52 research outputs found
The Wilson loop CFT: Insertion dimensions and structure constants from wavy lines
We study operator insertions into the BPS Wilson loop in
SYM theory and determine their two-point coefficients, anomalous dimensions and
structure constants. The calculation is done for the first few lowest dimension
insertions and relies on known results for the expectation value of a smooth
Wilson loop. In addition to the particular coefficients that we calculate, our
study elucidates the connection between deformations of the line and operator
insertions and between the vacuum expectation value of the line and the CFT
data of the insertions.Comment: 23 pages. v2: minor correction
Wavefronts Dislocations Measure Topology in Graphene with Defects
We present a general method to identify topological materials by studying the
local electronic density . More
specifically, certain types of defects or spatial textures such as vacancies,
turn graphene into a topological material characterised by invariant Chern or
winding numbers. We show that these numbers are directly accessible from a
dislocation pattern of , resulting
from an interference effect induced by topological defects. For non topological
defects such as adatoms, this pattern is scrambled by Friedel oscillations
absent in topological cases. A Kekule distortion is discussed and shown to be
equivalent to a vacancy.Comment: 6 pages and supplementary materia
Measuring Light Pollution with Fisheye Lens Imagery from A Moving Boat, A Proof of Concept
Near all-sky imaging photometry was performed from a boat on the Gulf of
Aqaba to measure the night sky brightness in a coastal environment. The boat
was not anchored, and therefore drifted and rocked. The camera was mounted on a
tripod without any inertia/motion stabilization. A commercial digital single
lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400,
with the exposure time varied between 0.5 s and 5 s. We find that despite
movement of the vessel the measurements produce quantitatively comparable
results apart from saturation effects. We discuss the potential and limitations
of this method for mapping light pollution in marine and freshwater systems.
This work represents the proof of concept that all-sky photometry with a
commercial DSLR camera is a viable tool to determine light pollution in an
ecological context from a moving boat.Comment: 9 pages, 6 figures, accepted at International Journal of Sustainable
Lightin
Deformations of the circular Wilson loop and spectral (in)dependence
In this paper we study the expectation value of deformations of the circular
Wilson loop in super Yang-Mills theory. The leading order
deformation, known as the Bremsstrahlung function, can be obtained exactly from
supersymmetric localization, so our focus is on deformations at higher orders.
We find simple expressions for the expectation values for generic deformations
at the quartic order at one-loop at weak coupling and at leading order at
strong coupling. We also present a very simple algorithm (not requiring
integration) to evaluate the two-loop result. We find that an exact symmetry of
the strong coupling sigma-model, known as the spectral-parameter independence,
is an approximate symmetry at weak coupling, modifying the expectation value
starting only at the sextic order in the deformation. Furthermore, we find very
simple patterns for how the spectral parameter can appear in the weak coupling
calculation, suggesting all-order structures
Defects in Graphene : A Topological Description
Specific types of spatial defects or potentials can turn monolayer graphene
into a topological material. These topological defects are classified by a
spatial dimension and they are systematically obtained from the Hamiltonian
by means of its symbol , an
operator which generalises the Bloch Hamiltonian and contains all topological
information. This approach, when applied to Dirac operators, allows to recover
the tenfold classification of insulators and superconductors. The existence of
a stable -topology is predicted as a condition on the dimension
, similar to the classification of defects in thermodynamic phase
transitions. Kekule distortions, vacancies and adatoms in graphene are proposed
as examples of such defects and their topological equivalence is discussed.Comment: 5 pages and supplementary materia
The Ferris ferromagnetic resonance technique: principles and applications
Measurements of ferromagnetic resonance (FMR) are pivotal to modern magnetism
and spintronics. Recently, we reported on the Ferris FMR technique, which
relies on large-amplitude modulation of the externally applied magnetic field.
It was shown to benefit from high sensitivity while being broadband. The Ferris
FMR also expanded the resonance linewidth such that the sensitivity to spin
currents was enhanced as well. Eventually, the spin Hall angle ({\theta}_SH)
was measurable even in wafer-level measurements that require low current
densities to reduce the Joule heating. Despite the various advantages, analysis
of the Ferris FMR response is limited to numerical modeling where the linewidth
depends on multiple factors such as the field modulation profile and the
magnetization saturation. Here, we describe in detail the basic principles of
operation of the Ferris FMR and discuss its applicability and engineering
considerations. We demonstrated these principles in a measurement of the
orbital Hall effect taking place in Cu, using an Au layer as the orbital to
spin current converter. This illustrates the potential of the Ferris FMR for
the future development of spintronics technology
Habitat availability mediates chironomid density-dependent oviposition
Abstract Knowledge of density-dependent processes and how they are mediated by environmental factors is critically important for understanding population and community ecology of insects, as well as for mitigating harmful insect-borne diseases. Here, we tested whether the oviposition of chironomids (Diptera: Chironomidae; non-biting midges), known to carry the Cholera pathogen Vibrio cholerae, is density dependent and if it is mediated by habitat availability. We used two multiple choice experiments in habitat-limited and habitat-unlimited environments and performed isodar analysis on counts of egg batches after controlling the polarization of light reflected from the habitats, which is known to affect their attractiveness to ovipositing chironomids. We found that, when habitats are limited, egg batch isodars indicate that chironomid selection is density dependent. Although a greater number of individuals selected to oviposit in highly polarized sites, oviposition was also common in sites with low polarization. When habitats are unlimited, chironomid selection is either weakly density dependent, or completely density independent. Chironomids oviposit to a very large extent in sites with high level of polarization, oviposit to a small extent in sites with medium level of polarization, and almost completely disregard unpolarized sites. We suggest that ovipositing females consider the availability of habitats in their surroundings when they choose an oviposition site. When high quality habitats are scarce, more females opt to breed in low quality sites. These findings may be used to limit the spread of Cholera by controlling the habitats available for chironomid oviposition
Efficient generation of spin currents by the Orbital Hall effect in pure Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level
We present a new ferromagnetic resonance (FMR) method that we term the Ferris
FMR. It is wideband, has significantly higher sensitivity as compared to
conventional FMR systems, and measures the absorption line rather than its
derivative. It is based on large-amplitude modulation of the externally applied
magnetic field that effectively magnifies signatures of the spin-transfer
torque making its measurement possible even at the wafer-level. Using the
Ferris FMR, we report on the generation of spin currents from the orbital Hall
effect taking place in pure Cu and Al. To this end, we use the spin-orbit
coupling of a thin Pt layer introduced at the interface that converts the
orbital current to a measurable spin current. While Cu reveals a large
effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall
effect of opposite polarity in agreement with the theoretical predictions. Our
results demonstrate additional spin- and orbit- functionality for two important
metals in the semiconductor industry beyond their primary use as interconnects
with all the advantages in power, scaling, and cost
- …