910 research outputs found
Direct Observation of Nonequivalent Fermi-Arc States of Opposite Surfaces in Noncentrosymmetric Weyl Semimetal NbP
We have performed high-resolution angle-resolved photoemission spectroscopy
(ARPES) on noncentrosymmetric Weyl semimetal candidate NbP, and determined the
electronic states of both Nb- and P-terminated surfaces corresponding to the
"opposite" surfaces of a polar crystal. We revealed a drastic difference in the
Fermi-surface topology between the opposite surfaces, whereas the Fermi arcs on
both surfaces are likely terminated at the surface projection of the same bulk
Weyl nodes. Comparison of the ARPES data with our first-principles band
calculations suggests notable difference in electronic structure at the
Nb-terminated surface between theory and experiment. The present result opens a
platform for realizing exotic quantum phenomena arising from unusual surface
properties of Weyl semimetals.Comment: 5 pages, 4 figure
Revealing puddles of electrons and holes in compensated topological insulators
Three-dimensional topological insulators harbour metallic surface states with
exotic properties. In transport or optics, these properties are typically
masked by defect-induced bulk carriers. Compensation of donors and acceptors
reduces the carrier density, but the bulk resistivity remains disappointingly
small. We show that measurements of the optical conductivity in BiSbTeSe
pinpoint the presence of electron-hole puddles in the bulk at low temperatures,
which is essential for understanding DC bulk transport. The puddles arise from
large fluctuations of the Coulomb potential of donors and acceptors, even in
the case of full compensation. Surprisingly, the number of carriers appearing
within puddles drops rapidly with increasing temperature and almost vanishes
around 40 K. Monte Carlo simulations show that a highly non-linear screening
effect arising from thermally activated carriers destroys the puddles at a
temperature scale set by the Coulomb interaction between neighbouring dopants,
explaining the experimental observation semi-quantitatively. This mechanism
remains valid if donors and acceptors do not compensate perfectly.Comment: 11 pages with 7 figures plus supplemental material (3 pages
Pluvio: Assembly Clone Search for Out-of-domain Architectures and Libraries through Transfer Learning and Conditional Variational Information Bottleneck
The practice of code reuse is crucial in software development for a faster
and more efficient development lifecycle. In reality, however, code reuse
practices lack proper control, resulting in issues such as vulnerability
propagation and intellectual property infringements. Assembly clone search, a
critical shift-right defence mechanism, has been effective in identifying
vulnerable code resulting from reuse in released executables. Recent studies on
assembly clone search demonstrate a trend towards using machine learning-based
methods to match assembly code variants produced by different toolchains.
However, these methods are limited to what they learn from a small number of
toolchain variants used in training, rendering them inapplicable to unseen
architectures and their corresponding compilation toolchain variants.
This paper presents the first study on the problem of assembly clone search
with unseen architectures and libraries. We propose incorporating human common
knowledge through large-scale pre-trained natural language models, in the form
of transfer learning, into current learning-based approaches for assembly clone
search. Transfer learning can aid in addressing the limitations of the existing
approaches, as it can bring in broader knowledge from human experts in assembly
code. We further address the sequence limit issue by proposing a reinforcement
learning agent to remove unnecessary and redundant tokens. Coupled with a new
Variational Information Bottleneck learning strategy, the proposed system
minimizes the reliance on potential indicators of architectures and
optimization settings, for a better generalization of unseen architectures. We
simulate the unseen architecture clone search scenarios and the experimental
results show the effectiveness of the proposed approach against the
state-of-the-art solutions.Comment: 13 pages and 4 figures. This work has been submitted to the IEEE for
possible publication. Copyright may be transferred without notice, after
which this version may no longer be accessibl
Tensile behaviour of pitting corroded steel bars:Laboratory investigation and probabilistic-based analysis
Localised corrosion in steel bars has been a long-standing issue in the durability of reinforced concrete structures, but a comprehensive scheme for the analysis of pitting corroded steel bars, especially with respect to the deformation capacity, is not currently available. In this study, the morphological characteristics of 27 pitting steel bars were captured using a 3D scanner. The measured data were used to establish the probability distribution model of the cross-sectional areas of the corroded bars. Uniaxial tensile tests were conducted, and the evolving deformation field of the corroded bars was recorded through Digital Image Correlation (DIC). Based on the 3D reconstructed model and DIC results, an analytical method for evaluating the mechanical properties of pitting steel bars was developed and validated. The results show that the two-component Gaussian mixture distribution model outperforms conventional unimodal distribution models. Comparison of the analytical results with experimental data demonstrates that the proposed procedure is capable of predicting not only the ultimate strength but also the gauge length-dependent ultimate strain of corroded bars. Additionally, there exists a strengthening effect in the ultimate stress at the critical sections and this effect should not be ignored for accurate predictions.</p
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Automated Measurement of Spatially Resolved Hair-Hair Single Fiber Adhesion.
The adhesion force between individual human hair fibers in a crosshair geometry was measured by observing their natural bending and adhesive jumps out of contact, using optical video microscopy. The hair fibers' natural elastic responses, calibrated by measuring their natural resonant frequencies, were used to measure the forces. Using a custom-designed, automated apparatus to measure thousands of individual hair-hair contacts along millimeter length scales of hair, it was found that a broad, yet characteristic, spatially variant distribution in adhesion force is measured on the 1 to 1000 nN scale for both clean and conditioner-treated hair fibers. Comparison between the measured adhesion forces and adhesion forces modeled from the hairs' surface topography (measured using confocal laser profilometry) shows they have a good order-of-magnitude agreement and have similar breadth and shape. The agreement between the measurements and the model suggests, perhaps unsurprisingly, that hair-hair adhesion is governed, to a first approximation, by the unique surface structure of the hairs' cuticles and, therefore, the large distribution in local mean curvature at the various individual contact points along the hairs' lengths. We posit that haircare products could best control the surface properties (or at least the adhesive properties) between hairs by directly modifying the hair surface microstructure
Binomial coefficients, Catalan numbers and Lucas quotients
Let be an odd prime and let be integers with and . In this paper we determine
mod for ; for example,
where is the Jacobi symbol, and is the Lucas
sequence given by , and for
. As an application, we determine modulo for any integer , where denotes the
Catalan number . We also pose some related conjectures.Comment: 24 pages. Correct few typo
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