3,913 research outputs found
Improving the Functional Control of Aged Ferroelectrics using Insights from Atomistic Modelling
We provide a fundamental insight into the microscopic mechanisms of the
ageing processes. Using large scale molecular dynamics simulations of the
prototypical ferroelectric material PbTiO3, we demonstrate that the
experimentally observed ageing phenomena can be reproduced from intrinsic
interactions of defect-dipoles related to dopant-vacancy associates, even in
the absence of extrinsic effects. We show that variation of the dopant
concentration modifies the material's hysteretic response. We identify a
universal method to reduce loss and tune the electromechanical properties of
inexpensive ceramics for efficient technologies.Comment: 6 pages, 3 figure
Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking
Typical quantum gate tomography protocols struggle with a self-consistency
problem: the gate operation cannot be reconstructed without knowledge of the
initial state and final measurement, but such knowledge cannot be obtained
without well-characterized gates. A recently proposed technique, known as
randomized benchmarking tomography (RBT), sidesteps this self-consistency
problem by designing experiments to be insensitive to preparation and
measurement imperfections. We implement this proposal in a superconducting
qubit system, using a number of experimental improvements including
implementing each of the elements of the Clifford group in single `atomic'
pulses and custom control hardware to enable large overhead protocols. We show
a robust reconstruction of several single-qubit quantum gates, including a
unitary outside the Clifford group. We demonstrate that RBT yields physical
gate reconstructions that are consistent with fidelities obtained by randomized
benchmarking
Josephson Coupling through a Quantum Dot
We derive, via fourth order perturbation theory, an expression for the
Josephson current through a gated interacting quantum dot. We analyze our
expression for two different models of the superconductor-dot-superconductor
(SDS) system. When the matrix elements connecting dot and leads are featureless
constants, we compute the Josephson coupling J_c as a function of the gate
voltage and Coulomb interaction. In the diffusive dot limit, we compute the
probability distribution P(J_c) of Josephson couplings. In both cases, pi
junction behavior (J_c < 0) is possible, and is not simply dependent on the
parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure
islet Reveals Segmentation in the Amphioxus Hindbrain Homolog
AbstractThe vertebrate embryonic hindbrain is segmented into rhombomeres. Gene expression studies suggest that amphioxus, the closest invertebrate relative of vertebrates, has a hindbrain homolog. However, this region is not overtly segmented in amphioxus, raising the question of how hindbrain segmentation arose in chordate evolution. Vertebrate hindbrain segmentation includes the patterning of cranial motor neurons, which can be identified by their expression of the LIM-homeodomain transcription factor islet1. To learn if the amphioxus hindbrain homolog is cryptically segmented, we cloned an amphioxus gene closely related to islet1, which we named simply islet. We report that amphioxus islet expression includes a domain of segmentally arranged cells in the ventral hindbrain homolog. We hypothesize that these cells are developing motor neurons and reveal a form of hindbrain segmentation in amphioxus. Hence, vertebrate rhombomeres may derive from a cryptically segmented brain present in the amphioxus/vertebrate ancestor. Other islet expression domains provide evidence for amphioxus homologs of the pineal gland, adenohypophysis, and endocrine pancreas. Surprisingly, homologs of vertebrate islet1-expressing spinal motor neurons and Rohon-Beard sensory neurons appear to be absent
Optical Flow on Evolving Surfaces with an Application to the Analysis of 4D Microscopy Data
We extend the concept of optical flow to a dynamic non-Euclidean setting.
Optical flow is traditionally computed from a sequence of flat images. It is
the purpose of this paper to introduce variational motion estimation for images
that are defined on an evolving surface. Volumetric microscopy images depicting
a live zebrafish embryo serve as both biological motivation and test data.Comment: The final publication is available at link.springer.co
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