64 research outputs found
Fourth order real space solver for the time-dependent Schr\"odinger equation with singular Coulomb potential
We present a novel numerical method and algorithm for the solution of the 3D
axially symmetric time-dependent Schr\"odinger equation in cylindrical
coordinates, involving singular Coulomb potential terms besides a smooth
time-dependent potential. We use fourth order finite difference real space
discretization, with special formulae for the arising Neumann and Robin
boundary conditions along the symmetry axis. Our propagation algorithm is based
on merging the method of the split-operator approximation of the exponential
operator with the implicit equations of second order cylindrical 2D
Crank-Nicolson scheme. We call this method hybrid splitting scheme because it
inherits both the speed of the split step finite difference schemes and the
robustness of the full Crank-Nicolson scheme. Based on a thorough error
analysis, we verified both the fourth order accuracy of the spatial
discretization in the optimal spatial step size range, and the fourth order
scaling with the time step in the case of proper high order expressions of the
split-operator. We demonstrate the performance and high accuracy of our hybrid
splitting scheme by simulating optical tunneling from a hydrogen atom due to a
few-cycle laser pulse with linear polarization
Carrier-envelope phase controlled isolated attosecond pulses in the nm wavelength range, based on superradiant nonlinear Thomson-backscattering
A proposal for a novel source of isolated attosecond XUV -- soft X-ray pulses
with a well controlled carrier-envelope phase difference (CEP) is presented in
the framework of nonlinear Thomson-backscattering. Based on the analytic
solution of the Newton-Lorentz equations, the motion of a relativistic electron
is calculated explicitly, for head-on collision with an intense fs laser pulse.
By using the received formulae, the collective spectrum and the corresponding
temporal shape of the radiation emitted by a mono-energetic electron bunch can
be easily computed. For certain suitable and realistic parameters, single-cycle
isolated pulses of ca. 20 as length are predicted in the XUV -- soft X-ray
spectral range, including the 2.33-4.37 nm water window. According to our
analysis, the generated almost linearly polarized beam is extremely well
collimated around the initial velocity of the electron bunch, with considerable
intensity and with its CEP locked to that of the fs laser pulse.Comment: 11 pages, 6 figures, reviewed, corrected and extended work, regarding
the intensity dependence of the emitted attosecond puls
Quantum entanglement in strong-field ionization
We investigate the time-evolution of quantum entanglement between an
electron, liberated by a strong few-cycle laser pulse, and its parent ion-core.
Since the standard procedure is numerically prohibitive in this case, we
propose a novel way to quantify the quantum correlation in such a system: we
use the reduced density matrices of the directional subspaces along the
polarization of the laser pulse and along the transverse directions as building
blocks for an approximate entanglement entropy. We present our results, based
on accurate numerical simulations, in terms of several of these entropies, for
selected values of the peak electric field strength and the carrier-envelope
phase difference of the laser pulse. The time evolution of the mutual entropy
of the electron and the ion-core motion along the direction of the laser
polarization is similar to our earlier results based on a simple
one-dimensional model. However, taking into account also the dynamics
perpendicular to the laser polarization reveals a surprisingly different
entanglement dynamics above the laser intensity range corresponding to pure
tunneling: the quantum entanglement decreases with time in the over-the-barrier
ionization regime
Biokémiai markerek jelentősége a neuroendokrin daganatok felismeresében és a betegek követésében
Circulating markers of neuroendocrine tumours are useful tools in the diagnosis of these tumours. Laboratory tests for general biomarkers have acceptable sensitivity for the recognition of neuroendocrine tumours as these biologically active proteins are typically synthesized by all types of neuroendocrine cells. Measurement of chromogranin A is widely used not only in the diagnosis of neuroendocrine tumours but it may predict the prognosis of the diseases and the effect of the antitumor therapy. It is also a useful tool for the detection of residual tumours. Neurendocrine tumours represent a heterogeneous group of tumours with the ability to secrete several hormones and, therefore, measurement of these hormones can also serve as neuroendocrine cell type-specific markers in routine clinical practice. In this review the authors summarize the significance of tumour markers in the diagnosis of neuroendocrine tumours as well as in the management and follow-up of patients with this disease. Orv. Hetil., 2014, 155(45), 1775-1782
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