363 research outputs found
A method for measuring the contact area in instrumented indentation testing by tip scanning probe microscopy imaging
The determination of the contact area is a key step to derive mechanical
properties such as hardness or an elastic modulus by instrumented indentation
testing. Two families of procedures are dedicated to extracting this area: on
the one hand, post mortem measurements that require residual imprint imaging,
and on the other hand, direct methods that only rely on the load vs. the
penetration depth curve. With the development of built-in scanning probe
microscopy imaging capabilities such as atomic force microscopy and indentation
tip scanning probe microscopy, last generation indentation devices have made
systematic residual imprint imaging much faster and more reliable. In this
paper, a new post mortem method is introduced and further compared to three
existing classical direct methods by means of a numerical and experimental
benchmark covering a large range of materials. It is shown that the new method
systematically leads to lower error levels regardless of the type of material.
Pros and cons of the new method vs. direct methods are also discussed,
demonstrating its efficiency in easily extracting mechanical properties with an
enhanced confidence
Giant Anomalous Hall Conductivity in the Itinerant Ferromagnet LaCrSb<sub>3</sub> and the Effect of f-Electrons
Itinerant ferromagnets constitute an important class of materials wherein spin polarization can affect the electric transport properties in nontrivial ways. One such phenomenon is anomalous Hall effect which depends on the details of the band structure such as the amount of band crossings in the valence band of the ferromagnet. Here, extraordinary anomalous Hall effect is found in an itinerant ferromagnetic metal LaCrSb3. The rather 2D nature of the magnetic subunit imparts large anisotropic anomalous Hall conductivity of 1250 Ω−1 cm−1 at 2 K. The investigations suggest that a strong Berry curvature by abundant momentum-space crossings and narrow energy-gap openings are the primary sources of the anomalous Hall conductivity. An important observation is the existence of quasi-dispersionless bands in LaCrSb3 which is now known to increase the anomalous Hall conductivity. After introducing f-electrons, anomalous Hall conductivity experiences more than twofold increase and reaches 2900 Ω−1 cm−1 in NdCrSb3. © 2021 The Authors. Advanced Quantum Technologies published by Wiley-VCH Gmb
Large Anomalous Hall and Nernst Effects in High Curie-Temperature Iron-Based Heusler Compounds
Abstract The interplay between topology and magnetism has recently sparked the frontier studies of magnetic topological materials that exhibit intriguing anomalous Hall and Nernst effects owning to the large intrinsic Berry curvature (BC). To better understand the anomalous quantum transport properties of these materials and their implications for future applications such as electronic and thermoelectric devices, it is crucial to discover more novel material platforms for performing anomalous transverse transport studies. Here, it is experimentally demonstrated that low-cost Fe-based Heusler compounds exhibit large anomalous Hall and Nernst effects. An anomalous Hall conductivity of 250?750 S cm?1 and Nernst thermopower of above 2 µV K?1 are observed near room temperature. The positive effect of anti-site disorder on the anomalous Hall transport is revealed. Considering the very high Curie temperature (nearly 1000 K), larger Nernst thermopowers at high temperatures are expected owing to the existing magnetic order and the intrinsic BC. This work provides a background for developing low-cost Fe-based Heusler compounds as a new material platform for anomalous transport studies and applications, in particular, near and above room temperature
Using Quantum Confinement to Uniquely Identify Devices
Modern technology unintentionally provides resources that enable the trust of
everyday interactions to be undermined. Some authentication schemes address
this issue using devices that give unique outputs in response to a challenge.
These signatures are generated by hard-to-predict physical responses derived
from structural characteristics, which lend themselves to two different
architectures, known as unique objects (UNOs) and physically unclonable
functions (PUFs). The classical design of UNOs and PUFs limits their size and,
in some cases, their security. Here we show that quantum confinement lends
itself to the provision of unique identities at the nanoscale, by using
fluctuations in tunnelling measurements through quantum wells in resonant
tunnelling diodes (RTDs). This provides an uncomplicated measurement of
identity without conventional resource limitations whilst providing robust
security. The confined energy levels are highly sensitive to the specific
nanostructure within each RTD, resulting in a distinct tunnelling spectrum for
every device, as they contain a unique and unpredictable structure that is
presently impossible to clone. This new class of authentication device operates
with few resources in simple electronic structures above room temperature.Comment: 13 pages, 3 figure
The French Didactic Tradition in Mathematics
This chapter presents the French didactic tradition. It first describes theemergence and development of this tradition according to four key features (role ofmathematics and mathematicians, role of theories, role of design of teaching andlearning environments, and role of empirical research), and illustrates it through two case studies respectively devoted to research carried out within this traditionon algebra and on line symmetry-reflection. It then questions the influence of thistradition through the contributions of four researchers from Germany, Italy, Mexicoand Tunisia, before ending with a short epilogue
Observation of giant spin split Fermi arc with maximal Chern number in the chiral topological semimetal PtGa
Non-symmorphic chiral topological crystals host exotic multifold fermions,
and their associated Fermi arcs helically wrap around and expand throughout the
Brillouin zone between the high-symmetry center and surface-corner momenta.
However, Fermi-arc splitting and realization of the theoretically proposed
maximal Chern number rely heavily on the spin-orbit coupling (SOC) strength. In
the present work, we investigate the topological states of a new chiral
crystal, PtGa, which has the strongest SOC among all chiral crystals reported
to date. With a comprehensive investigation using high-resolution
angle-resolved photoemission spectroscopy, quantum-oscillation measurements,
and state-of-the-art ab initio calculations, we report a giant SOC-induced
splitting of both Fermi arcs and bulk states. Consequently, this study
experimentally confirms the realization of a maximal Chern number equal to |4|
for the first time in multifold fermionic systems, thereby providing a platform
to observe large-quantized photogalvanic currents in optical experiments.Comment: Accepted in Nature Communication
Comprehensive molecular portraits of human breast tumours
We analysed primary breast cancers by genomic DNA copy number arrays, DNA methylation, exome sequencing, messenger RNA arrays, microRNA sequencing and reverse-phase protein arrays. Our ability to integrate information across platforms provided key insights into previously defined gene expression subtypes and demonstrated the existence of four main breast cancer classes when combining data from five platforms, each of which shows significant molecular heterogeneity. Somatic mutations in only three genes (TP53, PIK3CA and GATA3) occurred at.10% incidence across all breast cancers; however, there were numerous subtype-associated and novel gene mutations including the enrichment of specific mutations in GATA3, PIK3CA and MAP3K1 with the luminal A subtype. We identified two novel protein-expression-defined subgroups, possibly produced by stromal/microenvironmental elements, and integrated analyses identified specific signalling pathways dominant in each molecular subtype including a HER2/phosphorylated HER2/EGFR/phosphorylated EGFR signature within the HER2-enriched expression subtype. Comparison of basal-like breast tumours with high-grade serous ovarian tumours showed many molecular commonalities, indicating a related aetiology and similar therapeutic opportunities. The biological finding of the four main breast cancer subtypes caused by different subsets of genetic and epigenetic abnormalities raises the hypothesis that much of the clinically observable plasticity and heterogeneity occurs within, and not across, these major biological subtypes of breast cancer. © 2012 Macmillan Publishers Limited. All rights reserved
Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies
Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed
Recent advances in organic synthesis using light-mediated n-heterocyclic carbene catalysis
The combination of photocatalysis with other ground state catalytic systems have attracted much attention recently due to the enormous synthetic potential offered by a dual activation mode. The use of N-heterocyclic carbene (NHC) as organocatalysts emerged as an important synthetic tool. Its ability to harness umpolung reactivity by the formation of the Breslow intermediate has been employed in the synthesis of thousands of biologically important compounds. However, the available coupling partners are relatively restricted, and its combination with other catalytic systems might improve its synthetic versatility. Thus, merging photoredox and N-heterocyclic carbene (NHC) catalysis has emerged recently as a powerful strategy to develop new transformations and give access to a whole new branch of synthetic possibilities. This review compiles the NHC catalyzed methods mediated by light, either in the presence or absence of an external photocatalyst, that have been described so far, and aims to give an accurate overview of the potential of this activation modeL.M. acknowledges the Autonomous Community of Madrid (CAM)
for the financial support (PEJD-2019-PRE/AMB-16640 and SI1/PJI/
2019-00237) and for an “Atracción de Talento Investigador”
contract (2017-T2/AMB-5037
Solid-state synthesis of NASICON (Na3Zr2Si2PO12) using nanoparticle precursors for optimisation of ionic conductivity
In this work, the effect of varying the size of the precursor raw materials SiO2 and ZrO2 in the solid-state synthesis of NASICON in the form Na3Zr2Si2PO12 was studied. Nanoscale and macro-scale precursor materials were selected for comparison purposes, and a range of sintering times were examined (10, 24 and 40 h) at a temperature of 1230 °C. Na3Zr2Si2PO12 pellets produced from nanopowder precursors were found to produce substantially higher ionic conductivities, with improved morphology and higher density than those produced from larger micron-scaled precursors. The nanoparticle precursors were shown to give a maximum ionic conductivity of 1.16 × 10−3 S cm−1 when sintered at 1230 °C for 40 h, in the higher range of published solid-state Na3Zr2Si2PO12 conductivities. The macro-precursors gave lower ionic conductivity of 0.62 × 10−3 S cm−1 under the same processing conditions. Most current authors do not quote or consider the precursor particle size for solid-state synthesis of Na3Zr2Si2PO12. This study shows the importance of precursor powder particle size in the microstructure and performance of Na3Zr2Si2PO12 during solid-state synthesis and offers a route to improved predictability and consistency of the manufacturing process
- …