Magnetic skyrmions are hailed as a potential technology for data storage and other data processing devices. However, their stability against thermal fluctuations is an open question that must be ...answered before skyrmion-based devices can be designed. In this work, we study paths in the energy landscape via which the transition between the skyrmion and the uniform state can occur in interfacial Dzyaloshinskii-Moriya finite-sized systems. We find three mechanisms the system can take in the process of skyrmion nucleation or destruction and identify that the transition facilitated by the boundary has a significantly lower energy barrier than the other energy paths. This clearly demonstrates the lack of the skyrmion topological protection in finite-sized magnetic systems. Overall, the energy barriers of the system under investigation are too small for storage applications at room temperature, but research into device materials, geometry and design may be able to address this.
This study examined associations between different sources of chronic perceived stress and deleterious behaviors (eating disorder symptoms, insufficient sleep, and insufficient vigorous physical ...activity) among first-year college students.
The study used data on 885 first-year students (ages 18-20) at a large public university in North Carolina. The prevalence of deleterious behaviors was evaluated. Associations were estimated between different sources of chronic perceived stress (academic, future, peers, friendships, romantic, appearance, health, chronic illness, financial, work, family) and health behaviors after controlling for psychosocial supports and demographics. Moderating effects of gender and moderate-severe anxiety/depression symptoms were also tested.
19% of first-year student reported symptoms of eating disorders, 42% insufficient sleep, and 43% insufficient vigorous physical activity. Perceived chronic stress increased the odds of reporting these deleterious behaviors. These effects were not moderated by gender or moderate-severe anxiety/depression symptoms. Appearance- and health-related stress were associated with eating disorder symptoms; health- and romantic-related stress were associated with insufficient sleep; and health-related stress was associated with insufficient vigorous physical activity.
Outcomes were survey-based. The study was based on cross-sectional data from a single university, so the direction of causality cannot be determined, and more work needs to be done to determine whether this would extend to other populations.
Analyses of DNA sequences from cultivated microorganisms have revealed genome-wide, taxa-specific nucleotide compositional characteristics, referred to as genome signatures. These signatures have ...far-reaching implications for understanding genome evolution and potential application in classification of metagenomic sequence fragments. However, little is known regarding the distribution of genome signatures in natural microbial communities or the extent to which environmental factors shape them.
We analyzed metagenomic sequence data from two acidophilic biofilm communities, including composite genomes reconstructed for nine archaea, three bacteria, and numerous associated viruses, as well as thousands of unassigned fragments from strain variants and low-abundance organisms. Genome signatures, in the form of tetranucleotide frequencies analyzed by emergent self-organizing maps, segregated sequences from all known populations sharing < 50 to 60% average amino acid identity and revealed previously unknown genomic clusters corresponding to low-abundance organisms and a putative plasmid. Signatures were pervasive genome-wide. Clusters were resolved because intra-genome differences resulting from translational selection or protein adaptation to the intracellular (pH approximately 5) versus extracellular (pH approximately 1) environment were small relative to inter-genome differences. We found that these genome signatures stem from multiple influences but are primarily manifested through codon composition, which we propose is the result of genome-specific mutational biases.
An important conclusion is that shared environmental pressures and interactions among coevolving organisms do not obscure genome signatures in acid mine drainage communities. Thus, genome signatures can be used to assign sequence fragments to populations, an essential prerequisite if metagenomics is to provide ecological and biochemical insights into the functioning of microbial communities.
Purpose of Review
Acute myeloid leukaemia (AML) is a heterogeneous malignancy for which treatment options remain suboptimal. It is clear that a greater understanding of the biology of the AML niche ...will enable new therapeutic strategies to be developed in order to improve treatment outcomes for patients.
Recent Findings
Recent evidence has highlighted the importance of the bone marrow microenvironment in protecting leukaemia cells, and in particular leukaemic stem cells from chemotherapy-induced cell death. This includes mesenchymal stem cells supporting growth and preventing apoptosis, and altered action and secretion profiles of other niche components including adipocytes, endothelial cells and T cells.
Summary
Here, we provide a detailed overview of the current understanding of the AML bone marrow microenvironment. Clinical trials of agents that mobilise leukaemic stem cells from the bone marrow are currently ongoing and show early promise. Future challenges will involve combining these novel therapies targeted at the AML niche with conventional chemotherapy treatment.
Computer simulations are used widely across the engineering and science disciplines, including in the research and development of magnetic devices using computational micromagnetics. In this work, we ...identify and review different approaches to configuring simulation runs: (i) the re-compilation of source code, (ii) the use of configuration files, (iii) the graphical user interface, and (iv) embedding the simulation specification in an existing programming language to express the computational problem. We identify the advantages and disadvantages of different approaches and discuss their implications on effectiveness and reproducibility of computational studies and results. Following on from this, we design and describe a domain specific language for micromagnetics that is embedded in the Python language, and allows users to define the micromagnetic simulations they want to carry out in a flexible way. We have implemented this micromagnetic simulation description language together with a computational backend that executes the simulation task using the Object Oriented MicroMagnetic Framework (OOMMF). We illustrate the use of this Python interface for OOMMF by solving the micromagnetic standard problem 4. All the code is publicly available and is open source.
We present empirical conductance relations that are derived from incoherent scatter radar observations and correlated with all sky imager observations to identify the morphology of the aurora. We use ...75,461 events collected using the Poker Flat Incoherent Scatter Radar (PFISR) with associated all sky imagers observations spanning the years 2012–2016. In addition to classifying these events based on auroral morphology, we estimated the Hall and Pedersen conductance and the differential number flux from which the energy flux and the average energy can be calculated. The differential number flux was estimated using the maximum entropy inversion method described in Semeter and Kamalabadi (2005, https://doi.org/10.1029/2004RS003042), but now incorporating the Fang et al. (2010, https://doi.org/10.1029/2010GL045406) ionization model. The main results of this investigation are the power law equations that describe the median, 90th, and 10th percentile Hall and Pedersen conductance as a function of energy flux and average energy. These power law fits are performed for different auroral morphology including all events, discrete, diffuse, and pulsating auroral events. The median Pedersen conductance is found to be in good agreement with past empirical conductance specifications by Robinson et al. (1987, https://doi.org/10.1029/JA092iA03p02565); however, the median Hall conductance from the PFISR observations is found to be larger than the empirical Hall conductance formulas by Robinson et al. (1987, https://doi.org/10.1029/JA092iA03p02565). Pulsating aurora is found to be the most frequently occurring auroral morphology. Furthermore, pulsating aurora has an important contribution to Hall conductance since it has higher average energies than discrete aurora. The results from this investigation are applicable to space weather models and may enable better agreement between model‐data comparisons.
Key Points
Empirical conductance formulas are derived using 75,461 incoherent scatter radar observations with corresponding auroral morphology
Power law fits are presented for Hall and Pedersen conductances as function of average energy and energy flux
Pulsating aurora found to be an important contribution for the Hall conductance at higher average energies
The narrow genetic base of cultivated cotton germplasm is hindering the cotton productivity worldwide. Although potential genetic diversity exists in
Gossypium genus, it is largely ‘underutilized’ ...due to photoperiodism and the lack of innovative tools to overcome such challenges. The application of linkage disequilibrium (LD)-based association mapping is an alternative powerful molecular tool to dissect and exploit the natural genetic diversity conserved within cotton germplasm collections, greatly accelerating still ‘lagging’ cotton marker-assisted selection (MAS) programs. However, the extent of genome-wide linkage disequilibrium (LD) has not been determined in cotton. We report the extent of genome-wide LD and association mapping of fiber quality traits by using a 95 core set of microsatellite markers in a total of 285 exotic
Gossypium hirsutum accessions, comprising of 208 landrace stocks and 77 photoperiodic variety accessions. We demonstrated the existence of useful genetic diversity within exotic cotton germplasm. In this germplasm set, 11–12% of SSR loci pairs revealed a significant LD. At the significance threshold (
r
2
≥
0.1), a genome-wide average of LD declines within the genetic distance at <
10 cM in the landrace stocks germplasm and >
30 cM in variety germplasm. Genome wide LD at
r
2
≥
0.2 was reduced on average to ∼
1–2 cM in the landrace stock germplasm and 6–8 cM in variety germplasm, providing evidence of the potential for association mapping of agronomically important traits in cotton. We observed significant population structure and relatedness in assayed germplasm. Consequently, the application of the mixed liner model (MLM), considering both kinship (
K) and population structure (
Q) detected between 6% and 13% of SSR markers associated with the main fiber quality traits in cotton. Our results highlight for the first time the feasibility and potential of association mapping, with consideration of the population structure and stratification existing in cotton germplasm resources. The number of SSR markers associated with fiber quality traits in diverse cotton germplasm, which broadly covered many historical meiotic events, should be useful to effectively exploit potentially new genetic variation by using MAS programs.
Stable and manipulable Bloch point Beg, Marijan; Pepper, Ryan A; Cortés-Ortuño, David ...
Scientific reports,
05/2019, Letnik:
9, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The prediction of magnetic skyrmions being used to change the way we store and process data has led to materials with Dzyaloshinskii-Moriya interaction coming into the focus of intensive research. So ...far, studies have looked mostly at magnetic systems composed of materials with single chirality. In a search for potential future spintronic devices, combination of materials with different chirality into a single system may represent an important new avenue for research. Using finite element micromagnetic simulations, we study an FeGe disk with two layers of different chirality. We show that for particular thicknesses of layers, a stable Bloch point emerges at the interface between two layers. In addition, we demonstrate that the system undergoes hysteretic behaviour and that two different types of Bloch point exist. These 'head-to-head' and 'tail-to-tail' Bloch point configurations can, with the application of an external magnetic field, be switched between. Finally, by investigating the time evolution of the magnetisation field, we reveal the creation mechanism of the Bloch point. Our results introduce a stable and manipulable Bloch point to the collection of particle-like state candidates for the development of future spintronic devices.
We present a methodology for the determination of empirical masses of single stars through the combination of three direct observables with Gaia and Transiting Exoplanet Survey Satellite (TESS): (i) ...the surface gravity via granulation-driven variations in the TESS light curve, (ii) the bolometric flux at Earth via the broadband spectral energy distribution, and (iii) the distance via the Gaia parallax. We demonstrate the method using 525 Kepler stars for which these measures are available in the literature, and show that the stellar masses can be measured with this method to a precision of ∼25%, limited by the surface-gravity precision of the granulation "flicker" method (∼0.1 dex) and by the parallax uncertainties (∼10% for the Kepler sample). We explore the impact of expected improvements in the surface gravity determinations-through the application of granulation background fitting and the use of recently published granulation-metallicity relations-and improvements in the parallaxes with the arrival of the Gaia second data release. We show that the application of this methodology to stars that will be observed by TESS should yield radii good to a few percent and masses good to 10%. Importantly, the method does not require the presence of an orbiting, eclipsing, or transiting body, nor does it require spatial resolution of the stellar surface. Thus, we can anticipate the determination of fundamental, accurate stellar radii and masses for hundreds of thousands of bright single stars-across the entire sky and spanning the Hertzsprung-Russell diagram-including those that will ultimately be found to host planets.
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