2,783 research outputs found
Bloch Walls and Macroscopic String States in Bethe's solution of the Heisenberg Ferromagnetic Linear Chain
We present a calculation of the lowest excited states of the Heisenberg
ferromagnet in 1-d for any wave vector. These turn out to be string solutions
of Bethe's equations with a macroscopic number of particles in them. These are
identified as generalized quantum Bloch wall states, and a simple physical
picture provided for the same.Comment: 4 pages, RevTex, 2 figures, Submitted to Phys. Rev. Let
Linear Response Theory and Optical Conductivity of Floquet Topological Insulators
Motivated by the quest for experimentally accessible dynamical probes of
Floquet topological insulators, we formulate the linear response theory of a
periodically driven system. We illustrate the applications of this formalism by
giving general expressions for optical conductivity of Floquet systems,
including its homodyne and heterodyne components and beyond. We obtain the
Floquet optical conductivity of specific driven models, including
two-dimensional Dirac material such as the surface of a topological insulator,
graphene, and the Haldane model irradiated with circularly or linearly
polarized laser, as well as semiconductor quantum well driven by an ac
potential. We obtain approximate analytical expressions and perform numerically
exact calculations of the Floquet optical conductivity in different scenarios
of the occupation of the Floquet bands, in particular, the diagonal Floquet
distribution and the distribution obtained after a quench. We comment on
experimental signatures and detection of Floquet topological phases using
optical probes.Comment: 16 pages, 10 figure
Unsupervised learning framework for large-scale flight data analysis of cockpit human machine interaction issues
As the level of automation within an aircraft increases, the interactions between the pilot and autopilot play a crucial role in its proper operation. Issues with human machine interactions (HMI) have been cited as one of the main causes behind many aviation accidents. Due to the complexity of such interactions, it is challenging to identify all possible situations and develop the necessary contingencies. In this thesis, we propose a data-driven analysis tool to identify potential HMI issues in large-scale Flight Operational Quality Assurance (FOQA) dataset. The proposed tool is developed using a multi-level clustering framework, where a set of basic clustering techniques are combined with a consensus-based approach to group HMI events and create a data-driven model from the FOQA data. The proposed framework is able to effectively compress a large dataset into a small set of representative clusters within a data-driven model, enabling subject matter experts to effectively investigate identified potential HMI issues
Perception of Linguistic and Affective Prosody in Individuals with Aphasia
The current study was carried out with the aim of testing the perception of linguistic and affective prosody in individuals with aphasia. Convenient sampling was followed for the recruitment of participants. Comparative group design was used. The participants were divided into two groups. The first group comprised of 10 individuals with aphasia while the second group comprised of 10 neurologically healthy individuals. The study was carried out in native and non-native languages of the participants. Based on this premise, two tasks were configured. The first task required the participants to judge the prosody of sentences in native language and the second task required the participants to judge the sentences based on the prosody in the non-native language. Mann Whitney U test was used to compare the performance of the two groups. Statistically significant difference between the two groups was found on both the tasks. The theoretical premise suggests that the linguistic prosody is affected in left brain damaged adults however, the affective prosody is spared in this population. The findings of the current study contradicted this result as perception of linguistic and affective prosody was found to be affected in persons with aphasia
Comment on ``Can Disorder Induce a Finite Thermal Conductivity in 1D Lattices?''
In a recent paper [Phys. Rev. Lett. 86, 63 (2001)], Li et al have reported
that the nonequilibrium heat conducting steady state of a disordered harmonic
chain is not unique. In this comment we point out that for a large class of
stochastic heat baths the uniqueness of the steady state can be proved, and
therefore the findings of Li et al could be either due to their use of
deterministic heat baths or insufficient equilibration times in the
simulations. We give a simple example where the uniquness of the steady state
can be explicitly demonstrated.Comment: 1 page, 1 figure, accepted for publication in Phys. Rev. Let
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