2,832 research outputs found
Application of Time-Fractional Order Bloch Equation in Magnetic Resonance Fingerprinting
Magnetic resonance fingerprinting (MRF) is one novel fast quantitative
imaging framework for simultaneous quantification of multiple parameters with
pseudo-randomized acquisition patterns. The accuracy of the resulting
multi-parameters is very important for clinical applications. In this paper, we
derived signal evolutions from the anomalous relaxation using a fractional
calculus. More specifically, we utilized time-fractional order extension of the
Bloch equations to generate dictionary to provide more complex system
descriptions for MRF applications. The representative results of phantom
experiments demonstrated the good accuracy performance when applying the
time-fractional order Bloch equations to generate dictionary entries in the MRF
framework. The utility of the proposed method is also validated by in-vivo
study.Comment: Accepted at 2019 IEEE 16th International Symposium on Biomedical
Imaging (ISBI 2019
Neural network encoded variational quantum algorithms
We introduce a general framework called neural network (NN) encoded
variational quantum algorithms (VQAs), or NN-VQA for short, to address the
challenges of implementing VQAs on noisy intermediate-scale quantum (NISQ)
computers. Specifically, NN-VQA feeds input (such as parameters of a
Hamiltonian) from a given problem to a neural network and uses its outputs to
parameterize an ansatz circuit for the standard VQA. Combining the strengths of
NN and parameterized quantum circuits, NN-VQA can dramatically accelerate the
training process of VQAs and handle a broad family of related problems with
varying input parameters with the pre-trained NN. To concretely illustrate the
merits of NN-VQA, we present results on NN-variational quantum eigensolver
(VQE) for solving the ground state of parameterized XXZ spin models. Our
results demonstrate that NN-VQE is able to estimate the ground-state energies
of parameterized Hamiltonians with high precision without fine-tuning, and
significantly reduce the overall training cost to estimate ground-state
properties across the phases of XXZ Hamiltonian. We also employ an
active-learning strategy to further increase the training efficiency while
maintaining prediction accuracy. These encouraging results demonstrate that
NN-VQAs offer a new hybrid quantum-classical paradigm to utilize NISQ resources
for solving more realistic and challenging computational problems.Comment: 4.4 pages, 5 figures, with supplemental material
Theory of polygonal phases self-assembled from T-shaped liquid crystalline polymers
Extensive experimental studies have shown that numerous ordered phases can be
formed via the self-assembly of T-shaped liquid crystalline polymers (TLCPs)
composed of a rigid backbone, two flexible end chains and a flexible side
chain. However, a comprehensive understanding of the stability and formation
mechanisms of these intricately nano-structured phases remains incomplete. Here
we fill this gap by carrying out a theoretical study of the phase behaviour of
TLCPs. Specifically, we construct phase diagrams of TLCPs by computing the free
energy of different ordered phases of the system. Our results reveal that the
number of polygonal edges increases as the length of side chain or interaction
strength increases, consistent with experimental observations. The theoretical
study not only reproduces the experimentally observed phases and phase
transition sequences, but also systematically analyzes the stability mechanism
of the polygonal phases
Differentiable Quantum Architecture Search
Quantum architecture search (QAS) is the process of automating architecture
engineering of quantum circuits. It has been desired to construct a powerful
and general QAS platform which can significantly accelerate current efforts to
identify quantum advantages of error-prone and depth-limited quantum circuits
in the NISQ era. Hereby, we propose a general framework of differentiable
quantum architecture search (DQAS), which enables automated designs of quantum
circuits in an end-to-end differentiable fashion. We present several examples
of circuit design problems to demonstrate the power of DQAS. For instance,
unitary operations are decomposed into quantum gates, noisy circuits are
re-designed to improve accuracy, and circuit layouts for quantum approximation
optimization algorithm are automatically discovered and upgraded for
combinatorial optimization problems. These results not only manifest the vast
potential of DQAS being an essential tool for the NISQ application
developments, but also present an interesting research topic from the
theoretical perspective as it draws inspirations from the newly emerging
interdisciplinary paradigms of differentiable programming, probabilistic
programming, and quantum programming.Comment: 9.1 pages + Appendix, 5 figure
New Method for Numerically Solving the Chemical Potential Dependence of the Dressed Quark Propagator
Based on the rainbow approximation of Dyson-Schwinger equation and the
assumption that the inverse dressed quark propagator at finite chemical
potential is analytic in the neighborhood of , a new method for
obtaining the dressed quark propagator at finite chemical potential from
the one at zero chemical potential is developed. Using this method the dressed
quark propagator at finite chemical potential can be obtained directly from the
one at zero chemical potential without the necessity of numerically solving the
corresponding coupled integral equations by iteration methods. A comparison
with previous results is given.Comment: Revtex, 14 pages, 5 figure
Chiral susceptibility and the scalar Ward identity
The chiral susceptibility is given by the scalar vacuum polarisation at zero
total momentum. This follows directly from the expression for the vacuum quark
condensate so long as a nonperturbative symmetry preserving truncation scheme
is employed. For QCD in-vacuum the susceptibility can rigorously be defined via
a Pauli-Villars regularisation procedure. Owing to the scalar Ward identity,
irrespective of the form or Ansatz for the kernel of the gap equation, the
consistent scalar vertex at zero total momentum can automatically be obtained
and hence the consistent susceptibility. This enables calculation of the chiral
susceptibility for markedly different vertex Ansaetze. For the two cases
considered, the results were consistent and the minor quantitative differences
easily understood. The susceptibility can be used to demarcate the domain of
coupling strength within a theory upon which chiral symmetry is dynamically
broken. Degenerate massless scalar and pseudoscalar bound-states appear at the
critical coupling for dynamical chiral symmetry breaking.Comment: 9 pages, 5 figures, 1 tabl
cis-TetraÂaquaÂbisÂ{5-[4-(1H-imidazol-1-yl-κN 3)phenÂyl]tetraÂzolido}manganese(II) dihydrate
In the title compound, [Mn(C10H7N6)2(H2O)4]·2H2O, the complex unit comprises an Mn2+ ion, coordinated by two imidazole N atoms from cis-related monodentate 5-[4-(imidazol-1-yl)phenÂyl]tetraÂzolide ligands and four water molÂecules, together with two water molÂecules of solvation. The Mn2+ ion lies on a twofold rotation axis and has a slightly distorted octaÂhedral geometry. The molÂecules are connected by O—H⋯N and O—H⋯O hydrogen bonds involving both coordinated and solvent water molÂecules, generating a three-dimensional structure. Two C atoms of the imidazole ring of the ligand are each disordered over two sites with occupancy factors of 0.75 and 0.25
Anatomical study of simple landmarks for guiding the quick access to humeral circumflex arteries
BACKGROUND: The posterior and anterior circumflex humeral artery (PCHA and ACHA) are crucial for the blood supply of humeral head. We aimed to identify simple landmarks for guiding the quick access to PCHA and ACHA, which might help to protect the arteries during the surgical management of proximal humeral fractures. METHODS: Twenty fresh cadavers were dissected to measure the distances from the origins of PCHA and ACHA to the landmarks (the acromion, the coracoid, the infraglenoid tubercle, the midclavicular line) using Vernier calipers. RESULTS: The mean distances from the origin of PCHA to the infraglenoid tubercle, the coracoid, the acromion and the midclavicular line were 27.7Â mm, 50.2Â mm, 68.4Â mm and 75.8Â mm. The mean distances from the origin of ACHA to the above landmarks were 26.9Â mm, 49.2Â mm, 67.0Â mm and 74.9Â mm. CONCLUSION: Our study provided a practical method for the intraoperative identification as well as quick access of PCHA and ACHA based on a series of anatomical measurements
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