392 research outputs found
PIEMAP: Personalized Inverse Eikonal Model from cardiac Electro-Anatomical Maps
Electroanatomical mapping, a keystone diagnostic tool in cardiac
electrophysiology studies, can provide high-density maps of the local electric
properties of the tissue. It is therefore tempting to use such data to better
individualize current patient-specific models of the heart through a data
assimilation procedure and to extract potentially insightful information such
as conduction properties. Parameter identification for state-of-the-art cardiac
models is however a challenging task. In this work, we introduce a novel
inverse problem for inferring the anisotropic structure of the conductivity
tensor, that is fiber orientation and conduction velocity along and across
fibers, of an eikonal model for cardiac activation. The proposed method, named
PIEMAP, performed robustly with synthetic data and showed promising results
with clinical data. These results suggest that PIEMAP could be a useful
supplement in future clinical workflows of personalized therapies.Comment: 12 pages, 4 figures, 1 tabl
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright x-rays produced
by a laser wakefield accelerator can be predicted if the distance over which
the laser self-focuses and compresses prior to self-injection is taken into
account. A model based on oscillations of the beam inside a plasma bubble shows
that performance is optimised when the plasma length is matched to the laser
depletion length. With a 200~TW laser pulse this results in an x-ray beam with
median photon energy of \unit[20]{keV}, photons above
\unit[1]{keV} per shot and a peak brightness of \unit[3 \times
10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright X-rays produced by a laser wakefield accelerator can be predicted if the distance over which the laser self-focuses and compresses prior to self-injection is taken into account. A model based on oscillations of the beam inside a plasma bubble shows that performance is optimised when the plasma length is matched to the laser depletion length. With a 200~TW laser pulse this results in an X-ray beam with median photon energy of 20 keV, photons per shot and a peak brightness of photons s mrad mm (0.1 % BW)
Modified Thomson spectrometer design for high energy, multi-species ion sources
A modification to the standard Thomson parabola spectrometer is discussed, which is designed to measure high energy (tens of MeV/nucleon), broad bandwidth spectra of multi-species ions accelerated by intense laser plasma interactions. It is proposed to implement a pair of extended, trapezoidal shaped electric plates, which will not only resolve ion traces at high energies, but will also retain the lower energy part of the spectrum. While a longer (along the axis of the undeflected ion beam direction) electric plate design provides effective charge state separation at the high energy end of the spectrum, the proposed new trapezoidal shape will enable the low energy ions to reach the detector, which would have been clipped or blocked by simply extending the rectangular plates to enhance the electrostatic deflection
Mechanisms and dynamics of the NH<sup>+</sup><sub>2</sub> + H<sup>+</sup> and NH<sup>+</sup> + H<sup>+</sup> + H fragmentation channels upon single-photon double ionization of NH<sub>3</sub>
We present state-selective measurements on the NH + H and NH + H + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH, where the two photoelectrons and two cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states are identified to contribute to the NH + H dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold NH fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited NH fragment with roughly 1 eV of internal energy. The NH + H + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the NH + H channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states
Carbon ion acceleration from thin foil targets irradiated by ultrahigh-contrast, ultraintense laser pulses
In this study, ion acceleration from thin planar target foils irradiated by ultrahigh-contrast (10(10)), ultrashort (50 fs) laser pulses focused to intensities of 7 x 10(20) W cm(-2) is investigated experimentally. Target normal sheath acceleration (TNSA) is found to be the dominant ion acceleration mechanism when the target thickness is >= 50 nm and laser pulses are linearly polarized. Under these conditions, irradiation at normal incidence is found to produce higher energy ions than oblique incidence at 35 degrees with respect to the target normal. Simulations using one-dimensional (1D) boosted and 2D particle-in-cell codes support the result, showing increased energy coupling efficiency to fast electrons for normal incidence. The effects of target composition and thickness on the acceleration of carbon ions are reported and compared to calculations using analytical models of ion acceleration
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