7,458 research outputs found
A Novel, Fast, Reliable, and Data-Driven Method for Simultaneous Single-Trial Mining and Amplitude—Latency Estimation Based on Proximity Graphs and Network Analysis
Both amplitude and latency of single-trial EEG/MEG recordings provide valuable information regarding functionality of the human brain. In this article, we provided a data-driven graph and network-based framework for mining information from multi-trial event-related brain recordings. In the first part, we provide the general outline of the proposed methodological approach. In the second part, we provide a more detailed illustration, and present the obtained results on every step of the algorithmic procedure. To justify the proposed framework instead of presenting the analytic data mining and graph-based steps, we address the problem of response variability, a prerequisite to reliable estimates for both the amplitude and latency on specific N/P components linked to the nature of the stimuli. The major question addressed in this study is the selection of representative single-trials with the aim of uncovering a less noisey averaged waveform elicited from the stimuli. This graph and network-based algorithmic procedure increases the signal-to-noise (SNR) of the brain response, a key pre-processing step to reveal significant and reliable amplitude and latency at a specific time after the onset of the stimulus and with the right polarity (N or P). We demonstrated the whole approach using electroencephalography (EEG) auditory mismatch negativity (MMN) recordings from 42 young healthy controls. The method is novel, fast and data-driven succeeding first to reveal the true waveform elicited by MMN on different conditions (frequency, intensity, duration, etc.). The proposed graph-oriented algorithmic pipeline increased the SNR of the characteristic waveforms and the reliability of amplitude and latency within the adopted cohort. We also demonstrated how different EEG reference schemes (REST vs. average) can influence amplitude-latency estimation. Simulation results revealed robust amplitude-latency estimations under different SNR and amplitude-latency variations with the proposed algorithm
Photoemission spectra of many-polaron systems
The cross over from low to high carrier densities in a many-polaron system is
studied in the framework of the one-dimensional spinless Holstein model, using
unbiased numerical methods. Combining a novel quantum Monte Carlo approach and
exact diagonalization, accurate results for the single-particle spectrum and
the electronic kinetic energy on fairly large systems are obtained. A detailed
investigation of the quality of the Monte Carlo data is presented. In the
physically most important adiabatic intermediate electron-phonon coupling
regime, for which no analytical results are available, we observe a
dissociation of polarons with increasing band filling, leading to normal
metallic behavior, while for parameters favoring small polarons, no such
density-driven changes occur. The present work points towards the inadequacy of
single-polaron theories for a number of polaronic materials such as the
manganites.Comment: 15 pages, 13 figures; final version, accepted for publication in
Phys. Rev.
Entanglement capabilities of non-local Hamiltonians
We quantify the capability of creating entanglement for a general physical
interaction acting on two qubits. We give a procedure for optimizing the
generation of entanglement. We also show that a Hamiltonian can create more
entanglement if one uses auxiliary systems.Comment: replaced with published version, 4 pages, no figure
Temporary withdrawal of immunosuppression for life-threatening infections after liver transplantation
Optimal simulation of two-qubit Hamiltonians using general local operations
We consider the simulation of the dynamics of one nonlocal Hamiltonian by
another, allowing arbitrary local resources but no entanglement nor classical
communication. We characterize notions of simulation, and proceed to focus on
deterministic simulation involving one copy of the system. More specifically,
two otherwise isolated systems and interact by a nonlocal Hamiltonian
. We consider the achievable space of Hamiltonians such
that the evolution can be simulated by the interaction
interspersed with local operations. For any dimensions of and , and any
nonlocal Hamiltonians and , there exists a scale factor such that
for all times the evolution can be simulated by acting for
time interspersed with local operations. For 2-qubit Hamiltonians and
, we calculate the optimal and give protocols achieving it. The optimal
protocols do not require local ancillas, and can be understood geometrically in
terms of a polyhedron defined by a partial order on the set of 2-qubit
Hamiltonians.Comment: (1) References to related work, (2) protocol to simulate one
two-qudit Hamiltonian with another, and (3) other related results added. Some
proofs are simplifie
Temperature- and quantum phonon effects on Holstein-Hubbard bipolarons
The one-dimensional Holstein-Hubbard model with two electrons of opposite
spin is studied using an extension of a recently developed quantum Monte Carlo
method, and a very simple yet rewarding variational approach, both based on a
canonically transformed Hamiltonian. The quantum Monte Carlo method yields very
accurate results in the regime of small but finite phonon frequencies,
characteristic of many strongly correlated materials such as, e.g., the
cuprates and the manganites. The influence of electron-electron repulsion,
phonon frequency and temperature on the bipolaron state is investigated.
Thermal dissociation of the intersite bipolaron is observed at high
temperatures, and its relation to an existing theory of the manganites is
discussed.Comment: 12 pages, 7 figures; final version, accepted for publication in Phys.
Rev.
Constraining the initial temperature and shear viscosity in a hybrid hydrodynamic model of =200 GeV Au+Au collisions using pion spectra, elliptic flow, and femtoscopic radii
A new framework for evaluating hydrodynamic models of relativistic heavy ion
collisions has been developed. This framework, a Comprehesive Heavy Ion Model
Evaluation and Reporting Algorithm (CHIMERA) has been implemented by augmenting
UVH 2+1D viscous hydrodynamic model with eccentricity fluctuations,
pre-equilibrium flow, and the Ultra-relativistic Quantum Molecular Dynamic
(UrQMD) hadronic cascade. A range of initial temperatures and shear viscosity
to entropy ratios were evaluated for four initial profiles, and
scaling with and without pre-equilibrium flow. The model results
were compared to pion spectra, elliptic flow, and femtoscopic radii from 200
GeV Au+Au collisions for the 0--20% centrality range.Two sets of initial
density profiles, scaling with pre-equilibrium flow and
scaling without were shown to provide a consistent description of all three
measurements.Comment: 21 pages, 32 figures, version 3 includes additional text for
clarification, division of figures into more manageable units, and placement
of chi-squared values in tables for ease of viewin
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