35 research outputs found
Synthesis and search for superconductivity in LiBC
Following the recent theoretical prediction of superconductivity in hole
doped LiBC by Rosner et al [1], we have attempted to synthesise Li deficient
LixBC (x = 1, 0.8, 0.6 and 0.4) and look for superconductivity in this system.
Our synthesis procedure, following the recipe for MgB2, involves reaction of
elemental components in a Ta crucible at 900o C under 50 bar of argon pressure.
X-ray diffraction measurements indicate the formation of P63/mmc structure up
to x=0.6. However, no diamagnetic signal or zero resistance, corresponding to
the superconducting transition, was observed in the temperature range of 300 to
4 K. This is possibly related to the presence of disorder in the B-C stacking;
evidence for which is suggested from a study of the vibrational modes of LixBC
through infrared spectroscopy.Comment: 7 pages, 6 figures 1 tabl
Critical properties of superconducting Ba1-xKxFe2As2
Magnetisation and magnetoresistance measurements have been carried out on
superconducting Ba1-xKxFe2As2 samples with x=0.40 and 0.50. From low field
magnetization data carried out at different temperatures below TC, HC1 has been
extracted. The plot of HC1 versus temperature shows an anomalous increase at
low temperatures. From high field magnetization hysterisis measurements carried
out in fields up to 16 T at 4.2 K and 20 K, the critical current density has
been evaluated using the Bean critical state model. The JC determined from the
high field data is >104A/cm2 at 4.2 K and 5 T. The superconducting transitions
were also measured resistively in increasing applied magnetic fields up to 12
Tesla. From the variation of the TC onset with applied field, dHC2/dT at TC was
obtained to be -7.708 T/K and -5.57 T/K in the samples with x=0.40 and 0.50.Comment: 14 pages; 7 figure
Drastic ground state changes induced by Ni substitution in NaxCoO2
We report on the effect of Ni substitution at the Co site on the physical
properties of NaxCoO2 system by investigating the series NaxCo1-yNiyO2 (x=0.75,
0<y<0.15). An upturn in the resistivity is observed in all Ni substituted
samples as the temperature is lowered, suggestive of the occurrence of a
Metal-Insulator Transition (MIT). The temperature at which this transition
occurs increases with Ni content. The temperature dependence of the resistivity
in the metallic region in the Ni substituted samples shows a T2 dependence,
which is qualitatively different from that observed in the pristine sample. The
evolution of the Fano asymmetry parameter, extracted by analyzing the lineshape
of the IR active in-plane Co-O mode, both as a function of Ni concentration and
temperature corroborates the occurrence of the MIT. It is argued that the
progressive substitution of the Co4+ ions with Ni increases the probability of
double occupancy and therefore the on-site Coulomb interaction energy leading
to a shift in the thermodynamically driven MIT to higher temperatures.Comment: 17 pages 9 figures; submitted to Journal Of Phys. Cond. Ma
Dislocation Driven Chromium Precipitation in Fe-9Cr Binary Alloy: A Positron Lifetime Study
The influence of initial heat treatment on anomalous Cr precipitation within
high temperature solubility region in Fe-9Cr alloy has been investigated using
positron lifetime studies. Air-quenched samples with pre-existing dislocations
exhibited a distinct annealing stage in positron lifetime between 800 and 1100
K corresponding to Cr-precipitation. During this stage, Transmission Electron
Microscopy showed fine precipitates of average size 4 nm, dispersed throughout
the sample and from EDS analysis they are found to be Cr-enriched. The
existence of dislocations is found to be responsible for Cr precipitation.Comment: Revised version Submitted to Phys. Rev.
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
Towards Simulation of Dislocation-Based Creep Mechanisms: Application to Oxide Dispersion Strengthening Steels
International audienc
Emerging trends in molecular systematics and molecular phylogeny of mayflies (Insecta: Ephemeroptera)
Current trends are reviewed in the molecular systematics and phylogeny of the Ephemeroptera (mayflies), an ancient monophyletic lineage of pterygote insects. Theories of mayfly origins are analyzed, followed by a discussion of higher classification schemes in light of recent developments in molecular systematics. Ephemeroptera evolution is a classic example of ancient rapid radiation, presenting challenges for phylogenetic analysis. The utility of combined studies of morphological and molecular data is substantiated with examples and the role of molecular systematics in unraveling the taxonomy of cryptic species complexes is highlighted. The importance of DNA barcoding in mayfly taxonomy is discussed in the light of recent progress, and future contributions of genetics to the study of taxonomy, ecology and evolution in mayflies are discussed