49 research outputs found
Electron-phonon-scattering dynamics in ferromagnetic metals and its influence on ultrafast demagnetization processes
We theoretically investigate spin-dependent carrier dynamics due to the
electron-phonon interaction after ultrafast optical excitation in ferromagnetic
metals. We calculate the electron-phonon matrix elements including the
spin-orbit interaction in the electronic wave functions and the interaction
potential. Using the matrix elements in Boltzmann scattering integrals, the
momentum-resolved carrier distributions are obtained by solving their equation
of motion numerically. We find that the optical excitation with realistic laser
intensities alone leads to a negligible magnetization change, and that the
demagnetization due to electron-phonon interaction is mostly due to hole
scattering. Importantly, the calculated demagnetization quenching due to this
Elliot-Yafet type depolarization mechanism is not large enough to explain the
experimentally observed result. We argue that the ultrafast demagnetization of
ferromagnets does not occur exclusively via an Elliott-Yafet type process,
i.e., scattering in the presence of the spin-orbit interaction, but is
influenced to a large degree by a dynamical change of the band structure, i.e.,
the exchange splitting
Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions
The rise of topological phases of matter is strongly connected to their
potential to host Majorana bound states, a powerful ingredient in the search
for a robust, topologically protected, quantum information processing. In order
to produce such states, a method of choice is to induce superconductivity in
topological insulators. The engineering of the interplay between
superconductivity and the electronic properties of a topological insulator is a
challenging task and it is consequently very important to understand the
physics of simple superconducting devices such as Josephson junctions, in which
new topological properties are expected to emerge. In this article, we review
recent experiments investigating topological superconductivity in topological
insulators, using microwave excitation and detection techniques. More
precisely, we have fabricated and studied topological Josephson junctions made
of HgTe weak links in contact with two Al or Nb contacts. In such devices, we
have observed two signatures of the fractional Josephson effect, which is
expected to emerge from topologically-protected gapless Andreev bound states.
We first recall the theoretical background on topological Josephson junctions,
then move to the experimental observations. Then, we assess the topological
origin of the observed features and conclude with an outlook towards more
advanced microwave spectroscopy experiments, currently under development.Comment: Lectures given at the San Sebastian Topological Matter School 2017,
published in "Topological Matter. Springer Series in Solid-State Sciences,
vol 190. Springer
Legal Facts and Reasons for Action: Between Deflationary and Robust Conceptions of Law’s Reason-Giving Capacity
This chapter considers whether legal requirements can constitute reasons for action independently of the merits of the requirement at hand. While jurisprudential opinion on this question is far from uniform, sceptical views are becoming increasingly dominant. Such views typically contend that, while the law can be indicative of pre-existing reasons, or can trigger pre-existing reasons into operation, it cannot constitute new reasons. This chapter offers support to a somewhat less sceptical position, according to which the fact that a legal requirement has been issued can be a reason for action, yet one that is underpinned by bedrock values which law is apt to serve. Notions discussed here include a value-based conception of reasons as facts ; a distinction between complete and incomplete reasons ; and David Enoch’s idea of triggering reason-giving. Following a discussion of criticism against the view adopted here, the chapter concludes by considering some more ‘robust’ conceptions of law’s reason-giving capacity
Deformation Aware Augmented Reality for Craniotomy using 3D/2D Non-rigid Registration of Cortical Vessels
International audienceIntra-operative brain shift is a well-known phenomenon that describes non-rigid deformation of brain tissues due to gravity and loss of cerebrospinal fluid among other phenomena. This has a negative influence on surgical outcome that is often based on pre-operative planning where the brain shift is not considered. We present a novel brain-shift aware Augmented Reality method to align pre-operative 3D data onto the deformed brain surface viewed through a surgical microscope. We formulate our non-rigid registration as a Shape-from-Template problem. A pre-operative 3D wire-like deformable model is registered onto a single 2D image of the cortical vessels, which is automatically segmented. This 3D/2D registration drives the underlying brain structures, such as tumors, and compensates for the brain shift in sub-cortical regions. We evaluated our approach on simulated and real data composed of 6 patients. It achieved good quantitative and qualitative results making it suitable for neurosurgical guidance
Sketch-Based Pruning of a Solution Space Within a Formal Geometric Constraint Solver
In CAD systems, formal geometric solvers enable the designer to draw a sketch and to provide constraints that are compiled into a construction plan by symbolic geometric reasoning. Then the plan is interpreted in order to generate the required figure. In case there are multiple solutions, they allow to scan the entire solution space. But when the number of solutions becomes too high, it is very time-consuming to examine each of them to determine which one is the closest to the user's will. In this paper, we introduce a sketch-based heuristic that enables to easily eliminate most of the solutions and to keep, among a solution space represented by a tree, only one branch, or at the worst a small subtree of solutions, that has the best likeness with the original sketch
Different findings in high resolution computed tomography (HRCT) and magnet resonance imaging (MRI) of the lung in two patients suffering from connective tissue disease with interstital lung disease (CTD-ILD)
Pareto front vs. Weighted sum for automatic trajectory planning of deep brain stimulation
International audiencePreoperative path planning for Deep Brain Stimulation (DBS) is a multi-objective optimization problem consisting in searching the best compromise between multiple placement constraints. Its automation is usually addressed by turning the problem into mono objective thanks to an aggregative approach. However,despite its intuitiveness,this approach is known for its incapacity to find all optimal solutions. In this work,we introduce an approach based on multi objective dominance to DBS path planning. We compare it to a classical aggregative weighted sum of the multiple constraints and to a manual planning thanks to a retrospective study performed by a neurosurgeon on 14 DBS cases. The results show that the dominance-based method is preferred over manual planning,and covers a larger choice of relevant optimal entry points than the traditional weighted sum approach which discards interesting solutions that could be preferred by surgeons. © Springer International Publishing AG 2016