5 research outputs found
Probing magnetic ordering in air stable iron-rich van der Waals minerals
In the rapidly expanding field of two-dimensional materials, magnetic
monolayers show great promise for the future applications in nanoelectronics,
data storage, and sensing. The research in intrinsically magnetic
two-dimensional materials mainly focuses on synthetic iodide and telluride
based compounds, which inherently suffer from the lack of ambient stability. So
far, naturally occurring layered magnetic materials have been vastly
overlooked. These minerals offer a unique opportunity to explore air-stable
complex layered systems with high concentration of local moment bearing ions.
We demonstrate magnetic ordering in iron-rich two-dimensional phyllosilicates,
focusing on mineral species of minnesotaite, annite, and biotite. These are
naturally occurring van der Waals magnetic materials which integrate local
moment baring ions of iron via magnesium/aluminium substitution in their
octahedral sites. Due to self-inherent capping by silicate/aluminate
tetrahedral groups, ultra-thin layers are air-stable. Chemical
characterization, quantitative elemental analysis, and iron oxidation states
were determined via Raman spectroscopy, wavelength disperse X-ray spectroscopy,
X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy.
Superconducting quantum interference device magnetometry measurements were
performed to examine the magnetic ordering. These layered materials exhibit
paramagnetic or superparamagnetic characteristics at room temperature. At low
temperature ferrimagnetic or antiferromagnetic ordering occurs, with the
critical ordering temperature of 38.7 K for minnesotaite, 36.1 K for annite,
and 4.9 K for biotite. In-field magnetic force microscopy on iron bearing
phyllosilicates confirmed the paramagnetic response at room temperature,
present down to monolayers.Comment: 19 pages, 6 figure
() Imino and methyl protons (in bold) in Watson–Crick base pair and T·T mismatch
<p><b>Copyright information:</b></p><p>Taken from "Structural roles of CTG repeats in slippage expansion during DNA replication"</p><p>Nucleic Acids Research 2005;33(5):1604-1617.</p><p>Published online 14 Mar 2005</p><p>PMCID:PMC1065260.</p><p>© The Author 2005. Published by Oxford University Press. All rights reserved</p> Owing to the asymmetric arrangement of the T·T mismatches, two T·T pairing modes are present. Rapid transition between the two pairing modes is possible. () Numbering scheme of (CTG). Nucleotides in gray represent the extended stem regions that promote hairpin formation
Sequence Context Effect on Strand Slippage in Natural DNA Primer–Templates
Strand slippage has been found to occur in primer–templates
containing a templating thymine, cytosine, and guanine, leading to
the formation of misaligned structures with a single-nucleotide bulge.
If remained in the active
site of low-fidelity polymerases during DNA replication, these misaligned
structures can ultimately bring about deletion mutations. In this
study, we performed NMR investigations on primer–template models
containing a templating adenine. Similar to our previous results on
guanine, adenine templates are also less prone to strand slippage
than pyrimidine templates. Misalignment occurs only in primer–templates
that form a terminal C·G or G·C base pair. Together with
our previous findings on thymine, cytosine, and guanine templates,
the present study reveals strand slippage can occur in any kind of
natural templating bases during DNA replication, providing insights
into the origin of mutation hotspots in natural DNA sequences. In
addition to the type of incoming base upon misincorporation, the propensity
of strand slippage in primer–templates depends also on the
type of templating base, its upstream and downstream bases
Fracture statistics of brittle materials: Weibull or normal distribution
The fit of fracture strength data of brittle materials (Si3N4, SiC, and ZnO) to the Weibull and normal distributions is compared in terms of the Akaike information criterion. For Si3N4, the Weibull distribution fits the data better than the normal distribution, but for ZnO the result is just the opposite. In the case of SiC, the difference is not large enough to make a clear distinction between the two distributions. There is not sufficient evidence to show that the Weibull distribution is always preferred to other distributions, and the uncritical use of the Weibull distribution for strength data is questioned
Influence of threshold stress on the estimation of the Weibull statistics
The influence of threshold stress on the estimation of the Weibull statistics is discussed in terms of the Akaike information criterion. Numerical simulations show that, if sample data are limited in number and threshold stress is not too large, the two-parameter Weibull distribution is still a preferred choice. For example, the fit of strength data of glass and ceramics to the two- and three-parameter Weibull distributions is compared