Large Coercivity in Nanostructured Rare-earth-free MnxGa Films

The magnetic hysteresis of MnxGa films exhibit remarkably large coercive fields as high as 2.5 T when fabricated with nanoscale particles of a suitable size and orientation. This coercivity is an order of magnitude larger than in well-ordered epitaxial film counterparts and bulk materials. The enhanced coercivity is attributed to the combination of large magnetocrystalline anisotropy and ~ 50 nm size nanoparticles. The large coercivity is also replicated in the electrical properties through the anomalous Hall effect. The magnitude of the coercivity approaches that found in rare-earth magnets, making them attractive for rare-earth-free magnet applications

Universal Properties of Linear Magnetoresistance in Strongly Disordered Semiconductors

Linear magnetoresistance occurs in semiconductors as a consequence of strong electrical disorder and is characterized by nonsaturating magnetoresistance that is proportional to the applied magnetic field. By investigating a disordered MnAs-GaAs composite material, it is found that the magnitude of the linear magnetoresistance (LMR) is numerically equal to the carrier mobility over a wide range and is independent of carrier density. This behavior is complementary to the Hall effect that is independent of the mobility and dependent on the carrier density. Moreover, the LMR appears to be insensitive to the details of the disorder and points to a universal explanation of classical LMR that can be applied to other material systems.Comment: Accepted by Phys. Rev. B (2010

Ferromagnetism in thin-film Cr-doped topological insulator Bi2Se3

We report on the observation of ferromagnetism in epitaxial thin films of the topological insulator compound Bi2Se3 with chromium doping. The structural, magnetic, and magnetoelectrical properties of Bi2Se3 were investigated for Cr concentrations up to 10%. For a Cr content up to similar to 5% the films are of good crystalline quality, with the lattice parameter a decreasing and the lattice parameter c increasing with increasing Cr concentration. The Curie temperature reached a maximum T-C=20K for 5.2% Cr. Well-defined ferromagnetic hysteresis in the magnetization and in the magnetoresistance was also observed in these films. (C) 2012 American Institute of Physics. [doi:10.1063/1.3688043

Molecular and evolutionary basis of O-antigenic polysaccharide-driven phage sensitivity in environmental pseudomonads.

Pseudomonas protegens CHA0, a bacterial strain able to suppress plant pathogens as well as efficiently kill lepidopteran pest insects, has been studied as a biocontrol agent to prevent ensuing agricultural damage. However, the success of this method is dependent on efficient plant colonization by the bacterial inoculant, while it faces competition from the resident microbiota as well as predators such as bacteriophages. One of these naturally occurring phages, ΦGP100, was found to drastically reduce the abundance of CHA0 once inoculated into plant microcosms, resulting in the loss of plant protection effect against a phytopathogen. Here, we investigated the molecular determinants implicated in the interaction between CHA0 and the phage ΦGP100 using a high-density transposon-sequencing approach. We show that lipopolysaccharide cell surface decorations, specifically the longer OBC3-type O-antigenic polysaccharide (O-PS, O-antigen) of the two dominant O-PS of CHA0, are essential for the attachment and infection of ΦGP100. Moreover, when exploring the distribution of the OBC3 cluster in bacterial genomes, we identified several parts of this gene cluster that are conserved in phylogenetically distant bacteria. Through heterologous complementation, we integrated an OBC3-type gene copy from a phylogenetically distant bacterium and were able to restore the phage sensitivity of a CHA0 mutant which lacked the ability to form long O-PS. Finally, we evidence that the OBC3 gene cluster of CHA0 displays a high genomic plasticity and likely underwent several horizontal acquisitions and genomic rearrangements. Collectively, this study underlines the complexity of phage-bacteria interactions and the multifunctional aspect of bacterial cell surface decorations. IMPORTANCE The application of plant-beneficial microorganisms to protect crop plants is a promising alternative to the usage of chemicals. However, biocontrol research often faces difficulties in implementing this approach due to the inconsistency of the bacterial inoculant to establish itself within the root microbiome. Beneficial bacterial inoculants can be decimated by the presence of their natural predators, notably bacteriophages (also called phages). Thus, it is important to gain knowledge regarding the mechanisms behind phage-bacteria interactions to overcome this challenge. Here, we evidence that the major long O-antigenic polysaccharide (O-PS, O-antigen) of the widely used model plant-beneficial bacterium Pseudomonas protegens CHA0 is the receptor of its natural predator, the phage ΦGP100. We examined the distribution of the gene cluster directing the synthesis of this O-PS and identified signatures of horizontal gene acquisitions. Altogether, our study highlights the importance of bacterial cell surface structure variation in the complex interplay between phages and their Pseudomonas hosts

Hard Instances of the Constrained Discrete Logarithm Problem

The discrete logarithm problem (DLP) generalizes to the constrained DLP, where the secret exponent $x$ belongs to a set known to the attacker. The complexity of generic algorithms for solving the constrained DLP depends on the choice of the set. Motivated by cryptographic applications, we study sets with succinct representation for which the constrained DLP is hard. We draw on earlier results due to Erd\"os et al. and Schnorr, develop geometric tools such as generalized Menelaus' theorem for proving lower bounds on the complexity of the constrained DLP, and construct sets with succinct representation with provable non-trivial lower bounds

Centre-specific bacterial pathogen typing affects infection-control decision making

Whole-genome sequencing is becoming the de facto standard for bacterial outbreak surveillance and infection prevention. This is accompanied by a variety of bioinformatic tools and needs bioinformatics expertise for implementation. However, little is known about the concordance of reported outbreaks when using different bioinformatic workflows. In this multi-centre proficiency testing among 13 major Dutch healthcare-affiliated centres, bacterial whole-genome outbreak analysis was assessed. Centres who participated obtained two randomized bacterial datasets of Illumina sequences, a Klebsiella pneumoniae and a Vancomycin-resistant Enterococcus faecium, and were asked to apply their bioinformatic workflows. Centres reported back on antimicrobial resistance, multi-locus sequence typing (MLST), and outbreak clusters. The reported clusters were analysed using a method to compare landscapes of phylogenetic trees and calculating Kendall–Colijn distances. Furthermore, fasta files were analysed by state-of-the-art single nucleotide polymorphism (SNP) analysis to mitigate the differences introduced by each centre and determine standardized SNP cut-offs. Thirteen centres participated in this study. The reported outbreak clusters revealed discrepancies between centres, even when almost identical bioinformatic workflows were used. Due to stringent filtering, some centres failed to detect extended-spectrum beta-lactamase genes and MLST loci. Applying a standardized method to determine outbreak clusters on the reported de novo assemblies, did not result in uniformity of outbreak-cluster composition among centres

Determining Magnetic Nanoparticle Size Distributions from Thermomagnetic Measurements

Thermomagnetic measurements are used to obtain the size distribution and anisotropy of magnetic nanoparticles. An analytical transformation method is described which utilizes temperature-dependent zero-field cooling (ZFC) magnetization data to provide a quantitative measurement of the average diameter and relative abundance of superparamagnetic nanoparticles. Applying this method to self-assembled MnAs nanoparticles in MnAs-GaAs composite films reveals a log-normal size distribution and reduced anisotropy for nanoparticles compared to bulk materials. This analytical technique holds promise for rapid assessment of the size distribution of an ensemble of superparamagnetic nanoparticles.Comment: Correction Appl. Phys. Lett. 98, 216103 (2011