5,251 research outputs found
Groupwise Multimodal Image Registration using Joint Total Variation
In medical imaging it is common practice to acquire a wide range of
modalities (MRI, CT, PET, etc.), to highlight different structures or
pathologies. As patient movement between scans or scanning session is
unavoidable, registration is often an essential step before any subsequent
image analysis. In this paper, we introduce a cost function based on joint
total variation for such multimodal image registration. This cost function has
the advantage of enabling principled, groupwise alignment of multiple images,
whilst being insensitive to strong intensity non-uniformities. We evaluate our
algorithm on rigidly aligning both simulated and real 3D brain scans. This
validation shows robustness to strong intensity non-uniformities and low
registration errors for CT/PET to MRI alignment. Our implementation is publicly
available at https://github.com/brudfors/coregistration-njtv
An algebraic method for solving the SU(3) Gauss law
A generalisation of existing SU(2) results is obtained. In particular, the
source-free Gauss law for SU(3)-valued gauge fields is solved using a
non-Abelian analogue of the Poincare lemma. When sources are present, the
colour-electric field is divided into two parts in a way similar to the Hodge
decomposition. Singularities due to coinciding eigenvalues of the
colour-magnetic field are also analysed.Comment: 20 pages, LaTeX2e; references added, other changes minor; to appear
in J. Math. Phy
Quantum splines
A quantum spline is a smooth curve parameterised by time in the space of unitary transformations, whose associated orbit on the space of pure states traverses a designated set of quantum states at
designated times, such that the trace norm of the time rate of change of the associated Hamiltonian is minimised. The solution to the quantum spline problem is obtained, and is applied in an example that illustrates quantum control of coherent states. An e cient numerical scheme for computing
quantum splines is discussed and implemented in the examples
Classical light analogue of the nonlocal Aharonov-Bohm effect
We demonstrate the existence of a non-local geometric phase in the
intensity-intensity correlations of classical incoherent light, that is not
seen in the lower order correlations. This two-photon Pancharatnam phase was
observed and modulated in a Mach-Zehnder interferometer. Using acousto-optic
interaction, independent phase noise was introduced to light in the two arms of
the interferometer to create two independent incoherent classical sources from
laser light. The experiment is the classical optical analogue of the
multi-particle Aharonov-Bohm effect. As the trajectory of light over the
Poincare sphere introduces a phase shift observable only in the
intensity-intensity correlation, it provides a means of deflecting the
two-photon wavefront, while having no effect on single photons.Comment: To appear in Europhys. Let
Geometric Aspects of Composite Pulses
Unitary operations acting on a quantum system must be robust against
systematic errors in control parameters for reliable quantum computing.
Composite pulse technique in nuclear magnetic resonance (NMR) realises such a
robust operation by employing a sequence of possibly poor quality pulses. In
this article, we demonstrate that two kinds of composite pulses, one
compensates for a pulse length error in a one-qubit system and the other
compensates for a J-coupling error in a twoqubit system, have vanishing
dynamical phase and thereby can be seen as geometric quantum gates, which
implement unitary gates by the holonomy associated with dynamics of cyclic
vectors defined in the text.Comment: 20 pages, 4 figures. Accepted for publication in Philosophical
Transactions of the Royal Society
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