1,075 research outputs found
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
Evolution of magnetic polarons and spin-carrier interactions through the metal-insulator transition in EuGdO
Raman scattering studies as functions of temperature, magnetic field, and
Gd-substitution are used to investigate the evolution of magnetic polarons and
spin-carrier interactions through the metal-insulator transition in
EuGdO. These studies reveal a greater richness of phase behavior
than have been previously observed using transport measurements: a
spin-fluctuation-dominated paramagnetic (PM) phase regime for T T
T, a two-phase regime for T T in which magnetic polarons
develop and coexist with a remnant of the PM phase, and an inhomogeneous
ferromagnetic phase regime for T T
Hard Instances of the Constrained Discrete Logarithm Problem
The discrete logarithm problem (DLP) generalizes to the constrained DLP,
where the secret exponent 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
Anorgasmia in women
This article reports on the etiology and treatment of anorgasmia. Etiological factors include childhood and adolescent experiences, current individual attitudes, and lifestyle factors, as well as the quality and dynamics of past and present committed relationships. It is important to assess the nature of each of the previously mentioned factors in determining the nature of the orgasmic dysfunction as well as assisting in the development of a treatment plan. Treatment approaches for anorgasmia need to address individual factors (e.g., performance anxiety, poor body image) as well as interpersonal problems. A systemic treatment framework would appear to be the most useful approach to treat this sexual dysfunction, as this type of strategy identifies and treats the difficulties experienced by the anorgasmic woman within the total context of her life. Of course, this approach necessitates the involvement of the partner in therapy, and treatment is unlikely to be effective unless the problems experienced by both the woman and her partner are addressed. Limitations of past research in terms of inadequate evaluation of treatment, low sample sizes, and poorly defined interventions are discussed. Finally, directions for future research to advance our understanding of the most effective treatments for anorgasmia are considered. <br /
Magnetic Interactions and Transport in (Ga,Cr)As
The magnetic, transport, and structural properties of (Ga,Cr)As are reported.
Zincblende GaCrAs was grown by low-temperature molecular beam
epitaxy (MBE). At low concentrations, x0.1, the materials exhibit unusual
magnetic properties associated with the random magnetism of the alloy. At low
temperatures the magnetization M(B) increases rapidly with increasing field due
to the alignment of ferromagnetic units (polarons or clusters) having large
dipole moments of order 10-10. A standard model of
superparamagnetism is inadequate for describing both the field and temperature
dependence of the magnetization M(B,T). In order to explain M(B) at low
temperatures we employ a distributed magnetic moment (DMM) model in which
polarons or clusters of ions have a distribution of moments. It is also found
that the magnetic susceptibility increases for decreasing temperature but
saturates below T=4 K. The inverse susceptibility follows a linear-T
Curie-Weiss law and extrapolates to a magnetic transition temperature
=10 K. In magnetotransport measurements, a room temperature resistivity
of =0.1 cm and a hole concentration of cm
are found, indicating that Cr can also act as a acceptor similar to Mn. The
resistivity increases rapidly for decreasing temperature below room
temperature, and becomes strongly insulating at low temperatures. The
conductivity follows exp[-(T/T)] over a large range of
conductivity, possible evidence of tunneling between polarons or clusters.Comment: To appear in PRB 15 Mar 200
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