-segments and arrange adjacent GA-sequences side-by-side (‘GA-ribbon’), while folding the intervening DNA sequences between them into loops (‘associated DNA-loops’). (2) Genome navigation uses the GA-ribbon as a search path for specific target genes that is up to 730-fold shorter than the full-length chromosome. (3) As to the specificity of the search, each molecule of a target protein is assumed to catalyze the formation of specific oligomers from a set of transcription factors that recognize tetra-GA-motifs. Their specific combinations of tetra-GA motifs are assumed to be present in the particular GA-sequence whose associated loop contains the gene for the target protein. As long as the target protein is abundant in the cell it produces sufficient numbers of such oligomers which bind to their specific GA-sequences and, thereby, inhibit locally the transcription of the target protein in the associated loop. However, if the amount of target protein drops below a certain threshold, the resultant reduction of specific oligomers leaves the corresponding GA-sequence ‘denuded’. In response, the associated DNA-loop releases its nucleosomes and allows transcription of the target protein to proceed. (4) The Alu-transcripts may help control the general background of protein synthesis proportional to the number of transcriptionally active associated loops, especially in stressed cells. (5) The model offers a new mechanism of co-regulation of protein synthesis based on the shared segments of different GA-sequences

Gravity waves and the LHC: Towards high-scale inflation with low-energy SUSY

It has been argued that rather generic features of string-inspired inflationary theories with low-energy supersymmetry (SUSY) make it difficult to achieve inflation with a Hubble scale H > m_{3/2}, where m_{3/2} is the gravitino mass in the SUSY-breaking vacuum state. We present a class of string-inspired supergravity realizations of chaotic inflation where a simple, dynamical mechanism yields hierarchically small scales of post-inflationary supersymmetry breaking. Within these toy models we can easily achieve small ratios between m_{3/2} and the Hubble scale of inflation. This is possible because the expectation value of the superpotential relaxes from large to small values during the course of inflation. However, our toy models do not provide a reasonable fit to cosmological data if one sets the SUSY-breaking scale to m_{3/2} < TeV. Our work is a small step towards relieving the apparent tension between high-scale inflation and low-scale supersymmetry breaking in string compactifications.Comment: 21+1 pages, 5 figures, LaTeX, v2: added references, v3: very minor changes, version to appear in JHE

Saber on ESP32

Saber, a CCA-secure lattice-based post-quantum key encapsulation scheme, is one of the second round candidate algorithms in the post-quantum cryptography standardization process of the US National Institute of Standards and Technology (NIST) in 2019. In this work, we provide an efficient implementation of Saber on ESP32, an embedded microcontroller designed for IoT environment with WiFi and Bluetooth support. RSA coprocessor was used to speed up the polynomial multiplications for Kyber variant in a CHES 2019 paper. We propose an improved implementation utilizing the big integer coprocessor for the polynomial multiplications in Saber, which contains significant lower software overhead and takes a better advantage of the big integer coprocessor on ESP32. By using the fast implementation of polynomial multiplications, our single-core version implementation of Saber takes 1639K, 2123K, 2193K clock cycles on ESP32 for key generation, encapsulation and decapsulation respectively. Benefiting from the dual core feature on ESP32, we speed up the implementation of Saber by rearranging the computing steps and assigning proper tasks to two cores executing in parallel. Our dual-core version implementation takes 1176K, 1625K, 1514K clock cycles for key generation, encapsulation and decapsulation respectively

The Rossiter-McLaughlin effect in Exoplanet Research

The Rossiter-McLaughlin effect occurs during a planet's transit. It provides the main means of measuring the sky-projected spin-orbit angle between a planet's orbital plane, and its host star's equatorial plane. Observing the Rossiter-McLaughlin effect is now a near routine procedure. It is an important element in the orbital characterisation of transiting exoplanets. Measurements of the spin-orbit angle have revealed a surprising diversity, far from the placid, Kantian and Laplacian ideals, whereby planets form, and remain, on orbital planes coincident with their star's equator. This chapter will review a short history of the Rossiter-McLaughlin effect, how it is modelled, and will summarise the current state of the field before describing other uses for a spectroscopic transit, and alternative methods of measuring the spin-orbit angle.Comment: Review to appear as a chapter in the "Handbook of Exoplanets", ed. H. Deeg & J.A. Belmont

Hemorrhage rate after coblation tonsillectomy: a meta-analysis of published trials

After the surgical procedure of tonsillectomy, hemorrhage ranks among its serious postoperative complications. In this systematic review, we analyze hemorrhage following tonsillectomies performed using the coblation technique. 24 prospective, randomized, and controlled studies were included in the meta-analysis. Data of 796 patients who had undergone coblation tonsillectomy were analyzed. Hemorrhages occurred in 33 patients: 2 classified as primary and 26 as secondary hemorrhages. 5 could not be classified into either group. Overall, the total hemorrhage rate for the coblation procedure was 4.1% with a 95% confidence interval from 2.8 to 5.5%. The overall hemorrhage rate of 4.1% found in this meta-analysis shows that coblation is a safe and effective technique for tonsillectomies with a secondary bleeding rate similar to what is reported for comparable techniques such as bipolar diathermia