71 research outputs found
Spiral ground state in the quasi-two-dimensional spin-1/2 system Cu2GeO4
We apply density functional theory band structure calculations, the
coupled-cluster method, and exact diagonalization to investigate the
microscopic magnetic model of the spin-1/2 compound Cu2GeO4. The model is
quasi-two-dimensional, with uniform spin chains along one direction and
frustrated spin chains along the other direction. The coupling along the
uniform chains is antiferromagnetic, J 130 K. The couplings along the
frustrated chains are J1 -60 K and J2 80 K between nearest neighbors and
next-nearest neighbors, respectively. The ground state of the quantum model is
a spiral, with the reduced sublattice magnetization of 0.62 mu_B and the pitch
angle of 84 deg, both renormalized by quantum effects. The proposed spiral
ground state of Cu2GeO4 opens a way to magnetoelectric effects in this
compound.Comment: Extended version: 8 pages, 5 figures, 1 tabl
Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisites CuBi(SeOOX
We investigate the antiferromagnetic canting instability of the spin-1/2
kagome ferromagnet, as realized in the layered cuprates
CuBi(SeOOX (X=Br, Cl, and I). While the local canting can be
explained in terms of competing exchange interactions, the direction of the
ferrimagnetic order parameter fluctuates strongly even at short distances on
account of frustration which gives rise to an infinite ground state degeneracy
at the classical level. In analogy with the kagome antiferromagnet, the
accidental degeneracy is fully lifted only by non-linear 1/S corrections,
rendering the selected uniform canted phase very fragile even for spins-1/2, as
shown explicitly by coupled-cluster calculations. To account for the observed
ordering, we show that the minimal description of these systems must include
the microscopic Dzyaloshinsky-Moriya interactions, which we obtain from
density-functional band-structure calculations. The model explains all
qualitative properties of the kagome francisites, including the detailed nature
of the ground state and the anisotropic response under a magnetic field. The
predicted magnon excitation spectrum and quantitative features of the
magnetization process call for further experimental investigations of these
compounds.Comment: 21 pages, 6 figure
Hidden magnetic order in CuNCN
We report a comprehensive experimental and theoretical study of the
quasi-one-dimensional quantum magnet CuNCN. Based on magnetization measurements
above room temperature as well as muon spin rotation and electron spin
resonance measurements, we unequivocally establish the localized Cu+2-based
magnetism and the magnetic transition around 70 K, both controversially
discussed in the previous literature. Thermodynamic data conform to the
uniform-spin-chain model with a nearest-neighbor intrachain coupling of about
2300 K, in remarkable agreement with the microscopic magnetic model based on
density functional theory band-structure calculations. Using exact
diagonalization and the coupled-cluster method, we derive a collinear
antiferromagnetic order with a strongly reduced ordered moment of about 0.4
mu_B, indicating strong quantum fluctuations inherent to this
quasi-one-dimensional spin system. We re-analyze the available
neutron-scattering data, and conclude that they are not sufficient to resolve
or disprove the magnetic order in CuNCN. By contrast, spectroscopic techniques
indeed show signatures of long-range magnetic order below 70 K, yet with a
rather broad distribution of internal field probed by implanted muons. We
contemplate the possible structural origin of this effect and emphasize
peculiar features of the microstructure studied with synchrotron powder x-ray
diffraction.Comment: 17 pages, 17 figures, 1 tabl
Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisites Cu3Bi(SeO3)2O2X (X = Br, Cl)
We investigate the antiferromagnetic canting instability of the spin-1/2 kagome ferromagnet, as realized in the layered cuprates Cu3Bi(SeO3)2O2X (X = Br, Cl). While the local canting can be explained in terms of competing exchange interactions, the direction of the ferrimagnetic order parameter fluctuates strongly even at short distances on account of frustration which gives rise to an infinite ground state degeneracy at the classical level. In analogy with the kagome antiferromagnet, the accidental degeneracy is fully lifted only by nonlinear 1/S corrections, rendering the selected uniform canted phase very fragile even for spins-1/2, as shown explicitly by coupled-cluster calculations. To account for the observed ordering, we show that the minimal description of these systems must include the microscopic Dzyaloshinsky-Moriya interactions, which we obtain from density-functional band-structure calculations. The model explains all qualitative properties of the kagome francisites, including the detailed nature of the ground state and the anisotropic response under a magnetic field. The predicted magnon excitation spectrum and quantitative features of the magnetization process call for further experimental investigations of these compounds
High Sugar-Induced Insulin Resistance in Drosophila Relies on the Lipocalin Neural Lazarillo
In multicellular organisms, insulin/IGF signaling (IIS) plays a central role in matching energy needs with uptake and storage, participating in functions as diverse as metabolic homeostasis, growth, reproduction and ageing. In mammals, this pleiotropy of action relies in part on a dichotomy of action of insulin, IGF-I and their respective membrane-bound receptors. In organisms with simpler IIS, this functional separation is questionable. In Drosophila IIS consists of several insulin-like peptides called Dilps, activating a unique membrane receptor and its downstream signaling cascade. During larval development, IIS is involved in metabolic homeostasis and growth. We have used feeding conditions (high sugar diet, HSD) that induce an important change in metabolic homeostasis to monitor possible effects on growth. Unexpectedly we observed that HSD-fed animals exhibited severe growth inhibition as a consequence of peripheral Dilp resistance. Dilp-resistant animals present several metabolic disorders similar to those observed in type II diabetes (T2D) patients. By exploring the molecular mechanisms involved in Drosophila Dilp resistance, we found a major role for the lipocalin Neural Lazarillo (NLaz), a target of JNK signaling. NLaz expression is strongly increased upon HSD and animals heterozygous for an NLaz null mutation are fully protected from HSD-induced Dilp resistance. NLaz is a secreted protein homologous to the Retinol-Binding Protein 4 involved in the onset of T2D in human and mice. These results indicate that insulin resistance shares common molecular mechanisms in flies and human and that Drosophila could emerge as a powerful genetic system to study some aspects of this complex syndrome
The role of cholesterol metabolism and various steroid abnormalities in autism spectrum disorders : A hypothesis paper
© 2017 The Authors Autism Research published by Wiley Periodicals, Inc. on behalf of International Society for Autism Research.Peer reviewedPublisher PD
Large expert-curated database for benchmarking document similarity detection in biomedical literature search
Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe
A dataset for dental anxiety and psychological distress in 1550 patients visiting dental clinics
Objectives: Information was collected to identify anxiety in dental patients visiting a dental clinic using the Dental Anxiety Scale, their level of psychological distress using the Brief Symptom Inventory-18 and identifying a correlation between these groups as well as the gender and age.
Data description: This data contains a set of 1550 patients’ answers to questionnaires taken before dental treatment in a dental clinic. It is divided into male and female patients as well as according to their age. The level of Dental Anxiety can be interpreted by answers chosen in the Dental Anxiety Scale (DAS) and the level of psychological distress by answers chosen in the Brief Symptom Inventory-18 (BSI-18). This dataset should help to encourage more research in the field of dental anxiety and we hope to see more comparisons with our data in the future or in different regions of the world
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